Project Engineering of Process Plants.pdf

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PROJECT ENGINEERING of Process Plants

B.
RASE, H. F. AKD

RASE, 11. F.

Pipi~igDesign for Process Plants

PROJECT ENGINEERING of Process Plants HOWARD F. RASE Associate Professor of Chemical Engineering The University of Texas and

M. H. BARROW Project Engineer Foster Ti7heeler Corporation

Original Illustrations by Assistant Professor of Drawing The University of Texas NEW YORK

london

. JOHN WlLEY

. Sydney

8 SONS, INC.

PREFACE I n the early days oi the chemical industry, new plants were des~gned by a chemist and a mechanical engineer \ ~ i t hthe assistance of one or two draftsmen. The design work progressed slowly, but since the processes were simple, the job could be completed in a reasonable amount of time. The simplicity of design methods used in industry's early days contrasts sharply with the complexity of modern plant design. The joint efforts of specialists in engineering, construction, and management and a close interrelationship between them are necessary ior the design and construction of a modern plant. The supervision and coordination of these specialists has become the job of a specialist. He is called the project engineer. I n many cases the project cnginccr has a background in chemical engineering. I n addition to chemical engineering he must understand mechanical, electrical, and civil engineering problems. He must keep informed on procurement practices and he well schooled in the ways of office management. I n the past this vast amount of know-how not included in a chemical engineering education has been gained by trial and error or from experienced project engineers. I t is the purpose of this book to record information and techniques used in plant design and to discuss ideas that many project engineers have developed through years of practice. It is written from the point vii

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Preface

Preface

of vier!- of a project engineer, hut is not intended only for him or for the indiridual aspiring t o becolne a project engineer. It should he useful t o any engineer wlro designs process equipment, since he must know the tlicories and techniques of mechanical design, procurement, and construction, in addition to hasic chelniral engineering principles. Project Engineeririg of Process Plnnts is also intended a s a test for chemical engineering plant design courses. Most chemical engineering curricula in the United States h a r e courses in process plant design. The student finds such courses inraluable for three reasons. H e is able to integrate the compartmentalized k n o d e d g e obtained from bmic courses. H e has greater opportunity for original thinking. And, third, he gains the healthy self-assurance t h a t conles with being able t o apply his kno\dedge to n comprehensive practical problen~. 'l'l~e principles of chelnicnl engineering have been nhly rcconled in sucli texts as Hougcn and \V:~tson's Chei,iici~l Process principle,^ and Brown's V n i t Operations, and the student s-ill h a r e such hooks i o r reference in making process design calculations. The cwnvcrsion of these process calculations to a workable plant design is project mgincering. Project Engineering of Process Plants has hccn planned to acquaint the student ivith the niethods, organization. and pliilosopliy of project engineering. The book is rlivided into four sections. T h e major steps in plant design are outlined in the first section, and the business and 1eg:ll phases of plant design are discussed in part t w . P:~rt three gives principles of cquipmcnt design and selection and design of structure foundations and piping. E q u i p e n t common to all process plants is considered in detail d l e r r a s o t l ~ c requipment is treated briefly in a single chapter, althougli references t o more conil~lctesources of inforlilation are given. X o attelnpt has heen made t o providc n handbook or guide t o the selection of all types of equipment. Technological progress is too rapid t o make such a n undertaking n-ortlinMe. Instead design principles and reasons for current practices arc elnpha~izcilso that the reader can derelop a sound basis for his own decisions. T h e last part of the book is a clcscription of construction operations, and any enginecr cngaged in plant dasign is adrised t o accept the first opportunity t o observe the coi~stroctioll of a plant from start t o finish. After t h a t experience the engineer 11iua11y becomes a much better designer. T o aid in making the book useRrl t o both student and practical engineer, a n effort is made to adhere to the f o l l o ~ i n gprinciples:

2. Yisualization rif equilment is facilitated hy isonirtric and pictorial v i e m or rross-sections supplemented by other r i e x s . 3. Design equations, unless con~pletelpeinpirical, should be developed sn that their l i n ~ i t a t i o nwill ~ he unrlerstond. 4. Oily ronrlnonly w r d drsign mrthorl. -iio~llrl hf p r ? s m t r d ;i. E X R I I I ~01 I ~ achl:d S c i c i l i i t i ~ i i sspecifications, and contracts are a t times prefcmblc to detailed e s l h n a t i o n s . 6. Conipilations of design data arid sources of inforniation sliorrld he given tliroughout the text. 7. Economics sl~oulrlbe discusse
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1. The rclationahip between each design phase ran be hetter understood if the scrpencc of chapters fo1lon.s the usual steps in plant design.

T h e authors are grateful to the illany conipanics which furnished illuatratiuns. Specific nrknordedgments arc made in the text. Thanks are :rko due Professor hl. !-an \\'inklc for his many helpful suggestions.

CONTENTS 1 The Pro,j~ctEngineer Part 1

MAJOR STEPS IN PLANT DESIGN

Plant Location Preliminary Data for Construction Projects Process Engineering Flow Diagrams Plot Plans Scheduling the Project Engineering Design and Drafting Part 2

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BUSINESS AND LEGAL PROCEDURES

9 Procurement Operatims 10 Office Procedure 11 Contracts and Contractors

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Part 3

DETAILS OF ENGINEERING DESIGN AND EQUIPMENT SELECTION

12 Vessels 13 Heat Exchangers

Contents

Process Punips Colllpressurs mil T a r ~ u u ~Pnu n ~ p s Motors :ind Turl~incs Other Process Equipment Piping Design Thermal Insulation Process Instrunlents Plant Ctilitics Foundatious Structures and Buildings Safety in Plant Design Part 4

CHAPTER

CONSTRUCTION OF THE PLANT

25 Construction

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THE PROJECT ENGINEER The design and erection of a process plant could nerer i ~ ecompleted solcly by nlelnhers of one branch u f cngineering. Instead such an undertaking must result from courdiuatcd efforts of chemical, mechanical, electrical, and civil mgincera, chemists, and specialists from man:other fields. This combined effort, horvercr, must be directed by a single individual wlio can guide the engineering, anticipate the routine problems, and nchcdule the rarious phascs of work. It has, therefore. hecome the practice in process industries to assign this overall responsibility for thc entire design and erection of a process plant to a singlc! individual called the project engineer or manager. The duties of thc project engineer for a process plant, other than requiring a round chemical engineering background,' demand knowledge of other engineering fields, hueiness administrationl and economics. Although it is not neressary for him to he an expert in any of these, he must have sufficient knorvledge to cr~ordinatcthe activities in all of them. The larger operating companies in the process industries, w c h as chemical and petroleum, maintain extensive staffs of technologist,^ in all hranchcs of engineering for research, de~clol)ment,and plant maintenance. Such a firm will ordinarily explore any new process under consirleration both tecllnirally and economically. However, rvhen an *Sonre

practicing projrcl engineers have mechanical engineering training and

additional study in chemistry.

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Project Engineering of Process Plants

The Project Engineer

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~ q ~ e r a t i ncorr~pany g ~leciclvstu build :I couil~lrteplaut or a binglr process unit, an engineering and condrnction fir111 sjieriiilizing in such work is usually retained. i i i o r of v o r k hetween Kumerous variatirmi art> ilo-silllt in I the engineering and euu;tructiou fir111 c o ~ t r c t riind the opcrating company (customer). 1. Prorrsa rlerciopnit.nt, pruress ~lesign.euginecring and construction by contractor. Examples: (01 Fort4gu customers desiring plants of American deaign. it]I Sen-ly i ~ r i i ~0 1 .d young process industry firms. I c J Established firms uot having the pcrsmnel available for active participation in any pilase of the iiesign or firnls which prefer to have contrartor hantllc all phases. id I Contrnctor frmishing patented process or developing a snitable process. 2. Process developed by customer, pri~rrss design a joint effort, engineering and ronstrnctiun hy contrnct(~r. This is a common arrangenlent when the customer lins. tlrrol~glii~envlr scale and pilot plant uwrk, developed a proccss arirl ~vishet.to luilcl a full-scale plant. The contractor use? the customer':: basic (latn. 3. All process design done by customer. When the customer has a large process design group that has been cli~scly associated mith a process, it is often advisable for this group to upp ply a complete process deaign t o the contractor. I t is not uncmlruon, l i o ~ e v e r ,for the customer to rcquest the contractor t o check the dcsign. Other variations of tbe division of responsibility are possible. It is important to note, however, that the projert enginecr's role is extremely important in any arrangement. \\-lien both the contractor and custouier are participating, the customer's project ellginerr nud the contractor's project eugineer havc dutics essentially r a l l l ; and the chart in Fig. 1-1 depicts the duties of both. The customer's project engineer niust supply tile contractor's project engineer with all the information concerning the custnmer's requirements and preferences. He must check and approve all designs, and obtain comments from various design and operating groups in his own organization. The contractor's project engineer must be responsible for transmitting information to the rarious groups in his own organization, for guarding both the contractor'y and customer's interest in all engineering decisions, for contractual obligations, and above all for seeing t'hat the plant is completed on time and that it operates arcording t o specifications. Referring again t o Fig. 1-1, the dutics of a project engineer can be briefly traced in a clockwise manner around the chart starting a t the top. Assume that a process plant, Fir111 A, has, after economic studies

Fig. 1-1. Project al.gmiznlion

and basic research, decided to construct a plant. Firm A sends out inquiries to various contractors xvhich are prepared hy A's process dcpartmcnt and project engineer, These includc a dcscription of the proposed location of the plant, tlic scope of the project, the production required, and any other inforiuation not available to the contractor. The contractor assigns a project engineer t o the job, who immediately becomes the liaison b e h e e n the customer and all dcpartments of the contractor. Thc project engineer works with his process design and estimating groups in preparing an estimate for thc cost oi designing and constructing the proposed plant. The estimate is presented to the customer in

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hound fornl. It c:ircfuIIy outlin(>>all duties and oblign tionr of cwtomcr and contrartor, decrrihee the proreis units an11 equipmrnt, givrs the design spccifirationi, opera~ion:~land merirnnir:rl gnnrnnters, and .sets a completion rlatc,. Aseume that the contract is an-:irdcd to Contwctor B. H'.? project engineer then immediately starts organizing tlre jol, The project nlanager of '4 is rr~ntactetl ;rnd tlic p r n r ~ vrequiren~ents are firmly establislled by agrerlucnt wit11 -1's IIrocess groul~.using the proposal as a basis. The contr;~vtor'>prorr.ss group tlrrn proweds Kit11 the final process dmign. As the rlcign is l~cingdeveloped, n~cclianiral specifications are !!-rittc~~ an11 :~greerl uptm and :dl pl~niesof tlw projcrt arc s c l ~ d u l c dso that tlir c ~ ~ ~ n p l c t il;rtt i r ~ n r:rn bc met. T h r p r o c r ~ sinforination is transmitted to tlit- various dezign and ~lrnftinggroups by tire project engineer and his nsist:mts. They interpret and ilcvelol~ s are ronll~letely this infornrntion and ?e? that t l ~ c1 1 r o c ~ ~requirrn~rnts satisfied in the layout and ilrsigu and that euston~er specification^ are met. -4s -eon as the debiyn begins to talcc forin, purchnsing conrmit~nents are n ~ n d et o wsurr j~ro~irpt rlrlivery. Purr,lr;~ncsthat require engineering judgment arc rcvicn.ed 11y the projcct engineer an11 specialty enginerrs before being purrl~arcd so that the lwrt available crgiipnrmt vill he obtaincrl a t a m t i ~ f a c t o r yprice. .Is the design ilevelq~s,rel~rcscntntiwsof the conetrurtion ricpart1 1 m t are hiefed by the project engineer Crn the .scope :lnd details of the prujcct so that construction may be plannctl and lrcparation of the zitc 11t,gu11. l\Irml)ws uf the 01)ernting d e p r t m r n t s ( ~ f hot11 custo~nerand contractor are a s k d to revie~vtlrc design and to ~ ~ g g c s t ilnprorclncnts. r. I liruoglrout ;ill this activity thc. cuetonl~r's project engineer m t l tire c o n t m ~ t o r '1,rvjcct ~ enginecr and tlicir nsiktants 11:ivc been icrir~i-ing all dra~i-ings:ind n~:~lerinlrquisitionr. Cmrnrent.? arc assemt~lc~l and r e t u r n d t r ~the design groups so that thc 111~rrisaryclranycs ran 1,c madr. The oontractrds project engineer nus st see that these c11ange.i are pro]wrly ext,cutetl and that hoth tlic custon~er'sand contr:~ct~~r't: interests are gunrrled. Changw niust not alter the original prow?. requircnients, scope of !!-nrk," or specifications. 111 fnct, the prujrrt engineer's responsibilities do not end until the c,pcrating department 113s si~ownthat the plant meets tlre design specifications and process and meclranical guarantees. *If changes in thc scupe of work nw desired by tlre customer, he must ask for thwe changes in wcordance with t h e h n r s oi tile contract. The contrario~.can ;,+I, fur :~rlditionnlfees for tliesp elumgcs. (See Chapter 11.)

MAJOR STEPS PLANT DESIGN

CHAPTER

project engineer coordinates and directs the entire design project. His active participation increases after

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the completion of process engineering, but in many instances he also takes part in the early stages of job planning. He may assist management in the selection of a site and will also direct the gathering of preliminary data. His rnost intensive work, however, comes during the period of detailed engineering design and drafting, for it is this work that culminates in the selection of equipment and production of drawings for use in construction.

PLANT LOCATION The proper location of a plant is as important to its success as the selection of a process. Xot only must many tangible factors such as labor supply and raw material sources be carefully considered, but ulw a numbcr of intangible factors which are morc difficult t o evaluate. The selection of a plant site must be based upon a very detailed study in which all factors are weighed as well as possible. Such a study often requires a substantial outlay of money, hut false ecmou~ies a t this p i n t may lead t o great losses in the future. T l ~ c r e is cmsiderahle literature on t11c subject of plant location ranging from practical considerations to the theory of plant l o c a t i ~ m Ll~etheoretical aspects are rxtretncly interesting, and in grnrral s t c ~ n from the classical work of \ V e b e r ~ ~ ~ u b l i z hin e d1909 in thc German and translated in 1928 in English. Many excellent outlines or chcck lists h a r e bccn puhlishcd which aid in illant location studies by listing factors that must be considcrcd. 4 n aht~reviated listing of mule of thc literature in this ficld appears a t the end of this ~ h a p t e r . Tlresr references will incvitably lead tlre interested reader t o tile entire literature on plant location. r.

GENERAL PROCEDURE

Before proceeding with any plant location study, one must have a complete knowledge of the existing company organization, history, cost data, and marketing techniques. Just as a family must know its

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Project Engineering of Procerr Plants

r i t I [)nr!,l~:i-i!~:: :i II(.\V I I ~ u - 1 %so :I colmpitny 11111-1 :rls(~ knoll- itticlf lhciorc locating :I new plant. r\cquiririg such knor~-illledge, l ~ o w r e r ,is not :~ln-ayseasy. I n the fast g r ~ ~ v i nIWJW-s g dustry, many organizntionc have grown i r ~ m i?mall family-orvned concerns iuto lnrge corpurate mterprises in a short span r ~ fye:lrs. ('Iwlr('ut ,~rg:~nization and lroli,,y ~ F t c nfail to 11,. (lrfinr:il
Plant Locotion

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region or corninunity as being idedly suited. thcn a specific site in t11:it rcgion must be selected. Yasecnl" has emphasized the importance ui ~ l c t e r n ~ i n i nthe p specific site after the conilnunity has been sclcctcd. If d u r ~ n gthe study of sewral comn~unitiesa particular site in one is found that has nnwual appeal. tlir eutire stndy may he influenced by it. Such ~nflucnccin effwt y r e s undue ~ v r i y l ~t ot the sitc itself, I~eearrsc it is so o f t e ~ ipwsible for ouc or more individuals t o fa\-or thc appear:tncc u i :I g i x n sitc and 11lace excessive enlplia?is on its iuq~ortancc.

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PLANT LOCATION FACTORS

R o w Materials

I>h e selection of the sonrce of r:1~1- nmatcrials, :rlthough i t nlny not be a t the plant site, is an rxtrrmely ini]~ortantfactor in t l ~ cu l t i ~ n a t c I<]cation of the plant. I n many cases, the stud?- of the r a material ~ situation m:ly ~ ~ r e c e (tlic l c analysis of t , l ~ eother plant lowtionnl facturr, sinec pilot plant 7vol.k on a. p ~ c c s srequires a t least n knon.leilge of t l ~ r ultimate ~ : I K uiilterial supply. Process devclop~nent~ o r kand econ~~niic studies d l indicate the m i n i n m n ~stantlartl~for rurv ~uatc,rinlselection. Once thcse st:.ntlards arc dcterminctl, then all possible sonrrer of :~cccpt:ii~ler a x ninterials can be located :md more rlet:lilcd analysis of thc source; r a n prorccd. T h e extent of each raw riiatcrinl source must be determined in tlic light of existing and estimated future requiremmts. .In a t t c ~ n p tto estimate the life of tllc r a ~ vinaterial source hasctl on fntnre require~ n c n t s niust be made. Alternate sourccs or substitutes in t l ~ carea sln~uldalso hc located and evaluated. The rost of SCIK matrrial delivered to tllc plant site can then he dctermined for a11 tlmsc sources mectiug thc quality and quant,ity specifications required by the process. .Iccuratti frcigl~trates must be used in determining thcse costs. Bccause o l tlic conlplex freight ratc strncture that exists in tlic United States, i t is not 1111ssiblcto use soul? sinq~lcdol1:ir 11er mile figurt, iscc IJC!IJ\\-I.A ~ r l : ~ ~ srule i ~ ~s;t~a tl t , ~tlnlt if thv raw 111xtcrix1lo>cs ~ a l > i , l c ~ r ;ibk woigllt during processing tu the fimil product,, it is cheaper t o loetitc the plant a t the source of the raw material. As is true, hon-ever, wit11 all sue11 general rules, there arc a n u n ~ b c r uf notable cxccptions. X ~lrlivere,l ran- nintcrial cost analysis sliould n l w i y ~IF n1:idr for e;tch 111nntl w ~ t i u ubeing w n ~ i d < , r c d r

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Transportation .is stated previously, no simple dollar per nlile cost rule can be applied t o freight rates. Railroad freight rates in particular are cxtrcmcly complex. An example given hy Yaseen'Vllustrates this complexity most effectively. H e describes a nianufacturer d i n is ~'onsidcringa central Ohio location for a nen. plant and who has distribution in surrounding territory and also in the 1.0s Angeles area. A rnajor imnpetitor is located in Cleveland, Ohio. Considering Jlarysville as a locatim. it is found tlrat the freight rate per hundred pounds will he $556 to Lns .Angeles. The rate fn)m Cleveland is the same, h location in Pcnria, Ohio, only scvcn miles furthcr west of hlarysrille ill enjoy a rate of $4.83 per hundred pounds producing an advantage over tlrc (Ilevelmd ro~npctitur. I t is not possible to prcscnt a coniplete discussion of freight rates in this rhaptcr. The engineer in charge of obtaining information relatcd to plant location need m l y realize that transpr~rtation experts must bc cousultcd in crtnblishing freight charges and optimum location lvith r t q e c t to transportation. Such expert information is available from the frrigllt agents and traffic cxpcrts of tlrc railroads and othcr transportation facilitic;. In addition, thc traffic manager of one's own rompany can l ~ of e great assistance in obtaining the necessary inforwation and aiding in its interpretation. The effect of transportation facilities and ratc.; on plant location van he a rontrolliug factor, Industries such as the plastic industry, for instance, 15-hich must dclivcr many small slripnients to various users in the miniurum of time, find location near the majority of users inandatory. I,t,ss-tl~an-car-Itlad-lot (LCL) rates are very high; and, therefore. the distanre that the material must he shipl)ed should be kept t o a minimum. Railroad Freight Although truck transportation has increased inarkeitly in tlrc past tcn or fifteen ytm" it is safe t o say that fcrv process plants could exist ivitlir~ut awess t o at lcast one milroad. The railri~ads continuc t o carr? the hulk of industrial products. Disrnssions 5~1thrailroad freight agents conwrning frcight rates ant1 methods of handling in the various ronimunitics under consideration are necessary if a true picture i~ t o hc ihtainrd for comparing the relativc advantages of *everal locations. A .study of the railroad freight structure n-ill reveal several fundanrental r r c i l . Because of t l ~ crelatively high iwst ( ~ ft,ransferring rlripments fronr m e railroad tu another, it is desirable t r ~locate plants along major railrmtd ruutes so t l ~ st l ~ i ~ ~ u will ~ ~ nfollo\v ts the major

Plant Location

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lines betn-ccn the shipping point and ultiinatc destination. TVhere possihlc it is desirable t o have more than one railrond servicing a com~ i ~ u n i because ty of thc greater flexibility snch service providw. JInny larger communities served by several railroads have terulinal companies or so-callctl belt-line railroa~lsnhicli are often jointly orwed by the several railroads in the region. Thebe trrminal railroad; provide service hetveen the tracks of the major railroads entering the comn ~ u n i t yand all plant sites. Such service is rapid and proiluces cheaper transfer from road to road and ultin~atelyt o tllc pltrnt. Area< served by terminal companies, therefore, are t o be derirwl. If large amounts of LCL ehipmcnk are anticipitfd, the esistmce of a car-loading company in the area is advantagrou.;, These car loaders offer door-to-duor LCL service. They collrrt a nulnhcr of LCL shipments from an area having the same ( l f h n a t i o n , and are able to assemble complete carload shipments for delivery to the r:iiIroad Some railroads provide similar service in large communities. At first t l ~ m g h tit may seem that a plant should either be located a t the raw n~aterialsource or a t the market for its ~irocluctr. Considering t,ranq~ortatioaali~nc,horrever, an intermediate location may he just as advantageous. Railroads offer fahrii.ation-in-trw~lsit privileg~.~ for certain commorlities. This privilcgc pcrmits the material to be shipped t o a plant. processed, and then sent on its v n y t ( ~tlrc ultilnate destination for essentially the same rate that ~ ~ - o u hl da r e been clrargcd for a non-stop trip. It is n.ell t o check the existence of such pririlegcs for the comniodities to be produced. Many other rate pcculiarities lravc cvi~lvedas the railroads d c \ ~ l o p c dand conil1etition became keen. Trucking Interstate truck n~overnents,a s in the case of the interstate railroad transportation, are now regulated by the Interstate Commcrcc Commission. Truck lines are elasscd as schctlulcd or non-scheduled carriers, depending upon xhether the line offers a regularly scheduled service b e t w e n t v o points or operates on a contract basis a t timcs convenient to the shipper. Truck lines have been able to compete vigorously with tlrc milroads on small shipments and in particular on short hauls. Because of the competitive advantage in this phase of freight shipment, the truck lines have concentrated on the development of efficient means of handling less-than-truck-load-lots (LTI,). As with railroad freight, excessive transfer should be avoided. Location of a plant on the route of a major carrier providing direct connections to various shipping points eliminates the need for transfer and cuts costs. I n considering truck transportation in a given community. the fran-

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Plant Location

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W a t e r Transportation

tr:ili,~l~nrtntioni. nnii i t p o l :ll!Y:iy. hc tilt, r ~ l l v l ~ ~ l ~ s t t i ~ ~ c ~ r :t t i ~ ,I I I I I of g e t I I ~ It . is certainly an a,iv;rnt;~gefor n prow-s p h n t to 11c I~uateII: ~ d j i ~ ( , ~ton t n:iaigal)l~~ a t c,vcn thnugli initial oper:rtions do not require n-atcr sllipmenrs. \Inn? co~npiinics11:lre becn :ihlr t o ctirnprtc~rlfectivi~lyin ~ p1~11ts ~ ~ in l tht> (Iist:~nt111xrkc,t-eren tl~ou!J~these I I I : I ~ ~ I ? Snrcx ~ e r 11y c r a n ~ n ~ m i Ia, : I I ~ slri]) li~lui(l ~ilarket n r w .\ (':~lifornia ~ ~ r o ~ t u cill : I I I I I I I I ) I ~ ~ : Iin ?e:i-g~i~rg 1,arge.s to the P;rrifiv S ~ r t l ~ \ v e si itn ~ l cuuil~t'te \\-it11 plants 1oc:iterl in tlic J'acifir Sorth\\-cbt rerrit,~ry. :\ h r g e Gulf C'oa.4 r a w t i c 1 1 r o ~ l n ( w >hips 735 caustic by XI-going t a r r k ~ rto c a d roast tcr~iii~i:ilsfro111 ~11en1:cit is S c ~ r w i r i l ~11y ~ ~rtiil l m d tniuk to east coast u:ers. Here ~igain lor^ c w t water frc4gllt enables tlic p r o ~ l u i wto c u n q ~ e t r1~it11~ i r ~ d w t in ~ r the s ~ i i : ~ r k carc^ t In irilditim to occ:i~~ tra11sp~rtiitim1,tllc C n i t ~ dStzit?> is f i ~ v ~ r ewit11 d many ~ n i l e so i navigable s t r e a ~ n sa n d canal.;. Pcrllnps tile most ? p c taclllar c:ilial s y s t c n ~is tlic Intercoastal Canal \vl~irhI ~ I I X - i t lpre~tcrte,l ei shipping I:ine.. for barge traffic iron1 Bra\\-nsrillc, T c m s to S e w England. Tlle Grc;it I.akcr am1 large rivers sue11 a s the ~ l i ~ i i ~ s i()trio, p~~i. Hu11sti11. am1 'L'rnncrsc~ llrovirle a d i l i t i ~ ~ r ~tlroos;~nds nl of milei 111 navig a b k n.;it~.n\-:i>-s~nis>iugthrougli t l ~ el>ol~ui:~tiou centrr- ( l f the 1-nit~vl Sti~tes. I 1 v o r c s ~11lants Irave iound it ;~~l\-auingcwus to ojrerate their OII-II .sIrip ;ir~d b:l~jir.<.:1ltlroug11 tllc. .wvicc.- of .Aipping coll~l~;~nit.; art, I Y ~ I I : I I I I . Ti, *tin~lrl:ite I\-iiter tr:~nb]~orti~tion the i w l w i l gover11~ i i e n tI I : I ~iur :i rrunlber o i years ol~erate(lR large barge linv rallcil T h e Fw11,r:iI I h r g t , 1.i1iw \v;lltT

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I

Other M e a n s of Transportation

wrvirvs offcwcl 11y t l ~ c:tir linvs, expwss co~npariiw,the I'wt Ofliw Ik.part111e11t~aid pipt,Iincs vnry in illq~ortance (lcpen~lingupon the p s r t i ~ w l a r plant in question. Heenare of t l ~ ei n c r e a ~ ein airlinr trnffic and the t r l i ~ j ~of o present d a y industry, i t is a~lvantngcuust o he 111rated conveniently t o a n aiqlort if for no ot111~renron t h ~ nfur tllc convenience of company prrsontiel trtivrling ou plant hu.;ilicss. Although ieiv process plants n-ill require eontir~uous air freight shipnwnt, it is I I O ~ uncommon to call for a n emergency air sliipliient o i ; > u t s for plnni cquipn~ent. Here again tlic eonvenimt location of a n alr111)rt is :in adrantagc. Tllc,

Process W a t e r

T h e ~ ~ O C Ci ~Si ~~ l u - t r irca~n k : ~ l ) o ~ -:ill e uthcr. :I- users o i n-a(i,r. 1-11 process plant cuuld operate \vithout rratcr 3 5 a rooling medium and :IS ;I direct r:ix material in certain ] ~ l ~ a s icr fs :I process. T h e n.att.r i ~ ~ p l ' l y of an area, ~ I I I W ~ O Y C . IIIII-t 111: stuili~11IJ~EOTCt h a t area 1,:11i eveii IIC? runsidered as a pussil~lerite. .id\-icc rhould be sought from competmt iv:itcr experts, inrlwling grologists iincl cl~crnir~al rrrgini'rr.~ ;~~r~r~i:iliziirx in n-ater prol~lcuis. Prior to the study, a clutaileil estimwtr of water rrquirclncnts 110th for tile i~rescnt an11 the f n t w e luust 11c ~uacle. Thi? ~ I I I U I I I t11c,1i IIV i'ollon-etl by wrcful study of the v-atcr a v a i l a l ~ l rin t h e rt,gion heinlr t~unsidcrccl. IS well n-ater is to III, used a. twmplrtc stud? of tlie II;I..(. Iliatory of the underground \v:iter table is necessary. Because o i their l o ~ e temperature, r u n d e r g r i ~ u ~ iwater d supplies arc prefcrrrd if :i~lcqoatt,. n ~netliod ior predictilig Powell and Yon I ~ s s b c r g "Ilave clescril~e~l tire Suture a ~ a i l a t l i l i t yand rrlial~ilityof utidergror~~ld \I--;ltt.r bupl~ly hy tpsting existing ivell.!. IYater lrvrls in obsrrvatiim n-clls are ~rleasurc I t i i necm-iuy to clri~rk:Ire 1listw.y of I.~TL.I.flon. ~ I YI i k l<.sel i r i t ~ ~ iyears y 11;1rlc us pwsil~lt:so that :i.surnncr oi :111 n d c ~ ~ u a t..11111ily e

14

Plant Location


can :it 1ca.t hc l~redirtrrlirom historical data. Indubtries niuring into relati\-el? n e x areas oiten fail to consider the posribility of other plants fi~llo\vingsuit. The quantity of ~viltcrs1111ply sliould 110t only be adequate for inture riecils of the prol111sed plant in question. hut alsu :idequate for supplying the nnticil~aterlneeds i ~ iother industrie~that uliglit n ~ o r einto the area. I t is also desirable to mnsider alternate sonrces of supply that may be required as the preicrred water sources become delctcd. In addition to having t l ~ cproper quantity of m t e r arailablc. the quality of xvater must also be stu~licrl. Clletnical and h:~cteriological ~xalninationuf the hvater d l indicate the extent of treatntent required nnrl aid in the development of n-ater cost figurrs for comparison with other 1oc;ltions. Possi1)ility of the (,ontamination of thc water source I)? otlicr industries in the area should be anticipate~i. This c o n t a n illation may consist o i only raising the temperuture of the water t o sue11 a lr?-el that its use as a cooling rnediutn rvill be itrq10sbi1)le. l'lit~ cl~cmicalengineer is usually xell equipped t o tnakc cost c o n parism;. of various water supl~lics,hut he rarely ha': tlic background ncccssary to m:lke intclligent conclusions concerning the extent and relial~ility ui a particular supply. Such studies ilcscrvc tlic attention of n competent water consultant trained in geology and meteorology. Waste Disposal a n d Noise Abatement Tlic iorivaril-loo* engineer ~villconsider v a s t e disposal and noise al)ntenicnt just, as i m p ~ ~ r t a nint thinly populate~lareas as in a heavily populattd rity having spevial ordinances related to these ~ ~ r o l ~ l c t n s . Sothing is $11 in~principle~lor injudicious as duniping waste in tllc atmosphere or in nrarby streariie. I n addition to the moral or ethical c,insider:~ti~)ns, it is not el-m good economics. Eventually the comm ~ ~ n i t~vill y rise in indignation and impose laws which may be so burilrnsi,me t h t profitable operation ~ o u l r l bc impossible. It beIioovt,~tliv engineer. tlit!reiore, t o study tlic miste dispoiial and noise lruhlcms and to i.onsirlcr the ruethods and costs of a n effective control program for each region being studied.

15

A detailed kno~vledgcof tlie quantity of power and steam required for the operation of thv projrrted pliint must be (htuineil i~rfurctlir study can proceed. Tlie c o d 01 :dl fuels avail;~hiein the area slii,ulrl he carefully analyzcd S:rtural gar: l ~ i p e l i n r .are making ;I rlicap gas available in many parts of the country. Industrial rates for natural ga. appear attractive, h t they mnst 11e ex:~tninrd carefully. Imlltstrics located remotely f r i ~ n tlw l natural g;is snpply will 11e tile first to suffer slrould a n interruption in pipcline service occur (17 a n unduly c d < l winter cause a taxing of the facilities. Further, c l ~ t qrates for industries in cities served by pipelines often only apply to sunlmer coniiitii~nz ml~enthe demand is lo^. In such cases, alternate iuel supply tiinst be available for the winter months. Evaluation of power costs is greatly aided by the rr:tdy c o o p r a t i m nf local utility companies. Most of these org:inizations maintain staffs that specialize in industrial pmver. Tlic cost of produring power a t the process plant n-liicll will include rriting-off the construction of a p o w r plant, is prrhaps more diffirult to d~.termine. I t r i l l he l~aseil on t,lie iuel :~vail:il)l~,in t11c arc:^, t l ~ cr m n p ~ n y ' sr x p e ~ i c ~ ~~vitli c c other poxver generating operations, and particu1:rrly tlic eqirrit,rrce of u ~ i ! ~ . plants in the area. It is n d r a n t a g e ~ ~ uifs a progressive utility cotrlpany servils tllc region being considered. Even process plants generating tlieir o x n porver iirlrl it necessary because o i rapid espan9ion to purclinw large anlriunts of power from time to time. Only a dependable and mpidly g r ~ ~ a i n g utility system can supply such demands. Labor A large portion of the costs of any manufactured item is repreaentr~l 11y l a l ~ o rcosts. Althuitgl~ 1:tbllr rates nrc inore nnll more 11rro11iinp similar in n ~ o s tparts o i the country, iactors su(,li as skill. labor t.rl:lt i m s , and [lie gmcral wcliaw of tlir Inhoring forre affect I d ~ o rp r ~ ~ h , . tivity and efficiency m:~tcri:tlly. Earli region being consid~red ior plant 111eatiun nlust 11e surveyed to rlcterriiinc the nvaili~l~ility and the skills o i tlie lallor market. Thc skills need not exactly c o n i ~ ) ; ~ wit11 re those required by the process plant. This fact was tnost effectively rletnonstrated during the speculator influx of industry on the Guli Coast, rlf the United States. Chemical plant operating labor a n s recruited from iormer refinery operating men and oil field workers, both groups of ~ v l i i c lhad ~ experience which required the same degree of responsibility as t h a t in the chetniral plant. Maintenance tncn make u p a large portion of any process p l m t lnlmr force, and i t is necessary t h a t the crimmunity have availabl,, a t least

16

Project

Engineering of

Process Plants

nucieui uf sue11 forces a> ell a; training facilities for proviilil~gn r n men. The wage rates existing in a given conununity are i~nportaiit,but it, ~vouldhe a tlcfinitc mistake t o plan on the continuation of lorcr rates indefinitely. The t,rend in tlie United States has been toward a gradual elimination of differences in wage rates betwrcn ~ a r i o u sparts of tile country. Perhaps, a Inore important factor is tile stability of such rates in a com~nut~ity.Some communitier; have beeu notorious for xide fluctuations, a condition ~vhicb n~;tkc; c\-it11local union representatires will also serve to begin the cstahlishn~ent of amiable relations. Talks with the managcmcnt of existing plants \,-ill yield data on the imllortant problem of lahor turnover. A stable labor force is valuable in successful plant operation. A look a t the liotnes of the laboring force in a c o u n n u ~ ~ i tand y knowledge of the percentage of home ownerships slrould give some clue t o the contentment of the laboring group. I n addition to federal labor laws ~ v h i r happly throughout the United States, various state? and. rmnmunities h a r e enacted l a w affecting labor relations and ivorkmen'.- cmnpen?ation. minimum age, and otllcr la~v-:related t o lahor pmrtices. Tlrrsc l:~\v.ivary from rrgiou to region nncl competent legal advice is necessary for the porposc of interpretation.

Plant Location

11

Weather

V'eatlier data for a numhcr of years sl~ouldbe assembled for each con~munity heing studied Particular a t t r n t i m ,sI~ould be given t o severe eouditioni of ~vcathcr snch as hurricanes, eartl~quakcs, and floo~ls. These catastrophic events. 1vliic11 must be assumed as probable, increase construction cost. Extremely cold \yeather often Iiamper;; lirocess plant operation and requires special construction features to protect iquiliment frotn freezing. Predominantly warm weather permits che;lpcr con?truction, but clas~ically it is said to reduce the dlicieney of a labor force. Suclr a conclusion must bc v i e w d wit11 r c q ~ t i c i s n~vheu ~ the production rceords of process plants on the hot and h~nnidTexas nnd Louisiana Gulf Coast are con~pnreilwith those in o t i w part? of the country. C0.t. i ~ Ii r r n t i ~ yor air conditioning may be estimated using m a t h e r

i I

II

I

i

17

data frotn former years and experiences of existing plants. Air conditioning in hot sections of t l ~ ccountry can no longer be ciinsidered a u s u . Indeed, companies endeavoring t o opcratc their office: nnil control rooms vithout air conditioning \\-ill find it difficult t o obtain or keep employees. Community Factors

One of the most important aspects of plant location is oitr.11 orerlooked or only regarded ligl~tly. l'l~is aslicct is the effect of t l ~ cc l ~ i ~ r acter and facilitiw of tlic conmninity Ilcing sturlieil. I t is most difficult to obtain objective infornmtinn on a community bec:iure the u ~ u d sources of information, such as Chambers of Commrrce or Inilustrial C o ~ n m i s s i o ~tend ~ s t o prcscnt eou~owllatbiauerl i ~ l ~ i n i ohcr:lusc n of t l ~ r i r natural entl~usiaimfor t h ~ i Or T T - ~home to\\-11. h study of the cu~nnlunityshould hcgin \\-it11a I O I into ~ its hibtoricxl dcvclo]nncnt. Froni such a study! tlrc charnctcr o f a city ill emerge including its general :rttitude toward industrial cievelo~iments. Asswning that the historical study yield- a sati>factory report, tlir gencral facilitirr offered by the coniuiuniry should bc rrriexr-ed. .i m n tented group of p ~ o p l ertyrriro a ccrtain mini~numuunlbcr of facilities for satisfactory living. I f these do not exist, it often becomes a burden for tlie plant t c ~rubsidize such facilities. Bank8 must bc reliable and staffed wit11 competent r~&cialsand of surb a size that. t h y \\-ill be r:ilial~le of l~anillingplant :IS n-ell :IS e n pluycc accounts. Tlre v a l w of ;dcquate sl~oppingfacilities, cqicciai~y for the fetnale melnl~ersoi fa~nilyunits, cnrmot, I)? ovcrempliasizwl. Larger cities iifTcr thc advantage of factory \\-arcl~ousefacilities that replacement parts for plant equipu~cntcan be tcnilily olilainrcl. .irlequatc and gracious lrotcl facilities a1.e alvays \wlcome, esl~wially T V ~ C I Iit beromcs the job of plant iifiicials to entertain ri.siting dignitaries. At least one or nlorc hospitals fully accrcditctl by tire hmeric;m Hospital Association sl~ouldhe located in tlic area. 111 larger cities, ~ .I n n y~ ~ - o l k ejlrefcr rr to use public transjlortntir~~~ brcrnll?~a p r ~ ~ i l ~ c m transportation becnux (if t l ~ edifficulty oi parking in certain areas. Such pu11lic tranq1ort3tion must 11c cfficicnt and c:e~~nomical. Thc cultural facilities of the community are in~port:int t o sound growtlr. Churclres, lil~r:~riw, scl~ools,civic t111~1ters.uincc~!t awlcian i i l r g r i p , if nctivc imd I y n m i c , I 11111(:11 to t i n : I I make a comniunity prwgessivc. Fornmcl-looking plant n1:magern will realize tlmt tlte yuung people in a community will 1w the crnployees oi I I I advqunlc cultural opportunitomorron.. and a good school ~ ~ P ~ P i1nd ties d l in the fin:tl analysis makr ilettcr rmploycrs. 1lecau.c thv j)r,~cessi~xlu.~tri(y ~ k ] i c n ~011I ~ , T ~ I I I ~ I , : II I~: ~ I I I ] I ~ I K ~ ! I ! ,il 1.2 $lt+ir:~L,lv111;it :i unirersity of the first rl:ws lie 111carriliu thc st:ite umlrr con~i,l~:ratiun.

18

Plant Location

Proiect Engineering of Process Plants

I t s engineering and science departments should be accredited by the appropriate agencies (Engineering Council for Professional Derelopuient. hmcrican Chemical Society. etc. !. h study of the population trends in a community is often revealing sincc it indicates the gron-th and trnor o i a conn~innity. .ihrcakdorm of population statistics into age groups is liell~ful in l~rcdicting the poesiblc vitality of a region. , llic problem uf recreation deserres special consideration. Recreation nil1 inclurlc, of course, the cultural entertainment already mentioned: and. in ailrlition, outdoor activities and otlrer events ranging from country club dances t o sulall gatherings in homes. The disaiirantage of the extremely small communities or company tinms is t h a t the couipnny n ~ u s t*ul~si~lize the constructicln of parks, golf courses, and cluhs. Furtherl the so-called company torvn is predominantly occupied I)? e~ilployresand their fanlilies. M a n y people find such a situation ni~rron-ing sincc most of their friends arp other t,ml~loyeesand their fn~nilir.san11 all too often a f t e r - l ~ ~ i u rconvcrsatione s ric~elopinto "shop t : k Tliis geiicraliaatiou, l ~ ~ ~ n e ri*c rdangerous , since it depmds so uiuclr ion the individuals i n ~ o l r e d . I t ~ u i g l ~bet said. nrvt,rtheless, t,l~at it requirc,s people ~ v i t hIxtter than average imagination tn avuid thcsc pitfilll~. Extremely small couiniunit~icsmay fail to offer the opportunities for rrcreatiorr required by yonng prople and discontent often develops. Plants located near large rities i ~ a wavoided ew11 situations, rvhile some remotely icicatcd plant;? have overcome thcsc difficultica by the est,ab lialnuenf oi active recreation ~ i e p a r t n i e ~ ~and t s clubs. These hunian factors :ire all rather netn~luue, t n ~ tnone tile less important. They dionld not be overlooked in any analysis of plant sites. The efficiency, clmracter. an11 history of both state and local governtuent shonld he evaluated Ilocalitiee 1vhic11 liare snffcred long yrary nf corrupt 111. inefficient porern~ucnt are pour risks. State and local Iarw and repulatii~nsnliicli will affect plant operation and living conditions require the interprrtat,ion of a co~npetent attorney. These include d l tax ordinancesl especially those applying directly t ~ r the industrial ~,oniniunit,y. The existcncc of lorv taxes in not in itself a favorahlc situation unless the commnnity iy already well devrl~~peil a r ~ dis not in great deht. It is certain t h a t a e ~ r n m u n i t yhaving un
.

the data necesbary for t l ~ cinforliintion disrwrst~dalmvt. can he ol~tilineil u-itliont actually visiting tlir are:1.. The final site wlecriim. Iro\\.cver. require- careful x r u t i n y hy a c o ~ p sof mperts. I t is preferable t o avoid pul~licizing snch risits since real estate vnlnes invnriat~ly rise upon rnuior of nexr- pI:rnt construction. This necc~;;nry secretiveness is often hest accomplislied hy dealing 17-ith only one rcliahle real estate firm. Topngraphy and soil condition of each site must he evaluated Foundation c o ~ t sare greatly increased on site* liaring soil of Iorv heari t i a i t Good natural dr:iin:~gc is another ~leeir;iblrfeature; a n d d if tlie iitc is lorated near a streani or other 11ody of \r-ater, f l ~ ~ ohistory should t ~ e carefully cl~eckcd. O f t r n seemingly excellent sites have soffercd from pcriodic flouding that nonld never he predicted on inspection of tlrc nrca during noruial conditions. I n :1dditio11 to tlie advice 11i competent soil experts and constructim engineers regarding the feasibility of the site. officials of the neighboring plants can give helpful hints concerning the nature of r a r i o w locations in the area. FINDING INFORMATION

Tile forcgoirig brief sulunxrry of factor;: that ninst lie ~ I ~ t c r m i n cind a. plant lucation study indicates the need for a vast amount of i n f o r n ~ a t i m both quantitative (statistiral) and qualitative. Rerause of thc large nmul~er of agencies, puhlic and private, rvllicli u l l i useful inforn~ationof this type little actual original gathering of data must bc done. All sources of printed information rliould be cxliauded t~eforc tniiking a private survey on a given phase of the study. T o ;lid in the search for printed information, a euggeytcll list of sources tugc,ther ~ v i t h types of iniorm:ltion offered is giren in outlinc form belun.. The n.i~rkso i ltigglenian and Frisbeelo and Cornan" aided greatly in prcpuiiig this wtlinc. ~

Alter an area or regio~i ha.; h e m s~,lccted for plant location, the mlonnt of next i o l ~is the selectiut~of a sl~ecificsite. A c~~,nrirlcrable

~

I. Inriirrs and Aids to Scnrrhing .i.US. Gowrnmcnt Pablirntions* 1. Hi~.slihr~.~. H. S.. and hlelinnt. ?. H.. Suhjrct Guide t o 1'nili.d S l o / ~ sGo,.crnrrrrnt Puhlientior~s,.Imcl.icnn T.ihrarr .isuoci;~lion.Chicago. Ill. (19471.-Dr. ser.ihrs gorrrnlnmt, publirationr and p i r ~ csmmw [or n numhw of s c l e ~ r ~rq)iv-i. d 2. Srlinreckehcir, I,. F., Gu~.r,-ti,iientPublicalions nrid ?'iir.ii- 1 s t . The Brooki n g ~Institution, FTashington, D.C. (1936).-Anollicl. drscl.iptiw guide to g~vernnirnt publications, although sonwwlint imldnted. 3 . . I l o v / h i ~ Cntnlog o / thc 7.niicd S l o l c a Goswi-nmrnt Pzihlic,i/ions-lliijor indrx oi gmwnment publicniions. .A ypal.-pnd issue contains annual suhjert index. Lists prtietirally all pnl,liiations h t h rongrcsaioniil :md rl~p.i~~t~nml:rl. tinil rtnrtinp

1936 has included many proceeaed (mimcogloplird, rtc.) puhlirarioni iirmwd oi intrwst to the puhlic. Most large universities and puhlic lihl;iries serve as In

FINAL SITE SELECTION

19

Scxirr,, o j Cortg,i,~.~-C;i~Ulr t o Cong~wsion;tll i t w ~ t m c . 7 . C<,~,y;,rI,,>?,,l;,l m d B,,W.,,I l,,,liw-.\ ,I,,,,, I r r "ig,>,?rn,,,,~,lt < l c ~ l ~ : ~ ~ t ! l ~ ~ n t ~ :dI,nrc~noslxll,li.ll inlliccr oi tllris u v n ~ n ~ l , l i ~ . : ~ t i o'nl- l. w ~inclwk tlw f ~ ~ l l o v i n g -~unmorirc: ,,. 1,i.d ,,/ l x ' lj,,,.,<,,, ,,I Y i , , , , < i ' ~ , l , I i ~ " l i , , i , ~ .191I~-l!i;9. i,rrclt

b , l n d c z 1 0 I ' ~ t l d i w l i ~uf~ ~I / ,~
l i s t of


22

Plant Location

23

3. The Conference Board Management Record, Sational Industrial Canierenrp Board. Sev York, S . Y . (monthly).-Discusses labor trends and presents statistics. 4. Labor Union Publications. o. Economic Oittlook-CIO, Dept. o i Education and Research, Kashington. D.C.

i r i Lichor, 1)vrlen P~.css,Serv York, X.Y. i . Prrntic~-HnllT.;ihor Puhlic;rtions. Pwntive-Hall. S ~Ywk, T S.Y. o. L,ihi,, Rcplo>uwni i.i,nililion.s. 11. I i t d i ~11, I,,rbiri Arlicica. Rnnd School 01 Sar.i:il Scicnrr, S e w Yo&, X I - .

6. 11-ho'. TVtio

Cl~iriigo,Ill. 6. Ofici,ri Sterrms1,ip r r , d A i i l u w G u i d e , Trmipu~.tntionCuiilea. Inc., S c w Ycrk.

1 . T l i ~ l - w uo f Census. Digrsts of s I : ~ t e l a w rrlulinc: to t:LLI of Intetnal R ~ v m u r ,ITS. T ~ . ~ a s n t .Dek~t.. y IVasliingtrm, 1j.C. 3. . I l i i t ~ i c i p r i l I , 1 1 t I City l i n g .hw,.i;ttion. ('liii.;~go. Ill-I.irts offici:~lsand f o m ~oi m y gui-ernment. 4. .11~8u~u~?vze?t! A ~ ~ ~ ~Satin~xtl L o c , I n d w t r u l C o n i c v ~ nBmrd, ~~ SW Y w k , S.Y-Givrs c o n m n r r a prire indicrs in GO cities. '5, Ai t i m on lural trnniporlntiun svstrms. * i .h~nrriuanT:ixicat, .Association, Clrirago. Ill.-\l~.itc i w d;ili> on t;ixi srt~tictlc-. * X . i n ~ w i w nT~'lrpImnc& Telegraph Co.. S e ~ yYmk. S.T.-Conrart iol. itatistir:il ~ I onR pllones. "9. I T S . Post Oflicc Thpt., ITaahington. D(:-Contart iol. ~wwiptsfor inrli7-~hal {post utliws. 10. Drj,al.trnrnt of Commerce--Statistiral data on bucmra* onrvatmns n i all kinds. 11. Ranker's 1)iwi.turier. N . Rand-hlrSdIy. Chicago, Ill. h. R. I,. Polk Cunipany, K : i ~ l ~ v i lTl ~m. n . * Valunhl~in vulnp:t~ing comulrurili~~,. ci.

U. Lahor 1. Bnrrwu oi I.ahor Statistics. U.S. a. Monthly cn~ploymcntreport hy b. Cost of Living Indices. e. Handbook 01 Labor Stotis!ics. cast of living, f t e . d. Jfnntidy Labor Ret,i~zu-Wagc

Dept, of L:nhol., IV;rshinglan. D.C. etalrs. Puhlisl~ed irregularly since 1926-Wages. surreys. statistical dnta, hihliug~.apIr? oi

24

Project Engineering of Process Plonts

14. ,I.

Plant Location

2. 3. 4. 5,

Stalisiiwl Scwims. Dun & Rsarlrt~~rct

b. 5t:lndard & Pools Fcdrwl RPSCIT-rl h n k . 16. Prderol K m ~ w c.%l!r.iin

15.

Ronrd oi Go\e~.nor.; F r d r m l Re-srnr Syitern.

II~urliingron.I1.C. (yr~.iudic;tl)-Gi~c,sdqrnrfmrnt iiurr ielrr a d

rons~in7rrwedit

'lillil.

17. 1,or:tl I x ~ k ~ . I . C I i Comme~.ci.: VI~J-. county. CAI I t I l t l 1)rirlol~1i1rmt l~o:trds:stat? t ~ n i w r ~ i t i e s . 19. Bimnio! Suj.w!g 01 , ? ~ l ~ ~ ~ ~F&n~l ~ ! i u ~S~citciLy z, .lgmv>-.Kasl~iugton,D.<-.-

23. Statc and city 1ir;~Illrdi.partmm-.. 24. Sntion;tl Oilirr of Vital Stnrictiir. T.S. T ) ~ I I I .of I'ohli,, Hi.:dlh Knsliington. 1)C.-Birth? and deaths in ritii,~. 25, Olficiiil IIolcl Rcrlhuok & Diricli~ii,. 11wxic;ln Hutrl .liioriatian 1)ii.wlol.y

25

T r : ~ ~ ~ s ~ x ~ r t : r t i u ~ ~ - ~ i c [if ~ r .:ill ~ ~ti yj iltm i r ~:init r i II:IIIIW.

R a w ~Iaterir~ls-i~ualitativeinforn~:~tion. Fuel, IY:itcr: and Pmv\.t*r-rntes and adrlrcss~si ) i ' r~tility~iffirials. Labor-typical tvage rates, consnmer price index. 6 . Taxes-rates, Addresses i ~ fcity awl state officials to cor1t:ict for ~rdditionnlinforn~ation-ICs1)lanation of tax drurtnrc. 7. \Yeather-charts. 8. Industries in Area-oil and gas, clren~icals,and n1ct;lls-l)escril~tioli ~ oi existing facilities. l~rodurtionand list uf all plants on Gulf C ' ~ I : Irr-it11 m i l qu:rntities nv:rilnhl(,. Ilamcs of genernl managers, lists of prodi~ct.~, 3 lliscellnneous Statistics over Pt:riod of Ycarsn. Population. b. Retail Sales. c. New Construction. d. B a n k Accoonti. e. E n i p l o p i m t . f . Post Office Receipts. g. C h a n ~ b e rof C o n r ~ n c ~Statiitieal w Sinn~nary( i w ~ e dmontl~lyiincludes .stati.~tirson Port o i Houston tonn:lges. d q w t n ~ c n store, t sales, telephones in service, and t~r-enty-twco t i ~ c r1)uints \I-hick indicate city vitality. When i t is rcalized t h a t all this lielpful iniormation is available from one orgnnization a t no coat. the value of p r i m t e and pnl~licindustrial drvelopmant ilcprirtnm~tsbccon~esm ~ r cnpparcnt.

s Tlw above listing is I1y no ulcons coluplete. H?nv)- c m ~ ; l ~ a s iIirrbeen p1:icetl on tire nontei~lrni(~a1 dntn sources since it is assumetl t h a t onc trained in engineering will 11e\.e a n-orking knorvlecige of the sourccs of scientific and technical literature. T h e factual infonnatii~nnx-nilablc flrim industrial divisions of ~ I I ~ I I I bcrs of commerce, utilit:- con~panie.s:mid milrorids deserve special em~ i l ~ n sI~erc. is Altl~ough,us ;ill.enrly ~uenriunril.tlie iutevpret:~tionby tlresc organizations tvill l~rol~:iblyhe filled tvitli tile same enthusiasm fur alr area as that held by any a ~ e booster, a the faotunl data is usually reliable. It is ;irrangcd in a \-cry u d u l nianner and represents tire most rapid meiins o i obtnining n co~npil;rtion of ilat:~,p:irticularly f ~ i r:i prcliniinan. surmy. Certainly for ilct:iile~l surveys niltl\c ini11r111~iii1111 :I?;.cnrl;lcrl incluilcs thc f~111,:nr-ing: 1 I ~ k c t l i ilt(.o~~ir ~ ~ iI,[ ~. - r i r i . u r ~ ~ r ~: il w i ~:i~~I)!. ( . o I I I I ~ ~ I ' - .

CHAPTER

3

PRELIMINARY DATA FOR CONSTRUCTION PROJECTS After a rlte has been selected for the construction of a process plant, a large amount of infurmation must be acculnulated hefore design work ran begin. Engineers, purchasing agents, and construction supcrrisors must h a r e detailed information about the site and surrounding area. Several experienced men \vitl~backgrounds in both engineering and construction management ran obtain the nccdcd preliininary d:tta on a visit to the construction site. The information they gather includes data on engineering for use in design, procurerncnt pr:tctices in the area, and informati~~n necessary for planning construction. Tllesc preliminary data plus psocess requirements set tire hasis for design an11 constrnrt,ion of the plant. TYPICAL PRELIMINARY DATA

Preliminary data outlined below are typical of tllat gatllcred hy the engineer on his survey visit t o the job site. Engineering D a t a

Essential data necessary for the engineering of a ~wocess~ I a l l t1vIlicll should be obtained by the survey include: Weather Data

Fur domestic projects (U.S.) information on wcatlrer iuay he ohtsineil from government agencies such as the U.S. N'eatllcr Bureau, G.S. Depart16

Preliminary Dato for Construction Projects

27

ulrnt of Agriculture. and the U S . (:east and Geodetic Snrrey. Tlic h n ~ r r icau Society of Heating and Ventilating Engineers hare also cm~piled considerable n-eatlicr data, vhich may be useful in preliminary n-ork.

\YISD DIHECTIOS PREVAILISG 'scful in initial plant armngcu~ent. .is an illustration assume that the plant is t o be located in an area where the xind is predominantly fr,:,m ll the Southeast. It wmld be nndesirablc t o locate a process ~ v l ~ i r frequently discharges noxious funlcs on the Southeast side of the plant where they ~ o u l dhe constantly blown through the plant. Again, asaurnc that a process discharges particularly volatile and flannnable vapors that are Ileavier than air. I t xould be unwise to locate an open fired heater in the path that the f u n ~ c sw ~ u l dordinarily f o l l ~ ~ wGeneral . xind direction rnust bc considered in locating any process which is exiraor~linarilyh a xrdous or subject to fires. The efcct of wind direction m storage areas for flalnn~al~le products should also be rtudied.

Cscd in setting proper design conditions ipounds per square foot) for tvind loads on exposed rtructurcs, equipment. or hildings. Certain U. S. Gulf Coast areas, for instance, use 40 pounds per square foot because of ~ x ~ s s i l ~ i lof i t yhurricanes. The final value has considerable influence on structural and foundation design. TJsed in process design, in the selection of insulation, in determining plant-building typcs f l ~ rilrocess equlpnlcnt prote~tion,in building design for personnel ~ , u n ~ f o rilnd t , in selecting inaintenancc procedures. The design of the cooling vxter system and selection of equipnent are also influenced by atnlwpl~eric tcn~pcrature rengrs. Tctnpcrature ranges should he studied over a tvo-year period: or longer, to provide the best estimates of arerage values. REI.ATIVE H U M I ~ I T(range T by day, month, and seasonal :iveragei Required for design of cnoling towers, air driers for process air, and for determining personnel cmifort requirements for buildings. RAISFALL( I K I ~ X ~ ~yearly, ~ U I I I and , seasonal avelagcJ Required for plant drainage design, building design, and possibly in process deslgn. Ssow C ~ S D I T I ~ N S Required for structure design, maintenance procedures, and buildlng design.


28

11.

Preliminary Doto for Construction Projects

29

Plant Terrain Soils I I ~ I -l,c t c q > l i ~ r c dfor fonndation or load-canying character-

is ti^,?. 11. Chnror~rmnps sl~mvingground e1cv:itions ~\-llicIl:ire useful in planning 111nnt ~ i r n i ~ : ~and g c plant roiid\\-ay ayitenls sl~onldbe prepared. c. (I<~ncrnl slopr or I~crularitieiof the site, a r e also nccess:uy in pstimatIng l,i.clir~~innrp ar:~diug \\-hiclr in turn inriicales t h e type of construction gr:lcling c(l11ipment.

a . Promas n.atrr (n.atcr used in the 1n'occss). I,. I ' n m s cooling rvatcr. c. Sirnit:~rywater (tl~iai l l l h t he 11otiih1~ \ \ R I ~ c ~ I. d . Gtility water (n-ntcr 11wd for general clr;uiing and n~iseclluneous scrvirw I . e , S ~ V X IgIrIn w : ~ t i o ~IIII:L~XYI~I l \\-:it~rfor l x ~ i l e r . ~ ) f. Fire protect,ion x u t e r . g . \Vnter f o r constvnetii~nu j i Iqu:intitic:: of conbtru~.tionn-ntrr dcpcIId on type of l ~ r o j r o t nu11111cr , of construotii~nc~i~ploy(,cs, :mil the lcligtll 01 the cor~structiouperiod).

JTater f o r process cooling, sanitary nse, and steam generation must be che~iiicallypure or trcatcd t o thc extr.nt rrquircd for the pror.ct:s. T h c source of r a t e r supply m a y be fro111 *trennr he& or other natural Water provided turbidity and scdiulcntation is not excessive. Brackizl~ or ~ 3 1 t\\-ater is oftt.n I I S ~ ,f~o r vmiling, l x ~ tc:rrefnl selection of the 1u:ltcrials uf construction is necessary in order t o 11revent corrosion and de~m?its.

Elec:ric Power a n d Fuel Services

IYl~cnrlt,ctric pinver is to 11e p ~ r c l l n ~ c rthe l , 111c;ltionof incoming p w w r f ( ~ ~ l i , r:tml - . tlir plant sul~st:ltirn~ nrnst 11e rlctcrnrirrmi. Priuii~ryvoltages I I I U ~l ~ e deterniined early, in orllcr ti1 start cnginrcring :ind p r o c u r c ~ n m t 11i t h r I I I : I ~ 1)lant ~ t r a n r f ~ r n ~ and c r switcl~gcar. Tlic preliminary sllrvcy s I ~ o l ~ ldctcnuinc ,l the (1ire1,tion from ~vhirllthe lilies ~villconic; ~vhether ~ i i ~ i v cSro~n r tila llropcrty h i t to tlic substt~tion is to bc ove~11e:id i ~ n ~ l c r g r o u n\vlretlirr d. a zinglc fccder systrm \~-illhe pr,>vi(iril,or \\-l~etllcr t w or liiore sources i11.c to he conncctrd. h singlr sopply fccder system is 1 - 1 1 1 I I t i l l be I - i l l . I n r w t a i l ~arcas snl~jtwtt o ievcrc :~tinr,>plioricclwtril,ul disturlxinccs. Ilowevcr. p n . i , r fnilr~rofrlwil. ~w 'IYic ~ I O T T s- ~~ ~~ p p l i m c ra y he :t11Ic to reduce f r q n e n ~ y r ~ r~ ~ r o l ~ d ~ iofl i E:lilure ty by ridding one or nlorc n(lditiuni11 frciicrs provi~linypo~~-\-rr i r i ~ ~nnd i f f w n t dirrction. Pa>t I~istrlryof p o ~ fr; i i I ~ r e z !l!:r)111. !I?tcr~nini'd1'1.~1111tlw s ~ ~ p l ~ l i r~r ~ ' st w r or ~ lfro111 s 11t11wli1(.:11IIWS. 'I'hr . q i l l l i r r I I I U ~:?Is0 Iw givrm, 11s c w l y :IS l ~ r ~ s s i l ~t l eh, ,late I V I I ~ I L t l ~ c111:1nt xill start opcr;~tionI I ~\vl~enl m w r will be required. Ii tcluporary power is t o 11c provi~leilfor construction uses. i l ~ cnecessary nrr m g e m r n t s for inrtnllation ~ l ~ o u l be r l made early. Poor electric utility - . m i c e or n rrrord of high frequency of porwr failures ninst be considered n.l~enparts of the process becon~ehaanrdous under power inilurc conditions. I n certain processes many prime movers must be provided ~ v i t l ~ spare steam rlrivrrr for safety reasons. I n a major installation t l ~ c ilrq~licatimof drivers inay he rostly. Small paclc:~gr-typcstennl .rcenerntors are nsnally nmrr i ' r o n n n ~ i r ~t hl : ~ n

30


FTELSOI.HCK.:H T h e selection of the ty11c of fuel d r p m ~ l son heating value and scllinp price aud i~ elusely rrlatc,,I to tile rconomics of purcliaml 11o~r-1.r.S m i e of tlte sources are: ( 1 I Kntural gns; ( 2 ) fuel oils and liquefier1 petrolcum gas; (3) c o d 11s (1t11er si liil fuels; (41 plant n-astes. Snturirl gas is often user1 as a raw material in certain proceiscs. \T-hcn tllc process requires naturai gas as a raw material, gas is also used as [llallt fuel. S m i e oi the plant uses oi gas arc as fucl for priule mol-ers such as large internal cmnbuation engine-driven compressors or gas turbinrs. fucl for steam gmer;rtiou, engine iuel for el~,ctriralgcnernturs, ;md for produrtim of inert gases fur purging or blanketing srrvices. \\-hen natural gab il to 11e porcl~asedit is important to ohtaiti d ; ~ t aon tllc snpl~ly pressure and an :inalysis i1f the g,zs as 17-rll as a guarantee of its coniposition or the liluits of v a r i a t i ~ ~ n .Xatural gas in solnc areas is \vet or carries a certain nui,)unt of condmsatc. If such is the case. n trill> sl10111d be provided near its entrance to the property. I t uiust he decided and clearly pointed out in thc mntract for supply. rvl~icliparty shall furnisll the t r a p and ~vliercthe responsibility for drainage of the t r a p d l lie, i.c.. P~, rrrtain of the liquid tuatcrials ~ v i t htlir rupplicr or. tlie ~ I I I T C ~ I ~ S \Vhilc n-ill immediately ev;rporatc upon dischargr, other coti~poncnts~ u n yre111aiu iu a liquid state producing ;r l~azard. I n conge-tcd iudustrial a r e w the ilrninagc o i trapped r,indcnsate from natural gas can hecome a i,onsirlerable prohlem. LTnless there r ~ d he l some process use of these liquids it is hrttcr to insist on a dry gas, furnislicd at a certain prrssurc a t the user'; meter. T l ~ cpurcliaser lnr~st also ascertain precisely where tllc natural gas pipeline ~ i i m l t r r t h r property and decide which party shall supply the turter, the primary device, thc meter house, valving arrangetnent, and tlie pipiug acwssories. The a h u w suggestions are for supply services in the order oi niillions of c u l ~ i rfeet. They are not of itnlmrtnnce for wuall installations ~ v i t hservice connections perhaps of 3"-pipe aim or less. Ho~T-ever,it sliould always be clearly understood which party supplier and installs the equipn~cnt. \Then the final c i ~ n t r a r tis entered into with the supplier a drawing should be prepared locating the cmnccting point of tile owner's piping and showing the type flange, valve, joint, etc. to which plant piping will he connected. Tlicre data should be given the l~urchaserby the supplier. Natural gas supplicd by pipeline ~villnot ordinarily require auy aux-

31 iliary pressure vessel or capacity t a n k since the system ~ h o u l dprovide tlie required capacity. Pressures above 30 t o 40 psig for plant fuel syptenis are unnecessary. Csually gas supply pipeline prrssurcs arc much ahol-e this rang?. Ordinarily the prohlcui is more one of reduring pipeline prc.;.ttres ti] range.; suitable for plant services. For this reason thi, clue.tion of supply pressure should he dieruseed as early as possible. If the gas is to he used primarily ior fuel, a slipply line pressure range frmu 50 to 75 psig should be sufficient ti1 allow for plant surges ~ v i t hadequate i~pstrcaltipressure for satisf:rctory control and capacity in tlw l ~ l a n tfuel systeni, Pressures a t thc point of usage are ordinarily in tlic range of 20 to 30 psig, and ;ire l o ~ ~ - for e r hurncr headers. Fiiel oils arc usunlly drlirered by railroad tank car or uiotor tank trurk. Facilities for storage of the liquid fuel niurt be providctl. l:su>rIl>heating iurtst he provided for unloading. Tliis is more fully disrlissctl in Chapter 21. I n the preliminary survey, thought should be givcn to proper location of railroad or truck unli~a~ling p i n t so t h a t tlie initial p l m t arraugrnicnt stluli(.s vill inrhldc this facility. IiqlieJied petvoieii~~i yrrses or gases held in a liquid stnte arc t ~ c ~ o m i n g a n iml~ortantsourrc of foe1 for donic.stic llcating in some arras, Iioi\cv~.r. tlicir. usc as indu.;trial furls is still souicwl~atlimited. If the p1;tnt is small, this type fucl may he used to an arlwntage for i.datctl huililing hating. Coal is not ordinarily used as a plant fuel fur t l ~ cprocess plant : h o w r r e r , coal may 11e used ns a powr-generating fuel if the projcct is located in a r.oal producing area 01. if other iucls pr11vc uncconoulical. Neressary facilities ~vould)Jc require
Product a n d R a w M a t e r i a l Transportalion a n d Sforage

T h r p r ~ ~ l i ~ u i n adata r y roncerning plant terrain iuay 1r:rvr ronsiclcral~lc eff'ect on tllc 111c;ltionof w(,h iacilitiw ns ailr road unloa(ling and loading points, and packaging and storage facilities. C:rrtain plant. l o c n t ~ don sIq>iug s i t e h a w the liquid pr~lrluetsturagc :~rriingc~l so that ;ill lilading is hy gravity. T h e location of st,,ragr puints for hazarrlous prwlurtr tilust, :tddIle rarefully (,ousi(lrred since in order Lu m c ~ ts;tfct:- r~y~tirrtnerrts tional :rrre;lgi, nray be rerluircd It i s vcry import;lnt to dcterniiuc the dcgrw oi intcrpl:mt tran?lwrt:ition : ~ n dthe storage ~cquireulentsbeeituse uf their effect on plant nower rc(lr~ireliietits.


32

Ran. r ~ ~ n t e r i a so~iietinies ls enter plant;. and prodncts Icavc the ~rl:irit hy pipeline. TVherever any piping enters or learrs the plant the cxact p i n t s should he determined a;. early as possible si1 that interference ~r-itll {plant f:~ciliticscan be ax-aided. Procurement D a t a

Prelilninary data :~ffectlngprorurcnlrnt arc: 1. Earlicat date xlren inaterials rliay hc rrwivcil a t jdliite. 2. R w i c nl;1terials r ~ fmn.4ruction :rv;~iI;il~lcin a r c > . 3. Connecting r;lilru;i~isand nearwt sn-itch pi,int, councrting i n scrvi11n motor truck lines. 4. Slain iligil\r-ny locatime. 5 . 1,ocatioil of ncnr<,fr rnt:lrol111litan :irc:~ 6. Types of industrial equipnlent u-.e;~hlein l ~ l a n tcrr~,tion:~ruilahlc in tile imnlediate nrca. 7. Types of industrial drops in the immediate area suitable for repair ur maintenance or 1,arts snl~plyf , ~ construction r ~~pipuient. 8. Storage space and itorage area fur plant e q r i i p c n t and c o n ~ t r w timi material.

9, is intimately related to jirojcct Pr~~cureluent, as diicussed in xlleduliug and planning (Chapter 7 ) . Tllc procurement org:illiaation will be rrlort concerned with plant equipn~cntand construction material transportation. The nietllotls of tmnapurtation, t i n ~ erequired, ireiglii rates, constru~tionlunterinl, storage facilities ( a t the jobsite), field fubrir;rtioii r ~ f certain parts of the equipmtmt, and delirery data all affect ~ x w u r e m e n t . Transportation and jol~site storage l m s t seriously affect prelinlinary procurcmerrt planning or sclleduling. Tlir most vital question in procurenlcnt is a h - n y s iklirery or deliver? dates. A 11rojcot a t a reiuote locntion with a possible tmnsportation tinic of mie ulor~tli\,-ill require all scheduling t o iuclude t11k t r a w l tiluc. Arnilnhility of con11non materials in the :rrr3;t uf construction tlrgethcr wit11 11rice data rnust he ascertxinetl. Price differentials may ~ v a r r a n ttlrc procuring 11f a large pcrrmtage of materials locxlly and thus jlistify a lo(':ll procurenlcut ol~emtion. Certain materials such as ready-illisid cr~ncrctv or t l ~ enratcrinls required for concretc art. aln-ays l,urelln-id locally on ~louicsti~. ~wojcctr. Sourws of supply ;tnd )".ices for t l ~ e a r~lr;itrri:ll- illllit, lw :iscc~~~t:ri~~wl :ls :I 11:~rtof l,rrlin~ir~::ry~ u ] , v v y
All collt;trur.tion pllase> are rtfferttd lly locill wm,litii,w sil~cctlw construction orgn~iisationulrrst beco~ne:L liiirt of the locale for the x11ole

Preliminary Data for Construction Projects

33 lierioil of crcrtiulr. Tlw iollon.iug il;ltn I U I I \ ~ I E IICCUIIIIII:I~(YI :IS I Y L I . I ~ possible. Labor

o. Awn I\-RP(, rates, trade union rontrarts in forw and ~spirntirm o f lo1,:11~killml~ , r : ~ f t w r e n ,I:~tw.:IIUI:~v:iilxl~iliry 11. Tr:~ilcu~iionrr,lm,wltnlii~n:nanlr-.. ;i~idrc.ss~s of all 111c:il or arcn ~lriiolibrwinc.s :tgmts. r . Otliw project.: planned in area nrld times of peak erup1<1ymrnt. (1. I-niou permit.-if ~,onstructionpersnnncl arc t o be lnmugl~t into r l tllcil. work 11y ngrce1111wt I 'I~I(...,. :trr:\. ~ruiiln) r e m i t s rll~litI)? ~ h t a i ~ l efor ::re usunlly n w r r ~ : ~ ~ m p l e tsatisfied ely but sliould be a t t e m p t c d ~ c. .lr:
34



35

SPECIAL REQUIREMENTS FOR FOREIGN PROJECTS

Tlie data ili- data for any proiert. ('on~idcrahlcadditional preliminary data aud decisions ;ire rcquircri for foreign jobs. Construction Interference

Tlirse questions arc not usually as iniport:rnt for a complete p r l ~ j e r tas for \ \ - , I I ' ~ \vitiiin a n ol~erntingplant. C)~KHIIE.ID OR VSDER(:HOISDELECTRICAL ~'OS'ER LISES. Location, height ahovt! ground, depth lielow ground, voltages, source of power, area supplied, uwier or o p w a t ~ ~nearest r, srrit~,lipointfor q~cnirigcircuit ~ i u he d deternlineii. If guy derrick is used, ~villguys clear cal~les? Location of dea~l~nen. P I P I X ASII SEVERS. i)cterlnine location. O V E H H EOH . ~ L~SIIERGROGTD size, e t ~ , . Existing 11iping in tlie operating plant is often a sourre of con11y sillerablc extra cost to tlie cmstructor of the nen- facilities. ~ ~ ~ 1 11hllt.~ ( l u not I I R V ~ ,exact or reliallle rerurdt; of the locntious of underground lines. Tlie resl~onsibilityfor removal of such lines should he establialied. PLAST HAZARDS.I n many operating plants nliere work is being perf ~ ~ n n obnoxious c~l or llazardous vapors or funies may be relrased I n smne cases work may I I con~pletcly ~ stopped until the condition is cleared. Tlie r1~s11onsihilit,~ for costs of unprc~ductivelabor during such periods shoul(l be understood. Often serious restrictions exist on f l a ~ n ccutting or n-elding or the use of any open fire on tile premises. I t niust t ~ edeterniined if any s u ~ , rrstrictions l~ trill be in force. I n many h y ~ l r m a r l ~ c ~ ~ i psoceljuing pl:ints and other plants processing hazardous n~aterialsall niatcl~csand pocket lighters must 11e left a t tlie plnut gate. Smoking arras niay 11e ~lesignatetlor snoking may h r permittril in runstrurtior~ ~ ~ e r s m n i cliangc cl liouses. G P I A EQUIPMENT. ~ If the \ w r k is ill a n K ~ c m v r r .ANII ~ ; H . ~ D L I S OF ol~erntirigplant, tlic owner niay require rert,airl periuita or receiving procedures for material or e q u i p l e n t delivered L I rail ~ or truck. Permits niay be required for trucks or cars leaving tlie plant. If all materials are received by the owner, the responsibility for the diipnient, proper accounting, Iiandling, and delivery a t the construction site 111ust he determined and clearly understood. K A I L ~ A ASD Y H I , ; H ~ A YCONSECTIOSS. Exact loeati~lls shouki be determined for p ~ ~ s s i h lpersonnel e transportation use. T h e handling of plant and construction materials is greatly simplified by laying a spur railroad track directly into the plant frum the ncarest railroad.

Permits

T l ~ rcrrction of plantu in foreign countrirs. d i e r e most of the equipment ur ni:rterial n-ill 1x2 r n n n u f i ~ ~ ~ t u rine dthe Irnited State?. require? certain overall per~liitsor licenses in order to export the various i t e m from tlw T~-niteiilit:it?s zn(l wuiilly import perniits or licenses in nrrler to move the equipment inti^ tlie rountry ~vlierethe plant is to be erected If tlic countr?. is l:rnriln~~kccl; ~ n dsl~ipnimt; riiurt move through an adjacent, rountr)-, crrtain ]lcrniits for i n - t r a n ~ i tsliipn~entswill he requirrd A nunil~cr of niatcrials have heen classified by I1.S. (:ovcmnient;d ;~gcmcie~ as critical to the national economy. Explicit permits niust be ubtaincd to move these n~atcrialsout of the U.S..4. Tlie destination and ~ nffcct the granting of exl~ortpcruiit;. (:11n111lctt! uzr of s ~ i c ln~atcrials lists of all critical materials: tlie applicable rcstrictims on destinatiou and explanations of the ncecssary procctiurcs are available from the U.S. Government Printing Ofice. An :~pl~lieationt o the 1J.S. Government for a n expmt license niust ~ ~ l j u a l be l y accompanied hy a complete listing uf all materials aud equip~rleritc , , ~ n p o n m tusrd s in such equil~mcnt,together ~ ~ i t w 1 1i g h t or v1111uue ( a s required] and dollar valuc for each item. A numericnl and alphahetical designation has been rleveloped fur mrious items. ~vliichdesignation must he u w l in l ~ r e p ~ r i nthe g lists. The d ~ i p p i n gdates by yearly quarters must also be included. I,ater, as shipnicuts proceed tlie specific items must again be listed for each shipment anti checked off the rn:ister list. The preparation of the detailed lists is ro~newliatsimplified hy the intent of the governmental control, which is more con~wmedr7-it11 runxinunns than ~ i t precise h or exact evaluations. Care must he taken, ho\wver, to account accurately for items as they are sl~ippcd. Since export license restrictiom change frequently, i t is mandatory that each issue of all applicahle govcrnmcntal publications offered by the various agencies be c:lrefully slutlied. The data necessary to meet the cxpurt license requirements 1\41 only t,ent:itirely permit sl~ipnient. All itenis shipped niust be arcomp:rnic(l in dctnil by the standard export documentation to meet 1 - 3 custonis ant! sllipping rerpiretuents. l\Iwemcnt of shipments: t o dr~ckside. Ti-arrhousing, lighterage, and handling and preparation of h i p p i n g documents

36

Project Engineering of Process Planrs

arc ea~.lrspecialized fuiictiuns requiring ronridcrabl(: expcricnu!. 'rllc5c are lxst I~an,llt.

i

I !

Planning Export Shipping

The n:;ij~~rcost. in cxlxlrt diipping is orean frcigllt, n-l~iclris mted by the ton or hy cubic uieasurement. usually 40 cu ft. ~vliicliewris greater. The ti111uscel ilia>- be tlie short ton (2000 111'1, the long ton. 2240 lb or tire metric ton 12204.6 l l ~ j . \\-eights may Ilc based on gross. l~ackagedTI-cigllt, or net n-eight, drpmtling upon destination. .\kn>urrii parkaged din~cnsions arc o v r a l l ~ncawrcmentstaken a t right angles m l y . Requirements for ~ w i g l i t sand nieasurement vary x i t h tlie intc.mati~~nal nrc:i served. uild luiiy also r a r y rvitli the carrier, tlie coii~iiiodity,or t l ~ ccs111irt agreeu~ent. The forwarding agcnt cnn usually save tlie shipper his fcc many tilncs overl hy tiluely adricc on tlic pcculiaritics of the a s s t ~ s ~ m e noft ocean frcight rliargcs. JTllilc oceiui freight rates for all areas li:%vchecn set in il is t o ilc certain international agreements, tlie area into ~ ~ l i i cshipment :nnrlc should 11c investigated thoroughly. The standard rate?, roinmodity limits, tlic stcamsllip linei serving the xrca, awl partirnlar rer~uirt~ll1ents of the nwa ~ I i ~ ~hci lconsidcrcd. d Alarinc sclicdulrs arc subject, to seasonal riiangcs ]~roriliceliby cargir requirc~ncnts. Tlic mariue sailing datc, exccpt for ecrtain Iiasscngcr liners, is usually a t c n t a t i x one. Hcrc :~l,sotlic forn-nrding agent can ~ and save tlie siiip~ierexpense hy holding h i c k heavy piwcx I I cquipii~ent aroiding e x t r a ~ ~ n l i n a rdock y or liglrtrrngc clmrgcs caused by early reccillt of tlir equipment. As a simple illustration of possible occan freight chzrgcs, a s s ~ i n ct h t a section of 24-in. pipe 30 it in length, weighing 3000 lb is to ile sliil~ped. is Rates are t o he a s s e ~ s e ~on l weight or cubic mcasurc~nerlt,11.1iicli~v1~ greater. Assmuc the base rate for this coinii~odityto IIC 530.00 I I C ~toll per 40 r n f t (r~liiclicvcris g r c : ~ t ~ r l .TI:? irc~iglit will 111, 12000 1111 11.! X $30.00 or $45.00 1111 a weight basis. The cubagv xill 11t. 2 X 2 X 30

1 iI i

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or 120 ?u i t , Iim\-n'<>r,:11it. 'i'lic above 24-in. pipe, for inst:~ncc: could he made to carry considcrablr 1111ditional ~\-cigllthy plnl.ing s~nallcrcliametcr pip? inside ti113 large j~ipc. If uiaterials arc to 11e crated or lmckageri, by packing rclatiwly light ~n;itcrial-. slrcli as in>olation. together x i t h h(,avy ~iiatcri;rl-. >11cl1:Is luosc pilw filtingh, the ruliage can be made to appro:xh its freight n-eight r ~ t i n g . (:oniinudity Cln.4fication R a t r s 111ust Ire r;ircfully studied il: iuclr t.arc,s. Ccl,taiii co~niiioditiesrequire a Iiiglicr rate hecamc of 11cculiaritics of s t w l g e or liandling. h llnckage or cr:itc containing a iiighcr rate coiiiiliodiiy m:1y cause a n i n c r r n ~ cin basil. i r c i ~ l i tr;:t(, r v m t l r ~ ~ i g l i the iiiajor 11ortion of tlie contents n.oulil ~irilin:iri\ytr:ivel :it a l i n w rntr. h,lditional dock and lighterage diarges called licavy hit cli;u'ge. nrv :iplllied to single sliipments if the xcight cxccerlr a errtain liniit. These clinrgcs c:ui beconic a considerable portion of t l ~ ccr~strequired for ccjuill~ n c n ttr~11qiol.ta t'lon. All charges d r ~ ~ u lhe d carefully ascertaineri hut11 for the priirii~ryU.S. llort (or docki and for the receiving dock a t the dcstiniition. h funotioii of the for\\--arclingagcnt is t o warn thc sliil~perof tliest, costs and 11rohlcrn~ :ind wl~erc~ ~ o s s i b ltoe effect savings. T h e forn-arcling agent. Iio~\-c\-cr, cnu do little wit11 a piece of cquilnnent after it is fal~ricatcri. Thus these limitations should he considered in planning initial design. T~.:iveltilue is a i i ~ i s tiniport,ant factor in foreigi i q x s n t i ~ ~ nsin(%' s , this tinic must he adrlcd to tlic deliwry tiine prinuiscil tiy vendors or fahricators so t h a t cquip~nrnt\\-ill arrive on schc~lulc. A roulplcte study sl11111ld I,? niacle of marint, freight carriers serl:ing the entry-port, and averagc travel tiuic. devclo~~rcl.It will oniinarily he n~lvantagcoust o utilize :I siiigle stcamship line. Frciglit agrccuients iiiay bc rearlie11 and rnore pref~~rciitial liandliiig may be ohtaincd. Marine fwight carrirrr usually do not follow a definite iisrd echedule throughout the year. The schedule may vary from 11ort to port according to cargo and loading. If a singlc carrier is rclccted it inn? be possible to ~ o r kout definite srlicrlules so t h a t narchousing end storage costs arc rcduced. Forewarning of the shipment of pieres ni equijr~rrcntwith estr;iur,>c:irrit,r it$ 1,:kriy ;la Ij~issibleso tlint sli:ivc can l ~ cp~,ovirlc,lfur the diipnirnt.

38


i

Export Packing

Prrrautions should he taken to protect equipn~ent being s11ipl)ed to trol~icalrwuntries against exposure in sbiptnent, or during its dorage ~wiilrto prcction. .1nunit~erof plastic (non-honding) materials d i i c h are easily reinored arc a n i l a b l e for coating rt~ccl~anical working parts, or inacliined surfaces during shipwmt. There i> considerable argument for and against extensive export prep:iratim or packaging. If tlie shipment is to be unloadcd essentially a t thc jobsite nnil ~5-ouldthus 11e transferred itntnediately fro111 tlie original rarricr (sliil~lto the oxyner or erector, there would be little nced for any prep:rratii~n otlier than the nurlnal shipping precautions. If, however, tlir j h i t c or erertion point is inland and subject to arl~litionnlcarriers, lay-mers in foreign freight yards, or open sidings, the matter of pilferage may beconic serious. This is particularly trur in some of tlie Inore prinliti\-(, countries. It \~oulilappear iinpractical to assume that dolnestir. lirepiration. which is usually tlic absolute minimuni, can suffice in all ~,;t-cs. Crrt;iinly s~liallloose pasts sliould always be consolidated into larger crates or packages. For this reason it is often desirable to retain a ~varchousingor export packaging cotnpany a t a cnnsoliriation ylint. Tllese firnis also should assist the owner in avoiding heavy lift charges m i l nlultiplc consolidations of cori~~nodities where a higher tariff due t o one of the coil~nir~dities will alrply. Planning Freight Movement within Foreign Country

I n osdcr to develop litnitations in equipn~cntsize or wiglit, this 1"''liniinwry sun-ey d ~ o u l dinclude an investigation of a11 tlie foreign railroad and seaport facilities. The installations a t the initial port-of-entry of first foreign destination should be thoroughly inspected tu deterinirle (locking capacity. tlie eapacitics of cranes or lifting equipmmt, storage or n-arrl~ousespare, and the degree of protection afforded. Dock, storage, and handling charges sl~oulclbc ascertained. I t is often necessary t o liroviilc l~ersnnnelat the port-of-entry to process documentation and t o insure that the shipn~entswill be properly llandled and expedited to tlic jnilsite. Direct rail connections a t the entry-port will utiually eliminate additional handling nnd storage costs since heavy shipments can be unloaded by ship's tackle dirrctly onto railroad cars. Railroad freight rates, routes, schedules, and frciglit travel-time should be obtained from the serving :arc 1111ndledby several carriers or irtuvrrl tbrough carrirra. If sl~ip~nents ~listriin~tiori points. or cross tlir l~orrlersof otlier countries it may be necessary to provi,lc p t ~ s o n i ~ c!it! these u,>i.ntstr, ewwdite their movement.

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1 I

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39

T h e capacities of the serving rail systenis, incluilirig tlw type of rnllirig stork and operating srlirvlules s l ~ o u l ~bel inwstig:ite~i. In soiur of t l ~ c w n l l e r countries, sliip~ncnts of heavy industrial e r u i ~ n i e ~may t be .ser.i,111,~1y cielapd due tn the 1a1.k of propel. r.ar.- t o 1i;inillr p n r t i r ~ ~ l a r l
All large or beavy itenis of equipment should be listed ~ w l yin tl11: project so tlmt limitations in shipping may be discovered and the proper steps taken to avoid high costs in liandling or transportation. Heavy machinery well as large internal conihustion rriginci or coin-

40


pr~'%sr~r-, wciglling :IS tiiurl~ :is 100 tons. 3rc r:i~,ely-1iilqie11 ~.o~~ipIctcIy assenibled. I n foreign operations, shipping h i t a t i o n s may further reduce the amount of assembly possible. Personnel n i t h special skills may be required to ron~pleteasscmhly in the ficlcl. The manufacturer must be notified of any particular limitations in size or weight,. preferably ~ h ~ r i n g thc initial inquiry so that rztra clrnrgcs vill not hr a$srssr,l for dibuumtling or a d d i t i ~ ~ n aexlmrt l packaging. llanufacturers of large meclranical equipmmt sometimes require an inspectim of their equipment fjy tlreir own scrrirt, engineers, usually juqt hcforc the ~nacliineis grootrd 011 its foundation. T h r y may nlso requirc that their cnginccr he l~rescnt,n-hen e q u i l ~ n ~ e is n t h i n p initially operated. in order to meet tlreir gu;rrantee. If equipment, is being erected in foreign countrit,::, such requirement;, shonld he fully understood and agreed upon, or ~vaircd.in the purcl~ascrontrart, so that guarantee clnwrs are not affected. Large pressure vessels; ilia~netersin excess of 12 07 14 f t . or r e ~ s e l sof extraordinary length: more than 60 to 80 ft, are often only partially fahrirntcil due t<, railroad clcarancr requirenrents. On foreign project$ the dimensiiinr- or veiglrts may be even furthcr reduced. Thus the preliminary surrey information on size limitations must bc arailable for the fabricators of this type of equipment a s well as fur mechanical equip~ucnt. I n addition all the necessary tools or equiptuent and qualified personnrl ~iiustbe provided for i-onipletion of largr vessels hy the constructic~ti forces. Transmitting Correspondence a n d Drawings l o Jobsite

Airmail should he used for translnitting specifications, and correspondarc scnt by air express or air m r c for tlre foreign p r ~ ~ j c e t Drawings . parcel-post since tlrcy do not fall into the classification of correspondmcc. The preliminary survey should include a n investigfitiou uf the custu~ri* requircmtmts a t the ilestinatiun. I n certain countries all such packageare opened for inspection, and it is desirable to be familiar with the inspection procedure and facilities. I n a number of the smaller countries packages containing nothing but ordinary papers and drawing prints may be held by the local a u t l ~ ~ ~ r i triiet hs o u t notice to either party. \r-Irethcr dutiable or not. I t is sometimes advantageous to provide a direct printing rcproiluction machine a t the erection site. D a t a can then be mailed in sollie rcproducible form, and prints made a s required. The printing process should hc clieckeil for operation in the cli~nate,and the effect of the climate on tlie sensitized paper drtcnuined. l l n n y such pnpers quickly fail under higl1 temperature or humidity. The cost of dripping rrplncement papr3r coulil easily e x c e ~ dthe costs of shipping prints.

Preliminary Data far Construction Projects

41

Construction Personnel

C:onstructii,n operations in foreign cormtries hy U.S. contractors ill 11w111yrequire a nuunher of experienced key U.S. personnel in the labor rrnftsman categories. The percentage of U.S. expatriates t o uationals ustd on the project vill vary ~ r i t hthe degree of industrialization of tlre fmeigu c o u n t r ~ . I n certain European countries lahor in the skilled emits i. c;uily obtainable. Tlrc amilobility of skilled lahor sliuuld bc irrvcstig:ttcd since savings may he effected I>?- :I reduction of V.S. cxpltrixtes. Labur regulations, l a ~ ~ -:ml s . incor~letascs or otlicr labor taxes slrould I E inve;tigated and fully underat~~od.I n certain countries lnhor rcgulntions may also affect expatriate pcrwnnel. Any such l a m or regulations nrurt be explained to expatriate personnel a t the time of hiring. On large ~wojectsit is often conunon practice t o institute training prugranis so that the nalirmnls can become skilled in the varioui crafts. Courtrurticm personnel hiring for foreign operations is usually an invulved process. All pcrsmnrl so hired sl~ould be employed under a rrontract for :I certain number of n~ontlri. A bonus is frequently offercd :ISan incentiw to cou~pletethe projevt. All personnel sliould be subjected to a physical examination and all licccssary vaccinations taken to mect the rcquire~ilentsof the particular area. If the project is remote from a metropolitan area, medical facilities .lrould he provided. I t is sometimes possible tu erect so~ticof t,he permaI I V I I ~ tmilding* enrly in the project. I n such instanres facilities for a certain amount of lro~pitalizatinncan be prorided during the construction ~wriod. In t l ~ ~? ~ r i u i i ( i countrie? ve medii~als~rppliesare 11ftc11 uriol~tai~iable. Provisions niust he made to provide adequate ~rrcdicalsupplics for all em11loyrrl perso~nel,both nationals as well as cxpatriatc:: since many of the muntries require that an cniployer (particularly foreign) nus st proride iiicclical attention for all eml~loyeesregar~llcssof their nntional origin. Furtl~ertnore,tlic costs are lregligible cunlpared t o the possible ill-will gmcratrii if 111edica1care is not supplied. T.S. cxpatriatw tnnst ol~tnina passport and the proper vim ~ I I the I I . . r q r w m t a t i r e r . of t l ~ ecountry t o bc vikiteil. T o obtain :i F.S. lxissI I I " . ~ tlic. person I I I I I S ~ p r o ~ ehis U.S. citizcnal~ipby I~irtllcertifiwtt, or :~fii
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\vithout i w t to the employee. payahle t o the ~mploycc'shcnefiriary in I.;IW cli ( l t x t l ~or injury. This procedure is a good niorale huilclcr and is not an inqxxtant rust item. I t is important that personnel housing he adequate. All iurnishings ~ l ~ o o l bc c l of n good d ~ ~ r a hqriality lc and food sl~ouldmeet U.S. s t a n d a r t k (:ood housing and food is an important asset to any iorcign project. S i ~ t h i n gcan affect n~orwlc,so seriously as uncomfortal~lcliving conditic~ns c x poor food. Savings in follcl coats cannot possibly approach personnel transl~ortationcosts caused by a high lahor turnover. A ircqucnt prohlcm with expatriate personnel on extended foreign proje<,ts is the qucstion of single-status r s . family-status. If housing ~ n m tbe provided, tlic n u ~ u b e r of employees pennitteil to t a k e their fw~niliesmay hecon~ca n important cost item. It is the practice a t times on foreign projccts to allon key c o ~ ~ r t r u c t i opersonnel n t o more their fa~nilicrto tllc locality. At times i t is also c o m ~ n c ~practice n to permit rn~ploynicr~t only 1111 a single-status Lasir. These proccdurcs and practires yary wnriclcrably ~ r i t hovners and construction firnis and are also g~lvcl.neil11y tlrc local conditions. A11 such points inust 11c dcrelope(l and iliould bc ir~clr~,led in the printed form or t l ~ ccoz~tractwith the employee. REFERENCE 1. I.rcming, J., Jjoiicin Espo,-t Pocking, TI& Prornntional Swirn So. 207. Bureau 71 Furrign and Domustie Cammcl.ce, D ~ p t oi . Cu~nmc~.ee, IVashinpton. D.C., 1940.

CHAPTER

4

PROCESS ENGINEERING Process engineering is concerned n i t h the devclopn~cnt.craluation, and design of cl~eniicalprocesses. Pcrliaps in no other phase of rlien~iral mginrcring can t l ~ cengineer better npply the technical knowledge anll skill gained in his formal college education. A l t l ~ l ~ u gml ~m y operating conq~ar~iea may departmentalize proccss cnginccring into development. w o n m ~ i eanalysis, and design, i t is not uncommon for a single 1 1 r o i ~ ~ i : engineer to originate a new process and f o l l m ~it tliruugh the dc5ipr1 stages t o a con~plctedjilant. Indeed. many prore?s engineers ~ i t hulnsidcrable cxpcricnce arc called upon t o direct t l ~ cdesign of a n c pl:mt ~ ns project engineers on the Iiasis of their intimate knolvlcdge of t h r Inwcess. Thc complete discussion of process engineering and particularly of Ilrocess design n-onlrl rcqrrirr a book i ~ fe o n d r r a b l e length. C r r t a i ~ ~ l~ricf conmicnts, however, concerning the r a r i w s phase.; of proccss engineering \vill aid in integrating it into t t ~ coverall plant design pirtnre. FUNDAMENTAL ENGINEERING RESEARCH

Fundamental research in chemistry and cl~erriicnl cnginccring is perfornied to a large degree in the laboratories of universities and privately cndoaeil rescarch institutes. M a n y of the procc?r industries, Iio~r-ever. and a number of design firms have found i t necessary to conduct certain types of funclamental researcll. I t is the indnetrinl-typc fundanientnl research that pertains t o this discussim 43


44

XI,\\ ],~.o,lucl-;iri, ol'tc~lI N I ~ I I ill t l ~ el ~ i : : ~ k , :~~r ns ( Ic-t i t1111c'. of 1.11w11i-t? 111 irullt-trial lalmratiries v h e n stnil?-ing certain types o i rcv.?tiuni tn gmn iunrl;~n~cntal 1inon.lcdge in n ~ u c l ithe same manner as the clicniist~a t a nniv~,rbity or r~.,e;rrch institote. T h e difiermce is tl1:11 the inilrlstrial clrr.ni~dc l i ~ ~ o wreactions s t1i;lt. if sl~cce.:ful. havp w m e i ~ n ~ : ~ c d i aeolnte ~ w r r i a lsiprifir.;~nvc. 1111,c l ~ f . i ~ ~ iCIIRIIII,CI! c;~l ;ilro i- ~ , n g i ~ g cill ( I I!IW:II!I,~I f ~ ~ n ( I i ~ n ~ to ~ ' nhis t:~l I I ~ I l eIn y emnl~:lnicscarry out r ~ , n t i n l ~ o u t,xpcri1nent21l s programs 1111 unit olwralions, rc.:irti,in killrtiri. ;inii t ~ l e r l ~ l o ~ i y o n l l l i T c ~h .e lIllr110s~' oi m 4 1 C ~ ~ I ~ > ~ ~ I I I ~ ! IiqI ~to: I gxi11 ~ ~ I I IaI g ~ . r ; ~ tkw 1 1 0 ~ 1 c d gof~ ~these operation.. so t11;lt
..

Process Development S e n ' ~lesign princil~lc.s,novel re:lction; and nen' cornpinul~lsui.uZIll?. suggest applications oi industrial importanre t o alert tr~,llnicalnmnwgrm m t . Snch applications may he a new proccsr; or the i~n[~rovclucnt IIE an existing OM,. hot11 of rvhich r q n i r c tht! design an11 cun~tructionc ~ fncnfacilities an11 nlay involve ~,xpcndituresof several niillion ilollnrs. S i n w so 111r1cl1of engineering design is of a n empirical nature. it is seldom 110ssil,lc to j ~ n n p irom the heaker to the finished plant. h considcrablc amount ui what might h r called applied derclopmentnl research m n ~ he t ilonc. Tlic intormiltion obtained p e n u i t ~the design of [lrocess equip~nent with n rcasimahlc ~ r n o ~ i noit assurance. T h e process engineer \rho xill be concerned n.it11 the design and p r l l a l j s the ultimate o p e r a t i ~ ~of n a ~ x o c c shccinnes ~ intimately associated nit11 t h e study a t this point. H e ~ l i o i ~ lhe d supplied ~7-itl1ail data nnd interpretations o l data obtaincd in the l a h ~ a t r .His i~ackgroundof plant design and operation n ~ n k ehi? counsel extren~elyvaluable to the devrloplicntal groups. T h e p r n c e s er~zincercan he nssureil of haring all p o s i h l ~r h~t e necessary ior design r i ~ l ~ w l i ~ t i oonly n s i f IIC. 111:iintnins a clo>c Ii;li-uo n-it11 ~ h pr o e w s 11rvelop~ n i n dt t > l ~ : ~ ~ ' t n ~ ~ ~ t .

Process Engineering

45

Procc.>- d e r - e l o l ~ n ~ m often t hegins x i t h a b e n d - s c a l e 1aI1or:itory stud>-. Sn~nll-ccaleyi:ia, or ~ n c t a l~ ~ r ~ u i i ~ is n ~ce~nl lt p l ~ ~ yti,c dollt:~in rlatn i l f 2111 ~ x p l o r a t o r ynature. hell cxpcri~l~cntation is ~ - a I u a h l e;incc it is oiten an iilcxlm~sivemeans of proving the fwsil)ility of a process and of ilirccti~~:: the n-:iy tu f l ~ r t h c rrcsmrrh efforts. T h e extent of chemical cnginecri~rg kno~r-ledgea t the llresrnt time scl,lom p e r ~ n i tthe ~ design of a lien- plant from bench scale lahorntory d a t a alone. Tllrro are yo many unk11on.n;lnd intaugihles n.liich h a r e defied tllc.orrtiral annlysi? tila1 it i- new:w'y tu e m l u a t e these iactors cnlpirically on larger x a l c c ~ ~ r ~ i ~ ~ r~~l- ~c ncl nl ct~. l pilot plant or semi-plant equipment. I n pilot plant and semi-plant o11rr;l. tiun n procedure a s nearly like that. d l i e l ~n.iU hc e111~10yedin t h ~ caulnlercial plant is follon.cd so t h a t the d ; ~ t ; l~ ~ l l t a i n c can i i he used n-it11 cu~~fiilence in the araling up of the l ~ i l o tplant to ~,o~nnierci:il six Pilot plants are costly to bnild and operate. I t is not ilnciitnnvm fur :I single. pilot ljlant to cost clusc to a inillion dollars. I t is. tl~erciorc. inil~erativc that all tl~corctical knou.lcdge ; ~ r a i l a b l ct a the clhc~nic;:l engincer he used to rednre t h e anlount of pilot plant ~ o r requirerl k and. if l ~ ~ s i b l climin:rtc c, it entirely. It is p u ~ s i l ~ l vfor . instance, to o l ~ t a i n rcaction rate (latn for a new reactilln on s i l l l ~ ~hk~ m ~ ~ l l - scqllijllllt~llt. ~ak I-sing the principles of applied kinetirs, rate e r j ~ ~ a t i o ncan s then be ilrreloped ~ v h i c hd l ])ennit the calculation of reactor size for a nlnnher oi sful in the dcxlolxnent of the process inrlustries, a wntinuous cffurt i n r ~ s tIIC, 1na11c to strengthen the thcnretical h a r k g r o ~ m dof the various unit uper:ition>o t h a t more and nrorc resnlts may lw cnlculated, t h o e b y reilucing or clin~inatingcompletely niuch of t h e pilot plant and semi-plant rrork n o ~ v required. PROCESS EVALUATION Process evaluation consists of both a n engineering and cconomic analysis of a process and in thc broadest sense is a rontinoing oper;ttion. It ,sho111(1Ile s t a ~ , t , ,,.vr.11 ~ l I~efor,,:iny l : i h u ~ ~ : ~\!~!c~rl< t ~ ~ IISI> ~ y 1wc.11 11011r. A c;~rciulannlvsis oi co:t nt :in early st:~gc \!'ill incli~,atc,if the l)rol,esc pro-

46


posed has protiii?e and m a y :rlso suggest the direction of experimentation. Process er;rluation slluuld c,~ntinuca t regulilr iutervals a s significant and nclv d a t a are uncovered. This continuous recraluation of the c n g i u e c r i ~ ~and g cconouiic factors in the ~ ~ r u l ~ oprocess s ~ d aids in the overall pianniug III I;cuch-scale and ~ ~ i l plant ot 11-ork T l ~ e r rnre ift ten nlnny !\-a>-. of a r ~ c ~ r m ~ ~ l i s ah i given ng unit operation, Ililt thrse pwsihilities r a n be rcstrirtcd to only a l e v n-hen economics is considcrcd. Dybdal? has presented t h e relation of project evaluation to veil-planned experin~ental11-ork, particularly tlrr planning that occurs I~ctrveenlaburntory and 11ilot 11l:mt lvork. One of the ICSS tangillle factors in favor oi procrss eraluation a t t h i ~stngr is t h a t making :I c w t estimate requires knoll-ledge of tilt, cqui~iuicntto 11c cniployrtl and, t,l~erefore:automatically forces the chemical engineer to think objcctirely. Such thinking inevitably suggrsts nxmy itelus of inforumtion t h a t sl~oulcl be obtained from the pilot p1:iut ol~eriition. COST ESTIMATES AND PROCESS ENGINEERING ~ requirrli for tilt! studit+ thus Ear ~nentioncdis Tlic type of , , I I .cstinuite termed the predcsign cost r s t i u ~ ~ since tc it is 1 1 a d only 011 information that is available prior to the actual design 11f plant equipment. T h e predesign estiniate is not only \ d u a h l c in t h a t it rlirccts research projects into the rnwt profitable paths, but it is also ;I very real aid in design cnlculations. .Is the p ~ o r ~ drsign ?s of a plant procccils, alternate Ineans of oprratirm for portions of the 11lnnt often l ~ w o m eaplxu'cnt. Various ;irrangcul~ntsof heat excl~nr~gcr;;, prrsrure or teulllcraturr of reactllrs, a d operating pressure:: uf ni)sorhors are typical of t l ~ efactors to be considered in alternate designs. Cost estiniating does not cnd xlien the drririon to build a plant is ruade. Itquirics arc sent t o various contr:~cturs,and they must make preliminary design calculations and obtain quotations on thosc i t e m of equipment for lvliicl~they have little or nil recent cost d a t a . From this information contractors develo11 prelimi~iarycost cstirnates upon x h i c l ~t h r i r bids are i oi snrust . an:llysis uiust based. If t l ~ rconlrncti~rn ~ a l i e s:I fir111q ~ ~ ~ ~ t a tI ~ he exceedingly ~ n e t i c u l o u arid c ~ n t i n ~ r n c i emust s he k r p t a s lor%. a s pi~ssibleto insure the lvinniug of the contract. $wcalled cost plus contracts, d i i c h are usually pupular during nccelcrwtcd building programs t y l ~ i c a lof var-time periods. 11rotcct the contrnctor from t h e many incnlculable vr~ntiugencirs ~vliich ;~lw;tys aribe, in rush projects t h a t ent:iil considerablr risks. As the design ;in11 construrtim rv11r1~on p r ~ j c c t s p r o r r c d ~ .thc custoli~eruru:illy r t q i ~ c s t snc5v rr-tin~atvsof the ultimate cost enrh montll ur for suuic othcr mu\.cnii~nliutrrvni. Ear11 suiwssive estimate brcciulcs 11~1re:i~,curatesiuce 11101.~i u i ~ r n i a t i (is~ av;iilabk ~ 11s

Process Engineering

47

the job approacl~c?co~rililvtio~i.TIIM\i:~Ilvays11wr11i1c of gre:it r.:1111t. to the cuotra<,tor lor w i t duilit,- uf his (111-11 o l x , r : i t i o ~ ~ . ~ . O f t m the "running-owr" I I ~lirt.lin~inaryr - t i m i t t , ~van IN. tracecl to additions or to improvrnicnts in t l i v iwiginal ~lcsigir, Design - nien of c o n ~ i i l e r a i ~ l r experience in estili~atingrvork. l l o a t frequcntl>- ccncl~111;tn sprcializes in our p l m r of estimating, m r h n? piping or vessels. T h e 11rimary 11uty of cstitnating departments is to tic\-?lop ac(,nratc c m s t r u c t i ~ ~cobt n cstitnates based on reasonably firm design inforlnation a r ~ lthe latest cquil~rnent costs available. Such estimates a r c time c o n ~ u m i n gaud c ~ t l y l, ) ~ are t necessary in t h e d n . c l o p w n t of quotations b y contractors or appropriation estinlatrs b y operating companies, n-hich are presented t o management prior t11 the alloration of funds fur a project. Chemical engineers acting as procc?s engineers or project engineers ioftcnl I~owex-er,require n ~ o r rrapiil and less costly estiuratcs tlc nil1 in design decisions :ind in the ilirection of research and development. T h e process or project engineer r a n a l r w y s rcqurst dctailrd estimates from the estituating d c p r t n l c n t of his firm. I t sl~oulilbe realized, tliuugh, tlint such estimates a r e rostly. and for marly purposes are not nercss;try. Xichols"an.. given a n excellent cunnnentary on mcthi~ds of capital covt eatiniati!ig varying fro111the vcry wp]~roxiulatctuethod to a detailed estimate. Fig. 4-1. 1vl1icl1n.as l~resentcdby Kicl~ols,gives r ~ i u cdifferent estimate t y l ~ r sv i t h varying degrees of 11reci~imb a d on the infonu:ition available. From this figure t h e approxi~netccust required t o prepare an rsti~iiatcof e:icll type c:in be delerulined. T h e preci-ion of this estimate and n reeotnnlmded imtinguni.y for m c h type of estimnte is given. This 1.1lnrt wIiir11 is bi~serlon crrtain artuwl ihsrrvations of one large firm is an illustration of the type of c11:lrt thnt proves 11c~Ipf111 in d c c t i n p tlir type of estiluate most suitnlile f i ~ ra givcn purl~iise.' K i c h d s iilu>tr;itrs its

* Evyy cin ilr ',,V"

grour, ni+ing to u s ? e\-p?,il.lll.e.

r i ~ r . l l:a

vlhtt

sllotzl~lcun..ti.nct

o t l ~ilf i t n otvn l,:isr.
50

Process Engineering


51

:~liplii.atiim h y assuming :I ii\.c-million-ilolliir [irojrct and c o q x m n g a t>-pe A e t i l n a t e , the 111wt i i c c n r a t ~d. l 1 a ICV nccnratc type J estimate. T h e cost of t h r t>-g~; d t,.>ti~natt,noillil I K :ipl".urimately $25,000 Tvhilc t h a t for the type J n.onlrl lie $9.000. T h e best type J e t i u l a t r rwuld give a sprc;id tlptrrwn ~ l r i n i n n ~nnd n ~ mnrimnm ::ctii:il c w t of ahont 30%. ~vhilcthe type ; Ispread n-ould 11r a ~ ~ ~ i r o x i ~ n 20';. n t e l ~ -TI-ill tlrr iucrcase in iirecisirm from 30r; to 20" sprcnci justify tlw acliliti~~nal cost of $16.000 rcqaircd [or the tylle -1 e i t i ~ n n t e ? I n many instancrs. 11nrticularl:- design stndies, surh addcil cost n-i~ulilcprtainly not t ~ cjwtifiahlr. .%I1 too Ereqnently tillre and money are wasted in attet~illtingto estimate proiects ivitli greater precision than is pwsible vitli the terhniral d a t a availahlc. Estimates for Economic Evaluation

E c m o ~ n i ccr-alu;itir~nis an inilispensable g n i ~ l et o proccss decisions. t h e guidance of rescwrcl~,process There include decisions required ilrsigii, ciipital e r ~ w n d i t l i r r ~i r i i r i n t i u ~ ir e i p e d s t o ~ u n u a g e m m t i , and iq~tirnnni plant qicratirig conditions, % . C O I I I I J ~ P ~ cvalnatior~ C of a nelr- prqjcd requires tlic cstim;ition of the ncn- fixed capit:il required together n.itll r~-orkingr;iliit;rl. Assuming an ann~riill ) r o ( l u c t i ~ ~rate n and a rrlling price of tlie product, the annnal s:iler can bc calculated Friini the total vnlne of annual zalcs. the cost of uinuufacturing, selling. udministration, and taxes r a n he d r ~ l u c t e dto yield the incouic after taxes t o bc cxl~ectrdfrom the prilject. This i n r , ~ i n ~l ~e a nthen hc cxprrssrii :IS a pcrcentage of t h e ~,aliitali n v r l t l n t ~ ~ivliicl~ t is a nscful fignre for stndy hy ~uanagement. M a n y studies, of course. ( l i ~not require coiriplete e~wnomic evaluation. I n selecting alternate dcsigrs iir arrangrmerrts of equipment. ~ cquilnncnt cobt in the sereral cascs for instance, only a r o n ~ l i n r i ~ oI nI the need bc made. Sliort-cut p - ~ ~ c e d for u ~ ~s ~ t i u i a t i nthe g fixed rapital, t l ~ cnianufarturing rosts, and the armual return are most Irelliful v h c n uacd v.ith t h e proper judgu~cnt. M a n y metlrods have bee11 published. F o r cuuvcnicncc several of those currently regarded v i t h favor tiy practicing engineers will be prcscntcd below.

2 " r l o i s d Equipment C v r l

lrnere O ~ ~ O u~odu . ro Jsr r con t y i rae on i v r v s r ai Cnlton I I 1

Fixed Capital Cost Estimating

\$'hen the design of nnv facilities has progressed to t,lic niecl~anical design stage, the inost :rccnrate IU~:IIIS of cstiuiatiug tlie final c~isteof the pl:int is 11y a dctaile(l ellst wtimate typicxl of tlrnt produced by im esti~ u a t i n gd r l ~ n r t m e n tstaffed n-itli lrietr TT-1111ilcvote full time to cost estiluation. T h e estimate;. reqnirrd 11-: p r ~ c e sc ~ ~ g i u r e rho~~-t:vc:r, s, invariably muat 11c inade heforc ;L 1;irgr amunnt uf iufor~uationis available. I n znch rases, a. detailed estimate is s r l d u ~m~r r~a u t c d 11r ~ ~ c c o r : i t r . ~vlii(.li11;ir.c proved ]~npular. Fig. 4-2 iirescnts tivo short-ent inf~tl~ods,

Fig. 4-2.

Estinmrion oi total phnt costs.

Cliilton's m e t l ~ o d l presents a more derailed estimate nud permits the variation of ini]mrtant portions of plant cust in awordance ~ v i t ht h e estimatur's judgnncnt arid knon-ledge of the prticulwr sitnatiou Cl~ilton

52

Project Engineering of Process Plontr

givi~lgtilt, inst:illcrl co-t of :I in1111l11,r of iliffercut cquipmcnt itcnis haseti on an Engineering n n d .\'em Hecord index of 400. Tlie final plant cost is then corrected to rurrent cost by ~nultiplyingby ratio of the cunent Engineering S c w s Record index to the base index of 400. 3T:tny ~lrnrticingcnginrrri 11arc clrrcli~l~crl simil;ir pn~ccrluresfor tlicir o~rii11-e from information arailel~lein a rompany purc1i:rsing department. Ciist curre; ior cquilinicnt itcnis nmst irequcntly used in a particular in~lustr>-c:in he devclolied readily. To nriii~lrontinuonz revision of t11r;c ~ h t : ~rui.rcmt . cost.; can iic cstin~:~tcil by inultiplying the original cod by rost index to the value of tlw rntiil ~ , >If currcnt ralue of soruc ~~ul)li.ilird tlir index upon u-hie11 the c l ~ a r t sarc I~nseil. Screral sue11 in~lcxcsare a i l h T h a i compiled by Engineering X e t r , . ~Record is based largely on cwt oi steel, lunilier, foundation ~naterials,and labor. The firm of 31nrsl1all and Stercns of Cllirago, Illinois~ilauesquarterly index numl~ers ior cq~~ililiicnt costs covering a n ~ u n l ~ tof > r difi'crcnt i~irlustries. Eight of these are for proccss industries: and linvc b c m found very useful by n i m y prowis eugiucera. I n Fig. 4-2 tlie term buil~ling and structurc inr1111lps supports and foundation .Tudginent rnnat be used in sclccting the proper percentages for itenis 3 tlirough 11 to insure the maxi~uulnaccuracy. Some plants require special alloy piping which may greatly increase the portion of plant cost due t o piping. Similarly foundation conditions must also he carefully eraluatecl. If piling is required, the foundation cost may bc increased by as n~uclias 25%. It is important, therefore, t o realize that, reasonable accuracy in plant coat estimating of the type outlined a b ~ ~ r c rcquires tlie derelopnient of considerable amount of sound engineering judgment, based on experience with many prcrious projects. Tlic suggested pcrcrntagcs given by Chilton arc to be used as guides and corrected !vllcre\-er necessary for the special situation being evaluated. In approximating either thc cost of single equipnicnt items or entire plants, \Villian~sVias suggestcil that the linon-n cost of a siniilar but rliflcrent hize unit he nlnltiplicd by tli? ratio of .sizes t o the 0.6 p o ~ e r . For ~ x a m p l e consider . a 1200 sq ft cxrliangcr selling for $4000. Estiuiate tlic rost of n 2000 sq f t exchanger of si~nil:ir ~wnstruction. This cost $5440. \!-odd he $1000 X (2000i1200) '1"

Process Engineering

~ I K W I I ~:I ~icri~,s n l CIII~VKU

Manufacluring Cost

The total mnnufacturing cost can be estimnted ns suggested liy Dybclal' and as outlined in Fig. 4-3. I t is the sum of labor: orerhcad, fixed cliarges and maintenance, raw lnaterials, utilities, laboratory expenses, and royaltics. JIultipliers for obt,aining the annual fixed chnrgcs plus maintenance :lnd tlie general orerliead arc given in Fig. 4-3. Where nossible liowever,

t

56


rwnomic evaluation should supply tlie ini'ormation esrential for choosing the unit operations required. Experimental ~ v o r ki i nut a l ~ a con~~)lcte. ~ s and tlie process design engineer must recognize any deficiencies V-Iiicli exist so that additional data can be requested. Plants have been designed and built bawd on experimental data for production of a new product, but without data for t!ie purification of this product. T h r pnrification operations ~ l i i r l in-ere designed TI-ithout the benefit of lahorntory data proved inadequate and caused the entire operation to fail economically. Assuming there is ;rdequate inforn~ationtllc procer? engineer s1111ulil construct a schematic diagram in~lirating;ill the operation- required for the production of the dc~.&d ilnnntity and quality of finished prot1u1.t. Each of the unit opcrntions necessary may offer e r e r a l alteru:itcs fro111 an economic st:rndpoint. l\Iaterial an11 energy halances around each unit should then IIP ina~le:in11 the results recorded in an orderly fashion s r ~ that they may he used for the many ~lesigncalculations of individual equipment itenis and fur the n-riting of specifications. Orderliness and neatness are raluable x-irtucs in this T\-ork. Hnl-ing an easily understood flow diagram and an accurate material energy bnlnncc early in the process dcsign of a p1:int eliminate+ error and pcrmitr a numher of people t(, work efficiently on vnriuus phases of tlie design. Design Procedures The usual process design proreih~rrmight be srparated into tivo major diri~ions. The first inr-olres the actual design of equilment to be built t s specifying the ollernting i:onclitions for to order. The se~.onrIc ~ l n ~ i sof st:indard manufactured cquipn~ent. I n tile first catcgury, there is e q u i p mcnt, such ns distillation t o ~ c r s absurl~ti<~n , tolvrrs, adsorption and cxtraction units an11 reactors. Thoac items inrolviug niass transfer are designed by calculating the iileal numhrr of stages or the nun~bcrof equilibrium stages (in distillation this \vonld be tlic number of t r a y s ) . The actual number of stages is then detern~incdby the application of ~l appropriate empirically d e t e r m i n ~ efficiencies. I n some cases it has been fuund illore desirable to e~nploya (IifYercntial stage instead of an equilibrium stage and deterininc tile nun~l)crof trnnsfcr units by an integration. The hright of a. triinsfer unit can he r s t i n ~ a t e ~ l by certain grneralieed correlations. The design of packed colunnls is done in this manner. Reactors are designed by the apl~licationof clic~nicalkinctics as dcscribed by Hougcn and Watson:l Rate equations art, determined from experimental data, and empirical cunstants for the equations are rvaluated. If the effect of temperature on these constants has been establislie~i, it is possible to calculate reactor sizes for a nmnber of assulned operating ~ n ~ l i t i ~ This t ~ s tccl~~iic~uc . cn:ll)les con~pI~,ti, w ~ ~ n i ~ l:tnalysis nic of till. rr-

Process Engineering

57

artor 11c*.ig11 n-ithout cxcwsive experin~entati,m I n ~ n a n yri~scc:I I ~ T ~ - ~ ~ c L . , the reactions are so complex that rational analysis hy the principles of applied kinetics is too diffildt a t onr present state of knon.ledge. I n this case. the empirical pilot plant procedure must be used, in \vhich the optimum operating conditions are determined by a planned experimmtation program requiring many hundrrds of runs; and. tl~crcfore,consirierable expense. The application of kinetics and ma.ss transfer theory in pilot plant x~-orlisl~o~llil he a t t n n p t i ~ lwl~crercr possihle since it d l grc;ttly aid in limiting tlir n~nonntof E~lismian-typeinrestig:ition r r quired. .I large portion of the other unit operations equipment comn~only eniployrd in process plants is in thr: second category. I t is not actually designed hy the 11rucess ~wginccraltl~oughkno\vledge of the theory rrlated t o each item of equipment is extrcn~elyhelpi~rl. Itrnrs such as screens, crusllers and grinders, classifiers. settler? and thickeners, pumps. romllressors, licat exchangel.s, filters. centrifuges, rr)-.4allizcrs, agitators and evaporators are a11 purchased from conipanies that, specialize in one or morr of t l ~ c r citems. Theory for the design of niost of this equipmmt is vcry sparse and empiricism is the only guide. The proper selection of an agit,ator, for instance: must he entrusted to a rnanufacturcr who has specialized in the building of agitators and has a considerable backlog of experimental and actual operating data. The manufacturer can, hy application uf the princ,iples of dimensional similitude, specify a large agitator installation on the basis of tests n~arleon su~nlllaboratory equip~ n e n t . Similar procedures are follo~vedby the manufacturers of filters. ilryers, centrifugals and other equipn~entof this type. The process engineer must be familiar with the n~etlmdsof selcctior~ used by tlie manufacturer so t l ~ a tthe operating specifications required for each item of equipment ran be intelligently conil~ile~i.Then it will uot be necessary for tlie manufacturer t o carry on voluminous corrcspondcncc in order t o obtain additional facts required for the selection of the desired item. I n subsequent chapters information is giren t h a t d l aid in the selection of different types of cquipmcnt. I n specifying operating conditions for equipment or in the original design of process equipment: it is essential that the design engineer select the niaterials of construction. h-o one is more fa~niliarwith tlie process rhan the process engineer; and he, therefore, is in a farornblc positim t o aid the mechanical designer in the intelligent specification of materials wliicli will resist corrusion and erosiun. There are many handy tables ~ ~ l i i ch ha r e been printed to aid in selection of a material of construction that d l resist the corrosion of a given substance. There tables arc intended only as preliminary guidcs and extreme caution niust be eniployeil in their use. Often a sligl~tchange in tcn~perntureconditions can cause

58


a inctnl to corrode ~vhich~vouldordinarily withstand the attack of tlie Hoi~lin question. Tlie study of corrosion is still largely elnpirical, and i t is nut porsihlc for the average cngineer to k n o x the latest d e v c l ~ ~ p m e n t s since the wmhinatiorl of material:: and corroding agents is ahnost limitI This .suggests that for a11 bnt the zi~nplestcases a conipctent corro.ion cngineer should t ~ consulted. r The excellent periodicals in the field \ d l also pro\-e liclpful. .Is the design and selection of the prucess equip~nentis cninpleteil, specifications for each item should be sumlnarized in a n orderly fashion. U a n y organizations h a w developed f o r m for the various equipment items. There insure neatness and also prevent tile engineer from overlooking somc important item of information. T h e con~pletedforms can be reproduced and distributed to other departments in the engineering organization for integration into the complete plant design. I n addition t o these specifications, i t is desirable t o produce a final process flow dingrani. This diagram slion-s all major items of equipment, gives ten>p c r a t u r c , pressures, and H o i ~rates t~hroughoutall parts of the process. Tlie diagram then bcco~iiesan invaluable aid t o specialists \vho murt 15-ork on the ~nechariicaldesign of tlic plant. T h e proress engineer should prepare a brief hut complete written description of the operation of the plant. Such a description aids both management and all othcr engineers and draftsmen who must contribute t o the finnl design. Distribution of this information, I I I I ~should ~ ~ ,be made ~ v i t hcaution. IVorkers ~vitli incomplete background for understanding of terhnical process data may misinterpret the information with possihlc disastrous results. ~

Process Engineering

59

:~ccumulatingoperating data. Such data siioi~ldnot just he placed in the company files, hut it slionld he analyzed n.Ilile still "fresl?" a11d made a definite part of tlir organization's operating experience. SOURCES OF BASIC DATA

I n addition to the experiniental rlata in operating data nhirh arc uscil in the design of equil~nient,a large amount of hitsic pliysiral an11 clieniical data are also reqnircrl. M a n y cnmpanies niaintain very cscellent rlata hooks in u41icli such data are accumul:ited and periodically rrviscd. A single ~lepartnlentis often charged u-it11 the full-time d u t y of maintaining the data book. Tliuse engineer:: who do not h a r e such information available ran aecuniulate data hy requesting reprints of basic infiirmatiim appenring in the literature and hy obtaining comldations of data that have appeared through the years. Tllc following list 1.rpl.r.icnt.i soink' rec~~nnncnded conipilations of rlata which have proved useful and 11oplllnr with practicing engineers. S o atteinpt has heen made to list the vast anionnt of data t h a t has a l q ~ r a r c din the periodioal literature i:ir the rxccllcnt data that is pihlished I I ~n~nnufarturersof r a r i n w rllenlicnl ~voilucts. T h e list of referenres is not to be considrreii coniplcte, :in11the omission of certain material dues not necessarily indicate tllat it is not recomniended. Certain of these rcfercnces arc desirable as part of a p c r s ~ ~ n alihrnry l and are so indicated by a n asterisk, hut inany arc expcnsir? and are best ~ i i a d ea p a r t of a company library fur general tedmical use.

THE PROCESS ENGINEER AND THE PROJECT ENGINEER

Although the project engineer is in complete chargc of the plant design arid construction, it is necessary t h a t the process engineer he ready t o asrist the project cngineer a t any time. Normally, once the process design is completed the process cngineer will move on to other assignments, but, q ~ ~ e s t i o ninvolving s the process cmtinne to arise a s mechanical design proceeds. T h e project cngineer, eTren though having a background of 1nmcc~sdesign,should always refer these questions t o the process engineer v h o directed the original design. Only he will know tlie background of the design ralcu1:rtions. I t is of great value for the process engineer to accunipany the project cnginew
hlii.1~.1946. 2. Itollrfson. C:. I<..and R. E. Powell. 87m. R c a . I'hus. Chcaz.. Annotrl

Hriir.as.

B. Handbooks 8 General References 1.

Beil~teins H a n d b u c h dci. Orgmischcn Ckumie, Spl.inger-Vcl.lag. Bcrl~n. ( 4 t h

edition hrgnn in 1914, supplements currently appearing). L~ctest cdltiuns eovw literature u p to 1929 on w~I1-pstablishcdorganic ~compoundr;nmi reactions; h o a c v c r , it is drill primary source of information. 2. Rennett. H., T h e Chcmicol Formiilniy. Chernicnl Put~li~hine CO.. Rrnoklyn. S.Y.( 1 9 4 3 ) Formulas of many industrial plmducts. 3. Chrvziciil Econon~zcs H o n d h o o k , Stanford Rcsmrrh I n i t ~ i n t e ,C;tI.(. (loose-

60


"

Process Engineering

.

'li. F u r n : ~ ~ C. (!.. H o g c r s .lloriuol of Inriusfrinl CIw,,,i.i,y. 6th Xd.. T~iuSohtmnd Co., 1-en l u r k (1042). Good de6~1'l/1lireidormiition on well-rsti~hli~l~d III.OI,PI*C-. '18. Sax, X I . , Huridbor,i: of Dongei-our JIalei-inis, Keinlmld P ~ h l i r l i i n gCo., X C W I-ork (196l).

C. Compilations of Thermodynamic, Physical a n d Chemical Data 1 . . h w 1 r q l ~ c ,1 ) i s l i l l ~ i l ~ ~P~,~uilil~ri,~xn. ~n. :iwl P V T C h , J u (:IUI,, K . J . ( ; ~ i t y .I.. 1'. I{rrnnw!w ;d It. h l l , ~ i . s ! i l l n f i r mEqliiIibiii!7n Duta, K r i n l d d k'\hlishing Cu.. SCW Yolk (1050). I)~.eishilrh, R. R., Prcs~u~~c-l'~,li~,t~~~-l'e~~,lprrntii,i. Kdolior~sliips uf O r g u i i i c Cornvmnrls, 3rd Ed., Handbook Publishers I n e , Smalnsky, Ohio (1952). Horsley, L. H., Ateolropic Data, American Chcmical Society, Washington, D.C. (1952). 2. Fuels P m - F b i c Goses, Amwican Gas Association, S e w Yo& (1941). Gnwoira FacLv, American Gas .issoi:i;~tion X\:m- Yark (1918) S p i w s H . X , T d m i c d l l r ~ l o,,i F,trl, 5118 Pil., B r A 4 S ~ 1 i m : dColnn.. I V d d I'oivvr ( ! o n i ~ w n ~ w London . (1930). C!;hrifi,. v ; d i ~ z .Ir:inily i.li;~rlcand ld,lcs (01. ,,,:,,,y l?],,'< ,us [,,,,I>,

7. Solvcnls . Puhlishine Ca.. New Yark (19501. >li.llnn. I.. Inr/~i!rinlS o l ~ x n f sRcinhald

61

62


I,iotiiila. Eng. l?xp St;ttion Rullctin S o . 34. Louisiana Sttltc Univ.. I h t m Koog~. La. 119521. Striniioidi o! tiir l'zihalal. Ezehongcrs .lirn,ufuelureli. .4ssocinIion, 3rd Ed.. ,I!

l i m n a n . J . 11.. mil J . Iiayc, T h r ~ m o d l , , m m i c P ~ m p c r t i wo j Air, John Wiles & Sons. Inc.. S r w Yolk 11915) . . Kryrs. ?'h<,i,nr~riii,in,,iic Piopeiliea of S i ~ n r n ,Jolm *limnan. J . H . I Kilcy 6 Sons. In?.. Scm York (1936). Properties of ('mnmonly L'aed Rejrigc~orita,.Ail. Comlitioning and Refrigcrating M.lnc1iiner.y issociation. ll~;isl~ingtun, D.C. (1946) .ic & CIiarLs, Industrial Zirnnwirn;m I). T.. :mil 1. Lavine. P ~ y d ~ ~ - o n , c l iTable.* Rwrarh S ~ r ~ D i w i ~ c r S. c w Hnrnpi-liirr 11945).

D. Materials 1. E ~ w h a r t J. . I,.. rt nl., Jlr~clwriicid Prr,pv,-tiis of J l c l o l s it Alloys, Burrnu of S t m d a i d s Ciw C417, I~a4unjirun.U.C. (1943). 2. D u l l o n d . T. C.. E,iginwiiriy Ilrilcrinla JIoniml, Reinhold Pnl,lishing Co.. Sm 1.d (19511 (;mr~xliai.ilmil in simpk terms. 3. Hn1,;ilil. E.. (',,iriirion Giiiilc; Elsevic~.Puhlisliing Co.. Hrnwton (19.51). Handy tnhlri ui co~.roiionrwisiant milierial rrcommcnrlationa. 4. Sinmnds. H. K.. A . J. Kcitll, and XI. H. Rigclowl IInrdbook of P b s l i r s , 2nd Ed., Van Swlrand. S r w Yolk (19491. 5 Tecit~iicidD o h on Plmlics, hlnnufavtwing Chemists A w x . , Washington, D.C. (1952) Pwpexties and M;inr~fnrturrrs. T h e possession of t h e best tcclinicnl d a t e a n d tl~eoreticalknowledge for design of all type.; of pruccss equipment represents only a portion of t h e requirements for s u c ~ ~ ~ s . sprocess ful engineering. T h e process engineer must also h a r e a ~ v o r k i n gknowleclge of equipment operation a n d n m h a n ical design gained hy actual operating experience or at least b y observing operatinn. An engineer without this l ~ a c k g r o u n dwill often size equipiller~tin such a {say t h a t i t is impractical t o build and operate. Those engaged in mechanical design of cquipmcnt are reluctant t o question or alter t h e 11rorcss design since i t is not uncommon fur unusual arrange~ ments or designs t o be required due t o r~eculiaritiesof the r ~ r o c e sconditions. An impractical design, t l ~ e r c f o r e , initiated b y t h e process engineer might be used in t h e final plant design without question. So it is ilreessary for t h e pniject engineer to be on t h c 1o11k-out f u r all imprnctical process designs. H i s experience i n both merhanical and process phases of design makes him unusually qualified f o r such work, a n d as director of tlir project it most certainly ir his duty.

REFERENCES 1. Cldton, C. 1 1 , ('lictn. El~g..i i i . T o . 6. 97 (1949). 2 I l l . . J . Eng. f'rog,.. $fi. 57 (19501.

Process Engineering

63

3. Hnrrir. .I. \lr.;\.. J I - . Cltr.,,~.Eng. Prow,-., 4 $ , 333 (1848). 4. Houg~n.0. :mil Ii. Xf. Watson. C l i i ~ n i c n lProcevs Pn'nciplrr, Vol. 111, ~ o h n Kiev K- S m j . SPITI-ork.1947. 5. Long. If. J.. ('hrnt. Ertg.. G ,KO.6. 112 (1948). 6 . Sirliols, W.T., Inri. Eng. Chem., $3. 2295 (l!El). 7 "P~.oce?sEquipnlmt Estinrnlion," R ~ p o r tCIi
CHAPTER

5

Flow Diagrams CHARGE -

75% Propone 25% P r o p y e n e

98% Pure Ethylene Product

START

Secton 100 CRACKING FURNACES AND QUENCH Conversion: 65% Inlet Furnace Temp.: 110°F Outlet Furnoce Temp,: 1470°F Outlet Quench Temp.: 1 8 0 ° F

FLOW DIAGRAMS I t is important for the clieiiiicnl engineer t o he able to use the nintcrinl and cnrrgy balancc and tlie f l o diagra111 ~ in solving problems in desigir and operatinn Just as thc halancc slipct and incoiuc account enable the nccountant t o solre coniplcx financial jrrobltwi, the m:itcrial and e n t w y b;~l:inct~, togctli~rwith the f l o ~cliagram of a pri~ccss.aid the cl~cinir:ll cnginccr to risualiac and solve his prol~lcmsin a rapirl and straig1itfor1~-:ud nlannrr. Skctclring a flow diagram is almost an instinctirc ~nanipulntionfor the cxl~eriencedclieniical engineer. It is part of liis thinking process as \\.dl as liis cxplanntory technique. I n this for111 it is usually :I rougli skrtr,li or schematic flow diagmni. I n thc design mrl ronstruction of ;I l r l ~ n t:I more ~ ~ o n ~ p l tion' e t c diagram callcd thc enginccling flou. diagralll tleclllllcs tllc vital rag in tlie transmission of l~roccsainforniation t o all drllurtlllcnt~ of an cngincering design group. SCHEMATIC FLOW DIAGRAMS

I t seems desiral,lr to suggest tlic least nuniber of rules to f o l l o ~ in eonrtnicting sclieuiatic di;lgraius. By their very nature they slioul~l lw indiridualictic, aince tliey are used for varied 11urpoier. IVl~cnused 111 explain a process or mode o f operation t o a colleague, superior, or customer, originality often prorides the needed emphasis. Clarity. I ~ I I K P Y C ~ ,inwt nerer lie sncrificed, and, t o nisure t l ~ i srlnrity, the ~lldi?llW nulst IJC c ~ i ~ s i d e r ~ ~ l . 4

. *

Butones and Heouter to Storage

4

Section ZOO CONTAMINATE R E M O V A L and Acetylene)

t

- Go5 to Fuel

Section 400 DRYING

I lC02,Sufur Corn~ounds

Section 500 FRACTIONATION (95%Ethylene Recovery]

__f

Section 300 COMPRESSION 350 psig

Thrrc arc tltrw type* of sclieniatic d i ~ g r a u ~ins general use: 1. Block ~liagram. 2. Process flow diagmm. 3. Grnpltic flow rliagra~n Block Diagram

The bluck diagram is the simplest but least dewriptire of the scliematic diagraius. As the naulc iniplies, it consists of rectangular blocks vhich usually represent a single unit operation in a plant or an entire section of the plant. These blocks are conncctcd by a r r o w indicating the flov sequence. One such diagram is sllovn in Fig. 5-1. The b l w k diagram is cxtreniely useful in the early stages of n proreis study and is particularly raluable in presenting tlic r ~ w i l t sof econoiuir or operating studies sincc the significant data can be placed within the blocks. Process Flow Diagram

Tlic process flow diagram a s illustrated in Fig. 5-2 is used most frrquently by tlie process engineer in design work and in process studies. I t must bc dr:nvn so that the proccss flow and iq~r.rations:we innn(diatcly

68


Process Equipment

1 '11 i t ~ m sof l w i ~ w sc q u i i ~ ~ c nnrc t slion-11. inrlution nf t111 rvl;itix-c iiac diflrrcucw: ;iurl tltis ~ : I I I s o ~ n c t i ~ nl vx : ~ c ~ ~ o t t ~ p l 11: isI u.il~p :I diffwcnt rcalc for tlrc l ~ o r i z u n t ; ~tl~iui l for tl11. r(.t.tici~l. S i n w equipuirnt rarir; cmsirlcml~ly.it is not jmc.il~lr, t o li;irc -t;ind:il.~ . k c t c l ~ ( ~for s caeli itcni. T h c re]~rc.?t!ntatiousof ~ U I I ~ ~in(tors: I S . a l ~ ( tur. l biues. lic~wcrcr.can t ~ citi~ndardizetln> in Fig. 3-5. Notations

Certain cssenti;~linf~~rnxrtion must 11r provirlc(l n~ljaccntto e:wh itcn of equipnrent. Tliesc notations must suplily in a concise nianncr tlie dat: required liy ear11 user of the d i a g r a n ~ . Expcricnce has dictntcd t h r infor~ u n t i o nrrquired for tlic eilnnnon items such a s p u ~ n p sand r c s s c l ~ . Fol spcci:rl cqiril~~ncnt. the irrer;rll rlimensions and ~ i g n i f i c m toperating c h ; iwtcristics :IK often givcn. Tlrc following notations arc suggrstrd: TABLE 5-1.

Typical Equipment Designations

I t e m Numbers

All pieces of equipment s l ~ o u l dbe given a n item number which s h o u l ~ appear on or next to the equipment. If t l ~ citcnl numbering s y s t c ~ ui! planncd with c a w , i t aids inimeasurahly in t h e use of t h e flow dingrau :11111 ill tlit. e x ~ c ~ l t i oof n :ill 1d1:1wiOT 11111 (lesigl~::nd ronstn~ctinnx n r k . A typical s y - t c n ~TT-hichhas been used nit11 suwcss, in casc? wlrcrc the l l r w

Fig. 5-4. Engineering flow dinpram: ~olvmerisationunit reactor

section.

(Courtesv of Foster Wheeler

Cornnmtion l

-

p~

---

~

~

p~~

~-

Fig. 5 5 . Engineering flow diagram: gas treating plant. (Courtesy of Fluor Corporation.) diaaram in the d e v d o ~ m e n tstare. Line numbers h a r e not vet been assiened.

~~

Thia diagram is typicel of n flow

Flow Diagrams

69

e-. 1111it is

divi
Important process information sirould also be listed. Thc folloning :ire .suggestions for sevcral cullnllon iten~s. Service 1)innrctcr; height, thickness Special feature^ (lining, etc.) llesign conditions Operating conditions Hent Exchangers Service Diffewntial pwssurr. across sh?11 and t , u h Heat transfer arca D u t y in Btu/hr Design conditions Temperature and pressure a t inlet and outlet P1i"lps

(This information may he given on the flow diagram or on accompanying attaclin~cnts.) Sewice Size and type Fluid Puuip t e i i ~ p c ~ a t u r e Density a t pump terl~perature Design GPhI a t pump tcinpcrature Design differential SPSII ( S e t positive suction liead) C'o~~ipressors (This infortnation may be given on the floiv di~igliunor on accompanying attaclllncnts.) Service Stages Suction conditions First stage suction Seeond stage nuctinn Serond stag[, ~lisrll:~rge

70


B H P second stage Capacity SCFN Piping and Valves

.%I1 process lines and utility lines serving process equipnicnt are slro~vn on engineering flow diagranis. Often the main pruccss lines arc ~lra\\m heavy so that tlic primary flow sequence will be more apparent. IJtility TABLE 5-2.

Typical Valve and Pipe Symbols for Flow Diagrams SYMBOL

ITEM

Line Oer,gnof!ons

Valves B F l f t t n g

F

Angle V o l v e

-

-8-

Figure B F l a n g e

Gote V o l v e Globe Valve

--C

H O I ~Connection P l u g Coch

Reducer

71

Flow Diagrams

BHP (Brake liorsepowcr) first stage

Main Process

Condenrote

Steom S t e m Troced

-- - - - --

Woier

-..

..-

Nose: Uruollv no otternot is made todirtinouirh

-

lines are ilra~vnusing various synibols (Table 5-21 to pcrmit ready diffrrentiatim of the several scrviccs. Arrows are used wherever neressary to aid in following tlic flow. All required valves and check valves are indicated, but flanges and fittings are not shown except a t equipnrcnt. Common synibols for the valves in general use are given in Table 5-2. Sizes of valves for those other than line size are shown adjacent to the valve. Since the piping designer uses the flow diagram as his main source of information, much data must be supplied on the diagram. Temperatures and prensnres, flow rates: and a description of the fluid flowing must be provided. I n addition, the specifications for t,he lines must be given so that the size, material, and thickness of pipe, class of flanges, and rating i r f fittings and valves u-ill be known for each line. This information can be 2onveniently provided by means of a linc numbering system in which

each line cxtending from one piece of equipment t o another is given a separate number. These numbers can be recorded on forms together xvith the flon- rate. pressure, temperature, and fluid floving in the line. T h r linc number changes ~vlienercrthe linc size or linc specificatiiin cl~anges. T o avoill confusion, a linc number is eliminated when a line is rlclctrd. Thc line number can inrludc tlic arca designation. One typical system employs a number such as 3"06403E (Fig. 5-4).

3" Line size

0 Fluid class

6 Area number

403 Line number

I< Piping spec.

Since, as explained in Chapter 18, piping specifications are writtcn in detail for each class of service, thc piping designer can obtain all the information required t,o layout and design tlic ~iipingf r m i the f l c ~ ~ diagram, the line list, and the piping spccification. These line numbrra furtlrcr serve in the marking and identifying of shop-f:hricated pipe. A poorly numbered flow diagram, thcrefure, can rausc considerable con. fusion tllroughout the project. Valves are identified on thc flow dingram, lioth hy n u m l m and hg symbol. The numbers refer t o detailcd valve specifirat,ions and are very helpful t o both designers and material procurement men. .\lthougl~ some organizations do not number the valves on the flow diagram, alni~ist all use numbers on the piping drarings. Instrumentation

All instrumentation for the controlling, rccording, and indicating of plant operation must be shown on the flow diagram. Fsunlly. the process engineer indicates in a schematic fashion the essential instrumentation on the prricess flow diagram. This is further enginccred and added to the engineering flow iliagram x i t h all other required instrumentation. The Instrument Society of America has prcpared a set of standard instrrnncnt ~ynrbols~vlrirhshould lie followc~lt o avoid confusion. These are reproduced in Tablc 5-3. The instrunrcnt number is generally included in tlie syml~ol,as shown in the tabulation. Control valve and relief valve sizes should be shown adjacent to these items to aid in piping design. Arrangement of Diagram

.4 well-planned arrangement of the engineering flow diagram can do much t o assure efficient and high quality norknianship tliroughout all stages of the job. If some idea of tlie actual plot plan is known ~vhentlie flow diagram is drawn, it is very helpful t o have the diagram arranged in a similar manner insofar as it is practical. Such an arrangement aids

Project Engineering of

TABLE 5-3 ( I ) .

Process Plants

Flow Diagrams

Instrumentation Flow Plan Symbols.

(Reprinted by permission, Instrument Society of America, Tenfotive Recommended Practice) BASIC INSTRUMENTATION SYhiBOLS

Instrumentation Flow Plan Symbols.

(Reprinted by permission, Instrument Society of America, Tentofive Recommended Proctice) TYPICAL IiViTRUMENTATION SYMBOLS FOR FLOW

DISPLACWIENTTlPE FLOW METER

BASIC SYMBOLS FOR INSTRUMENT WITH SINGLE S ~ V I C E AND TUNCTlON

B A S K SYMBOLS FOR COMBINATION INSTRUMENT OR DEVZCEw m r w o SERVICES OR SUNCTIONS

BASIC SYMBOLS TOR TRANSMITTER

n o w RECORD^

or

ROTIMETLII OR 0TWm IN-THZLRn TlsI

now

RECORDEA. PNEUMATIC TRANSMISSION. TRANSMITTER LOCAL. RECEIVER MOUNTW ON BOARD

BASIC SYMBOL TOR DIAPHRAGM MOTOR V A L E

BASIC SYMBOL TOR sur. ACTUAFD IIPmGRALI REGULATING VNVE

BASIC SYMBOL TOR FLECTRICALLY OPLRATLD VALVE SOLENOID OR MOTOR1

BASIC SYMBOL FOR MANUALLY OPERATED CONTROL VALVE

BASIC SYMBOL TOR PISTON. OPEIATW VALVE IHYDRAULIC OR PNEUMATICI

>.WAY BODY FOR ANY VILVE

BASIC SYMBOL SHOWING PNEUMATIC TRANSMISSION INSTRUMENT tnCCTRlC TRANSMISSION SAME EXCEPT FOR TYPE OF CONNLCTlONl

BASIC SYMBOL FOR SAFETY I R P I P 1 VALVE

BASIC S Y ~ O L SHOWING PNEUMATIC CONNECTION FROM INSTRUMMT TO DIAPHRAGM MOTOR VALVE

r L o w RECORDING COMROLLLR. PHFUMATIC TRlNIMiSSlON WITH RECEIVER MOUNTW ON BOARD AND LOCAL TRANSMITTLR

Flow Diagrams


tBLE

TABLE 5-3 (4). lnstrumentation Flow Plan Symbols.

5-3 (3). lnstrumentation Flaw Plan Symbols.

(Reprinted by permission, Instrument Society of America, Tentotive Recommended Practice)

(Reprinted by permission, Instrument Society of America, Tentative Recommended Practice) TYPICkL 11: 1 AU: .INTATION SYMBOLS FOR TEMPERATURE

TYPICAL INSTRUMENTATION SYMBOLS FOR LEVEL

BLIMI LNP CONTROUU. INTDNAL TYPE

CAGE CLASS

L E V n RCCOIIDUI. PNEUMATIC TMNSMIISION. WITH BOARD MOUNTED IItCCIYLR t X T U l N TYPE IRANSMITTEII

-TFMPUIATURL WDICATLNC. POIN? CONNECIED TO MLRTIPOIN? WDICATOR ON BOhRD

TlMPDATURF m l C A T R l G AND RECORDING POINT CONNECTED TO MULTIPOINT INSTRUMENTS ON BOARD

TlMPERArURC RFCORDRla CON?ROUUI. BOARD MOUNTED (ELECTRIC MEISURFMEMl

mn RTCORDIWG

CON TROLL^. u ? t n N A L TYIC PNEUMATIC TIIAWIMISSIOII

L T Y U ALARM.

INTLMAL TIPC


TABLE 5-3 (5). Instrumentation Flow Plan Symbols. (Reprinted by permission, Instrument Society of America, Tentative Recommended Practice) TYPICAL INSTRUMENTATION SYMBOLS FOR PllESSUM

Flow Diagrams

TABLE 5-3 (6). lnstrumentation Flow Plan Symb~ (Reprinted by permission, Instrument Society of America, Tentative Recommended Practice) TYPICAL INSTRUMENTATION SYMBOLS (MISCELLANEOUS) --..-

PRLSJURE INDICATOR, LOCILLY MOUNTm

P D S U M .CCOU)ER WARD MOU)IIID

1IM PNSJURE RLCORDD. M A R D MOUNTED I-?EN PNEUMATIC TRANSMISSION

n

SPED RFCORDLOOI. LOCALLY n o u r n

BELT)

WEIGHT RECORDER. LOCALLY MOUNITD

1 P M R MACHINE >

0

MOISTURE RECORDEL LOCALLY H O U M m PRESSURI COHIROLLFR. BLIND TYPE Ishow con,roll.r dmcoy...ha &+rap il 0 ' rn0""l.dl

PRCSSURE RECORDING CONTROUL11 WIPrUCNTIALI. PMUMATIC TRANSMISSION: wnn PRESSURL wcomn COWINCD INSTMUMINT BOARD naumm


TABLE 5-3 (7). Instrumentation Flow Plan Symbols. (Reprinted by permission, Instrument Society of America, Tentative Recommended Practice) TYPICAL INSTRUMENTATION SYMBOLS FOR COMBINED INSTRUMENTS

Flow Diagrams

79

the layout men and pil~ingdesigners t o visualize tlie plant more readily and prevents thc ovcrenrphasis of a line that is artnally w r y short hut, appears long hccxuse of the arrangement of thc flow diagran~. There arc many methods of accomplishing good arrangement. Pumps can he placed helow other equipment as shoxn in Fig. .5-5 or all equipment may he arrangcd above n common hase line. Process lines ran he shown on onc dra~vingand utility lines on another. Or. 110th utility and process lines can be slro~rnon the same drawing. The lattcr is done so that the full picture ran he seen on one drarving. Oftcn, liovewr, this results in o v c r c r o ~ d i n gespecially if utility connections hecorne eucessirc, such as on large compressor installatione. Thc flow diagram, t o he read and understood easily, must not appear crowded. Oftcn a numher of scpnrate dra~\-ingsarc needed tn rcl~rcsent a process. l i n e s passing f r o ~ nequipment on one sheet t o that on n r ~ ~ t h e r are nlaintnined a t a constant elevation so that tllc continuation of the line on the next ihcet can he found ~ r i t hease. CONFIDENTIAL I N F O R M A T I O N

Because of their coml~lctcncss,process flow diagrams, engineering flow diagrams, and a t times hlock diagrams, contain confidcntinl information. They should never bc distributed indiscrirninatcly or alloyed t o he rcproduced by unauthorized persons. If unscrupulous individuals are permitted t o copy a flow diagram, they arc ahle t o ohtain unfair advantage by avoiding the time, effort, and cxpcnse requircd to originate a colnplete flow diagram. Such practice violates all known codes of ethics.

Plot Plans

I

PLOT PLANS After the engineering flow diagrams are completcd and before detailed piping, struct,ural, and electrical design can begin, the layout of process units in a plant and the cquipment within these process units must be planned. This planning is done by a group of cxperts including the project engineer, i~ipingand structural designers, and the process engineer. The results of their work arc plot plans: the lnartcr plot plan and the unit plot plans. The master plot plan (Fig. G - l i shows the location of each process unit, road\ray, and building. The unit plot plan (Fig. 6-2) shows the location in plan view of each piece of equipment ~vithina single process unit. The preparation of a plot plan is the mrist important function in the design of a process plant. Onc key to good operation, economical construction, and eficicnt maintenance is \wll-planned, functional ;mangemcnt of equipment and building$. A key to employee satisfaction and good public relations is a neat and esthetically pleasing plan. Each plant differs in many ways and no tnw plant sites are exactly to alike; hence, there is no one ideal plot plan. I t is possible, i~o~vever, describe some of the more important rules wfiicli insure a satisfactory arrangement. MASTER PLOT PLAN

Figure 6-1 is a skctrh of a typical master plot plan. Dimensions have been omitted for clarity. Generally the plant is divldcd lnto blocks 80

z &

82


~vIiic11are most conveniently separated by roadways. Kumerous factors infllirr11.etlie location of roadxiys and the arrangclncnt of blocks. Sonie of tlieac arc: PLANT TERRAIN.The drainage system can be planned from a contour map of the site. S e x t r ~ ~ a d w a yand s the general areas t o be used for process units and buildings can be chosen. Portions of the site requiring the least amount of fill and having the best soil-bearing characteristics are selected for tllcse areas. The highest area on tlic site may be used advantageously for storage of priducts so that gravity loading of tank cars will be possible. Adequate dikes must be built around these tanks to prevent rapid spread of fire if tanks o v e r f l o ~ . (See Chapter 24.) ESISTIXGH I G H ~ .LSD Y RAILROAD FACILITIES.Offices and warehouses niust be readily accessible from thc main l~igli\vay, and warehouses, storage yards, and product loading areas nlust be convenient t o the nearest railroad. If the plant is to have harbor facilities, product storage should be in the vicinity of the docks, tlioug11 far enough t o rnininiize the danger of duck fire. TYPESOF P a o c ~ s sITSITS. If the product from one process unit is fed directly t o another, the units sl~ouldbe adjacent t o reduce piping and purnping costs. Operation, maintenance, and utility distribution are often simplified by locating similar units in one section of the plant. S a r z r ~ . Safety rules are fully discussed in Chapter 24. P L A N T SERVICES. The power plant, shops, warehouse, cafeteria, and change house should be located not only for maximum efficiency and convenience hut also for minimurn interference with the process operations. One simple starting point for grneral planning is to make rectangula~ cardhoard cutouts scaled to each proress unit, p m e r plant, machine shop, tankage area, and office building. These cutouts may be moved uver a. dra\ving of tlie total plant site. Each arrangement can be furtller studied by preparing schematic block diagrams on which each area is shown as a recbangle and all interconnrcbing piping is indicated. Utility piping should also he included on this diagram. These block diagrams arc helpful in deternlining the space required for interunit piping and are thus a great aid in developing the final rnaster plant plot plan. The econoniica of ronstruction, operation, and future expansion for each proposed arrangement will determine the most acceptable plan. UNIT PLOT PLANS

Unit plot plans (Fig. 6-2) are prepared in niucli the same lvay as tlip master plot plan: except that tlie detail is much greater due to thr larg~v number of elements making up the process unit. Scale niodcls begun :it this stage and developed as design progresses are most helpful. Briefly, the steps in preparing unit plot plans arc:

Plot Plans

84

Project Engineering o f Process Plonts

1 . T.ist all m:ijor itcnrs ( r f e ~ ~ n i p ~ nmcli t v t :IS \-~wxls.heat rschangers, liamps, and coniprcssors. Indicate the size and xeight of each. 2. Decide vhicli equipment should be elevated. Csually the elevation of equipment is dictated by pump suction reqnirctnents or other proces requirements. Elevation of equipment is alvays costly and should h r done only if necessary for satisfactory operation of the proccss. 3. Study the process flom and operating procedures. Thc flow sequence and function of each piece of equipment should he thoroughly underutooil su that its arrangement in the plot can be functimal. 4. Determine maintenance methods for each item of equipment ~o that equiplncnt requiring frequent maintcnunce ill he easily :~ercssiblc. 5 . Stully all iipc~rating11azards so that the snfeut arrangement of equi11Iilent can be dcviscd (See Chapter 24.1 6. Plan tlw spacing of equip~nent in :tccor~l:~ncc:with the following rules: a . D o not spnce pumps closcr than three fect. Closer sparing hampcrs maintenancc. h. I~quilnieut~ i t hr m ~ o v a h lparts ~ must he :~rrnngcdso that the parts can he rcmoved witlli~ut di~msntlinglong lcngths of pipe or moving other equipment. Free access by hoisting apparatus is neceesary. c. Remember that foundations snch as sprcad footings oftcn exceed t,hc din~ensionsof the equipment they support. Hence both equipment and foundation sizes should be c o n d c r c d . 7. Study the crcction p r ~ ~ b l e nfor ~ s a11 equipment. I T l ~ r npmsible, its [~lnciment~ho11li1facilitate wcction.

Goo~lplot p h n i n g is more a matter of experienced judgment than of follon.ing :I set list oi rules, hecausc tlicrc~:Ire so many 7-dues to he met. A gruup of cxprricnccd c~~gineers car] ~levelrql:UI acccptahle plot 11lan in ;I relatively short time. Using models to represent equipment, these exlierts can gather around a conference table and propose numerous possible :lrrangelncnts vi\ridly and quickly. From the combined experience oi cnrh of tlie men participating, the merits and dcnlerits of each arrangc~lrtwtcan be readily iletermine~l. Plot plarming is d e f i ~ ~ i t r the l y jub for the most experienced and capable engirlccrs in a plant design group.

CHAPTER

7

SCHEDULING

THE PROJECT Careful planning and scheduling are vital t o any project as complex ~ as thc design and constructi~nof a procc; plant. After t h co~upletion of prelin~inary11rocess dwign \xwrk, f l o ~diagranls, and plot plans, a project sche~lulccan he developc~l. This project schedulc d l then hcco~iiea guide for lilanning and rec~mlingprogress tl~ronghontt,he job. PURPOSE OF THE PROJECT SCHEDULE

The srhe(ln1c sI10u1d i ~ i ~ l i r a tthe < , stxrt anil c~~rnl~lctinn ~Iatesfor cngias ~~onstruction ol~crationsfor licering, drafting, and l i r ~ ~ e u r e ~ n e;I-n tn-~,ll . each major item of cquilimrnt. If properly jire~~itrcd and i i ~ l l o ~ ~ c oi l~, n pletion of t,he project on time \ d l he asrure
86


p r d ~ l e n iarises w i t l ~parallel project ollerations ( t v o or more projccts being engineered siniultaneously) ~ i n c ethe f u n d a ~ n m t a i steps occur simultaneously. The ideal vork xliednle for any type of mginrrring organization r h i e h contracts services in proce.;~plant design ~ 1 n 1 he d obtained hy spacing them ronsecutive eontracts t o permit a 30- to 45-day interval Iwt~~-ecn Ideal conditions rarely exist in practice since the contractor is usually confronted ~ i t ah proniise t o "start v o r k i~nnietliatcly"regardless of his internal w r k program. The contractor's engineering scl~edules,however, aid him in planning the beat conditions possible. Once the preliminary scl~edulcis made, organization of personnel and planning for the job are greatly expeditrd. Tlic job schedule, lio\~ever, must be a vital inatrumt.nt. Aa xi-ork proceeds, more arcurntr inforn~ation bccon~csavailable and hcncc more realistic and n ~ o r edetailed scheduling i$ pc~ssihle. THE SCHEDULE SHEET

A srlledulc preparcd in grapliiral fomm as s11olvn for a rrndr riistillution unit in Fig. 7-1 has been found nioat convenient. Thc syml~olsarc used to indicate start and completion dates. Opposite each item two horizontal graphs arc sketched. The top graph sllo~vsthe planned scheilnlc. The hottom graph indicates time actual progres* of work up t o the time of issue (April 8j. Tlic second graph for each item simws t l ~ cprogrrss up to that time. If required, the time scale can be enlarged t o indicate tlic progress by weeks inatcad of months. Schedules such as these can he preparcd on printed forms and rcproduccd for distril~ution t o cxecutire personnel of thc contractor and customer. This graphical presentation pcrmits key personnel t o dctcrmine rapidly the progress of the job as vell as plan future work in accordance with the proposed schedule. H O W SCHEDULES ARE MADE

The key equipment and material items that are knolr-n to control job progress are listed a s in Fig. 7-1. The flow diagram and plot plan are most convenient sources of information for preparing this list. The plot plan provides a logical basis for division of the project into sections. The example in Fig. 7-1 is for one duch section or unit. Equipment Delivery Times Control Completion

The next step in preparation of a schedule is determining the earliest completion date. This date is usually controlled by tlie item of equipment having the longest delivery time. Once tlic probable completior~date is selected, engineering, drafting,

Scheduling the Project

Scheduling t h e Pro~ect

and construrtion are wlirdulccl in ,letail so t l ~ the i 111aitr.r ech~dule]nay IIc complctcd. The entire effort of the de.ip nud ronstruction organization must bc ~cl~etlulcd so that all work ~villhc cuorriinatecl. Information, equipment, and materi:~lsmu-t flo\\- 50 that no group Till be delayed. This goal will bc rcalizetl only if the p e o p l ~doing tlip sclieduling h a r e full k n o ~ l c t l g eof the scquenre of 11litnt design, procurement and construction operations, 21s n-ell a s the time ron~umcdby each.

terial listing. 1.isting of all in;ijw c q ~ l i p n r n tnnchor-lmlts. W h w r piling is to be used it is prohahle that piling arranpwients may he romplete at this time and pile driving could start. Preliminary construction operations are sometimes started a t this point. 12. Structural steel design or design of other structures rrquired for process operations. .4rrliitcrt~ralstu~licsof lilant hnildings. 13. Electrical conduit arrangements, underground electrical material listing. 14. Foundation drsign for independent electrical equip~llrnt undcr item 6. 15. Hcccipt of certified dimmsion ilran.ingr on items 3 tllrougl~7. 16. Completion of piping arrangements sufficiently t o determine and fix vessel nozzle orientations. 17. Release of vesscls for fahrication. Vesscl fabricators d l h a r e liecn selectcd by means of 3 above. 18. Release of founrlatiim dri~\vingsto construction forccs for erection. 19. Release of structural steel dra~ving;for llrocurcment and fahriratiol~ (of structural dcel: rclease of all niateriala for construction of clev:ited ~ constrl~ctiouf ~ r c ~ s . ~ e i n i o r r r ~conrrctc l rtr~lcturesI I tile 20. Construction stnrt: clenr site, preli1nin:lry grading and foundation excavatims. 21. Completion of preliminary piping material listing including valves and n~iscellaneouspiping appurtmnllces for procurement. 22. Complcti~inof ~nisceilancourmnior eiructural steel for pipe support and listing of all iniscellnneous items for field construction use in pipe u p l ~ i ~ manufaeturc. rt 23. St,art of instrument instali:i:ion ilm\vings: listing of all materials required for instrument inst:tllation. 24. Cmnpletion of piping design nnd rrlcaie of piping for fabrication. 25. Completion of architertural ilesign arid ulaterial listing for buildings. This phase may lie roulpleted inurh enrlier for buildings not used for process operations. 26. Completion of elcctrir;~l
Sequence of Operations in Plant Design a n d Conslruction 3 9

Tile following srqucnw (11 design and corictruction operation is typical for nlost prnccss plant projects.

J.;

:

89


88

I . Process (lerign and prorcss flow diagram preliarat,ion. 2. Preparation of engineering flow diagrams and preliminary plot plans. 3. Partial vessel design. JIajor vesscls are usually long-dclivcry items and they inay be partidly procured as s m n as process information is c o n plcte. 1-esscl iutern:tl such as mixcrs, stirrers, and other equipment related to vessels should lie specified a t this time. 4. Specification of mechanical equipment including electrical and steaui drivers, pumps, c~~mpreesors, material handling equipment, and other equipnicnt n-hich may ljc procurcd \vithout the preparation of cornplcte dra11-ing~. 5. S1iecifil.ation of iustrunicnts. Control valves arc usually postponed until preliu~iuar:- 11iliingnrrangenlents have been completed. 6 . Design of major clcctrical switel~gcar~ main plant an(l substatio~r transforlllerp. and mlallrr elertrical gear such as motor starters. a s soon as item 4 i- co~nplete. Siuglc-liue plant electrical distribution diagrams m u d he ~ , i ~ n i ~ ~ l csufficiently tecl to perlnit a study oi plaut loads. This work is uften dorie u11 a preliminary bu.%isfroni various process puwcr studirs. i . l k i g n and sl~ecifientionof heat cxclmngcrs, dircct fircd heaters, niiswllaneous Iientrr appurtenances, nn(l steal11 generating equipment. 8. Prel~aratiunof {~illiugspecifirations. including valrc spccifications and r ; ~ l v eitcni nulnber lists. This permits a ralvc take-off directly from tlic engineering flm diagram. 9. Fit~:llizingg~mer:~l 11101 [rl:m and a r m plot lilans. 10. Pluiiuing piping urr.:~ngeuicntsand listing' of materials for underground piping. 11. Fouridntiou dcsign for vcsrels and ot,hcr equipn~entfor wliich preliminary veudur datc ilavc, been ruxivcd. Prcliiniiiary foundation lull-

90


3.5. Testing. 36. Insukrtion installation. 37. Clean-up. 38. (lprration start-up procetlurcs. 39. .-\eceptancc of plant hy custi,nwr. A hricf study of this list \ d l indicate the depcndencc of each operation upon one or more of the previous operation*. A ro~uplcxinterdeprndencc exists in n-hich design gr<~ups depmd on infiirniatiun from other design tlic~ riesigncrs ~ (dclivcry groups. fabricators depend on infmnation i r o ~ can be delayed if this information is Intci ; and finally, tile construction crews depend on information from designers and material from fabricators. Example of Schedule Preparation

As in cxnniple of schedulc prcpnration ronsidcr the items in Fig. 7-1. The piping layouts in uiost proress plants require thc major portion of drafting manhuurs. Piping dcsignrrs and draftsu~cn,therefore, ]nust bc supplied as early as possible with vcndor's draving? of equipulmt and resscl sketches. Vessel sketches hased on design calculations and npplicahle codes arc prcpared by the vcssel dcsign griinp. These eketchcs are then released to thc procurement department accompanied hy a requisition or other document describing pertinent design requirements and guarantee desired. The release of the requisition to procurement for the purpose of obtaining bids is designated by tlie synlbol R on Fig. 7-1. (Rcfcrring t o the bottom portion of iteln 1 it is seen that, t11c timc of requi3itioning f m column C-1 was behind schedule.) Since the fractionating eoluulns (items 1 and 31 are more iml~ortantin piping layout, the time for requisitioning these is scheduled two weeks bcfme the less critical accuululators (item 7 ) . Vendor's drawings of equipment must he received hy the piping design group a t about the snmc time as vesscl sketches. Early sdicitation of bids (indicated by R ) aud pleccment of an order ( 0 )xvill assure on-tirnc reccipt (ED) of vendor's drawings. These i l a t e ~dcpcnd, therefore, on tile rapid finalization of proccss design specifications and cfficicnt procuremcnt operations. Vendor's dravings and vcssel sketches, along with flow diagrams and plot plans, are transmitted to the piping design group for use in preparing piping l a y o u t ~ f o major r lines. The completion date (Li of this layout is esti~nated f m n the numher of drawings requircd and the ~lunlber uE layout men assigned to the job. The piping layout contains inforumtion sufficient for the preliminary design of main steel structurcs and for orientation on ressel nozzles w t ~ i c l ~ in turn permit requisitioning of fabricated steel, R (itcm 5 ) , design of


91

foundations, UC (item 1 1 ) . and design of the electric rlistrihution systenl. Piping design continues during this period and reacl~csa stage of c o u pletion such that checking i ~ fdrawings can bcgin. Vessel rlra~vingsa1.r checked ( C D ) and sent ti1 the fabricator so he can prepare shop dra~vings. After approval of these shop drawings the fabricator is "released" to fabricate the vessel (FKI. Equipn~entdravings are also checked and returned t o the vendor with or ~vitliout comments. Then, checking ui structural steel, foundation, piping. and electrical drax~ingsf o l l o \ ~in~ the ordcr named. I n scheduling this ~ v o r kit must be remembered that vendor's and ressel drawings are necded for structural steel checking. For foundation drawings, structural steel, vendor's and vessel drawings are needed, and for piping and electrical drawings all previously checked draxvings are rcquired. This example serves t o illustrate the principles of schedule preparation. Detailed suggestions arc given helo~vfor esti~natingdelivery times and ~nanhourrequirements needed in thc preparation of a w r k a b l c schedule. INFORMATION FOR SCHEDULE PREPARATION Manufacturing a n d Delivery Times

Thc delivery date of equipment should influence all work thronghout the design organization, including process design. Major equipnlcnt, the basic design oi which ~villnot he greatly affceted by Iatcr computation, should he designed in detail as carly as possible sincc usually such itcms d l h a w the longest delivery. If extraordinarily large machines or Ilcary-walled vcsscls are required, these items should l ~ cspecified or sketchcd as early as possiblc and relcascd in a preliminary form so that procurenlent operatiuns may procced. I n order to determine probable lnaxiuium delivery tinlcs the equipment to be procured nmst be stndied and n list of d l major itclns prepared Tlic iollorx-ing list indicates probable delivery times for various types of equipment. Current quotations are tlie most reliable sourcc oi delivery timcs, bnt the filllowing list indicates probable values for various types oi equipnlent and can bc used for estimates. TIME FOR TYPICALD E L I ~ RORY ~\~ASUI~.LCTURINC VARIOUS TYPES O F EQUIPZI~:NT (1955) VESSELS n . Forged or heary wall chanlber~.greater than 3" thick 12-14 months b. Lnrge heavy plate vr*sclr. greater thnn 1" thick 10-12 month* ti-8 inrintllb c . I)rums or othcr liglrtwall vessel* d . Sulall vessels 6 6 months

94



accunrulated by the project cngineer, so that their work may hcgin before all process cngineering has becn cumpleted. Manhour requirements for process engineering drpend upon the type of process, the availability of fundamental data, the availability of process engineering personnel, and thc policies oi the firm performing tlrc ~vork. Owner-operating firms develop and aocumulatc process data hy experimentation and expericnrc with operating units, IThen the decisim is made to install a plant or process, tlic data are given to an cngineeringrontracting firm for resolution intu the various steps of unit-operatiun? and finally into forrrrs xliich may he used for detailed design. For such cares and for the process design of known processes, time required for pri~ressengineering 11y the contractor is often very small. I i the contractor is asked to pcriorni research and dr~eloprnentwork and complete proce::s design, the time required may be considerable. I t ~ o u l dhe unlvise to attempt a list oi suggested time requirements for proress design. Each j ~ i:: h usually unique anil the chief process enginrer ali~~uld be consulted when the schedule is being prepared. I t is rvrll to remcmbcr that time requirements for projects \vhich require conaidernblc rrsenrch and devcl~~pincnt arc the most difficult t o estimate. Difficult problems often do not conform readily t o schedules. A conservative estimatc is preicrable fur such problems. DESIGN-DRAFTING. Requirements are described below in greater detail. This work encompasses all functions aitcr the prucess and specialty engineering phases. The design-drafting for the plant illudratcd starts the second month after the contract is signed, and will reach a peak in tlic fifth to the eighth month. PROCPREMENT. Procurement must, proceed with each design stage or vendor prints will be received late causing a dclay in detailed design. The lack of vendor prints can as effectively stop work as lack uf equipment,. Procurenlent thus must place all orders with dispatch, in order to receive vendor prints as early as possiblc and secure early delivery of equipment. Procurement usually starts in the first rnontli and may or may not continue through construction. Certain procurement a t the jobsitc must continue as long a s the job is in progress. C~NSTRIJCTION LABOR.I n the illustration. construction starts on the fifth month aiter the contract signing. The delay allows time for a cousiderable amount of material and equipmcnt t o arrive soon after groundbreaking. I t is extremely important that construction work does not begin too soon. If bcgun early, idlc periods will be encountered in which it will be necessary t o await delivery of equipment and materials. Such conditions naturally increase cost. The time required for construct,ion of a given projeot usually can be

estimat,ed hy experienced conztruction firms. Alattozi' has given n construction sclredulc chart (Fig. 7-2) hascd on an analysis of a number of projects that ~r-illpermit estimation of the ronstruction time when thc total manhours oi labor is known. This manhour requirement is usually

95

Thousands of manhours

Fig. 7-2. Constmvtiun schedule. LKrprinted by petmission, M. Mtitiazi, Oil A! Gas J ~ u m u l 51, , XU.48, 100 (1983).1

given in the original job estimate or proposal, either as an artual manhour figurc or an estinrated labor cost. hIanliuurs can bc calculated from the lal)or i m t by ~liridingby the ax-cragc hourly wage ratc. If such informatirm i.: not available .\Iatt(~zi'suggests as a gucss 18,000 manhours for caclr $100,000 worth of materials and cquiprircnt.* Planning Personnel Distribution

Taljle 7-1 gives tllc l~ersonncldistribution for tlic cxanrl~leproject by 111011tl1 The incrcase in cngineering and draiting labor during tllti pcak part of tlrc job is uhuut 5007; above that a t the start. Operating on the hasis oi 40 hours per ~vcck,the engineering l~ayrollmay amount t o some $14.000.00 per \veek for tlic Gth and 7th montl~. Firmi contracting engineering must, tllerciorc., be prcpnrcd to accept considcrahle expmsc if a Iargc staff is to he maintained. Scliedules ior the rarious enginerring phasrs are rarely precise. Probably the most efficient or pra~.tiral ol)cration for firms cngagcd in engineering services is t o understaft' and wurk ~ m r t i r n eduring peak ~ o r k loads. h n o t l ~ e raltern;~tivcis stn8 vrrr;~tilitywit11 movement of l~crsonnel

96


into the u r i o u s operations as required. very effectively on the latter principle.

M a n y snialler firms oper:ite

TABLE 7-1. Typical Personnel Distribution

Time

Enpinemng

97


Dwign Category A. Found at'tons B. Structures and rtructur:ll steel C, Llrrhanical rq~lilirn~nt*

Procurement

Percrt~tsgcof Total Engineering Manhouro 7 15 3 7

Po.-sil~le Variation f 2.0 3.0 1.O 2.0

,

Month

No of h1m

KO.of hIanhourh

* Incl~,dpip u m ~ s ,compressors, hpnt exchnngms, and :my t y p ~m ~ c h : m i r n l eWil,m m t not ~ I W W L . A preliminary or overall cstiuialr of ilesign-drafting time 11i:iy sometimes be madc by a perrentage method working backward irom tlie particular process unit rost. For instance, materials for a certain unit have been estimated t o cost $4!000,000.00. For this particular type unit as based on similar past contracts two manhours of combined enginwring. design drafting, and material listing operations will be required for each $100 of iiiatcrial cost. Thusl a n estimatcd budget of 80,000 manliours could he ret. R y using tlic above pcrcentagcs the tentative distribution of v o r k might be as follom: Category A B

c

134,900

D E F

Total nrnnhoura t1io~vi.n Otlicr engineering services

Calculating Drafting M a n h o u r Requirements

A n u t ~ i l ~ eof r nietliods have been deviwd by various engineeringdetcrminirig ilciiyn-draititig nianlim~r budgets. contracting firms I hIost of tliesc methods are bascd on experiencc in tlie particular firm and are not ordinarily useful d ~ e applied n to other firms that 11ave different methods. Tlic distrihution of work by percentage sliomn belolxh o m r e r is applicable t o nearly any type of unit processing fluids. I n general iiicrlimical cquipnwnt, vessels, rind piping drafting consume from 53 t o 65 per crrlt of tltc trrt,itl t l t i ~ r i l ~ ~ for ~ u rm s y t y l ~ o]JI.
hlanliours 5,600 12,000

2,400 5,600 44,000 5,600

This appears t o be a simple and straiglitforxard analysis, but such estimates are not reliable unless the initial inanhour edilnate is accurate. I n order t o actually prepare a manhour budget a list of equipment must be prepared. From it a detailed list of d r a ~ i n g smay be prepared B y applying values of required manhours per dralving according tu category the total manhour budget and detailed budget: by category, can bc determined. 4 s an illustration of tlie method used in estimating the number of drawings required, assume t h a t the following items of equipment are a partial list of tlic items required for a process plant. The list is separated into ta.0 parts, I>, Tcseels aud C, Mechanical Equipment. Item Knmber D. Verrels T-101 T-102 T-103

10' diam X 60' long vertical vessel S diam X 45' long vertie:iI vessel 9'diam X 5S' long vertical vrsel

Scheduling the Prolect

Project Engineering of Process Hants

98

T!

IK

Dr,~nnig

hfanhour./Dran ~ n g

<4

200

B C

15P200 15&250 15&200 3W400

D E

F r o n ~t h ~ item; v a tentative draning 11st can he made n n m e d ~ a t e l y

D. Teistds A. B. F. G.

Fmmd:itions Structural Electrical Inctrrnncnt Insulation

I)~.awingsfor Teaseli Vessel dr:iwings (;ill details are nx~allyon a single 3 druiring for each vessel) 1 Far above, T-101, 102, 103 3 Ladders & platforms for T-101, 102, 103 3 Electric:ll 6 instnnnent conduit & lighting 1 Schenintic riraxrings of instrumrnt installation 1 Indntion dctnils fur T-101, 102, 103. Insulation is not shown on the pererntap. list since it is gener;~llyneeligible with respect tcl total deiigndrafting.

Subtotal

12

Dmn-ings for D.

For machines snrh as C-101, 102, 103 a shdtcr of some kind would he mnnilatory. Drawings A . Foundabions 3 4 Foundations B. Compressor bnilding 1 Comlirehsor b ~ d i l i ~ i g 1 1 Comprrsmr huildinp Comprt~sorbuilding 1 ll. Miscellaner~nsv e s d ? for compressor 6 auxiliaries E. Piping Piping Piping F. Electrical G. Instn~mrntations

Subtotal

6 2 1 3 1

-

30

-

Total for D and C 42

for Mechanical Equipment Compressor building, phn, section, details Compressurs C-101, 102, 103, fnumlntions .krr:~ngemmt plan Structural steel Hoof pl:w & rlcv:~tii~ns irchitwt~~r;rl details

.

Comprrssor buttles, starting air battles, water bottles, x i t e r syitm,, f i d , lrtbrication -rstrxm Process piping Cooling watrr & Iubricutim tystcms Starting air system PInn.s, seetiuns. details power & lighting Inrtallariim details Drawings for C Dmwings

Frotn the original list of 6 items, T-101.102,103 and C-101,102,103, 42 drawings have been listed. B y applying a tnanhour value per drawing, total manhours can be estiniated a s follows:

Category A . Foundations B. Structural C. Merhanical D . Teasels E. Piping F . Electrical G . Instrumentation (Insulation) Total

99

No. Drawings 8 7

-

Total Manhours 1 ,tj00 1,100

9 9

6 2 1

-

42

This example is very incomplete since no piping was inclu
100


ticei :onictinirs affect the original design. Screral months may i l a l ~ i c . therefore, h e t ~ r c minitial design effort and completion, most of i~hicliis consumed in awaiting data either from the originating orgnnizatiiin iJr the fahricntor. For this reason sewral jobs in varions stages of cornletio ion n-ill serve to maintain a relatirely cou;txnt v o r k Inad. I t is necessary in ~cliedulingwork for an organization to attempt thc. masinrum use of all personnel. One aid in accoiuplisliing this is the preparation of a bar graph or monthly time chart sllorriug the various pro/ccts in an organization. t11r4r starting times, and the anticipated tinrc for ear11 ph:w of lvork. Then a dra\ving -1irct coiint can hc utilized t(l detrrn~inctlie possible m a r i ~ n u m or i ~niniu~unrs of iuanpowr. X e ~ vjobs should be srheduleil to start during anticipate~iniiuimum vurk li~nila. Regardless of the nunlher of men available only one p r r o n can 11c em[iloyed on one drawing a t an:- particular time. I t ip; thereforr, not' good practice to use large draxi-ing sliects. Uettcr use of inanpower ran he realized by rcduction in dra~l-ingsize. This will i n e r e a s the numher of drarings and thus increase the possible use of manpover. There is, of course. a practical limit in size rrducti(,n: but the use of larger scales serves t o increase the number of drawings required. SCHEDULING DEPARTMENTS

Contractors as well a s operating companies that do a consiiler:~hlc amount of their olvn engineering design and drafting hoth find it desirable to establish a permanent scheduling dejlartlncnt. This ilcp,zrtment must be staffed with men having adequate bac,kground in all phases of thc design and construction of a process plaiit. The sclicduling of ir nlultimillion dollar project is hardly the job of a 10~7-paidclerk. It requirea a man of broad experience ~ h iso thoroughly familiar with four stages of process plant construction: namely, process design, mechaiiical design and drafting, procurement, and erection. Contracting firins have found the use of a scheclu1ing department advantwgeous since such firms are ordinarily engaged in the execution of tilore than one jol~. I t is preferable under such situations t o have tlic scheduling done by a group of men who have an overall vieir-point and are not interested in only one particular job. If a project engineer schedules his own job, there is a tendency to favor t , l ~ a tjob. It is essential, however, that the pmjcct engineer assist the scheduling group in the preparation of the pruject schedule. REFERENCE 1. Mattori, M . Oil and Gas Journal, 61, No. 46, 304; No. 47. 180: No 48, 100:

KO.49,

102 (1953).

ENGINEERING DESIGN AND DRAFTING After the project engineer has received proc,ess specifications and general mccl~anicalsl~erific:itions:x preliminary plot plxns, and prilject schedules, the urork of tlie specialty engineers and design draft,smen may bcgin. It is the job of thesc men to conrert the calr:ulations and decisions of process and project engineers into dran-iuga and specifications which are indispensable in the procurement, fabrication, and erection of process plant facilities. Engineering design and drafting efforts :ire usually rliriiled anlong groups CIE specialists in thc various phaws of t h r ilcaign. The work of these specialists may bc divided intu tn.u n~njorcnteguries: equilin~cnl specialty engineering and dcsign drafting. EQUIPMENT SPECIALTY ENGINEERING

Equipment specialty engineers in cooperation with process engineers develop the detailed mechanical specific~tionsfor process equipment. I n * A p u r t ~ uui llir gmel'hl n~rel~uuical specificatiuna air uilru m p v l i d by !lie campany for whom the plant is being built (see Chapter 11). These a1.e incorporated with the usual specifications of the design organization and become, upon approval I,? the rustonlrr, llie gmerul guide f u r 111 ~nech;mival design inrlu~liog piping, structural, elecirirnl, and equipment design. 101

ENGINEERING DESIGN AND DRAFTING After the project engineer has received process specificntions nnd gcnvral n~cclr:iiiical specificntions,* preliminary plot plans, and project xhedules, the v o r k of the specialty engineers and design iiraftw~enlnny begin. It is the job of these nlen to convert the calculations and dcei s ~ o n s of process and project engineers into drawings and specifications d ~ i i : l i are indispensable in the procurement, fabrication, and erection of process plant facilities. Engineering dcsign and drafting efforts : ~ r cn ~ n : ~ l l ydi~iilcd alllong groups of specialists in the various p l ~ a a w( ~ ft l ~ c'lciign. The v o r k of these specialists nxty be divided into tn.u 1n:rjor categories: equip~uent specialty cnginccring and dcsign drafting. EQUIPMENT SPECIALTY ENGINEERING

Equipment specialty engineers in cooperation with process engin~ers develop the detailed mechanical specifications for process equipment. I n * A portlun of the general nrrel~auieul sprcificnliuu a r t d ~ r uaopplird by the company for whom t h e plant is being built (see Chapter 11). These w e incorporated with the usual specifications of the dcsign organization and become, upon appmvnl I,? t h e customer, the gcncrul guide for all inrelmnic.;d design indudlug piping, strneturnl, clwtrirnl, and vquiprnent design. 101

102


addition they aid the procurement divieion in selecting the equiplnent I\-hich n i o ~accurately fulfills the process specifications. The follo\~ing sliecinlty grmps arc ~naintained: Engineers who specialize in pump and conPI-MPSASD COXPRESSORI;. pressor selection are included in this group. They maintain close rontart with pump and colnprcsior manufacturers and not only select the best cquipniertt for a given job but also advise process and project engineers on appliratim and in&llation problems. HEAT EXCHISGERS. This group is staffed tiy experts on heat exchanger design ~ I l ocan check quotations and specifications on all heat exchange equipment by making deyign calculations for comparison. Some contracting firms manufacture their own heat exchangers. In such cases this group does the design calculations. V ~ E S Emust ~ S be built to conform t o the requirements VESSELI)ESIGN. of the process, and any plant drsign organization must have a group of expert vesscl designers. These men design all pressure ressels, tanks, stacks, and ducts in accordance with customer specification and applicable codes. \-essel designers also prepare or supervise the preparation of vessel sketches and layouts of vessel internals. ISSTRI:MES'I'S. ' h i s fast moving field requires engineers who devote full time to instrumentation. They adrise the process and project engineers on instrumentation during the development of flow diagrams and also specify arid select all instruments for the project. FCKN.~CES. Contracting firms that huild furnaces maintain a large staff of furnace designers ~vhomake detailed process calculations necessary for proper sizing of furnace and heater installations. They also direct the design drafting on furnaces. Organizations which do not manufacture furnaces have a small group of furnace experts who prepare furnace specifications and select t,he best furnace for a given job. Piping n1:itcrials experts aid in the preparation of PIPINGMATERIAI.~. piping and insulation specifications for each job. They list all piping materials and accessories shown on piping draxings and select the materials in accordance \ ~ i t hthe specificat,ions and applicnhle codes. Each process plant project is unique in ~ ~ I ~ C E L L A N E EQGIPSIEST. OU~ some way and special cyuipment not handled hy other groups must also be selected or designed. Equip~nent such as dryers, filters, materials handling apparatus, autoclaves, centrifuges, evaporators, and mixers, 111:ly he required in many projects. Process engineers and the project mgineer can often rollahorate in the development of specifications and in the selection of such equilimcnt. Some companies, however, have found it advantageous to maintain a gniup of experienced chemical and mechanical euginecrs n.11~alx~cializein the wide variety of cheniical plant eqnipmerit not cotrirnon to all installatiuns. I n addition to their more routine

Engineering Design and Dratting

103

xork thcsr, men frequently dcvelop the inecllanical rlcsign of equipment that nus st be built to order bwause it is uot regola~lynianufactnred. DESIGN DRAFTING

The ~levelolimentof a complete plant design after equipment selection has been cr~l~~pletcd is so intiniatcly associated xith drafting t h t the term ~lesigndrafting is often used to describe the four major categories: piping design, structural design, electrical design, and instrument installation design. The design work in these categories is largely accomplished by drafting techniques. Piping Design

Piping design is important in pnicess plant engineering. I n the engineering of nrarly any process plant, piping rlesign and drafting ~vill usually c(insulnc from 40 to 60 per cent of tile total engineering ldesigndrafting) n~anlrourbudget. Piping itself is intimately wlatcd to pv~icesst~iiginecring. Drsigncrs the various ~ l i olay out the piping for a illant 111u.5t learn and uridersta~~il process requirculcnta better than personnel in otlwr pllnscs uf the ~vork. For this rwson organizations providing enginrering xrvices fov the process industries depend on their piping design personnel to lead the other phases of the design work. Piping designers do the folloving: a . Layout, arrange, and design all piping in accordance with the specifications and the applicable rodes. b. Orjcnt pressure vessel nozzles. c . Check drawings other than piping for clearanccs with structural steel, foundations, and other types of equii~lnent. d. Study all piping arrangements for strcss. e. Prepare stress calculations. f. List and specify all nlcchanical (manufacturedj expansion joints. g. Show all thrust and other forces (In piping drawings and tentatively locate all anchors and supports. h. Complete all fornlal calculations in a reproducible form. i. Design, select, and list all detailed pipe supports, hangers, etc. Structural Design

Personnel in this group design all foundations, all structural steel, a n U o r reinforced concrete structures, and all industrial-type buildings in conjunction with architectural designers included in this group. Since foundations are largely located below grountl, personnel in this group must work closely with piping persomcl designing the underground in-

104

Project tngineering of Process Plants

I 2x11 stallation. I t is rommon practice with crrt:~inolyniz:~tions~ L sIio\v undergrrrund ~ v o r ksuch as foundations, piping, and clcctrical conduit on the samc dra71-ings. This procedure is extrcmcly advantageous both in initial design and during erection. Designers in this group must, of course. conforn~t o all applicable national codes and the particular sprci: t if I k The n-orli rrn~sists01:

n. Preparation of design sketches and formal calculations. b. Preparation of all structural stccl d&il drawings. c. Prcparation of building rlr:~n.ingi nnd rlmign of heating, vmtilation.

:nld plumbing.* d. Listing nnrl specification of :ill mtitcriwls. Electrical Design Personnel in this group are responsil~lefor the complete electrical design required for the project according tu the particular specifirations and tllc various national codcs governing electrical installations. Sj)ecifically the work consists of: a. Prcparation of all electrical conduit layouts and final dra\~-ings. b. Preparation of all other electricel dralvings for substations, switchgear arrangements, etc. (Sate: Where reinforced concrete work is required for foundations, manholes, and supports of electrical equipment, electrical rlesigners usually prepare outline drawings d y . Final concrete design is donc 11y the structural designers. Usually the electrical dcsigners complete whatever structural steel drawings are required for switchracks, substations, etc. I f the structure is involved or extensive, t,l~is~ o r kmay be cou~pletcdor cllccked by structural designers. .\Ianhole designs for underground electrical s y s t e m rnust he designed to provide adequate space and ,' suitable arrangement of electrical equipment by electrical d eslgners. Structural designers set wall t,hicknesses, specify, and locate reinforcing stcc1.j c. Preparation of all clcctrical cquipnlent specifications. For niajor plant snitchgear and plant transformer substations, specifications arc usually prepared in conjunction with the project mginrer. d. Preparation of all instrurncnt electrical conduit drawings in eonjunction with instrument (system) design personnel. e . Complcte listing of all elcctrical materials, cable, conduit, etc. J. Thc horsepower, rotation, and other mecllanical requirements of motors are often specified by personnel in the mechanical group. Complete motor specifications, however, are prepared in conjunction with or by electrical design or engineering personnel. *Some organizations maintain a separate group of heating and v~ntilatingnirconditioning engineers, but often this work is suibrontractcd.

Engineering Design ond Drafting

105

Instrument Engineering Inatrunicnt cnginecring for the process plant is more fully covered in Chapter 20. The selwtion uf instrunrents and preparation of specifications fur instruments may he handled hy instrunicnt specialists before the drafting q ~ c r a t i o n snn,l need not l ~ edirectly associated ~vitlithe engineering requirrd for installation. The so-called instrumcnt drafting pcrsonnel liavc t l ~ cfollowing duties: a . Make general arr:mgen~cnt draxr-iilgs for instrumcnt installation sl~olx-ingthe location of all instrument. by aynibol and tlic mrinus run. of instrument piping in general. h. List all instruments shun-ing the 11ropr.r pilling r l m ~ ~ - i nnumi,rr g or other dralx-ing number on which the primary instrumcnt is located, the item nuinl~er.ant1 t>-pe of instrulnect (iudic:~tcd by sy111bol), type of capillary. or other connecting piping, air or process fluid. or electrical connection from primary instrument to controllcr and controlled elcuicnt. c. Preparc detailed dra~x-ingsof thc installation of all instruments locally nir~untcd,except control valvcy I\-l1ir11are shon-n by personnrl in piping design. The hook-up of contrul valves nit11 speri;rl appurtenances is usually detailed on the instrument installation draaings. (Sote: Thcse (lr:~xingsarc all scliematic except for connection details to erjuipi11cnt.l d. Prepare control pancl detail dr;rxings for fabrication and crcction of t l ~ ccontrol panel and prepare back-of-board drawings for thr rontrol roum installation. Prepare initial board-front layout xi-licn gmplric panels are wed. e . List all ruisccllirncous piping or o t l ~ e rmntcri:lls used cxccpt clcctrir:il n-iring ~untrrinlsand electrical conduit. This may he done in conjunction with or by the electrical groul~. Personnel from the electrical group v o r k in conjunrtion with personnel from this g r ~ ~ utup avoid duplicating the inatcrial take-oE. f. C h w k :~dcquacyof vemlor's dran.iugs. Instrument vendor'? dr:in.ings suffiw for i n ~ t r u u ~ c nrli~nension t detail. 1)1;1\\-in;s prcpareil by t l ~ c instrunlcnt group ;tiow iinrtnuuents d r a r n rli:igra~n~~~atici~lIy or in outlinc. 1,~r:rlly111ount(>(l invtrunlcnts. wch as liqui~llevci dcriccs. n41ich ~.onnt,ct, p l ~ y ~ i c d to l y other cyuipment must be shown dimmsionally for in-tallation. (1. (:heck pipin:: ~lrnwing; for pruper l o ~ , : ~ t iof ~ ~irrificcs n and ~nnnu:~l au,l :~utonraticctnrtrol dcvic~~s, tl~rrmo-rvrlls.11ress11rcpr~ints,ctc. C l ~ w k :tlI clrawingr for proper 1uc:rtion of utlier prin~aryde\.ices.

Types of Process Plant Drawings Two ninjilr t y r . ; of rlra\vinas are rrquircrl for prorc;F plant projrcts: i s I I I : ~ u i : c t ~ r rSe:irlv . r i g s r e ~ I rI

106


all drawings that are prepared by the process plant designer are used in procurenlent: either by direct release t o vendors ior price or for material listing (take-off) and suhscquent procurement, 1. Dran-ings prcpared by tlie process plant designer. (I. D r a ~ ~ i n g prepared s for the installation of cquipment, either fallrirated a t tlie site of construction or manuiactured or fabricated elsewllere; also uscd for ccrtain matcrial listing. b. l)r:lr~ings prepared for thc n~anufacturcof equipment by others with initial or general design by purchacr. c. Draxings prepared for the construction of facilities; also used for material listing. 2. I\lanufacturer's dra~vingaand data." n. Dra~vingsprepared hy the manufacturer for his own use in manufacture or fabrication; sometimes called shop drawings; b. Erection d r a ~ i n g sprcpared by tlre manufacturer for us? hy the purchaser in erecting thc equipment purchascd; c. Dimension dmrvings. data sheets, catalog tear shccts prepared by the manufacturer for use by thc purclraser in design.

Installation Drawings

The peculiarity oi the process plant requires the prcparation of drawings t o hc used primarily in locating equipnrcnt to a greater extcnt than drawings shoving the details of manufacture, construction or erection. It woul~lhc impossible. for instance, to construct a catalytic-cracking unit vithout soruc grapliical illustration of the various pieces of eyuipmcnt in p~~sition.For any such installation thc locations of equiprncnt must be rarcfully planned and located by means of dmwings to determine space rrquireurents. Thus, all parts of a major plant must hc dralvn in considerable detail in position and t o scale. Conncctiun dimensions must be s11o1r.n on the drarl-ings to permit ercction. The importance of location or inatallation dran.ings becomes more a p p a r m t alien it is realized t h a t structural steel, pumps, compressors, wsscla, and other cquipment must propcrly fit anchor bolts set in thc conrretc foundations. T l ~ c(limenaions of the cquipmmt and thc locations must he h o v n before design drawings of the foundations and supports can he ~wu~pleted.Tlic constructim forces must have these design d r a ~ v ings beiore construction starts. Vendor-Prints

Proper handling of vendor-prints (manufacturer's data and drawings) is \:ital to thc success of a project.. ' h e lack of suclr data or lnisuse hy

Engineering Design and Drafting

107

careless distribution m e t h d s often results in serious crrors. v.hich increase the cost of engineering, procurement, and erection, TVhile it would be un~terirahleto attempt to dercrihr the variety of mcthids and proccduree used by the various engineeriug organizations, it is hcliewd that the details of the use of vendor-prints and wnlc iliwu*sion of ilistribiitim ~ u e t l ~ o dwill s be lrelpful. The three types of prints suhmitte~lby vendor.< are sllop dral~ings: erection drari-ings, and dirncusion drarvings an11 data sheets;.. Shop drawings are not ordinarily furnislrcd by the rendor except for fabricated piping, pressure ressels and tanks, structural stccl, and 0 t h items designed in accordance ~7-iththe purcl~arer'sspecial rctluirernmts. Such drawings are not required by the purchaser for ure in plant design. and with certain equipment they ~ ~ o u divulge ld the vendor'.; "knorv-ho~~." Shop d r a w i n g of mechanical eyuipurcnt usually ci~nsiatof a large nuuuher of dram.ings s11~1rvingeach piece or part of the asembled item. Thcir nrulrber alonc would prcserrt a prohlrm Vendor-prints designated as erection dra\~ingsare use11 by the pnrcliaser t o identify manufactured equipment and in~licate ercction scqucnce. The third type of vendor-print, the dimension drawing and data sheet, is used hy the purchaser as a source of data for plant desigr~. For manufaet,ured mechanical equipment, the rendor does not ordinarily furnish the purchaser with all the details used in actual manufacture hut instead furnishes only the information necessary for installation. This information consists of a singlc outline drav.ing showing in plan an11 elevation all piping or other conrlcction dimcnsi~ms,di-assembly dimensions, anchor-bolt locations, total weight and veight of parts whicli may he disassembled, and overall dimensions f o r clearance purpos~s. F I X rertain reciprocating machines, dire~tion.frequency, and dcgree of oprrating forces mny hc included. Flow diagrams for lubrication and coding systcrns and iring diagrams where required should be furnished. Individual data sheets are furnished by the vendor for auxiliary equipment supplied v i t h large machines. The purel~asershould carefully l k t R T ~ by suhitem numbers on llata vhicli is prrall such R U X ~ ~ ~equipment pared by and distributed in the purchaser's organization so t h a t the-c data may he identified by tlrc engineering, procurement, and erertiim groups. hlnnufacturers of large machines do not ordinarily stock or warclrousc these machines. Each macliinc is nranufacturctl on tlre basis of an order. If the manuiactnrer has previously nxmuiaetured i d c u t i c ~ lor similar equipment, prclirninary data may be supplied n-ith the proposal. Proposal data, howevcrl is usually only approximate and canuot bc used in design of the process plant. Often a month or nrorc ruay

108

I


: I~ctn-IWIorder plncmicnt ;in11 vrcrillt

,If

I ~ I I I ~ I I : Ii l~: ~ t i ~1111.

major equipment. Venilor-pints are required for all types of equipnimt except that n-hich is rorn~r~only manufartnrrd in quantity and in standnrd fisrrl di~nrncint~s. I t n-ould he unnecessary. for i n ~ t a n rt~o , r e q ~ ~ e vendor-prints st on nrrlin : ~ r yf n r g ~ itcrl ~ l fla11:r~ sinrc tl~(wc;arc ~ ~ ~ i ~ n u f a r tto u rilin~msini~s ed :in11 s~~crifications fixed by various cndcs. Tlrr: s:me vould 11r true for ordinary valves or any similar commonly manufactured equipment not specially designed for the single apl~licatim. Filing a n d Distribution of Vendor-Prints

The handling of venilor-print* in a design organization s l ~ ~ u lbe d rarcfully plannwi and an cxnct procedure h u l d 11e follu\vcrl. I ~ r d k proper idcntification is the most common source of errilr. Sncli errors cause ~vastcdeffort and may delay the release of the manr~facturerto prnceed v i t h fabricatinn. The lnost important requirement in vendor-print liandling is idcntific:~. tion r~-iththe proper equipn~entitem number. Sperific iustnwtions tliould be issued to vcndor;, prefcrnbly starting wit11 the inquivy, reilucsting the inclusion of the equipment item number on their drawings. \\'it11 large organizations it is possible to h a r e design and procurcnicnt prwecding parallel on similar work utilizing almost identical erluipnicnt. Casual identification in such cases may be ~iiislcading. The u w of a purcl~ase order number for identification hy the vendor is insufficient since more tlian one item may be incloded on an order. All drawings or other data received should he date stamped upon arrival. tlwn clicrked by some single person or group, prcferably the same group \\-hose function is distribution of internal as well as extcrnal data. I n solnc organizations sn1.11group. are callrd production ~lel~artmcnts and have the responsibility for receipt and recording of &,sign d a t a ; the filing of all record or pernlaucnt. datn; the identification of data and the proper distrihutim of data both internally and extcmally. I t is also conunon practice to have all rcproductim serviccs such as blue-printing under the s:me department. This makes the flow of all design data the respi~nsihilityof one drpartment ~ v l ~ i cish imperative for the large organization. Clerical personnel when trained t o the routine can usually follow tlic steps. Tlic production department should have in its possession a card showing the item number, vendor, and other descriptive data for each piece of equipn~entrequiring a vendor-print. The card is originated by the peraonnel originally specifying the equipnlent. The descriptive data are added to the card as it progresses througli various groups concerned \\-it11 the articular equipment item. By the enforcement of simple rules such


109

as continuous display of cards by each temporary holder, the moven~ent of prints through all dcpartnicnts can he follorved. Vendor-prints should he checked for proper identification. If the vendor has failed to include idcntification, the data and attachments should be referred t o the originating department for identification. Usually the data can he identified by inspection of the purchase order or the original specific'I t'ton. Vendor-prints may be submitted for l~rcli~niuary use: for purr~Ii;isrr'.: approval, or as certified prints, After identification ;in inspection of tire record card xi11 indicate if the prints are for preliminary use or. for approval. Final certified prints must include the vendor's certificatior~ and thus can be easily noted. After determination of status, tlic prints r ~ , ~ l p p ~ o v i ror l : Certified .ill vendor -11ould be stamped, P r e l i ~ ~ r i n n For data should be so stamped rcgardlcss of thc degree of imjrnrt;mce. One? the method is instituted design-drafting prsonnel vill a11vays look for the stamp and misuse of data will be awidcd. This ~~rocerlure assures that the correct item number and status will ahvays Rppear on the vendorprints. If niisscnt or lost they can be easily identified. LXatriI~ution.names of recipients or dcpartnrcnti, and dates sliuuld all he rccorded on the record card. Since all movement xi11 be tlirough the production department the status and location of all data can be detcrmined a t any time. Vendor-prints submitted for approval require special handling. Since ~nanufacturcrsare often instructed t o withhold fabrication until approvnl is received such drawings or data must 11c handled with the utniost dispatch. The open enril system mentionrd above is very advnntagcous -.ince it forces action. 1)rnrrings :mi data submitted for allproral can be signed a colored card ti1 indicate urgency. Approval dra\vings or data muy be checked 111 designers or specialid gruups. The final approvnl stamp sliould only be affixed by t l ~ eproject engineer. After n11]1ruvnlall copies should be rcturnctl to the Production Dcp:trtn~ent for recording, internal distribution, and return to the Procurement l k p a r t m e n t and to the rendor. T l ~ creceipt of final certified vendor-prints rclcnsci the pur1.1i;iser's design completely. Dates for r e l ~ a s eof construction arc uftm fixed as a set interval after receipt of eertificd vcndor data. These data niust, therefore, be rccorded and lutndled in a manner similar t o that already discussed. Another function of the Pro~luctimDeplrtrnent sl~ould11(, ti113p11yric:ll removal of all superseded vcndor datn. This may be a diHicult procedure a t times since design personnel often have what they consider good reasons t o retain superseded data. If this prartire is permitted each (lcsigncr \\-ill shortly he nraint:~ining liis o\vn acl~:irnte file, but \~itliout,


Engineering Design and Drotting

control. D a t a n.1iicl1 is superseded shoulil always he destroyed. All files of prints from first t o ]:id issue ~ h o u l dhe ~n:lintained hut only in the Pri~dui.tion Dcpartuicnt and sliould nut bc released except by some authority.

number on t,he erection drawing prepared 11y the 11urclmser. Thc piece number usually includes the drawing numhcr on x h i c l ~the piece is sl~own. 9 1 1 aucli numbers uiay be liste
110

Drafting Practices

Each of the specialty groups and design drafting groups produces d r a x ings of ~ o m etyllc for 11sc in furtl~erdesign and in construction. I n addition proccss cngincers and project engineers require a crrtain :nnount of drafting assistance in the i~reparationof f l m ~diagra~ns,sketvhes, and plot plans. Standard equipment purcliased from n~anufacturersrcquires no drafting. The sllecialty vnginccr nccd only obtain certified endo or-prints from thc manufacturcr for tranxnittal t o other design groups. Such equipment includes pumps, coniprrssors, motors, instruments, and furnaces and heat excl~angcrs (if they are being purcl~ased direct frorn a manufacturcr). The design of piping, vrssels, structural ~ t e e l ,foundations, clcctrical systems, and i n s t r i u n e n t ~ t i ~requires n a nurnher of drawings to correctly portray the design calculations and decisions. Some typical niethods used for these drarvings and process plant drawings in general are given here. Piping Design

Process piping is usually drawn single-line cxeept for the large sizes (12 in, and above) which are drawn double-line, showing the width of the pipe. Details and n ~ ~ t 11n e s drawings and instructions in the pipe spccifications indicate where pipc i.; to be bent or fabricatcd frorn fittings. Fittings are rart,ly slio~vnin M a i l on drawings, symbols being used throughout. Tlie diameter of flanges is always drawn to scnlc so that clearances may be readily determined. The conventional synlhols arc used for indicating valves. Fare-to-facc diniensii~nsof valves may or may not be shown on piping drawings depending upon practices followed. Tlie proper scale for piping drawings varies. The use of a small scale in. = 1 f t usually results in a s e r i ~ u s l ycongested dmxing) such as particularly n-hm the piping is for inrolvrd processes. Wlim all piping is extraordinarily large. 6 in. and above, ?& srale may be acceptable. Details for srn:rller piping bhould be inrrrased in scale, however, and sholr-n elscwlicrc. Many firms insist on :j/n in. scalc being thc minimum for all piping drawings. Piping may be shop fabricated or firld fnllriwtrd. All piping2'$2 in. and bclow which is ordinarily screwed is fielll f:rl~ricated. All piping 3 in. and ahove is usually xelded and tlanged and, thrrefore, shop fal~ricated. Each piece of pipe t o be shop fabricated is given a consecutive serial

111

PIPING STRESSAKALYSIS No detailed drafting is required for this part of piping design except simple sketches. The loration of anchors and supports and all forces are usually marked on prints of the piping dravinga for usc of personnel designing pipe supports. Tlic forces are not ordinarily added to the dra~vingsfor reproduction. Anchor points ior pipe are shown by means of a symbol placed a t tlie point of anchor. A schedule of various types of meciianical expansion joints is sornetimes prepared under tlie direction of pcrsunnel in this group. The schedule lists tlic r a r i i ~ u stypes of joints t o be procured, giving dimensions (not vendor data) and the required thrust and stress clinracteristics. Manufacturer's shop dra~vingsor dimension sheets are usnally required since only the manufacturer can supply certain necessary data. Upon completion of pri~curcmcntand receipt of drawings, final data may be added to the expansion joiut scheriule for use in erection. PIPE SPPPORTS The various types of pipe supports such as slmes and hangers (see Chapter 18) are usually indieatcd by symbols or numbers on the piping

112

Project Engineer~ngof Process Plants

r l r ~ i ~ i g .There . numbcrs refer to standard detail ~ l ~ e e l sIf . ext.raordinary forces arc involved thc design of both the attachment and the support may be checked hy structural designers. Usually all necessary materials for the various attachments are listed on the standard detail sheets.

9 certain amount of nketching is required by personnel listing piping anrl fittings. The ~v,.orkronnists primarily of the preparation of lists, of piping nrntcrials ~vhiclrnlust i n r l ~ ~ dall e valves and other piping accessories. s11c11ns bolting :mrl g a ~ k c tmaterials. Piping material listiug or take-off is limited t o field-fabricated pipe when part. of tlre piping is shop fabricated since the fahrirator lists his 015-n material. K h e n all pipe is field fabricated, all materials must be listed, assuming the process plant designer is also erecting the plant. Vessel Design

Prea-ure versels, tanksl drums, fractionating columns, and other separating cquipnrent are usually designed and manufactured in acrordnnce XT-ithcodes as described in Chapter 12. The code design of mc11 equipment specifies materials, temperature stress, and manufacturing or construction pmctieea. The purchaser must prepare an outline drawing shoving the diameter and length of shell, the location and type and size of all connections or upenings, thickness and type of materials for shell and heads, all intcrnnl and external appurtenances required for attachments, and rqjerating conditions for design. Since vesscl design involves total slicll stresses including those caused by wind forces on vertical towers, the diameter and numbcr of anchor bolts lnuvt also be specified. Design-drafting requirenlents for vessel procurement are satisfied upon the completion of the T - e s d outline drawing. Vessel internals such a s fractionating column trays, after process requirements are spt.eified, are often structurally designed by other firms specializing in tray manufacture. This is particularly true when stainless or alloy tray n~aterialsare used. Vessel designers, however, may be required to prepare nominnl layouts of trays according to process requircments. Other internals such as mixing equipment are oft,en mechanically designed for support and location by the vessel designers. Vessel design personnel usually prepare schematic drawings showing vessel insulation det,ails. The vessel manufacturer is responsible for construction of the vesscl in accordance ~ v i t hthe proper code requirement when the vesscl specification requires code construction. H e must, in effect, guarantee that the


113

equipment mcets requircn~ent.sfor the allowable n-orkin,w 1xessures ; ~ n d temperatures. R c must, therefore, clieck thc purchaser'z il~sign. Since pressure vessel fabricators preparc shop drawings for manufaeturing use. these dram-ings are also used for vendor-print purposes. Purchasers of pressure vessels generally require the rendor t o submit prints of shop dmm-ings for approval prior t o rclcase for fabrication.' A considerable period of time usually elapscs het71-een initial reisel inquiry and releaec for fabrication since all piping layout :lnd connections must be fixed before resscl nozzles can hc located or oricnted. For large rcsscls this period of time is usunlly required in any case by the vessel f:thricator for procurement of plate, heads and appurtcnanr.cs. Structural Design

Tlrc location of process equipment m : ~ ?bc based on procc,ss. safety. or nmintenanee requiren~ents. Structure>, supports) shelters. and foundations are: therciore, of a secondary nature and il~eir~lcsigniuu-t depend upon layout and arrangement of tlre various pieces of process equipnient. Design oi strurturnl iyrtrnls i. usunlly h a d upon stand;rrdized requiren~cntsof t h 111a11ual ~ of practice publisl~eilhy the .hrerienn Institute of Stcel Construction (see Chaptcr 231. The process plant designer or purcliascr must prepnrc out,lincs or single-line arrangement ilra~vings sho~vingall structural members, their sizes and connection points. Connection points are usually what arc knoxl-11 as ~vorkingpoints in industrial practice. Infornlation must br included such as t r ~ p - o f - ~ t ~~niniunun el. clca~wms. ztnir? and hnndrail dimensions, grating or fluor plate boundaries, l:~~ldcrs. platform or other support connections. Tlrc rrndor or structural steel fabricator uses purrhazer's ilraxing.: f ~ r rreigl~testimates in prcparation of a price proposal, and for prcparation of hie shop dra~vings. Ear11 piece of steel inurt be detailed for fahriration in the sllop. This pmeticc is similar t o methods fnllo~vcdby thc piping fabricator. Structural stecl is often sol11on a tonnage h;~si?. The total or final l ~ r i c rih u s ~ ~ a l lbased y on calculatril n-cights of material dripped. \Then orders arc plnred on a l u m ~ ~ - s ubasis, ~ n all purchasers‘ dr:~x~-iugr must be complctc a t time of inquiry. I n addition to structural rletails the stet31 fahrieator also p r e p a r c (singlc-line) erection drawings, fi~llo~vinpstanrlar~lizcd picot-marking procedures used by tlic industry. 'I'l~csc
114


requests a n approval from the purchaser for some change in structural member size. Changes may be required in order t o provide clearance for ladders or piping. Thc details are. Iri~n-ever.s ~ ~ p p l i efor d the purchaser's use or record. It is ~vellto point out that all g c n ~ r a lpractices ~ I I I I O T T - P in ~ ordinary huilding conrtruction arc not acreptahle in process plant design. T o i h s t r a t e it usually makes little diffrrence if structural member substitution by a fabricator results in a liicr~lherharing strength equal to or greater than the originai. Hut replacc~nents i ~ rchanges made hy the \'endor for process plant structures slli~uldhave prior approval from the purchaser. I n addition t o the general outline drawings prepared by the purchaser, notes on drawings arid sprrifications s l ~ i ~ u l11e d included to advise the fabrication or rrcction n~ctllodto be used (riveted, bolted, or welded), and the galvanizing or painting specifications. W i ~ e n galvanizing i~ required, purchaser's drnn-ings arc? affcctrd Lwausc nil ~niscellaneous coonccti(~nsusually made in the field must be done in the ehop before galvanizing. F i ~ l d~ c l r l i n gor other changes arc not ppriiiissilble since the galvauizing ~ % - ( ~ uhcl d disturbed. If cllanges must he made, the member must usually be renioved and regalvanized. Electrical Design

Schematic single-line wiring or circuit diagmms must bc prepared for the process plant .shorving all electrical equipment, Iond distribution, t,ransformcrs. and sn.itcl~gear. F:lectrirnl (lesigners use these diagrams to lay-out and shon- in detuil all conduit runs and accessory equipment. A11 conduit, i.ircuits, a i d equipn1ent a l e assigned numbers or synibols. In addition to the detail dra~vingssllolving conduit runs and connections, sclicdules n u s t be prepared wliicll list by number :ill circuits and conduits, tlie drawing on n-liicli tlie cnnduit is sllown, conduit length and size, and cable length and size. Otlier tabulations are also prepared showing the proper sequmce and setting for power control apparatus. Drawings prepared for the clcctrical i~lstallationare extremely schematic and 15-ithont dimensions except on details showing terminal points of conduit rutis: the arrnngeuirnt of conduit in hanks, entrances of conduit to buildings, or exact a r r a n g e ~ n m t r required for clearance. For thrsc drawings area plot p1:tns are needed as well as vendor's certified diuierision prints for all proccss equipment requiring electrical connections. Usually clcctrical drawings prepared hy the process plant designer are used only fur erection of the plant and for ~ x r t e r i n llisting. 1Iost elpctrical equipment is always procured by nwans uf ~vrittcudescriptions.


115

Instrument Engineering

Design-clraftiug opesations for indrumentation in-tallntion are very g s usually similar to tlrose for the electrical install:~tionin that d r a ~ ~ - i n are s < , l ~ c ~ ~ i aand t i c are used priluiiril>- for inaterial li.sting. Instdlatiull y for those instrun~erlts details, again schematic, are u s ~ ~ a l lprepared ilirectly connected t o other equipment or for iustruulents located in a control center. The latter drawings are dimensioned but not necessarily draxl-n t o scale. Tahulntims situilar to tho>? 11reparid for tlie rlectrical installation are prepared for all in;trument control rircuits I ~ o t electrical l~ and pneumatic. Vendor data for indrnnlr~ntntion and area plot plans are required for instrunient design drafting. Drawing Scales

A frequent time waster in many organizations is the arbitrary assignment of fixed srnlcs for wrtain y of r i g s r e a r 1 of the variation in design or scope. S o ~ l o u b tso~lieof the fixed scalc thinking is derived fro111 certain arcliit~cturalpractices in n.ilic11 one tracing may y e11ci.k for ir~terfcrences. This procedure be used as a so-called < ~ v r r l nto is rarely practical for process plant drawings ~viicredrafting to a precise scalc (measured) or in great detail is undesirable. A usual scale for piping drawings is 3/8 in. = 1 i t . T h e next lowest readable scale is in. = 1 f t . For congested dm!\-ings :!h in. may be too small. The best scale is one which provides n clear picturr or vlricl~[ulfillr the intent of drafting by providing a graphic illustration of data. T h e actual scope of ~ v o r kcovered by a drawing has little t o do v i t h economy except for some saving in printing costs. The highly congcstrd dralving complctcly cmered in car11 square inch of spiicc, as is tllc usnal result \,-hen l/i in. scale is used for process piping, is in reality a t r c m m dous time vaster. It is inefficient in the initial drafting, in rlmking. in material listing, and in erection. Process plant drafting does not usually require absolutc precision such as would be found in machine design. I n nearly all depign work tlic practicc of scaling draxings t o detrrrnine dinlcnsions is strictly limited t o estimating. JIost drarvings for tlic process plant must bc made t o some certain male in order to show relative sizes and locatii~nsof equipment, but extreme prccision is not required nor justified unless tlic design is purely a developnient of some mechanical ~levicc. The majority of design drawings for the process plant are prepared for erection purposes rather than for marruia~~turc. In drafting practice the centerlines of cquipmcnt only are lorated as precisely as posriljlc to scalel so tlmt discrepancies :Ire not, curnulatire. All dimensions which arc necessary f11r crection, construction, or elear-

1 16



I r I I I I r i Sc:ili~~g, ~ cscellt ~ i r ~ r~ I cctinuiting E purpose, is unnecessary. I t d l probably he ohviour in any case that v i t h scales such as 3/$ in. = 1 it, accuracy closer than One or two incl1e.s ~~-onlcl he impractical.

M o d e m Drafting Techniques

.iltliough many ailvanrcs liarc heen mndc, in all hrnnches of science. relatively f r ~ vimprox-cnients have bccn made in thc most basic of all rngincering functii~ns,thc lxel~arntionof drax\-ings. S o methods have yct I m n rlrviscil to ron~plctcly rliminnte the pninstnking manual proccdurr of (11.:ifting. For the 111,ucw; 11l:urt: t l ~ crrwt of Ia11,r consumcd in ilr:ifting ol~crationsalunv o f t m reaclics 5 j ; of the total erected plant n ~ t . Thus it is extrcnlcly important to utilize time-saving proce~lnres in this pl~aseof engineering, pnrticularly for firms contracting engincering xrvices t o industry. Since the d i w ~ v e r yof blue-printing thc only nlnjor change niadc in drafting p~~oceilure has lwcn the substitution of pencil teclmiques for inkcii drmings. Several decades ago all dra\vings ti~adefor reproduction 1verc first prcl~arcdin pencil, then traced in ink. Impruvcnlcnts in dmfting procedures. materials and reproduciion processes permit ]~rotlnction of p i n t s from pencil dra~vingsequal to prints from inked draffings. Few process pl;mt engineering fimms any longer use inked drawings except at tinies for final flox diagrams or for certain standard draxvings. Linen drawing sheets prove much more satisfactory under the severe services found in process plant design-drafting and reproduct,ion than the various tracing papers. The niucli better working surface of the linen sheets n-ill save sufficient t,ime to warrant the slight additional cost. A number of mcthods conimon to the printing industry are being used to ndvantage in drafting operations by the nlore progressive finus. Many titue-saving possibilities are offered by the offset printing process. Drtails a ~ i dinst.ructions that. nus st appear on all drawings can bc reproduced on the linen drawing sheet by this process instead of hcing hand draxvn. 1-: ~.' ~ ~ frequently ous nscd dctails are sometimes printed on smnll sheet? nnd distributed along xvith larger dran-ings as standards. Althougll ilrafting labor is savecl, rcfcrenres to the sheets niust be made and the printing and l~andlingof an additional drawing consumes time. Such dvtails may be reduced in size by a simple photographic process and reproduced directly cn the draving sheet by offset printing. Although the size may be reduced, the reproductions produce sharp legihle prints. The same process may he used for reproducing catalog pages, manufact u r e r ' ~dimension drawings, or any descriptive data required for erection of thc plant. I n general any detail which can be printed directly on a n original

I

117

drawing x d l ravc r1r;tfting inanhours. lI,,rL of thcsc various printing processes and reproduction methods are extensively used by the major manufacturing firms. Any dctail manually added t o a dra~i-ingmnst be checked. Hence printed data should always be less costly. ..machine similar to the typewriter which pcrn~itstyping directly on ~ l r a ~ v i is n ~extensively s used for adding standard notes to clra1~-ingr. The laborious dmdgery of hand lettering lengthy schednles and lists may thus l ~ eeliminnted. .iny capable typist can he trained to operate the ~rr:icl~ine so that a further cost reduction in labor is porsihle. Such mar~kiine;usunlly repay their initial cost in a few nlonths hen l~ropcrlyllsed. I~ncioul~tcdly niany of tilt, firlns cngnged in contracting cngincering t o industry could profit by invcstignting drafting and rcprodu~:tion lilethods used by some manufacturing firn~s. TYitli di.sign-drafting c ~ ~ s for t s the process plant approaching $0.07 per minutu per person it \vould appear that any method which offers labor saving possibilities sl~ouldbe d c o n l e d .

PART

11

BUSINESS

AND LEGAL PROCEDURES

project engineer not only works with engineering T p r o b l e m s but also deals wit,h procurement operations, ofice procedures, and contract interpretations. HE

PROCUREMENT OPERATIONS To purchase the needed equipment and materials a t reasonable cost and to have them delivered a t the proper time is one of the most important phases of process plant. construction. The procurement department of an engineering organization does this work, hut not without the help and advice of the project engineer. Even though many purchasing agents in the process field have engineering backgrounds it is impossible to expect them to be well informed on all the phases of technology. It is, therrforc, necessary for them to seek the advice of the project engineer nhcnever engineering judgment is needed. In like manner the project engineer must depend on the purchasing department f w up-to-datc procluct information and prices, contacts with vendors, and above all for the procuring of materials on schedule. It is important, therefore, to be conversant r ~ i t hthe organization and operation of a purchasing department for process plant construction procurement. Pn~curementfor a process plant project is different from the purcliasing operations required for n nianufacturing plant, ~vlierethe buying process corers only a relatively few standard commodities which arc bought in quantity a t regular intervals. Personnel engagcd in purchasing for a process plant project must have a n-ider experienc~,and must he an-are of p o ~ ~ i beourrcs le for inan? inore kinds of eqnipment. ORGANIZATION AND OPERATION OF A PROCUREMENT DEPARTMENT

The SAPA (Rational Association of Purchasing -4gents) V ~ a recoms mended a variety of organizations for procurement departments. One typical of procurement for prnccss plant con4r11rtion inxy consist of 121

124


turer, horrcver, ehou1,l not l ~ cmade f ~ , long r p r r i ~ d hcvcn on a singlc projcct. The procuremcilt operations on a major process plant ~vill usually continue over a t least one ycar, and priccs may fluctuate during that time. The procurement department must knuw price trends and rescrve the right to take advantage of these changes for the sake of economy. Expediting a n d inspection Expediting and inspecting are oitcn directed by the procurement dcpartment. The primary funct,ion of project expediting, hoxever, is expediting movement of materials to meet the construction scl~edule,and nccd not be directcd by those engaged in the buying operation. PROCUREMENT PROCEDURES

The lrrocuremcnt of materials for a process plant l~ruject can be divided into several phases. 1. 1nquir:r-A formal request for a quotation of price. 2. Qnotation-The iormnl rcply to t h r rtquest for price. 3. Rid con~parison-Ol~jective study of all quotations received for a particular item. 4. Purchase order-The formal order scnt t o the successful l~iddcr. 5. Inspection-The examination of materials during fabrication and upon completion t o insure highest quality. 6. Expediting-The acceleration of progress on manufactured equipment by the purchaser. The Inquiry

Actual detailcd opcrations of the inquiry phase are: ( a ) accurnuletion of data in the form of epecificatir~nsor dmxvings, (b) sclcction of r m d o r s to mhonl inquiry is to be directed, and ( c ) typing and mailing. Item ( a ) is a responsibility of engineering, ( b ) evolves from past experience or engincering development, and (c) is a clcrical operat,ion. Many companies have standard inquiry fr~rms. The iorm invariably has this is not a n Order printed plainly on the sheet t o avoid conful;inn. Drawings and specifications where applicable arc attachcd to the inquiry. The method of quoting is outlined and rcquests for delivery date promise, terms oi payment, and a price breakdown arc made. The date on which the quotation is required is given, and !nitten quotations are requested. The number of inquirics solicited for a given item depends on conipany policies. If procuremcnt is being done by a contracting firm for a customer, the customer's desires will be followed. I n fact many process firms furnish contractors with a list of acceptable vendors and specify the minimum number of inquiries to be solicited. Three inquiries is the

125

Procurement Operations

usual minimum uinw t h r c ~quutittimli !\ill in*ure r~~lcction of on the basis of price, dclivery, and quality of product.

it

vendor

The Quotation

Tlie wllw lvrnilori ~ u h m i t shis qllotstion on a special iorm upon which n ~ l e f r g c n c r ~ lo n i t i ~ I ~ . d f i n i t i n a n t c 'Tl~csr :ire luintr,l in ~ n l a l ltype, but s11011lilnot he disregarded since they are a legal p u t of the c l o c ~ ~ ~ r t e ~ ~ t . The epccific information pertinent t o the cquipn~entbcing quoted is i y p c ~ on l the qnotation form and should inelude tire follm~-ing: Q~uintit!/ and Description of Jlnterinl Being (Jiwteil. T h r dcscril~tion mxy 11c brief 1y1vci:illy if it is ~.cfcn.edt o a specification n-hich givw a rolnplctc ~lchcription. h~lditi,maldeseriptivr literature anll i l r n ~ v i n gare ~ nlso ;~ttachcdif thcsc aid in hetter dcscrihing tlic item. Price. The price should l ~ cgiven as both a unit price (pricc per itcuii 2nd R total price (price for total number of items and also l~riccf m lliv total order) . Estimated TPeights. This information is nwcssnry in planning hrst slliiiping neth hods and in comp:iring bids. T ~ j p eof Quotiition. (a) Firm price-Price quot?d is binding on tlw scllcr if acecpted n-ithin a givcn time limit (usually 30 days) ; ( h i Esc;llation cl;ruse--1\Iany quotntions during the days of initial material ' shortages and inrlctcrminablc costs of Wurld TVar I1 cont:tincrl c s r a l'I t 1011 rlausca ~vhichpt~rnittedthe u p ~ a n adjustment i of priccs due t o incrcaicu in labor, material, and transportation betwcen the date of placing of thc irrdcr and shipment. Trode and Qrluntity Discounts. Certain qnantity discounts and clisci~untsapplicable t o ljuycrs v h o will rcrell (such as contractorsi are regnlarly givcn. The nniount of the discount s1111uldbe givcn on tlic quotatiuo. Any cliscount that is treated hy the rrnilor n-it11 the grentert of -errecy s1111uldbe looked upon ~ v i t hs u q j i c i ~ ~ n . The usc of trade iliec~~unts on metcrinls listed in c a t a l o g i.; ~~:rrtienlarIy :,ilrantagcous for both \-endor nntl lmyer. .k catalog m:iy Ile printcil m c c n year or less v i t h complete ileecriptions and yo-callr~llirt prires i\vhicli :Ire priccs aborc the actual anticipated sclling price) given for carh item. The actual price c:ln thcn 11evaried to allon. for changing ci~stsby re\-iring the discount shect and not the entire ccdalog. Uiseounts are oitcn quoted as a series of percentage discounts sue11 as 20. 10 and 5. To calculate the actual price the list price is multiplied hy (100 - Discount)/100 in this care, by 0.80, 0.90, 0.95. A series of disrounta is used because one discount may not apply to every situation, bnt various combinations of discounts can he devised which ill hc applirnhlc. Terms. Thc terms of payment including the amount of cash discount i

128


tabulation of bids. All such tabulatioris I\-liicli require engineeri~igjudgment zliould be subtnittcd to the project enginecr for approval. The purchasing department should be particularly careful t o indicate all terms and transportation factors and should point out the difference in these items. Copies of the quotations should be supplicd with the tabulation to aid in the cnginccr's study. The contract~~r's project, enginecr vill oitcn submit tlicse tabulations to the customer's project enginccr for his approval.

I I

I

I !

I

The Purchase Order

After selection of the vendor, a p u r ~ h i s corder based on the successful ~ ~ u o t a t i oisn issued. Purchaie order forms arc ubed for this purpose.* Tllc inforniation on these i ~ ~ r n liiay i s bc divided into three catcg~~ricslieading, main portion, and standard printcd notes. The location of each of these on tlie purchase order has bccn specified by the American hssociatirm of Purchaxing hgents.5 HEADISG. Gives company name and address and spaces for ven~lor's name and address, shipping address, and instructions. F.O.B. point, ternl., date of order, p n ~ h a s e - o r d e rserial nun~bcr,and date iilaterial is w n t c d . 31~1sPORTION.The main portion of the form, usually precedcd by a reference t o tlic vendor's quotation, lists the quantity, dcscription, am1 pricc for each item. The total price of the ordcr is also given. If the order can be referred to specifications and drawings, the dcscriptio~ican I I brief ~ and the specification and drawings transmitted as a part of tlic order. Whcn available the approximntc weight of cach item is listed sincc this information oitcn proves useful t o recipients of purch:~scorder col~ies,such as the engineering dcpartn~ent. PRISTEDNOTES. A number of standard notes; terms and conditions of tlie order arc also printcd on the purchase urder. Thesc include instructions for mailing the bill of lading (carrier's receipt): packing list (list of contents, dimensions, and \\.eight of each shipping package or cratc), and invoice (list of items shipped or on order showing prices and other cliargcs).t Instructions for identifying all shipments, letters, and d w u n ~ c n t sv i t h thc purcbascr'a order number and equil~rncntitem uu~nbcrarc :~lsogiven. It is very important that, thc wnrlor follow these rcquerts; other\~iseconsiderable dclay and confusion is causcd in identifying tht. 111ateria1s. tu the origiu:d ordcr (rhangc o~.d?r)UI.C :dso in i%-idcIIW. * Furms i w 'l'lw wording Churlye O d r i is printed pron~iuentlynn thr Cure to cull :rttcntiou to the changes and differentintcit from thc original order.. i 0rde1.l~transaction of business dcpends on the prompt reccipt of i m x r a t e eoples of all these items. The construction departnlent materials men use llie parking lists to check inruming material. Tlic accounting dcpnrtmcnt must check the invoices against t h o older and cerliiv them to the eamutiollcv's office ior pym~nL.

-

Procurement Uperarions

129

The purrhaw orrlrr form sliould also includc all the purchaser's rtan~lnrd notes on policy printed (not typed) directly on the original document; otherwise, loose addendums or attachments will be required. Each loose piece of paper represents an added cost in handling and can easily bc lost in transmittal. The folloving notes are standard with moet prorurent ions. ~ ~ w orgxniz nt Gzraranfee. Some type of guarantee clause should be included for all equipment and material purchased. Extensive and elwhorate, guaranter clauses usually requirc additional correspondence, with subsequent waivers or amendments. The best guarantee is always the integrity of thc vmdor. 'l'he following is typical. "All equipment or material* furnished on this order shall be guaranteed, for a period of not more than twelve (12) months from date of delivery (or date of operation or usel against operational failurc, due t o rnanufacturcr's design; or mechanical failure, due t o manufacturer's workmanship, when the equipnlent or material is being operated or used in accordance !\-it11 the original q~ecifications. All parts or materials found to be defective wit,hin the specified time interral shall be replaced without cost to the purchaser, F.O.B. nianufacturer's plant." A primary vendor (one who receives order) does not guarantee manufactured parts of equipment furnished t o him by another manufacturer, beyond that other manufacturer's guarantce. The primary vendor n-ill usually acknowledge the guarantce clause by stating that the overall guarantee is limited to the gnarantees of the subvendors. hlanufacturcri, however, accept a certain moral responsibility for any equipment sold since their reputation is a t stake. B u t no manufacturcr will ordinarily acccpt any responsibility for loss of profit in production caused by failure of his equipment, and practically all guarantccs are limitcd t o rcplaccnient of tlie item d i i c h fails. Inspection. A paragraph should bc included stating, in effect, that. "all equipment and material furnished shall he subject t o shop and field inspection by the purchaser or his delegated agents, and the vendor shall notify the purchaser a t least-days in advance of its readiness for shop inspection. If the purchaser does not wish to inspect certain eqni11lnent the vendor will bc so notified, but shall undcrstand that any sncli inspection rclcase does not in any way relicve him of tlic responsibilitirs sct forth in the guarantee clause." Another clause frequently used is that "purchascr's inspectors, or representatives shall havc access a t all times to n~anufacturer'splants or shops for the purpose of inspecting equipment, during the process of ~nanuiacture." Quality. A statement is included on the quality of materials. "All materials i'urnishcd or used in the manufacture of purchased itcnis shall be new and of first quality and in exact accordance with tlic annlicable .. specificntions."



Labor Clauses. A typical labor clausc might be: "The vendor agrees t l ~ aall t labor used in the manulnrture of the specified itenis furnished shall be employed and paid uuder the applicable regulations of the Fair 1.al10r Standards -4ct of 1938, and its subsequent or future amendments. The vendur further agrees that all invoices submitted to the purchasrr shall bear a written certification of his compliance n-it11 the abovc regulations." A number of laws cxist regarding discriminatory practices. The particular area in which the work is to be done and the type of labor used all should be investigated previous to order placenlent with unknown firms. Serious difficulties may bc caused hy the use of an open-shop firm if closed-shop workers are erecting the equipment. Shop fabricated pipe may be a source of many labor entanglements, particularly if the pipe is not fabricated in the area where it is to be erccted. The piping specifications should include a requirement for a stamp ccrtificati~inon cach piece of pipe giving the manufacturcr'a association with the applicablc labor union. Subcontractor Clmrses. Thc purchase order ia frequently used as an instrnmcnt in placing sulicontracts. The standard niltes in the purchase order need not repeat the phrases in the subcontract. I t is suficicnt to state: "When equipment, materials, or services are bcing furnished under a subcontract, the executed subcontract, form shall apply and become a part of t,his order." The subcontract form itself is legally an addendum or attachment to the order. Shipping Imtructions. The point of origin and tiic tlcstination of material corcred by thc purchase order must bc listed for use by both vendor and purchaser. The mcthod of transportation is sclectcd early in the negotiations if possible and should bc indicated on the purchase order. When t,ime is limited the purchaser may request truck shipment, railway e x p ~ s s or , air cxpress. If shipping methods cannot be decided a t time of order placement, the statement, "Shipping instructions will be issued later," should be included on the order. The vendor must bc informed of shippit~gmcthods for large equipment so that assembly of the equipment for shipment can he planned. Patent Protection. Since the patent law holds the user of a patented item just as liable for suit by the patentee as the sellcr who has knovingly or unknowingly infringed, the patent protection clause is inserted in purchase orders to protect the purchaser. It requires that the vendor compensate the purchaser and/or ultimate user of the material for all custs vhicli may develop due to suits filed by the party claiming infringelnent." Many other special terms and conditions peculiar to the particular transaction may bc included as part of the purchase order. All such notes shuuld be clearly pliraped and above all sbould be kept to the minimum. I t would secm that clauses protecting t h e buyer should be

limited to those protecting against fraud and cont,ingenries beyond tile control of the buycr. Certainly man r i l l never devise clauses so cleverly n-ordcd that they will protect against practices which are legal hut nevertheless unethical and damaging. Tlic bcst protection is a reputable manufacturer.

130

"Acceptance"

131

Order

Lcgally, the purclinse order hccomes a contract only after arceptancc hy the seller. I t is, therefore, conlmon practice to send an "acceptance" copy of the purchase order to the scller .so that he may sign and return it. The signcc for t,he vendor must be an authorized agent of the manufacturer. INSPECTION

.In important phase of procurement for procesa plants is the inspertion (JI equipnent during and upon completion of manufacture. The advantages gained through careful devclol)mmt of specifications and drnvings hy the purcllasing conipany can bc h a t by careless ~vorkniilnrhip and errors made in the manufacturer's shops. Particularly on major items [ i f equipmcnt, therefore, it is ~vorthwliilefor the purchascr to send his inspcctor to the vendor's plant. The pririlegc to inspect equipmcnt a t the plant is usually agreed u p m prior to the placement of tbe order and is included in the purchase order. No reputable manufacturer vill d e ~ i y inspection privileges and many wclcome a competent inspector's suggestions. I t is the inspector's job to witness tests on merhanicnl equipment such as pumps and emupressore, to observe and approve fabrication nicthods of vesscls, pipe and structural steel, and to encourage the bcst worknianship on equipment bcing manufactured for his cmployer. He should be a person of considerablc practical kn~~~v-lioru xvith an ability to spot mistakes and also an ability t o get along wcll with p e ~ ~ p l e A . large portion of a competent inspector's work consists in preventing mistakes before they occur. Thc inspector's reports are made directly to the purchasing department. The projcct engineer should be notificd about rejeetcrl equipment. t ~ u i :tiljustments on rejected items are handled by the purrhasing drpar' ment. If inspection is madc a t thc sitc of construction, arrangements are made for replacement of rejected material and for returning it to the vendor. I t is sometimes possible, in the case of equipment surh as pumps and filters for the vendor to correct faults in the field. For this work a technical representative of the vendor is sent to thc jubsite at the vendor's ixxpenre. Beranse of the high cost of inapcction, only ~nnjorequipment items ran

132

133

Project Engineering ct Process Plants


I I ~inspcctcil prior to .;hipment Stwl; it1.m- such as T X I ~ E S and instruments must 11e cliccked upon delivery a t the construction site.

IIc must IIC certain tliat the vcsiel design groulj coml~lrtrsthe final dcrilcd dran-ings on schedule so tlie fabricator d l not he delayed .liter t l ~ cmanufacturer receives final dravings and fabrication begins, the progress of the ~vorkcan be reported by the purchaser's inspector n-bo IIILI.;~ observe the shop operations daily. The expediter need only visit tlic shop occasionally, but he continues to follow the progress of the vessel until it is delivered. JTlien the inspector'r report indicates that x o r k i* Ilcing delayed, the expediter will visit tlie shop, determine thc causc of tlie delay, and help tlic fabricator overcome it. If the falxicator has :I ilumbcr of orders from other companies, the expediter niust make more frequent, \-isits to he certain illat liis job is not unduly delayfd bccansc of ~\-orkon other orders. I n sununary an expediter's duties may bc briefly 1iut1inc.d as f o l l ~ t ~ s :

EXPEDITING

The ]iri~n:wyfunction of expediting is t o assure dclircry of purchacd n~:itrrialsa t the jobsite in acc~~rdancc n-it11 the project schctlule I\I:~tt,rial such as valves and fittings arc- ava~lablcfrom supplier's n-arehouses anrl ran he dclivcrcrl a t ally ti~nt,. The 11rogrc.s of specially h i g n e i l equi11~ncnt:Iiu~vcvcr,such as 11rcsurr ve-..cis or large wmlwessurc, must l ~ r fullo~\-cdcontinuously by employees of the purcliaser cnllcd expediters. llanufacturers estir~xttcprohal~ledelivery dates for equipnrnt to be fallricated in their shops, but tlicsc e.stimatcs depmd on proiiipt dclivcry IJE ~n:~terialsfroin tlieir supplirri; efficicnt srlicill~lin:, ( i f s l i ~ ~~vork, p mil early receipt of draxings from the purchaser. The l~urcllaser'seuprditer can do nlucli to :Issure that c~tiniatedddi\-ery dates will be ~ n c tlly vorliing with botli the manui:icturcr and his 011-n organization. His ~ v o r kcan be explained more clearly by describing tlie progress of a large steel presmre vcsscl from the inquiry stage t o delivery. .In inquiry is sent t o three or niurc inbricators and it includes s p c c h wtions and a preliminary sketcli of thc vessel. The vessel diameter, plate thickness, type of liead.; and number and sizc of nozzles arc given. From this infornlation the vendors are able t o develop tlieir quotations wliich give costs and estimated delivery time. During tlic inquiry pcriod ( t ~ too tlircc m e k s ) enginecring w ) r k proceeds in the purchaser's offices and by the time tlic or11c.r is plaretl the nictal specifications and vearel sizc and tlrickncs.; h a r e been cr~nfirnie~l. If changes have been made, a rcvisc,d sketcli is attached to tlie purcliax order. The fabricator is informed by a note on the order t l ~ he t is "relcased t o purcliasc all materials on the basis of tile preliminary sketches." The expediter reccives a cupy uf llic purchase ortlcr a t the same time it is sent to t l ~ cvendor and it then becomes thc responsibility of the expediter to re? that delivcry is mule on tinic. After tlie f a l ~ r i w t i r11as heen told to prucccd xith thc ~ ~ u r c l i : ~111 se materials, tlie purcliascr's expeditrr visits the fahricatoi.'~ ~11011 autl obtains copies of all material orders. H e then cIle14
1. Accumulate data wbicli may affect delivery. 2 . Anticipate delays and bottlenecks and resolve tllcse directly with the vendor. 3. Assist vendor in obtaining priorities. 4. Assist vendor in resolving his procurmlent problems. 5 . Change delivery schedules when necessary. 6 . Correspondencc with the subvendors and suppliers of the primary wndor. 7. Be a x ; m of changes of engineering schedules in his 0x1-n orgnnization, and to relay this informntion to the vendor or ial1ric:ltor d l e n nccessary. 8. Expedite his own organization to complete vital dra\\.ingi ori Although delivery on time is essential, early delivery nlny bc a (lipadvantage. llaterials obtainable from stock should not bc ilclivereil until needed or extensive warehousing facilities u-ill hc necessary. Spccially built equipment buch as a vessel must be lifted twice if delivered before foundations arc ready. The cxl~editcr,therefore, must aid iu : i u d i n g surli early deliveries. AII expeclitcr must have a ~vurliingkno~vlcdgcof fabricating l~roccdurcs, 1muxnnnent methods, sources of supply, and slripping practict,s. I n :&lition lie must he able t o work effectively ~ v i t hpci~plcin his o ~ and n the fabricator's organizations. Since liis priniary duty is to encourage people t o finish a job on time, his actions must be diplomatic in order to void resrntincnt,. GENERAL PURCHASER-VENDOR PRACTICES

134

135



1. I n general all transactions between purchaser and vendor should be kept on a formal basis, i.e.>in writing. 2. Instructions t o vendors shall always be sent in the form of a changed purchase order or addendum to original order. This should be a docnnient similar to the purchase order, carrying the signature of the purchasing agent, and identified with the original purchase order hy some similar nunierical designation. 3. It is good policy for only procurement personnel t o discuss prices. materials, or equipment with vendors during the inquiry stage. Since it, is uncil~ical to disclwe a n y vendor's proposal t o another vendor, the fewer persms having this inforination, the l e ~ schance there is for accidental disclosur?. 4. Price re-negutiation may or may not he permitted after a. formal prnlmal is rcceircd. This is usually a matter of policy ~ i t hthe purchaser. If one vendor discovers an error in the purchaser's inquiry or for some reasim is allo~vedto revise his quotntii~n,all othcr vendors pnrticipating should hc allo~x-edthe s:une privilege. 5. Suffivient timc should he allowed for receipt of proposals before deriding the successful bidder. 6. A good policy is to require that all changes, additions, or deletions be handled by the procurement department only. Under certain conditions this policy may require additional time, but i t avoids confusion. It should be the complete responsibility of the procurement department t o negotiate the con~mercialpart of an order (pricc, terms, and delivery), regardless of the technical requircments. If equipment is being manufactured in accordance with the purchaser's dcsign, the fabricator may ask a nnmbcr of technical questions which can only be answered by the engineering department. These questions should always be addressed t o the procurement department and then relayed t o the engineering department. h iurmal reply is then forwarded b y engineering t o procurement for transmittal to the vendor. I n this manner thc procurement department can retain full responsibility for all changes in price caused by design alterations. 7. Order cancellations of fabricated equipment or materials of special design may be required because of changes in design or scope of work which are the fault of the purchaser. Cancellations may also be madc because of failure on the part of the vendor to manufacture the equipment properly. Cancellation clauses are written into the purchase order, by stating simply, "This order may be cancelled within 30 days after I purchaser." This statement is used when placcnient without r w t ~ I tlic the intent of the purchaser is to limit the vendor's action until the purchaser is ready to prureed with the work. \Vhcn work has been started by the vendor and it is decided t o cancel the equipment because of

changes in scope of the project, tlre vendor must be formally notified t o "immediately stop work and incur no further costs t o the account of the purchaser." The vendor is then a ~ k e r lt o submit. cancellation elrargc. accompanied by proof of his costs up t o tlie tinie IIE cancellation. Thi; purchaser may accel~tdelivery of materials purchased by the rendur for use in co~upletingthc order, or the materials may bc retainc~lin the ' vendor's warehouse and their value deducted froni tlrc c:inrell a t ion charges. Even if equipment is cancelled because of tlie rmtlor's failure to perform satisfactorily, cancellation charges are incurred by tlre purcllaser. I t is the purchaser's responsibility to have some kno~vledgeof tlrc vendor's capal~ilities. Cancellalion slrodd never he undertaken \ ~ i t h o u tcunrplete iinodcdgt. of the costs involved. These include the vendm's labor rosts, inaterial costs, loss of profit, and the purchaser's loss of time and engineering manilours. PROJECT ENGINEERING AND PROCUREMENT COOPERATION

The many duties and responsibilities of the procurement department can be met only through cooperation bctveen procurement and project engineering groups. Mutual understanding of the duties and problems of each and an atvareness of their interdependence are needed. Projcct enginecrs should remember that changes in dcsign produce delays in fabrication. A change that may actually be rather simple can become quite complex when large organizations are in~rolved. Drawings, orders, and suborders must bc altered before the actual e l r a n ~ ereaches the manufacturer's shop. Only alterations whirlr are absolutely nccessary should be made during the fabrication stage. REFERENCES 1. Hnrl.iman, Norman F., Principles of Srirnlific Puichnsing, MiGraw-Hill Book Co., X r w 1-ork,1928. 2. Hcinritz, Stua1.t F., Purchasing, Prenti<:e-Hall. I n e , Kerr Yo&, 1947. 3. Johnson, E. R., G. C. Huehncr, and G. L. Kilson, Transportalion Economic Principles and Pmctices, D. Appleton-Ccntory Co., Scrv I-urk, 1940. 4. Lewis, Howard T , Pmczrrrrntnt Pi.inciplcs and Cnscs, Richa1.d D. Irwin, Ine., Chicago, 1949. 5. National Association of Purchasing Agents Handbook of Purchasing Policies and Procedures, Volumes I and 11, Piational Association of Purchasing Agents, Xcw York, 1939 and 1942. 6 . Revised Amencan Foreign Trade Definitions, National Forcign Trade Council, 111 Broadway, Yew I'ork, 1941. 7. Rindsfass, C. E., Puichnsing, McCrnw-H111 Book Co., Xcn Vork, 1915. 8. Stuffleb~am,G. T., The Trofic Dictiurrory, Simmons-Brondrnan Puhlidling Ca.,

Kew York, 1950.

CHAPTER

10

OFFICE PROCEDURE Enaineerine engineer. I n - is only one of the functions r~f the project . . addition to technical duties, he must manage his officc. The stalt' of this office usually consists of assistant projcct engineers, a secretary, and a file clerk. It is, of course; only a small part of a large engineering office vhich includes other project engineers or project managers and tlieir staffs as well as departments such as accounting, purchasing, drafting, and engineering specialties. There is a constant interchange of ideas and instructions between the project engineer's office and the other dcpartments, as well a s direct contacts and correspondence ir-ith people outside the company. Therefore. he also must develop facility in holding conferences, correspondence, and filing. A discussion of each of these functions i d be of vnlnc since poor crccution of any of thcsc will produce mistakes and faulty design no matter how competent the engineering. CONFERENCES

Thc project engineer must exchange ideas with many people during a working day not only by means of formal policy-making conferences, but also by informal conferences or get-togethers ~ v i t hmen fro111 other departments, customers' representatives and sales engineers. As is always the case in dealing with people the intangible, and for the most part unteachable, qualities such as humility, open-niindcdncss, : ~ n d courtesy are important. 136

Office Procedure

137

TIlimility is one of the most essential personal trait; in any field xicncc. Any true scientist is aware of the many assumptions and gaps 11f kno~rledgein his field and never prceumes knoving everything. Being Iiumhle, howcver, does not mean being obsequious. Tcntativc l~ositions i,sn he held vithout reticence. Open-mindedness is important in dealings hoth individuals and groups If two ideas of equal technical merit are proposed. one by you nnd mother by a pcrson ~ v h omust executc the idea, it n-ill 11c ailrantapeous to use the otller pcrson's idea. I t is logical to :~ssutnctlinl lie will r using his own method. do R I ~ t t c job I n large confcrmces, too: open-niindr~lnesspays iliridcnds. I n thwc -ituations it becomes tlic ability t o listen to utht,rs. Often in conicrenc~.~ :in ;rtiuusl~licreis created ml~icliseems to com]~cleach particillant to p r f o r n i . B y resisting this tcmptation and rcrnaining open-minded, onc can ci~ntrihute imnieasurably a s the confcrcncc procccds by offering carefully conaidered conclusions based oil au analysis of t l ~ cprublcn: and the ideas presented by tlic othcr mcn. 11ost pcople have had the merits of court,esy drillcd into t h c ~ usince cliildliond. Thew lessons are often forgotten when antliorized visitors arrive during busy moments. Sales engineers, in particular, arc giwn iinproper treatinent a t times ~rlicnthcir arrival is inopportune. Compctent ?ales engineers have considerable k n o ~ ~ l e d gabout c tlieir particular fielils, and aid the cngineer in keeping infonned on nexv developments. Timc spent ~ r i t hthem is not ivastcd cvcn thougli no purclmse of thcir 1)rotlucts is anticipated a t the time. Formal Conferences r.

1IIC f o r u ~ a~onferencc l has bccomc an important tool in m o d e r ~industry. For the proccs.; plant project it l~erniits:r sllnring of ideas hetvccn kc? personnel and specialists rvhich ~vould tnkc wccks if handled l g correspondcncc. T o be successful, liowvcr, a fornud confcrcncc must h a w a c:ipal~li~ ltxder :lnd a defillitc pllr]lu6~!Idlirh should ile knon-11 serrr:ll day:. beforc tlic niccting. TIE 11urposc must be a specific o ~ i cif niucl~is to Lc accoinplished. C d c r e n c c s on gcncral subjects require too ni;n~yl~eoplr, accomplisli nutliing, and often creatc misunderstandings. V-hcn need r~rircsfur the discussion of n specific phasc of work. only 1 1I K V ~ J ~n-110 ~ I ~ can ~ contribu(c inost to tlic ~lixussiunsliould l,e rrqrlwtt,il t o attend. Thc conference leader should then outline the course oi discussion and see that the original plan is folluwcd but refrain from strong d:~t~w~rm of t shis oivn ideas. ('otril~lctenotes of tlic vonfert~ncc.sl~uuldhe itii~rl~'.F P I nietiiories ~ are inl':illibl~~, ;ind it is desirable tu liave ~.ccorclsui ;ig~.cr.tlrcntsi m ~ l,lcci~iui~s

138

139


Office Procedure

so that responsibilities are clearly outlined and xvork assignments completely understood. Thc conference room should be well lighted, comfortable, quiet, and furnished in good tastc. A blackhoard is alxrays useful in group discussions and should be part of the permanent equipmcnt of the room. The conference technique is often misused in modern business. Too many unnecessary conferences are convened. Some organizations have so many that there is little time for work. If one man can make a decision, i t i t senseless to take the time of other persc~nncl. Conferences shi~uld t ~ rcalled only when a decision must be made requiring the knorrledge represented by many backgrounds.

employees. There is no one perfect form. Usually the one used by a firm has evolred as the company developed, and it p8rticularly suits that organization. Management and other personnel become accustomed to the for111 and much tinle is saved because of this familiarity. \Vitllin thr <.onfines r ~ f the form the engineer is free 111 rxcrcise llis ingenuity anrl vriting talent. The most import:int consideration in report xwiting is the audience. In writing a report for the president of a largc cllemical company. for instance. an engineer should realize that niost of this man's tiuic is spcnt in management. He no longer practices his technical skills and its intricacies are no longer part of his thinking. If it is necessary to discuss theory in tlic report, background should he sul~plicrl anti. if possible, it should he described in terms understandable to the laylnan.

TECHNICAL WRITING

Tlic engineering graduatc is often criticized for his lack of ability in expressing his ideas. Gcnerallp the undergraciu~teengineer takes one or two courses in report I\-riting and these pro\-ide his only gui~lancein rwitten expression. Tllc?e courses are invaluable, hut good self-expressinn in any form can nevrr he developed snlely through courses that teach tlie tecl~niques of the art. Good self-expression, rather, is a by-product of thoughts and experience beyond the limits of the individual's specific field. I t is unfortunate that the rigorous curriculum of a formal engineering education leaves little time for reading and study in other fields. Many practicing engineers realize this lack and use some of their free time for rcading nonscientific literature. n i i t i n g done by the project enginccr must bc suited for rvi~iclyrarying audienres. Such writing includes: TECIINICAL REPORTS. ( a ) Contract proposals; ( b ) descriptions of plants visited and their operations; ( c ) detailed conference notcs; ( d ) technical instructions such as operating instructions. TECHSICAL ARTICLES(written for publication in trade or professional journalsi. ( a ) Interoffice; ( b ) design instructions; (c) various CORRESPOSDENCE. types of letters outside the company. Technical Reports

The preparation of a technical rcport as such has been described in many forms"&"." and is usually a part of the engineer's training. Each firni has its own niethod of composition. Generally the first page is a letter to a superior often called a letter of transmittal. This is followed by u title page, an index, a summary, and then the main body of the repcrt. Tlie engineer-contractor's propusel is one type of report. The form of report used by a given firm must bc followed by its

Technical Articles

Periodical technical journals are distrihution centers fur n w theories and ideas. Technical men must read articles nr abstracts of nrticles in thew journals in order to be familiar r i t h tlic latest dcvelopuents, and. when possible, sliould contribute n c a ideas and experimental data to the general knowledge by submitting papers for publication. The quality of such contribution reflects on both the author and his employer, and great care should be exercised in their preparation. As;1' 1111ing the information presented in tlie article is reliable, tlic nest ~ n n s t important aspect is the mode of presentation. Technical writing should be free froni long, ponderous sentences and slioultl be as clearly w i t t e n as possible. Since the suhjrct luatter is often difficult to ~,ompreliend,tlie least a writer can do is make tlic individual sentences easy to understand. Correspondence

Correspondence makes up the major portion of a project engineer's writing. If correspondence is excessive, the projrct engineer is little more than a "paper shuffler." Nearly all large business firiiis are confronted \ ~ i t h a tremendous volume of paper. Althougli in thesc modern tinier, conirnunic;rtion~have been greatly simplified, the written word is still thc only legally aeceptuhle neth hod of indicating respmsibility. Recording reasons for actions by one party as instructed by anotl~erin many organizations is practiced largely because of a lack of individual trust, initiative, and usuallp self confidence. The phrase "get it in writing!" is a common stateuient in industry. From this idea lnucli of the needless correspondence evolves. External correspondence is necessary but can bc reduced by careful planning. Internal or inter-office correspondence is used for issuing


Office Procedure

inns itistr~~ctionsor ili>filiing rc;l~ou:ildity. TT'lic~i rrrl):~li ~ ~ s t r ~ ~ c t \\-ill snffice,Lion-crer, it is ~rastefulto insist on )nitten n~eniorand:~.Of coursr, iudg~nentninst he nsed in dcciding whcn rcrhal instructions arc ailcquntc. Certainly romlilcx instructions invoking nrlniprical 1 1 t ~11
The example is a transniittnl letter common to larger firms. It proridcs a reronl for icreral files and nlro in this case s h o ~ sthc status of a I r i n g . .ill numbereil itenis cxcept 9: 10, 11, 12 are printed on the letter. Item 6 identifies the firm and is necessary since copies of such lettcrs arc sometimes attached to formal external correspondence. Initials of recipients of copies. (Itcnt 4 1 , are often used on interoffice communications. Files (Item 8) refer to the particular record files for the departnlcnt or project and aid tlie file clerks in filing tlie letter. Second sheets (~vhcnthe Ictter is longer than one page) omit all printed hcadinga except, 6. Tltr ilatc and project nunihcr is addcd hy typing. Copy sliccts are simil:~rto second shccts showing item 6 only.

140

lnlerofice Correspondence The interoffice lettrr, not?, or nlcnlorandi~nlis usually i r l r ~ n t ~ hh).l n printtd lieailing on some type of fornl. Intcritfficr or Intcr,lirisiiill correspondenre in cnginrcring scrvicc i)rgnriizations is oitrn also 111:rdl~ rcadily irlcntifiahlc hy use of colored stationer?;. Some typical forms arc s h m n here.

i2j (3) (4)

(5)

(0) SYZ Chemiral Co. J a n u a r v 2 . 1955 Interofire TO: R . D . Plow ( 2 ) (7) -1pprq1. S o . 2 2 4 6 From: S . S . S h e a r Copies: E . D . , M . N . , R . J . (8) File 4 , 15, 6 Subject: Dwg . 2246-02-El, Revisions

Date:

is t c b e r e v i s e d a c c o r d i n g t o t h e a t t a c h e d marked p r i n t . When r e v i s i o n is c o m p l e t e a n d c h e c k e d , k i n d l y r e t u r n two ( 2 ) p r i n t s t o the writer prior t o general distribution.

(9) Drawing 2246-02-El

.-

(10)

S. S. Shear

Proj . Engr.

(11) A t t a c h m e n t 1 (12) r .

3lcni~trao~li1ni lortns are soii~rtimcsurcd for interoffire comnn~nir:I t '1011. They arc generally lettcrsizc (8% s 5 ? 4 ) . The firm niunr a p p w r on thesc forms, and itcniu 1 and 2, 6 and 7 arc usually includcil an the Ileading. Such nien~orantiamay bc llandvritten notcs.

General instructions to personnel are usu:illy issued on sonic type of r e ] ~ o ~ l u c i forin l ~ ~ c so that distribution to several people can hc made. The follon-ing fornl is sonletinics used. Example of a General Instruction

Exclmple of Interoffice Letter (1)

141

SSS/ef

Ilie nuinhers are used here for purposes of diseussii~n,but do not appear on tlic actual lctter. One peculiarity of the interoffice lctter is thc omise n the closing, sion of the salutation, such as Dear Sir, or G e n t l e ~ ~ ~and sucli as you1.s truly. Thcrc is, ho~\-crcr,identification n1ateri:rl in itcus 5 , 6, 7, and 8.

SYZ C'lwn~iralCn. l h g . Ikpt.

Letter So. 2 8 3 2 Date: J a n u a r y 2 , 1955 Subject. Use o f V a r i a b l e - t y p e M a c h i n e s To: Chief Draftsman, A l l P r o j e c t Engineers, Design S e c t i o n L e a d e r s , E n g i n e e r i n g D i v i s i o n Department Heads, P l a n t Maintenance D e p ' t . Four (4) v a r i a b l e - t y p e machines have been i n s t a l l e d i n room 3 0 8 ( t h i r d f l o o r n o r t h - e n d o f E n g i n e e r i n g B u i l d i n g ) and have b e e n i n u s e f o r s e v e r a l weeks during operator training. W e are e n c l o s i n g c o p i e s o f a s h e e t s h o w i n g t h e v a r i o u s s i z e s of t y p e f o r m , n u m e r a l s , a n d s y m b o l s w h i c h are a v a i l a b l e . You may c a l l E x t . 3 2 5 f o r extra c o p i e s . The m a c h i n e s h a v e b e e n p r o v i d e d t o r e d u c e h a n d l e t t e r i n g o n d r a w i n g s a n d , b y means o f t h e smaller type, t o reduce size o f p r i n t e d forms. Supervisory p e r s o n n e l are e x p e c t e d t o become f a m i l i a r w i t h t h e


142

a p p l i c a t i o n of t h e s e machines s o t h a t t h e y can b e used t o the fullest extent.

other types 11f correspondence so tlmt they will receive special handling. The follon.ing is a typical design letter.

G e n e r a l i n s t r u c t i o n s are b e i n g p r e p a r e d a n d w i l l be i s s u e d s h o r t l y . A . D. Hochstad, c h i e f Engineer This general letter includes a letter nuvnbcr wlich simplifies filing and identification when rcvisinns are ncccsiary, Such lctterl; are often issued on special forms .;o that they can he identificrl easily. Thc use of difierentcolored stationery is probably the sirnplest method of identification for the large firm.

Example of a Design Instruction

(1) ABC EXGISEERISG CORP., PRIKCIpIA, P;. J Customer XYZ CHEM. CO . Date 1 1 / 2 1 / 4 2 (4) Contract 6-25316-2 (5) ~~~i~~lnst. yo. E-22 DES. SECT. E (7) Sheet 1 Of 1 Dwg. (9) Vendor X (10) Mat'l B;JI (11) Spec. X (2) (3) (6) (8)

It h a s b e e n a g r e e d i n a c o n f e r e n c e o n 11/21/57 t h a t a l l e l e c t r i c m o t o r s s h a l l be as m a n u f a c t u r e d b y G y r e E l e c t r i c Co.

TRANSMITTAL LETTERS(INTEROFFICE) A large anlount oT data nnlst bc tranrferrcd through an organization. Tranzmittd lettcrs or formi snvc typing time. Th? follo~vingform only requires filling in or chccking the applicahlc pllrases.

The a p p l i c a b l e c a t a l o g numbers a r e :

Exclmple of Transmittal Letter

H.P. Up To 5 h p

Volt. 220/110

C a t . No. E-A-1222

6 t o 3 0 hp

440 440 2300

E-B-2136 E-C-3145 D-4460

31 t o 5 0 h p 51 a n d a b o v e

Date: To: From:

Projert KO.

\Ve are attaching c o p i e s of:

(12)

Drarving KO. n/nI Ko.

Vendor Print

Vendor

Approved

Kindly revise as noted Return to Vendor

Approved as n

o

t

e

Release for fabricntion

d

.

-

For your use in design

Release for construetiun For your use and record

For preliminary use only When revised, please return

prints to writer.

~ E S I G X~SSTRTTC!TIOS ~,F.TTERS

I n addition to the gencral instruction letter it is desirablc to provide a npecial fonn for engineering and dcsign c l ~ ~ n g e 1;ngincering-contracting x firms use different names for this correspondence such as "Design Instruction," "Engineering Memo," or sometimes "Design Letter." The most important requirement for such memoranda is a visible difference from

143

Office Procedure

1I 1 1 1 1

G F S P V ------

A . L. G e r u n d , P r o j . E n g .

(~-i-lT~-lT-~TITITIT~ H h l E I / Proc. EF 1 CF C Total

Items 1, 2, 3 are self-explanatory. Itcm 4 s h o ~ thc s contract number as assigned by the contractor, "ABC Eng. Corp." Thij tylle of nu~nerieal designation is finding \vide use in industry where autolnatie accounting systems are used. In this instancc the first number refers to tlic type of general work such as design and erection of a cllernical plant. The first digit of the second numbcr refers to the type of contract, the next four digits are the consecutire contract number. Thc last number indicates the part of the project. Item 5 givcs the subject and numbcr of the instruction. The subject in this case is E (electrical dcsign) ; 6 sho~vsthe basic design section or group to which the instructions are directed primarily; 7 is a sheet numbering metilod designed to prevent misplacing of sheets. Items 8, 9, 10, and 11 provide a means of designating the type of information in general. In this case! 9, vendor, and 11, specification, are checked because the information concerns a vendor and is a specification. If a drawing or bill of material ncre involved, items 8 " 1 . 10 would be checked.

144

Office Procedure


Itrm 12 pro\.ides a simplified rnctl~odfor in,licating t l ~ c(Ii.;tril~utim and nuu~bersof copies of thc Design Instruction. The lcttcrs refer to ~lcsignsections or departments as follorva: G F S V M I EF C

Grnernl Foundations Struet~~ral, s t d or concrete Trseels Mrchanienl equipment 1n.ztrumentation Engineering file Customrr

B P H E

Buildings Piping Went apparatus Electrical Proc. Procurrment, (IF' Contract file

145

Gentlemen: I n order t o effect a possible saving i n driver c o s t s i t h a s been decided t h a t t h e s p e c i f i c a t i o n f o r motors above 5 H . P . w i l l i n c l u d e t h e words " o r equal" a f t e r t h e Gyro E l e c t r i c Co. c a t a l o g number. For o t h e r acceptable motor manufacturers p l e a s e r e f e r t o o u r Approved Vendor L i s t t r a n s m i t t e d i n o u r l e t t e r No. 55, November 16, 1 9 5 5 . It i s s u g g e s t e d t h a t o n l y two ( 2 ) b i d s b e r e q u e s t e d i n a d d i t i o n t o p r o p o s a l s from G y r o . Yours t r u l y , XYZ C h e m i c a l Co. E. G. M a r t i n , C h i e f E n g i n e e r

I n this vase copies are checked for E, Elcrtrical; Proc.. Prorurement; EF, Engineering Filc; CF, Contract File; and C, Customer. Commercial Correspondence

The types of lettprs written to outside firms may he ( n ) correepondcnci. between an ovner and contr;~ctor; ( b ) l w t w r n purchaser and vcn~lor; (c) various engineering or procurement instructiuns to subcontrxtors, vendors, and consulting firms. OWNER-CONTRACTOR CORRESPOKDENCE Operating firms usually carefully restrict cxtcrnal correspondence to executive officers or kcy personncl. Corrcspondcnce between an owner and contractor originating witli the owner usually will all be signed by an executive or in the name of the cxecutive by the originator (see example). Contracting firms to the contrary cannot restrict thc I!-riting of corrcspondence since Inany functions must occur eiinultaneo~~rly and any such restriction ~ o u l dbe impractical. Tlic project manager, l~oaever,should see copies of all correspondence as it passes into the general contract file. All correspondence betnccn thc owner and contractor will ordinarily be directed to 'the contractor's projcct enginecr regardless of subject. Some examples iollow: Example of o Letter from Owner to Contractor

XYZ Chemical Co.

ABC E n g i n e e r i n g C o r p . 1223 8 t h S t . Principia, N. J. A t t n . Mr. A . L . Gerund S u b j e c t : App'n No. &2324. D e s . I n s t . E-22.

AUC Engineering Corp. 1223 Eighth St. Principia, PIT. J,

( 1 ) C o n t r a c t 6-25316-2 ( 2 ) L e t t e r No. 85 ( 3 ) F i l e s 5 , 7, 15. F e b r u a r y 6, 1956 ( 4 ) Mr. E . G. M a r t i n , C h i e f E n g i n e e r XYZ C h e m i c a l Co. Dinwiddie, F l a . ( 5 ) A t t n . Mr. S. S . S h e a r , P r o j . Eng.

( 6 ) S u b j e c t : L e t t e r 168 a n d D e s i g n I n s t r u c t i o n E-22. Telephone C o n v e r s a t i o n 2/2/1956, Gentlemen:

Dinwiddie, Florida

E. G. Martin, Chief Engiueer

Example of a Letter from Contractor to Owner

L e t t e r Number 168 F e b r u a r y 2 , 1956

ABC C o n t r . 6-25316-2

This w i l l confirm our telephone conversation i n w h i c h we a d v i s e d you t h a t y o u r l e t t e r No. 168 ( F e b r u a r y 2 , 1956) w o u l d n o t a f f e c t t h e o r i g i n a l s p e c i f i c a t i o n of o n e m a n u f a c t u r e r , Gyro E l e c t r i c Co., f o r motor d r i v e r s . Following our u s u a l p r a c t i c e t h e procurement d e p a r t m e n t o b t a i n e d t h r e e b i d s f o r motors b a s e d on

146


preliminary data. This was unnecessary since your original specifications had indicated only a single manufacturer. Proposals received were analyzed, as is our practice for all equipment. Gyro was found to have an acceptable delivery, and the prices were lower than other bidders on all items. The analysis in this case was not transmitted to you because the low bid was received from the manufacturer that you had originally specified. A letter of intent was issued to the vendor January 2, 1956 in order to place the equipment on an early schedule. Our confirming purchase order, based on final specifications, has now been issued to the Gyro Electric Company. If our priority is not changed, delivery can be expected in early June. Yours truly, ABC Engineering Corp. A. L. Gerund, project Engineer Correspondence between an owner and contractor is usually numbered a s shown in item 2. The letter is addressed t o the chief engineer and t o the attuntion of the project engineer, items 4 and 5 . Item 6, the subject, is described in detail. %h' en tlic contract number is not placed e l s e ~ ~ h e r it e , should be included in tlic suhjcct.

Office Procedure

Gyro Electric Company 2286 Enoch Ave. Portland 6, Pa. Subject: Proposal 3427, October 23, 1942 Gentlemen: Please accept this communication as a letter of our intent to purchase equipment essentially as described in your proposal 3427, provided: a. Prices quoted are firm. b. Delivery promise of six (6)months or better as based on our priority rating will be maintained. c . You agree to proceed with engineering, design and manufacture immediately by placing this equipment in your schedule. Please acknowledge receipt of this letter immediately. Our formal purchase order will be issued together with complete specifications at an early date. Yours very truly, ABC ENGINEERING CORPORATION N. A. Mayberry, Jr., Purchasing Agent Example of o Letter to Vendor on Design Dota

AM! Engineeling Corp. 1223 Eighth St.

Letters to vendors concern changes in design and materials, extra charges, delivery dates, and statcnients of intent. Ordinarily vendors are notified of ordcr placement by receipt of a purchase order. Preparation and diatribut,ion of a purchase order is time consuming, and when it may delay delivery, a letter of intent, as in the accompanying example, is written in order to place equipment on order beforc the issuance of a formal purchase order. Example of a Letter of Intent

ABC Engineering Corp, 1223 Eighth St. Principia, N. J.

(1) Contract 6-25316-2 (2) Files 7, 15. January 2, 1943

fiinc~piu,K. J.

Contract 6-25316-2 Files 7, 15. February 16, 1956 Robertson Tubing Co. 897 Field St. Portland 6, Pa. Subject: Our P.O. 5316-87, your letter of February 12, 1956 Gentlemen: The stainless steel material substitutions requested in your letter of February 12 have been submitted to our engineering department and approval has been granted. Type 309 is acceptable where Type 316 has been specified. Our original specification will be revised and

148


Office Procedure

t r a n s m i t t e d ; however, p l e a s e p r o c e e d immediately on the basis of this letter. Yours v e r y t r u l y , ABC ENGINEERING CORP. N. A . Mayberry, J r . , P u r c h a s i n g Agent

h transniitt:d letter form is sonicti~ncsu x d for transmittal to outside firms. Example of an External Transmittal Letter

Date: To:

C o n t r a c t No. L e t t e r No File_--_

~

--

-

.-.-

Gentlemen:

We are e n c l o s i n g - . - c o p i e s r e v i s e d Drawing No.

of p r e l i m i n a r y f i n a l B/M No.

F o r approval-For your u s e and record K i n d l y r e t u r n c o p i e s w i t h y o u r a p p r o v a l o r comments a s s o o n as p o s s i b l e . Yours t r u l y , ABC E n g i n e e r i n g C o r p .

gr:u~rs arc trunsuiitted ovcv \Vestcrn Uniuii lincs nnrl tclctype nre-mgc+ over telepllone coulpany lines. Both Western Union (telegram) and tlre local telephone system (tcletype) will install telcprintrrs or ninrhines over n-hirli nlexlgcs may be sent or rcceired in any office. TELEGRAMS Xo chargc is made for installation or u ~ of c the TTestern Vnion teleprinter, hut a firm must he n-ell knmm or must ha^ sonrr i~:ickgroi~~iil 1,-liich would inrlicntc its nac. Unless tllcrc is an existing al~urtagcui machines in the particular area, there is not much difficulty in haring a t~lcprintrrinstalled. The keyboard of the machine is almost identirnl v i t h a standard typewriter. TIIVoperator sign& thc loi'al i~ffict,,and ~rlicn acknovlcilgcd, the message is typed on a continuous (1.11111dlct't. The ~l:l[lcr i5 814 incllcs rvidc, siniil:~r to stant1:trd stntionci.)-. T l i ~ ,nle.2sag<,nl:ty I K rrlxodurril in ser~,rulcopics. Tllc lilcnl officc wccircs tho mess:lge ani1 relays it tu :I local officc in tlic rity of dt,stiirntion. If tlic recipient 1 1 : ~ n telcprinter, it is rcprotlnced on l ~ i smnclrine. I f tlre recipient ]la- 1111 nrachinc, the nrcssagc is usually telephoned and then a copy is muilt~~l. \\:lien the rccipient is in a mctropolitan nrca the message may be iidirrrcd by incssenger. The telegram mrrsagc charge is based on the number of ~vords:mil type of message. The str:tigllt xirc ~vliieliis ~uostexpcnsivc is trans~nitt
WUX

(1) (2) 2324-832 RELET EIGHT THREE SEND MORE INFORMATION ON PRICE AND DELIVERY. PREFER ORIGINAL SPECIFICATION TWO ZERO SIX DASH ONE. LETTER FOLLOWS. ( 3 ) XYZ CHEMICAL MARTIN

Kindly r e t u r n one copy of t h i s transmittal f o r o u r r e c o r d upon r e c e i p t of e n c l o s u r e s . Telegrams, Cables, Teletype The telegram (domestic), cable (foreign), and teletype are used for important written communication requiring immediate action. Tele*This letter mas prepared by someone clse agent's signature.

149

but

was

issued over the purchas~ng

The abbrc~iation\YVX a f t r r the company nanre indicates that tlrr cunil~anylias a teleprinter. Item 1 is a nwnbcring systeni a ~ ~ n e t i n l w used for cost accounting purposes. The numbcr 2324 is the aplx'ol~riation nunlbcr as is used by tllc accounting department in charging costs against tlrc ; ~ l ~ l ~ r o p r i a t i iTlir ~ n . second numbcr, 832, is a c~~nseeutivc trlegriurr

150

Office Procedure


LOSGDISTASCETELEPHOSE VERSUS TELETYPE A N D TELEGRAM The typed com~illinicationprovided 11y tpletypr and telegram is in many instance- tiiorc satisfactory for l~usinessuse than telephonic communication. S o recurd of a telephone conversation is ohtained unless recorded by a third party or a machine. There are times when a long distance call, though more expensive, is preferable. If a pcrsonal or conreraatimal touch is needed to settle some problem the teleplionc is superior. Hcaring a person's voice often gives better insight into the particular situation. Unfortunately some employees abusc this privilege and carry on rcunions and personal conver~ a t i o n sx i t h distant employees before getting to tlie business of the call.

number and has notliing to do xvith cl~argesbut may I I uscd ~ for filing and reference. Item 2, "Relet," is a word condensation meaning "reference to letter." "Retel" is used to refer to a telegr~m,"Rephone" is o ~ n e t i m e sused for rcferencc to phone messages. Such condensations are conntcd a> m t , ~ ~ o r dThe . local telegraph office will supply cost data and acceptablr abbreviations and condcnsatione. Nunihers after tlic telegram are spelled out since transmitted nurnbcrs may be changed or mixed in sending and spelling numbers eliminates the possibility of such error. Cables are similar to telegrams, but more attention sliould be paid to phraseology of cables because of the h i g h cost per word. Regardless uf cost. however, the niesmge of a tclegrani or cable should be clear. Saving the cost of a vord and sacrificing clarity may mean sending another wire or cable.

Style of Written Correspondence

TELE~PE The t ~ l e t ~ y pteleprinter e is similar to tlie W c ~ t e r nUnion teleprinter except the prorednrc is different. The operator signals tlic local teletype office giving call letters and number of distant party desired. The operator then must wait until a connection is made with the distant office hefore a message can be transmitted. Teletype messages can be transmitted only to another ~nacliine. These machines opcrate ~lluclithe same as telepl~onic communications. No relaying or transfer of messages occurs. Keys struck on sender's macliine type tlie message on sender's and recipient's machines simultaneously. T y l ~ e dconversation may be carried on since transmission is instantane~~ur. Chargcs for messages are on a time basis similar to long distance toll calls. A nominal monthly charge is made for teletype macliincs regardless of service. Teletype form may be varicd to suit the ~ c n d e r . The number of vords affects price only as it affects tlie sending time. A message can only be transmitted after connection is n ~ a d cwith recipient's receiver, thus thc addrcss or salutation can be simplified. If n firm has several branch offices the teletype is extremely useful in transmitting identical messages to all connected receivers sirnultaneously.

Either teletype or telegram systems offer continuous or instantaneous service by means of leased wires between points. If a leased wire is obtained, the machine instantaneously operates connerted machines. The cost is high, since this amounts to continuously holding a line. The leased wire may prove economical, lion-ever, when the number of messages per day to a given office is very large.

151

I

!

1

!

-1 !

i 1

I

1

Corrcspondcnce functions as a inlxtitute for conversation and should be as natural as the dignity of tlrc subject permits. Ponipous and liackneyed phrases should bc avoided, and letters should be eliort and to the point. 11ost people compose lcttcrs that arc rclnscd and easily understood when they dictate sur.11 letters ~ I :aI scretary, or better, to a dictating macliine. Aftcr an cr~gincerpractice$ the art of dictating, his dictated icttcr sounds ni~uchless stereotyped and more eon\-ersational tban a letter he composcs on papcr. The use of a dictating machine has many ndvantagcs. Tl~ouglltscan he recorded as they occur ami the secretary need not be interrupted. The transcription of dictated uiaterial, liowcrer. requires an above average secretary; one who can spcll, punctuate, and paragraph accurately. Secretcrrial H e l p

A cmipetent secretary is a necessity for the smooth operation of a project engineer's officc. 4 n intclligcnt pcrsm prcfcrably with some background in science or related fields as ell as a good knowlcdgc of English usage is required. The quality of correspondence is largely governed by her ability to transcribe dictated matcrial ~vitlineatness aml accuracy. This must he done with minimum rlisturhance of other staff mcmbers. h secretary with initiative will prove inralual~lein catching errors. In addition to all these qualities tlic sccrctary sl~ouldbc pleasant and neat in appearance since she ri~ustalso serve as receptionist for the project engineer and his staff. FILING SYSTEMS

h filing systeni for :my typc of lnwinese operation can hecome extrenicly cuuil~erso~nc unlcss it is kept in a consistent and logical manner. Thc

152


funilm~entalpurpwc in keeping files is to p~.ovi
Any engineering organization should maintain some type of general file x-here policy and other general matters applicable to all operations may be reconled. The folloxx-ing is a typical filing system used for a proccss plant project general file. The numerical dcsignutions arc used t o indicate filc categories mi :dl c o n i n ~ ~ ~ n i r a t i oson sthat filc clerks nced not be rcquiscd to decide on the proper file. 1.00 Ihginecring, l)cpartmental Policies. 1.01 Process Ihgineering. 1.02 i\Icchanieal Engineering. 1.03 General. 2.00 Design Data. 2.01 ;\lechanical Equipment. 2.02 Electrical. 2.03 Instrumentation. 2.04 Vessels. 2.05 Piping. 2.06 Structural Steel. 2.07 Foundations. 2.08 Architectural. 3.00 Specifications. 3.01 l\Ieclranical Equipment. 3.02 Elcetrical. 3.03 And utllcrs. Tliesc files can be extendcil as much as desired. Additional sections might be, 4.00 Material Listing; 5.00 Construction Operations; 6.00 l'rocurement; 7.00 Contract Pdicics. The n(lvnntng? of thc clecin~alsyst,eln is apparent. As an illustration, 2.04 could bc subdivided: 2.04 Tcsscls. 2.0401 Forged Chan~bcrs. 2.0402 Plate Vesscls. 2.040'3 T l ~ i nP l a k Tanks. 2.0404 Bins. 2.0405 Elevated Storage Tanks, Water; etc. or, 2.01 l\leclranicnl Equipuient, cxtmded: 2.0101 Pumps, l
Office Procedure

153

2.0104 P u m p . PI!-iti~cIliq~luccnicnt. 2.0105 Turbines, etc. Thc only information which should hc filed in the General File is that which may be useful in establishing general policies. .is an illustration assume that a certain type of pipe or plate mxtrrial specification is heing discontinued becnusc of n~anufacturer'spolicy I t should be of immediate interest t o all persons concerned that the partirular specification has hecome obsolctc. A general letter 77-odd be eirculatcd to thc intcrested department heads; a copy of this information n.ould he filed in 2.04. T h e actual filing of data in some ,single l m a t i m sue11 as a general file enables anyone intcrestrrl in the l~istoryoi tlrc various policies t o find wanted information aithont disturbing a particular depart~nent. Hcnce, thc gcnernl file has some features of a library. Project File

Any firm engaged in contracting services should establish some single t,ype of filing system xs-hich shoilld be used lox all projects. Such systems have the dccided advantage ol being familiar t o all pcreonnel, and the training of clerical personnel in filing hecoulcs a minor task. If each individual establishes his oxvn private system of filing, there x~-illresult as many systems as there are individuals, cnch of which xill be completely foreign t o all other persons cxccpt those directly involved. The following project filing system is simple and easily learned. 1.0 Contract. 1.01 Estimate. 1.02 Contract Extras. 2.0 Design Instructions ( M a y he in loose leaf hinders). 2.01, 2.02, 2.03 (Divide the sanle as for general file). 3.0 Correspondcncc t o and from Custonier ( E x r c l ~ t1.0 and 6.0). 4.0 Correspondence t o and from construction Department. 5.0 Progress and Cornmitnrent Reports. 5.1 Engineering, 5.2 Procurement, 5.3 Conutruction. 6.0 Accounting Correspondence. 7.0 Procurement. 7.1 Shipping, Traffic, I':xpediting, 7.201 (Divide same as General File 2.00). 8.0 Conference Xotes. 9.0 Daily File (copies of all outg<~ing correspondence filed according t o date). The last file, 9.0 is important since it ])rovides a pmitivc means of locating a letter when only the approximate date of vriting is linox~n.

154

Office Procedure Project Engineering of Process Plants

HUMAN RELATIONS AND PERSONNEL MORALE

The office functions that 11avr 11ern di~cuascil:rnd most of the technical phases of thc project engineer's duties all inrolvc contact v i t h other people. High personnel morale, and skillful human relations niake the many personal contacts in an ofice pleasant and profitablc. Few individuals can ignore the fact that nearly every function in life is based on relations with others. An cnginccr may be extraordinarily capable in lris field and yet be completely unsuccessful or limited in his usefulness because of his inability to work x i t h others. There are doubtless as many approaches to the problem of human relations its there are personalities, and tlierc is no sirnplc solution for all situations since no t v o persons nor groups of people react in the same pattcrn. It is certain, hori-eyer, that few people are callous to a ronsistcntly pleasant personality or to thouglltiulness on the part of another inriiridual. Organization moralt? is affected by many iactura. I t may be produced by salary inequities, poor working conditions, incompetent executire personnel, or a lack of inccntire for advancement. Salary problcnls arc always difficult ior thc engincer who sometimes ieels that bargaining is unethical. Altllough working conditions are often not as important to the engineer as to other types of personnel, any environment wliiclr is pleasing to the individual sliould improve his general attitude and thus his production. The usual complaint of the young engineer is the feeling of being "buried" in a large organization. The group leader who consistently takes over all details or iails to distrihutc responsibility is only creating a bad mmale problem 1vhic11 oftcn results in higll labor turn-over. Many times the intcrest o i younger personnel can be held by added responsibility. Bottle-necks in engineering organizations can often be traced directly t o a single individual, who fails to undcratand the advantage both to himself and the organization, of maximum work dist,ribution. The engineer's admirable faculty of becoming absurbed in a particular prohlcm oftcn results in misunderstandings. Thus engineers sometimes gain the unfortunate reputation of being oblivious to everything but their work. They become accustomed to rcducing everything to somc factual or logical basis. Huulan relations, holvevrr, arc seldom factual or logical. Cnless the engineer makes an effort t o ~ w r dunderstanding the requirements of compatibility hc may find liimsclf isolated by his personality regardless of his technical ability. REFERENCES 1. Crouch, W. G.,and R. I,. Zrtter, A Guide Lo l'ech,iicnl li7riling, 2nd Ed., Ronald Press Co., N e w York, 1954.

155

2. H o ~ d l ,A . C..I l n ~ r l h o o k of English in E , t g b w r i n g I!soyr. 2nd Ed.. Johu IVi1e.v 6- Suns. S c , w 1-ork. 1940. 3. brrvkes. F.. and R , IT-infrry, K,poi.l PI-epncolion,Iona S t a t e C a l l ~ pPress. ~ 2nd Ed., .4rnes, Iowa, 1851. 4. Kobc. I<. A , . C h c n ~ i c a lEngineering Reporls, 3rd Ed., Hernplrills Rook Store, .instin. Tpxai. 1950. 5. Mills, G., and d . Walter, Technical Il.,.ifing, Rinellart Broa.. S p w York, 1954. 6. 5Yci1, B. H., The 2'ech,~ical I
CHAPTER

11

CONTRACTS

AND CONTRACTORS I n simple terms a contract is a n agrccnicnt bctrreen t ~ or o more pnrties hy ~ ~ d i i cthey l i legally tlind tl~eniselvest o do certain things. The forin of contrnct used varies v i t h different firms and with the type or r ~ v q ~ofe scrvi(.c rcipired Cnntr:~cts can be made for engineering services only or for cunq~lctccngineering and construction including the 1111rchasc and creetim of materials. A contract may he a sirnple instrument i r ~ e l ~ :IS a purcliasc order or it may he a lengthy and extensive doculnent. I n all cases tlic documents become effective when fornially signed by officers of each firin. T h e purpose of a contract is t o protect both parties and to assure tlint crrtain duties x i l l be performed in a prescribed n a y . It is a corntnon crror on the part of the l a y n ~ a nt o assume t h a t construction contracts re prilnarily for tlie orner's protectim a p i n s t tlic cuntractor. Contracts niny be w i t t e n to favor either party. An agrecrnent of any kind, 1 1 0 ~ ever, is binding on all parties to the ttgreemcnt. ENGINEERING AND CONSTRUCTION FIRMS (CONTRACTORS1

The construction indoitry i? :r niost irnport:mt :ind nrcesmry part of tlir natiunal uconuniy, :ind renders a uniq~reservice to induslry 2s a \\-hole by maintaining staffs uf higlily developed specialists in every field of engineering. ' ~ majority 1 ~ of process firms have found it advant:igeous t o cngngc IS6

Contracts and Contractors

157

the wrx-icv- of :in ~mginec~ring :ln,l c ~ n ~ s t r n r t i ofir111 ~ i K I I , ~ ne~x-f:irilities 31.e reqnir~(1. An e x p c r i ~ i i ~c ~~ n~tlr n ~ t i norgnni~:~tion g V : I ~ :iln-:i?- (lo n better and nlore rspcditious jilh of cnpinerririg nnd ~ . ~ ~ n < t r n r t ithan on f < w r c s of t l l v oprvatinc I~olll)~:lny i!llil+ lllllst engineering an11 cimst~.~ir.tion usually be ha-tily cxll:~niled for :I nvw lilant pro.iert. ~ tl::~t rontrnl~urtlynrin any rontr:~ctnr'sI~ui.incs~ since hi* rrl~utntion is his n i ~ ~ iml~ort:mt st :~sst.t. 310-t r,riticisnis of cmitr:retors a r r directed t o ~ n r dtlieir c r v i c e rh:~rgr.s. so(.~ilillic~.ci:~l 0rga11i~:itionr : ~ n O I I C ~ R ~ ~I -v i t l i ~ nprofit. t (~'c~~i~icl~,r:~tiu~i oi rontr:~ctor's fcrs n-it11 rcqlwt to tli~.productii~nv:~hlr of a n erwti,il I ~ l a l l trrill iilnnlly sl~on-tlr;~t instvacl of l~cingcsorl,it:mt they :lri, in ~.~,:iiity Inore likrly to 11c ~ i i o ~ i ~ . s:It . large percentagc~of prorFss 111:lllt.arc, ,i~,.ignt~ilto pay-out their totnl cost in from three to five years, inrlrl~lrig n r ~ r e: : i c e i n t i r i i n t n : ~ n e e . Hon-ever, fen. plants art, currt t ~ n c t ~nliic11 d (lo ]rot c~~iitinlrc to olwrntr with niinor ~nodification- i o ~ . tv11 to t ~ w n t yyears. It xronl~lw ~ n 111oi.c i cquitnblc to consider tlrc contractor's fee over tlic life of the lllant rather thnn ns a lump sum e:ll~n~d i r i 18 or 24 months. JVliru S ~ , Y I W I ov1.r t h r n ~ a n yy ~ : i r sof nornial o111,r:i~ s ~ n ~inilcrd. ll rion the f i seenis SELECTING THE CONTRACTOR

.i nunihcr of statutt,s :ire in effect in rach state gnverning the method.; of letting contracts when pul>lic or govcrnmrntal funds arc involved. These methods arc not nsually f ~ ~ l l o w eind lrrivate industry, but tlie practice of receiving hiils 11s prul~osnlrin the f o r ~ nof estinmtes for work or services is follu~vedby l~racticnllyall firms. l ' l i t ~ sclcction of a contractor ~111)uld be based on an analysis of propnsed prices ol~taincdI I issuing ~ inqnirics and on tlic contr:irtor's 1 . ~ ~ 1 ~ u t n tor i~m o r - I in certain types i ~ f~ r o r k . Tlrc preparation of rlntn to he w e d in ol~t:~iningp r , ~ l r o ~ a from ls contractors is usu:~llyn rostly i~ndcrtakingfor the owncr since the i n f ~ ~ r n l a t i o n n-ill beco~uethe h r i s f ( ~thc r ~.ontmctor'sproposnl, an11 tlicreforc must he :I.? complete as possillle t o avoid misunderstandings. T h e best ~ a t oy :rssure colnpletcness is for expcriencril design engineers to prepare thc ilata. Enough i n f ~ ~ r n i a t i oniust n he g i r m the contractor ti1 design the type of plant desired in tile nlanner preferred hy the osvner. l l n n y process f i r ~ n sh a r e extensive nieclianical and process specificatiinis ~\-liicI~ liavr heen compiled to provide a, ccrtain uniformity in purcliwing :ind cngineering dcsign of eolnnionly used equipruent. In i u c l ~



cases copies of tlicsc s110uld be given t o the contractor prcparing a proposal so that they may be incorporated into his preliminary design and estimate. I n addition romplete descriptions of tlie o~vner'sand cimtractor's dutir.~. the proposed plant site, transportation facilities. utilities, al-ailahle ratv ~natcri:rli, and processes t o he used should bc provided The extent of process information required will m r y ~ i t the h project. In some cases the contractor will act as a licensor and provide n cornl~lete process design. Often. lio~verer,the process firm has developed its own process. I n that, casc the process firm ~ i i u s teither supply tlie runtractor nit11 a coniplete process dcsign or furnish enough process data so t h r rantractor can make a preliminary design. Contractors must prepare a preliminary design in ordcr to make an estinlatc of the r o d for use in their proposals. Tliis proposal should contain the following information:

investigate by visual inspection similar installations built hy the contractor. I)iseussi(~nsn-ith otlipr owners are also advantageous. For the major projrtt the owner should make every effort to deternine tlie contrartor':: lin~itations.his financial hackground, the condition of his equipment, and his general busincss and labor relations. Financial status sliould also be ci~nsideredin the selection of c o n t r a h r s for major projects since the contractor m w t usually make fixtensive expenditures before reimbursement is forthcoming. Althongli contracts niay be relatively simple or extrc~nelylengthy, it is doul~tfulif the length or rcstrictivc terms of a contract h a r c much cffect on the general type of work a contractor p e r f o r m The hest insurance for the oxner is tlie intcnt and integrity of the contractor, a s proven hy past performance. It can probably be shonn that most of the problems bct~veenoTvners and contractors are the result of ineptitude on the part 11f either tlic owner's personnel or tlie contractor's pcrsonnel which lead to unresolved misunderstandings and finally become iilajor issues. Thc contracting organization, just as any other group, is sullject to the couuiiun frailties and human errors. Reliable firnis, liowever, will alri-ays make every effort ~vithinrcasun t o satisfy their cnstmicrs since their rej~utationis a t stake. Furthermore, unless tlic contractor is completely incapable, basic design and construction will always be within the limits of tlie various national codcs of practice.

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a. General description of tlic project. b. Scope of the contractor's ~ i ~ r k . c. T)cscription of each portion uf the plant with nccompunying f l o r iliagranls and plot plans. d . Estimated utilities. e . Auxiliary equipment t o be constructed (warehouses, shops, etc.). f. List and brief description of major equipment (punips, vessels, heat exchangers). g. Ilechanical specifications to bc follo~ved. h. Statement of product quality and production rate. i. Propseii cost and fees.

Tlicse are some of thc major items. All information necessary to describe tlic proposed design and thc contractor's intcnt sliould he included. Clear, uncomplicated illustrations, charts, and schrmatic flow diagrams arc invaluable. Executives who must examine proposals are busy and greatly appreciate such aids t o rapid comprehension. Contrerts shuuld never be awarded on the basis of prire alone. Price proi~osalsfrnrn the larger process plant constructors are usually ~vitliin n few pcrcmtagc points of each other for a given installation. The owner sliould use extreme care in accepting a luw proposal from a n unknown firm. Although the contractor may be sincerc in his offer, inexperience can cause errors which later may result in an untenable situation. In~rpericncedowners so~netinicsmake the error of assuming that any contractor is qualified t o construct any plant, if he has had construction erpricnce. Contractors are also sometimes guilty of the same t,liinking. Before selecting an unkno~vn contractor, tlic owner should he certain of the contractor's ability. Hc should obtain from the contractor names and qunlificati(~nsof personnel who will be assigned t o the contract, and

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S O F A CONTRACT Contracts may be entercd into for the development, cnginccring. procurcmcnt. and construction of a process plant or for only one of these pllases. Contracts n~;lyhe h e h e e n an owner and a contractor or bctrvecn a primc contractor acting as an agcnt for an ulvner and many subcontractors. The bases for contractual agreements are practically uliliniitcd. The following dcscriptiuns of various services arc those gencrally used for process plant design and erection. All are assunied t o be betu-ccn an operator or owner and contracting firm or contractor.

THE A

1. Contractor as a consultant; contractor performs consulting or supervisory services only with cnginccring prncurement and construction 11y others. 2. Owner t o perform all engineering and procurcment, rontractor to p e r f o m erection serviccs only; this may bc varicil to 11xvc erection perforuled 11y several contractors. 3. Owner to pcrform it11 pri~ressdesign furnishing data t o contractor; contrnctur t o perform all detailed engineering, procurement, and ereotion. 4. Contractor to perform primary researrh and devclopmcnt, engincering, ~~rocuremcnt, erevtion, and initial operation: this is s(~nietiniescalled it "tom-key" contract.

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TYPES OF REIMBURSEMENT (Contract Classification) Tlrc rlassification of contract2 in accordance ~vitllthe mode of reimI~ursementis tlrc most familiar method and tlic most important from a legal and business point of rien.. Cmtracts are. in fact, uiunlly named according to the reimburmnent policy. A hrief description of tlie rriilre important of these contract forms is given below Reference to Fonle detailcd works in this field2,3,"" will prove valuablc to those reqni~ing more informatiun, but thc nced for legal advice on all such n~atter::s l i ~ ~ n l ~ l bc obvious. Cost-Plus Conlract Tlie term cost-plus simply m e m s that tile contractor is to he reimbursed for all costs al~l~licable t o the contract plus a perccntagc of thcsc costs for his overhead and profit. Usually the pcrcentagc varies m-ith each type of contract and service. Tlrc reimbursed costs for cnginccring services may bc 21s nnlch as 215-2207~,or more, of the cost of engincering lahor. Other costs suclr as travel, communications, reproductions, clerical labor, arc gcncrally in the order of 105 t o 1151: of thc actual cost. The higher percentage on engineering labor is based on the sale of contractor's knom-11or~-and thc cost of thc contractor's kcy pcrsonncl. Construction cmts include skilled and common labor m g e s at 110 to 125C/o, construction supervision charges on a siinilar basis as for cngineering, and heavy construction tool charges hazed on fixed rental rntcs for m:%ohinc.~. Actual cost plus a small llercentage is usually charged for s n ~ a l ltools and otlrer expendnhle equipment. If the contractor prucrrw all plant inatcrials and cquip~nent Ire charges a t a pcrcentagc bctwcen I05 and 115% of tllc actual purc1l:i~c pi-ice to cowr purchasing costs. If the onmcr pays for a11 l~crsonnclcosts in procarcmcnt, the percentage based on tllc cost of materials or cquil~. nlent may he much lower. The usual criticism of the cost-plus contract is that sincc the contrectur's l~rofitsincrpase directly ~ i t l rhis costs, tllc 071-ncr I I W no r m t ~ o l over the costs and thc contractor accordingly incrcascs his rusts ns 11111rir as possible. This idea is erroneous. Under tllc cost-plus contract tlrc owner's auditors and engineers have continuous access to all the rontractor's rccords. I n addition t l ~ cm n c r cstwisri :~nthorityover all tlw curlll.:lr~t~w's pcr~onnrl:~nd111r i~ctivitivbr ~ l a t dto Lht. runtr:%ct. 111 i:~(,t the cuntractor acts alrriost as a division of tire customer's cu~npany. For these reasons nnlcss the oxner's personnel arc cumpletcly incxl~crienced thcrc is littlc possibility f t ~ rextmordinary curt euccires. The on-rrcr usually also retains full control of nll coniuiitn~mtsor dishursemmts, t l ~ u s the owner nctually is nlure responsible for coats llian tlrc contr:rctor. If


161

tllc owner is cxprrit~ncertin cngincering and constrnrtion operations, there is littlc possibility f i ~ rcxccssire costs because of the cost-plus feature. 11tiny of thc: larger proccss firms prefer the cost-plus contract t o other t,ypes since it gives them m u r l ~more freedom and control over the contractor. T l m c is c o n d e r a b l e advantage t o thc owner in tlic cost-plus rontract d l r n proccss drzign is incolnplctc or many rhanpes art. to hr nr:irlc, in the origina! design. I n reality, tlle cost-plus contract, if prupcrly cxecutcd and if placed with a reliable contractor, can he as effective :ind 3s econon~icalas the lump-sum, or guamntecd maximum (ir other ty11c- of fiscd price contracts. Experienced c ~ ~ n t r a r t o rho~vcvcr, z, generally prefer a fixed-pricc :ur:ln:emcnt, sincc this form of contract, after rpccifications arc accepted. permits tlic contractor more irccdom. I n the case of a cost-plus operation a nrrlcll stricter accounting of costs is necessary and thc contractor's pcrsonnt.1 arc in some respects only in the employ of thc owner. Thc cost-plus contr:ict, ho~icvcr,is gcncrally the only satisfactory mcthod of operation v.Ircn the work cannot be specifically anticipated or l i ~ a n yconstructim px111len1s exist which are difficult or inipoesihle to estimate at, the start of thc job. Cost-plus with Fixed-Fee Contracts Thc cost-plus contract with a fixed fee is similar t o the regular costplus form except that the contractor can only earn a spccificd fee. All othcr payments arc reimbursement for direct costs only. There arc many possible variations of the two cost-plus type contracts. Lump-Sum or Fixed-Price Contracts The lump-sum contract allows nothing over or under a fixed singlc sum. Thc contractor agrces t o perform certain services which are sperifitxl in detail by the owner in an inquiry or by blre contractor in a proposal. I f any changes arc made by tlie owner after the contract is in effect, an adjustnient may or may not be made, depending upon contract tcrms. If costs are increasd, however, the contractor usually can demand an extra payment. Such contracts often cause bad relations between tlic partics because of conflicting interpretations of original specifications or drawings. Tlie fixed-price contract for the process plant requires the preparation uf a detailed estimate. Prelinrinary data uiay be furnished hy the owner or contractor. Owners sonletimcs rcqnest contractors t o accu~~iulate their own data for the proposal, or t o employ other firms t o prepare data for inquiry purposes. Thc contractor's proposal or the owner's inquiry for the lump-sum or

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fixed-price job must be in much greater det:d than for other typcs of contracts ~vllichhave ~ ~ r u v i s i o nfor s contingencies. I.ikc other f o r ~ n i the , lump-sum contract is suhjert to criticimr. S i n w the contractor is limited to a fixed price, all p s c i h l e savings increase his profit. Thus the contractor m a y be acc~isrdof cfferting savings a t the expense of quality. Generally, lio\i-ever, sperifications for the various parts of the process plant are very complete, and there is little possibility for extensive change from t h e original proposal.

produced ccrtain standard pllrases ~ h i c h]la\-e p.oved immune to inisinterprctation and, Iicncc, are strong protection to both parties.

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Guaranteed Maximum Contracts

T h e guaranteed maximurn cost cr~ntractis similar t o the lump-sum contract exccpt t h a t the guaranteed price m a y apply to inaterial (and cquiprnent) only, or iahor only. Escalation on either material o r labor m a y he permitted or the contract m a y he ~ v r i t t e nt o exclude all escalation." Guaranteed maximum contracts are oftcn x r i t t e n to alloff t h e contractor a bonus d e p ~ n d i n gon the amount of cl~nryerunder thc niaxi~nnm. T h e owner participates t o a considerable extent mith t h e guaranteed~ costs. maxinium c m t r a c t since hc must hc continuously alvare I I all T h e contract types t h a t h a v c been discussed represrnt t h e most c m m o n types used for process plant projects. M a n y others which incorporate features from several of the common types a r e used. THE CONTRACT FORM

T h c most conventional type of contract consists of two parts. T h c first part is called the agreement. I t includes a n outline of the general scopc of work. usually by references to a proposal or specifications and dranings, the contract price or terms of paymcnt, and the rieccssary formal signatures \vitncs& and notarized. T h e signatures m a y sometimes be on the last page of t h e document,. T h e second part consists of general conditions. Such items as completion date, cancellatinn, subcontracts, insurance, and m a n y other terms are discussed. A third part m a y also he added t o include exhibits, certifications, and special deacriptions of rfrtain items included in t h e second part. Rather than attempt a detailcd discussion of contract fcatures, more can be learned b y actually studying typical contracts. T w o contracts typical of thosc used for cost-plus process plant projects are given belom. Contrary to popular belief, engineering contracts'are not difficult t o understand. They must necessarily be wordy so t h a t no misunderstanding is possible. M a n y years of legal experience and court decisions have *Escalation is a clause in a contract that pernlits s change in unit price for material, equipmmt, ot. labor after a specified fixed period of time. .I cuntrart signed in January, for instame, may allow incrcnses in costs niter that datc up to a c e h i n percentage of the original quoted price.

Typical Cost-Plus Contract for Engineering Services Only

This Bgreement entered into this day of by and bctrvcen XYZ Company, licensed to operate in , her+ inafter designated COSTR.ACTOR and PIX) Chemical Corporation, a Drl:~~r-are Corporation, with its principal ofices in Chicago, Illinois, herrinafter designated CUSTOMER. WITXESSETH: That it is agreed by and between the parties hereto as follows: Article 1 . Scope of Work The CONTRACTOR shall perfor111 all the nccessary engineeri~igand drsign as requirrd in the preparation of dl clrawinza: the listing of all niateri;ila:, the preparation of all specifications; i i ~accordance with the COKTR.iCTOR'G proposal, nttachcd hrreto as Exhibit I. ~

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Article !. Timp of ( ' o ~ ~ ~ p l e t i u n The COSTR.4CTOR agrees t,o proreed ~r-it11thc ~ o r kimmediately and T O diligently esecute and pr,rform the vork witli the utmost disp;rtcli. Unless prrvimted b!- circrirnstancrs hcyond his control as described hrlow, .Article 13b of 1':irt 11, Gcneml Conditions, tlic CONTR.4CTOR proposes to complete tlic ~vork wthin t~vclve(12) months after start. Article 9. CONTRACTOR'S Compensation The CUSTOMER will reimburse the CONTRACTOR for all dirrct costs as shown below under Direct Costs, Articles 1, 2, 3, and 4, of Part 11, General Conditions. 11. GENERAL CONDITIONS Article 1. Direct Costs, Labor, and Laboratory Services a. Salaries and xvagcs of ail personnel engaged in the ~vork,inclnding, b11t not limited to, engineers, designers, checkers, draftsmen, tracers, m:~teriol listers. vari-type operators, requisition typists, reproduction machine operators, strnographers and otlms of thc COXTRACTOR'S personnel ~vhoengage in xork on this specific contract. 6. Sdnrics and wages of CONTRACTOR'S Laboratory Trclrnicians and direct costs, as spproved by CUSTOAMEIl for use of CONTRACTOR'S laboratory equipment and/or laboratory services. Article 2 . Direct Costs. .Ifaterials a. Materials used in reproduction operations. b. Rental costs for spr,cial equipment. Article 9. Direct Costs, Miscdlnneous a. Comrnuniration costs including trlelrhrnir, teletplx, teh-grnph, rnhle, postage. b. Traveling and living espemr.5 of COXTRACTOR'S pmsoimrl diem travel is requested and authorized by CUSTOMER.

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c. Ilixella~ieous insur:mce cust. incurred by COSTRACTOR d e l y nr :fi rrsrdt CIS this contract. d. Conrultin: service costs, \\-hen authorized b>- CCSTOhlER.; as costs for labor, nlnterinl or equipnlnit rental.

for snhstantiation of costs. All such recorrls shnll be kept in acronlanrc ~vitli ~ n r t l ~ o :~ccq>t:~ble il~ to CUSTOMER'S auditors, and he nmrle avniln1,lr to tllr CI,.STO1\IEK for noditin: us required. COSTRACTOR sh:~llnot hr rcimbursrd for eusts i n c u r r ~ din the 1ircp:~rationor ~uaintcnanceof such revorili.

Articlr, 4. Direct Costs. Pius Percentage The co.qts hilled thc CUSTOMER bv COXTRACTOR for salnrics and n:iacshall be inere:~sedlry fixed percentagrs aceonling to the schedule of ri~ct-I I I I , ~ ~ , ~ Ikhibit IT, rscept for overtime hours as discussed under .irticlc 10e. h r t 11. .ill other cost- slin11 br increasrd by a pcrccntage according to the Schedule US Coats nnder Eshibit 111.

Artirle 3. CO,\-TRACTOR'S Estimatps Estimntvs prclxlred by C O S T K C T O R for CUSTOMER nrr r~ndrrqoodto hr COSTlt.iCTO1t'S beat analysis of iwrk ro bc clone or completc~iduring t h ~ i nest trr-o 12) cunrtwtire monrhs as based on his nornul xhedul,. of the work. The COSTR.iCTOK does not rcprcscnt that such e;timatcs are to be con.:iderrd exact n-ith respect to amounts billrd to the CUSTOMER.

Article 7 . CO.\-TRACTOR'S Billing Proccrlrue a. .ill invo~eessubniitted to the CUSTOMER by the COSTR.kCTOI1 shall be d a t : ~ n t i : ~ t e dby reference to rprrific pa>-rolls for labor costs; and by reference to rrnilor in\-oiees for m:rteri:ils. b. D~lplic:~tcs of insurance certificates shall be submitted for C O S T R A W O R ' S r c i ~ ~ ~ b u r s c mof r n tinrliranee premiums. c. Expense nccounts for ernployecs shall be suhctnntiatrd by hotel statementi, nwiprs, travel ticket stobs, or other tmnsport:~tion recripti as proof of csprnir. d . On or before the 5th day of each month, COSTR-iCTOR nil1 fl~nii.sh CL7SSOhlF.R nn estimate (in q ~ ~ a d r n p l i r a t rof) totnl c r p e n m on hlmr nnrl nl:itrri:il (liitrd scpnrtltely) for the nrxt t ~ follnrring o months. One of thesc n~rinthsshall be for the month in which the estimate is tendered. The estim:itr shall inclr~demanhours in the categorips, engineering, drafting, and clcricd ~ i t h estimated totnl dollar cost itemized with manhours. e. On or before the 5th day of each month, CONTRACTOR ihnll in\-oiw CUSTOLIER for costs incurred in the previous month. Inroiecs sh:~ll Lir ,3111)mittetl in qundruplicate :lnd separately for each category of cost: lal~or,n~:~tcri:~l, co~iununirations,t r a w l mpmsc, and insurance. .ill such costs s l d l bc computed :icwrdiug to the Schrdule of Costs undcr Exhibits I1 and 111.

Article 0. C'O.\'TRACl'OI1'S Persoimel a. The COSTR.iCTOR -1inll nislgn a project engineer or project n~gincerto the nark :~ceepti~ble to and as :igrt:eri upon n-ith thr C'CSTOAIKR. Pcr-ounrl so :wi:ned sl1:1Il not be rmmwed from the work nor ;rs;i:nrd utlicr ihitie- by till COXTRACTOR ir-ithmit :ipprovnl from the CUSTOMER. b. The COSTR.4CTOR chall provide the CUSTOlIEK rvith :Llist of a11 key ]lrr-
A~ficle6. CUSTOMER Paywzents a. When found t o br: in accordance with the terms of this agreement CESTOMER shnll reimburse the CONTRBCTOR for a11 billed costs, un or beforu the 5th dav uf the month follomine the month in r7-hich invoices lire submittiid by the COSTRBCTOR. b. The CUSTOMER. if he elects to do so. mav withhold from . nxvnients to " COSTR.~CTOR 5% oi billed lnbor costa u p t o completion of contr:ictetl iiorl; :in11full neccptnncc by CUSTOMER of CONTR.ACTOR'S ~ o r k . If the CCTSTOMER elccts to pay CONTR-4CTOR in full 3;. inroicrtl, within the i n t c r ~ n l for payment specified above, CUSTOMER shall he allowed a reduction iu hillell lnbor costs of onr-half (%) of one per cent (1%) on labor charges. All monirs rritlrheld h r the CCSTOMER shall be due and ~ a v a b l ethirtv 1301 d a r s aftcr recell~t of -final regular bllhng from C O N T R ~ ~ C T Oand R ac"ceptnnce nark by CUSTOMER.

Article 10. 7'i.oz.d Explmses, Ilolida~s, Vucation I'eriods, COS1'12ACT011'S 1'ei swt,iel Thc CCBTOM3f. n-ill reinibi~rrcthe COSTR.iCTOK for out-of-puckrt espcnx: of prrsonnel living away fnun homr, trn~eling,or nthe~n-ise~ni~lrrgnin: espewe st the requwt of the CIISTOMEK, u p to thr :lnlorint; ileccriliid in Scht,dule of (losk, Eshibit 111. The travel timr for suclr COXTRACTOR'S percunncl shall be fro111 tinic of departure from COXTRACTOR'S home
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Article '7 L'O'V7'RACI'OR'S Labor and Cust Accoanli~igI'roced~ire t : i i ~records ~ of time rxpendrd by COXCONTRACTOH h l l i ~ ~ a ~ ~ ldiiily 'I'KACTOK'S huwly rated pcrsonnel and weekly records of time expended by monthly salaried personnel. CONTRACTOR shall maintain sepnratrly records uf :dl rwts ap111iwblr to t l i ~cvntr:~ct including ~xryrolla,n1ntrri;il invoicri, eslrw-~. nccuiinte, cunmli~nicatiunrecords, :lud any other records n.hich iir:ry bc ruqiiirtrl

I65

Articlr 11. Iloiirlays. T'acutio,~ I'eriuds-C'O.\~TRAC1'011'S 1'er.sonuel a. The COSTHICTOH n-ill :il~iUhall enst; ill c o n n ~ d o nxith paid holid:~>-s, rlr \:w:ition p e r i d s nonn:~llyn l l a i d CO?;TK.\CTOR'S per-onncl rmployeil r n CISSO\IKIt'S work nhrn such periods frill rrithin the dnratirin of tbis contract. b. The CUSTOME:R may reqwat of the COXTR.iCTOK that ccrtain per. so111d be wurked o w r neek-ends or on hulida:-s. When n ~ n t ~ ~ sngreed lly with tlic COYTK.iCTO11 the CUSTOMER shall rcimbursr the COXTRACTOR for such costs according to the personnel polieirs of the COYTRACTOR, and such pxynlrnts shall be handled according to overtime or premiuni paymentc. c . The CUSTOMER may request the COSTR.ICTOR to postpone vacation pr4o
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rmplo!-rc's vacation is postponed, unless and escept mutual agrrrmmt is reached for s ~ m i f i cimplo?-rrs between COXTRACTOR and CUSTOXIER. Article 12. Empimyrnent of A'l'pir Personnel. Severance, and Twmination Payments, COKTRACTOR'S Personnel a. -411 COSTR.iCTOR'S prrsonnel shall be consirlrrrd to be in the employ of the COSTRSCTOR and the CUSTOMER accepts no wspunsibility for pay~ n e n t ito iuch prrsmind :~ccorrlingto COSTRSCTOK'S policies if terminated by the COSTR-iCTOR. b. Khere COSTRACTOR rmplo5-i personnel according to COSTRACTOR'S estimate of rrqnirrd u~ork,CUSTOUKR a?sumes no rcapr~nsibilityfor duration of such work nor in any TT-ayacrepts an). obligation to COSTR.iCTOR or prrsonnel 3s 10 length of n.ork or m~ploymrnt. c. COSTR.ICTOR hall have complete freedom as to employment of persr~nnel according to his past policirs, excrpt CUSTOMER d l not aceept incwnses in ~ w s o n n d131m1. r:itrs orer average rates shown for various cat~eoriw of ner" &m.l in schrdulr of costs, Exhihi 11. d. Chanpes in ratrs of COSTKACTOR'S kev nrrsonnel. if mut~rallvanreed rlpon bet& CIETOMER and COKTRACTOR, may be acrepted by CCSTOlIER; l ~ o i r v r ~ tlii ~ , CUSTOMER r i w r w s the right to rcjcct any and ;a11 re-classification.., rate ch:mges, or any changes in rate structure, which would tend to increase custs. Article 13. Completion of 1rol.k. O r c h m e a. COKTRACTOR shall make every effort to complete work as early as possihlc. CTXTOMER shall not hold COXTRACTOR responsihlr for work hold-up clue to lack of data to be supplied by or through efforts of CUSTOMER. CONTR-iCTOR accepts all responsibility for nccnmulation of data or the rspeditiug of data from manufncturers for eqnipn~mtlisted in proposal under Exhibit I, as ile~-elope~l and/or designed b?- COYTRACTOR. b. In the event actions beyolid the COSTlLICTOR'S control, strikes, firm, or an?- other occilrrmcea not thr result of COXTRACTOR'S actions 81ffert CONTRhCTOR'S work to surioudy delay completion of the work, thit. ;xgrrcment may be r:mrrlled I1y mut1~11 cmsent of both parties. c . CONTK.iCTOK may ~ w r kcertain personnel overtime hours if it is mutnally agrerd iipon by both parties that such rvork is necessJry. COXTRACTOR r i l l nnt lw rt%nhurird for excess manhours nor overtime pay to personnel whew prior conseht is not obtained from CUSTOMER; ho\vrvrr, COSTRACTOR may, if he so desiri.d, n-ork personnel overtime hours up to n rnnximmn of 10% of normal vorking hours, with such excess hours and preluinm costs charged to his own account. d. COYTRACTOR agrees to work prrsonnrl ovrrtirne hours as requested by CUSTOMER ,lp to :r ~nasimumof 20% in exmrs of normal hours per week prr employee. Thc COKTRACTOR shall be rcimburied by CUSTOMER for all rrs~iltingrosts far overtime work. e . Plus-pe;rcentages s h o ~ min Schedule of Costs, Exhibit 11, for salaries and rrages ~11nllnot be npplic,l to premium payments to CONTRACTOR'S personnel for overtime hours. Arlirle 14. Cancellation of Contract a. ('USTOMER may canr1.1 this agreement a t any time upon giving the CONTRACTOR written norir~!t m (10) working h y s in ndvimce of such :iction. b. In the evrnt of cancellation, the CUSTO.\IER will allow thr CONTRACTOR a reasunable period of time to prepare records or any of the data


167

involved for transfer to CGSTOXIER. T l ~ cperiod of time requirrd for turning l X P T m r l ~r c ~ o r & I I ~data shall in no c:w escrrd thirt!. i30l h\-iirnln dnte

such as may be espccted for n~atcrialsor labor in connrcrion iiith the tninsier of data to CUSTOMER. e. Plus-percentages shorrn in Schedulr of Costs, Eshibit 11, for s11:iries and wages shall not be applied to labor costs for manhours espmdeil :xftcr COXTRACTOR givrs or receives notice of cancellation. f . COXTRBCTOR may cancel contra(.t by ( 1 ) giving CUSTORIER initten notirr of such action thirty (30) days in advance and ( 2 ) iu the t:\,.n1 only of failurr on the Elart of CUSTOMER to f~dfillhis part of this agreement. Such failme may be considered to be in effect if the CUSTOMER refum to r e i m h ~ r i e thr CONTRACTOR promptly, or fails to n h h m r s e the COXTR.iCTOR aitcr receipt uf COXTRACTOR'S invuices wilhiu tlii ugrci.,l perincl of tinli,. g. Tn the event of rancellation by t h i COSTRACTOR, d l fonni s h l l apply as written imd(,r this Brticle I1 as applicable for cancrllntinn b y thi! CVSTOlIER, escept that t 1 1 ~im~cellationnotice shall he given to thr, CCSTOlIER by the COY-TR-\CTOK thirty (30) t of written dcmanrl by the CUSTOMER. d. Crmcellation of the contract by the CUSTOMER or thr COSTILICTOR shall constitute a request for the return of all data covrwd in the :ibove parngrapla a, b, and c of this Article 15, of Part 11, of this agrerment and the CONTRACTOR shall proceed irnn~eiliatdyactwrdingly f.xrrjrt as follo\vs under e. e. In the event the CUSTOMER fails to reimburse the COSTR:\(:TOR \~-ithinsixty (GO) da>-s zfter prrsmtation and receipt of CONTKCTOK'S invoices COSTRACTOR may withhold all data, drawings, and othw pertinent parts of the work drscribed in this Article 15 up to such timi, as CCSTOlIER meets his obligations or some mutnal agreement is reached by br~thparties. Article 16. Insurance The CONTRACTOR shall provide insurance coverage in acconlmce with instructions from the CUSTOMER: (a) for all records or data, or an?- of the CUSTOMER'S property located on the CONTR.4CTOR'S premises or in his possession; ( b ) for any automobile used in CLTSTO\IEIt'S n-ork; i c ) f i r any employee of the CONTRACTOR traveling a t the request of the CUSTOhIER.

168

Project Engineering of Process t'lontr The CYSTOAIER sgrccs tu reimburse the COSTHACTOK for all such insurance premiums. Article 1 7 . Patents. Royalties a. The COSTRACTOR agrr- to save the CUSTOMER harmless from all or nn!- costs ariein~from patrnt infringements in any desipn ntilized by tllc COYTRICTOR except for proerss design initiated b?- the CUSTOMER or (leii~n in aceordance vith CVSTOhtER'S explicit, instrnctions. b . The. COSTRACTOR will irnmcdiately bring to the CUSTOMER'S a t t i w tion drsigns req~~ested by CrSTOMER xhirh in COKTR-4CTOR'S opinirm wor~ld constitute infringement. c. The CUSTOMER ~villnegotiate for and be responsible for the payment of all royalties, fec?, nssewments, or other costs arising out of use of licensed processes or ~nrthodsor materials the use of which require lirensing. Article 18. CONTRACTOR'S Qualification, Engineering Design a. Thr COYTRACTOR represents that he is a qualified designer of the equipmelrt and processes for which he accepts responsibility in Exhibit I, Proposal. h. Thr CONTR4CTOR accepts full responeibility for all basic mcclianic:il,

strnrtuml, end elrctrical design rnrthods used in engineering vork performed bv him. c. The COXTRACTOR accepts full reqmnsibility for process designs inclndcd in Exhibit I. Article ID. Guarantee. CONTRACTOR'S Liability a . Thc CONTRACTOR guarantees all equipment basically designed by him against failure from fault.? design for a period not to exceed one (1) year from datr of first use in operation, rvhen such equipment is erected and usnl in the service for which it was designed and intended mechanically or proccss-rr-i:e. In the event equipment is not put into operation the CONTRACTOR'S time goarantee is limited to eighteen (18) months from date of completion of work or from receipt of equipment a t point of erection, n-hichever may first, occur. b. The CONTRACTOR'S guarantee is limited to equipment designed by himself. Equipment designed or manufactured by others is limited by the gnarantee of the designer and/or manufacturer, except that the CONTR.4CTOR will prepure specifications for such equipment to obtain the best possible guarantee in every respect for the CUSTOMER'S best interest. c. The COSTRBCTOR'S liability in the event of mechanical failure of equipment designed by himself shall be limited to replacement or repair of any such equipment vithout cost to CUSTOMER. d. The COXTRACTOR'S liability as to process production shall be limited to

Contracts ond Contractors

169

h t i c l c 20, Assig~inie~it of Co~itract Irirlwr p;lrry rhnll aizign this Agreement in rrhole or in part \I-ithont the consent of the other. T h e above paragraphs include most of the terms ordinarily ft!und in contracts for engineering services. Tlic policies of the organizations in\.ulved a n d scope of the contract affect the t e r m and conditions. One of the i ~ a s e sfor a n y agreement must be some statement of intent on tlie part of both parities. If either p a r t y can show t h a t the intent of the otlicr was fraudulent a n agreement can usually hc dissolved. .Inother rcquirenicnt of a n y contract or agreenient nlurt b e a n understanding or "meeting of the ininds," a s i t is sonietinles called, ~vliichis essentially undcretmding bet~vccnt h e parties of t l ~ c i robligations. Generally most contracts include statements, sucli a s tbc follon.ing, to indicate the general understanding and intent. Article 31. Intent The COKTR.4CTOR and the CUSTOMER mutrlall:- agree that these docum r n t s form tlie b:~.+ of a wurking agrrmrnt vhereb)- the COSTK.iCTOR is t o perform ecrtain aerricrs diligently and as ccnnoniicnlly SI: possible and the CUSTOMER is to reimburse the CONTRACTOR for a11 normal and rmsonablc costs plua a percentage xvhirh constitutes the CONTRACTOR'S overhead and profit. It is further agreed that neither COXTRACTOK nor CUSTOMER shall prolit from errors in nor omissions from these documents resulting in interpretations
~

Exhibits Refermcc \\.as made in the contract t o several exhibits. T h e follo~ring rill serve t o illustrate o r outline t h e more important requireulcnts. Exhibil i-Proposal

A proposal for a n engineering contract such a s this is usually divided proposal attachcd hereto as Exhibit I. e. The CONTRACTOR d l not he held liable for CUSTOMER'S loss-of-profit or for cost of raw material, operating labor, and other production costs in thr event of process failure. i. The maximum liability with respect to costs absorbed by CONTRACTOR under the above paragraph d of this Brticle 19 shall not exceed fift>- (50) per eelit of the total of sums paid the CONTRACTOR as fees and/or profit o w r 2nd above direct costs according to the schedules of costs under Exhibits I1 and 111.

into t ~ r uparts consisting o l (0)Process and ( h ) .\lccl~anicalq ~ r r i f i c a t i m i . k'rocers sperifications ~lescribe t h e pruccss in detail including r:t~v material and finished product specifications, lieat a n d rl~aterialbalances, and necessary flow diugmms t o describe the prucess graplrically. If parts tlit: prucers nrc dcsigned b y others, t h e proposal should clearly s t a t c the responsibilities. T h e ~neclianicalsperifications list and describe all equipment b y means i l f rkctclics ; ~ n d1vrittt.11 deacri~~tions.General specifications for purely

170


n~crli;mical q u i p m c n t , such a s pumps or compressors, a r c inrluded in sufficient detail Lo enable nlanufacturers to estimate prices. If possihlc n~anufncturcr'snamcs and catalog numllers a r e included so t h a t identification is fised altliougll the specificiations m a y not he coniplete in all I t a i l Prclinlinary plot plans showing the scope o i r o r k , skctchcs of pressure vrsseli., and specification sheets for heat-exchange equip~ncnt, a s ~vellas specifications for various parts of the work such a s t h e structural, piping, electrical, and instrumentation phases a r e included. 1Io.st of tlie specifications included in a proposal are not complete since n considcrable part of cnginecring which mill follow upon signing of the contract cimsists of t h e development of specifications. It is n o t uncommon f o r a C U S T O M E R t o prepare complete detailed specifications or 1l:rvc tliem prrparrd h y a11 engineering firm for tlic CUSTOAIER'S use in obtaining bids from other firms. T h c degree of completeness uf specifications usually depends upon the trrlns of thp contract or types of bids or propos:ils t o be obtained. F o r l ~ c t - p l u smntracts, such a s thc one described above, mecllanical i;pecificatioris niay be brief ~vliile fixed-price contracts ~ e q u i r edetailed specifications. If coiupletc specifications are supplicd b y the custonicr, the plrrascology in the bcginning o i the contract is somewhat different. I n t h e a l ~ o v econtract, for instance, Article 1 of P a r t I would he changed, where t h e wordu "CONTRACTOR'S proposal" appear, to read "Specifications." Exhibit 11-Schedule of Costs, Labor Prrsomnel Sal:ir!- or \Tage Range 1. Project mun;lgcr 600-700/month 2 . l'ruject e11ginet.r 50&600/1nonth 3. Spci:ilt?- engiurer 5W00/month 4. lIe?ign engiucer 50&600/'month 5. %tion iradrr 3.l.'+3.45/11our 3.0&:1.?5/hrn1r 6. T)c.;ignrr & l n y u t 7. Srnior draftimm 2.85-3.1.i/honr 8. I)r:~ftsmnn 2.50-2.85/hour 9. Tracer, B. P.rnachine opemior 1.50-175/hour 10. Sperifieation writers 2.8Kll5/11our 11. llntcrial lister 2.6%!2.85/hour 12. Variable-typewriter operator 1.25-1.50/hour 13. Ty~,iit-s~~et.ificatio~~s r ~ hills r of material 1.15-1 .?5/hour 14. Strnogmphic-clerical 1.1&1..50/ha11r 15. I'rocnrcll~wt personnel, buyers, clerical 1.3&1.05/hour 16. Isboratory technicians 2.85-3.15/hour

Billed Plus Percentage Paid wages plus 150% Paid vages plus 150% Paid wages plus 150% Paid rr-ages plus 125% Pnid wagrs plus 12576 Paid r\-ages plus 1257& Paid wages plus 110% Paid wages plus 110% Paid wages plus 50% P a ~ dwages plus 110% Paid mges plw 100% Paid wages plus 100% Paid wages plus 50% Pnid wges phis 50% Paid wage. plus 50% Paid wages plus 125%

For all orlm prrsrn~nelin ellginerring rntegories rewiving monthly salarim reimbursement sl~allnut be lras than paid salary plus 110%. For all other per-


171

Overtime Payments Salaried employes, or employees not paid on an hourly hasis may reciive overtime payment for hours w-arkcd up to a m:~simr~m of 30% of normal monthly sular?-. Such owrtinlc is ralc~ilntnl on the ixlsis of Irours o w r 8 per day or 40 per veek. The rate per hour for monthly salaried persnnncl is e m puted by multiplying the fixed monthly salary by a fi~ctor,0.006. This is e;;;rnti:illy equal to the nominnl hm1r1~-rata the COSTRACTOII shidl br rrinlburard for such overtime pay on the. basis of rat1.5 noted ;iborr n-ith r c p w t to the culnilation of plus percentages. Hourly ratrd, nrrkly paid rmplo~-~,cs are , :i r:rtr rrf 1% times paid for :dl honrs worked over X per day or 40 prr ~ w e k :it their fixed hourly rate. COSTRACTOR shall be rrinrburml for :ill premium wages paid snrh miployees; hin~wrcr,the ;ihorr plus percentages qh;~l!he applied only to hours worked at the fired homly r n t w As an illustr:~tion,niwme a person in category 8 earning $2.50/hour \\-urkrd 44 hours. COKTR.\CTOR'S billing to CUSTOMER would bc 46 x 2.50 or 66115.00 plus (44 x 2.50 X 1.10) or 8236.00. Exhibit Ill-Schedule of Costs Material o r Services 1. Comrnu,cications. c t u a l costs of telegrams, eablrs, teletype, local (n.here chargeable) and longdistnnce telephone calls, plus 10%. Equipment 11-1. or rental rosts shall not be included in costs tn CIJSTOILIER. COSTKACTOR shdl maintain accuratc records of 311 such costs in acconhnce 11-ith CfiSTOlfER'S requirements 2 Puataoe. " , Parcel Post. Air Alazl. Alr Pared Post. Actual costs of all uleh charges plus 10%. Records shall bc kept as above for 1. 3. Telephone SFIU~CP. Where CUSTOMER requests telephone 5rrrice or installation of tclrphones or other communication cquipment, COSTHXCTOR shall be reimburird for all such costs plus 10%. 4. Ofice Space and Equipment. COXTRBCTOR agrees to furnish ofice space together ~vithall necessary office furniture rrithout churge, for t ~ 12) o of the CUSTOMER'S engineers. Secretarial or strnographic assistance labor shall be reimb~~rsablc in accordance xith item 14 in Exhibit 11. Snch perionm'l assigned to CUSTOMER shall be understood to be in thr employ of the CONTRACTOR and shall observe all common rules and practices as required by COXTR-ACTOR. 5. Siqplies. 411 necessary supplies, except as included belo\\- under A, rr.ilriireil for the work shall be furnish~dbv the CONTRACTOR and no costs for such shall be billed to the CUSTOMER. 6. R~oroduction Services. CONTRACTOR shall be reimbursed for :dl eoits . incurred in preparing or printing, blueprints, blur-line prints, photocopir, ditto. mimrograph, either vhen performed by himself or by an outside firm for CTSTOMER'S requirements. Such costs shall be in accordance ~vithstan~lanlloc:rl

172

Contracts ond Contractors


com~nerclalpractice- ~ ~ 556. l u Labor cubts for blueprint or other ~n;iehinrnperstors shall hc reimbursed in accordance \\-ith item 9 of Exhibit 11, whm snch prnonnel are workrd overtime a t CUSTOMER'.i: reqneit. When CUSTOMER e l r ~ t ihr , mny nrrrjit charges for all matpriali u.wl in rrprodiirtion and reimhi~ri-r COSTlt.\CTOR for lnhor w n l in t h e operarioni nc notrd ahorc in item 9 of Exhihit TI. COSTK.ACTOR shall br rrimhur?cd for costs of all mntrrinls wril ,,I,,* ?..-.~ - ,,,. 7. Cu~rsultationService. COSTR.iCTOR rhdl be reimbursed for an>-srrvices rtquirrd of ontsidc firms as 3:rred upon with CTSTOMER. Si~cbro51s sh:111 I,,. Idlnl to Cl-STOMER liluq 5%. S . Lnborntory S w z ' i c p . Kherc COXTRACTOR provi-, and other nurm:!l living expenses. Receipts for cxpenFe items, hotel bills, tickr,t stubs, nnil any other subetmtiation of pnyment shall he obtained as far as powible and held on filr by COSTRACTOR for CIJSTOMER'S inspection mhm req~icstnl. Fisrd rate? .specified above shall apply to t r w e l within the continrntal lilnits of tht. U. 9. For foreign tmvel per diem rates shall be adjustrd to m w t local ronditiims. Telephone or other communication costs shall be r~~imhursnblr; h o w n r thr ernployre shnll use collect calls if possible so that records m:~? be kept of thrse costs. .Automobilr tmvel costs hen insurance requirements are met shall hr reimhursable a t 80.10 per mile. 411 costs incurred by CONTRACTOR for travelling expense shall be reirnbursnble according to the above plus 5%.

IXDEX Genrral .4crecment. Ilefinitions. r t I. Scope of Work. Srtirlc IT. Contractor's Costs and Terms of 1'a)ment. Artielr, 111. Dirrct Costs. Cunstruction Supplies, Fidd Pureh:~-in:. Articlc IY. Cons,~ni:~ble Article V. Construction hhterials and Tool:, Field Purchasing. Article VI. Construction Labor. Article VII. Transportation. Article VIII. Completion of Work. Article IX. C:~nccllationof Contract. X . P r o t r h o n of Xetcrials and l'roperty. Article XI. Insurance. .\rtirlr . \ r t i h X I . Guar:~otccs. Srticlr XTII. .iisiqnmrnt of Contmct. Article XIT'. Siirplns h-laterials. .

Exhibit 11. E-timite. Exhibit 111. Enginrering and Other Labor. Exhibit IV. Cmztruction 2lateri11l and Labor. GESERAI, AGREEMEST This Agreement m;dc and entered into tlrL-ila>~ of by and betweerr ARC Chen~iealCo., (arldrrss), hereinafter referred to ns ARC and XYZ Encinccring and Construction Co., (:~ildresi),brrrinnfter rcfrrred to as COXTRACTOR, &tnecseth that: Whereas ABC desires CONTRACTOR to i,rrform rrrt:iin servicci; more coi11pletcly described in the hercto attxhctl, listed, or referrnrwl ilrnn-irxc :iml sprcifications undrr the Scopr of Work Article 1 ; Now therefore, for and in consideratiml of the paymcnt,s 11rwin;lftc.rrjwified to be made to thc COXTRACTOR by ABC, :inJ in consideration of tlie terms lierei~li~icludedthe parties hereto do agree as follui~s:

Typical Engineering a n d Construction Contract

T h e complete engineering a n d construction contract is usually similar t o t h e form of contract for engineering serviccs exccpt t h a t it includes additional clauses undcr P a r t 11. T h e following contract is similar t o those prepared for cost-plus with fixed-fee contracts. T h e first page of t h e documcnt consists of a title: Agreemont between ABC Chemical Company and XYZ Engineering Company Including Engineering, Procurement, and Const,ruction Services At The Colorado Plant T h e second page, or pages, consists of a n index similar t o illat Eollo~ving. Inrlcxes a r e most belpful for t h e longer contracts.

i

DEFIKITIONS 811 papcrs, dmwings, documenk altncllrrl hereto 1. Contract Documents. or includcd here\\-it11 by rrfrrenee constitute the contract documents an(\, if ;irp:irate liereto, arc to be con-iclrred :IS part or 1l:irtj of tbis ugrrnuent th? -:1111l, :Iif ntt:~checl h r x t o XTZ Engiurrring Coml~:tny,its eseou2. Contjactor. P:irly to :~gr,:rn~ctir, tive ofiicers, enginrrr, constn~ctioniupcrintendnit. 3. ABC. P ; ~ r t yto agreeniant, S13C Chemicnl Co., its executivr officers, project engineer, inspectors, field cowtruction enginerrs. 4. Place of Worlc, Construction. The expressions "jobsite," or "field" are nnderstood to mean the placc of crretim of incilitiea. Albrrt County, Statr of Colorado, .4BC Chcmicnl Co., Colorado Pl;mt. (\I:d :iddress .shuulrl be included.) 5 . Place of Work, Engineerirly. Coatrxtor's lmne or hraneh ofierr. (%hi1 addres or addresses should be included.) 6. Wori:. The tern) work shall hr underitowl to incln
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7. L o r d Laws. Tllr

Contracts and Controcfors

I;in-- of thr place or building shall gorem.

8. Jobsite. The trrm juhsite slinll be undcr~toodto mean place of erection or con.wuction as desienatrd ahore in 4. 9. Drawings. Dr:iir-in:; iir 11rinti ihall be undrrstood to mean reproductions from drni1-ing. prrp:irnl hy eirlier party but identified by written matter as a part of the w ~ r k( v r G a h o w l . Tracingi shall br, nndcrstood to mean original drawings from ivliich reprod~~ced cupivs or prints hare bcrn obtained. Dram-ings may be wid to he identifid ir-lien their idrntifying numbers are included in the contract ilonnnmts or :idilt,niia thereto. 10. Supplies; ('omti.iicti(~~i ifoti'i~iols.a d .llnteriuls. (a) Supplies are undernature exclusive of tools, such stood to mean those m:itrr~:il. of a eo~l.~u~~:ible ns m e r y cloth, ~:indpaper,drinking cups, i.lcric;rl supplies, fuel?, lubricants, and any other such i t ~ n lvhieh l :ire nrcrssary for construction but do not necesiarily enter into the ~~rmrmnent plant or remain as :I part of the plant after construction is complete: ( b ) conrtnxtion materials :Irr: the h ~ a v i e rmatwi:~lswed in conct.rnr:tion sucli :is scafioliiing, form lun~her,f o m ~tics (but not reinforcing rod) : constrwtion buildingi togcthrr with all thrir parts including electrical lighting, plumbing, lmting or ventkiting rquipmmt ; trmporary electrical service connections for electricaily driven ron.~tri~ction eqnipn~cnt.mircellaneous piping, and miscrll:~neous bnlk material; i ~ fall kinili used for constn~ctionbut removed after crrnrtruction i; complrted; (c) uintrri;~liare generally ~lnilrrstoodto mean permnnrnt materials -ilrli ai the eiilnl~oliiwt of concrete, or stone, sand, and cement; brick, mortar, niiscrllancous fill m;itcrials, n-elding rod, rivets, miscellaneous bolts. 11. Co~zstmctio~i Tools. (o) Smnll tools, ronsumable: icren-drivers, pliers, pipe and other wencher less than cighteen in. (18") in length hack r a m , hack saw blades, chisels, h a ~ n n ~ r r welding r, sots, ~vrlding (oxyncet>-lune) hoses, etc.; ( b ) hand tools: hand took are gmrmlly unrlcrstood to nleari the larger tools such as axes, shorcls, s p n i l y wheel l>:irroi~-s, rnnent buggies, dollies, sledge hammers, drills, grinders, hammers, rivetetc.; ( c ) driven tmls: electric or pneiinx~ti~:, puns, r:inlking tools, inip:ict 77-rrnches, e t c : Id) m:rhinr tonlr, smill: portable pipe and conduit bmiing and thre:~iIing machines, electric or pneun~ntir:1i11i-t~, portablr air compresmrs, ~wlilingmachines, etc.; i e ) ronstrnrtion tools, large: steam or electric drivm hoisting mginer, guy, :ind other typesof ilr:rricks, inelnding cuhlrs, sheavci, Iirioks, slings, sidfdrir~ncmnee, grading machines, tractors, trucks inchding a11 their :1lil,urtrn:mrw IIeavy rn:~chinetools installed (fixed base) for use during conotruction inrh ;IS 1;1thw,drill 13WSWS, metal P:I\VS,etc. 12. Security. The word recurity sh:ill be lirnd~mtourl to mean ARC'S plant, security or protectiun organization, or the organization prtwided by CONTKACTOR to police the riin.
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ings, sprcifirations, labor, material?, and r.rjliipment as arc rrrluired to prucurr, fahriwtr, w e t , inml in>tidl, ready for 11-e or oprmtion, :(I1 etjuipmrwt to l>ro\.iilp the facilities awl prrirrses herein dwrrilx4 in :~rcor~lance rr-it11 C:OSTR.\i:TOR'S proposal :itinched licrrto :ri Exhihit I .

i I

j

Article I I . COh1TI1.Af'TOR'S ( ' o s t s mid T m m s of Pn!ilizmt 1. ARC shall rrirnburse COSTKA('TOR for nll rmsts indicatrd :IF direct rosts as described hrlox ,-dus tlie prrcvntagr; indimted fur the 7-ariiriir 1r.irt; of the work. 2 . CONTRACTOR'S fee dinll hc cmnputed n- n summntion of thr plns perrentages :~dderl to COSTRSCTOK'S direct ro+ and d ~ n l lnot crrrnl right hundred, and fift.y thorlsand dollars 1S830,000.001, exet'pt as notcil brlmr. 3. Estimated Selling Price: the COSTR.iCTOR eitimatcs the cmts rlf labor and material and rynilxnrnt to complr.tp the faditie; derrribrd in Eshihit I, plus the above fre to br nrit more than t.i?lit niillion, six h~udrcil:mil tiventyfive t11ou;;ind dollar. lSS,R.25,(H)O.UO)in ;icer,r,lmw nith the detailed e-timate included herein an Exhihit (1. ('OVTRAC'TOK dues not en:mntee ertimntr hilt agrtw that the fee in itrm 2 abovi. ~Ii:dlbe n niauim~imvhen the estim:~triltotal cost is equal to or ruweds t h :nnount ~ :~hol-e. 4. Fee Increasc rlr Cliangr,. The C'OSTl(ACTC)R'S fee in itcm 2 iibii~eshall br increased or changed only. ( o ) TThm :,nil if thr :~huvrestim:~tml total selling prim: exceeds thp actual coits of the ~ o r k the , C0STR.iCTOK'S fee >hall b r increa.ed by an :nnonnt q u n l to t w n t ? per cent (XI':) of tlie differrmrr between CONTR.iCTOR'S cstinl:lte and a r t i d total mst. This increase shall he nnderstood to be a bonus p:iynient; ( b ) d ~ e and n if the scope of xork hcrein shall bc increased by ARC by additions or c h a n q s increasing COSTRACTOR'S vork or equipment or materiulr in mutonlly :tpreerl upon c11:1nges,the CONTR-iCTOR'S fee shall he increased by an a~nounteqnal to ten prr rent of thc artnal costs of such increases or chnnges. .ill such extrxs shdl he kept separate from total costa of original estimate and shall not affect the honr~spaymrnt above in section a ; (c) when and if the scopi, of ivork herein shall be r r h : e d hy .4BC as changrs or modific:itions, the actn:il cost rduction sh:ill be conlputed as a percentage of the above e.timntrd belling price item 3 and COSTRACTOR'S fee ilia11 he red~wcdhy a likr l~erccntage. Thr n~arimrtmred~~ctinn in COX'TR.4CTOR'S fee d m to reilnrtirm in -rope uf w ~ r kshall not eucrrd one hunilrtvl mil eight~yfivethowaml dollars (SlS3,000.00), t w e p t in the e w n t of cnnceliation under Article IX. 5. Accounting :ind Billing l'roceilure.

( N o t e : See Articles 5 a n d 6 of t h e Exnniplc Engineering Services Only Contract. T h e hilling pri~eedure f o r a n y contract \vli~,reo ~ v n c r p a y s direct costs plus n percentngrx consists in prescntntion of t h e contmctor's invoice plus substantiating dnte in llie form of attached papcrs or refcrcnce t o t h e contractor's rccoriiu. Generally for labor charges copies of actual payrolls lilust he included. V s ~ i n l l y papcrs such as vendors' invoices a r e held b y contractor since obtaining sufficient copies for o x n e r a s ~ v c l as l contractor is w ~ n e t i m e sdifficult. I n order t o prove a n expenditure f o r equipment t h e contrartor ordinarily h a s three instruments: 11) contractor's purcliast. order, 12) a ficld irceiving report, a n d ( 3 ) a ropy of t h e vendor's invoirr. Thcse a r e sufficient in most cases since if t h e contractor ackno~vledgcst h a t h e h a s t h e vendor's invoice he is com-

178



regulation?, orders, dirrctirrs, or statutes npplic:~hIc to wage and emp1o)-ment practices, and to act in accord311(~1'vith the poliric>sof ABC on matters which affect area practir.c? and n-llirh nlizht tend to set prrwdent.. Constructi~nlahor wage rates in Exliib~t ST- form the hasis for COSTR.iCTOR'S estimate in Exhibit IS. The COKTR.\CTOR will nut enter into agreements with various lahor organizations nnplo:-ril in tlip ir-ark iihicli tmd t o increase such rates withont previous notificntion to A13C. 2. The COXTRACTOR r i l l n1nint:iin si~it;~hle temporary sanitan- and shelter facilities for use of its rrnploy,e;. C0STRACIY)It'S empl~yecssha.11 not trespass on nor usr sanitary or other of .iBC's plant facilitiiw. 3. The COXTR-iCTOK rrill employ n c o m p e t ~ ~ registered ~t nurse and provide suitnhle cxamin:ition and first-aid facilitiw contiimo~ldy at the jobuitc during constrnction. Pro\-isions d l alio be m:ide for prompt mrdic:rl aid and hospitalization in the nrarest facility for snrh servicri. 4. COSTR-iCTOR'S rrnpli)y~csirhrn on A1IC's plrmises shall rumply with ,211 general rules and regnlatii,ns :is reqnired b\- ABC. COXTRACTOR'S emp1uyee;i shall not 1m1-c COSTI{.\CTOI1'S n-- ~lltholity,unless in the line of duty and/or n-hcn :~ccrirnpmiedby an mmplriyr of .iIX 5 . Disrrgar~lfor rides mi practicw ns rcqriired b:- ABC by an employee of tho COXTRACTOR ?11:111he sufficient jnstifiriitii,n for disn~i,-sal. 6. Employers ilid~iirpc~d for r:nl.e hy COSTK.iC:TOH or by ABC's rrquest shall not br: re-empla?-t,il 111-COiiTR.iCTOR for work nndrr this agreement. 7. COXTR.\CTOR'S ~ ~ m p l o y cs11:ill s he prorcssed for idrntification and he provided xith identifiration b:idgcs nrcrptable to ABC. The processing of COSTRACTOR'S prrsonnrl to meet smurity regnlatims shall be carried out in st,rict acrordanrc with instn~etions from .\BC. The COSTRBCTOR will maintain a t the johsite a srpnratr file on vnch employee regukirly employed in COSTRACTOR'S r o r k or intermittently visiting thc jobsite. All employees visiting the jobsiti: s11:ill fiillon. initmetions with reg:iril to secnrit,y and ident.iat the jobqite. .Any of ABC's security ficntion tha same as i f reg~dnrlyenililr~y~d officers m:by at any lime requcst pmprr identifiration a l ~ d i o rthe employme& history oi any per,xmnel. 8. Certain of COXTRACTOH'S personnel may be prmnitted to bring personal nutornobiles within ARC'S pl:~ntprtwi>cs. Infractims of rules or rceulations with regard to us? of anti~molilesd l automnt,icnlly rerokc any such pcrmit. In gcnrml all construction per,mmnel sh;~lluse thc ABC plant gate desigmted for COKTRACTOR'S entranci:. T h r n other entrances are used COXTRACTOR'S personnel nmrt obtain a special pass from wcurity. 9. Tendor's reprtwntntivcs or other pr7sons visiting COXTR-ACTOR'S officrs for business purposes shall romply ~vithAAC's plant regulatiol~swith regard to visitor3 and m s t bc identified by delegated COKTRACTOR'S personnel. The COXTRACTOR shall be responsible to ABC for such persons. Unlcss special permission is obtained such persons are not to be allowed access to any part of the work except COXTRACTOR'S ollices.

2. Unlcre prevented by r;i~i;cs he>-onrl his control COVTR.\CTOR proposes to romplrtr all the fncilitie,+hwcin inclnrlcd not more t l ~ mc~izhteet~ n m n t h ~aftm rzerwtion rlf thi* n~rrc~ment 3. CONTR.iCTOR agrees to schrdnli hi? rr-ork for cnrnpletion in arcortlnnrr ~vithtlir prere- part of thr completr,il n-rrrk rhall not necrs;arily constitute acceptance on thr part ~f SHC, ;1n0 COSTR.iCTOR shall lir obligated to and s11;ill he rrslmn.~il)lefor error? complete any unfinirhcd parts of the f:~cilit~nr omissions discovered aftcr onerntion bv ABC the samr a . if the facility had not brrn put into opei-a t'Ion. 5. When all "arts of the ~ o r :ire k comulrtnl to the sati~S;rctionof ARC, then BBC shall proLvide COSTR.4CTOR \rich an :i~~thorizedaccept:lncr at rrhirh time 1111 frinils or paymenti due :ind/or ~ ~ i t l ~ lsliull ~ d i lbe due and piy:~hIc to COXTRACTOR.

ARTICLE VII. Trarrsportation CONTRACTOR shall route all rn:~t~,rials over carriers designilted by AUC by means of traffic maps 11rovidcd for the COXTRACTOR. Article VIII. Completiu~rof Work 1. CONTRACTOR agrees to diligently prucecd ~ r i t hall parts of the work for ABC's best interest.

179

A r t d e I X . Ca~icellationof Contract 1. This agreement m l y hr, rxncellcd by .\nC nt nny timr npon giving COXTRACTOR written notice ten (10) < l a y in nilranci of s w h actiun. The n re:~soll:~ble timr: firr transfer of all parts of COXTR.iCTOR shiill h ~ nllo~~-ed : the m r k in his posse-+ion to .iBC:. The pei.io
182



Exhibits for Engineering a n d Construction Contracts

Lump-Sum Contract Forms

S e ~ e r a Exhibits l have been referred t o in tlre above contract. The discussion a t the end of the engineering rontrart has described a typical proposal in some detail. For such a contract as the above, the proposal mm~ldbe in greater detail, describing in addition to the process and process e q u i p l e n t all facilities, types of architecture, and any points r ~ h i c hmay be peculiar to t,he particular installation. Exhibit 11, the estimate, would in this case be quite detailed. The follo~vingform is sometimes used. The first part of such a n estimate 3r summary and the esti~nat,efor unit A is included below. Exhibit 11-Estimate,

dollars

Combined Estimate Englneermg and Cler~cal

Facil~tles

Power srrviees Genrnd utilities Plant buildings

6,000 12,000 18,000

-

Subtotals 320,000 Fee Total combined estimates and fee Estimate--Unit A Foundations Structural steel and building Process equlpinent Pipmg Electr~cnls

Eng~neeringand clerical Total, Material, Labor, Unit A

.

Material

112;000 207,000 340,000

Lab01

33,000 48,000 85,000

Total 3,996,000 2,303,000 615,000 151,WO 267,000 443,000

-

-

-

5,855,000

l,G00,000

7,775,000 850,000 8,625,000

Materials 95,000 154,000 1,890,000 619,MX) 96,000 142,000

Labor 115,000 126,000 230,000 226,000 59,000 48,000

183

Total 210,000 310,000 2,120,000 846,090 155,000 190,000

-

-

801,000

3,830,000 166,WO 3,996,000

[n actual nractice estimates arc much more detailed. The above estimate for Unit. A is condensed. The item "process equipment'' includes all mechanical equipment, pressure vessels, tanks, heat exchange, and condensing equipment and insulation. Estimated costs of each of these would be shown separately. General items such as supervision and clerical operations for construction are also separated in the usual estimate exhibit. T h e various exhibits attached t o a cost-plus contract usually include much detailed information on construction craft rates, consumable supplies, and contractor's tool rental rates.

The lump-sum or fixed-price contract is much less involved, and a typical form for such contracts has not been included. Since a fixed price must be established, the original specifications: descriptions of the work, and types of equipment are described in detail in the contraetor's proposal or owner's inquiry. The contract then need only carry the standard general clauses. CONTRACTS A N D ENGINEERS

The contract phase of project engineering requires a competent legal department. Men who are trained in both engineering and law are ideal members of this group. All project engineers, however, should have a n understanding of contracts since it is their duty t o execute many of t'he terms of a contract. I n developing this understanding, the engineer should avoid an overcritical attitude toward the legal phraseology. It shuuld be rememberd that the long sentences, big words, and hackneyed legal exprc:<' w o n s are part of the conservatism of legal practice which have proved their durability through decades of legal decision. ETHICS AND THE CONTRACT

There is never any intention among reputable contractors or owners t o deceive through fine print or confusing terminology. The cont,ract should be thought of more as a written agreement between gentlemen. It is nritten because memories are poor, and written records do much t o preserve friendly business dealings. Legally the contract contains provisions for cancellation and penalties for failure in performance, hut these actions are costly t o both parties in both time and money. Above all, the mtegrity and technical cornpetence of the personnel of both organizations are the only criteria for successful project plant projects. The contract protects against willful negligence and illegal acts. It cannot protect either party from unethical practices or incompetence. REFERENCES 1. Eshbach, 0. W.. Handbook o f Engineering Fundamentals. 2nd Ed.. John Wiley & Sons, Inc., k e w York, 1952. 2. MeCulloush, - . L. B.. and J. R. McCullouah. - . The Engineer at Lnlu. Vol. I . Iowa State College Press, Amps, Iowa, 1946. 3. Sadlcr, W. C., Legal Aspects of Engineering, John JVilcy & Sons, h e . , Yew York, 1940. 4. Sadler, W. C.. The Specifications and Law on Enaineerlna Works, John W i l w &

Sons, Inc., New ~ m k 1948. , 5. Simnson, L. P., and E. R. Dillavon, Law for Engineers and Aichitecls, 31.d Ed., West publishing Co., St. Paul, Minn., 1946.

DETAILS OF ENGINEERING DESIGN AND EQUIPMENT SELECTION

CHAPTER

order to participate intelligently in selection of equip ment and design of process facilities, foundations and structures the project engineer must understand to some extent the details of engineering design and equipment selection.

12

I

N

VESSELS The design and fabrication of the many sizes, shapes and types of vessels required in process plants is a complex task requiring the cooperation of process and project engineers, vessel designer, and fahrirator. Vessel design requires the skill of an experienced engineer who specializes in the field. A working knowledge of the various cudes, fabrication properties of materials, and procurement problems requires full-time attention to this one field. The greatest need is for project and process engineers to familiarize themselves sufficently with hasic design and fabrication procedures so that an intelligent exchange of ideas with the vessel designer can be effected. The purpose o i this chapter shall be to develop background information which will aid the project engineer in directing the design and fabrication of process vessels. It is not possible to develop all the details of vessel design and nu attempt will be made to repeat information that is now prcsented in various codes and standards which are available to anyone.' VESSEL FABRICATION The Shell Pressure vessels and tanks for process plants are usually of cylindrical shape. Bending rolls are used to form the cylinder. 'The codes referred to in this section, unless otherwise stated, are the API-ASME and the ASME codes for "Unfired Pressure V e ~ s e l s . ' ' ~ . ~ I87

188


A bending roll is shown in Fig. 12-1. The top roll imposes the bcnding forces on the plate and the distanec b e t w e n the top and bottom rolls controls the diameter of the cylinder. The rolling may be done cold on thin plates of smaller size. Prior t o rolling, the ends of the plates are shaped t o the desired radius in a press using a radius-forming die. B y this procedure, perfectly round vessels can be made. After rolling, the edges of the plates are planed t o prepare them for welding.

Fig. 12-1. Bending 1.011s:241 inehcs long, 96ineh OD shcll being rolled from %-inch plate. (Courtesy uf Lulicns Stccl Company.)

Welding

Welding bas bccome the most common means of joining metals. Bursting tests invariably prove the weld t o bc stronger tlian tllc shcll itself. Such welds, however, must be made by compctcnt welders. Elaborate tests t o qualify welders arc given in the various vessel codes.l.2 A number of very excellent weldinc- nrocesses are in use. Shielded arc . welding is perhaps the most common method used in vessel fabrication. An arc is produced between a metal electrode and the base metal. The heat created causes melting of the electrode and portions of the base metal near the arc. Tlie weld is formed by the fusion of the metal from the electrode and the base metal. The welding rods (electrodes) are coated with a flux which, when heated, produces an inert gas blanket around the arc and deposits a protective coating of slag ovcr the weld to

Vessels

189

i~rcl-entoxidation. Arc nelding can be ~rlanualor automatic. For large longitudinal and circumferential seams automatic welding mael~ines p r o w particularly advantageous. For circumferential seams the cylinder is mowd :ind t l ~ ctorch remains stationary. The opposite procedure is fnllo~veilfor longitndinal seams. h c e t y l ~ n egai ~veldingis common, especially for welding thin plates and small attachments. I n addition, acctylenc welding is a necessity in :my vessel fuhri~xtions11op fur n l m y utility purposes. A few of it. uses are: f1:nne haril~ming of small 11art5, cutting, and tack-~vcl~ling .ccti,in~ l~riorto antonlatic arc ~vcliling. Gns \velding is alsu used ill brazing n.hic11 is the joining of metals with a nonferrous filler without ~nelting the base metal. Other welding procedures such as atomicI~yilropcu, flaA resistance: thcrmit, and submerged-melt xvelding are use11 for sl~crialtypes of work. For a detailed discussion of welding t c c l ~ n i q u ~tbc ~ s , rwdcr is refcrred to standard n-urks on t b r subject. TT-clrling of vessel -rams generally requires the application of ~ c v c m l luyers of ~vcldmaterial. It is necessary that great care be exercised in making surh "multipass" ~vclrls. The surface of each weld pass must hc tl~orouglilyclcanr~land cxainined hefore proceeding r i t h the next pass t o insure good penetration nnd freedom from cracks, slag inclusion, and other n-cakcning dcfccts. A faulty weld can be disguised by a satisfactory final meld pass. The wider's torch has also l ~ c c o ~ na en invaluable tool for cutting metal to any desired shape. 3lechanically guided cutting torches are used cxtcnaivcly and job.: that xvonld bc tedious when handled by ordinary mecl~aniralmethods can be done a i t h case when a cutting torch is used. Shell Plates Plates for the fabrication of vessels are usually ordered by thickness. Plates made by a sliearcd-plate nlill are preferred because they are of I ~ r t t e rquality and are available in a greater number of sizes. They can I I obtainul ~ in n rvidc varicty of thirknrsses, the most comiuon being in., 1 in. to 1y2in. in increments f r ~ m in. to 1 in. in increments of i ~ % f in., an11 1y2 in. to 4 in. in increments of % in. Lengths up t o 800 in. are produced in the thinner plates. The maximum width obtainable is around 195 in.. although widths over 100 in. carry a n extra width charge. If both the circumference and length of a shcll are greater than 195 in., it b c c ~ ~ m cnecessary s t o employ two or more plates to fabricate the vessel (Fig. 12-2). Since extra charges on w i d t l ~start a t 100 in., it may prove economical t o use more than one plate in certain instances for sizes requiring plates ovcr 100 in. wide. A comparison b e t ~ w e nplate width extras and tlle additional costs of fabrication with ~nultiplcplarea iunst be made.'"

190


Vessel Heads

1de:illy. a splirriral-shnprd prrssurr w s w l is the niost desirable sinre it withstands higher l~ressuresfor a given nietal thickness. Spherica! vessels are used in the dorage of volatile liquids and gases, but they are not suitable for the construction of tlie usual process vessels. The cylindrical-rliaped vessel is the next best design and is u w l most extmzively. The heads for sucli vessels ilia? be flat, cllips~~idal(elliptical dished), dished, hemispherical, or conical. Examples of such designs arc given

Fig. 12-2 Shell fahrieat~dfrom more than one plate.

in Fig. 12-3. Flat heads can he employed economically only on small vessels ( 3 ft rlr less) or on vessels operating a t low pressures. Flat lieads may he welded to the vessel or installed as blind flanges on smaller vessels. Heads other than flat heads are manufactured by pressing or spinning large flat plates to the desired shape. Sizes from twelve inches t o twentyone ft in diameter can be manufaeturrd by spinning. Pressing is more generally confined t o smaller heads and is only economical when there is a deniaud for a large number. Often the process requirement,s dirtate the style head t o be used. A conical head, for instance, would be used for the bottom liead of a settling drum. If no certain style is dictated, however, the choice between licmiapherical, standard dished, and ellipsoidal heads is a question of economics. As the thickness required to withstand a given pressure increases in the order hemispherical, ellipsoidal, and dished, the cost of forming decreases in the same order. A l t h ~ ~ u gith is difficult t o generalize. i t may he said that in the range of low t o nioderate pressures the standard dished head is used. At higher pressures (above about 200 psig) it proves t o he more economical to employ tlie ellipsoidal (elliptical dished) head d e of standard with 2 : 1, ratio of major to minor axis. A ~ ~ i assortment heads is manufactured, and it is always desirable to use these whenever

Vessels

192


Vessels

possible. The use of a nonstandard liead requires the nrannfacturc of additiunal dies needed in the forming process, and thus entails additional expensc.

shu\\-ing (he trusrez for support and bubble cap assemblies is given in Fig. 12-4. Grid and perforated plates are becoming popularl and their support is even less of a problem because of the lightweight of such trays.

193

Nozzles

All process vessels require nuzzles for the fluids t o enter and leave the vcasel. for drains, l~andhi~les, and uinnholcs. Tlicrc, nozzles may be fabricatcd of pipe, pipc couplings, forged steel nozzles, cast steel fabricated plate, or other suitable material in accordance xith tlic code requircn~ent. .UthougI~ thc codes'.? permit the usc of both fusirm rveldcd or threaded attacliments, the usc of tlrrcaded attachnicnts is gencrdly avoided. Cutting of holes into tlie chell of tlic vessel for the installation of uozzles !wakens tlic vessel; and, thcrcforc, reinforcement around tlic nozzlc is required. Detailed rules for such rcinforce~ncntare given in the codes.',"orged strcl v.elding necks of lengths sufficient t o protrude hcyond vcsscl insulation are mars-pruduccd by scvcrnl manufacturers. The lengths uf such nozzles have been standardized, and it is customary in designing vcssels to adhere to standard lengtl~s,whethcr tile nozzle he purcllased ur fabricated from pipe. So-callcd melding-type nozzles arc also available. These arc made x~it11integral reinforcing necks and do not require tlic additional reinforcement necessary for wclding neck nozzles. Connections for srnall drains and vcnts one inch and under are usually made x i t h pipe couplings. A hole s~nallcrthan the inside dianlcter of tlic pipe coupling is drilled or cut into thc vessel and the coupling is w l d e d to the surface of the vcssel unly. The urc of nipplea instead of couplings is ronaidercd poor practice, since tlie tlircads are constantly exposed during installation and can easily be daniagcd. Vessel lnternals

A large percentage of process vcssels requires certain internal elcments to eflcet the changes in the materials passing through thc vcssel. T h ~ s e include bubble trays, packing, and packing supports for distillation to\\-en, lirating bundles, baffles, agitators, and othcr simililr ilrviccr. I'sually, the vesrcl intcrnals are not manufactured by thc vrrsrl f;lhricator, since nlost such items are of special design t ~ n drcquire a tcchnicnl know-how peculiar to a particular organization. Bubble trays and calls represent a typical example of vessel intcrnals wllich arc purchaseit fro111 n ~r~anufacturer specialiaing in tlicse items. T h e vessel fabrieatur, lio~vever, provides the tray supports. Lightweight alloy steel plates and bubble caps are in extensive use a t this time, and the support problem is 1nuc11 less t h n in the day uf the heavy rvmt iron tray. A typical modern-type bubble tray arrangeuieiit

Fig. 12-4. Bubble t r y . (Courtesy of Frite \V. Gliisch & Sons, Ine.) Key:

.idjoetablc ~ e i seal r plate. Trapezoidal minor blvsa. Channel-shaped minor truss. 4 9r 4.4. Top-type tl.usr liangm.s. 5. Thermal expansion joint hrlwrm tray floors nnd supporting ~I.II.SCS. 6. Intepml minor support in truss. 1.

2. 3.

i 6 7.4. Periphanl tray rlnmp8. 8. Removable cap and riser :~ssrmhly. 9 6 S.i..Hold-down meclhniw ior

internal tray mnnlr.:tya. 10 6 10.4. Downromer clamping hst.s. 11. Adjustuble ~reirs. 12. Fabricated stlvctuml majot. l m ~ m .

I t is dcsirahle for all vessel internals to be designed so that they may bc removcd from tlie nlan\\.wys in the vessel. Large pieces of equipment must be arranged so that they may be taken apart and removed in sections.

194

External Appurtenances

I n a&lition to the nozt,ler, inanholes, and liandholes that m u d he con. nected to the average process vessel, certain other exterior atta(.li~l~ent? are usually rcquired. These includc angles for the support of insulatim. lugs and various brackets for the support of platforms and ladders which are to be ~ t t a e h c dtu the vessel, and skirts for tlie support of the tower a t the required elevation. Thcse items are supplied by the vcssel fabricator and ~velriedto the vessel prior to shipment. Structural grade steel is normally employed. Stress Relieving

Residual stresses are produced around the wclded seanis of vessels. Such strcsscs weaken the vessel a t these points, particularly in thicker ressels (above 1% in. tliicki. I n these instances and in all c a m where liiaxiniuro safety is rcquired, the wssel 1s stress-rclieved t o eliniinate surh residual stresses. Tlie codes',2 permit a higher joint efficiency if stress relieving is used.* Strcss relieving is an annealing or heat treating process which relieves residual stresses. The operation varies, depending on the material of construction. For instance, carbon steels are heated t o approximately llOO°F and then cooled slowly. Most austenitic stainless steels are heabed to around 2000" F and then cooled rapidly in order t o prevent carbide precipitation characteristic of these metals in the range of 800 t o 1600" F. Precipitation of the rarbides in stainless steel destroys the currosioo resistance. A mell-equipped vessel fatxication shop has large electrically heated furnaces capahle of receiving almost any size vessel that can be shipped in one piece. 1,arge vessels that must be welded in tlie field can be stressrelieved around tlic rvclds using gas fired portable furnaces. Several low temperature strcss-relieving processes are also used. These employ special oxyacetylcnc torches which apply heat to the area a t the welds, followcd by n water spray. Because of the widc differences in physical properties of metals, it is imperative that the propcr stress-relieving procedure be outlined by a compctent metallurgist. Radiographing

When the greatest confidence in the soundness of a construction of a vessel is desired, radiographing (X-raying) of all welds is done in urder t o detect defects. Hecnuse of the greater kno\vlcdgc oi weld quality, the codesl.2 permit a lower safety iactor in the form of a higher joint effi* S e e Table 12-1.

Vessels


195

ciency. I t is particularly advisable to radiograph the Iargc longitudinal and circumferential aeams of all important vcssels. Shop and Field Fabrication

Because of the superior equipment and working conditions in a fahricator's shop, field fabrication should he kept to a minimum. Large dia~neter vessels (20 t o 30 f t ) , however, must be field fabricated. Rolled sections (arcs) of the shcll 7 to 8 f t wide are shipped t o the jobsite. V h e n planning any vessel over 10 ft diameter by 35 f t long, railroad agents should be consulted. Sizcs above this d i i c h can be shipped depend largely on tlie railroad facilities scrving the area. Lengths up to 60 to 80 it have been handled using special cars, but such shipments must be carefully planned early in the job. Vessel Inspection

The vesrcl codes require inspection by somc puhlic inspertnr, such as state, municipal, or insurance company inspccturs. before the vr.sscl can he certified as romplying nil11 llw mdcs. Prior to this inspection, the purchaser should havc inspected the vcsrcl during all phnses oi its fabrication. This includcs inspection of the plates and heads as they arrive a t tlic fabricator's shop, study of mill test reports,' and thc follo~vingof all operations including the final hydrostatic test of the completcd vessel.? THEORY OF PRESSURE VESSEL DESIGN

Rules for the design and fabrication of rmfired pressure ressels h a r e been carefully outlined by two major codcs whir21 arc used by tlie proccss industries. These are the ASME and the API-ASXIE codes for unfired pressure vessels.l,2 They are based on the judgment of experts. A11 process vessels should be constructed in accordance with tlic rules of onc of there codes. Before proceeding with a discussion of design equations a hricf theoretical background is desirable. The formulas given in the codes for determining the minimum shcll and ticad thicknesses are very simple and easy to use. Many occasional users, therefore, forget the limitation and the basis of these equations. Such indiscriminate usc, which has been encouraged by the large numbers of so-called rapid vessel design calculation charts, lead t o poor design. * M i l l test reports give the physiral and e h e m i ~ a lproperties oi the piirticul;lr stpel that was used b y t h e steel mill in ~rrnnufaeturingthe platcs being used f u r the vessel. i Vesscl~are hydrostatiealiy tcsted t o on?-and-a-half timcs the maximum working prewurc. A t this test pressu1.c all neklrd joinis are subjertcd t o impact by hammer. the weight of whirh is equal :ipp~.uximatel>-t o thc t h i c k n w ui the shell in trnths of a n inrh. A numhrr oi variations of t h r e t w t s nre possihle depending o n the vcssel size, thickncm, material, and athcr siruilar iiicturs.

196

Vessels


Thin-walled Vessels Thin-TT-alledvessels as defined by the ASJIE Code have thicknesses less than one-half of the inside radius.' Such vessels constitute the niajority of tliose encountered in process plants although high prebsure operation, such as tliat necessary for ammonia synthesis reactors (10,000 to 12,000 psi!, rcquirc thicker walls and the usual analysis for thin ~ ~ a l l s is not applicable. For thin-mlled vesscls equal stresses along the entire

197

I n the r.ast3 of :I s p h ~ r eR,,, . and K ,arc equal 111K thc r:dius of thc spht:n,. and hecause of this symmetry 110th S, and St arc the same. Ilence,

I n like m;rnucr. wing thc s a ~ n cgeneraliz~~rl equation. Den IIart(1: l ~ a i ilemonstratrd Biezcno's classical construction of a pressure v c s ~ c lhead of .?ur:lr currature tliat the ur~nlbranes t ~ ~ s r are e s the s:urrc urer I~otli1111' Iicad and 1111.cylinder and the tliicknrssee ;\re constant. I t is interr.sting t o note that the popular 2 : 1 elliptical hc;rtl very nearly approachc: this i i l ~ x lshape. For a cylinder I?,,, is infinite and R Lis equi~l10 lhe ritdiuh of 111~1ryli~rdcr. Hence S, St I'

=

thickness of the \\.all enn be assumed. The 1,ressurc a~,tiiignitliin snch a cylindrical vessel produccs longitudinal and circuinferential or tangential dresses as shown in Fig. 12-5. These stresses can be ealculatcd by nsi.uming rquilihriun~between tllc opposing forces. The derivation for thc riiiil~leryiiniler is familiar t o inany and is givcn in :my standard work on strength of niatcrials. I k n Hartogs has presented a iiiost cnliglitcning gcner;tlizcd derivation frolu which equations for any slrcll produced by rerolntion of a n clement can readily he deduced. His gencml cyuation is 3s follo~rs: , -= S, P -S +

R,

R,

=

S , = -I'R = f -

I'D," 2t

The ni~ridionalstress, 1vhi1.h in the case of a rylindcr is caller1 the lougit ~ d i n : ~strrss l (S,,),is ohtained 11y considering the shell in the ~lirertionof th~~ t m t r line. r From Fig. 12-5 it is seen that the t,otal stress :it the en11 of t h cylinder ~ is aD,,,lS,. Opposing this is the pressure acting in the lorigitudinal direction, 1'aUm2/'4.

t

n-here S, = meridional stress, the stress in a plane v i t h the center line of rohtion for the membrane and acting perpendicular t o t'lic ccntcr line St = tangcntial stress, acts in a tangcnt t o the circular cross section perpendicular t o the center line I f 1 = uormal distance between the center line and a point on the shell (for a cylinder, the radius) X,,= ladius of curvature in meridional plane, infinity for a cylinder P = internal pressure, psig t = thickness of shell

' Thc Al'I-ASME

+

Code specifies one-tenth of iuaide dimnrter.

'l'l~us t l ~ ct;~ngcntinlstrrss is the, larger ;1ni1 nwil 1 1 the ~ only on,. [.on-i~lerctl in calculating the wall tl~ickncs,*rcquircd fur ;I tllin-w~tllcd rylinder to \vithrtnnd a givcn internal Ilresture. TIE tangential stress in a cylinder is often referred to a s the hoop stress. Codes Some very excellent rules and regulations governing the design and fabrication of pre.ssure vesfiels and tanks liavr l w n pulilisl~ctlin the for111 of codes. The folio!\-ing is a rcpresentativc, hut not romplctc, list of rob : I I I I ~ i~r~gaiii~:itionr wl1i1.11I I Z ~ C i:orui11l:11(~~I 1111c.sfor ves~1.1:mI t:mk 1~111stl'ucti(1n.


198

\PI-.iSME Code; Unfired Pressure Ywseis for Petroleum Liquids and Gases. S M E Roiier Code Section VIII; Rules for Constmrtion of Unfired Preszure

l~esiels. American Petroleum Institute; Specifications for Oil Storage Tanks, Section xo. 12-C. Underwriters Laboratories, Inc. Kntional Board of Fire Underwriters. .\nrerican Factory Mutual Fire Inzurance Companies. .\rnericnn Bureau of Shipping Rdps for Clafsificntion and Construction of Sterl leiiels. Of thc above named organizations and codes, the code published by the American Society of Mechanical Engineers (ASME) and that published jointly by the ASME and The American Petroleum Institute (API)" are the n u ~ s videly t used rules for vessel design and construction. Knowledge of thc historirnl bnrkground of t h e e codes is of valuc in their interpretation. Samansl' has compared the recent editions of the two codes most cffectirciy using nn historical approach. The American Society of Mechanical Engineers, between the years 1920-1925. forn~ulntcdthe Boiler Construction Code, Section V I l I of ~1-1iichappwred in 1925. This section was thc first edition of ASME Code for Unfi~erlPressure Vessels. Although it represented t,he first complete conlpilat,ion of such regulations, i t was based mainly on practices existing in thc steam polver and boiler industries. A t about this same t,ime the petroleum industry began its remarkable march of progress, and the need for vessels that could withstand high pressures and temperatures hccame mnre and morc common in that indudry. Because of the narrow range of temperatures corered by the AShlE code a t that time, en,oineers in the petroleum refining industry considered the ASME code of 1925 inariequatc for their use. Their thoughts were prcsented before the Boiler Codc Committee in 1925, and it was agreed t h a t the pctrolcnm industry should publish its o\\-n practices and mei,hods of pressure vessel design for thc benefit of both the petroleum industry and all other process industrips. A joint cornmittce of the A P I and the AShIE was formulated. The API-ASME rode which they developed was first issued in 1934 and was folloa.cd by revised editions in 1936, 1938, 1943, and 1951. Since the issuance nf the first, API-ASAIE code, the AShlE code has been extensively revised. Tllc latest 1952 edition of Section 8 contains complete rules for the use of cast iron, nonferrous materials, and high alloy steels 3s well as rules for carbon and low alloy steels corered by the API-ASME code and previous editions of the AShlE code. The API-ASkIE code, in fact, now refers to the rules for high alloy steels and clad steels by referit w j r lc;+~.nrdthat thr .API-.ASME C O ~ will P be disrotitinilv,l. It ia lwlirvrd, however, that many o~.ganizationswill continue to use it for several years to come. *.As

hook

n-tmt ti, prrss

I i

Vessels 1W ence t o the ASXIE code and thus avoids repetition of these regulations, I t is not surprising that certain differences have developed between the two codes. many of which are minor and result froln differences in wording that h a w produced variations in interpretation. Perhaps the m0i.t important variation is the definition of qualified inspectors; the ASME.: mrle seems to have improved the system of inspection. The ASME code now contains a more complete list of permissible materials and a more recent method for calculating thickness of vessels subject t o external pressure. These differences are due t o variations in philosophy that occurred between the groups responsible for formulating t,he rules. Situations continually arise in the design and fabrication of pressure vessels which make int,erpretation of the code difficult. The Boiler Code Committee, therefore, accepts inquiries about code interpretation and mccts monthly for discussion. Decisions made in these meetings are sent to the inquirer as well as pnhli.hed s ~ ~ h s e q u e ~in~ tJfechnnicnl lg Engineel.ing, the official publicat,ion of the ASME. In like manner, questions can he addressed to the American Petroleum Institute concerning the interpretation of the API-ASME code.

I

! ,I i

/i I

Working Formulas

The theoretical formulas present,ed above for thin-walled pressure vessels have proved reliable by actual test, and are used in both the M I ASRfE and ASME codes. The API-AShIE simply adds a corrosion allowance and an efficiency factor for the longitudinal joints and presents the formula as follows:

where P

=

D,

=

S

E

C 1

maximum working pressure or design pressure, psig mean diameter in in. = allowable working stress, psi (values of S are given in both codes',2) = efficiency of longitudinal joint (values of efficiency vary from 50 t o 95% depending on type of joint and whether stress relieving and/or radiographing are used. See Table 12-1 for typical values) = corrosion allowance in in. = thickness in in.

The use of a mean diameter instead of an inside diameter is an attempt to more nearly estimate the mean stress value across the thickness of the shell. A more convenient equation in terms of an inside diameter can be


Vessels dereloped from eq. 1 hy ralling

Dm= DI Hence

t

=

+ (Dl + 2 t )

PD1

2

2SE - P

+C

(where D L = inside diameter)

(2)

T h e A P I L i S J I E code lists cq. 2 and a similar one hased on t,he o ~ ~ t s i r l c diameter. The .iSJIE approaches the prol~lem of ohtaining n mnrc accurate mpan stress value by adding 0.ti of the thickncss to t,he radius glrmg the equation, I'R t = (3) SE - 0.W where R = insidc radius in in. C:oniliarisun wit11 equation 2 will indicate only a slight difference if R is cl~angedt o 1 1 , by multiplying nulucrator and dnlrminator by 2. Similar comparisons between the basic theoretical equations and the i\-orking quntiuna presented II? the codes can be given for c:lr.l~ of t l ~ c v e ~ s e lshapes. It is helpful for the project engineer to bccome fn~riiliar v i t h the barkground rlf each frequently used formula as given by the codes so that the limitations may be clearly understoo(1. I n p a r t i d a s it should he rccognizcd that sllell t11ickncs.s formulas girt! I~ared on the thickness required for the stresses created by internal e c . I.(~arlingssuch a3 de:d loads (due to w i g h t of vessel anti ~ , o n t t v t ~n-iml i . ]
202


I

TABLE 12-2. Summary of Formulas for Design of Thin-Walled Pressure Vessels (Internal Pressure)

ASRlE

Purpose 1. Tliirkness of shells (Internal pressure)

M

API-.1SRIE

1

(b) Spherical

1=

=

PR +C SE - 0.6P

t

=

PD1 2SE - P

PR +C 2SE - 0.2P

t =

p,D1 4Sh - P

+C +c

(b) Dished (standard ASME with Knuckle mdius 6 % of crown) (c)

Hemispherical

( d ) Conical

t =

PD1 2SE - 0.2P

t

0.885PRc S E - 0.1P

+C

=

t = 1=

+C

t =

+C

PD1 4SE - 0.4P

+C

PD, 4SE

t=-+C

PD,

2 cosa(SE

SE

- 0.6P)+ C t =

PDc 2SE cos a

+C

Leeward side 2P,y W U D ' S + ZS-

1=-

PD,

4~

1. Buckling Nomenclature

corrosion allownnce. in. outside diameter of shell, in. outside diameter of shell including insulation, in. DL = inside diameter of shell, in. D, = mean diameter of a cone a t the point of consideration, in. = 11 = D' =

S

allowable stress for buckling, 2 X 1 0 6 ( t / D ) psi , S o = stress due to dead weight, psi S , = longitudinal stress, psi S,,, = stress due to wind, psi 1 = thickness of shell or head, in. 11' = weight of vessel. Ih a = one-half of the included angle of a cone a t the centerline of the conical head

SB

=

Shell Stresses D u e to D e a d Weight a n d W i n d Loads

0.885PR,

3. Thickness of cylindrical shells based on combined loads (a) Combined dead weight, internal pressure, and wind loads Windward side

C

R,

moment of inertia, (in.I4 bending moment due to xvind, lb-ft = working pressure. psig = wind pressure. p f = inside rndius of shell, in. = radius to which the head is dished measured to centerline a t thickness of crown plate, in. = alloanble working stress (see tables in code), psi = =

T h e calculation of thicknesses for shells subjected t o external pressure (vacuum vessels) has been presented in the form of charts in both cotles. T h e detailed design and application of stiffening rings is also outlined.

2. Heads (a) Ellipsoidal (2:l)

P P. R

( a ) Cxlindrical

203

Vessels

inside diameter of a cone a t the point of consideration, in. L), = mean diameter of shell, in. E = joint efficiency, fraction (see codes) h = distance from top of vessel to point under consideration, ft D,

=

T h e codes for pressure vessels state t h a t wind loads and loads due t o dead weight of the vessel and its contents should be considered in analyzing the stresses d-hich occur in a given vessel, but no sperific rules governing tliis are stated in t h e code. On the x i n d r ~ a r dside of a vessel the stresses due to rvind and internal pressure (in tliis case, longitudinal stress) act t o produce a tension on t h e vessel wall, while the dead weight stress produces compression and therefore is opposite in sign. On t h e leeward side: the stress due to wind and weight both produce compression, while the longitudinal stress due to internal pressure is again acting in tension and is opposite ill sign. These two conditions can be expressed mathematically as follows:" Windward :

S

=

S,

- Su

+ S,

(4 1

Leeward:

S

=

S,

+ So - 8,

(5)

where S S,

=

So S,

=

= =

allowable stress stress due t o mind load stress due t o dead r ~ e i g h t l o n g i t ~ u d i a stress, l PD,/4t

F o r estimating purposes the allowable stress in t h e ahove formulas m a y be taken a s the joint efficiency multiplied by t,llc allowable working stress listed in the codes for t h e material in question. I n addition t o the conditions considered thus far, the x i n d and dead weight loads can also produce buckling on the leeward side of a cylindrical vesscl. T o be on the safe side, i t is advisable t o assume t h a t the internal *The ahove analysis is hnwd an the most commonly used and simplest t,heow. the maximum stress theory. Other theories in use include t h e maximum strain, maximum shear, and modified strain-energy. Brummerstedt%eviews these theories.

204


Vessels

l ~ r r s ~ l lisr l ~ ZI~rofor tl~isr a l ~ : ~ ~ h t5inw i ~ ~ n~. I I ~ , , I ,pr?>.llrc I I : I ~ i11f'rr;l.w~tile stal)ility of a v e s ~ r l . Thc allo~vahleFtrcs. for hnrkling is equal to thc I stres:: due to vind lciad plus that h e to dead \vcight loail ISR = s, + S,, 1,. 11. L)ol~ncll" has 'lone eonsidcrable expcri~nentalrvo1.k on the hurkling of shclls and has dcreloped the following empiric:d equation for cvnlu:~ting t l ;~llo\\-:~hlc ~ rtrt,~.

whew l I< I:'

Ilence suhst,it,uting in eqs. 4 and 5 =

S

Leeward allowdjlc stress

S

= --

=

sh~,lli hirkncss sll~!llr:~(lius = m~ululusof ~,lasticiLy S, = yield point,

=

+-

2lh2 IV PD, - .T I ) ' ~ TI),,,~ 4t

\ \ ~ i n d ~ ~ -allon a r d able stress

---

21',h2 If7 - I'D, + T I ) ' ~ nL),,i 41

=

=

.Jnrgmsen7 has simplified this formnls for the usu:~l carhon steel shcll to S H = 2 X 106(i I>) ~r-hichW:IS d ~ r i v e using ~ l a factor of si~fctyof 4 on this stress ralrul:itnd from 1)onnell's formula. r . 1 he :~llm\-ahlcstress formulas can he further cxpanrletl as folio\\-s: \\'ind lo;~d= S,, where '11

= =

P,,

=

.111)'12 21

= -

(Imsed on the \veil-kn~nvn hcnding stress formnla, l~cn~ling momentsection modulus I

The above three formulas and that for the. rircumfcrential stress sl~onlrl he used to determine the controlling thickness. Since the operating weight, of a vessel depends on the thickness finally chosen, the m i g h t must first be assumed. Several short cuts t o this estimate have been suggested. .Jorgensen7 has developed a formula: TI' = 1.5.lillht 0.1G3h112 for insulat,ed towers having cast iron trays. Nelson%uggests calculating the w i g h t based on the thickness t and height h, using a metal density of 0.283 lh!cu in., and then increasing this value by 18 per cent. Lo allox for liquid, insnlation, trays, etc. Employing this procedure eq. 8 for the xindward side becomes

Ijcnding moment ( 1 , 2 ) P , X (D'j12)h2lb of force-ft unit wind pressure, * psf

+

D' = outside diameter of slicll in in. Inrlu~lesinsulation and 'or h I

= = =

1

=

other projections distanre from top of vessel to point, lwing considered, f t moment of inertia approximately a ( D ' ) W 8 , (in.)' thi~,laessof shell in i n

1

+

2P,,.h2 TI)' PI),, '4 - S 411

+

(11)

eq. 9 for thc lee11 an1 side becom~s

Hence

-

t

48 P , D ' h ' V P,h2 - 24a(Df)'t TD'~

= =

=

2fJ,,RhD ' - PI),. ' 2 . S - 4h

(12)

and cq. 10 iur buckling 11rc111nt.s

Dead load:

where TV I),

=

weight of vessel plus i n t e n d s and liquid mean diameter of shell in in.

*The unit wind pressure is related t o thp wind velocity by an empirical formula dercloprd hy tlic TJS. Weatlier Bureau. 100 mph wind is agpl.oximately e q u i d e n t to 30 psi; a 125 mph \I-ind, to 40 psf. i

Eq. 11 through 13 provide a method for estimating thickness for typical to~vers. Eq. 8 t l i r ~ ~ u g10, l ~ howrwr, should he u s d whcn nrorc accurate information is reqnirrrl and the thickness ran t h ~ nhe rletmn ~ i n d11y succwsivc al)prmiiootiu:~of t l ~ rweigl~t. I ) I I P C ~ 011 the internid p r e ~ u r e In c x t r ~ ~ n c tall l y t o w w the thick~~rils

207


Vessels

alone is often not adequate to x i t h s t a n d the combined stresses produced by wind and u-eight. Sincc there stresses increase from top to t h e bottom of the tou-er, i t is usually economical to increase t h e thickness of the lower

others several thicknesses m a y be indicated. Each case must be considered separately. Generalizations are to he aroided. T h e a b o r e principles and c q u a t i m s arc briefly illustrated in the fol~~lowing example. T h c calcnlations represent only the preliminary thickness calculations in p r e s u r r ressel design. Detailed stress calculations when necessary lnupt he mndc b y a competent vessel designer skilled in engineering mechanics.

206

Item No. T-lo/ Service P / m f 8 FeedStob//,rer Inside Diameter 7t0" Length ~ 3 ~ 0 " (Tangent toTongent) Operoting Temperature O Operating Pressure psig Design Temperature O F Design Pressure

F

550 /00

Downcomer Clearance

FOR INTERKAL PRESSURE THlcKNEss O F SHELLREQUIRED

600 l20>,

5%

Corrosion Allowonce Weir Height

.I process sketch of a fractionating tower is given in Fig. 12-6. EXAMFLE: Prepare the mechanical design assuming a maximum !%-ind velocity of 125 miles/hour (equivalent to 40 psi
3"oN t r o w / " o// tmys

From API-ASME Code: E S

=

=

0.80 13,750

NOZZLES

No. -

Size IInches1

/

/6

2 3

3

4

5

3(

/'? 16

8

Service -

Overhead Vopor Ref/un

*

F e e d /n/et Reboiler (Make Tongenfio/) Bottoms

Des;gn h t e r n o l disfributor to provide even d i s f d u t i o n across length of troy.

Nearest Practical Thickness

=

in.

COK~IDERING STRESSESAT BOTTOM TANGENTLINE Estimated operating weight (not including skirt), Dm = 7.05 ft Pounds 30,000

Cylinder: (1/12) (5/8) (a) (7.05) (53) (489) Heads (two a t 1622)

= =

Trays (alloy steel trays 26 psf) (a) (7)'(26) 4

= 15,000

Liquid on trays (base on water and 3 in. depth) ( 1 5 ) [ ( ~(7)2/41(V12) ) (62.4) Liquid in bottom of tower (7 ft)

=

Insulation (3 in. plastic insulation)

=

3.244 -2---

9,000

Nofe: Provde manwoys, ?ope q/oss. ondlevel control connecfions.

Fig. 12-6. Process vessel sketch. section of the tower. Fabrication procedures and plate costs must be considered in selecting the thicknesses. Theoretically, t h e thickness of a tall shell should increase steadily from t o p to bottom. Such a design is, of course, impractical. I n some rases a single-:hell thickness equal t o the maximum required a t the bottom m a y prove the most economical. I n

Weight of water when full during hydrostatic test Weight of vessel full of water

8,600 85.494 1b = 133,000 = 189,844t

THICKNESS BASEDON WINDWARD STRESSES AT BOTTOY TANGENT 2 P ha - W PD S = (13,750)(0.8) = 11,000 = aD't aDt 41

+-

*Volume of 7-0"ID 2 : 1 elliptical head. t 85,494 - 9,MH) - 19,650 1 3 3 , m = 189,844.

+


208

Vessels

209

DEVELOPMENT O F A VESSEL DESIGN =

0.072 - 0.0292

+ 0.232 = 0.2748 in.

THICRNESBASED O N LGEWARD STRESSES 2P,hZ s=-+ - -IVsD't

sD,t

PD, 4s

Inspection indicates this not to be controlling. Use reight full of vnt,er ns a-orst ron
=

9500 approximately (based on corroded thickntss, 0.625

- 0.125 = 0.500)

All of the above ralues are less than the unmrrod~dthickness based nn tho circumferential pressure; hence the 1:~ttcris controlling. Design Conditions The allowable working stress t o be used in the various for~nulasis given in tabular fonn in each of the codes. It is t,he minimum tensile strength of the particular mctal divided by a safety factor. This factor is 6 for the A S N E Code u p t o 650" F, and 4 for the API-ASME Code. The allul~-ablestress corresponding to the design trmpcmture should hc selected from t,he applicable tabulation. T h e maximum working prcssure or design pressure and the design temperature must be selected by thc vessel designer in cooperation with the project or process engineer. As spccificd by the codes, thc design prcssurc should certainly not he 1c.s than the maximum relief valve settings. It is customary t o use a design prcssurc of appnlximatcly 20% above the niaximum operating pressure anticipated. Unusual operating conditions m a y require selection of higher design pressures. I n a similar manner, the design temperature should be chosen a t a reasonable value above the normal opcrating temperature, such as 50". Higher margins of safety may be used in processes where greater increases in temperature are possible. It should he remembered t h a t every possible contingency cannot be considered in the design, since the cost would then become prohibitirc. But the vessel should be designed t o withstand all reasonable possible contingencies, and suitable pressure-relieving devices should he installed t o protect the vessel aiid the personnel in ease ol unusual situations.

Setting Basic Dimensions The size and shape of no st proccss vessels are determined by the process eugineer. B y training and experience he is the logical pcrson t o make such decisions. The diameter and height of a distillation toner ;ire sct n-ithin limits, by thc distillation design calculation. The rolume of accumulator drums. reactors, and scttling tanks are similarly dictated by the process calculation. Anyone n-ho has made such ~.alculntions, Ilorrercr. realizes that tlwre is ronsiderahlc Icc!!-ay possible in thi. final 1,110ice. For cxuniple. nn accumulator drum nus st have a certain rolunie. hut an infinitc 11un1hi'r of lengtl~to diameter ratios can be cniploycd ti1 give t h a t volume. Other factors being equal, i t is necessary t o choose the mart economical design. Brunimerstedt~ llnr sho~vnthat a length t o diameter ratio of 3 : 1 or 4 : 1 is most eronouiical for l o ~ vprcssure tanks in the range irom 50 to 75 psig, and length to diamcter ratio of froni 4 : 1 t o 6 : 1 is preferablr for prcssllres a l ~ o r c100 11sig. Other fartors. sncli w.+ plant layout, appearnnce, and foundation conditions must also ht: eonsidcrcd. Ahove all, the process engineer must specify wssels so that standard materials can be employed throughout. The usc of sta~liiard heads, for instance, rill avoid extra charges for special pattemp. T h e prucess engineer ~villdo well to consult with the resscl designer during the early stagcs of vessel planning so that tllc most econmnical design can be realized Engineers concerned with the detailed mechanical dcsign and fa1)sication of :t vessel are not in a position to c11:mge basic dimensions, sincc it is asramecl that tllesr d i ~ u c n s i m s: ~ r crcquire~llor the process. It is, therrforc, irnpcrative t h a t the basic dimensions ho set intelligently by the pr(~cessengineer s i ~that t11t.y ill fulfill hut11 I ~ r w c s s rcquiremeiits and tilt: rrquirmicnts of economical design. Materials of Construction Selection of the materials of construction for the vessel must be a rooperatire effort between thc ~ c s s c lilcsigncr, projcct enginper, and process engioccr. The ~uctnl:,cuiployrd must rrsist corrosive or crusirc? conditions and must also ]lo.2scss sufiicient strength a t tlic ol~cratinpt m ~ r perature and prcssurc t o permit a practiml dcsign. V i s e sclectiun oE materials will insure lo\!- uiaintm:mrc costs a n ~ iImv first cost?. .4uy attempt t o list recommended materials vuuld bc incnmpletc and niislwding. Selection of materi:rls for rorrosion resistance in particular is an euq)irii.al science which depends on the exact conditions of uw including even t h r presence of t r a r r irn1)aritii.s in tilt, r r ~ v i r i ~ u ~ l i rsurut rounding the mctal. Ihginecrs sliould urr so-called "linndy" material icli~ctiunr11:uts wit11 r:wticnl. F : s ~ ~ t ~ i ~ ~ results, i m t a l p r ~ v i o u s~ ) l a u tex-

210


perience under similar conditions, or the opinion of a corrosion expert are the only safe guides. Transmitting Process Specifications

\

The most efficient means for transmitting information about vessels and tanks is by sketch or drawing. The process engineer can make a simple ~ k e t c bof the vessel which indicates the operating condition. the number and size of nozzles and types of internals required (Fig. 12-6). H e also s h o d d recommcnd the material of construction (particularly in the rases involving corrosive fluids) and the thickness of insulation. Any requirements which are unique or unusual should he discussed with the v e s d designer. T h i ~includes the proper c , ~ r ~ o s i oallorvance n to he used in determining tlie thickness of the vessel. Detailed Mechanical Design

After receiving the process sketch, the ~ ~ e s sdesigner el can procccd wkh the detailed mcchaniral deaign of the vessel. Tlic design is invariably based on one of tlie codes (API-AShlE or ASME) ; the choice of code is usually dictated by tlie industry for which thc vessel is being designed. If t h r w is no preference on the part of the ultimate user, the designer is free tu use his judgment. Many states and cities h a r e codes or special requirenicnts that must be fulfilled, although a large number of thesc are based directly on the A H - A S M E or A W E codes. A summary of these reqnirements for thp United States and Canada is cuntained in Synopsis of Boiler Codes, Rules and Regnlations b y States, Provinces, and Cities, Kational Bureau of Casualty and Surety Undcrwriters.lj There is, of course, no rule forbidding construction superior t o t h a t outlined by the codes, and in inany cases the ultimate user or the designer elects to follorr- certain rules in order t o realize a better design. I n such eases, specifications arc written by the designer, uvhich include appropriate references t o the code as well as the additional requirements which are desired. After completion of the initial mechanical design, which includes calculation of the required tliickness of the sl~elland heads, a preliminary sketch of the vessel is made which shows the major details including the size and number of nozzles. Exact location or orientation of the nozzles is not attempted. This initial sketch can be made in such a form t h a t it will eventually, after suhsequent revisions, become the final and complete vessel drawing, or it can be made on a smaller-size sheet as a temporary working dra~ving. I n either event,, it finds its greatest use a s a means of transmitting preliminary information t o vessel fabricators for the purpose of obtaining quotations. Since steel plate and other materials

I

VESSEL DATA

I SECT.

9 8

7

6"

1 1

1" 2'

ISOf R F

I 3001IRF 1

3 0 0 'RF

REBolLER T O

I

( LEVEL GAGE 1 LEVEL CONTROL . ~

-

~

2

I

I

12.

150'RF

REBOILER RETURN

I

5

3

150'RF

BOTTOM OUTLET

I

4

10'

150XRF

VAPOR O U T L E T

I

3

2''

3OOfRF

REFLUX I N L E T

1

2

4'

ISDXRF

FEED INLET

2

1

18 ID.

150'RF

MANWAY

FURH15H COYEP h, WLT5 NUTS AND GASKETS

SERVICE I

I

I

SPECIFICATIONS FOR:

CUSTOMER:

2

REMARKS I

MANUAL WELDING

?

6

CONN.

'

B-@

I

NO. REq'D

SECT.

A-A

I

REMARKS: A. W R GENERAL NOTES 5EE OP-545-64A

UEVA

3-11-55

8. TRAY5 TO 8 E V4'THICK CARBON STEEL WITH 10 GA. C5. RISERS AND 12 GA.TYFE 410 ALLOY CAPS. REV8

-

REVC

Fig. 12-7. Vessel drawing, e n g i n e e r i n g c o m p l e t e .

ADDED CROSS ANGLE AND

NO.

-

ADJUSTABLE WEIR TO WWNCOMER

(Courtepy

3-21.55 328.55

REDUCED SKIRT HEIGHT FROM 10LO' TO 5'0: ADDED NOTES A & 6 REDUCE0 CONN. 2 TO 4'

-

of F o s t e r W h e e l e r Corporation.)

REVISED BY

E-2

SPLITTER

Vessels

j Trc

ta~ hkl an shi inx me de det

the bar USL

If free req are tllc

I !

S!/7

anc Th, lint clec cas, reft lies A cul: ske size is r it cox te~r. me2 the

.

1I 1

I

I

I

21 1

required for fabrication of vessels often have long delivery timcs, it is necessary to place the order for the vessel as soon as possible. and it is not feasible to wait until a final design lms been made. Once the order has been placed, the vessel design can he developed ti] an extent sucll rllat t h fabricator ~ can p u r c h a s ~the major material items, such 3:- shell plate and heads. The plant design procee~lssinlultaneously witli the devclopn~entof the ressel design and as piping dra~vingsare complctcd, tlie orientation of nozzles and manholes and exact li~cations of vessel internala can be finalized. The vessel drawing is then completed after being cllecked by the piping designers for orientation and possible interferences, thc structural steel designers for location of lugs, the process engineer for process requirements, and the project engineer for economical design and process requirements. Vessel dmwings pass through the hands of a number of different, cngineera for checking and cunimcnts. I t is important that the engineer who is asked to check such a drawing check only those features f i r ~vllirh his training and experience qualify him. I t is a waste of tinic for 3 pvocesa or project engincer t o concern himself witli a detailed clicck of the mechanical design of the vessel. An example of a finished vessel drawing is given in Fig. 12-7. I t will bc noted that important information such as design conditions. operating conditions, code, and material specifications appear on the drarving. T h e weight of the vessel d l e n both empty and full of watcr should he ineluded since this helps the structural and foundation groups plan their work. It has been found by most companies t h a t nozzle details and support, dctails, such a s saddles and tower base plates, are nmst i.onvenicntly standardized. I t is unnecessary, therefore, t o repeat, t h e details on each drawing; instead, a standard drawing is included as an attachment to the individual vessel drawings. Tlic fabricator prepares shop drawings from the vessel dra~vingreceivcd from the purchaser's engineering department. These shop drawings w e working drawings for use by thc welders, boilermakers, and machinists. Standard d d i n g symbols, a portion of ~vhirliis shown in Fig. 12-8, are used t o guide thc welders in their operations. It proves worthwhile for the purchaser's engineers to check tlie fabricator's dra~vingsagainst the original vessel drawings since it is possible for the fabricator to misinterpret certain features of the original drawings. This checking should be done without delay so that the fabricator can continue tiis work. Last-minute changes in the vessel design or specifications should be avoided unless absolutely necewary. Even the smallest change can cause considerable delay, confusion, and expense


212

~.

~

~~~

BASIC ARC A N D GAS W E L D S Y M B O L S TYPE O F W E L D BEAD

FILLET

PLUG OR SLOT

GROOVE SQUARE

BASIC RESISTANCE W E L D SYMBOLS T Y P E OF W E L D SPOT

JECTION

SEAM

FLASH OR UPSET

V

BEVEL

SUPPLEMENTARY WELD ALL AROUND

J

U

SYMBOLS CONTOUR

WELD

FLUSH

CONVEX

STANDARD LOCATION OF E L E M E N T S OF A WELDING S Y M B O L

I

F ~ n i s hsymbol

Groove angle, n c l u d e d angle of countersnk for plug welds

Contour symbol R o d a w n i n g ,depth of Iilbng l o r plug ond r o t welds

Lenglh of weld P S I C (~c e n ~ e r v t o ~ center1 of weds

S z e , w e or strength for r e i s t o n c e w e d s

Weld a l l around symbol

Reference n e

F ~ e l dweld symbol

S p e c f c a t l o n process

T O (may beomitted when reference I S not u s e o ) Arrow connecting reierence l n e to

201ic weld symbol

Fig. 124. Standard wrlding symhols. (R~ilt.:imnhy pet.mis?ion, 11'eirling llnnrlb~rni~. .\n~el.ivan \Velding Socirty.)

REFERENCES 1 . APl-AS.\IE Code f o r Unfiied Pirsraii. l'esnels, 8111. Soc, hlech. Engrs.. Smv York (1951). 2. ASJIE Code (01. Cvfii-ed Pressure I~rawla,Am. Soe, h l ~ c l l Engl.~.. . XCU. l w k (1052) and (1956).

Heot Exchangers Double-Pipe Heat Exchanger

As tlie n a n ~ eimplies, the double-pipe heat exchanger consists of t ~ v oconcentric pipes. One fluid flo~vsin the internal pipe and the other in the annulus hetwccn thc inside and outside pipes. Such exchangers are m o d conveniently arranged in the form of hairpins, similar to the extended surface exchanger of Fig. 13-1. Thc usual practical length of these hairpins is twenty it,. Such exchangers are very easily made in practically any shop and rontinue t o prove useful where very small surface requirements exist (approximately 100 sq f t ) .

HEAT EXCHANGERS Chemical processes invariably require the addition or removal of heat. Careful design and application of heat exchangers, thcrcfure, lins t w o m e a n important consideratiun in plant design. The completc design of heat exchangers is seldom the job of the pl.ocess engineer or the project engineer. Such equipment is generally purchased from the heat exrhanger manufacturer and is designed and guarantecd by the manufacturer. The project engineer, hoverer, niust nndcratand the methi~dsof designing and fabricating heat exchangers. An undrrstaniling of these techniques permits closc coopcration tletrecn the projcct enginccr and the manufacturer's representatives, a cooperation that can rave both time and expense. HEAT EXCHANGER TYPES

Many different types of heat exchangers are manufactured. A few of the most widely used heat exchanger types will he discussed t~elov. Special designs can alxays be deviscd, which may be advantageous for a particular application. It is, however, preferable to use standard designs or so-called "stock" i t e m wherever possible. Exchanger manufacturers are able to produce certain exchanger types and sizes on an assembly-line production basis. Any deviation of conscquencc from these stock designs will require special operations and, therefore, increases in cost. 21 4

Double-Pipe Extended Surface Exchangers

One of the advantages of thc double pipe exdcsire t o benefit from changer is its Ion. cost. .i this lor7 cust and a t tlie sanic time to h a w the advantages of larger surfaces proinpted the dcvelop~nentof the extcnded surface tube. Typical examplcs of puch tubes arc shown in Fig. 13-2. The longitudinal fin is used most frequently in double-pipe exchanger dcsign (Fig. 13-1). Transverse fins are employed princi11ally for cross-flow arrangements in either extcndcd aurfacc tubc-and-shell exchangers or in air-cooled exchangers which are growing more pq)ular in arras whcre water scarcity is a probl e m Usc of fin tubes is particularly desirable for gases, viscous liqnids, or strearus of small flow rate. Such fluids pruduce high resistances to heat flow, which are partially or7ercume by thc larger effectire area introduced by the fins. For surface requirenients below 1,000 sq ft the use of extendcd surface double-pipe exchangcrs often eRects a considerable saving. Particular consideration s h d d be given tu such units for surfaccs below 500 sq ft. The d o ~ ~ t ~ l e pipc sections can he arranged in r o w and connected in series (Fig, 13-3). Fig. 13-1. Extended swiner double-pipe exchanger; G-fin. (Courtesy oi Griscam-Russell Company.)

215


Heat Exchangers

217

, n t i.5 ~iiostne;irly oljthe otlirr fluid. I n s l ~ e l l - : ~ n ~ l i-qt u~i~pll ~~ ~ ~this proaclied by the so-called "1-1 exchanger" n-hidl consists of one shell pass and one tube pass (Fig. 13-4). If a 1-1 eschanger is supplied with a float-

Arrongernent of four parallel bonks of three sections connected in series. Tube rennertorr are used to connect the elements of each bonk in series, with 90" threaded adaptors being

supplied for the tube inlet and outlet
Fig. 13-3. Typical arrangement oi doublc-pipc exelmiger sections: G-fin. tesy of C.riseom-Russell Company.)

(Gout.-

Fig. 13-2. T i I l l i I : : ( u ) , ( h ) , ( c ) , and ((1) rmss-fins: ( c ) 1li11-fins;( / I I m g l I ~ l d m ~fins l I R c p ~ i n l t dhy lximiwr,n, R. J. Sldi;,, C i ~ c c z .Eag., 61. X o . 12. 142 (1051) :airrl hewn Fintuhr Conrpnny.)

Shell-and-Tube Heat Exchangers

I(!.

h r tile most ii-idcly u m l heat cxcha~rgertype is the shell-and-tube.

.Is lieat ~ , x r l ~ a n gsarfncc r r r ~ q u i r c ~ ~ w nhccmnc ts large, rlouhle-pipe esr,l~nngcr ~lwignz rcquirc cxccssive spacc. Tlic shell-md-tube design, hoirever. p r ~ ~ v i d c21slarge, surface area per unit volume of space occupied. Alttr~nigl~ dificring in cr,rt:iin d c ~ i g ndetails, thcrc arc z e v t ~ a lstandard I - I - I cxc.11ang1.r types fnbriciite~l by all rxcllmger manufacturers. .ipprosi~l~atcly ninety per cent of all l x a t exchange duties can he I~andledby onc or t.he other of the basic designs. Counterflow 1 - I Exchanger

Tlic n ~ u s trflicimt c\;cl~:il~g~, of hcnt con be nccomplisl~edhy a counterli<~r\:wwnuwiwt ill I\-lii~hm e fluiil flows in an oppositc direction fruin

Fig. 13-4. One-onc erchangrr: single-pass slrcll, single-pnss t u t r s , fixed t l d ~sheet. (Courtesy oi Engineers and Fahriearors. Inc.)

ing head on the tube bundle (Fig. 13-9). the outlet nozzle on the HoatingLead side must pass through a packing gland, since i t must be free t o move with the floating head. The 1-1 cxcliangrr is employed \\-hen tubeside friction losses must be kept to a niininlun~and when temperature requirements are such t h a t true countercurrcmt floiv IIIII-t be used.

218


1-2 a n d 2-4 Exchangers

The 1-2 exchanger, as illustrated in Fig. 13-5, consists of one shell pass and two or more tube past3- It.wn numljcr of t n l ~ rp a w s I . 'This design is perhaps the most c o n ~ m t ~ofn all shell-am-tube excl~angcraand

219

Heat Exchangers

difficuli to maintain. eincc the longitudinal baffle requires a more complex (lesign. The tx\-o-pass shell is hest used for clean fluids. Reboilers

The primary sourcc of heat supply to most distillation columns is thc reboiler. -1 reboiler is a heat exchanger designed to supply heat anrl permit easy control of dist,illation toxer conditions. One of the earliest Vapor out

t

Fig. 13-5. One-two exihnngcr: single-pnsi: shcll, two- pa^ tubes, removable tuhe bundle. (Courtesy oi Enginecra and Fabrientors, Inc.)

it is the simplest to maintain. I n the 2-4 exchanger, as illustrated in Fig. 13-6, two shcll passes in a single shcll are provided by installation of a longitudinal baffle. This exchanger may have two or more erennumbered tube passes.

Fig. 13-6. TKO-four exchanger: two-pass shell, four-pas tubes. rcmovnble tihr bundle, cross baffles arrmged for side-to-side flow. (Coul.tesy uf Engincrls and Fahl.icntors, Inc.)

Shells with more than two shell passes are impractical but the advantages of additional shell passes can be obtaincd by connecting exchangers in series. I n this manner two 1-2 exct~angeraconnected in series would be equivalent to une 2-4 exchanger. The two-shell pass exchanger is more

Liquid in

Fig. 13-i. Kpttlc-type reboilcr: Engineers and Fnhsicntors. Inc.)

Liquid out

removable two-pass tube bundle. (Courtpry of

methods for supplying heat to the bottom of the distillation colurnn was t o insert an exchangcr hundle in the t~ottomof the tower. Thiv is still done in somc cases hut is not very popular because maintenance is more of a p r o l l e n ~ . Largc bundles in to~versare difficult to design and cumbersome t o service. Kettle-type rehoilcrs (Fig. 13-7) are ronstructed similar t o small evaporators. A uwir is loc~tctia t the cnd of thc bundle so that the liquid completely covers it. -4 large vapor space is provided. All the heat furnished by the kettle-rcbuiler is returned to the tower hy the overhead vapom from the reboilcr. Tlic kettle-reboilcr, therefore, acts as a srparation stage similar to a tl~eorcticalplate. Thermo-syphon rehoilers, as illustrated in Fig. 13-8, are the most commonly used in the process indnstry. The thermo-syphon design is sirnilar to a standard shell-and-tube heat exchanger except that t,he inlet and outlets are usually located in the middle of the shcll so t h a t flow can be divided equally between the two halves of the exchanger. This divided flow arrangement insures low pressure drops on the shell side.

220


The liquid from tlrc 11ottmr of the distillatim ton-cr passes to the tlrerni~~-s>-pI~on rrhoilrr nnid is partially vaporized. This less dcnsc liquid-1-allor ~iristurethen p:i-xs h c k to tlir ton-cr. Thc ~ x t eof cir~ l~rcs.!ure i1riq1 tlrro~~gli tlic .rstem :rnd tlrc cul:ition is gox-erue

t

f 1l:rny ol~r.mti~r.: hrlierr that iulmwlini: postioual to the height r ~ liquid. in' vc~rticalrontlenscrs is better controlled than in the liurizontal con~lenscrs. T h e vertical unit, however, is more difficult to rervire and t tuhe hr~nrllr require-. a clear space aborc it equal t o its lengtlr so t h ~ the can he removed. Horizontal rehoilprs arc t h ~most T\-idcly I I P P ~ .hut v ~ s t i r a lwhoilrrare prcf~rrccifor ccrtail~in?tall:rtions. 1 1 1 v,,rtic:rl sd1111I(,sst11r 1 1 r o ~ + -trc:un is usually passed inside the tuhc. This is an advantage for ioi~lingfluids since tlii,? are more econonrically Irandled inside tlrc tul~r-. Shell

I Liquid in

liquid-valwr density 011 tlrc 11tlrrr ;.irk of the system. Careful consideration must 11c givcri to tlir ~lesipnof i~ipingf , rt h e s ~ n ~ ~ - ; y p treboile~s i ~ ~ n SII t h t circulstion ~villnut he liuriteil by cxcessi1.c pressure drop in the ~'ipingsystenr. A safety factor of a t least t x o should be applied to all pressure drup calculations connected with rt,boilcr piping design. Condensers

Conden,scrs are usu:dly ctan11:lrd 1-2 excl:angers rritti vapor belt or annular distributors on thc vapor inlet nozzle. This design pcrmits hetter distribution of the valmr and elinrinatcs excessive entrance losses. Other ~u~~rlitieations arc nrade such as the :~rrangvmentof inlet and outlet nozzles for split flow in order to keep pressure drop to a niinimum.

221

Heot Exchangers

and

Tube

Heat

Exchanger

Nomenclature

and

Parts

I n I'ig. 13-9 the iri~lrortantpasts of a 11ei1texchangc~~wr.sIrr~\r-nirnll tlrc u s i ~ s ltclminology c ~ u p l ~ ~inydescribing ~d these part.; is g i r t - n Tn :rdrlition to the floating hracl design illustrated, several otlier types of he;ul; Iran he provided. If expansirln is not a l~roblenr,fixerl-tulle sheets and fiam-hvad e a r l r n r ~ ~ c rcan s he used. Tliese esrlrangrrs arc rheaper t l r m tlie floating lrcntl rxchangers hut provide no means for alleviati~m of ciiilesentiul esl~:rri~ion l ~ r t ~ w ethe n slrcll and tuhes. TKOtypes of floating 11t~:rilsnrr in use. I f t h liwrl is the split ring type, the floating I i t d cover must be reuioved hefose the tube hundlc. Tlre "pull-tlrrouglr" floating lienil is designrd so t h a t the head diameter is less than the di:uircter of tlie sllell. T h e tube bundle c:tn then he remored \vitli(lut ren~o\-ingt l r ~ flo:rting head corer. T h e poll-tlrrougli arrangement, iio\~ever,retlurcs t,Irr number of tubes that can he l~lacedin a shell of a given diameter. I n ordcr t o avoid the use of a floating head and internal girslieting, it is possil~lrto enrploy r - t u b e s to make up a tuhe bundle. T h e W x n d s ex[)and freely ~vitliteml~eraturechange. Sin1.e cleaning 11f such l~uncllcz is a difficult task, their use is restricted to only (.lean fluids. The segmental bafles shomn in Fig. 13-9 are the most xidcly used means for providing proper distribution of the shell-side fluids. Orificetype l~afflcsform annular spaces around each tuhe through n.11icl1 the shell fluid parses and can be used for clean, nonfouling fluids. T h e limited usefulness of the orifice-type Imffle, as w l l as prcjudiccs against it by many former users, has p~acticallymade i t obsolete. Coil-in-Box Cooler

Vertical Exchangers

Although tlrc majority of heat exchangers are placed in the horizontal position, certain situations arise in xhich a vertical exchanger is preferable. A vertical condenser is often preferable t o tlrc horizontal condenser ~ ~ I r esubcooling n is required. Suhcooling can be acco~nplished in a Irorizontal cirrici~~nscrby l~roviding:I loop seal so t h a t a portion of the t u l w is corcred by liquid, hut thc aluount of surface covered is not pru-

K h c n adequate x a t e r supply is available, the sulxncrged pipe roil, or coil-in-box cooler, is one of the clrcnpest cooling surfaecr. Material t o he cooled passes tlirouglr a series of straiglit pipes connected by return bends. T h e entire coil is placed in a large trouglr or box ronstructe~lof roncrete, wood, or steel. Cool water usually enters the hottoiu of the box and passes over a weir from the opposite end. It is simple to huild llilw coils, and the boxes arc usually large enougl~t o acconrnrodate addi-


Heat Exchangers

223

tional lengths of coils as other cooling loads become necessary. This flexibility, together with the low cost and ease of replaring corroded or eroded tubes, n l a k r thc coil-in-box cooler popular for cooling corrosive or erosive streams. They are particularly useable i&en the outlet temperature is not critical, as in cooling matcrials to be pumped to storage. Temperature control of the coil-in-box cooler is much more difficult than for the usual shell-and-tubc exchanger. I

Pipe Coils

One of the easiest, although not always the most efficient, means of supplying heat to or removing heat from a tank or a piece of pilot plant, erluipmcnt is ~ ~ i at hlielical pipe coil. Such coils are easily fabricated, and can be placed in a small tank made from large diameter pipc and used as a sample cooler or as a pilot plant cooler. Pipe coils are also used for heating contents of tanks and reactors. I

j I

1

\

Trombone or Trickle Coolers

The cooling of extrenicly corrosive matcrials is often a difficult and expensive job. The trombone, or trickle, cooler has heen used rritli marked success. I t consists of straight lengths of pipe connected in series by return trends. TTatcr is allowed to trickle over the pipes and is collected in a trough beneath tlie unit. Some of the water e v a p ~ ~ m t eass it mores down thc pipes. The pipes can bc fal~ricatedof prartirnlly any material that will ~ ~ i t h s t a nthe d fluid flowing insidc. Ceramic tubes have been particularly popular for corrosive rnatcrials such as wet HCI. Air-Cooled Exchangers

Many portions of tlie world suffer from serious water shortages. The development of the air-cooled exchanger has permitted pmcri.: plant construction even in areas d i e r e water scarcity is a definite psol~leu~. These units usually consist of a largc number of tubes ~vithtrnnsvcrse fins. Tlie fluid to be cooled passes t,hrough the tubes and air is forced past the tubes by either an induced or forced draft fan. Beranse of the high resistance of gas filrus these air coolcrs require largc surface areas, and therefore a large space, per Btu of heat transferred. FABRICATION OF SHELL-AND-TUBE HEAT EXCHANGERS Standards

The Tubulal. Xxcl~angerl\lanufacturers' Association has puhlisl~eilrietailcd standards for tlic design and construction of shell-ancl-tube heat exohangers.*3 The mechanical standards have been divided into thrre parts representing three different classes of heat exchangers, Classes R: C, and A. Class R is designed to meet the requirements of petroleum I

224

refinery and high pressure petrochemical operations. Class C is designed to uiret general process conditions involving mode~;rte pressures and I i- r1r.ienc.d tcinpcrature.. and relatively noncorrosive! fluids. Clnsc ; for the use of alloy materials of construction for handling particularly corrosive or liigli temperature fluids. Class R spccifies Iargcr corrosion alloxmres than Class C : and in general, has more rigid constructim requirements. Overall tube lengths are spccificd by these stanrlards as eight, tn-clve. or sixteen feet. Tlirec-quarter and onc-inch dianictcr tuhrs arc tile nmst common, although the use of one and-a-quarter and onc and-:%-lialf.ns !vcll as smallrr sizes is permitted r h c r c special conditions varrant. Shell sizes have also been standardizcd Sizes up ~ I tn.mty-three J inch. inride noniinnl diameter. are made of pille. .4horc txcnty-three inch. they arc fabricated from rolled plate. The minimum pitcli of tubes is set a t onc and-a-quartcr timrs tlie outside diameter of the tube. Minimum baffle spacing is one-fifth of the shell inside-dian~ctcr,or t v o inrlrcs, n.liiclic~cris greater. 1-erit and drain conncrtions are three-quarter inrli. Tiirse t~ndmany otlicr st:indx~.di. including dimensional tolernncrr, are ~,art,fnli>s~~ccificd by the E s c l i i ~ n ~ c r Xanufacturcrs' Association. One of the greatcst benefits of such standardization is in thc simplicity of stocking spare parts.

Heat Exchangers

I

operation. They are w t in a preliminary fashion by f o r c i n ~a plug ngainst tlie tubes. Thc plug prevents the tube from turning when the roller expander is inserted. -4 cross-section of an cxpanding operation is illustrated in Fig. 13-10. The tubes are expanded into grooves in order t o produce a stronger joint. Expanding of tnhrs rcquircs experienced operators, rincr overexpansion dl unnecessarily thin thc metal and produce rapid tube failure.

of rollers-no

Fig. 13-10 Tube expanding operation.

Fabrication Procedure

Various parts of a slirll-and-tuh~ licat eschangcr are illustrated in Fig. 13-9. Refwenre to this figure mill :+id in un~lerstantling tlie following iliscussiori. Tlic sIrel1 portion of tlic licnt rxv1ii:iigcr. hcing n pressure ressel, is fahrirated in the a n i c iiimncr as that d i s c u s 4 in Chapter 12. These shells arc fabricntcd in accordanct! with tlie .%PIASME or .4SLIE Code for Pressure Vcs~el;;. ; \ ~ ~ t o ~ n n wc~lriir~g tic is use11 allnost cxclut.ivcly on tlic I~~ngitudiu:dscams an11 also 011 most of tllc circumferential reams. The large flangcs rrccdcil for the c1i;mncl and shell covr3rs require carcful facing operatiuns. Aase~nblyof tlie tul)e bundle is an interesting oper:itioii. Tube sheds are cut. from stccl or brass plate. Tlie cutting operation is ilsually n n~echanical operation for brass, but eldi ding-torch cutters nrc used for steel tube sheets. Tlie tube holes are the11 drilled in the tube slieet aiter being laid out in their 11n)per pitch and orientation. T11w groorcs nre lnilled illto t l ~ ctube Ilult,>. f-lo11,s arc ; t I s ~drillc
225

I


!I I

E

~

I

i

1,

i .1 I

(Courtesy of Bridgeport Brnrs Company.)

Tubes may bc a number oi different metals: stainless steel. various copper alloys, including bronze, brass, or admiralty metal. Aluminum. AIonel, nickel, and other materials arc widely used in sevcre scrvicca. It is not uncommon t o find conditions where the fluids both inside and outside the tubes arc extremely corrosive, and in addition, require a different, metal on each side. Tubes xvhich combine two metals can be used t o incct this problen~. The metals are permanently bonded togcther, one facing tile inside and the othcr the outside. Combinations include stwl mcl admiralty, alurninum with copper or brass, and alloy stccls wit11 copper alloys. ITsing the same pitch (center to center tube dimension) it is possible t o place more tubes in a given shcll employing a triangular pitcli (locating tuhcs a t the apiecs of equilateral triangles) than by employing a square pitch (locating tuhcs a t the corners of a square). The use of the square pitch, h o r e r e r , is recommended whenever fouling fluids arc t o be enconntered outsidc of the tube. This arrangement affords larger cleaning lanes and, therefore, simpler maintenance. For cases in which fouling fluids must be handled inside the tubes, sizes smaller than %'' O D and Xo. 14 BWG* are usually avoidcd.

* B K G refers t o Birmingham Wire Gage and is s measure uf tube thickness. Handhooks list the thickness corresponding to the various BWC numbers.

226


Heat Exchangers

After completion of the bundle, it is brought to a test rack where n hydraulic test is applied. Bundles are then lowered rertically into the exchanger shells and the final hydraulic test of the exchanger is made. After the outside of the shell is painted with a rust-preventative paint and all flanges are covcrcd to prevent damage, the unit is ready for shipment.

k,, = conductivit,y of tuhe, Rtnl (hr) (o F) (ft) A, = average of A, and 4 o, sq f t A. = outside surface area of tuhe, sq f t A ; = inside surface area of tube, sq f t Since Rd = l / G d hy definition, then - "

HEAT EXCHANGER DESIGN

The basic equation for llest exchanger design is perhaps familiar in noa at, engineers 7%-hohave had an introductory course to the subject of heat tmnsfer.

where Ao

required effective surface of the heat exchanger based on t'he outside surface area of the t,ubcs, in sq ft q = heat transferred in Btu/hr AT = mean temperature difference between hot and cold fluid (this is the driving force)" F Ud = design overall coefficient of heat transfer in Btu/(hr) (o F) (sq ft) based on outside surface area Ra = design overall resistance l/Uri, based on outside surface area =

The amount of heat transferred is directly proportional to the surface area and the driving force AT, and is inversely proportional to the overall resistance t,o the flow of heat Rd. The total resistance Rd is composed of a number of rcsistances in series, and, as electrical resistances, they are additive. These resistances are: 1. Resistance of fluid film on inside of tube.

Hence

Ao

h-4,

+

a +-+L,

1 +

Xusselt"' she\%-ed liy ilimcnniorial analysis that the inside film ro~ffirient \va* rclated to thc properties of the fluid and the diameter of the tube as follows:

where D G

= =

p =

lc C,

= = =

inside diameter, f t mass velocity, lb/hr-sq f t viscosit,y of fluid, W f t - h r thermal conductivity, of flnid, Btu/(hr)(' F)(sq ft/ft) heat capacity of fluid, Btu/(lb)(o I?) length of tuhe, f t

Lx: = Reynolds' number I.I

4. Resistance of scale on outside of tube, ro. 5. Resistance of fluid film on outside of tube. 1

Inside Film Coefficient

L

2. Resistance of scale on inside of tube, r,. 3. Resistance of tube ir-all.

R -d= -

A0 'I" A0L" 1 -+r,-++ro+ h , A* .I, .4,,,kz6 ha The overall coefficient Ud is the more familiar trrm in commerce and n-ill be used here. The major problem in heat exchanger design is the evaluation of the individual resistances that appear in c q 2. Eitin~:rtiiin of the insidc and outside film, especially thc outside coefficient, have been the most perplexing problems.

ro Ao

1 ho-lo

where hi = inside coefficient, Btu/(hr)(sq f t ) (o F) ho = out,side film coefficient, Btu/(hr) (sq f t ) (" F) r , = inside scale resistance or fouling Eartor, (o F ) (sq ft) (hr) fRtu ro = outside scale resistance or fouling factor, (" F ) (sq ft) (hr) :Btu L, = thickness of tube, ft

-"" -

k

Prandtl numher

I t is in~pmtantto realize that each of the terms are dimensionless and consistent units must he eniployed within eacl~term. a, a, c, and i arc constants which must be determined experimentally. and, following Nnssclt's derivation in 1910, considerable experimental work u-as done to evaluate consistent constants that would apply to all fluids. hIost of the early work was done with air and water, and the correlations were hascd on properties developed at the temperature of the filni. This ternpcr:%turcx-oulrl a1)pc:ir to ire corrcrt theoretically, hat it was tedious to einploy in design since it had to be estimated by trial

228


Heat Exchangers

and error. I n 1929 3Iorris and ~ ~ h i t l l l a n attempted 14 a correlation based on a number of fluids and used the average hulk tempcraturc instead of film temperature. They obtained a relation that x:ts consistent for fluids being cooled and anotlier relation for fluids heing heated. Dittus and A o e l t e r V o l l o ~ e dv i t h their wll-kno~r-nequation l~ased on bulk t ~ m p e r a t u r eand flow in the turbulent region iahorc Reynolds nutnl~cr c ~ 10,000) i rrherc the ratio L/U had no effect.

are widely used in heat exchanger design for all fluids. Other e r p'I.t 'tons have been dvveloped d l i c h are more accurltte for specific fluid*. The ,3eder-Tate curves, liowevcr, h a r e proven t . 1 ~luost 11-idely applicable and are included in the Standards of the Tubular Exchanger 3lanufacturers .4zsociation.2:J The Sieder-Tate equations can be rearranged by multiplying each side by c,p/DGc, and the form

Cooling: The desire t o find one equation which 3-onld exprcss hot11 heating and cooling encouraged furtlier inrestigdtion. Sieder and Tntc" rcasonrd that the relation Iletn-ecn tlie viscosity in tlic hulk of tlir fluid to tlrar a t he wall prodnces a change in the velocity distribution of tlic indiviclll:tl fluirl streams. One type diitrihutiort is ohtnined in heating :~ndi~notlier in cooling. I n cooling the viscosity a t the wall is greater than i~ thc bulk of thc fluid, and the opposite is true for heating. They derided to introduce another din~cnsi,mlcss tcrm, the ratio 111 tllc riscosit? it1 the hulk of tlic fluid t o that a t the rvall, p/+,,. The exponcnt mas dctcrniinrd experinient:~lly, and the following equations appliwble t o both heating and cooling w r c devclopcd from tllc data: Streamlime flaw (Re

=

2100 or less)

Turbulent flow (Rc

=

10,000 or above)

Thc transition region wliich lies in betrwen lteynol~ls'nunlt~crsof 2100 and 10,000 as not easily represented 1)y an eqnatii~n. Instead it \{-as found simpler to plot cq. 6 on11 7 a s follows:

This products a single straight line on logarith~niccoordinates for the turbulent region and a series of lines for various values of L / D in the .;treitnrline region. The transition region was then determined 11y extr:leurvc.5 and cllecking ~vitll,xpcl.iment;il i . l i ~ ( : ~ . ] d a t i n g the t\vu sets The Sieder-Tate curves and equatiuns have beconic the standard and

229

resnlts. This f o r ~ nis particularly nscf~lllor gases since c,p/k tends t o he constant orer riorn~altemperature ranges for n ga;, and thc lmhlrtn of finding values oI gaseous conductivities, wliicl~ is a difficult one, is eliminated. Outside Film Coefficieni Double Pipe Exchanger

The film coefficient uutsi0c the tnhes prcwnti n more 11ctplcxin: problem. I n the simple case of a plain doublc-pipe exr.Ir:mgcr thc fntnili;~r engineering proecdure of employing an rquivalent diameter I),. in place d the term II is follu~vedusing the equation for the inside film e~xffiricnt. This equivalent dianleter is defined as four times the hydraulic radius wliicll 11111~be four times the cross ecctinnal area divided hy thc T\-cttcd perimeter or thc heated perimcter. The former is tlie same equivulent di:tmcter as is used in pressure drop calculation and is D? - D l . (I).? is tlic inside diameter of the outer pipe and D , tlie outside diameter of the innrr pilie.) Based on the heated perimeter, D, becomes (D,z - D , ~ I , ' ~ > , . httclnptz a t currelation of data using hot11 types uf equivalent diatiietcr produced equal accuracy. Until more data b c c o l ~ ~available, e II~I-ever, the urt: of tllc a a u ~ eequivalent dianietcr required for prcssure drop - D l ) secn~smost convcnicnt. enlcul:~tious (D2 Extended Surface

Tllc outside coefficient of an cxtenrlcd iarfncc cxehanger is compli~~aterl by t c ~ u l ~ e r a t u rvariations e along tllc f i n Some weiglltcd value ill the heat transfer coefficient for tlie conihination of fin and plain-tube surface nlust be obtained. It is difficult to establi~lt a satisfactory base arca on the outside of the tube because of the many variations of fin arrangements that are possible. Hence, all extended surface calculations are based on the inside surface. 1 (I;

= -1 + -1 hi

h,,

231


Heat Exchangers

where h,, is the fin-side coefficient based on the inside tube surface area. h,, is related tu the average outside coefficient for both fin and bare surface. hi, by the expression

based on the inside area as does hi. IIence t'he factor must be added to l / h , and the resulting design h , used to determine a design h,, from Eq. 9. Then

230

q = hI,Ai AT = h,(A,,

+ A o ) AT

an effect,ive fin area equivalent to the total fin area illmukiplied by the fin efficiency R A . = outside tube surface area exclusive of area beneath the fins q = heat transferred The tin area is not as effective as the outside tube surface and the fin efficiency serves to correct this area to an equivalent amount of outside surface. Rlurry'j and Gardnerg have derived an expression for the fin efficiency tan h mh n= mb \\-here Ale

=

k = conductivity of fins and tube, Btu/(hr)(' F) (sq ft/ft) = perimeter of fins, ft = cross sectional area of fins, sq f t = height of fin, ft

P a, h

The fin efficiency, thereforc, provides a means of accounting for the \-ariation of material of construction, slze, and arrangement of fins. De1,ormzo and Anderson4 correlated data for a number of extended surface arrangements using the Sieder-Tate form of the equation plotting:

De is the equivalent diameter defined as

r:

*1

( h 2 - Dl2)

- cross sectional area of fins1

T

ahere Ill Dz

= =

total \vetted perimeter of fin side

1

outside diameter of inside tube inside diameter of outside tube

This correlation enables cak:ulation of h , which can be converted t o hi, using Eq. 9. Knowing h , , the inside film eoeffirient, the clean inside coefficient 1,ri can hc mliwlat,ed. The design value of T i i must be determined by adding thc nppropriatc scalc or fouling factors. The fouling factor on the fin side has the same complex relationship to the resistance

Shell a n d Tube Exchangers Outside Coefficients

The outside or shell side coefficient of a shcll and tube heat exchanger has proved the most difficult coefficient t o correlate. It was early agreed that for forced convection outside of tubes an equation of the same form as that used for flow inside the tubes would apply.

where Do = outside diameter of the tube, f t But because of the variations in baffle and tulle arrangement it has been a real problcm to eorrelatc data for all shell and tube exrhnngcrs wit11 one equation. Colburnz proposed the equation

where a = 0.33 for staggered tube arrangement and 0.26 for in-line tube arrangement Essentially these same data are presented in the Standards of the Tubular Exchange Manufacturers A s s o c i a t i ~ n . ~ JG,,, is there callcd Geir (effective mass velocity) which is defined as the pounds per hour flowing divided by an effective cross flow area. This effective cross flow area represents the factor most difficult to define and no attempt is a r t w ally made to do so in the Standards. It must someliow take into accuunt design clearances, baffle spacing, leakages, and by-passing. Such factors vary with the manufacturer. I n our present state of knowledge each manufacturer has developed some means of obtaining an effcctive area that permits good correlation of design data with actual operating performance. Curiously enough it has not been until recently that a systematized approach to the problem of shell side coefficients for commercial exchangers* has been made. A research program at, the Cniversity of Delaware under the joint sponsorship of the ASRIE, API, TIC>IA, and many exchanger manufacturers and operating companies is in progress. I t involves the study of idealized models in order to isolate the variables, and will be follomd by a study of full-scale con~mercial

* Short20 has made a study on a lnhoratory exchanger which has heen u i great aid to exchanger designers.

232


Heat Exchangers

exchangers. It is l~opedthat u>efuI ancl IIICIW wliaI>lt~mrrelations \\-ill be produced from this n-urk. For thr reailrr 77-lio does not have access to the various confidential conlpany chart? or procedures for empirically estimating the outside coefficient, the equation presented by Donoliue7 is suggested as the most reliable. nonohue proposed the equation:

( )

hDo - = 0.22 DG,

'6

c here h

latent heat. of condensation, Btu/lb 32.17 at = temperature difference between saturated vapor and condensing surface, F Do = OD of tube, f t I, = tube length, f t 18 = lh hr G' = Xass ratc of condensate, (lb/hr) (sq ft) Q.

(T) C,p 0 33 (f)O1'

1;

where G, is defined as W S , and If'

=

1h;hr of fluid flo~ring

s*= d(crossflo\v a r m ) (hafflehole area) = v SnS, i-

= =

The crossflow area S,is arbitrarily based on the inside diameter of the shell. S,'

where B

=

N

=

IIj

=

=

[ ( I D ) - ( D o )( N ) ] [ B ]

IV

Vertical tnhe: G' = 7TDo

(14)

baffle spacing, ft number of tubes at or near inside diameter inside diam of shell, f t

Horizontal t,ube: G' p =

The haffle hole area is: Su

=

Area of segment

- area occupied by

tubes

Donohue's correlations based on this effective area exhibit reasonable accurary when applied to wmmercial cxchangcrs. There are many other correlations for arriving at an effective arca involving much more tedious calculations. The order of accuracy oi such correlations, h ~ n ever, does not appear to justify thc additional effort required. condensing Coefficients

The cr~ndensationof vapors on the shell side of horizontal exchangers is an important operation. Unfortunately the tlicory, altl~ouglirolmi~inous, is very inadequate. I t can be said with impunity that thc dcsigu of a process condenser, particularly one inrolx-ing mixtures of vapors is an art. The novice can best use typical ovcrall caefficicnts and avoid a large amount of calculations, the interpretation of which is difficult and qucstionablc. Using a highly idealized mechanirm Nusselt,l7 considered the condensation of pure vapors on both horizontal and vertical surfaces. The follo~vingcxprcssions were derived based on viscous flow. Horizontal tubes

h

=

0.725(kl3Xp;'g/Dopj

Vertical tubes

h = 0.913 (I;f3Xp,2g,/pjL at)'

233

=

W L

-

deusity of condensate, lh,'cu ft

Subscript f refers to properties at the film temperature. Because of the similarity of eq. 17 and 18 they are often written as one equation using an averagc constant 1.50 and an appropriate value of G'. Horizontal tubes in vcrtical r o m present an additional problem since splashing increases turbulence. In addition thicker films rle~relop on each successive tube which inakes the lower tubes lees effective. If the tubes are staggered, results nould be expeetcd to differ from that obtained fur the in-line arrangement. LIclldan1s,'3 Donohue,G Kcm,I2 and others liavc proposed ~uctlio~ls for calculating thc G' for banks of tubes to be used in the Nusselt eyuation. Kern suggests the follo~ving:

Horizontal tubes: IT

G'

W Nti3L

= --

here .VL = total number of tuhes IT7 = total cundenaitte flow rate, lb/hr

For siiiqile rapors approximate condensation coefficients for the outride of i~orizoutaltubes and for the inside nud outside of vcrtical tube?' can be predicted fnlm the equations of Nusselt. For turbulent flow of the condensate and high vapor veloeit,ies there result larger coefficients than predicted from the Kusselt equation. AIrthods for calculating coefficients urrder these conditions have been ,ii*cussctl.':J Often vsl~urseuter a cundenser superheated. Part of i.lle condenser

234

Heat Exchangers


acts as a gaa cooler and that portion in gas cooling service operates with a much loum transfer coeficient. Such situations are hest handled by cnlrulating mrli section wpiratrly. A weighted overall transfer coefficient and a weighted i t are reported.

235

condense first nt the l~igllcrteu~pernturesand arc aui~cooledns tbey progress tm\-ard the end of the rxcl~nnger. Tlic cxclinngcr designcr sl~uuld he s~qipliedwith x condensation curye for use in designing such excliangers (Fig. 13-111. The temperature oi the condmeing mixture ia plotted versus thc heat rcmovcd from tbe mixture and is ohtained from flash m p o r

r refers t o the condensing section G refers t o the gas cooling section Atwt =

9 9% -+At, 4to Po

where q = total heat transferred q. = heat transferred in condensing section qo = heat transferred in gas cooling section At = mean temperature difference The cr~ncleuwtiou[if a single vapor in the presencc of noncondensablcs or the condensation of mixed vapors is a difficult proccss to analyze. I n each case Trapor must diffuse through a gaseous film before reaching the condcnsing surfacc and the phenomenon is one oi heat transfer combined n-it11 mass transfer. Rigorous methods for considering both diffusion and heat transfer in the determination of a condensation coefficient have been d c s c r i h e d . V h e s e metllods are admittedly tedious and involve trial-and-error solutions. Many "short-cut" methods have been proposed, thcreforc, involviug certain simplifying assumptions which were known to be incorrect. The methods in current use can be divided into t v o classes. One considcrs heat trnnsier alone, assuming that tlie lieat flows through a series of resistances, including a vapor film, a condensate film, tube wall, dirt, film, and a co(rling liquid film T h e other, the more rigorous, considers both heat and mass transfer. It is neitlier possible nor worthwlrile to reviciv the various methods which have been proposed. Curiously cnough, the accuracy of any of the available methods is poor. The best, proccdure is to adlrpt the method m ~ l s tconvenicnt for one's o x n use and employ it continuously. Calculations hxscd on this method should bc compared a t every opliortunity with operating data so that tllc designer can develop a sense for the relationship h e t u w n the actual coefficient and a calculated cocfficicnt. The members of the Tubular Exchanger Alanufaeturers' Association are well aware that existing condenser calvulatiuns arc inadequate and attempts are being made to remedy the rituatiou. 111 the cundenaation of multiconiponent nlixturcs tlie licavy matt&~la

Heot Duly, ~ t u / h r 4

Fig. 13-11. Condensnbion curve

equilibrium calculations. This curve is a great aid in designing a condenser, since it indicates thc desuperlieating and suhcooling regions and also is uscd in obtaining a wcigl~tcdtcmperaturc difference, as described below. Boiling Coefficients

The calculation of boiling coefficicnts in the design of rehoilers and similar equipment is, at this atagc of dcvclopnicnt, practically impost.ible. Most designs are based or. some allou-able h a t flux (q/A in Btu/(hr) (sq f t ) , since q/A = C A t , Zi can he determined from the a l l o ~ a h l eheat flux and a n acceptable value o i At \vliicIi is based on practice. For organic liquids in forced circulation Kern" suggests a maximum of 20,000 Btu/(hr) (sq i t ) and 12,000 for natural circulation. As in coudensers, often a portion oi the reboiler is used in tbc t r m s f e r of sensilile heat, and in these cases the scnsible heat rrgion and the boiling region are considered separately. Pipe WaM Resistance

The pipe v a l l resistance given in eq. 2 is rcadily calculated, since the conductivities of most metals used in heat excbangers are d l known. It is most often vcry small in comparison t o the other resistances and car1 be neglected.* * Kot true for liquid m r t d lieat trnnsfrr whwe pipe wnll resistance may be controlling.

238


Heot Exchangers

the generalized chart f i r liydrocarl~onsin TEXlh.23 For nonviscous liquids (brlon. one i,entipoi:r I at ml~derateterripcrature ranges, the value of F, is 0.5, and tlic caloric temperature then is simply the arcragc of the inlet and outlct teniperatures. Such is the case for most inorganic solutions. Sieder21 has suggested the following rules: (1) For water-cooled units. use an F, of 0.3 for the shell side hot fluid; (2) for steam-heated units, use F, = 0.,55 for tlic shell side fluid being heated; (3) for oil-to-oil excliange~susc 0.45 for botl~hot and cold fluids. The average temperatures thus calculated are used to evaluate the properties appearing in the heat transfer film coefficient equation.

t o the loss of one velocity head and that the channel and floating head

Pipe W a l l Temperature

In the Sicder-Tate equations it will be noted that a value of the pipe wall temperature is required in order to evaluate b. SiederZl points out that this can frequently be assumed t o bc equal to tlie outlet vater temperature in oil-~5-atercoolers. I t may also bc estimated by simple calculation based on fi1111 c~efficients~vhichwere calculated assuming r/p," = 1.0. The following equations are used:

+ R(T - t )

Cold fluid in tubes:

t,

Hot fluid in tubes:

t,=T-R(T-t)

where t,

=

t T

=

R

=

R

=

=

=

t

pipe mall temperature average cold fluid temperature average hot fluid temperature ho hi(4ilAo) h,(Ai

losses bc assumed to be equal to four velocity 11cads per pass. An accurate shell-side pressure drop is just as difficult to ealeulnte as an accurate shell-side coefficient. A number of equations have been proposed. The equation presented by Chilton and Genercnuxl is perhaps the most familiar.

where AP = pressure drop, psi per pass urn, = velocity based on flow through space betveen tubes p = fluid density g, = 32.17 N = number of horizontal rows f = friction factor This equation gives the pressure drop across the tube bundle. Values of the friction factor were determined by Grin~ison'o and these data as later analyzed by Colhurn are presented in TEhIh Standards23 correlated with tlie Reynolds numher. Just as for flow inside the tubes. tlic friction factor obtained from the chart is divided by the correction ( e / h ) '.I4. In addition to the cross flow pressure drop a pressurc drop also occurs as the fluid passes through the baffle opening. Tbis opening can he considcrcd as an orifice with a discharge coefficient of 0.7, as shown by Donohue.7 Pressure drop througli tlie baffle opening then becomes:

+ ho for standard tubes

h,hi,di &)(hi

+

239

+ hi,)

for h n e d tubes

Pressure Drop

The problem of dcterrnining the pressure drop in a shell-and-tube heat cxchanger is conil11ic:it~riby the progressi~echange in temperature of t,he fluids. Sieder and Tate,2? hoxever, discovered that for flow inside tubes the usual isothermal friction factor rould be used, if it is divided for Rcyncdds' numbers above 2100, m d by a correction, + = ( l l / l r , , ) " . ' 4 (p/I*w)O.", for Reynolds' numbcrs belov 2100. I n addition to the actual friction loss in the tabcs, therc arc loares in the channel and floating heads due to abrupt changes in direction, and losses at the entrance an(l exit. Kern12 suggests that the entrance and exit losses be estimated equal

where u = velocity through baffle opening, ftlsec p = density, lb/cu ft g, = 32.17 A P = pressure drop, psi per baffle opening The total shell-side pressure drop ia the sum of pressure drops of cross-flow, baffle opening, and tlie entrance and exit. Research scientists a t the University of Delaware are studying and correlating she!l-side pressure drop data. These data should prove valuable, since the accuracy of existing methods is quest,ionable. DESIGN PROCEDURE

Designers of heat exchangers must be given certain information hefore they can begin the design. In order to prevent delay, the projrct engineer should see that each manufacturer who is Lidding on an excliangcr is


Heat Exchangers

Exchanger Specification Sheet ~-

Cllrtourrr ---

luh no. Referenre no.

lddr?"r - --

1n'iuiry no.

I'h."t

Date

-~ ~~

locatlo"

srmice 01 ,,nit sire - ~Sllrinco per unit

Item no. Type

Connerfcd in

Shrllr pcr unit

Surface p ~ ahell r

Performance of one vnlt

Heat -. rxohanged-Bta,hr Tranafer mto-rrvier

I

I

I

X1.T.D. (Corrected! Clesn

construction

Fig. 13-12. Excbaneer specificstion sheet. [Reprinted by prlmissian. Stundards oj the Tubular &rehangcr M a n u f o c t u r ~ r s.4ssocinlion, 3rd Ed. (1952) I . 240

I

I

241

provided with all the necessary infurlnation t o complete a satisfactory design. The Tubular Exchanger AIanufactnrers' Azsoeiation has prepared a Standard Exchanger Specification Sheet23 which serves a s a handy reminder of the information required. \lost exchanger n ~ a n u f a r turers use this form t o transmit information on the heat exchanger they are proposing. The same sheet is also valuable as an inquiry form (Fig. 13-12) since the upper portion of the sheet describes the performance of the unit and has space for information that mnst bc supplied by the ultimate u m . The following essential data* are required. Fluid Circulating. Common materials such as water need only be identificd h p name. Complete descriptions of less conunon materials are necessaryl however. If thc fluid is a complex misture, its c,on~por;ition should he given and if it is compo.;ed of several phases (rapor and liquid), these should be defined and the amount of each estahlirhed, including the amount of ~ a p o r i z a t i o nor condensation expected in the cnoling or hrating process. Generalized correlations are available for cstirnating ]nost physical propertics of hydroearhons when the specific gravity anrl boiling point are known. It is prcferahle, howerer, to pro\-id? tlrc designer ~ ~ - i t h ai. nluch physical and chcmical data as is possible. Specific Gravity or Density Jol. Liquids. This inforlnation is required for the calculation of mass flowing and the estimatiun of other properties from generalized charts. Molecular Weight. AIolecular xeight is important in defining the properties of a gas. T'i~cosity. As scen in the discussion on tlworetical aspcrts of hrnt transfer, viscosity data arc perhaps the most importnnt 11hysical data required. Viscosity is significant in both hcat t r a n d e r and Ixessure drop equations. B t least t ~ v ovalucs of viscosity a t differrmt tcuq~eraturcs within the operating range should be given. Additiond v d w s can normally he obtained by interpolating on a logarithmic plot of tenlperaturc versus viscosity, assuming a $traight-line relationsl~ipwith trmprrature. For hydnxarbons morc accurate estimation is possible using .-\ST11 kinematic viscor;it,y-trinperi~tt~re graph paper (Chart 11. .&ST11 D-341 1 1.atent Heats and Sperific H ~ a t s . Altl~ouglrthe (Iuty ~f the r x ~ l ~ i u ~ g e r theat exchanged in Rtus per hour) is included ill tlw tabulation. latent heats and specific heats should also bc given. Thc man~~factnrers' dcsigner can then check the duty calculations. Specific beats are alsu used in t h calculation of transfer coefficients. Whcre pussible, several ~ a l u e sa t tenlperaturcs in the operating range should be given. Covosion. The designer should be given any information on the corrosive characteristics of the fluid and any unique hazards asrc~ciatedn-it11 the transporting of the fluid. * A m w e lletnilcd discussion a i this prohlcm has been given l,y Oti.,r.'" Sanre oi his *wewtiuns hnvo I w n inwr~ml;ttr,rlin tlic ;hove diseusrion.

242


The procedure for the design of a heat exrhanger has been outlined in several bonks on heat exchange. K e r n ' V n particular, has given some excellent illustrative prohlrms xhich show the pl~ilusophyand factors involved. Since tlie calculation of film coefficients depends upon the type and design of exchanger, it is necessary t o assume an exchanger type and size in order to determine the overall coefficient by calculation. The general procedure is as follows: 1. Specify process conditions. I n addition to the quantities flowing, this includes specifying the inlet and outlet telnperatures of all streams. Charts for the deterniination of optimum cooling ~vateroutlet temperature have been prepared. I n general. hoverer, thc ecuno~nicfactors are not well defined, and use of such charts is questionable. Certain conditions, however, make the selection of the outlet water temperature simple. For many waters it is necessary t o keep t21e flon. rate above four ft per second to prevent the growth of algae and it is further necessary, a s suggested by Iiern, tu avi~iilheating the water t o temperatures much higher than 120" in order t o prevent excessive corrosion. T h e r e cooling tower water is elnployed the operation of the cooling to~vershould be eonsidered in conjunction ~vitlithe selection of the outlet water temperat,urc. When heat is being exchanged bct~veentwo process streams, the optimum temperatures must be determined by an economic study, balancing exchangcr eirsts and utility costs. This study must include the other exchangers, coolers, and heaters required for the two streams being considered, since alteration in tlie outlet and inlet tenlperatures of the heat exchanger will affect the size of the other units. 2. Route the fluids. Certain general rules for the routing of fluids have been developed through the years. High pressure fluids and corrosive fluids should be routed through the tubes, since it is cheaper t o design a tube for high pressure than an entire sliell and only the tube need bc resistant t o corrosion. Higll-fouling fluids, including water, should be routed tln-ough the tubes. Because of the flexibility possible in baffle arrangements, extremely large volumes of fluids and very small volumes of fluids, as v.ell as viscous fluids, are best passed through the shell. When lox+-pressure drops are required the shell side should be used. 3. Assume a design overall coefficient and calculate a trial area. 4. Select the length, arrangement, pitch, and size of tubcs. Standardization nhere possible is desirable. This permits ease of maintenance, requires tlie stocking of feurcr parts, and makes for more attractive plant appearance. It should be re~nembercdthat short tubcs are much more expensive per square f t than longer tubes (twclrc or sixteen i t ) . 5 . Detcnnine the niinimum numlwr of tube passes I~asedon the total number of tubes corresponding to the trial area. The number of tube

Heat Exchangers

243

passes depends on the alloivablc prrssurc r l n ~ pand cost of ronstruction. A reduction in the nuuiher uf tulle passes helow the nlininlrnri will result in a lower transfer rate and tlius highrr surface areas. At this point a check of the tube side pressure drop shonld \IP made t o be certain that the nnrnhcr of tube passes chosm is satisf:irtory. 6. Select the numher of hell passes which xi11 give a correction factor ( F T ) for the log-mean temperatwe diffcrmre of 0.75 to 0.8 or greater. Below these values of F, the curves for Hie corrrctiun factor k~ccome quite steep and a small change in ten~peratnreconditions cansci a large change in correction factor and consequently the ultimate mean teniperature difference. I n this regiun, therefore, it is reasoned that inherent errors in the assun~ptionsmade in the derivation of tlie correction factor become significant and thus the rrgion below 0.75 to 0.8 should he a v ~ ~ i d e d . If the FT correction is too low for a me-shell pass, often a tvo-sl~ellpass arrangement mill provide a larger F , wl~ieh ill be accept,zble. I t is t o he remembered that twu one-shell pass exchnngcrs connected in series are equivalent t o a two-shell pas? exchanger. 7. Selcct a ~tsn(1nrdexclimger to rnrrt as closely as possible the requirements of items 3, 4, 5 , and 6. Determine the tube side transfer coefficient. 8. Proceed t o the shell side and assume a trial baffle spacing using a sniall spacing for a small amount of fluid and a large spacing for a large amount. Thesc spacings according to TEhI.4 may he varied from onefifth the shell diameter to one shell diameter in order t o meet the heat transfer and pressure drop requirements on the shell side. 9. Determine the shell side coefficient. 10. Calculate the overall clcan coefficient and then a design coefficient based on proper fouling factors. 11. Determine required arca. Compare this to the surface area of the unit selected. The ideal chilice is of course the minimum arca that will produce the required heat transfer. If the exchanger selected docs not meet the requirements, it is necessary to assume a liiglier snrfacc area unit and repeat the procedure. These steps require t,rial and error in many portions of the calculation. For tlie novice or one who rates exchangers only occasionally. tlie joh proves tedious. Frequent calculation of exchangers, and particularly calculation of exchangers in similar serrices, enables an engineer to develop know-how or perhaps a e,lairvoyanre ~ l i i c heliminates to a large degree the laborious trial-and-error procedure. Short-Cut Methods of Heat Exchanger Design

Many so-called short-cut methods for the design of lietit exchangers have appeared from time to time in the literature. A number of such

244


Heat Exchangers

articlrs privent r u r w c or nomogr)i~~lis for drtti~~niiniiig film rocffit,ienfr. Hntcliinson" has compiled charts in graphical form for the determination of film coefficients for a 51-ide assortment of ron~pounds. I n addition. many article* have presented a series of charts rlesigned to reduce the labor in heat excliang~rralculations. Unfortunately, ho~vcvcr,the occasional user of such charts finds i t just a s difficult and time-consuming to design a n exrliangcr using these charts a s to follon- t h e method previo u l y outlinnl. Sieder?' l ~ psr c . ~ t ~ n t r:Id number of l m t transfer ta1)Ie~:in hooklet f m n v11ir:li ennlile rapid estiu~atioilof film corfficicnts. T h e d a t a are presented in tabular form in order to climinnte mistnkes t h a t arc so often made when using graphs or noniogmplis. T h e sources of all d a t a are pliiinly given so t h a t one m a y evaluate the information intelligently. These tahles are particularly recommended for engineers who only occasionnlly need to clierk heat exchanger ratings, such a s t h e project engineer. T h e only truly slinrt-cut nietliod of lieat exchanger dcsign is t h e one in n.liich the overall coefficient is a s s u m ~ dlinwil on previous experience and from n.hicli a n a r r a is citlrulatetl. Such a nirtliod i . valid for rapirl estimation and comparison of heat exchanger quotations. T h e selection of a n orerall coefficicnt can often be made with a fair degree of accuracy, particularly when good opcmting information is available on exchangers in similar services. I t \v~iuldhehoove the project ll coefficient,^ for various enginecr to keep a record of typical o ~ ~ c r ntransfer exehangcr 3erviccs. Fair and Rases have prerenterl ii tahle of typical resistances for a represcntatix-e number of fluids. Tltese r a h e s givcn in Table 13-1 are TABLE 13-1. Design Resistances for Shell-and-Tube Heat Exchangers* .

Aroni:~ticliquids Benzene, tolwne. ethylhennene, st,y~.cllc Dowtherni Inorganic solutions CaC12 Brine (25'h) Heavy acids KaCI Brine (20 9;) Misc. dilute solutions Light hvdrocarhon liouids 3 , C;, G Chlorinated liydn,c;i~~h,,ns ~ I i x ~ l l i l n e o uorgnrrir s liquids .Iretone

Roiling liquid

.

Condensing vapor

TABLE 13- 1

245

(Continued)

Liquid Fluid ( S o phase change) Amine solut~ons Saturated diethanolamine and monoeth:inolamine (CO? arid H7S) - , Lean allline sohltions Oils C~.udeoil T1ie.d oil Fuel oil (hunker C ) Gas oil Light Heavy (tyl~icalof cat. cracker feed) Gasolinc (400' ZP) Heating oil(domrstic 30' ;\PI) Hydroformate Kerosine Lube oil stock Xaphthas Ahso~.ption Light virgin I h h t cntalvtic Heavy Polymer (Cars) Reduced crude Slurry oil (fluid cat. crarker) Stenm V.ater Boiler water Cooling tower (untreated) Condensate (flashed) Rivcr and well Sea wuter (clean and below

Boiling liquid

Cnndenshg vapor

-

125'F.)

* Reprinted by permission.

Petroiezim Refiner, 93, KO. 7, 121 (1954). rrsistanres for ;tram mag. be m u d l higher wlwn noncondmriblps are present as is often t h e ease with low pressure cxl~nustste;~m. P A r;ihe uf O.OOi is suggested ahen doubt as t a the quality 01 m t e r mists. iCondensing

0.007 0.007

Gases in turbulent flow Air, CO, CO?, and N2 Hydrocarbons (light through naphthas)

0.001 0.01:3 0.0035 0.003

0.035

based on operating d a t a and current design practice. T o obtain a n estimated overall design coefficient for a shell and tube exchanger, proceed a s fr~llolvs:

0.001 0.004 0.007

Resistance 0.045

....

. .. .

1. Read values of resistances for the two fluids. Note t h a t no dist i n c t i m is made b e t w e n shell and tube sides.

246


2. Calcul;~tethc rlvcrall design coefficiciit hy taking the reciprocal of the sum uf these t x o resistances. Other exrhnnger t,ypes are estimated by nlultiplying the overall design coefficient for shell and tube exchangcr by 0.25 for extended surface exrliangers and 0.30 for coil-in-box exchangers. The method is recommended for most stanclnrd exchangers, rnusual designs, very large or very small rscliangers, and partial condensers cannot be estimated by this method. EVALUATING EXCHANGER QUOTATIONS

In evaluating heat exchanger quotations the more ohvious factors such a - price, delivery timc: terms, and manufacturer's reputation ~ h o u l dbe considered first. In addition thc important mechanical and design factors should hc carefully scrutiniacd. A tabulation should be made for each quotation romparing the materials of construction, various design featilree, shcll and tube thicknesses, surface areas, and other special features. It is possible that designs for the same service by diffcrcnt manufacturers d l show largc yariations in surface area with comparable variatiuns in price. In sucll cases it is necessary for the project engineer to estimate a surface area for the service in question for comparison. REFERENCES 1. Chdton, T. H., and R. P. Gcnereaux, Trans. Am. Inst. Chem. Engrs., Z8, 161 (1933). 2 . Collhrn, A. P., T m n s Am. Inst. Chem. Engn., 29, 174 (1933). 3. Culbum. A . P., and T. P. Drcw, Trans. A m I m l . Chcm. Engrs., 33, 197 (1937). 4. D c L o r ~ n z a ,B., and E. D. Anderson, h-ans. A m SOC. Merh. Engrs., 6'7, 697 (1946). 5. Dittus, F. IT., and L. M. K. Boelter, Univ. of Calif. Pub. in Eng., 2, 443 (1930). 6 . Donuhue, D. A , ind. Eng. Chem., % , 6 2 (1947). 7 . Donohue. D . .A,. Ind. Eag. Chem., 41,62 (1949). 8. Fair, J. R., and Howard F. Rase, Petroleum Refiner, 33, KO.7 , 121 (1954). Y. Gardner, K. A,. Trans. Am. Soc. Mech. Engrs., 6'7,621 (1945). 10. Grimison, E. D., Trans. Am. Soe. Mech. Engrs., 59, 583 (1937). 11. Hutrhinson, F. W.,induslriol Heat Transfer, T h e Industrid Press, X e w Y o ~ k , 1952. 12. Kern, D. Q.,Process Heat Transjer, McGraw-Hill Book Co., K e w York, 1950. 13. Mebdsrns, W. H., Heat Trommission, 3rd Ed., McGraw-Hill Book Co., New Yolk. 1954. 14. Morris, F . H., and W. G. Whitman, Ind. Eng. Chem., 90, 234 (1926). 15. Mnrmyl W. M., J . Appl. Mechunics, 5, A78 (1938). 16. Tuuselt, IT., Mitt. Forseh. Arb. Ing., 89, 1 (1910). 17. Korselt, W., Z . V e r . deul. Ing., GU, 541, 569 (1916). 18. Otcn, P. S.. Chem. Eng. Prugr., 41, 411 (1948). 19. Sakiadis, B. C., and J. Coates, Louisiana State University Eng. Exp. Station Bulletin No. 34. Baton Kouge, La., 1952.

1

Heat Exchangers

247

20. Short, B. E., 1Jnircrsity of Texas Puhlication Xo. 4324. 1-55 (1943). 21. Sieder, E. Y.,Heat Transfer Z'obles, American Locomotive Co., xea y u r k , 1952, 22. Sieder, E. P;..and G . E. Tatc, Ind. Eng. Chem., 98, 1420 (1036). 23. Slandnids o/ l'ubrtlar Ezchanger Xio,~u!nctimis Association, 3rd Ed., Tubular Exchsngcr Manufacturers Association, Inc., S e w I'ork, 1952.

Process Pumps

249

RECIPROCATING PUMPS

Although the usc of a reciprocating action to produce pumping had it,s origin some 2000 years agol it \!-as not until 1840 that Henry R. Worthington invented the direct-acting, reciprocating. steam-driven pump. These steam-driven pumps hecame extren~elypopular and in the years to come motor-driven unit's also came into use. Application

PROCESS PUMPS The modern process plant xould be inoperative were i t not for the pumps which maintain the steady flow of fluids through the plant and make continuous procrsscs possible. Improper and ill-considered selection of pumps could create serious bottlenecks and cause unsat,isfactory operation of tlrc plant. Close w p c r v i ~ i o ~therefore, i, by the project engineer of selection, purchase, and engineering of pump installations is imperative. Since pumps are prorluccd by tile nlanufacturers in standard sizes, it is only necessary to select thc sizc and type that most nearly fit,s the service in question. Closc collaboration with manufacturers' represrntatives is helpful and strongly nrged. To obtain tile maximum benefit from such collaboration and to properly judge the manufacturer's rccummendations, it is cssential that ccrtain basic fundamentals of pump opcrat,ion be understood. The pumps most cotnnmn to the process industries (centrifugal, reciprocating, and rotary) will be discussed in this chapter giving particular emphasis to the theory and information required for intelligent pump selection. The lack of colnnlent on many special types of pumps designed for specific services docs not imply that these are not t o be considered. Indeed, certain services ahsolutcly require n special design and manufacturers' representatives should be asked for recommendations in these cases. 248

In the early t w n t i r t h centnry. the rmtrifugal pump began to encroncll npon thc field of the reciprocating pnmp. The uniform discharge of thr centrifugal pump gave it a distinct nilvantage. e q ~ w i a l l yin the process industries d m e steady flow 6000 4000 rates are a necessity for satisfactory opcration The applications 2000 of centrifugal pumps x-ere limited , only by design restrictions on 1000 capacity and pressure. Improve- 5 600 mcnts in dwign, l i o ~ ~ r e have r, 0, 400 gmdually eliminuted t h c x restrict,ions and there are now fe~vappli- ,E cations belonging exclusirrly to 100 E, 60 the reciprocating pump. Nodern a 40 reciprocating pumps are bcst 30 suited to high head and lov ca20 pacity. Fig. 14-1 presents a qual10 , itativc picturc of thc range of 2 o o o o 0 0 o o w 2 0 0 0 u.-efulness of rariow pump types. o w 2 It is oftr-n found advautngcous to . . 5Gallons perminute '. . I' elnploy slean-drivcn reciprocnt- Fig. 14-1. Pump selection r h a r t . I.idaptcd i w P ~ ~ for P tewol.ary J installa- from R.L. J ~ C ~ cho,~. ~ S , E,!@ plo0,. .;g; 234 tions or for interniittcnt m t l (19531, I,? pcrmisaionl varying conditions such as tank a r m transfrr pumps. I n such installations the ru~gedness.flexibility. and ccononiical ctraracteristics of thcsc pinnps may he used to an nrlv:mtngr. and theil. unstend? (Ii~chargeis no iiisa(1rantage. T l ~ rcriprocatin:. c 11u111l1 is often prefcrrrd for thr pumping of liighly mhatile lirlnid.; irsprri::lly xhere gassing conrlitioni are possil)le). slurries, and viscm; liquids

-

'

Description

Thc following tabulation gives an abbreviated list of terms useil to classify reciprocating pumps. The majority of all surh punlps wed in

~

,

250


tlic process industries are steam-driven: direct-acting, duplex or simplex, donble-acting or single-acting. T h e double-acting is more c o m n ~ o ucxcept for higli-prt?ssure service for ~ v h i c hthe single-acting pump (usually the plunger type) is more frequently employcd. Reciprocating Pump Classification

(Basrd on tcrmrnology of the Hydraulic Institute) I Unve A. Stcam 1. Direct-acting; steam piston directly connected to liquid piston through piston rod. 2. Crank and flyrvheel; pump with crankshaft, on which the flywheel is mounted. Used for large installations, and uith compound cross arrangements. 3. Types of stcam ends a. Simple; one high pressure steam c)-lindcr for each liquid cq-linder. b. Compound-tandem; a high- and lowprcssure CJ-linder on same rrntrr line. c. Compound-cro.$s; a high and low cylinder arranged side by side a i t h cranks $10" apart. B. Power; motor driven through crankshaft 11. Nuniber of liquid cylinders A. Single or simdex: - . one B. ~ u p l e x ;two C. Triplex; three (power-driven only) 111. Liquid ends A. Pistnn (Fig. 14-Z), packing carried on piston B. Plunger; packing nng is stationary: preferred for high -pressure operation beeansr of else oi servicing and vi8ibdity of packing gland 1. End-nackrd ( F i e 14-21 2. center-packed ( ? ~ i ~ . G - 4 ) C. Jingle-artinp; one pumping stroke per revolution D. Double-acting; two pumping strokce per revolution IT. Armngrment of cylinders -4. Yertlcal; usually for designs with three or more liquid cylinders B.Horizoutal Reciprocating pumps have become standardized over t h e years. T h e various types of pumps and their 11arts a r e illustrated in Figs. 14-2, 14-3, and 14-4. Brief comment on certain of the these items is in order. Materials of Construction

T h e folloxing a r e t h e most frequently used material designations for steam pumps a s given b y t h e Standards of the H y d r a d i c Institute? Bronze Fitted (Symbol R F ) . a . A bronze fitted pump consists of bronze piston rods (except end packed plunger pattern) iron liquid pistons or plungers, bronze or rubber liquid valves, bronze liquid valve scats, guards, *Reprinted by permission from the Stondords oj the Hydraulic Institute, eopyripht 1055 by the Hydraulic Institute, 122 East 42nd St., New York 17, N. Y.

Process Pumps

251

and springs. iron or steel liquid cylinders: b. Bronze fitted piston pattern pumps includc bronze lined liquid cylinders. Bronze fitted plunger pattern pump%include bronze hushed plunger glands and throats. Fully Bronze Fitted (Symbol F B F ) . A fully bronze fitted piston pump consists of bronze piston rods (except end packed plunger p a t t e r n ) . bronze liquid pistons or plungers, bronze or rubber liquid valves, bronze liquid valve seats, guards, and springs, iron or steel liquid cylinders. Fully bronze fitted piston pattern pumps include bronze lined liquid cylinders. Fully bronze fitted plunger pattern pumps include bronze hushed plunger glands and throats. Acid Resisting (Symbol A R ) . All parts of the pump in direct contact with t h e liquid pumped a r e made of corrosion resisting matwisls of suitable properties for t h e specific application. 411 Bronze (Symbol AB). All parts of the pump coming in direct cont.act v i t h the liquid pumped are made of bronze. All I r o n (Symbol d l ) . All parts of the pump coming in dircct contact with t h e liquid pumped a r e made of ferrous metal. Standard Fitted. Individual manufacturers m a y use the tern^ standr~rrl or regular fitted t o designate the material used in punips of their regular production. Discussion of Reciprocating Pump Types

Because of t h e smoother flow characteristics of t h e duplex pump, it is prcfcrred t o tlic simplex. T h e steam slidc valve action on a duplex p i n i p is such t h a t short stroking (iailure of pump to makc full stroke) can occur. This condition in effect increases t h e clearance volume and is a disadrantagc on pumps operating a s wet vacuum p u n p s or in liigl~ly volatile liquid pumping service. Under such conditions the lack of full d i q ~ l a c e m e n tpermits the accumulation of excessive volumes of vapor in t h e cylinder. T h e simplex design does not have this defect and is, therefore, indicated for such services. P ~ s ~ VS. o s PLUNC.ER Pistons are differmtiated from plungers b y their shape and the mode of packing. Referring t o Figs. 14-2 and 14-3 i t can be seen t h a t a piston is a flat disk while a plunger is more like a long barrel. I n addition, piston-type p u ~ n p scarry packing on t h e piston itself to reduce leakage from the discharge t o t h e suction side of t h e piston. T h e plungers in a plunger pump operate through stationary packing in the heads of thc cylinder and a r e classified as end-packed or center-packed according t o the packing location. Thp end-packed plunger pump reqnires no packing hox on the piston rod mhilc thc center-packed pump, like thc piston p u n ~ p , does (see Figs. 14-3 a n d 14-4).


Process Pumps

253

R r r : i ~ ~ rall c pwking lciik:ip{, on 11l111rg1.r p u l n p is clrnrl>- visil~lct,, tilc oprrator and hecause of the ease of repacking or adjusting the packing, thc plunger deeign, although more expensive, is prefcrrpd for revere

L-IW Fig. 14-3. Portion of end-packed plunger. pump

Fig. 14-4

Portion of eenter-packcd plnngcr pump.

services such as Iiig11 prcssurc operation. l l a n y users prefer the plunger I I I I ~ I I ~for I diffc.rcnti:~l pressures nbow 400 psi, erpcrially in high t r n q ~ r r n turc, service. For p r r s s ~ ~ above r ~ s 1000 psi tlic plunger pui~ipis a11110et universally specified d i e n the reciprocating pump is indicated. Reciprocating Pump Paris

(See Fig. 14-2.) CYLISDEHS liquid oylinders are cast iron for most general service pumps: hut, a t high pressures aad tcmperaturcs east or forged stccl is required. the latter being used for extremely high ixcssures.

254


The cylinder sbouki 11e drsignrd for tire full stalling pressure whicl~is the pressure a t d i i r h tlic forces on the liquid piston and steam piston arc equal. Wherever exresaive \,.ear or corrosion is expected a cylinder liner is either bolted or pressed in place. .\lost process pumps are equipped x~itli liners, and a variety of material can be used depending on the liquid and pumping conditions. Xickel and chrome-steel alloys are popular in hot oil pumps. Steam cylinders are generally cast iron sincc the usual steam pressures for pump operation seldom exceed 250 psig. The dimensions of the cylinders and the length of stroke are expressed in this order: steam cylinder diameter, water cylinder diameter, and length of stroke. EXAMPLE: 10 x 4% x 10 10 in. itram cylinder

Process Pumps

255 Other piston packings such as combination duck and rubber, bronze, and monel, arc r~serlfor special conditions. The Standards of the Hydraulic 1nstituteQive detailed recommendations.

Dwk valve. Flat circular valve of rubber or metal, guided by stem fastcncd to valve seat.

Wing valve. Circular valse with guides cmt or foigcd integral, with or without faring. Faring may be rubber, leathw, fiber, or other material.

4% in. water rylirrder

10 in. stroke

VALVES Of the liquid cylinder valve types illustrat,ed in Fig. 14-5 disk and ~ i n g valves are the 1n11stfrequently used t,ypes, the latter being employed for high pressures (above 300 t o 400 psi). The discharge disk valves are mounted on a valve plate which is removable once the head has been removed. Each wing valve is covered b y a pot cover which can be removed for inspection and servicing of the valve. Ball valves because of their free opening are specified for pumping viscous liquids or slurries. Many other valve types are available for particular pumping problen~s. The steam cylinder valve arrangement is standard. Slide valves, direct ronnected or operated through auxiliary pistons, or balanced piston valves are used. The latter is preferred for use wit11 superheated steam.

PISTON RODS Rods are u-ually alloy steel of high tensile strength and hardness, and are preferably made in two parts t o insure ease of dismantling.

PACKING Proper choice and installation of packing is a must for satisfactory pump operation. The h a m pistons are usually sealed with hammerediron snap rings. The liquid pistons are provided with bakelite rings for temperatures below about 250 t o 350" F. and hammered-iron rings for higher temperatures.

Ball valve. Spherical valve oi rubber or metal. Fig. 14-5. Rccipmcntmg pump, valve types. (R~printedfl.om Standards oj t h e Hydi-nulir I n s t i t , d ~ , rupyright 1'355 117 Hydraulic In*itutc, 122 E. 421x1 St., Xeru York 17. X. B.)

Leakage along the piston rod is prevented by the st,uffingbox packing which is r~suallygrapliitc impregnated ael~ertoson thc steam end. On the liquid end the stuffing box packing varies wit11 the typc of flnid and pumping conditions. hsbcatou, rubber, semi-nletallic, and lnetallic

256

I


packingi are ur;ed. For severe conditions such as tho-c cncountercd in the pumping of hot oils metallic packing is indicated. Stuffing box- on pumps operating a t high temperatures (ahore 400' F.) should be weter cooled. Pump8 operating under a liigli vacuum on the mction side or thwe pumping volatile liquids should bc fitted with a lant.ern ling in the stuffing box for the introduction of sealing liquid.

Process Pumps

I

Double-actlng pumps

I

%

Air chambera installed on reciprocating pumps produce smootl~erflov. The air compressed during the pumping stroke cxpands while the piston is reversing and thus forces liquid from the chamher to tlic discharge line. The volume of these chanihers should be six to eight timer the displaccment of simplex pumps and three to four time:: that for duplex pumps.

Flanges on pump cylinders are cast as an intcgral part of the cylinder and may he faccd as raised or flat-faced flanges. Care must he exercised in specifying the proper companion flange to the pumll flangc. If tlie pump flange is flat faced, the companion flange iiiust he spccified as flat faced. The strain produced in tightening a raised facc against a flat-faced flange on the pump may crack the casing. The Hydraulic Institute recommends the specification of tongue and groow typc joints when temperature and pressure conditions require greater gasket pressures than those obtainable with flat-faced flanges. Sizing Reciprocating Pumps

~

0 0204d,2PC

Actual Capacity

The theoretical capacity is never met in practice because of leakage t,hrough piston packing, stuffing hoses, or valves. The amount of air or othrr gas carried into the pump also reduces the theoretical flax rate. Bs is so often the case in engineering, the relation between the actual and throretiral rapacity is expressed as an efficiency called the volumetric cificiency ( E , ) :

1 I

where G, G

I

slip

~

I

= =

act,ual capacit,y theoret,ical capacity

Another term o f t m used is slip.

I

!

where G = gpm D = dinm of plunger or piston, in. P = piston speed, ft/min C = number of cylinders F = factor, 0.5 for single acting, 1.0 for double acting Z = correction for volume occupied by the piston rod during a unmuing stroke

=

Certain designs sucli as end-packed plungcr puinpa require no correction.

Theoretical Capacily

The theoretical cap:icity of a reciprocating pump depends on the displacement of the liquid piston or plunger. E x p r e s d as gallons per minute the equation for calculating the capacity becomes

257

most raws the Tllc rnrrcctirm Z
Hence

E" 1-100

Slip

=

Slip

= ---- =

G - Ga D

Leakage Theoretical Displacement

If the leakage can he assumed constant ~vithspeed. the slip will increase with dwrcasing speeds. At high speeds, however, the leakngc inrrrnacs. The d i p is usually less than 10% (0.10). A value of 370 (97% volumetric efficicncy) is often used for calculating piston diameters fur pumps operating at norlnal speeds. When in doubt, however, 10% iia a safe design figure. Recommended Piston Speeds

!

Based on years of operating experience, the Hydraulic InstituteR has recommended in its standards design speeds which were cllosen at speed8 that would produce the tniniluum wear on the pump.

258


Typical values corresponding to the lengt11 of str~lkecommnnly uwd a ~IUIII~ for ?i11111ler: and ilul~lcxare reporte~l in T:ll)le 14-1. Alt111~11gll TABLE 14-1.

Recommended Piston Speeds*

Sinigl<,a n d Duple.; 131recl-.Actm: Steam Pumps Length of stroke Sprrd, f t h i n 3 37 3% 4 5 6 7 8 10 12

42 46% 53 59 64 68 75 81%

\

Process Pumps

259

pumps operating a t pressures above 300 p s ~ git is often desirable t o base the selection on a speed 0 8 of normal to reduce danger of shock. W a t e r Horse P o w e r (Liquid Horse Power)

Water or liquid horecpol~-eris the output horscpolver of the pump and is calculated in the same manner for all types of pumps. Basically the valculation originates from the general energy equation which is most conveniently applied by a n energy balance bet~veenthc suction and discliarge of the pump. Kinetic and static effects arc usually negligible and the work done by the pump is:

where PD = discharge pressure, psia P, = suction pressure, psia W = 1%-ork,hp G, = actual gpm pumped p = density, lb/cu f t Viscosity or Trmperature Correction Viscosity, or Tcmperutnre, Multiply SSU "F basic speed by 250 1000 2000

70 83 105

1.00 0.89 0.80

5000 6000 7000 8000 0000 10,000

210 260 330 41.5 5'20 650

0.65 0.62 0.58 0.55 0.52 0.50

Note: Base col.rrrtion on tempel.ature or visrasit,y, d l i c l r r r e r is controlling. For

intermdate values, interpolate linearly. *Adapted hy permission oi thp Stnndnrris of the llydroalic Inslittile, Copyright 1955 hy tlic Hydraulic Institute, 122 East 42nd Stwet, New Pork 17, K. Y. v i t h a short stroke can make more revolutions per minute, one with a long stroke ean run a t a higher piston speed. The values given are avernge values bared 11n a widr variety of pu111l)s and conditions. Individual ~n:~nufacturers'recommendations should be used when obtainable. For

The friction effects caused by entrance and exit losses and losses within the pump are all included in the evaluation of the mechanical efficiency. M e c h a n i c a l Etiiciency

The term mechanical efficiency E m is defined as the ratio of work done in the liquid end t o that done by the driving end of reciprocating pumps and generally represents the overall efficiency including the hydraulic losses and mechanical losses. The volumetric losses arc evaluated in the calculation of G,. Steam driven pumps

WHP

E m = -IHP

Power driven pumps

Em =

WHP -BHP

where W H P = water h p I H P = indmator h p B H P = hrake h p Typical valurs of inerl~aniralcfficienries E,,, for reciprocating pumps as reported by J a c k s h r c given in Tahle 14-2.

260


TABLE 14-2.

Process Pumps

Mechanic01 Efficiencies of Steam-Driven Reciprocating Pumps*

Stroke 3 4 li

8

\Iwlxniic:il Etficimcy To 300 psi .\bove :i(M p i 1)iffcrnitiel 1)iffewnii:il Pi-ton l'lunger Pllmger

.i)J

41

ii0

51 54

50

55 60 G5 GS

44

n-here P = stcani linc prcssurc a t pump, psis G = Ilack pressure, psia

R

=

intermediate-pressure cylinder area high-pressure cylinder area

R1

=

lo\\--pressure cylinder area high-pressure rylinder area

Keco~~ullcndcd values of i, to be uscd ~\-licuh:ick pressurc is not known: Simple Compound Triple-expansion

16 psia 6 psia -5 psia

111like inunner tlic iuri:e exrrtcd by the liquid cylinder, since it is al~~my: a single cylinder, m ~ u l dhc

.

E',

Relation Between Pressure in Steam Cylinder a n d W a f e r Cylinder

T l ~ cf o ~ c cexerted by t l ~ ch a m cylmdcr 1s =

where I), hZEI'

= =

("I")

(T) *Da2

steam cylindcr diam, in. mean effective prcssure dctcrmincd from the indicator card diagram in psi

Thc most conniion p~.occsspunip has only one steam cg-lindcr per water cylinder. I n such 11ump&the stcam cscrts full liressurc during thc entire stroke and the indicator diagram is thus n rectangle. The mean effective pressure, therefore, is simply tlic Iicight i ~ fthis rcctanglc. \d-liich is the stcam line pressuro minus tlie back liressure (c1iscli;~rgcirr Ion. pressure steam line prcssurc). Thc value oi hack prcisurc hen not definitely kuon-11can be assumed to be 16 psia. Value;. of LIEP for various steam engine drives can be approximated as follorvs: 8 Type

Formula

Simple cylinder

MEP

=

P

Compound

MEP

=

P 2P - - - bR

-b

R

=

(P,,

- P,)

\\-here PD = discharge pressure, psia P , = swtion pressure, psis D ,= liquid cylinder diam. in

I'.:"(

- --

Recausc of the mechanical fri~.tioneffects tlic water cylinder forcc is less t11an the steam cylinder force. The ratio of thcsc trvo forces is the mechanical efficiency.

This cqu;ition may IK ux11 to calculate tlic stc:i~ncylintlcr iliameter rrlieu the p ~ s ~ u r c:md j \r:~tc.r c?lii~der
A v ~ , r yi111]~~rtt~n1 gri1~111 of punlps in tlie proctw incIt1.4ries is the coritrollcd roluuie l~unip (Fig. 14-G) IT-hicli is used extnirively in iceding

Project Engineering of Process Plods

Process Pumps

ticcurately controlld strc:ims into a process and in proportioning the flo~vsof sevcrid stre:nns to re:ictors and treating or hlcnding tanks. Thesc pumps act not only as 11urnps but also as positive rolumetric metering devices. They are plunger-type reciprocating p u n ~ p s v i t h hall-type valves on hot11 suction and discharge. Units arc built for pumping against discharge pressures up t o 25,000 p i g . Both simplex and duplex designs

porcelain, and rnl~berrequire uuique design features. Onc of t h i ~nlore familiar >perial designs is the diaphragm l ~ m n p ircc Fig. 1 4 - i i Tllv plunge'. of this pump is attached to a flexible ruhbcr diaphrngnr, v l ~ i , , l ;is the only material in contact ~ v i t hthe fluid heing pumped The up and d u a n i~iove~nent of the diaphragm p r ~ ~ d u ct le~~rpruilping i ~ c t i m Thesr pulnpsarc mcll suited for pumping heavy slurries such a s thc sludge from a Dorr thickener.

262

263

CENTRIFUGAL PUMPS The development of the centrifugal pump has been phenomenal. and it is now used for almost eTrery type of service. Indeed, m o d nlanuf'ic t urers produce centrifugal pumps ranging from capacitica of 5 gpul and 2 to 5 psi differentiala t o large multistage pumps capal~leof 11umping 2800 to 3000 gprn a t 3000 p i g discharge prcssurcs. Many designs arc h i l t for successfully handling fluids up t o 850°F: highly viilatile Ruiils, :mil slurries. Special pumps have been designed for evcn morr: in~prcssivcoperating couditions. Punlps a t tllc Col~madoRiver nque'luct can l~unlp90.000 gpm a t 444 ft of head and those a t tlie Grand C o d e Irrigiition Project, 607,000 gpm a t 310 ft of head. Special installations of ccutrifugal pumps in series have heen designed for pressures above 5000 psi. Classification of Centrifugal Pumps Fig. 14-6. Controlled volume pump. (Courtesy of Milton Roy Company.)

can be obtained. A spccial duplex design has been offered which produces a constant flow rate without pulsation. This is accomplisl~edby causing one plunger t o deccleratc a t tlie samc rate t h a t the other plunger accelerates. The units arc equippcd with variablc speed drivcs and micrometer adjustmcnts for accur:~te variation of the piston speed and thus of the flow rate. The uiaxirnum safe speed of these pumps cxcccds that recommended for tlic usual rcciprocnting pump, althougl~in pumping liquefied gascs lower speeds are rccummended. Controlled volun~epumps can be obtaincd either with electric or airnoto or drives. The air motor is often used in hazardous locations in prefercncc to thc more expensive explosion-proof electric motor. These pumps arc \viilely uscd as chcmical feeders, and are constructed of various u ~ r t a l sfor the different services. hlaterials used include cast irons and steels as n-cll as corrosion-resistant alloys and plastics. Other Reciprocating Pumps Spwial dt,bigr~r(11rrriprucwtmg 11un1psare oiten required in thc prtncest: induatrics. Thc use uf surh corrosion rcsistant materials as stoneware,

The confusion t h a t exists in many fields because of misleading nomenclature has not cscaped the field of centrifugal 11uml1s Originally a cvntrifugal pump was a pump t h a t produced its puniping action by means of centrifugal force. As the field grew, howcvcr, new iuq~ellerdesigns produced only part or none of the pumping action hy centrifugal f o r w A11 of these pumps, h o ~ v c ~ ~arc e r , classed a s centrifugal pumps since there is a basic relation between them. I n its broad sense then a centrifugal pump consists of an impeller which produccs a pressure head by rotating in a casing. Thc various cl:wes of these pumps are best dcfined according to the impeller design wl~icll varies from radial t o axial flow types. The classifications given helow conforin t o those suggcsted by the Hydraulic Institute (see Fig. 14-81 1. Radial type. This impeller dirccts the flow of fluid by centrifugal force radially t o the periphery of the impeller. The velocity head thus created is then largely converted t o pressure head in the ~liscl~arge portion of the casing. The vanes of these impellers are usually I r a c k ~ a r dcurved and have a single curvature. The radial impeller is by far the most, connnon type uscd in process plants. Specific speed: 500 t o 3000, single suction up t o 6000, double suction

/

Proiecf Engmeering of Process Plants

264

U Y L T I D U I Y SHEAVE THREE C 9 0 0 V C S

Process Pumps

265

2. M i r e d F l o ~ c . Head is developed with thin impcllcr partly rr.Il. trifugal force and ] ~ a r c I yby the push of the ranes. This is accolnl,lisllcl~ 11y u ~ a k i l ~the p vitncs d0uI11y ~ w r v e dor ~cren.-sI~apcd so t h a t t l ~ ediJcllarge js a combination of axial a n d radial flows. Specific speed: 4500 to 9000

3 "-BELTS

PLAN

Open

Semi-open

Closed

I M ~ x e dFlow Fig. 14-8. Itnpeller types.

i

Axlol Flow

(The three impellers in the top row are mdisl.)

.In inter~nediatctype brtvcen the mixc&flon. an11 the radial i. t l ~ c Francis-type ilnpeller. I t has :ill :~xinlinlet and :I ra
Description of Pump Types and Parts

S E C T I O N A L ELEVATION Fig. 14-7, niwl1r.:wn pump. Dorrco V-type pump. Engineers.)

(Courtesy

D~~~conipany,

I n the acculupanying illustrations aever:il of tile illore C U I I L I L ~ ~cI I~ ~ i t r i i ugal pumps a r e illustrated and parts arc identified. T l ~ cdisrasciou n.ill he confined priluarily to t h e r:idi:il imprllcar rle.+n 5inct. it is bv filr tile uiost c v m n o n in prucvsi 11u111ps.

266

-


The unique requirements of the process industries which often require the pumping of fluids at high pressure and temperature and under corrosive condition. h ~ r caused e the devclopn~entof complete lines of pumps specifically designed for process plants, called proccss pumps. These can he divided into three major typcs: general service, hot oil, and chemical pumps.

267

Process Pumps

of the plastic rasing together. These plates ~ x o t r c tthe plastic and a; in llrunps c ~ ~ n s t r u c tof t ~ alloys, l the bolts do not pass ihrougli tlie gasket.

Water Cooled S t u f f t n g Box Jacket

General Service Pump

Thesc are moderate-priced pumps designed for services which do not require the spccial alloys and mechanical design featurcs necessitatcd hy high temperature or corrusive cond~tions. Hot Oil Pumps

Some manufacturers rcfer to their line of hot oil pumps as process pumpsdthough it ~ o u l dseem desirable to reserve this term for the ilcscription of all pump types employed in pumping process streams. Hot oil primps are specifirnlly designed for pumping hydrocartir~nsand ~-nrimi.;otlicr cheiiiirals or solutions under conditions of high tmpcrature (1q1to 800' F.). These conditions require special constrnction to prcvent undue strain caused hy uncven temperature distribution in the pump hody and supports. In addition stuffing box design and materials of construction must be given special consideration. Generally, these pumps are designed so that the entire rotating element( hearing bracket, shaft, and the impellcr assctnhly) can hc removed without disconnecting any piping or mo\-ing the puml, case or driver. A spacer type coupling (Fig. 14-9) is uscd, and thc pump cover can he unbolted. The rotating elcrnent, and hearing nswn111ly can then be removed as a unit. This makes it poseihle to take the rotating part of tlie pum11 to tlie shops for repairs.

/

I

-

Cover

'\

Water Cooed Bearlnq House Jacket

Chemical Pumps

P u ~ n p sin this category are constructed of corrosion-resistant materials such as alloy stecls, ruhher-lined steel and evm plastics, glass. or stoneware. Hccnuse of the unusual properties and high pricc of such materials, the nieclianicid dcsigo of these pumps is unique, but simplicity of design is stressed in order to reduce the use of ex1.1msive alloyr. The cnsting of certain alloy steels is oftrn a difficult problem. I n order to avoid strains and shrinkage which cause porosity in castings, tapped 1lolcs and busses are vliniinatecl by cla~npingthe two portions of the caring. 'I% icrrange~nmthas the furthcr advantage of elinlinating the 11:iss:~geof holts thr~n~gti gaskets where corrosion can occur unnoticed. .Z typical r~lrcmicnlp111np%-it11a casing c1111str111.ted of plastic is s11on.11 in Fig. 14-10. hletal muunting plates nrc uscd to clatrip thc t x o portions

Thrust Bear~ng

l iFlexible

Spacer Coupling

Fig. 14-9. Typical process pump (hot-oil pump).

All chemical pumps should be designed so that leakage and corrosive action can be easily detected, and so that dismantling and servicing of the pump is simple. There should he suitahlr means for removing stuffing box leakages ~ ~ i t h o damaging ut tlie nonalloy portions of the pump.

268

Process Pumps


Rotation of Pump

In ~perifyingmotors and planning pump in.stallntinns it i n r r c v a r y ~y that t h r draigiration of rotation he stanclardized, It is c r ~ t o ~ n n111 frnm n rlcscrihc the rotation of the pumli as clwk\i-isc or rn~~ntrrrlorlin.isr , t11c 1iu111p. 11o>itio11nt, 1 1 1 ~
269

~ T ~ r C. I R~ C~I.4R, I ~ . A S D DIFFISION C.\SIS(;S .-Iltl~or~gl~ several I I I ~ I I U ~ : I C ~ I I ~ ~ninlic I.;, -iirgIe-dngc pumps wit11 rirculnr casi~igsand claim a n advantage in pumping abrasivc liquids, t h 111ajorit~oi all .single-stagc pumps are built n-itli rolute casings designed so that the avcrage velocity through all sectinns \\-ill be the same. Alan? ~nultistagepumps have n diffnsio~rcasing. Diffusers (see Multistage I ~ n ~ ~ e l l e rhsc)a t e d between stages produce a gradual clinnge fro111 vclocit,y liead to ~ i l ~ ~ - s uheail. rc

I

\~~ERTICU.I,T OR

HORIZOSTALLY $?LIT

Pulnp rasings are either wrtically (Fig. 14-9) or l~orizontallysplit

r Fig. 14-11 I . H o t oil puiuy-. are nsually c~mstrurteclx i t h vcrti~,;rlly.plit

1.

Fig. 14-10. Clrcmirnl pump rvith plnsiii: cnsing.

Sucliolr AND DI~CIIARGE NOZZLE ARR.IX(.E~IEST Altllelnpli gcnel.nl >errire nnd cliemic;d liu~iips ordinarily arc rcntrr suctiuri and top discharge, it is piwsihle to order alternate ilischnrgr nozzlc 1oc:itiims ;it 45' :md 90' \\-itli tile lrorizontal in any of four rlnallrants. I n ail~iitiont o ceiiter suction and top discllarge designs hot oil ~ I L I I U ~ I S arc also built n.it11 top ruetion and top discliarge. T h e latter is morc
(Courtcsy of llisriun I'nn~p

r
Pump C a s i n g s

C a s r s c .\IATERIAI.S Tlic t,ype scrricc ilcterminr~t l ~ econstruction m:~terialsrequired fur the rasing of a centrifugal p u ~ ~ i p .(:e11cr:11 x r v i c e p11111]1 r,asings n l i i r l ~ operatc wit11 rold liquids are cast iron or semi-;;tee1 up t o 300 to 450cl:. and l~ronzefor nll-bronze ~ U I I I ~ S . Hot oil pump casings are constructed of cast .;t,ccI. For lliglr prrssl~re niultistage pumps opcr:~ting ;~llu\-e 1500 psi, hen-ewr, n forged stwl "barrel" liiust be usccl. The intt.rnnl itsrnlbly is fitted into thi* I~arrel and each stagc bas a scpamte inner casing. The outer casing or b a r l ~ is ~l under full discl~arge11ressure arid tlic inner casing is 1111dera comprcsrirr force due t o the differential pressure bctn.ee11 stages. T h e "harrel" is designed as a pressure wssel. T h e casings for chemical pumps vary) depending on the s c r ~ i c c .

. permits the sopport of tilt! 111111111at the sllaft rcntrrline :I> <:lsing~. rIllis that it can expanrl or contract \ v i t l ~ , ~ udanger t of niiaalign~ncnt. Ca-ings vplit on the Iiorizontal centrrline are most r o ~ i i ~ i ~illo 1iunil1.~ ~i iluving iiqiellcrs niolmte~il i r t v e c i ~the l~carings (douhlc-suclion rir. lo\\I"."IUT ~ ~ ~ ~ ~ l t i s t aTghce- upper ). 11a11 is then rmiovable for. rcaily :iccc.ill r,;~scof repairs n.itl~outdi-turl~ingtlit' 11i11ingsince the suctioil and discharge nozzles are lucntcd in tlic Lottom purtion.

t.

T h e casing uf the puliq~m a y he cast intcgral with a rigid fuot support or hox type f r m i e having bolt lioles for mounting. M a n y pumps, particularly in services above 500" F, are supported on pedestals (saddle mountingj a t or near the centerline of the pump. As mentioned prcviously, the vertical split hot oil pump (Fig. 14-9) has a support of this type a t the liorizontal centerline allowing free expansion and contraction \\-itl~out disturbing tile alignment.

270


Process Pumps

271

silmitt,ing suet,ion prcrsure to the Lack sidc of the impeller, t h w achieving R IIIOTC balanced c1cl;ign In any evcnt tlirust bearings are ilrsigne
..

.A,

Fig. 14-11. Douhle-suction centrifugal pump. (Courtpsy of Pwifir Pump Company.) Many manufacturers offer water-cooled pedestals for pumps operating ahovc 500°F. Stepanoff'" cautions that water cooling on turbine driven inrits uiigllt do more harm t11;ln good in certain cases since the turbine mounting is never water cooled and often reaches thc same temperature as the pedestal. I n this case rnisalignmcnt would result if the pump pedestals nerc water cooled. ASD DOCDLE-SUCT~OX PUXPS SINGLE-SUCTION Although double-suction pumps c:m he mide vertically split so t h a t the casing can be supported at the shaft cenierlinc, such an arrnngcmcnt is less connnicnt for scrviring. Hence practically all double-suction pump casings are horizont:llly split. It then fullows that hot oil pumps are generdly pingle suction. Essentially a double-suction inipcller (Fig. 14-11) appcars t o be two single-suction impellers tiiuclling bnrk to bnrk. The liquid enters both sides of the impcller. Since the same suction and discharge pressures act un both sidcs of a double-suction impellrr, t l ~ utlieoretiral axial thrust is zero. Actually, a su~itllthrust bwring is uwd o r tllere punips. The aingle-suction pump lina sartion and discliargc prrssnrc acting on the front imd 1n1y di.wlli~ry(,~ ~ r e h - ~ 1111 i r vits I ~ i dd t a . Ail u i a l iorce outward is thereby rrcatcd ~ ~ h i crcquiwa h :I larger tl~rust bearing. Smle singlesuction p u ~ n p sare built \nth a balancing hule tl~roi~gli tlw inlpeller for

Impellers are cast in one piece and are made of cast, iron, bronze. alloy such as 11-13% chrome steel, or other materials suitable for t,hc liquid to he pumped. The impdlcr is keyed to the shaft and held Feeurc. Several radial impcller types arc shown in Fig. 14-8. They are closed, seuii-cluscd or semi-open, and open. The closrd impell~ris u.sually installed un hot oil pumps and is very common on all typcs of pumps handling clear liquids. The inllwllers of this design h a w sidc rvalls called shrouds which totally enclose the w n c s except a t the periphery and the suction. Closed impellers a1.e in~t:illetl to pro~41lea running contact between the impeller and the casing, thus minimizing leakage from discharge to suction. Seini-open impellers have only one nall or shroud, the bark one. Ope11 impellers have no shrouds, alt>hougllribs or partial shrouds are provided for mechanical strength, especially on the larger sizes. Liquids containing solids in suspension or viscous liquids arc best handlcd 117 open or semi-open inipeilers. These impellers C:UI he cleaned easily and operate with a minimum of clogging. The open impeller requires the ilimplest caating and the least metal; and, tlierrforc, is the lowest in cost, a particular advantage wheu special alloy coustruction is required as in chemical pumps. Rccause of the leakage rneountered in the semi-np~nand open impellers, which increases with near. the effiricncy of thprc pump. after prolonged service is not as great as for the closed impeller. The open and semiclused impeller designs, llo~ve\.rr,give a sliglltly imj~roveilinitial efficiency duc to reduction in disk friction. Although the semi-closed nnd open impellers arc cheaper to fabricate, i t does not necessarily follo~vthat a semi-clo*ed impeller pump, for instance, is cheaper than a closed impeller pump for the same sen-ire. Indeed, hot oil pumps with semi-closed impellers are more expensive than their closed impeller counterpart. This is due to thc mechanical difficutics in making the rlcarance between the semi-closed impeller and the casing a. mininium in order to reduce leakage and maintain efficiencies. Wearing Rings

Most pumps with closed impellers (hot nil. etc.) are provided with wearing rings as illustrated in Fig. 14-9. Sincc these rings arc rerno~able

272


and renervahle. ;I n-orn 1711mpill ".!~icll ti;(, r~luningrle:il;i~~rcl~ctxrcnthc impeller and the casing has become excessirc can he restored to satisfactory operation at n small cod by installing IT rings. The majority of d l hot oil pumps have both casing and impeller rings. Some arc furnished with casing rings only, hut the impeller hubs are oversiacd in such pumps so that impeller rings can be installed when the Iluh has hecome Tvorn. General service pumps x i t h closed impellers usually cmne eqnipped v i t h rasing rings only although some designs have no xvearing ring*. Ahsence of rearing rings is a disadvantage on large pumps n-herc the cost of replacement of an impeller compared to t h a t of a wearing ring is great. Because of the mechanical problem: inrolverl with alloy construction, wearing rings are o f t m not used in clo.-ed-impeller chemical pumps. Care is exercised, however, in the design and manufacture tu provide horizontal xvearing surfaces on each ride of the impeller. Since clearances between wearing surfaces arc Yery small (0.01 in.) it is necessary that thc t v o matching surfaces he made of different materials or o t least of the same materials ~ v i t hdifferent surface hardnesses. Closed iuqicller pumps designed for handling ahrxsire fluids arc equipped with a flushing chamber. Injection of clean liquid into this chamber prevents the entrance of abrasive material into the clearance between the rings. Single Stage a n d Multistage Impellers

Up to about 600 ft of head (600 ft-lb of force/lb of mass)' differential single-stage pumps arc used almost exclusirely. iibove this head, 1 1 0 ~ ever, multistage impellers must he used. 3luitistagc pumps have two or more stages connected in series and can he pnmps of the volute or diffuser-type (Figs. 14-12 and 13). I n the forn~er,each stage discharges into the next through a rolnte. I n tire diffuser pump the liquid discharges into :t diffuser after leaving cach stage. Thc diffuser converts velocity head into pressure head and then discharges the fluid to the suction side of thc next stage. The diffuser-t,ype pump is characterized by highcr efficiencies although in recent years volute designs have been introduced that have similarly high effieicnries. Diffusers permit operation over a wider range of operating conditions a t a sustained high efficiency. lcristal and Annett' report that a t reduced capacities volute multistage pumps can develnp large radial thrusts on thc impeller which have been known t,o cawe shaft failures, but radial loads on diffuser-types a r ~ *The term 1ien.i is aiten sxi,~.eisedin it. Actually it is s. work term on a pound of m:ws hasis. Thc correct units are iaot-pounds of farce (ft-#) per pound of mass (Ib).

274

275


Process Pumps

balanced. This objection has been largely overcome, however, on some volute primp designs by the uc of a douhle volute xvith outlets 180' apart. Opposed forces thu; crrntcil i n u r e rncli:il halancc a t any capacity. On other dczigns radial unbalance is partly ilverrome by staggering volutes radially. Volute multistage pumps are popular cipecially in tlic tn-11 and thrce stagc designs. In high pressurc-high teml~eratnrehot-oil pumps tlic diffuser type predon~inatcs.

with the shaft,. General service nnd many clicmical pumps empl(ly greazc-lnhriratctl hall bearings for both radial and thru.:t bearing. Hall bearings are also useii in mo.1 11ot oil punlps but they arc, oil lubricated. Tlic hearing horising on hot oil pmnps provides an oil reservoir in mhicll the correct oil level is niaintnind hy a rnnstnnt lcvel oiler. Slingcrs or rings attached t o the shaft continuously discharge the oil in trougkrs leading to the bearing. Bearing housings on such pumps arc n-ater rooled. Large high-pressurr multistage punips oftcn miploy sleeve-type radial bearings and Kingsbury tbrust bearings since these bearings are sur~erior for high speed, hcavy duty service. Lubrication of Kingsbury bearings in thesc large pumps is nccomplislied by an oil pump. gear d r i v n from t h r pump shaft. The oil is eirculatcd tilrouglr a small cuoler for tcml~eraturc control.

IrnDeller wearng r n g i

Shaft and Shaft Sleeves

To ~vitlrstirndthe forccs acting on it. the shaft of n rentrifngal pump ~ n n s thc nindc of high tcnsilc steel in alloy (SAE 10'35. SAE 4140. SAE 2340. and various alloys such as 11-13s cchri~me). I n 2111 but very small pumps the shaft is pri~tertcdagainst wear and corrosion lly a sleeve over thc portion of tlic shaft xhich extends throng-h the stuffing hi~x. The choice of sleeve material depends on the nature of fluid being pumped. - ~-

i

r

~

~

~

-

-

-

p

~

~

p p ~

1

~

-

Fie. 14-13. Diffuser-typu nltiltislagr rrntriiog:il p u r r q , . Conrluiny.)

~

~p

~

~

f C u u ~ t r s yof k ? r d ~ . Pump

The prohlcni of I~alancingaxial tl~rnstis in1port;rnt in nlultistagc pumps. T'olutc type designs h n w an allvantage lweanlc 1iydr:rnlir b:ilancc can h i ap])r~xiniated11y arriu~ging11art of tlic inlp~llerrfacing in one dircction nnrl part in the other (Fig. 14-12). Diffuser-type punips cannot he $0 nrrangcd becallse of the nm~lianicnlproblems. The stagcs in tlic diffuser design must, thcreforc, he arranged all in the same direction and axial Lhr~istovercome by means of a lly(lraulio balancing dcvirc employing n balancing rharnl~erwl~ichis connectd to the suction line (Fig. 14-13), The area oi tlic balancing disks is such that the hydmnlic axial thrust of the pump is balanced by the pressure diffcrmtid ijetivccn tlie back f a r e of the 1:1rt stage irnprllcr and the lj:ilani,ing cl~:i~nl,rr. Bearings

Ail pumps, whether e(pipped with hydraulic balancing derices or not, arc ronstmcted ~ ~ i t hot11 l r :I thrnst bearing and n railin1 Iwaring Thc thrust hcarinp is lockrd ~ d i i l vtile r;dial hearing is iree tu inn\-e axially

Stuffing Box

As can be seen in Fig. 14-9 tlie shaft of a pump passes through n stuffing box a s it cnters the casing. The proper design of this stuffing box is :In important factor in tlic successful operation of n 1nnnp, sinre it prwents leakage both in and out i ~ fthc p u n i p The stuffing box can either be packed at: slro~vn in Fig. 14-9 or equipped with a ~nerlianical seal (Fig. 1 4 - 1 4 1 Packed boxes m:~y 11c packed solid or provided with a s c d cagc or lnntrrn ring locnted in the middle of the course of parking (Fig. 14-9) When a punip is operating a t 1mv snctirm preswres air leakage into tiltpump through tlie stuffing box is prcrented by using a lantern ring-seal cage-(Fig. 14-9). Scaling liqnid is injected into the lantern ring and is distribut,ed tlirougllout the packing producing a cooling and lubricati~ig action. A small portion of the liqnid leaks to thc outside through t h ~ stuffing box gland. The liquid being pumped ran he used as a sealing liqnid by piping discharge liquid t o tlie lantern ring. If the liquid being pumped, hoiwver, is corrosive or erosive anothcr sealing liquid must be used. I n petroleum r a special sraling oil is used. retineries, f ~instance. For high teniperatnre operations a circnlating-type stuffing box c5n

276

Project Engineering

of

I N rnqrliqwl so tli~ttt l ~ ccxtvrn:~l si.;iling fiui,l ~ ; U I I N 1,1ro1?11 mid rerirculated. The circulnting-type stuffing box is designc~lso that cool sealing liquid enters one side of the stuffing box, circulates tl~roughit, and t,lien passes to a cooler from \vliich it is recirculated. Sealing liquid (seal oil) systems are often installed in plants having large numbers of pumps that require sealing fluid. The oil can he piped to tlre pumps i n n cornmon header and returned t o n cooler tlrrougb a n o t l m header. The f l o of ~ scaling oil into the pump is controlled by a presiurc 3 constant iliffcrential trrtwccn the suction regulator ~ \ - l ~ i maintains cl~ and seal cage pressure. I n addition to the ~ e a l i n goil, hot oil pumps are often equipped v i t h a !~-aterjacket arounrl the stuffing box. Khenevcr the Lubricating liquid leaking tlirougli a stuffing 110s is a t a high enough tc~~~pcr:tturv to cnwc flasl~ingof flannnnl~lr,noxious. or diaagrecnblr v:~l~nrs, a smothering gland may 11e used instmd of the usual pacliiug gland T l ~ csmotl~eringgland is arrangcrl so that colrl ~ v a t c r i,ntcrs a t the point wlicre scaling liquid touelics tlie gland. T l ~ ex i t e r corrls t l ~ esraliny liquid thereby preventing vnporizatiropcrl?- packeil. (kneral service pumps are usually parked wit11 asbestos-inil~regnaterl g ~ i p h i t e . Packing frrr chcmical pumps must he selected for the specific liiluid to bc hanclleil. I n Irigl~tc~nperuturcservicc snrh as that encountered wit11 hot oil pumps nietallic packing is u;cd. lletallic 1)acking is inteuded for use with h a r d e n d rtcel shaft *lee\-es. Only a soft grade (if packing should be used with sl~nftswlricli h a r e bronze rlervcs. Packing problems have hecome increasingly
277

Process Pumps

Process Plants

sures. It is, tl~crcforc,l~:~rlicula~.ly inrlic:~lcd fur usc in serriccs wtlcrr leakage cannot be tolcratrcl such :IS the puniping of light hydrocarbons which are near the boiling points o r the pumping of corrosive and toxic materials.

/

r Corbon

Gond

Cooling O u t l e t

(Rototesl Fig. 14-14. Merhnnicnl rrnl

(Cmrtcw oi Dumrnctnllir Corporntion.)

For higl~lycorrosive or high temperature liquid:: a d ~ ~ u b mechanical lc seal is employed. It is designed so that a cool lubricating liquid can be injected across tlie seal faces preventing contact by the pumped liquid. Couplings

Flexible couplings (Fig. 14-91 of the steel-spring-grid, gear, spacer, and ~ r i nand rubber bushing type arc used. Thcsc couplings can coml~cnsatc ior slight misalignments but arc not intended a s universal joint?, and g c a t care in alignment r ~ fthe shafts is necessary. Thc flexible coupling is usu:~llyfurnislrc~llry the pump manufacturcr, Irut he n n ~ Ire t told tlrc dimensions of driver shaft so the coupling can be properly liorcd. Base Phtes (Bed Plates)

Pump manufacturers usually supply a base platc on xhich thc pump is mounted and which is drilled t o rcceivc the motor or turbine specified for the service. The purchnwr inus1 supply the pump manufacturer with certified dimensional drawings furnished by thc driver manufacturer (for economic reasons it is usual practice to purchase pumps and drivers separately). The equipment is shippcd separatcly, for mounting in the field. T h e base plates for small lnunps are usu:~llybuilt of steel channel. Base plates for largcr pumps arc east iron and havc a rimmed trough sloping

278

279


Process Pumps

toward one enrl for draining Ieakagc tu waste. Grout holes arc a h provided. On extrcnwly large installation^ i t niay be marc eronunlicnl to inount the pu111l1and driver on sf!pmtc stwl 11alls or sol? plnrri nn t l ~ r integral foundation, rather than provide a common tlase plate.

The curves are usually based on the pumping of clear, cool water. The characteristics for pumping other liquids are not necessarily the same as for water. The characteristic curve is not to he confused with the so-called test curve. Test curves are obtained f11m1an actual test of a particular pump

Drivers

Centrifugal pumps are driven by direct-ronnectcd nn~torsor turhines. \Vlien two pumps arc installed with one to serve as il sparc, a motor is often used for onc and a turbine for the other thus supplying the niaxiinum flexibility. Materials of Construcfion

A distinct advantage of the centrifugal pump is the vide variety of ~naterialsfrom n.hich its various parts can be cmst~wctctl. Casings car1 he rnadr of niatcrials ranging from glass and atonc~vnreto tlie toughest alloy ;.trel.;. Gelieral statcnicnts, thcrcforc, are of little vuluc. It might he said that in 11roccss plants bronze parts arc avoi(1ed in serviccs opemting nhovc 250" F. and cast iron ia not uscd a h w 350 to 400'F. AIl~lys such as 11-13% chrome steels are frequently used for operating ternpcratures abovc 400" F. Centrifugal Pump Calculations Horsepower a n d Efficiency

The water horsepower is defined and calculated for centrifugal and reciprocating pumps in like iixumer. Thc llrake li,mcl~on.er.definul a,< the energy input to thc punip shaft, is rclatcd t o the watcr horsepo~vcr hy an efficiency. This efficiency for centrifugal punips is an uvrrall value and includes mechanical, hydraulic, and volumetric efficiencies.

Performance Curves

T h e graph in Fig. 14-15 illustrates a typical head-caparity or performance curve for a centrifugal pump a t a constant specd and is rallcd a characteristic curve. The corresponding cfficiencics, brake horscpomrrs, and the minimum values of net positive suction head rcquired a t cach flow rate are also given. Tbese curvcs arc furnished by the pump supplier for each size and type of pump that he manufacturers. The headcapacity curve represents the work per unit mass of fluid pumpcd called head (ft-lb of force/lb of mass) a t each possible flow rate. The head, which is often callcd feet of head, can be converted to the differential pressure under which the pump operates by multiplying by the density.

U. S . Gallanr per Minute

Fig. 14-15. Pcr.fol-minrc ruri-r for ;i eent,rifugal pump Inera Company datsi, hy permmsior~.)

(Adapted fmm .Illis

Chnl-

and may bc purchased with t h a t pump for an adrlitional charge. Charaot,eristie curves represent the average performance of tlic type pump purchased and small variations i-wtn-ccn indiridnal pnmps product4 on the same pattern are possible. It is grnerally not necessary or econon~ically rou~rdto rrquebt tcst curves except for large expmsive pumps in ~vliiclicase tlic tcst cost will be only a snlall fraction of the total cost. The niark

I which appears on cliar:irtcrist~ccurves designates tlic head and capacity fur rvliich tlic p u n q ~was snld. The illark

indicates the gu:lrantced efficiency. In general pumps are selected so that the operating point correspunds t o or i3 rlwc t o the best efficiency point (the maximum efficiency obtainahle. usually designated as BEP) As the caparity of n rrntriiugal pntnp is inrreascd, a p i n t is reached at wl~iclifluid velocity in the caring is st] great that local pressures in the

Project Engineering of Process Plants 280 casing decline to thc rapor pressure or helon-. This point is called the cut-point or hreak-point hccauw vapor bnbbles are icrrn~cdand a rapid decline in head, efficiency. and c:ipncity result?. Fur t l k reason performance curves should never be extl~:ipolated.

Affinity Laws

Through the application of the principles of dimensional anwlysis (111 the physical jlropertics affecting pulnl> operation the folloa-ing re1:rtionship is obtained.*

t where Q = capacity, IYI ft w ~ i tima II = pump hcad, St-# '111 II = speed. r r r o l u t ~ i o n ~ u ntime it D = impeller diam, length g, = Ih-ft '(time)2;+. 32.17 if t,ime unit,s are seconds p = density, mass.'oubic length F = viscosit,y, absolute # = pound of force Ih = pound of mass Call the dimensionless expressions a,, aa, and r, in the order in which they appear. For true dynamic similarity, 8 1 , s 2 , and a3, must be constant for similar pumps or for t.he same pump at different speeds. sd, 15-hich vill he recognized as a Reynolds' number since Q'W is proportional to the wlocity, cannot he maintained constant with changes in pump speed or size if the same liquid is pumpcd. I t has hcen shown, ho\'ever, that for practical applications the Ileynol~is'nomhcr can be neglected in considering the conditions for dynamic similarity. Thus the conditions for dynamic similarity are constant values of a1 and m.. The form of e q 1 can hc altered I I :~ppropriate ~ mathematical operation to give the follo~\-ing:

Process Pumps

281

The following conclusions can n o x be made. For the same pumps or geonletrically similar pumps Q/(g,H)'*D2. nW(y,H)", and nQ",/(g,H)"' hare unique ralaes rorresponding to each cfficiencg and these values rcmain ronstaut rrgardlcss of tthe imlxller diameter or pump speed. The constancy of t,he various dimensionlcsa g o u p s expressed above is an ideal case and not completel? true. I t is, hmvc\-er. a useful approximation and several relationships can be derived t h t ~ are t of considerable value to the chemical engineer in determining operational characteristics of a pump vhen the pump diameter or speed is ~ h t n g e d . For the Same P i m p Opcraliny at Dijjerent Spertls: D

=

constant

Hence at an? givrn cfficiency: Capacity

Q

nD

and (g,~)h~~'

are constant (y,~)'~

----

Hence

:. (2

=

K'n

where Zi' and 1< :irr c ~ ~ n . ; t ~ m t s

nl) (!7,HJ

=

constanl

=

J

or Calling n D / ( y , H ) % = a', it ran t ~ cst,strcl that for conditions of simiInrity of Row a,,a2. a110 a ' p ;ire cor1sla111. It has been s l ~ o \ v nthat ~ ~ for similar pumps or for thc salue pump a t different speeds the velocity diagrams a t the impeller are geometrically similar when thc pumps are operating a t the scum effiricncy.

11'D2 - - .J' H

Hence a t constant diameter

vhcre .l and J ' are constants

(1)

282

Process Pumps


BHP 1WP

a

()H rr n3

a t constant I )

283

For geon!etrirnll!/ ,sinzilur p i ~ ~ n pwith s different impeller dianlerers but same speeds:" .\t Hie siuiie eficicncy puints: Capaczly From 13q. 2 ahove,

Q

T h e application of these I a v s is best illustrated by t h e following examI . Remember t h a t these laws apply only for efficiencies of the same value.

=

Iin113

At constant t p c d Q

=

li"L)\n.hcre

K a n d li" a r e constants

or

Head

At constant spccd from c q 4 al1o1r

HIiP I n like manner

Gallons pet M8nute

Fig, 14-16. Estirnat,ion of p e r i o r m a n w curve f o r new conditions.

EXAMPLE: Given the performance curve a t 3500 rpm illustrated in Fig. 14-16. I t is desired to calculate a new performance curve a t 1750 rpm. SOLUTION: 1. Select any efficiency and read off corresponding values of Q and H. 2. Solve for H 2 and Q r

3. Plot these as one point on the Head capacity curve. 4. Plot the value of the selected efficiency opposite h)? as a point on the efficiency curve for 1750 rpm. 5. Enough additional points are selected to enable sketching in thc desired curve. 0. BHP curve is calculated in a similar manner. A whole series of curves can thus be calculated for various speeds. The line d B in Fig. 14-16 indicates a line of constant efficiency (50':;). There are nunlerous such lines corresponding to each yalue of efficiency. I t is only on these lines that the affinity laws may be applied.

Application: A series of curves can be prepared for different diamctcrs when one curve is k n o v n in a nianner similar t o t h a t described allove. CHASCIYO IYPELLKE L)IAMETERS IN THE S.AJIECISISG. Even more import:mt to tlic chemical engineer than the variation of head and capacity in a series of geometrically similar pumps a r c the changes produced by reducing t h e impeller dinmcter of a given pump. A smaller impeller m a y he installed or t h e existing impeller turned-down on a lathe. T h e new ilnpellcr aud casing con~i)inationis no longer g~om&caIly 3ilnilar to the original arrangenient, but the rffect of the diameter change r a n he approximated ~vlienit is assu!ned t h a t the reduction in diameter reduces the discharge peripheral velocity without affecting the efficiency. T h e pcriphernl velocity is dircetly proportional t c ~thc imj~elleriliani&r and hence Q a u a D . Head is proportional to u'/2g, (udlere u is periphcral velocity). These approximations yield t h e following relation. whicli apply a t equal cficienries just a s the previous equations hased un the affinity Ian-s.


286

287

Process Pumps

,'

for water a t the BEP t o obtain values for the viscous liquid. These factors are correlated v i t h the Reynold~'number and are given in the Standards of t h r Hyclraulic Institute!! or in Centrifugal and Axial Flow P ~ r m p s ,by Stepanoff1O The fdlon-ing relations apply:

where H , and H , = head for water and the viscous liquid, respectively E, and E, = ~fficiencg for lvatcr and the viscous liquid, respectively Ca and CI: = corrections for the head and efficiency Since the specilic speed is constant a t the best efficiency point:

Thus (3, (capacity ~vhenpumping the viscous liquid) rr~rrespondingto H , can hc calrxlatcd. A second point can he estahlisl~eda t the shut-off point (0 gpml sine? viscusity has no effect a t 0 flow and hencc the efficiency (zcro a t zcro flow) and head remain tlie same a t shut-off. Thesc t v o sets of points permit the sketching of corrcctcd curves for the riscous liquid. The Hydraulic Institutes has developed a chart more than two points can be estimated so that (Fig. 14-17) f r m ~vliicl~ a loore accurate curve can be drawn. NPSH (Net Positive Suction HeadJ

Peiliaps no d i c r suhjcct in pump design and selrrtion has bcen disf russc~lmore profusely and ~ v i t hless reason than the calcul:~tioni ~ SPSH. The calculation of KPSH is simple and requires no detailed explanatiun. K P S H is simply tlie total suction pressure a t the suction nozzlc of the pump minus the vapor pressure of the liquid a t the pumping temperature . ~

.

Capacity in 100 gallons Per minute

Fig. 14-17. Viscosity correction curves for centrifugal pump performance. (Reprinted from Stundurds of fIyriiaulie I n s t i t u t e , copyright 1056. Hydrnulir Institute, 122 E. 42nrl St., S c w I-orh 17, X. Y.)

USE OF F I G .

14-17:

Given the i:ompirte prrformanre rhararteristirs of a pump v h e n handling rmter. Inrate t h e water enparity at maxin~omefficienr.? (1.0 X Q.*). C:tIrul:tte 0.8 X &,

--

~

p~

0.8 X Q.. m i l 1.2 X Q.,. Head thc wrluea of Cr (rfficiency rot.rcction), P a (enptw ~ t cw~.pction). y and C n ihcnd r.orrwtion) f w all font. capacities hy entering t h e d ~ r t ;,I t h r m t c r mpacity and miding up\r.ard t o thc corresponding head If", ~ l i r nhmizont;illy (either left or right) to the i l r s i r d viscosity i:twr-es u i t h r liqtlid in qrwst~on, and t h m p r ~ c p e i l i ~ l n ~ i i itdo the i.iit.ious c o n w t i m ~ t ~ n eM-lilltil,ly ~ . P;LCII R P : I ~ . iap:trity. m i pfficiency for n n t m by the curr~sponding c~,s~wr.tion ti, ohtain tlir ~ : w r w I e dr;rlucs. I I I I I i n i s t i t . 1)1tin. s t r I I i t . T h e h a d a t sllu-ofi can 1,- t ; h n a s ;il>pi,ximately riir i : m c as that i u r wnlc~..

288


Process Pumps

expressed in foot-pounds of force per pound of mas? (usually rcfcrrcd to as S P S H in feet of liquid punipe~lI .

the dwsity. psi =

KPSH or

=

h, - h,,

XPSII = h',

- h:,

h. = total suction head in ft-#;lb absolute (includes atmospheric ' I ,pressure) , h., = absolute vapor pressure in ft-P ;Ib h', and h',, = ditto except gage pressures in ft-#;lh

xhere

I

Vapor pressure is m ~ s generally t reported as an ahsolutc pressure. socalled Reid vapor pressurcs are gage value.?. S P S H is important in the selection an11 installation of punrps x l ~ i r h handle fluids near or a t the boiling point. If pufficicnt head ahore t11c vapor pressure is not provided, operation of the pump d l he in~possil~lc or unsatisfactory. As the pressure a t the suction of the pnmp ncar- t l ~ c vapor pressure of the liquid, vapor bubbles form in the punlp casing anrl arc subsequently collapsed a t the discharge portion of the casing. This action. called cavitation,* can cause severe pitting oi the imp'llcr ; ~ m l casing. In addition as vaporization increases pumping ceases or hecoioes erratic. -4centrifugal pump can only produce the head in ft-#/lb indicated hy the performance curve. This curresponds to a very lo^ prrsr;ut~ for low density material such as vapors and thus the pump caunclt pso~luc~, the discharge prcsmre required by the system. The NPSII most suitable for 8uccesaful operati1111as repostcd IJ? tllp Hydraulic Institute9 is correlated with sperific speed for hot vatel. anrl correction factors are givcn for liydrocarbona. Xmufncturers reco~nni~~nrl tlie NPSH required for their pumps. Thcae values usually apprar on the performance curve furnished with the pump. (See Fig. 14-15.)

The so-called head of a centrifugal pun111 is actl~allya unit of n.11rli heing correctly cxpressed as ft-lb of force per lh of mass (it-#/lbJ. 31though it is usually just referred to as f t of 11e:td. If this fact is c1e:wly understood, the effect of specific gravity or density of the pumped fluid on pump operation is easily followed. The actual ralucs of head on the periorrnance curve are not aflected by density 'since head is expreawl ILS t11e xurk per unit 111:1ssof fluid that tile ~ I I I I I I ) )d l : ~ r ~ w u ~ p lfor i s l ~:L give11 volume flow. To calculate the wol.k dune per unit Litr~e,l i o u - ~ , v ( , ~ ~ the vuluiue of flow nrust be converted to uiass by inultiplying by thc density. In addition, the differential pressure in psi also depends on

For any given piping n r r a n g r n ~ o ~a t bystcm hrad c n l ~ erim 111' S U ~ P T iu~posedoil the head-c;~l~:icitycurve for tlie l~ump. The system head rurve is composcd of the putmtial (static) lica11, lm.ssure lie;ld, and friction lrcarl. Only the latter varies with flow. Such a plot is shown in Fig. 14-18. The point at wlricli the : I t v o curves cross (Point A ) is tcrmed the operating point for the system. This is the only tlor rate 17-hirh the puml> will delirer unless the characteristics of thc system are changed. Fig. 14-18. Opwnting point of a centrifugnl The usual way to aceou~plish IJ,,n,p, this rhnnge is by throttling the discharge valve. Throttling adds an addkional quantity of head on the system and moves the curvc to thc left thus reiluring the capacity of the pump to some point R which depends on thc amount of throttling. Series a n d Parallel Pump Arrangements

1: I!

I

I

I

*When cavitation occurs in a pump, noisy opemtion ami undue vibration of thr l n ~ ~ t t j > im n gi t n1.e ubsewed.

cn ft,

Operating Points of Centrifugal Pumps

p

Specific Gravity a n d H e a d

(y)(2) (A)

I

IVhen it is impossible to mect the head requirements with a single Imnp two or more pumps in series may he used. Thc flov rate througl~ tach pump is the same a t any given t,ime for pumps conncctcd in series. The heads of the head-capacity curves for the t x o pumps arc adriitivc. Tire clelivery for a given system can he dekrmined by the intersection i ~ the f y s t r ~ ncurve with the nelv combined performance curve. 'To incrcese capacity beyond that available with single pumps, parallel :~rrangcmmt.can be used. I n parallel arrangement the pumps llrodncr equal hearls, and the new head-capacity curve is determined by adding the caparities. Parallel arrangement is often used in pumping statir~ns rvhere demand varies widely. All but one of the punips can then be cut out at low demand periods. The satisfactory operation of pumps in parallel requires that tlie pumps have stable cliaractcristic curves so that TI-ideswings or surges in pumping rates can he avoided. A stable curve is one having n head which constantly increascs toward zero capacity.

290


I

ROTARY PUMPS Rotary 1111nil1.: a r r p~~aitivc~ l i q ~ l a c c u i c npumps t whirh, through rotat~ uienns a t the suction sirlc, :ind rrl
Process Pumps

Each b.a.: sperial advantages for particular a l q ~ l i c a t i o ~ Bc~s. rausc of tlic clwc cle:irance.~ r i r c for certain rotary jnr~nps. allra.:ive fl~iid. cannot be s u c c r s i u l l y lianclled. This doca not apply. lio1verer. t o all rotary p u ~ n p ~Certain . special ~lcsigns of lielical pumps can han~lli. s o l u t i ~ ~ n scontaining Iwgc solid particles. Rotary pumllx arc most often applied in proc:iilr;u~t:~grorlsly IYS plants for pun~llingviscous liqnid n-hicli T T - I I U ~h~r difficult for ccntrifog:ll punips to li;inrlle. T k n z i t i e s a s high as 400,000 wnti-tokes rxn riisily he pnmpccl. Rutary pulnlk are Fig 14-20. Pelighrr;tl pomp itnprller ilimvniannfactured ~%-l~icli are cilp;t- ing r,a,trl.n, hle of discllargc pressures u p t o 5000 11". Engineers engaged in the s e l e c t i ~ ~ofn j~unlpssllould not fail t o investigate tlie many special dcaigns of r ~ ~ t a pumps. ry particularly those for difficult pumping jobs in tlie low capacity range (helow 500 g p m ) . ~

Full pump (a)

(b)

Fig. 14-19. GPLLI.P I I ~ I P S (. a ) External gear pump. (Courtrsy of Gro. D. Ropm Conipmi); ( b ) intmm gcar pump. (Courtesy of Viking Pump Cumpany.) Fig. 14-196 illustrates another t,ype of gear pump, called a n internal gear pump. T h e crescent shape on the inside of this pump acts a s a seal hctween tlie suction and discharge ports. Tfic.:c pumps are manufactured in sizes producing flow rates a s high a s 1000 gpm and pressures of 200 psi. Theoretically most rotary pumps should deliver t h e same volume ,regardless o i discliarge pressure. A certain amount nf running clearancc. however, is necessary in all designs and this causes a small arnount of leakage (slil~!. Tlic slip is inversely prupr~rt,ionalt o t h e pressure differential of t h e pump and is also afiected b y the r i s c ~ ~ s i of t y tlic liquid being candled. Usually, however, the capacity varies only a small amount wit11 discharge pressure. Numerous rotary pumps other than t h e gear type are manufactured.

291

~

PERIPHERAL OR "TURBINE" PUMPS Periplicrnl or "turbine" pumps (Fig. 14-20) drrelop high lieails by re-circnlating thc liquid to the vanes. I n this manner even sm;ill c a l w i t y pumps can he designed for high heads, and i t is in this service t h a t they find their greatest use. SPECIFYING AND SELECTING PUMPS T h e succcssiul selection uf t h e hcst pump for a givcn servicc requires r310sc c o ~ ~ p e r a t i owith n the nianufacturer'a reprcscntativc. TIII, widrly used st:mtlard specifirntion shect aids in the orderly priwntation i ~ 11rorcss information (Fig. 14-21). Recansc t l ~ csprcification skiccts are written in :rl~hreviated form, however, engineers arc pronc ti1 provide sketrhy or iriailequ:~t~~ information. Full details of the pumlling prohlrni nlnit IIB given. ln cmpl,lyiny s;~fi.tyiar.ti~rson tlie required capacity iuid I I C : I ~ . ii is I m ~ l e r ; ~ lti) ~ lgivc ~ : hoth tlic 11l1eratinga n d the celcnlatcd design valurs. It oit1.n lin]~lwnsthat tlle arhitmry safety fnctur I I S C V ~11roduces :I design value n-llicll nccessitntcs the selection u f a mure exllt,nrivc ]lulng. In

f


Process Pumps

,\ncli cases a reductiun of the arbitrary safety factor mill yield lower (Ie-ign cunditions for n-lii(,l~ a leas expensive puulp can be selt.ctc(1. H ; ~ v i n g .. I~lltlldcrigtr :lmd operating ralues, the pump cnginccr cnn spot snrh >ltll:lt i i n s anrl inform the project engineer a t once. E s t r u ronsidcr;~tion must be given to selecting a pump rr-hie11 i? to scrrc as a spare for two pum1,s ol~cratingin diifcrent servicrr." Tllc ~ x r 11cr k unit mass (heacl) required for cneh scrricr :I. ! d l a s the lliftercuti;rl prc.surc :ind capacity nus st he cmnpnred. This i; 11artiri1l:trly ncwzsnry fur centrifugal 11uuil1ssince the liead ~lcreloperl\I? a riritrifngal ln111111 reniainr the ei~rncior a given capacity rcg:~rdleas of the s p w i f i ~ : gral-it?. Tlic spare ruuat of course 11c rliosc~tfor the ~ n : ~ x i u ~ n~m ,o~iditim.

PROCESS SPECIFICATION FOR PUMPING EOUIPMENT PROCESS DESIGN CHECKED B Y DATE GENERAL SERVICE

PLANT

PIC RLJ

SPEC. NO

3,20,5Z

ITEM NO

Furnace Feed

I 1

NO OF PUMPS I N REGULAR USE REOUIRLD AS SPARES

FLUlL

CPLA-2 BR-DO0 P-105

I 1

I

,,n,.uLru

VAL

I

I

CORROSIVE OR NON-CORROSIVE Sllghrly Corroslve CORROSIVE COMPOUNDS I ~..lr,._ SOLIDS ! IF A N Y I Q U A N T I T Y H A N D L E D G / H AT 60°F A N D 761 .''. SPECIFIC GRAVITY AT 60°F A N D 760 M M 1 U.~UL PUMPING T E M P E R A T U R E 'F 150 VISCOSITY-CENTIPOISES AT PUMP'*" T ' L . D 1

I

1

0

293

1

INFORMATION TO BE SUPPLIED BY MANUFACTURER " ,,rlll:lIlee cllr\-c..> 'The uinnuiacturcr sliould 11e rtqncatcd t o sup11ly 11cli installation and opcrnting inrtru~,tiulis,and wrtificd ~litncnaionvrlh a w ings for all pmnps purcllnscd so t h a t accurate piping layout untl fuundatiou iiraxvings can 11c ni;rdc.

PUMP INSTALLATIONS PRESSURE

Location

OISCHARGE CONDITIONSI(AT PUMP)

-PRESSURE P S I i ABS OR -5P G R AT PUMP TEMP A N D SUCTION PRESS -LAPACITYAT OlSCH COND

GA I

ZZO paig

0 810

GPM

294

-REMARKS --i SPECIAL R E Q U I R E M E N T S OF -PUMPSO R ORIVERS.ETC,I TYPE O F P U M P RECOMMENDED

-

Ccntrlfugal

-

M O ~ O F

TYPE OF DRIVER R E C O M M E N D E D REGULAR SPARE

Turbine

---

- - ~

~~

Fig. 14-21. Procc% ylccificatiou form lor pumping equipment. . . t ~ ~ r ~ u ~li. s s1,.~ .J:wks. ~ ~ i ~L'hew , Eng. P r c l g r , 3,234 (lY53).l

~~

[ K e p r i n t ~ d by

P u m p s s l i r ~ u l dbe located a s close a s possihle t o the source of fluid to rcduce the l e n R t l ~m i l cowplrsity of the suctiol! linr. Frcc s11acc fur srrricing both around thc pump and above the put1111 e h ~ ~ u be l d provided I n the case of rcciproc;~tingpump. this space should be ~ d c q u a t etu perinit the ~61110v:11of p i ~ t ~ l and l s rods. I n ndriitiorl t h e area :iroullil the pumps sliould he free o i undue safety Iiazanls. If t h e pumps a r c in u pump liuuse, ;rdeqn;rte air clinngcs shordd he ~ x o v i d e d . Special cxl~aust,ducts a r e necessary a t the stuffing bow^ IIE pumps handling rolatilc ur poisonous tnaterials. \Vhcrc possil~lc,tliertlSore, pump houses sliould he avoidcd. I n general they create addit,iomal expense and liazards and have little real adwmtage. \Then practirnl, process putiil~sd ~ o u l ~hel instullctl in a line o p l ~ ~ ~ ~ i t r Ilazardous procc.?s units. ;\ roadwly or frcc area can then be Iol.:lkll betn-ccn the unit and the p u m l ~ s.;o t h a t they can be serviced \\-itl~out undue interference in pl:rnt operation. This in-linc arrauge~nent makes elertrical c,~ncluit instdlatiun :mi steam piping inuclr s i ~ u l ~ l e:iltl~ougl~ r the 11roceas 1)il~ingti1 mid from t i i t , ~ ~ u m pcan s t,ectnue c m ~ p l i c a t d . It the pro~,csspiping WOLIIII Ix too complex for n certain p u u r l ~it , ilia)- be pwiernblr to plncr that one ~ I U ~ I J I \vitlii~lt h e proc~.ssunit i ~ r e ~ i111 . g e n t ~ ~puulpa l; t ; k i n g m e t i o ~Srtm ~ tl~r area and discharging to auother area arc u ~ u s tuti~rnabletu the rrmotc in-line arrangement. I n operations wlierr fire is not :I hazard punips d~uul~ bei yroul~edclwe to the unit;: being served.

294


Foundations

All plmqis regardless of type rcquire sulistantial foundations ahich n x capable of absorbing the vibrations created hy the pump. Fuunda-

t i m s are generally concrete poured on solid ground n-hich requires in that they pxtenrl beneath the surface of the top soil (see grade or floor level a minimum of one C'llaptw 2 2 ) . They rxtenrl a h ~ m f~iot. Fonnilati(nis for pnnips to be installe(l in-line are often made a ronstant height a l ~ o r cgrade. If the punips vary greatly in size, ho\\-ever, the fin~n~lati~:m lieigllts above grade may be varied so that the pump centerlines are a t the sanlr level. IVlien .so arrangc~l,servicing of the punips \\-ill II(, (mier, since t11t.y x~illaln-ayr hc a t onr height above ground. P I I I I fIo~u~n d a t i u ~ ~sh(iuld r be p1111red rarly to allinn. ixdequate cnring time hci(~rethe pump is installed. Approximately one inch of space Iietvcen the hascplatc flange and the top of the foundation should he allonwi for grout. Tile fonndation bolts (if t l ~ rsizr sprrifird hy the lmgt11 (it is better to have thcni too long 11u11rl1 vcnilor rind of ~r~ffirient since they c:in nlr\-a?s he r,ut 1 :Ire liclil firmly in thc iounil:~tion. Tliey arc cncuscd hy a 11ilic clcrl-e of three to four ti~ncbthe rlianietvr of the holt. This llern~itsmol-cment of the bolt to conforin to tlic tiaseplate holes. After alignment of the pumping unit, a thin mortar consisting of one part renient and t ~ v uparts sand and water sufficient t o make a fluid plastic Inass, i.: injwted under thc haac of the pump. This operation is called grouting and insures fin11 attachment (if the pump base t o the foundaiorni is h i l t around the baseplate to hold tlie fluid gruut. tion. A ~%-iiode~l Holrs proviilcd in tlrc hareplate of the pump permit the escape of air and enable tnmliing of the grout mixture. IIIOP~c h e s

Alignment

1)etailed instructions for the alignment of all pump types are furnished the ~nanufacturcr. Proprr alignnient is essential to satisfactory pnlnp opwation. If the niotor or turhine operates a t :I temperature much differcnt from tlie liu~iip,find :digmilent should he checked under operating conditions or prollcr alloi\-snce made during the initial alignment.

ti?

Suction a n d Discharge Piping

Adcquate provisi~msshould be made for expansion in the design of all hot oil p~itnppiping so that none of this exl~ansionforce is exerted on t l u [ m i p 1,asing. Clever arr;ingemrnt of the piping so that it ran expa@, trcrly i d 1 often ubr-i:~tcthc nrtd of rwstly cxpanrion joints. Hut *uctiw :ind d i s c l ~ a r glines ~ i n ~ IIF t anchored or s u p p ~ r t t ~sol that the pump casing will not be required tu vithsiand expansion thrusts.

Process Pumps

295

Suction lines should be as short as possible and rlcsigned t o keep frietion losses to a minimum. This is arcumplished hy using a n adequate line size ( ~ ~ s u a l one l y Ilr two sizes* larger than the sortion nozzle on the , a minimum number of lirntli. l u m p i , long radius ~ l t i o v can11 Pockets n.11cre @IF or air can nccunulate s111i11ldIJC :ivoided in sudion lines of centrifugal pumps. Eccentric rrduccrs m-it11 t h r ;Iul~ing ~ i d e installed do~vnwardshould be used a t the suction nozzle so that no air pocket ran form. Suction lines should be sloped, where possible, one-friwth inch to tlie foot ton-an1 the pump when the pump is M o w tlie source, ani:l in rlie opposite direction when pump is above the source. Elbo~vsentering double suction pumps shonlrl be installed in tlie vertical. ITlien in>t:illcd horizontal or a t an angle, tlie result is unequal distribution of flov ti, tht: t i w 8idt.s of the impeller. Unless pumps are ~naniiolriedin parallel, a gate valve is usually not used in the suction line. h strainer, howcvcr, app~oxiinatclythree l o four t,imes the cross-sectional area of the suction line is desirable and should be used at l e a d dming plant rtart-up when loose m a t r r i a l ~may he in the lines. IVlien gate valves are installed in tlir suction line, it is recornnierded that they be installed with the stem horizontal t o eliminate chances for vapor collertion in the top of the valre. This practicr, though often recommended, is not follo\ved generally. T o assure minimum turbulence a t the pump suction, a. straight run of pipe approximately three pipe diameters in length should he used between the suction nozzle and the last elbow. Common suction headers for a series of punips operating in p;irallel should be designed for equal velocities a t all points (this approximates equal pressure drops for any pat11 and assures good distribution). Discharge lines can he made smaller t l ~ a nthe discharge nozzle and sometimes are. The available head and economic consirl~rationsdeciilc the size t o use (see Chapter 18). Velocities in these lines mnge from 3 t o 15 ft/sec. h check ~ d v is e placcd hetween tlie discl~argenozzle and the gate valve t o prevent liquid backup in case of pul~ipfailure. A relief valve sliould be installed on the discharge of pouitive displacement pumjie between the pump and the gatr valve. I t sliould be ~ c tto open st 1070 in excess of the maximum or king pressure of tlie pump. A relief valve is not necessary for steam-driven reciprocating pumps which have a stalling pressure less than the niaxirn~nnallowahlc pressure on the liquid cylinder. Pumps having flat-face flanges require tlir use of flat-fiice companion flanges regardless of piping sprrification. *This, obviously, is a mle-of-thumb. Tho size should he governed by thr friction caleulntioos and NPSH required.

296

Project Engineering of Process Plontt

Auxiliary Piping

Auxiliary piping (cooling m-ater and gIand oil piping) particularly t o centrifugal pumps i~ a small hut extremely important item. Manufacturers' sugge.stims on this phase of the piping s l i o ~ l dbe heeded. -411 and thc nrrangtmient, o i tlic piping should ho ralrc. s l i o ~ ~IFl ~ :lcccsiihle l such that ~crricitigand inspection of tlic pump will not be impaired. Priirision for piping o i stuffing box leakage and otlicr drainage away intm the O I I I U ~u i w t )N' ~ m t . i O e j . Sucii I ~ n l i a g eis often collected in :I colirmon siimll for all 1,ulnps from \\-liicl~it is then pumped to n-aste hy :m auto~naticallycontrolled sump pump. REFERENCES 1. Addison.

Hrrhmt. Ccntiiliranl

and

Other. Hotodvr~nmicP ~ r m p r ,Chapman :mi

l\.leG~.aw-HillRook Co., SCW York, 1949. 3. Cllurdi. A , H.; Centrijugal P u m p s nnd Blotam. John ITilcy 6 Sons, Inr.,

COMPRESSORS AND VACUUM PUMPS

?;rw Y w k , 1944.

4. Fincll, V. C., Pump Handbook, Sation:il Press, Milhrap, Caiii., 1948. 5. Jacks, K.L., C h e m Eng. Prngr., 40, 234 (10633. 6. Iicnt, K.I.. .lfechnnieul Engineer's Handbook 11, l l t l l Ed., John Tl'iky 8. Sans, Ine., X e a 1-ork, 1936. 7. liristal, F. A,, :md F. 8 . Annett, Pxrnps, 2nd Ed., hlcGmm-Hill Book Co., Ncw \-ark. 1953. 8. Sirkd, F. F., Direct Acting Steam Pumpn, hlcGwrr-Hill Rook Co., X e w I-ark,1915. 9. Slmrioi-ds o j the Hydinulie Institute, 10th Ed., Hydraulic Institute. S e w 1-ark. 1955. 10. Stepmuff. .\. ,I., Cmtl-ijiigol om1 Arb1 F l o v P u m p s . John IViley 9- Sons. Inc., Kew I-ol.k, 1!)48. 11. Taylor, Irving, C 1 , e n ~ .Eng. Progr., j:, 336 (1948).

Tlnnsjmrting gases and vapors is xe important as the uiovemtnt of liqnirl.~in many clicmical plants since some processes require that feerl gasc:: be coinpressed to elcrated prcssures. T h e compressor station is a plant ~yithina plant coluposed uf complex and cxpcnsire machines wliicll require not only skilled operation but also careful eiigincering in selection atid installation. Coiuprcssor ~i~niiufaeturers usually provide the service. of their engineers to tlic curtoincr or prusl~ectircrurtoiiicr to aid him in sclccting the proper units. Here again, l ~ u m r e rtlic , project engineer must knolr certain fundamental facts if ior no o t l i c ~reason than to m a b k him to ask pertinent questions and carry on intelligent conrersationi with the manufacturer. A listing of conipressor typcs is viinilar t o that for pumps. Uccnurr of the co1iipressi1)ility o i guscs, hoivcrcr. ttic ilesigli of a cunilmwor is f a r I.~ uirm coml,licatrtl. Furthcmiori,. tllc oa. of wcilmratiug I I I I I I I ~!I:IS ~lcclincd to relatircly siiiall prol~ortions,wliile the rcci1,riw;iting ,,IIIIIpressor still does the major l~ortioriof all gar c u r n p ~ e s s i ~ altliorigli ~n, riucc 194.5 centrifugal comllressor w i g c has increased rcmarkal~ly. RECIPROCATING COMPRESSORS

Briefly, as defined by tlw Compressed Air and Gas Iiistitutr:' a reci1~rocating compressor is one in which the compressing clrrnrnt is n piston follon-iug a rcciprocntillg ~iiutiunill :I ~ylildclr. B~V:LII-I, 1 1 1 the 111ar1y t y l ~ e sof reci1rror;lting coinpr<:ssorr llcilig built today it is ,lifficolt to 297

298


299

Compressors and Vacuum Pumps

preparc a rational list of general types. T h e Compressrd Air 8nil Gas I n s t i t n t ~ ~ b u g g e s the t s frrlloving listing:* 1 . I I I - I . C'c~mprrs-irinrti'reted in m r end of eylindrr only. 2. Ilouhle-.&ctiny. Compr&on occurs in both cnds of cylinder. 3. S!IIFIP-S~:I~~. C O I I I ~ ~ ~ Sfrom S ~ O Iinitial I to final stagr orcurs on rach working stroke of the piston. 4. .\Iultiiragr. Gas rompreised from initial to intermediatr pressure in first cylindcr and is conlpletrd in one or more iribsequr!nt c>-linder. 5. Vertical. C:ompressing element in verticnl position. 6. 1lorizont:d. Compressing element in horizuntal position (most common in pnrrsr induitrirs) . 7. Angle. i\h~lticylindrrcrmpressor with cylinder axes a t an angle with pach nthcr (pnrtic~ll:it.l:-ronnmm to imall :~ndportable air compressors I . This tennii- hnsrrl rntirrly on the compressor cylinders. The use of a n ~ l eas a nolo:!. t?-pc no!!- more grnrrall?- refers to large direct connected machimy in which the comprrsaor cylinders are horizontal and the poxrer c>-linders are a t an angle u-ith the compressrr cylinders (see bcloxr). 8. Straicht line. (Single frame)-Horizontal or vertical units with 3 single frame h:~vingone or mrirt, cylinders in line. 9. Dnplex. Tiro par:illrl cylimirrs connrrtd to a eonnnon crank shaft. 1 . Air c . Cooled by natural atmospheric air circul:rtion iim:~ll eompressors only). 11. Wntrr coolcd. Kater circulated througl~jackets surrounding the cylinders (most process comjiressors) .

- .

I

-

Steam

..

.

.

- Flywheel

First

' I

T h e large higll-specd multicylinder compressors which were introduced in the early 1940's have become common t o process plants but their complexity makes the above terminology inadequate in many respects. It &-odd seem preferable t o describe t h e modern process compressors on the basis uf the type of drive. Reciprocating Compressor Types Direct-Connected Steam-Driven

T h e majority of early conipressor installations mere steam-driven units. Use of tl~eseunits is noiv largely confined to small (10-300 111)) I m pressure installations, single stage or txvo-stage tandcrn units n h i c h produce maxiniuni pressures of about 150 psi and 5CiJ psi, respectively. These compressors operate a t 250 to 500 rpm a n d are most popular a s air conlpressurs. T h e steam end is similar to t h a t on st,carn-driven recij~rocalingpumps. Larger 1200 to 1.500 hpi stcan-drix-cn compressors arc generally of t h e horizontal, duplex type in single-stagc or two-stage designs (Fig. 15-1). T h r w cxn hc built for high-prcs*urc operation u p t o 50W psi. Choicc of such :i unit will depend largely on the steam balancc in a n existing or

* Rrprintcd and

Gna

hy pmmimion Cimprrasud Air H n ~ i d b o o k ,2nd Ed., Cumpressed hr Instilutc, I\lcC;~.an-HillBook Co., A-.Y. (1954).

Second stoqe

-

Fig. 15-1. Plan and pictorial view of t~o-stag?,stpun~ilriren~.cciprorntingr o ~ u pwnsor. (Photograph hy eourtcsy of Ingnrsoll-Rand Com~inn~.Pirtorinl ndapted by permission.) Motor-Driven

There is a wide variety of motor-driven rcciprornting rolnpressor designs ranging from small single cylinder niodi\ls (,5 to 150 h p ~to large opposed multicylinder compressors (150 to 4500 h p i . T h e smaller units a r e arranged for flat belt or V-belt drive whilc the larger unit;; a r e designed f o r dircrt-connected synchrmons nmtor; ( F i p . 15-2 and 15-3).

Compressors and


Vacuum

Pumps

30 1

Units such a s t h a t illustrated in Fig. 15-3. composcd of four to six eompressor cylinders rcquire the uiost careful dezign. Inertia forccs can he zrc:it in sucli installations, arid tliesc must be carefully halancrd in t h r ilesign. T h c opposed arrangement of cylinders in Fig, 15-3 mininlizrs these forcer. Complete balance, lion-ever, is never achieved and due con:ideration of the magnitude of unbalance must be given in the design of coinpres~orfoundations. Syncl~ronousmotors can bc conreniently designed to operatc a t the h v speeds required for reciprocating machines. If a .;yncl~rononsm o t o ~ .ito be eniployed in a hazardous atmosphere, horvever, it is ncecssary t o srparatc the motor from t h e conlpressor b y enclosing the motor in a brick r'r coi11,retr room. A motor shaft cxtension rvhich is supported 11y ;in outl~oarilh a r i n g is uicd. T h e r o o n ~is rentilated so that tile p r c s s u ~ i n d e is higlicr than in t h r ronljireswr rooill, iinrl a n y air an11 gas le:~k:rgo I,! into the iiiotor room. I n many haznrdous :III~III.>will go ~ ~ instrad u t phcrc?. l ~ o ~ v e ~it -11:~s ~ r . I)wn found satisfactory t o rnrase the niotor coll e c t ~ring ~ ~ in a s l m t inctnl housing and iunirrtain :I liii-itire llrrszurc in this bowing using an inert gas such a iiitr~~gcti.S i r h :in a r r a u g c ~ i ~ ~ ~ n t is i t 1 r t i c i 1 1 1 r l cunrenient and for lurrcr bol.se11uner inrt;ill;itiotr~ 11jclo~v450 lipl it is porsihlc to employ induction inotors crr1noniical1~which r a n be made explosion-l)ruoi. Induction 111ot111.s, I t o ~ ~ - e r ercr. illlire re~luctiongears b e c a ~ ~ sofe their higher speeds (compressor inaxi ~ ~ i u rpnl n i is generally around 5 0 0 ) .

Intercooler

Turbine-Driven Steani turbines instcad of clc,rtric tnotors ?:in ilr used to ilrir-c the I Y I I I I ~ ~ r c s o dcscribcd rs al)ovc. Stcan1 turbines ;irv used en p u w r c a t s art, high :mil rtcani costs are 111n. Engine-Driven Large coniprersors designed for motor d r i r e can also be driven h p diesel. gas-diesel,* or gas cngincs. T l ~ c s ccngincs arc connected through a flyn-heel t o the rom]~reszorw i t . I t is desiralils, liorvwer, t o cmi~loytlir compact "nnglc-type" coniprt:ssors ~lescribed helon. ~x-llcndiesel or gas fuel is inrlirated. For rcwtaiii !~igli-presswe,high-rqxirity i ~ p p l i c a t i o n ~ beyond t l ~ srangc of t h e "anglc-type" i a b o w 2500 h p ) i t is nrccssary to use the engine d r i r e connerted to a "ntotor-driven" type unit.

Knockout Drum

~ i s c h a r a e Svnchrbnous Header Motor

iubricatina Oil Pump

Suction Heoder

Angle-Type An anglc-type compressor has liurizontnlly mounted cornprrssur cylinders d i i c h are driven b y power cylinders n ~ o u n t e da t an augle of approxin ~ a t c l y90' to the horizontal. *TIN,z n ~ - d i e s ~mI x i m c : m 0 1 > , ~ 1 1 on < ~ villws gas o v
g:t-

SIII>,>I? vxi
302


T h e early gas engines were siniply modified steam engine compressors. ~ I h e y n-cre improred during the 1920's and many large installations of horizontal. 4-cycle gac enginc-driven. dnuhle-acting compressors were installed ezperially for gas transmission senice. These units are still produced hy some nianufacturcrs: but have dcclined in popularity because of the advent of angle-type compressors. Perhaps lone of tlic most q w t ; r c u l a r clerclolm~entsin compressor design took place in the late 1930's and early 1940's x h e n the 2-cycle gas-driven, angle-type roniprcssor was introduced. It had three i~nnicdiatelyapparent advantages o\-cr its lower speed horizontal predecessors; namely, higher tlicrnial efficiency. lower (apprr~ximatelyone-half) space requirement. and Irnver COP^ per horsepo~verinstalled Tlierc are tn.o designs of angle-tyle compressors. On? is the so-called "right angle" (Fig. 15-41 with the power rylinders arranged side by side; it lias tile advantage 01' easy accessibility to all power cylinders from one platforni. A w r m d t y l i ~ ,t h r 1--angle ~ i t ht l ~ r1mvcr cylinders in a V-arrangement (Fig. 15.5) has tlie a d ~ m t a g eof more cylinders per unit length of engine. Rotli 1 : ~ ~give s excellent service and have proved very popular. The "ripllt-:~nglc" t > y c has 5 , 6. 8 or 10 p o m r rylindcrs and tlie "V-angle" type has 6 , 8 , or 10 rylinders. Botli deliver from 250-300 hp per cylinder. Tlic opcrating spec11 ranges around 300 rpm and as many as six t o seven stages of coiiil~ressi,nncan bc inrorporated nn one compressor. Botli two- and four-cycle engines arc manufactured. Four-cycle engines opcrate extreniely xell a t nick variations in load below the rated capacity. T~vo-cyclemachines operate satisfactorily high above rated capacity. I n two-cycle operatinn 811-called scavenging air is pre-compressed in an auxiliary scavenging air compressor which is connected t o the crankshaft. This air enters tllc cylinder toward the end of the expansion stroke and aids in expelling or "scavenging" the remaining gases. T h e four-cycle cnginr arcomplislics the intake and compression of air in each cylinder and thus requires no scavenging air compressor. T l i c ~ eare certain inherent ndvantagcs t o each type ~vhichare discussed fully in lncclinnical engineering literature. The two-cycle engine became popular since it required smaller spacc and lcss weight per horsepower and operated w r y economicnlly a t the low speeds required for reciprocating machines. The four-cycle engine requires no scavenging air compressor arid recent designs aff(~rrlsavings in space. T h e four-cycle operation inlirrently lias high rffirirncy, and tlie two-cycle has more uniforri~crank action since every down stroke is it power stroke. T h e f m ~ r - r y r l ccan he runtrollcd from 100% t o 50% of operating speed n l ~ i l c I n t h r final analysis instdlcd t111:rnngc for a t\vo-ryvl~:is 100% to 60:;. cust c~~uip:lriions :%longnit11 cunrp:irison of engineering features will dict:tte tlic cl~oiccof any style unit.

.


303

304



1)icseI-(driven. angle-type conipressorF are used xhere gas is unavailable. Gas-diesel units are employed if the gas supply may be interruptable (seasonal availahilityi. Tlir gas-driven and certain gas-diesel models are -~mt.kignited ~vitlllow voltage ignitors. In hazardous areas a low fire hazard ignition system should be sp?cified. Ttre p o w r cylindrrs of anglc-type comprersnrs are r a t e r cooled. Lubri<,ationis force fed t o the power end by a gear pump directly connected to the cri~nkslrait. Reciprocating Compressor Parts

Fig. 15-5 indicates somc id the major parts of a reciprocating compressor. Brief comment on several of the more important parts may prove helpful. Cylinder. Compressor cylinders are built to handlc pressures u p t o 25.000 paig. Most manufacturers havc many cylinder styles and are al,k to selcrt the one rnort appropriate for any particular service. Low pressure cylinilers (up t o 1200 to 1500 psig) are generally cast iron or so-called semi-steel (high quality cast iron). I n the medium pressure range (1500 to 2500 psig) cast steel construction is used, and in the high pressure range (above 2500 p i g ) forged steel. The cylinders are designed for water cooling. Water is circulated around the cylinder barrel and valves to remove the heat of compression. For low compression ratios, air cooled cylinders can be used. The cylinders of most compressors are lined with cast iron or other remowhlc liners. Pistons. The pistons are cast iron or fabricated steel depending on the ~ i z eand type of cylinders. T m or more snap-type rings of cast iron or other rnsterinl recommended by the manufactnrer prevent leakage past tile piston dnring the compression stroke. Pistons are flat-faced, rounded, or conical depending on the valve arrangement. Tire piston rod is constructed of forged carbon steel (alloy steel when ~rorrosionis expected) and extends through a water-cooled stuffing box packed vitli metallic, composition ring, or another recommended packing material. A second layer of packing on the crank end serves a s a w.iper ti) minimizc oil loss from crank end. The packing next t o the cylinder is force-feed lubricated on large compressors. The cylinder support or distance piecc forms a chamber next to the compressor cylinder wbich can he vented so t h a t hazardous gases leaking through the stuffing box may be condncted safely out of the area. Compresso~Valves. I n 1915 tbe introduction of pressure actuated suction and discharge valves sparked develolnnent of the modern compressor. There are numerous different types of these valves. All pperate on essentially tbe same principle. The pressure difference across the valve causes flexible metal strips or thin plates t o move against or away

Water Coaled Exhaust Monifold

Cyllnder H e o d ~

Inlet Dirtribution Woter Head

Power Cylinders

Drive

skoft

rGos Manifold

307



fro111a s ~ r i c suf ciincimtric ur purallei rect;ingul;~ropmings. The differential pressnrc ~'erpircil(11 accomplish the movement is increased on certain (lcsigns 11y t l ~ c;il~lllicationof a countrractine., force in the for111 of spring tension (helical or leaf s p r i n g or miglits. This countcrarting force cushions the valve artion. The ralve s h o w in Fig. 15-6 consists of thin stccl strips xhich cover a number of parallel ports. The strips are flexible and open or close depending on thc pressure differential across the valve. For example, tlic strips on the suction valve n ~ o v ct o an open position on the suction stroke when the prc.5siir~'i l l thc sllctiiln line cxecetls t h t in tlie cylinrler. Thc goal in valve design is grntlc opening and closing and sufi(.imt valre area t o cnable low pas velocity through the valve. It is sometimes desirable t o employ a double-deck ralve assembly which is simply tivo valvcs, one monnted above tlic other and arranged t o operate in parallel. This design inc r w c s the effective valve area and reduces valve losses. It is particularly desirable for hig11-c:~pacity, low-eomprcssion ratio operation n-here valve losses may be a large portion of the horsepower requirements. 1-alrc parts arc constructed of carbon steel, stainless steel or chromc alloy depending on the type valve, the operating conditions and the corrosive ~ ~ a t u uf r c gas.

separate lubrication systems. A force-feed typc luhricator sulq>lies sllecial cylinder oil under controlled f e d rntw t o the emil~ressorcylinders and pistun rod packing. I t s function is to create an effective piston seal and to protect the coniprcssor valve parts. Too ~nnelioil. however, xill lead t o carbon formation on the valves causing valve Icakage. Another lubricator supplies tlie p o m r cylinders and s(,avenging Illomer. I n addition, there is a continuous rerirrulating lullt, oil . y s t e ~ ~n.hic11 i cunsists of a rotary pump driven off the coniprcssor crankshaft, an oil filter, and a cooler. This systenl supplies lubrication f11r thr crankzliaft, bearings, and connecting rods and also serves as a ci)ol:tnt for the pi)n-er piston. Oil is pumped from beneath the cranksl~aft,tllrougli tlie filter and then tlie cooler to all parts of the systen~. A 11ressnre regulator maintains the proper luhrirant pressure. All reciprocating compressors require lubrication of a similar nnturr. On some small units certain lubrication streanis can be combined. The Compressed Air and Gas Institute'? giws smnc rxlnnhlc s~~ggrstions on lubricants, but manufacturers' recmnnendations are more specific and, hence, more useful. All reciprocating compress(~r cylinders reqnire oil I u i ~ r i r a t i o n ,and ~ suitable separators must be provided a t the discharge of the compressors to remove unxanted oil from ga? strcnnis.

306

Lubrication of Reciprocating Compressors

.

,

l h e proper lulrricatiim of :I reciprocating compressor is a complex prohlet11 anc1 careful iltt(.ntinli niust he gircn t o tlie ri~niprcssurmtmfacturer'r; r r r ~ , ~ ~ ~ l n i , ~ ias ( l :w(.II ~ti< :IS~ Iliow ~ ~ s of oil co1~11~11ly Iul~riratinj:rllrri:~lists. A typiwl g:~>or i l ~ w - d ~ ~ i:~ngle-type v ( ~ ~ ~ , r o n ~ ~ ~ r ens ~z x~ yrhave t11ree

Reciprocating Compressor Regulation

The gas delivered by a reciprocating compressor can he rcgulatcd by one or a combination of several methotls. The incthod used depends largely on the typc drive. Regulation in uiwt proreises is conwnicntly based on the maintenance of w constant rollillrcssor discharge or suction pressure. Wlietl~crto use the suction or discharge pressure l:irgely depends on the process for xhich the compressors are t~cingselected. Often in process plants it is d e s i r a b l ~to niaintain a given prcssure in a systeui into which the compressor discharges. I n this instance discharge pressure is used as the sensing element. IVl~ensuction pressure is nhove atn~ospheric pressure it is sonietinies prefc,rat~lc10 cmtrol the suction ~ ~ r c w u r c . y for plant air compressors: a Start and Stop Control. C o n ~ n ~ o n lused pressure s r i t c h starts tlic nmtor when t l ~ eair pressure falls below that required and stops tlie motor xlien it reaches the desired prcsure. Driver-Speed Control. Direct-acting, steam-driven co~iipressorscan best be controlled through variation in the speed by means of governors of the throttling type or automatic steam valve cut-off type. Gas, gasdiesel, and diesel-driven conlpressorz are controllrd from 100 per cent * I t is possible to obtain at nddilionnl cost S P P I . ~ :n~ o r l l u l x i ~ n l ~~dy l i n d c t ~iiiwinp s pistons fitted with carbon rings, but this is justified only ~vhcneanrprcsscd gases must not come in contact with oil.

308

Project Engineering o f Process Plants

t u 50 or 60 jrrr w1it of wpacity by mc.;ma u f a gul-cmor ( o m l)c : i ~ ~ i m : ~ t i cally actuated) vhich operates by controlling thc amount of the fuel admitted to the p o w r cylinders. I n most processes this range of control is c n t i r ~ l yadrquate, although snction valve nnloaders and rlrarxncr pockets as drscrihed helm7 a r r an aid to smoother operation if suction or (liirhargc pressures vary. \Vhere this variation is rapid automntir control of the u n l o a d ~ r sand clearance 11ockrts is indicat~il. Clenrnnce Pockets. Clcnrnncc pockets arc. usually provi(1rd in c o n iwwsor cylinder; as s l ~ u n nin Figs. 15-4 :md 15-5. 'rllc clc:~mnc?vnlves ran t ~ carranged for autoniatir opcmtion or iiiilnual operatinn. \\'h(v ol~enerl,the increased clcnrancc addrd t o the (,ylin(lerreduces the r:ij~:wity uf tlic macl~ine. It has heen demonstrated by Yorkl4 that althnugl~the, volumetric c f l i ~ i c n lis, ~reduced by the ollming of a clenrancc porkct, c o n ~ ~ r e s s i o rfficimry n is essentially unaffccted ithe gas in tlic clcarancr pocket is co~nprcsse,lhut returns this energy in the recxp:insiou rtepl. E r c n rm romprcssors not designed for elcamncc control: there are rlearancc plugs n.liic11 permit manual change in ron~prrssorenparity if ojlcrating conditions cliange permnncntly. Siiction 1.nlz.e or "Free Air" Cnloorlem. T h e suction valve unl~~niler as shown in Fig. 15-7 (KO. 2 nnd Yo. 31 h d d s thc suction valves open wit11 steel fingers I'nrtcncrl to the pneumatically o p r a t e d unloader piston*. , I his nctim 11rcvmtrthtx piston from compressing gas during tlic partirular s t r ~ ~ kine ~vl~icli the unloaiiing i~ccurrcil. Compressor capacity is therehy rcduccd. Step-Control. So-called firc-step or. for small compressors, three-step rapacity control is employed on constant rpccd nmtor-driven compressors. T l ~ ccapacity is controlled in fire (100, 75, 50, 2,5, 0 % ) steps or tlircc (100, 50, O%,) as the case niiglit be, through tlic usc of clrarancc pockets, suction valve unloaders or ;L comhin:ition of hoth. Fig. 15-7 illustrates a typical five-step control employing t w unlonilcrs and one clearance pocket on a double-acting cylimlt~r. -4 g o ~ w n o ris ;~ctaatedby the comIreasor discliargc pressure cont~.,~llcr.Tlic gorrrnor selt,rtively energizes or dc-energizes one or morc of tlir solenoiiis v l i i c l ~control air t o tlrc unloaders ( K O .2 and Nn. 31 or rlcarancr purkvt valves ( K ~ I1. I . C o n plete unloading is necessary for starting synclmmons motor-driven units under load.

Clearonce Pocket

100% Capacity

75% Capacity (Cleoronce Packet Open 1

50% Capacity (Suction Volver Held Open Crank End Cleoronce Pocket Not Effective)

8 25% Capacity ( SucI8on Valves Held Open Heod End Crank End on Cleoronce Packet)

.

S e l e c t i o n of R e c i p r o c a t i n g C o m p r e s s o r D r i v e

T h e selection of the t y y 3 reriprucating compressor for a given plant is primarily dependent on the type of drive most suitable for the plant fuel and po\ver conditions. Fuel, steam, and electrical costs in the area or plant iuust he evaluated hcfore a n intelligent derision ran be made. Ench situation is unique in itself. If porvcr costs are extremely low: the

309

Compressors a n d V a c u u m Pumps

0% Capacity (Suction Valves Held O p e n Both Ends )

fig. 15-7.

Fire-step elenr:incc conti.01. (Conrt~syof Wo~.thingtonCorporation.)

motur drive should Ire used. Compressors of all sizes r a n be obtained for motor drire m i l the advantage of l o ~ vl,o~~-er c o d slii~uldnot 11e overlunkc~i just because a number of other plants constructed in different parts of tlie country h a r e used otlicr types of drives. Gas-drivcn compressors 11ave become p:~rticul:lrly advantageous for rcfincrics m i l pctro-cllcmical plants since sup]~licsof gas arc p r ~ l u c c d as "nxste" after the heavier portions are rcmoverl for ~ ~ ins the e process. Chcmical plants operating in arcas l ~ a v i n glarge uniuterruptnhle gas supplies also find the gns-engine drire advantageous. In arcns ~~-11ere gas is sold a t a low price only during the Tvnrm n ~ o n t l ~the s gas-rliencl engine drive rliould be cmsidercd. IYhen low cost stealn" is available or ~vlleulow pressure prowss steam must be obtained from high pressure steam, turbine-driven coinprcssors *Unfol.tunntely plant stcam costs are oftcn unrealistic hook mlucs and do not actual conditions.

rcflect

310



T h e c w t of rr,Iuction gears and steam piping, are s o ~ n e t i ~ n einrlic:~tcd s IIOII-cvcr,n ~ u a tnot be overlooked in such a (leeision. On m a l l and niedium-sized cr~nlprcsaorinstallations ~lirect steam-drive often proves advantngeons. I t is important t o rnnke a tliorougl~cconomic study c o n binerl ~7-itI1a n engineering eraluation of tllc easc of operation a n d suitability of the various types of drivers for the particular plant situation. Reciprocating Compressors in Hazardous Locations

I n the prilccss industries equipment for hazardous areas is designed to he explosion-proof as discussed in Chapter 24 Sucb design is practically i~npossible x h c n compressor installations employ gas or diced drives nnd synchronous motors. I n such cases explosion-proof construetiori n-ould be proiiil~itire. It is possible, however, to build these units v i t h lo^ fire hazard crmstmction, using rlliclded spark plugs for gas engines and an enrlosed collector ring with a n incrt gas or air purge for synclil.onous motors.

/

suction

Discharge

\

CENTRIFUGAL AND AXIAL BLOWERS AND COMPRESSORS Classification a n d Terminology

T h e C o n ~ p r c ~ s eAir d and G a s Institute13 has for convenience classified centrifugal and axial machines as follons: 1. Blowers (turbo-blo~ers).Discharge pressure not exceeding 40 paig (based on air). 2. Compi.c,ssors (tirrbo-comprrssors). nisc,h:~rgi:pressure exceeding -10 psi:. 3. Fans. Chnrchz has defined these low spccd centrifugal machines as operating in the w r y lolr pressurc mnge belo~v1 psig and with large volumcs.

steel

Shaft

hluch of the terminology of the centrifugal machines is similar t o t h a t centrifugal p u n ~ p s , and, therefore, only brief alrcady presented I comment nred be nrade concerning most of t h e terms listcd below: 1. Single-Stqe. One impeller or one row of vanes 2. Jldtistage. TKOor more impellers or rovs of vanes 3. Centrifugal. Have radial inrpellers and the flov through the machine is in a radial direction. These impellers may be open, semi-elosed, and closed. They may have straight or back~vardcuwed blades. I n multistage units diffusers are located between stages for efficient conversion of velocity head to pressure head (Fig. 15-8). 4. Axial. Flow of gas is in an axial direction. This motion is created by vanrr attached to a rotating drum (Fig. 15-9). St:itionary vanes separate each row of rotating r a m s and serve in the same manner as diffusers on centrifugul machines. 5. Stane Groiin. Defined bv the -4ir and Gas Institute as any group of individual impellers and diffusers oper;~tingas a unit on a single shaft, in a single casing and n-ithout cooling betrr-een individual impellers. 6. Multistage Croup. Two or more stage groups driven by a single driver with intercoolers bet,ween groups.

-

-

1

Diffuser

LCasmg Drain

7. Characteristic Curves. Plots of the discharge pressure versus the inlet capacity. 8. Performance Curves. Show the shaft horsepowr versus the inlet capacity. 9. Equiz,alent Air Presswe. A term ~vhieh has been l i d in cornparing centrifugal or axial conillrcssors and unfortnnately :ilq~earsrrell entrenchcd. It is the pre~erlrcin p i g that a compressor will drvdop operating a t the r;itcd capacity when handling air a t 14.4 psi absolute and 60" F.

.I

II -.i '

As with centrifugal punlps, centrifugal a n d axial compressors or blouvers aceomplisl~the pumping or compressing action h y the rotation of wries I i i n ~ l l ~ r sT. l ~ rrrlocity imparted t o t h e :;IS Ily (11,. i m j d l c r is convertcd to p r e s s ~ ~ in r e a volute or a difl'uscr. At first gI:mce a m ~ ~ l t i s t a g e centrilugsl conlpwsror (Fig. 15-8) ~ n i g l ~1)ct mistaken for a i i l ~ ~ l t i i l a g c

312



wntrifugnl pump. The iml)ellers of the rompreszor, Iio~vever,generally decrease in ~virithfrum the 1011- lo high prcs.sure side because of thc decrease in fluid ro111iiie:I? t h ga- I ~ r u n i c scoln1)rrsscd. Some experts hcliere that the centrifugal compressor is beginning a pcriod of popularity similar to that of centrifugal pumps in the part

these may provc helpful. . i s wit11 oentriiugd pu11qx the ranc shapc of the impeller influences the head capacity characteri-.tics. Many shapes and types :ire built. The three important centrifugal iliipeller types are s h o r n in Fig. 15-10: ( a ) Forward curved; ( b ) backward curved; (c) radial.'

313

7 Stator blades

Backword

Rodlol

Forward

Copaciiy

Fig. 15-10. Impeller typcs and tppirnl characteristics.

Fig. 154. . k n l compl.czsor. (Adaptrd by pcxn~ission.CI:wk I3rothrs Cornpsn?.)

(lernilc. The rrntrifug:il ninrliinc 112s definite atlra11tag1.r over tlic ~.i,rilrrocating machinc ior estremcly high rulumcs and in the lower p r c s > ~ ~ r o range (sce I1e1on.l. At lover volumes the efficiency of the centrifng:ll l y it berolues u~~econon~ieal. The range c ~ ~ m l ~ e sdrops o r off ~ q ~ i r lthat uf applicability, l ~ u i v c r t ~ is, c o n t i ~ w d l vb e i ~ ~innreased g as new design techniques are developed. Impeller Types

Before discussing the various types of centrifugal fans, blowers, am1 m tinil1c1lc1.s s n-1ricl1 will be co~iirnul~ t o :,I1 rulrrprci~urs:I fen c o ~ l ~ ~ : ~UII

Typical? characteristic curves for these impeller shapes are sho~vn. It can be seen that a maximum head is reached a t point M. As v i t h pumps. operation a t or near this point produces unstable operation or surging since tlie niachinc .ivill "hunt" b e b e e n two capacities for one discharge pressure. The maxilnuln or critical point for the for~vard-curved blade ilhistratcd is so far removcd from the origin that the efficient operating range is in the unstnble region. For n givcn diameter, however, tlic iormard curved impeller can handle a greater r i ~ l u m eof gas than the other typcs. It has, therefore, become popular in some fan applications when operation is a t high capacity and low pressure. Such operation is in thc range nherc the unstahle region cnn be most ronveniently avoided. For higl~pre~suresand high speed the back~vardcurved and radial designs have proveil tlie most effirient and reliable and art,, therefore, used almost exclusively on centrifugal blolvers and compressors. '-The term radial as hwe m ~ p l o y dimplies mdinl ~ a t m n g ~ m e noft the impellet. hlndes about the axis. Thesc may be peddle-vhccl itremcl. ~ y p cor may be eurrctl :tt inlet c n d Since nll erntrifugal machines impart n rnclinl motion to the gas as opposed to thc axial machine, the term radial is also o s d to describe rentriiugnl I,IUWCIS and eoml,~~csso~~s. iThcpc rw,-cs :are only rcpresentntire oi the general t y p c Pronaunced valktion can he obtained by alteration oi the impeller blnde curvature.

314


Because of the high speeds employed for most blower and compressor applications carcful static and dynamic balancing of the impeller is imperative. Factory tests a t about 25% over the rated speed should be made before delivery so that balance can be checked. Single-Stage Blowers

Single-stage hlon-ers are regularly furnished in two types, both of which have ovcrhung impellers similar t o those of centrifugal pumps. The imr~ellermay he mounted on an extended shaft of the driver or the impeller may he nionnted on a separate shaft supported by two sleeve bearings and nttaclicd to the motor shaft by a coupling, as in most centrifugal pumps. These nnits operate most economically a t flow rates above 8000 standard cfnl and a t discharge pressures from 2 to 9 psi. The casings are constrnctcd of cart iron hut can be made of special alloys for corrosive serrirc or for high inlet pressures.* Thc casing is shaped in the form of a volute ~ ~ - i tnl itangential discharge and a single or double au~,tioninlet. B y rotating the casing the discharge nozzle can be located in any desired position. t For a l h ~ v e rdeveloping higher heads a diffuser (see Chapter 14) passagc is located in between the impeller and volute. Impcllers may be open-type with radial blades or closed-type with radial or backward curved blades. Those with radial bladcs are cast in one piece and are generally designed for high tip speeds and thus a high compression ratio. Single-stage hlolvers are used extensively in the process industries. They are employed a s gas boosters in processes as varied a s hydroforming and water g w pr~~duction.They are most frcquently used as sources of large rolnmcs of low pressurc air for flotation, pneumatic conveying, ventilatiun, and for foundry cupolas and other o w n s and furnaces. Multistage Blowers and Compressors

T o obtain higher differential pressures multistage units have been designed (Fig. 15-8). Fully enclosed impellers are used exclusively in these units. They are keyed to the shaft. Large impellers h a r e machined alloy disks and cover plates with vanes, generally backward curved, formed from stainlcss steel plate vhich arc rivcted or welded in place. The fully enclosed impcller providcs better support for the vanes and is better suited for multistage design. Each impeller is surrounded by a vaneless type diffuser (Fig. 15-8) for converting velocity head to prcssure head. At the inlet to each inlpeller guide vanes direct the gas to the impcller eye. The first stage guide vanes can bc made adjustable so that the characteristics of the conlpressor can be modified by changing the angle of the vanes. *Single stage cnsings have been designed for opernt~onat 900 psi. t Kumber of positions is limited only by the nunrber of bolt holes in tne moms


315

The stationary separation walls between stage? are called diaphragms (Fig. 15-8). They are constrncted n-ith a passageway for conducting the gas from the diffuser of the previous stage t o the inlet guide ranee of the next. These guide vanes may be cast integral with or attached ti, the diaphragm. If high compression ratios arc necessary in each stage, temperature ripe will he great. Diaphragms may be designed for internal cooling of the gases t>et~\-cen stages hy florv rif cooling ~ v a t e rtlirougl~a baffled passage in the diaphragm. Kormally, l~owcrer,Atncrican centrifugal compressors are nncodrd. The casings are cast iron or steel depending on the operating conditims. Thcy are horizontally split permitting casy access for repairs. All etationary elements such as the diapl~ragmsare also liorizonally split. Jlultistage centrifngal hlon.crs and comprcssors are xi-idely used in many process plants for the movement and comprcs~ion to moderate pressures of large volumcs of air or gas. Perhaps the most, familiar application of inultistagc hlolvers is supplying air to hlast furnilces nnd Bessemer converters a t 30 psig. The blast-fnrnace t ~ l o w r sare usually rated at 100,000 standarii cfm n-hile the Dessemer hlon.eri 1111111p 30:000 to 40,000. Similar units arc employed for copper convcrtixs. Many applications of centrifugal blorx-ers in other process industries h a r e ex-olved, such as (1) compressing flue gas from furnaces or lime kilns to 10 t11 15 psi for brine treating; ( 2 ) supplying regeneration air ior fluid catalytic rracking units (20,000 to 600,000 cfm a t 15 to 25 p i g ) ; (3) boasting gases in any process involving recirculation; and (4) aerating sewage. Most multistage blower applications require from two t o five &ages. As the differential presenres become greater the term centriiugal compressor instead of blower is ernploycd. The growing popularity of rcntrifugal compressors in the past few years has been astounding. They arc designed for shaft extension a t both ends, pcrniitting the coupling together of up to three ronlpressnrs so that one driver can be cmployed wit11 rcsulting savings in initial ci~stsand space. Such a n arrangement is shown in Fig. 15-11. This unit was designcd fur oxygen con~pression with tln-ee compressors in series compressing oxygen from 11.7 psia t o 350 psig with intcrcooling hetwecn rompressor bodies. Units for handling from 2000 cfm to 120,000 r f m arc manufactured. Ecunomy a t high flm. rate. has madc the centrifugal compressor a standard choice for large refrigeration systen~ssuch as those required for dewaxing plants. This same characteristic has brought about the use of centrifugal compressors as an initial stage in the cornpression of large volurncs of gas such as feed gas to annnonia rmvcrtors or natural gasoline plants. I n such instances the centrifugal compressor rompresscs the gas u r from e 40 to 150 psig. The from its initial Irnv preseurc ti, ;I ~ ~ r e s ~ of lowcr volnn~eof gas a t thv l~iglirrpreswre :tllon-F reduction in thc size of t.he reciprucating compressor ~ \ - l ~ i crcccires h the g;rs from the centrifugal



enable competition with gas-driven reciprocating machines in areas where cl~eapgas is available. Sereral gas turbine-driven ecntrifugals have been installed'

(similar to the sliding-mne pump in Fig. 14-19) has an eccentrically mounted rotor to vhich sliding vanes are fitted. T x ~ ~ - i n i ~ e lblolvers ler have two mating lobed impellers which rotate in opposite directions (Fig. 15-12). The impellers do not touch and, therefore, no internal lubrication is required. This is an advantage in the cumpression of air.

318

Regulation of Centrifugal a n d Axial compressors a n d Blowers

319

If the mupressor is turbine-driven, varying turbine speed is the most satisfactory and economical metbod of control. For constant speed drives it is preferable to control by throttling the suction. For a constant discharge pressure and a given mass flow rate tbe borseponer ~onsumedis l e s for throttling the suction than for throttling of the dischargr. This has been very clearly discussed by Kassarik.'" A second method of regulation for constant speed machines is the use of adjustable first stage inlet guide vanes. These n ~ a ybe operated through gears and linkage so that they automatically change the prrssure~ d u ~ ncharacteristics e of the compressor by changing the inlet angle. The iulrt guide vane incthod is more efficient in pon-er utilization tlrnn suction throttling. Hecausc of the rr.lati~-cly flat cliaractrri~tic curve of centrifugal machines it is prefrrablc to use actual flow rate as thc sensing dcvice for actuating the controls on a centrifugal. This flow is generally measured by a veuturi meter. Centrifugal machines are ideally suited in many al~plicationsas first stage units feeding reciprocating compressors. I n surh instances it is necessary to control the discharge pressure of the centrifugal to insure smooth operation of the reciprocating machines. This may he done by means of n preszurc controller in the disrliargt, line of the centrifugal mi~chinr. I t i:: importnnt to be certain that one control does not work against another in designing the complex controls for such installations. I

Fans

Fans can be built as centrifugnl or axial flow units. The axial designs are called prq~ellcr-typeunits. The same principles already discnssetl a p They are used most irequently in process plants for ventilating, for conveying and re~noringdusts, for supplying draft to boiler furnace draft fans, for circulating hot air or gases, and for similar applications. Rotary Compressors a n d Blowers

Gases are compressed and moved in rotary compressors and blowers by the positive action of tlrr rotating elements. There are several popular designs of these positive displacement machines. The sliding-vane type *One imge installation employs 10 gas-lwhinr driven e ~ n t r i f u g d sfor reinjaztion of natural gas into gas field at 1935 palg A series-parallel arrangement of comPIPSSOIS is used.

Fig. 15-12. Two-impeller of Dresser Induslries.)

I

I

1

!

I I t

blower. ( C o u r t ~ s ya1 Roots-Conncrsviile Blower Division

The t~o-impellerblower has h e n used for many years and has proved a rugged piece of machincry. It operates 8 t Ion- speeds around 450 q m and at differentials up to 11 to 15 psi. This blo\~eris used extensively for supplying Iowpressurc air to flotation cells, cupolas, and pneumatic conveying systems. For volumes helox 10,000 standard cfm it appears favored over the centrifugal h l o w r because of 101%-erfirst cost. To control capacity on constant speed unitsl the discharge is by-passed to thc suction or the gas is rented. .4 thin1 popular type of rotary positire displacement compressor is the ~ . o t a r y - l i r ~ ~ ~ i d - ptypc i s t ~ ~asn shown in Fig. 15-13. The ~~iultiblade rotor of this machine revolves in an ellil~ticalcase, partially filled 75-itl1 water

320



321

or otl~erliquid. The rotor revolves a t sufficient r11ccd t o thron. the liquili shape of t l ~ ccasing forces the against the caring valls. The elli~~tical liquid to fill the l~uckctc;of thc rotor on tl~c,~iilesand wccrlt. IIII tll? top and hottoni. This motion dra~vsin gas at the inlet ports, and eonipresses

Capacity, cubic ft per min

Rotation

CHOOSING COMPRESSOR TYPE FOR A GIVEN JOB

Capacity, cubic fiper min

Fig. 15-14. Cunirlwsaoi.-type relrrtion charts. LReprintcd hy permiwion, I . J. 1ial.asaik. Ciirm. E w . , id, Xu. 10 (194i1, and \Vol.tllington Pump and hlachine Corporation.]

322



32:

operation and volumes too small for centrifugals thc rotary compressor such as the lobe-typc appears advantageous. .ill these types, of coruse, overlap. Karassik'o has presented scveral charts (Fig. 15-14) illustrating the fields of application. These a r e f o r illuztrative purposes: of rourse, and sllould slot hc used blindly in choosing compressors or blo~vers. RIaintenancc coats should not he overlooked in t h e selection of co111pressors. It is wcll known, for instance, t h a t centrifugal machines require less n~aintenancethan reciprocating machines. T h e unbalanced forces characteristic of rcciprocating machines cause greater strain and w a r on moving part,s. T h e rcpair of a centrifugal machine, howevcr, is more complex than t h a t of a reciprocating machinc. It has been found advantageous to maintain spare centrifugals in the plant warehouse for compressors in important services. VACUUM PUMPS Most of thc equipment described thus f a r can he built for use as vacuum pumps. T h e principles of operatim are tllc same cxcept t h a t the inlrt pressure is h e l , : ~atmospheric ~ pressure which necessitates ccrtain design changes. Volumes a r e largc a t these low pressures and compressor cylinders, for instance, must be correspondingly increased in size. Steam jet ejectors with dircct contact condensers and in conjunction n i t h barometric condensers are extensively employed for production of vacuum especially for m c u u m distillation units. Applications of various types of vacuum-producing equipment are illustrated in Fig. 15-15. COMPRESSOR ACCESSORIES Low caparity single-stagc r e c i p r ~ ~ c a t i ncompressors g a n d centrifugal hlolvers requirc few accessory items. Air cooled cylinders, grease, or simple oil lubrication suffice. Large compressors so typical of modern chemical and petroleum plants demand a large number of accessory items. Several of t h e more important items are:

0 I S C " I I I C C TO POI1I)" PYYP

t

Fig. 1615. Vacuum-erpiprncnt seleelion chart.

(Cawtrsp of Ingersoll-R:md

Conl,'an~.)

I. Reciprocating compressors A. Auxiliary lubricating and cooling oil system. Provides forced lubrication and piston cooling oil in addition to lubricators o p r r ~ t e dErum compressor crankshaft. 1. Lube oil grar pump (motor driven). 2. Lube oil cooler (shell and tube). 3. Oil strainers. 4. Oil filtrr. B. Intercoolers and nftercoolcrs. Shell and tube or extended surface (fin) exchangrrs for cooling cornprrsed gaws bet,wen st;~gesand aftm final discharge (aftrrcooler). In high prcssnrc installations less rxpensive constroction can be realized by pasing the compresed gas through the tubes. (2. C>-linder cooling water. Each cumpressor cylinder should be provided n;lh a separate valve for controlling flom. Closed cooling wnter systems often

prove fearihlr. Carefull? treated xmter is employed and large volumes of ~vatrr ;In,lirrd x i t h a trnll~rr:1tllr~ rice (I[ only tell decreer or Ims. In a closed system if the m t e r has been properly treated, higher tempemtnre watcr can be used, 130-150" F, rvithout cscrssire corrosion or scaie formation. This high temperature permits the socccssful uppliration of air coold exchangers for cooling thc watrr in areas where ~vateris scarcc. D. Kntickout drums. Condensate in compressor cylinders can have disastrous effects. If condensate is expected to fornl, provision siiould be made for its complete re~novalafter rach cooling stage. E. Suction ;and clircharg~:surge drmns or bottles. Because uf the pulsat~ng action of reriprocatin: rnnrhines surge riru~uaon both the sucfion and discharge side uf each cylinder are necessary. Thcse arc drsigncd tu hsvc a volum*


325

5 . Tlier~nalreI:ty to 1,ruteet against operatin: overloads, 6. .\Iotor trmprl;~tnrcindicator :and alann. son^ uf t h w motor :mt,--orivs are r a t h r erprmirr but ;arp entirely justified mi the 1000 h1r :,lid largrr motor.; e~lcounteredin con~pre--orpracticr. .\ hnowleilge of the ch;~racteri.dirsof the pon-er ~llpply3 r d continnity o/ o11er:~tirn1required in thr. prow-s run aid the electricnl e~x$tiwrgrcxtly in th<, reliability of uperntiun and tnxzinnnn niimx d c s i g of u >ysr<,nlfor ~uazin~mn life. Tlie lrrojcct engineer slior~ldsupply this information us n-ell ar inforniution on the ciSect of short pon-er interruptions on the procw. COMPRESSOR INSTALLATION

opmitiu: in ierit,-. U. I~r?trutilent:rti~~t~ 1. Pressure gxgesmd temperzturc intlicntors. 2 . Flov contrullera (ventnri) on suction to cr~ntrol sperd of drivc or suction presure. 3. Suction gressure controller. Drives , (:as rngine or gur-diesel for reciprocating rolliprcssors 1. 8t:irting air compressors (250 piig). 3. Starting xir surge tanks. 3. D i e d oil t:inks, pump;., and filter. 4. Enpine oil :mr li11rn11,cooler, filter, :tr;iincr.

Inatalltitioir is a i ~ i i p l cmatter for small low speed loncliincs but witL the 1;irgcr unit:: Inan?- ~ : o ~ n l ~11roblems lcx arise. 13ec11nscof the u n l ~ a l s n r r ~ l g c n t cart in fi~und:if w c c i ~~li:~r:iiwristir id large reciprocating ~ix~chine.. tion ~lc.;ign :~ndpil~ingl:~youtis essmtial. Tlic high r p c c ~ l1111crationof rentrifugnl ~nachinc., 11111liosaccurate nligr~luent imperative in order t o a1-oil1 damiiging ~ i b r a t i o n s . Compressor manufacturers furnish rcco~ii~ilended foond:~tio~idralvings for thrir units 11asrii on firm .t hc a t suilicicnt height and of sufficient capacity to lift coniprcsaor parts. Aclcquxte pipc sizes slic~uldbe used t u eliminate uriduc prcssurc 11rol1 erpi~ciallyin thc suction hc:i~lcrs t o rcvillrirati~igcolupressors. I n cornprcssor ~ " . : ~ r t i wa velwity of 30 to 35 ft/sec has been found ~ i i o s tsatisf:ictory. I t is unxiae to i~ntlwsiaecol~ipressurpiping. T o e l i m i n ~ ~excessire te friction loss changes in piping direction must he avoided as tnucli as possible, and where they are necessary long radius e l b i ~ ws h d d 11c osc

326

IIC avoidcd on reciprocating machines a t the inlet. The discharge line of a centrifugal s l i ~ ~ n be l d a very long hend, about 10 degrees. On reciprocating unit? overhead piping is nut rec~~mrncnded since in order to prcvcnt excessive ribration anchoring problems hcconlc r r r y (liffic~ilt. The ancliuring and supporting oi discharge piping is. in an? event. a priihlem TI-hicli drserve; careful attention. Tibration in iniproperly anchore~lsystems can cause fatigue and bursting of the line due to fatigue. Piping for centrifugal compressors must he carefully supported and anchored tu avoid strains on tlie compressor casing. All conipressor piping should be thoroughly cleaned of scale and foreign inatter, During initial operation. particularly, strainers should be installed in the suction lines.


327

q = heat added from surroundings,* ft-# 11' = vork done on the surroundings, (work of expanaiorr), ft-// # = poun~lsof forre S o \ \ - the exart different,ial for the energy hmrtion 1. (internal nrerg?) is d l : = T ciS - I' d17, and fur a reversihlr process dq = T d S (n-llrrr. s is the entropy and ?'the absolute temperature). Hence, with the restrirtiuri of a reversible proress (ideal frictionless operat,ion) Eq. 1 hrromrs:

COMPRESSION THEORY

To thc engineer who must only occasiorrally he conrcmed with the calculation of compressor periormance, tlic formulations and numenclature familiar to the compressor industry often appear baffling. If, lion-ever, 1ic understands scveral basic principles uf tl~ennodynamics,he realizes that all the many compressor design equat,ions are bared on tlicsc plinciples. Thermodynamic Energy Functions a n d Work of Compression

Although reciprocating compressors conihinc in tlicir operation a f l o ~ and nonflov procces: tlie overall result is a flow proccss. Hence. conipressor equations for all compressor types can be based on the eqnation for flow work obtained from t,he general energy balancc. It is convenient t o base all calculationi on the ideal reversible process. I n this manner rigorous calculations can be made with relative ease and then corrections t o the actual case applied in the form of efficiencies. The Overall Energy Balance

The ovcrall energy halance in differential form assuming potential, surface and c1ectrir:tl effects t o he zero or negligible can be expressed as follu\vs:

where P 1' m

pressure, #/sq f t volume, cu ft = mass, lb u = velocity, ft/sec g, = factor 32.17 for c o n v e r h g from absolute to engineering units ti = internal energy, it-# =

=

Subscripts 1 and 2 refer to the initial and final state. Theoretical Work of Compression

For the usual case of coulpression d ~ e r ekinetic energy rfferts are negligible eq. 2 becomes:

-W =

If

~

d

~

(3

For fans and other differential pressure hlowers V may he considered constant and work is equal to TT(P2-PI). Nq. 2 and 3 arc true for reversible flow processes only. Irreversihilities such as frictim effe~trincr~mc, the total work that must be done. Some autl~oritiesu reicr to the

It is possible to devchp eq. 3 for rcvcrsible flow work by considering thc area in a n ideal PV-diagram. This method is perliapi m o coli~ cise, but unfortunatcly the limitatiuns of tlie expression arc obscured when tlie general energy balance is not uscd directly in the developuient. Eq. 3 can be related directly to tliem~odynamic energy functions when the exact differentials of certain of tl~csefunctions are cunsidrred under tire restrictions of constant temperature (isotliermal) and constant entropy (isentropic). These cxact differentials, the development of ~vhicll can be found in any standanl elieuiical engineering therniodynamir tcstbook, are:


328 where V

=

P T S G H

=


rharts that permit the calculation of enthalpies and entropies when A1ollier ~liagrarnsor tables of cnthalpg are not available. If thc gas obcys the ideal gas Inn., solutions to the integration of

volume pressure = ahsolute temperature = entropy = free energy = enthalpy

l2

T7 d P can be simplified as shorn helorv The use of \Iollier diagrams

when possible, ho~l-ever,is strongly urged since no assumption of ideality is necessary in their use ; u ~ dthe results are for the avtual gas.

Reversible Isothermal Compression

,I(:

Applying

- S dl'

= - S dT =

+ 1. iIP

!

0 a t constant 2'

i1 1

.:

dH

=

'I'dS+T'dP

T (IS

=

0 at constmt S

T' ilP

=

dH

I

l1 V

* A reversible isentropic process is a n adiabatic one since dq = I' dS for n rc\.ersihle process. It is often common, therrfore, fol. iorntropic rumpression t o b r inllcd adiabatic. Such a practirc is not recommendrd since :dl ntlinbatic processes are not nccessnrily isentropic or rcrwsible. "?'

,.~C<

r. .~ <,,

i;.*

~vllf'r~ P

=

n

=

V R*

= =

1'1,' = n1lT pressure n ~q ft, number of 113-moles volume cu ft. Gas Imv constant in vnnsislent unit,s 1,514 (#/sq ft)(cu ft,)/(h-rnole) (a R )

Equation G may be witten:

=

molal volume, cu it 113-mole.

I
iil'

term \vill yield the ~vorli. Secondly, if d n e s of enthalpy and ent,ropy at the initial and final condit,iolls are available, the work can be calcnlated as 1 H - T A S for isotherm:d \vorli and AH for isentropio. Indeed, the ease hg TI-hichisentropic reversible work can be calculated from a Mollier diagram for a giveti gas has been a major fact,or in t,he adoption of isentropic work as the standard or base for comparison. I
y

Thc I d e d Gas Lar5- is cspresscrl as:

H hrre 7 ,

Eq. 4 and 5 indicate two distinct methods for det,ermining the reversible work of compression, First, if the relation betveen P and V is lino\\.11, for the isothermal or isentropic process, the integration of the

Equations Based on Ideal Gas Law

I

Reversible Isentropic Compression*

Applying

329

COXPRESSION (IDEAL GAS) R ~ \ ~ S I B IISESTROIX .E Similarly for the isentropir rase:

i

\diere 111' = enthalpy change for an ideal gas, H t r ~lh-mo!r. C , = molal heat capacity at constant pressure, Dt,u '(Ill-mole) (" F)

*It seems p r ~ f e r n h l rto rrrnember one gas ronit:iot ;and n i c k < , 1~0n\i~1~si011s 3s req i 1 i 1 . 4 I n conrpwsrion rnlculntions lrss rhance fot. rwol. o r m w if : ~ l lunit; tire k q > t m i w t . ~ , u u n t l s .:m
330


Call this R' the gas law constant in heat units. :.R'dlnP

=

C,dhT

where Corn= arithmetic mean of inlet and outlet heat capacity Hence

Tz

=

TI( P z / P I ) ~ " ~ P -

+

Now for an ideal gas Cum K ' = CDmand calling C,_/Cm = li (Ratio of heat capacity at constant pressure C P mt o that a t constant volume C,_) the following is obtained:

Eq. 10 provides a rapid means for calculating the theoretical final compression temperature for an ideal gas when the initial temperature, compression ratio, and the heat capacity ratio are known: From eq. 9 above: - W,

=y 1

C, d~

=

Cnm(Tz-- TI)

Substituting eq. 10,

Compressors ond Vacuum Pumps

331

Rased on the assumptiorls of these rlerivations the values of k must hr hased on it11 average of k at the inlet and outlet. Thcsr equations an. true for an ideal gas and the I; can be evaluated from the heat capacitirs at 0 psia and the average temperat,ure hetwecn the inlet and discharge. The discharge temperature is, of course, not known at first hut a rongh g u e s usually suffices. For most rompressor prohlems variation in specific. heat is small x i t h temperature and values a t rooni temperat,ure are satisfactory. Eqs. 8, 11, and 12 all have unit,s of TI-orkper mole (ft-It] per 111-mole). There are many variations of these equations, hut all are hasically the same although the multiplicity of compressor formulae in the literature often cause confusion. I t is advisable, however, to understand the development of one form of t,he equation such as t,hose above and the11 conrrrsion can he made t o any other units that may be convenient. For example to ohtain the total work per unit time the equations need only he multiplied hy the Ib-moles/minute of fend t o t h r compressor. The ~vorkprr unit ~veight* (ft-lh of force per lb of mass) can be obt,ained by dividing eq. 12 by the molecrrlar weight of the gm. Horsepower reyuired for t~omprcssionran lw calculated hy dividing the value of ft-lh per n ~ i r i ~ ~~htninccl ~te firm onr of the equations above hy 33,000 ft-lb per minute per horsepomr. Since the equations are developed on s molal basis the mold heat capacity should be employed. k can be calculated as C,_!(C,m - R'). Polylropic Compression Coefficient

I t is corrvenienl to convert C,,* t o an expression in terms of k.

Then

It is often argued that since actual compression is ncither isentropic nor isothermal, becausc of certain internal irreversible effects, it is prefvrahlc to calculate a work of compression baaed on tlrt, esprcahiun PV" = constant, where n is defined as the polytropic. coustant. Thc value of n for a given gas can be determined from compressor ~ ~ ~ I o I . I I I ance tests using indicator card diagrams d ~ i c hare in effect plots of 11ressure versus volume. Log P

+ n log V

=

log constant

Hence the slope of the indicator diagranl line will give a value of n. These values are neresaarily approximate, liowcrer. The cxpreasion for work in the polytropic case is

Hence or or since P l v l

=

KT,

* T h e work per unit weight (ft-#ilb) as with pumps is unfurtunntcly aften referred wnt~.ifugaleomprpsior pnrlnnee. T h e tcrm it u i iwnd stiould he re~nenlberedto be actually it-lb of foreellb. t o as Head piirticolarly in

332



Tlic I~orscl~on-cr ~Irtcrlirincdfro111 this c.quntion i.< an eh11l:ltiolr of 1111, indicatpd horsepower. Becausc it is so eary to calculntc iscntrnpie I I O ~ P I ~ I O I ~from C ~ cntl~alpy diagrams, the use of the isentrq,ic hnsc for all enlcult~tions11ili mricl~ merit. The calculation of cornilressor xork is at Iltist an al~priiuimation 2nd the ~a111coht::inrrl niwt hr rnrrcrtcil to h n k c llr~rsrprwcr11y 1111, cpplication of an appr~priilt~' e f f i ~ % u fc~~c t o r . I t woulil swm prcf?r:il111!. tlrcrefore, to base all calculatims on the .~ilnplcrisentropic case and us? r:ffir.iencics haserl on the th~orr~tic:~l ismtropic llasis. For recipro~.atin: marllines the compression nrtually appro:~vhes iscntropir operation bcr;lllsc of the ~atcr-jnclictcilrylinrlcr. hut for uncm~l~rl rcntrifugal romIressori that is not the ease althi~ugl~ the iscntriq~icbasis is still rccomrnrnrled (see belun.) .

xr-hrrc 1)

+ CC, = volume: comprr~scdmmsurml a t inlct condit,ions

333

Compressor Operating Efficiency

(I~~uqircssor efficiency ran he defined in a nu~nbcrof ways depending on thc )la+ clioscn. .in efficiency i-aluc ~vitllout referc.nr:c to t l ~ cbasis. therefore, is meauil~glcs~.The use of compressor efficiency,in a111-el-cnt. 1s ;in attempt to awount for the internal irrcvvrsibilities nnrl u ~ c r l l a ~ l i e ~ l losses n-llich occur in actual colnpressii~n. Thcse losses difler for I.?~.iprocatingand centrifugal ct~~iq~rcssion. For reciprocating compressorh, t1ici.e losses :irn fl~iiilfriction losirs including lusrrs tirrough r:rlvcs :in<{ inlds and i ~ ~ l t l e t~nerhanical s, frietim in moving parts SUCII :is tlic pi4toll : I i t I . Lo-ses for emtrifugal coulprrssors i~lclu~le flui~lfrivtii,~~, 1e:tkagc olong shaft rind between itngcs, disk frictiol~iiud 111~(:11alli(,:~l loss~~s in the h r i n g c aurl i~:~cliing.Si~nreof the morc frequ~:ntlyuser[ cfficitmcics arc listcd helo~v.

Compressor Efficiencies !Iis ~lrsirablcat this ]mint to define tlic various cfficienr:ir.s used in the ~ ~ l r r ~ ~ r cindustry. ssor

Isotlienllal efficiency: Volumetric Efficiency

1

I !

I

1

I I

I

-4s r i t h reciprocating pumps the actual volume of gas t&m into the cylinder of a reciprocating comprcvsor is lcss than the displar,ement of the cylinder. The ratio of act,ual volume measured at inlet conditions to thc rlisplaccment is called the volumetric efficiency. The relation hetween volometric efficiency and the clearance (C) cxpressed as a fractiolr of the tot,al displaccmcnt ( U ) pcr stroke is easily derived. The clearance of thc cylinder is filled with compressed gas vhicb re-expands on the return stroke. I t is this re-expanded gas volume t'hat ~ P ~ I I I Y ' the S amount of g;~st,hat cnn be rrreived hy the surtion strokf,. For irlenl gascs the clearance volumc at, suction ( V I ~is)related t o the clearanix volume a t discharge (Tryc) by:

11.L172;= I ) , vl:

Fract,ional voh~metricefficiency

-

IL

=

Inld- ri~lnme - l~isplae~~uient

!

1 !

Iicversible isothermal work X 100 = Er Actual shaft input rorli The actual shaft I\-orli is c ~ p i r a l c n tto the brake horscpo~r-r3r. Isentropic efficicrrey: I ~ ~ w r s i lisentropiv ~lc n-orli X 100 Actual shaft inpnt xork ~p~

-

13,

llechaiucal efficiency Indicator horscpo~ver - Indicatot. hnrsepo!r-er X 100 = h',, Actual shaft input ~ r o r k Hrakc hursepuwer

I

Polytropic efficiency: I'olytropi~.w o k X loo = I?,, .Ictual shaft i n p ~ vork ~t \Then the lldytn~pir:cxl~oucl~t is dctc.rnrincrl f m n ;ln :ictil:rl inrliwtol~ rlingram the pdytropic efficiency bnscil 011 the n w l u e thus dctcrlnineil iapproximately equal to the mechanical efficirncy.

334



335

ugals more nearly approach 11olyti.opic compression than isentropic. I t is: tl~crefore,arguedl and R-it11 merit t h a t the isentropic efficiency of a giren machine ~villr a r y markmlly x i t h the gas. This is true because all tlic losses icxcel)t iuechanical loises x h i c l ~are oniv a small per rent of the totali heat the gas being cu~npresiedand increase the deviation froni iscntropic condition-.. Tliesr various deviatimn rrquire different isentropic efficiencies for c a d i gas considered in one machine.

isentropic base, and e~nployingisentrupic rfficiencies to correct tlleoretical work to actual work. Table 15-1 presents pime t y p i r d isentropic rers nrny bv ci~nsi,lercdto be equirciprociiting ~ O I I ~ [ I I ~ C ~dSfFi O~ ~i ~ . n e iivhirli alent to t h e niechnnical efhirnries a s well.

Suction Volume CFM TABLE O F CORRECTION FACTORS DUE T O COMPRESSION RATIO Where p, Compre$rion Ratio

Inlet Volume in C F M

1500

2000

3000

4000

5000

7500

15,000

60,000 30,000 8 over

:

k =

0 84

I n l e t pressure, psjo

R o t t o of ~ p e c t f l c

heats,

60

70

80

90

100

Pdytropic Efficiency

Fig. 15-17. Rrlirtioualiip t ~ t w t , c nismtl.opir and poiytropie effirimey ior rent) eao~pressws. (.Adaylcd I,? jirrmiwinn. Clwk Brothers Camp;iny.)

Noter: Asterisk lndicoter figurer applying only to high molecu1.r weight hydrocarbons. Factors apply on one comprerror body with sir or less impellerr.

TABLE 15-1.

I n Fig. 15-16 typiral polytropir: ~,fficienr.iesfor wntrifugal conlprcssors arc plottrd reran? thc inlet volulnc. This curve rcprrsentr a n rstimate for :my gas. Tlic [~olytropir:efficiencies, of course, :tko vary 71-itl1 the gas being cmsirirred although nut a s rr~uclias the isentropie. It is, thrrefore. possible t o select a, polytropic efficiency for a given machine aliicli can be used for a n y gnr from a curre such ils Fig. 15-16. Tlic arlvantagcs of working wit11 the isentropic basis, ho17-ever, are too great to be orerlouked. Tlic pu1ytro~)icefficiency may be cimrerted to an isentropic efficiency for the gas being consi~iervdl ~ yuiemsuf Fig. 15-17, and this makes i t possible to use l\Iollicr c l ~ n r t sur entliall~ytables. ~LECIPHOCAI.ISC COYPHE~SOH E;WICIENCY Since reciprocating r o ~ ~ ~ p r e ~so s i onearly n approaches adiabatic c o n pression there should be no hesitation in basing all calculatinns on the

Reciprocating Compressor Efficiencies

bhp

II

=

Isentnipic hp Efficiency

2.5 3.0 4.0

80-89 82-90 83-90

*Multiply the above values by 0.95 for motor-driven cumpressors Temperature Rise w i t h Compression

T h e actual final gas temperature from reciprocating compresstirs can be estimated from eq. 10, or better, a hlollicr diagram, iirrer. tilt, nrncliine

336


approaches isentropic con~pression closely. For uncoolcd centrifugal compressors, ho~vcver,the isentropic temperature riac is not comparsble t o the actual since most of the losses in a centrifugal serve t o heat the gases being comprrsscd. An approximatim of the actual rise can bc obtained from the follon~ingrelation: Isentropic efficiency

=

E,


337

and bhp curves for any inlet pressure. I f the inlet pressure rcmains constant and thc inlet temperature changes. thc iscntropic head remains cmstant if thc compression ratio changcs t o fulfill this constancy (eq. 11 I . Dixhargc pres.surc curves for i11l1.t temperaturf changes, therefore, can be calculatcd from the new cornpression ratio.

C,, ATs C, A16

= --

where AT, = act,ual tcmprmtnrc rise ATs = isentropic t,enlperature rise Centrifugal Compressor Performance Curves

It has become customary for Inany people in industry t o think in terms of air comprcsion nnrl niost michines arc tested n.itIi air. Thc purchaser. however, should r e < j u e ~at pcrformance curve for the gas to be ccmpressed Inlet C a p o c i t y , cu f t / m i n

The same relations developed for centrifugal pumps expressing the effcct of speed changes on performance curvcs can be applied, altliougl~ ~vitllless accuracy, t o centrifugal com~mssors. These are applicable a t the satnc cfficiency points: Inlet Copacity

.

(lti)

cuft/min

where G) = inlet volume N = rpm H. = isentropic head, f t - g l h

based on the design inlet conditions. Volume is gcnerally plotted on sue11 curves in cfm a t inlct conditions versus disr11al.ge pressure in psia. I n addition brake horsepower is also shown. These pcrformance curves (Fig. 15-18] are givcn for sewr:d spceds if the speed of the d r ~ v c ris variable. Another more useful curvc of isentropic head and cfficiency can be plottcd from Fig. 15-18 that r i l l bc independent of inlet pressure variation. This is done by choosing various points on Fig. 15-18 and caiculati ~ i gthe corresponding isentropic head and then the iscntropic efficiency (Fig. 15-19]. Fig. 1:-19 can bc used to dcvelop volume rcrsus discharge pressure

Centrifugal Compressor Impeller Size a n d Speed

Thc v o r k 11r~lucedby one stage of a centrifugal rouipresso~~ is a function of thc kinetic energy and can hc esprcsscd in ft-# per lb as fo1lon.s:

where ITr u

= ft-#/lb = peripheral velocity, ft'sec y, = 32.2 conreraion factor (poundxls

I<

=

per lb of force) ovcrall prrs.sun: corfficient varitls het\i.tvvl (1.5 and 0.05 dcpmding wi itnpdlt~r:mI st:~gr tkxigt~.

338

Compressors ond Vocuum Pumps


hccomes for S .;tagc;:

One large manufacturer designs the major portion of its centrifugal machines for a normal peripheral velocity of 770 ft/sec. Hence for an average value of K = 0.55, 10.000 ft-lb of forcellb per stage is a good average value for estimating the required number of stages. The numher nf stages ii thus set by the overall compression ratio and the x ~ o r kper stage. The peripheral velocity is related to the impeller diameter and the rpm as follows:

where

=

N

=

It is preferable to calculate the hp for each stage separntely since apbe added to the discharge of each stage in order proximately 5 psi sl1~1n1d to allow for friction lusrca in interconnecting piping and intercoolers. For mechanical reasons, it is desirnhle to h a r e approximntcly the same work in each stage. IVit11 actnal gases this does not necesrarily ronform to equal compression ratio per stage." '4 Dodge' repwts that maximum pressurc ratio in any stage of multistage machines is 11etn.ecn 3 and 5 . Each case should he considercrl on its own meritd. ho\wvvr. anil the eriinomical rompression ratio determin~~d in CIIoperation n-ith the cnmpressi~rnianufacturcr. Typical compression ratios used are: Large pipeline rornprc~:ors 1.2 ti1 2.0 1.5 t o 4.0 Process eom~~ressors 6:l ?mall pilot plant high pressure

diam in in. rpm

Hence

N

=uT20a 11

""A

-i 2 0 \ / G , aD d\/ri D

-

The final d c c i r i ~ ~isn l~asedon many factors. I t is, of course, desirable to use as few stages as [,ossiblc. The limitation is the gas outlet teniperature. The discharge teniperatnre of the gas from a cylindcr .should be kept below 300" F. Compressor manufacturer's murt estimate the actual discharge temperature sinct: it depends on the cylinder c ~ o l i u g water arrangement, although a rough idea for estimating can be obtained from the isentropic calculation (cq. 10).

A standard nnpeller size can thus be chosen and the required rpm calculated. Multistage Compression

Rlultistage compression as discussed in this section shall refer to eompression v.ith complete intercuoling het~veenstages. This is accomplished by passing the compressed gmcs thruugh 1,-atcr-cooled intcrcooiers between stages of a reciprocating i.oml~rersor or l ~ e t w x nt ~ centrifugal o compressors. I n this manner the gases can he cooled to near inlet ternperat,ure after each stage nf cotn[~rrs.;ion and the compression process thereby approaches i s ~ ~ t h e r moperation al for which the work of cornpreasion is the least. (That isothcnnal operation theoretically requires the least n n r k for a given roniprcsrion ratio can be seen by comparing eq. 8 and 1 1 . ) The total work of compression in a multistage operation is simply the sum of x o r k in tlrc various stages. Assuming k and the suction temperature t o each stage is constant and setting the differential of total work with respect to intermediate pressure equal to zero the opti~numcompression ratio per rtage is found to he the S root of the overall compression ratio: ( P outlet;P inlet)'/" for each stage x h t w S is the number of stages. This is the xell know1 rule of equal wcork (equal con~pression ratio) for raclt stage. Strictly this derivation l101ds true for ideal gases only. On the basis of eqnal cornpression ratio per stage the total work

339

Calculations for Actual Gases

Most of the equatiuns presented thus far are for ideal gases. At liigh pressures sonic gases deviate markedly from ideal beharior. Tlie pc,rfect gas law has been empirically corrected to apply for actual gases by a multiplier called the compressibility factor.*

Pu I

-

=

zRT

The compressibility factors of all gases have been found to correlate (Fig. 15-20) ~ i t h i nengineering accuracy n-itli rctlnccd teml~eratnre7 " T r and reduced pressure P / P c , lier re T s m i P are the ahsolute temperature and pressure and Tc and P c the absolute critical tcmpcrature and pressure of the gas. For mixtures it is satisfactory ti) calci~lntethe r(,duced temperature and pressure employing pseudo-critir,:il tcuilvrntnl.rand pressures. These are determined from the molal average of the critical temperatures and pressures of the romponents. * I t is often referred to as tlic si~pc~.eomp~.essihility factor. Such sope~.lnlives,however, do not alter its value or rncamng.

1

i

340

Compressors and Vocuum Pumps


341

Cumlxcssit~ilitycan be t l ~ u u g h tof a s :I correction factor by rrllicl~the ideal gas rolumc must be multiplied to produce a n actual rolume. EXAMPI.E:Calcnlate the volunlr occupicd by lGO0 113 of nrrthanr at 60" F and 2000 p i g . Critical tmmprraturr of nwtlxine is -116.5" 1.' 2nd critical prcssurr is A73 p i g .

From Fig. 1.5-20, r = 0.78

1600 . = 100 It,-moles of methane 16

Basis -

T h e volumetric cfiricncy o i reciprocating macllincs is affected b y t h r deviations frinn icienlity, :nld t':~ilure t o c ~ n f i d c tllcsc r deviations n ~ u ylend to niis-sizrd compressor cylinders. Eq. 14, ~vbirliexpresses the rc1:ltion between volun~etriccficicncy, elcarancc a n d con~pressionratio, can 11e derived f o r actual gasps 11y using c ~ ~ n ~ p r e s i b i l icorrections. ty The expanded volume, a t suction conditions is:

I T ~ n a l l yT2 is no1 know1 but cnn 11r approsirnated from t h e ideal gas rrlatinnship

where 1 refers t o suct,ion conditions a n d 2 t o discharge conditions. T h e project engineer niust supply compressor manufacturers ~ i t h accurate values of co~npressibilitiesfor t h e gases t o be compressed so t h a t cylinders m a y be sized correctly. If a n entllalpy diagram is available for the gas being r o i n l ) r ~ s e dt11r , theoretical ireutropic work and temperature can be ralcu1:ited accu-

342


rately and rapidly. T h e difference in enthalpy in R t u per pound molc between initial and final rmclitions a t constant r n t r o l ~ yis equivalent to the isentropic ~ o r kfor a n a e t u d gas (see illustratirc examplrs). If an enthalpy diagram is not a\-ailable, generalized enthalpy charts can be used such a s those of H o u g m and \Yatson.Q T h c ideal gas entlialpy can be corrected to actual gas cnthalpy by using these generalized charts, but the calculation requires trial and error and is time consulning. I n most caws t h e theorrtirnl isentropic horaepo~\-ernred not be known with great acouracy and approximate mctl~odsare justifiable. S u ~ ~ i c r o u ; ; ~ncthod.; h a r e been prop0sed.3.j.l3~,'4 R i d g ~ a y l 3studied ~ t h e effrct of rol~~pressibilities of gases on t h e indicator card diagram and proposed correcting the ideal gas horsepoi~er as calculated l1y equation^ 11. lln, o r 12 to a r t u d ga.; horsepower I y mnltiplying by the aritlimetir average of the snrtion and disrliarg? romp~cssitiilities. This same procedure can also be deduced b y consideration of eq. 9. Compression work for the actual gar can be ertimntrd a? f o l l m s :

Compresrors and Vacuum Pumps

343

temperature. All the formulas presented previously are on the mole basis, and the examples to follow illustrate their use. EXAMPLE 1: A centrifugal compressor is to be selected for comprrssing 462 lb per minute of pure nitrogen at 80" F and 14.7 psia to 40 psia. Determinr the iollo~ving: i n ) Hrnke horse11orver; (b)Sumber of stages; (c) Inlgeller diameter; (rii S p e d in rpni. Properties of S i t r o g m Xolnl heat capacity: 6.97 Btuj(lh-mole)(O R) hlolecular weight: 28 8.97 k-1 - 1 . 4 1 - 0.286 = 1.10 and -- ---- k = k (6.97 - 1.9Xi) 1.4 a. Basis:

=

16.5 lb-mdcs per ~uinutc

($%a)

For a n ideal gas

- (AHf)(7i8)

= 6500 cfrn Inlet ~ n l u m e= (16.5)(3i9) From Figs. 15-It; rxnd 15-17 Isentropic efficiency = (0.767) (0.955) = 0.733

bhp

483 0.733

= -

=

660 hp

Recause of thr lox pressure operation there is no need to correct f n r d ~ r i a t i o u s from ideality. An assumption of ideality is completely within range of accuracy. b. Xnmhcr rlf stagrs: use 10,000 St-#/lb per stage.

Since R i d g ~ a y ' sapproxin~at~ion is hased on correcting the ideal gas horsepo~ver,k shonld hc c ~ a l u a t c dat 0 psi, and w should 111, a n ideal gas specific volume (RT1/P1). T h e method has been popular a n ~ u n gcompressor mginrers because of the ease b y which values iiir ideal gas h o r s e p o w r can he corrected to horsepower for a n actual gas. Illustrative Examples of Calculation Techniques

There is a distinct advantage in using a molal basis for all compressor calculations. T h e basic quantity is then independent of pressure and

966.000 Work per stage -= 8.630 ft-#/(lh)(sttlge) (28)(-l) c. The selection of the impeller diarnetel. depends ronsidernbly on the required rapacity of the mtlcliinc. manufacturer'^ data indicate an 18 in. inli>ellcr for the inlet capacity of 6500 cfm. Fronl eq. 17:

Exanrrr.~2: 1800 standard cfnl (60" F unri 14.7 psin) of natural gas colnposeli of 80.2 mole per r w ~ tC H 4 . 10.3r; C2Hs.6 . 5 ' , (':,HI. 2 . 0 ' ; i - ( ' ~ H I oi~nd . 1.0', is to be compressed in n multistagc reriprrwiting ro:npveswr. The $:IS entcrs the compl.essor ;tt 85 psig and 85" F and is to be compressed to 2400 pslil.

n-('iH

344

Proiect Engineering of Process Plonts

Determine the follon-ing, first assuming a n ideal gas nnrl tlren n n actual gas. .,\ssume complcte intercooling b e t ~ r e e nstages aurl 10'; cleal.ance for all cylinders: ( a ) S u m h e r of stages. (b) Horsepower per c?linrlcr. (c) Total brake horsepower. (d) Elisplacement required for each cylinder. Basis: G ' o-; = 4.75 lb-mo1es;min. Properties of gaseous mixture

Comp nent CHn ('2He

CJls i-CaHlo n-CJ11o

hlolr, r'

/o

80.2 10.3

Criticnl pressure,

wt

Ihcbionnl mol w t

16 30

12.8 3.1

673 717

hlol~rulnr

psin

Vractioual Critir.11 pressurn

Critical temperature,"lt 343 550

539.0 73.9

1:ravtirmnl rritical tPrnpcr:lture 275.0 5fi.7

ll.5 2.0 1.0 100.0

Compound

Mold* C, nt 150" F

CIIr

C ~ ~ + I S Cr Hs i-('411~o n-C,lTlo

* 150" F nssunicd as an

8.!17 13.78 1!)..58 25.82 2616 A r c r a ~ ?C,

R.ar.tionn1 C,,

=

(C,) (mole-irncbion) 7.1'1 1.42 1.27 0.52

0.26 10.66

a v e u g r tm~pw:~tm.e.

Often values of i: nrr t:rhnI:ited. These call be r~rt,
Assuming ideal g m a. Assume tljwe stages.

Fig. 1531. Enthalpy-entropy diagram for

b

n a t w a l gas.

[Rcpl.intcd hv permission, George Grangcr Bmnn, Trans. AIAIE, 160, 70 (1[145).]

345

Compresrors ond Vacuum Pumps

Use three stages.

Suction. 100 psia

1st stage discharge 290 psia

2nd stnge 510 psis

3rd slage 2400 approx. psia

h. Horsepower per stage. (Correction for thc increased pressure needed to overcome intercoolsr 3f' mill he t~r~pjpctcd )

First it:ige: 1.23 -(1544)(545)[(2.0)0.'Y7- 11 1.13 - 1.0

Efficiency from Table 15-1

=

Tot:rl bhp

=

(li.i)(:3)

990,000 ft-!,.'lb-mole

per stage

82 %

bhp/c! linder c.

=

=

=

(990.000) (4.75) (33,000)(0.82)

=

174 hp

322 lip

or 86 5 for each rylinder Displacement of firat stage:

IXsplacernent of second stage

Displacement of third stnge:

From the displncenlents c;~leulatcdabove, standard cylinrlcr sizes and eompressor speed ran be selected. Exact cle:irnnues for the machine selected XP given hy the manuiacturer. I t is particnla1.1y iniportnnt on gas-engine driven cornpressors to select cylinder sizes PO that the cngine will maintain a relatively constant load. In this way fuel economy will he high. Mnst'? has presented an interesting description of the cylintler selection process.

Act~ialgas a. The number of stages should not he altered hy deviations from ideal gas b and c. As a first assunlption ass~nneequal compression ratios per stage. Enthalpy charts for various natural gases :ire available. One such chart for n natural gas 0.7 specific gravity is rcprotluced in Figure 1621. I t can be used for the gas in question since the properties are very similar Referring to Figure 16-21 the compression in any stage is follmved on a corlstant entropy line from i d r t to discharge prmsure. Intercooling is traced on a constant pressure line.

Motors ond Turbines

349

t i I I 1 1 : 1 t : I Ii I f 1 1 n g r o s I-trlikr csliaust steam frorn wciprorating machinery, turhine exhaust stealn is free from iiil and ot11i.r contan~inantr. .4lthirugh tlie dctailed design of clcctrir inotors and turbine. is rntmptr({ to specialists. the project engineer hmefits from understanding eolne of nf o ] w m t i ~ n:!nd ~ froin linnrrinfi tlw tyln- of t 1 1 ~f ~ ~ n ~ l : i ~ n rprinriplcs ntnl inulors :m,l turhinr- tli;~tare ~ n a n ~ ~ f a c t u r c d . ELEMENTARY PRINCIPLES O F M O T O R O P E R A T I O N

MOTORS

\Vl~enthe p I ? s of a magnet : I ~ P~iintlcto f:iec cnch otlier, as slioivn in r gull p r ~ r c c i lin t111, ~ l i r w t i o r Fig. 16-1. the lines of in;ignctic forcc in t l ~ xir of north t o sin~tli:tnd in a straight line. An electric conductor n-I1ic11is carrying a current elso produces a magnetic field around the nire. The dirrction of this field is recalled hy mast studrnts d i c n they ~ i s u x l i a egrasping t l ~ ccondurli,~in tlir right linnd i ~ i t the l ~ tlnnnh 1111inting in the direction of cul.rcnt An\\.. Tlic utller lour fingcri, rhcn, in(lic:~tc the direction of the mlgnetic ficld :lnlund tlic conductor. For illnstrntirc pnrpow~":t l ~ ccro.9-scctim uf a roivhctar 1i:lving ;r (id in tlie I L I I ~ I I I \ ~ i~xlicaie. that the current is flon.ing t o r a r d tilt, rc:rder, d i i l e that hn\.ing :I cross indicates, :IS in Fig. 16-2, that, it is floxving away from tlie r(wlcr. IS t l ~ ccunclucli)r slio\\-n in Fig. 16-2 is plaecd in thc gap hetween tllr. tiyo i1111rs of thc magnct of Fig. 16.1: the field elro~min Fig. 16-3 rr.wlts. The force lints a h o ~ ethe conductor nre implemented by tlio;.c from thc flux of the magnet rvhile tliore lines he lo^ the conductor oppose tlic forces f r u n ~the magnet. This situation produces a resultant force in the illustratilm of Fig. 16-3 in the down~varddirection. I f tlic conductor is 11~lii .stationary and the magnet is free to move, this resultant forre will 1,:luse the inagnet to muve. Conversely, tlic magnet can be 11cl1lr t ~ ~ t i o n a ran(i ? thew inmc ha4c tlic con~lnctori d 1 then m o w . Althongl~o~ersi~nplificd, principles explain tlie operation of nmst motors.

AND

TURBINES

I

Motors and stcam turl~incsarc the most common drivers for machinery in a in'ol!er plant, hut the h i c r bct\wrrl tlictn is not :I ,.imiilc on(,. Porrcr and stcanl rosts and availability niust hc carefully c~~nsidert~d for cach particular situation .4lthough electric mutors arc inherently innre efficient, steam turbines arc more reliable. Tile operation of an electric Inotor depends on equipment such as s ~ r i t c hgear and transforulcrs n.llir.l~, tliouglr usually reliable and good for niany years of service, can fail ~vitliout varning. The steam turbine, on the other hand, requires only a constant supply of steam and such supplies in a nell-dcsigncd plant arc seldom interrupted villiout previous I n wuie areas p o w r costs may he so high t h a t stearn turbines sllould be used n.1lerevi.r possible. Certain services, sue11 as 1oxr-er-speed pumps, 11oaevcr: arc not rcry efficiently 11andlcd by turbincr. Since tlic turbine is prilnarily a higll-syed machine (3,000 t o 5,000 rpm), expensive gear reducers are rerluircd vhcn used to drive Ion-speed apparatus. I n such cases lowspeed motors can be ctnployed withuut the use of gcar reducers. Even when tlic power costs indicate that electric motors should be uscd in a plant. turbinel: may bc advantageously used for some services. Because of their greater reliability, they are very often specified as driveti fur rllarc ~ ~ u n l ~ ~uther i l ~ lsinlili?r d nlacl~inery. 1,arge noncondensing turbines can often be used for the dual purpose of driving a Iargc pump or compressor and for iupplying Iorwr pressure process steam for heating purl~ohcsin the plant. Higll-pressure stuani is supplicd t.u the inlet of the 348

M O T O R STANDARDS

!

1

P c r l n ~ l ~no s other item of process equipment lins been more c n r c f ~ ~ l l p st:rn~lavrliat~d than the electric mntor. The Sationnl Elrctric I\l:~nui;rcturcrs' .issocintion puldialres, an11 regularly rc,viscs, coniplctr ~t:indnrils for motors and gencmtors. These standards are often r e f e m ~ lto as NEXA standards9 They include standard ratings, rliinensions, t c ~ t s . and classification of all motor types. I n addition, the Xntional Elt.ctric Cnde ( a standard of the Xational Board of Fire Undcrrriterr, the S a tional Fire Protection Association, and the American Standards Association) outlines installation methods for motors and gives complrtr instrurtions for their use in 11azardous and semi-11azardous loc:~tions. This c<~clc1 ~ 1 heen s ronwniently interpreted and sunnnnrized in linnd-

356


Motors and Turbines

moue. The process is repeated continuously. I n a standard motor the armature is tilade up of a number of loops and may consist of two or more poles. This discussion is adniittcdly an oversimplified description of the direct current motor. The reader is referred to milre detailed acrounts contained in standard TI-orksin electrical engincering4.l1.l2 There are three basic direct-current motor types:

Direction of M a g n e t ~ cF~eld Fip. 16-1. :I

hligrwtiv field around

p'rmiiutnt niilpn~t.

35 1

Fig. 16-2. Diwcrion oi magnetic field in an rlertl.icn1 conductor,

Shunt-wound Motor

A slnint-~vrninii,direct-current motor is one in which thc field coils and arrriature arc connected in parallel. With this zrrrang~mentit is possible to perniit only a small portion of the current t o pass througli the field circuit. Shunt-~vmnd motors operate a t practically constant speed regardless of the load. Series-wound Motor

Fig. 16-3. Ilistortion o i m n g n ~ t i c field lip inlr.oductiim af rondurtor.

Fig. 16-4.

A aerie;.-n-uund mutor lias the ficlil and armature circuit,^ connct.tcd in serics. .is the load dcvreasez, tlie arlunture current c1eiwii.i~~an11 the iniltor increases spccd. If such a motor is arranged for belt drive and t h e belt breaks suddenly producing no load, the motor will peed up to dangerously high rpm, causing complete destruction of the niotor. Series niotors liave extreinely high starting torques and are adaptable t o such services as crane motors and drives for mobile equipment.

Simpliiied direet-

eurvmt mutor.

hook forn1.l Tlic Underwriters' Laboratory, Inc., has issued standards fur the construrtiim of various parts and fittings for electric motors and appurtenances.

The Compound-wound Motor MOTOR TYPES A N D APPLICATIONS I

Direct Current Motors

A stronger msgnctio ficld can be produced by replaring the magnet is wral~pedwire in the shown in Fig. 16-3 ~ v i t han i r m core around ~\-l~icli form of a coil. As cuvrent is passed tlirougli this wire, a strong magnetic field is produced in the air gap. If the single conductor, shown in Fig. 16-3, is replaced hy a loop, as illustratcd in Fig. 16-4, tlre principles of a direct-current motor can be illustrated. Tlic loop ~vircis called the armature (or a t least serves to illustrate the function of the a r n ~ a t u r e )and the helically-mapped iron core is called thc field coil. If a direct current is permitted to flow in both the field windings and tlic armature, magnetic fields will be set up in both. Tlie south pole of the armature will be attracted t o the north pole of tlie ficld coil causing the armature t o rotate. At the instant the north and south poles are (~ppositeeach other a device called a "commutator" reverses tlie flow uf current in the armaturc, causing it again to

i

I

I

1

The iwrnpound-wound niotor 118s two field windings. O11c is ri~nnertwl in parallel with the armaturc. and the other in series. -4s n~i$it he :us11rrtc(I, these motr~rscomhine features of \loth A u n t - am1 serir.i-\viiunri ir~otvrs. Tliry Iinvc relativrly l ~ i g lstarting ~ torrpwi and will qiccil 111) as tlic load becomes lighter hut not to excessively high slieeds. Thcy arc p a r t i d a r l y useful on appar~ttui; producing varying loads and wliere constant speed is not required.

Direct-current motors cannot be started under full-current loads. It is necessary t o einliloy a starter wit11 a large rwist;mcc so that the rurrcnt can be increased gradually lnlt,il the motor rearhes its nrrnnal s i ~ r e d . Despite the larger initial cost of the dirri+current motor, r o n ~ l ~ a r e d with an alternating-current niotor, tlirre arc rases in wliicli tlit, greater ease of speed control inakes the dirert-currmt motor il ilesirahle choice. Tlie speed of a ,I-c inot,lr is easily controllc~~l, either by rl~iingirigthe, v,~ltt~ge a t the arnlaturr or l ~ ycliwngitig tht, strciigtli of t11v ~iii~giietir field. Reducing tlre strength of tlic magnetic ficld increases the spccd

I

t

!

353


Motors and Turbines

oi tho niotor \\-llile rcducing tllc vultagc :it the : I ~ I I I : ~ I I ~dc~.rcases C t h sprrtl of thc motor. U(ltl1 of tlicsc operations arc :11~1~~,111plisliri1 by introducing variablc resistance in series n-it11 t l ~ eficld coil3 or tlic armaturr windings, respectively.

current. Tllc revolving magnetir field cuts acres.; the coppcr rondur:tors gn the spirrel i,agc and sets up voltages and magnetic fiekls in the r(,tor, the polcs of wIiic11 are nttrattcd by the opposite polps of the revolving field. The rotor of an induction motor must rotate a t a lower speed than the rcrolving magnctic ficld. If it s11011Id rotate at the same speed, thq r i ~ o l r i ~lirlrl ~ g n-o~llrlnot cut across tllc ficl~l ~ )tllc i rotor :IIIII 1111 r r i l l : i f i i . r ~ ~ n ltlicu il he induced in the rotor. The difference in the speed of tilo rotor and the spced of the rcrolving field is termed "slip" and is generally csprcsscd as per ccnt slip. i ~ r l it is re>lIizc(I The s l ~ e i dof the revoking field c:in br c a l r ~ ~ l : ~ twlirn that tlic electromotive force passes through il eau~pletccycle for ew,+ pair of polcs per revolution. Hence, the spwd of the revolving ficld is-

352

Alternating-Current Motors Alternating-currcnt motors may be diviilcd into two general types: induetiwi and syncl~roni,us no tors.

I

I

, I

i

e n i e r n p motor1

Fans

I i1

I

I

I

where f = freqnency in cycles per second I' = numhcr of poles

,,:

This spec11 is tennrrl the syncl~ronousspced of the motor. The actual rotor speed of an induct,iori motor is this synchronous speed corrected for sliu. (ion dip Actual speed = (synchronous speed) The squirrel-cage induction motor is unsurpassed in sturdiness and economy through a wide range of horscpo\vers. B y altering the design of the squirrel-cage rotor, principally hy changing the locatii~nof the rotor bars xitli respect t o the periphery, it is possible to ohtain motors miill varying characteristirs, from low t o high torque, and from I m t o high slip. I n general an inriuct,ion motor ~vitirnormal torque and norn~al darting current is used. I n starting large cquipnic~t,l~articrllarlyq u i l l mcnt under load, such as coinl~ressor,-,it is often necessary to specify I~ightorquc, lo^ starting current mi~tors. I n this dcsign a higher resistive ~liaterialis used in the rotor bars. I t is important for the project engineer l o realize that there are a numhcr of induction motor types manufactured and thc electrical enginccr should be permittcii to specify thc type which has the best electrical characteristics for tlie job. Wound-rotor induction motors are sometimes used instead of tlw squirrel-cage rotor. h wound-rntor ~ n r ~ t oisr composed of insulated coil-: arranged t o form poles on the rotor and the same in number as on the stator. This motor can be started with low current by adding external revistnncc t o the rotor circuit. I n this eamc manner the speed of the motor can be controlled down to about half its normal value. The voan(l-rotor mi~tor,hoa-ever, is inorc expensive than the squirrel-cage

354


type; and is, therrforc, only used on systems rvhich ~vouldrcquire unacceptably high starting currents. Thc stator of a single-p11:ise induction motor can only havc one winding and thns t h r magnetic field does not inove, although tile polarity changrs. If the rotor in suc11 a motor is turned 11). hand an11 made to cross the magnetic ficld, rotation will then procepd automatically as it continues to cuc across tile magnetic ficld of the stator. Hand-starting is. of cmnw, nut ilesirahle an11 a u t ~ ~ r n a t imeans c have been designed. The nlost common means of starting the single-phase induction motor is en~ployed in the split-phase motor which is equipped ~ v i t han auxiliary n-inding locatkd t o differ in its magnetic position from the main winding. The main or primary winding and the auxiliary winding prodnce a torquc on the r o t i r npon application of current, causing tlrc rotor t o nlovc. As tlic rotor attains normal operating specd the nnxiliary rircuit is n p m c d Several different designs of split-phase motors are ~ n a n n f a ~ . t n r e d . ~ ~ l l . " I t is intcrrsting to not? tli:it in polppl~aseinduction motors the rnt~ition of the inotur ran be changed i ~ yinterchanging tlie cunnectiuni ti1 any two of thc terininals. A single-pliase in~,tnr.on the otlwr h a n k vill rot:itr in tlir direction in which it is started by thc anxilinry st;lrting devirc. To changc the rotation of a single-phase motur requires a change in the starting device. Single-phase motors are most frequently used in small horsepower and particularly fractional horsepower applications. Although polyphase fractional horsepower motors can be built more cheaply and are of simpler construction, it is often not convenient t o bring polyphase current t o loeations requiring small motors. A small pump or o t l ~ e rstnall rnachinc may be needed in a remote portion of a plant. In such a case single-phase current used for lighting in that nrca is usually availnl)le and the inotor may he connected to existing lines ~vithoutthe added expense of installing three-ptlasc powcr lines. Synchronous Motors

.is the namc inq~lies,the rotor of a syncl~ronuusmotor rotates a t the same speed as the stator winding field. The magnetic field in the rotor, therefore, must he induced by means other than crossing lines of flux created by the primary or stator. Thc rotor field rurrent is generated by a small direct-current gcnerator called an exciter, which is either aeparately driven or directly connected t o the synchronous motor. A synchronous n ~ o t ~isl r started as an induction motor. The excitation then begins, and the poles of the rotor move in step with the revolving armature field a t ~v1.1lich time synchronous speed is reached. The speed of a synchronous motor dcpencis upon tlw frequency of the powcr supply and thus provides dependable conetant-speed service. This

Motors and Turbines

constant speed, lion.ever, is not its greatest advantage. advantages are:

355

The p r i n l a r ~

1. They can he constructed to operate a t very IUK speeds ( h e l o T ~ 500 I . ~ I I ~ and I

high efficiencies nnd arc, thcreforr, uwful for operation of slolvmoving machinery sucli as reriprocnting con~press~~r.. 2. At lolv speed ratings and a t high Iiorsepo\\-el ratings t l ~ cc<,st synchronous motors is often leas than induction motors. 3. A synchronons motor ran be designcd to operate 11-ith a Ic:rrlin~ uower factor which is advantageous rdwn the inductive load in a plant is large. The lrading pmvcr factor of the synrllrnnmls motor tcnds to cancel tlie lagging power fartur of t l ~ rinduction motur. Starting Alternating Current Motors

Sinall single-plia.se motors are invariably started by applying fllll ~ o l t a g cacl.osa the line. A11 squirrcl-cage induction nlotorr can he startell a t full-line vnltagc. Standard or cross-the-line manual or n~agnetically operated starting rrluipinent is manufactured for this vl.vic,,. Lon. spcrd synchronous motors are often started under full-line voltage, but higher speed synchronous nmtors are preferably started on reduced voltage to lower tlic current (Iran-n from the powcr circuit. Hesist;~nceand aututransformer reduccd-vnltagc starters are used for snrh ccrvicc anrl are :rlso nsed for starting squirrel-cage induction motors w11en it is dcsirnhlp to reduce the starting current in urder to avoid affecting uthcr loads on the power circuit. MOTOR DESIGN AND SELECTION Classification

The National 1 l c r t : l ;\Ianufaetnrers .4ssociation"a rl:is:ific~l ir~otors*in accordance v i t h n~ecl~anical protection and mctliods of cooling as i o l l ~ ~ v s : Classification of Motors According to Mechanical Protection and Methods of Cooling

Abbrwinted list appiicablr lo proreis plants. lldapted from rtandards of thc Sationsl Eleetricd h1:muiacturers .\ssorintion.~ I. Open machine .hopm rnachint, is orir having ventilating openings 11hirh pcrniir p:l..:axe of external rooling air ovrr and around the windings. 8.Drip-llror~frn:~rhine A drip- roof machine is an opm machine in vhich thr w n t ~ i a t ~oprnillgs n~ a1.r * For brevity several lrw inryurtant catcguriss h a r e been omittebfrom t h e NkZRIA list.

356


Motors and Turbines TABLE 16-1.

termed :iirtialit. .\. Tr~tnllycnclosed non\rntil:itcil ~ii:iri~ino A totall!- enrlosrd noslrentilatrd n~:irliinei i n tot:iliy cii<~lwrdii~:~<.Iiit~c n-llich i: not c q i ~ i p p ~Em d corrlii~~ by nnc:ms cstiwxd to thc i.iidwing parts. B. Totally rnclowd f:m-cooled m : ~ c l ~ i n r A totall>- ~ n c l o ~ r Snn-roolr.
357

Relative Costs of Motor and Control Enclosures*

h i v i n g u n i t s locaterl in(ior,rs n-it11 n o iiaz:~dori. : l t l i ~ i ~ ~ j iI)TOIIICII~ hv~ van use t h e drip-proof motors a n d s a w c m r i d c r a b l c nionc3y. I i r i ~ p fe t i q ~ l i a ~ i z tehse desirability of locating s t a r t e r cquipincnt r c u ~ o t c f r m n liaz:~rdous a r e a s or i n specially ventilated rooms t o avoid tlic use of cxploiion-proof s t a r t e r s a n d c o n t r d l . Tile reason f o r t h i s c a n b e rurdily seen i n T a b l e 16-1. H a z a r d o u s Locations T h e X a t i o n a l IClcciric Code' l ~ a sdrfincd various 1i:izardous Iocatiiins. h l o t o r s a n d control equipment a r e ~ n n n u f a c t u r c df o r t h e variou; c l u s c i of hazardous Iocatiuns listed I~elo\~\..

C l w I. Highly intI:umiihl~~ g : ~ sor v:1por-i. Uivisim I . II:~z:~rdorls: ~ t ~ n o ~ p l i te1i.t ~ r r s continr~o1~4y or ran ocior i l ~ l r ~ u g course of norinnl o1,cr:ltion. Division 2 . Flnnnn:rble liqniils bandled and processed hut norninll>-routint~~l. Ilivision :i. L o c n t i o ~ ii~h e r e iqit;ible deposits of paint m i l otlirr fini-lies r.:m ;~ccr~mul:itr. C1n.s 11. Comhuatible dust. Uirision 1. U w t sllrpmded in xir curitiiiuuu.~lyor dixing rottrsc of normal oneration. Division 2. Suspension of dust not likely but idlere drporits oi d w t can I W I I ~ a ~ lw~ ixniteil l h>- sparks. C'la-3 111. L'mribustilde lilhc. ur il>.ings. l)irisiou I . 1.ocations iu s-llicli ignit:~l~lc fihrc. :,re 11;1a,llr~d ul- u a d

Motors and Turbines


358 i

i

2. 1.ocati0w in n-hich rnsi>- icniriblr films xrr stored.

I l ~ l ~ ~ i p n ifor c n t thr-r tbrw rl:i.z-e- of :~tmn-idiert.sran he tested and nppruvccl for t h fo11o!\.ine ~ iltmo~pherict y r s : I 4 . .itrrwphrrci rontninin~;icet?lrnc. gas. Group B. Hydrogen or mlini~i:~ctnrol G r m p C. Eth!-I ether rapor. G r D. I , petroleuiu, n;~phtlin, ;tlcohols, lacquer-solvent, \-awrs, aceton<,,natural IS. Group E . Xletnl 1111st. Gmnp F. Carbon black, coal or rohr dust. Grortp G. Grain d w t .

359

these ratings go u p to 75'C. Yew types of special purpose motors are i n d a t e d with silicune tlasc niatcrinli and tun be opcratcrl rvitIl ],iglles temperature rises. Operation of motors for proli~ngcil perioils above tlir, nornial rated liorsrporwr \\-ill produce tcunpcrature rises in tlic abiive the guilrnnteed wlhr-ahle; anrl. tlicrrhy. i ~ o l . t c ntllc life or c i ~ , ~ ~ plctely destruy tile ~ ~ s c f u l n e sofs the motiir. Most niotor manufacturers will he producing niotors to confo~.rnto tlie revised S E X 4 Standards of 1952. Cbnngc t u the new cloign rl~oulil be complete late in 1955. Tliesc new designs xviil he m ~ a l l e rin size for a given liorsq)i~a.cr rating.

I t is possilile from this list to d~.cidetlie g r w p i n h w11icl1 a l ~ n o e tany nornlally occurring iiazardous rxlnterial \\-ill fall.

TABLE 16-2. Suggested Motor Voltage Ratings* ~

Mechanical Features Tlie highly coinpetitire field of motor construction has produccd e m tiniious iiill~ru\wiirntin iiioiirr design. A typienl modern niotor is illnstvatcd in Fig. 16.5. I n a~lditionto tlie electrical icomponenti already diucuisecl~the shaft ~vliiclicarries tlie rotor is supported b y benrings niounted in t l ~ eend d~icldb. Thpse hearings r a n Ilc oil-lubricated sleeve-type or grr:iic-l!ibrirated hall bearing. Ball hcaringe a r e partirularly popular l~ecauieof the small a ~ n o u n tof maintenance required and the inherent c l w n l i n e i ; ~associated with sucli bearings. Electric motors a r e directronneeted to nioving inaehinery, such a s pumps and centrifugal c o n pwssor.; b y means of a flexible coupling. Belt, gear, and chain drivcs a r e also availablr. I n additiun, t,liere a r e gear ~ n o t o r a~ v h i r hhave integral gears h i l t in tlie n ~ o t o rhousing. These gear motors can be designcd for r;irial)le specd. Motor Ratings Horsel~ower,tlie niost iniport,ant rating of a motor, represents t h e ~ Standard horxyowcrs have been specified b y niutor's ~ O I T - Poutput. X E l I A a u lh,],~ 2 , ? ~ , ' A ; , ~ h , ~1,/ ~ 1% ,% , 2 ,,3% , 5 , 755, 10, 1 5 , 2 0 . 25, 30,40, 60, 75, 100, 125, 150, and 200. ( I n t h e fractions1 sizes 1/4, */", and :we the most con~nion.) I n addition. tlic motor speed in rpm a t full lo;d aml varionr percentages of full Imd, tlic voltage, full-load amp r a g c , number of phases, a n d frequency of alternating current should also he stated. ,. l b c thernial characteristics of a niotor a r e also important and appear on the nameplate of all motors a s a n allo~vahlctemperature rise above the iiiiil~ient tvmper:it~~refor cuntinuous operation. T h e ambient tempernturc fur ~ i i o i tgeneral purpwr nrotor. rlioukl not exceed 40' C , and tlie usiuil wlli~rabletenipclwtuse rise is 40°C'. Totally enclosed motors are rated for a temperature rise of 65'C and with special insulatio~i

Nominal systrnl voltnge

Motors D. C . or myrlhm 1 ubase

~

pon-rr Motors Poly11. C, or phase 1 ~jlia?,, 110 11.5 110/%?0 115 220 230 440 . .. ... 550

...

.. .

... .. . ...

.. . .. . .. . .. . ...

Motor 11ors~:pm~er ITp to 5 ITp t u 7,; 1/, to XIO % to 1,000 %to1,000 50 and larger I50 and largrr 250 and largrr 500 and larger 1.000 mil larger

* Reprinted by permission, Kropi; Virtor J., C'hem. Eng., 68, KO. 7 . 123

(1051)

Xote: Thrse are prrniiisibk horsepo~r-rrratings for indic:itrd r-d1:igrs. Selrrtion of motor voltage drpends on motor costs and the partirulut diitritxction system. A tgpiral a4rction for a plant having 120, 460, 2100, and -1180 fealers and 13,800 prini;~ry roltngr might hr: Motor Horsepower Fractional 1-1.50 15~1000 1 m and larger

Motor Voltage 110 singlr-phnse 110 23M) or 1OO0

13,200

Selecting Motors Although tlie selcction of a motor for a given servicc should be hanrllrri by a competent electrical engineer, it is necessary t h a t the project engineer supply adequate information so t h a t the electrical expert can reach intelligent conclusions. T h e operating characteristics of the innrliinc to be driven must bc clearly outlined. Tlie horseporver, the speed of rotation (rpm) and speed variations. if required. a11 n u ~ s tbe specifie~l. I n a d d tion, the possildity of overload, the variability of loads, the ~iiagnit,urle

360

Projed Engineering of

Process Plants Motors and

AC Motors

DC

, E

Turbines

361

are based on combined experience uf a number of plants and call be termed values in general use. .1 iliacussiun of thc proper motor for rarioui: applications in yrocei:; plants is a lcngthy and involved one, and generalizations are dangerous,

Fig. 16-7. Single-\-rlacit:- stngc impulse tw1,ine. IKcprinlrd hy pwmi.sion. 11. T. ICcnt, .lfeciionied i3nginrei.s' Hmdboolr, Vol. 11, 12th Ed.. John n'ilry 8- Soria

(19501.3 16-8. Two-drcel turbine showing stationary guidc buckets. (S;me rricrrncc as 16-7.) Fig. 16-9. Rp-cnlry nozzle. (Samc refel.cnct. as 16-7.1 Fig. 16-10. Ilelir:\l flow stage. (R:~rncd e r e n c c :IS 16-7.)

Fig.

Wound rotor Synchronous Slnqle phase

Maqnetlgfull or reduced voltoqe. or full mnqnetlc with secondary resistance. Mmqnetlc f u l l a reduced voltaqe. Mrmud or m q n e t l c full voltwe.

Mrmud, ssml-moqnetlc

prucem plant nroior xpl,lic:h>ns. [Reprinted \>y permission. Victor J. I
Fig. 16-6. Typicnl

i1 not i~n~xwsihlc~, ~ t ien~t el r w t i y c11;irt I
of starting torquer. and if intermittent service is anticipated, the frcqucncy of starting sliould he given. The a t m o q ~ h e r i cconditions nnticipated including the possibility of Iiazardous or corrosive gases should be defined. T h e elcetrieal engineer must also he provided rvitli s complete dcscription of the pou-er supply, power costs, and a list of other po~verusers iu the plant so t,l~a.tan intelligent choice of control equipincnt and motors can he made for maximum economy and maximum poxes factor. The choice of the proper voltage to bc applied to a given motor is a n important one and a. suggestion of desirable motor voltage ratings bas hccn presented by Kropf" and is reproduced in Table 16-2. These suggestions

Turbines Inn? he broadly cl~issificdinto t x o ~ul~divisions based on tlic ~lioclcof tra~iimissioni d Iirnt energy into ineclianical encrgy. T h e in~pul.-~ ~ x ~ t ~ t<,[ i i ~wlvrl ,i ~I I H L ~ W d w s i f i w t i ~ n i . 'UI(, f u l I , > ~ $ i tl,ri<>f types. l i s h g r r ~ p r w e ~sui~ir, ~ t s of tlic, tiiore it~ipurt:~ut

362

Motors and Turbines


in F i r . 16-7. Full ~,xpansionof the steam takes place in the i~oszlc,and thc revolving tmckctr: rrccive the .stcan1 without further 11ressurc dn,p and transform the kinetic erlcrgy into work. (bj V E L ~ C I T Y - ~ ~ ~ TURBINE. ~ ~ ~ ~ : S IDn Eurder D to use more efficiclltly thc available thermal m w g y , velocity compoiln(led turhines have brrn rlcwlnperl n.11irlr rcdircct the ateam issuing iron1 the first roll. of bu~.kcts inti1 a second and evcn third row of moving buckets. In this manner ~ u o s t of the velocity of the steam is dissipated. The re-directing of the stcam can be accomplished in several ways. Stationary guide buckets may he used as in Fig. 16-8, or a re-entry nozzle (Fig. 16-9) or the helical-flow "age (Fig. 16-10). The lattcr design employs a specially constructed ~vheclwith semi-circular buckets cut into the rim of the wheel. The -ttmn expands in the nozzle and enters the semi-circular bucket, makes n c ~ ~ m r ~ l180' e t c turn in the hucket, and then is redirected hy the reversing chamber into subsequent buckcts.

I.

363 process plant applications. One of the advantages of a turbine is that i t p r ~ d u e r ~[.lean s lo~r-rrpressure steam n-11icl1IWI bc e ~ n l ~ l o v as c ~ llroccsE l h a m (heating, etc.). The well-~lrrigncd plant, therefore, car1 elnllloy a number of single-stage turbine. as pl~rnpdrives anrl at the ~ a n l etilnc ~ m v i d ethe nccessary quantitics of low pressure pnmaa stcall1 fol. use throughout the plant. T l ~ emore expensive multistage turbine is generally necdcd on large loads, fur which case the steam economy is an in~portantfactor. Tl~esc high-efficiency turhines are then often operatcd as emdensing units for driving generators and large centrifugal cornpressore. In p o w r stations many ingenious means have heen devised for ot~tainingn~axilnnmsteam economy fur each unique situation. A straight condensing cycle can bc cu~l~loycd, or a feed heating cyclc in ~ h i c hsteam is w i t h d r a ~ wfrom the turhines a t various points for heating feed r ~ a t e r . Extraction Turbines

I I ~ ~ d e rboiler n plants produce extremely high-pressure steani. and it is necessary t o reduce the pressure of the stram froin the i~i~ilers 1)eforc~ piping i t t o parts of the plant for process use. Extraction turbines prove extremely useful for this purpose. Steam is withdrarvn automatically from these turbines a t intermediate stages for use as process steam. The remaining steam passes from the exhaust of the turbine t o s condensing system. B y this means it is possible to generate large quantities of poi^--er and a t the same time provide the required amount of process steam at several pressure levels.

Reaction Turbines:

Actually a practical true rcaction turbine is not manufactured. In fact, thc insistence on a rigid definition of impulse and reaction turbines is not advised since t h r last stages in multistage impulse turbines produce m a l l amounts of reaction. What is often referred t o as the reaction turbine should more properly be called the impulse-reaction turbine. The "reaction" turbine is constructed of rows of moving blades attachcd to a wheel or rotor and an equal number of fixed blades attached t o the casing. The fixed hladcs act as nozzles. I n passing through the fixed blades the steam nndcrgoes a prcssurc drop; and, therefore, an increase in kinetic energy or velority. I n entcring thc rows of moving blades an impulse is produced just as in the impulse type turbine. These mo\,ing blades. i~orwver,are designed so that a pressure drop wilt also occur :is the stcam passes through the hladc passages, producing a reaction. The turbine is thus driven hy a cou~hinationof reactive and impulsive forc~,s. Uoht turbines are of the axial-flow type, that is, the direction of r:teanl flow is approximately parallel to the axis of the turbine. One notahlc exception is the Ljungstron~turbine, a reaction-type with radial flow. It is noted for high capacity and efficiency. Single a n d Multistage Turbines*

Single-~tagcturbines ate built in sizes up to 1500 hp in speeds ranging 1ti1111(iM) to ilround 7000 rpm. T l ~ e yarc1 invarial~lyd~signedto opcrat~, as n o n c u n d m r i ~ ~ngn i t anrl Irnvc become particnlarly popular for many

Turbine Application

-

Koncondensing single-stage turbines make up the largest group of turhines for process use. They are gencralip designt.d to o p e r ~ t rat steam pressures up t o approximately 600 psi and a t exhi~ustpressures from 0 t o 100 psi. Special noncondcnsing, so-called "supcrposcd" turhines :~r,, available for operation at steam pressures up t o 2000 111 and exllnl~st pressures up to 600 ib. These turhincs havc prove11 particularly :idrantageous for power stations in which high-pressure stcam is ~ ~ r o t i u c e ~Tll.i ~ , lower-prcssnre stcan1 can then he uscd in the standard ~ n u l t istage condensing units. Condensing turbines are dcsigncd for steam pressnrrs LIII to 900, and in some cases 2000 psi \vith exhaust conditions a t 28 in. oi mercury vacuum. These units are most frequently used for large-scillc, industrial power generation and for driving large compressors and pump^. Mechanical Features

A typical lnnltistage turhinc is shown in Fig. 16-11, Casings are 11urizontally split with the steal11 inlet nod outlet in thc lo~vcr11:11f for e;lsy

364


s i r i r i n g T,mv pi,,wllrr r:lsiugs :rrc r.onstr~~?trd of cnst il,r>n :IIIisl oftc:: ~ a i packing glnnr: ~nctallizrd$7-ith an alloy snrh as a stninles. ~ t c e l: ~ r n ~ uthe to minimize v e a r nt this point. I ) i ; ~ p I ~ r a g m\\-lli(,h ~. makc 1111 the -.lationnry blading of nrultist:~gr turliinci, are grnernlly r~)nitrurti.dof n qtainless steel. The diaphragms are horizontally split in the sanlc nianncr n8 the casings and for the same reason. 'l%e nozzle material varies, depending upon the conditions of operation. ('nst brxss and hronzc, moncl; stainlc.?~steel, all have bem n s r d Wf-i~ilingbc:trings arc providml on small turbine; n-l~ilcforred lullrication drsigns are necessary for the lavger units. 'I'hese hearings are horizontally split and babbitt-lined They may bc r r m o v d from the unit vitllout ili.sturl~ing the c:r.sing or rotor. Althougl~the cnd thrust i ~ n:In inr]iulse turbine is small, a tllrust hearing is ]mr~~icIcii to ni:~intain tllr rotor in its correct positim. The thrust henring is usually a hall-l)c:win?: type, although Kingsbury thrust hearings arc also used. Packing glands are necessary vhere the shaft leaves the casing, and these are most generally carbon ring glands. Tlie rings are constructrd in several segments so that they can easily hc rcmorrrl. I n ~nultistagrturhiues interstage glands are also required. These 11111y be cnrl~m-ring type or Inbyrinth type glands. Since condensiug tur1)ine~opcratc at s1l11atmospheric pressure it is necessary t o seal the glands ta prevent air leakage into the turbine r a ~ i n g . This is most conveniently arconiplislied hy the use of steam. I t is piped t o the glands and a small amount continnously bleeds into the gland housing. Turbine Control

The speed of a turbine can be controlled by t,hrot,tlingthe steam t o the t,urbine or by rontn~llingstcam flov to the nmzlrs in a multist:~geturliinc. For nozzle control the first-stage nozzles are divided into several groups cach of which is served by a separate nozzle valve. The nozzle valves are designed to operate either open or shut (at full-steam pressure) and thns the throttling action is kept to a minimunl. Nozzle valves are opened one by one as the load increases, and a t full load all the valves are open. At fractional loads only some of the valves are opcn. Tlie adventage in nozzle control is that throttling losses are eliminated. Sozzle control shows economies on the large multistage maehines in

EXHAUST END SUPPORT

Motors and Turbines

365

~vhichprolonged partial loading is :mticipated. Most small and medium sized turbines typical of process plant applir:rtions are ilcsigned for -tcnln throttling. Often, hon.e~-er.Iiaird-~.ontrollcdvalws arp wetl t ~ ir ~ ~ t - o uexcess t nozzling so that rnasimun~ fractional load eciinon1:n-ill he rcalizcd. The slxed sensing device, or governor, may be the common centrifugnl type d ~ i c hconsists of t v o rotating \\-eigl~tsrlirect-conncctcd ti1 tlre turbine .Irnft or ronnected through gears. The centrifugal forre on the rot;~ring \wights is resisted by tmsion in connecting spring.-. Tile poritiun of tlrc \wights is indicatire of the spred: and the movement, therefore, can lrc, tr;~nsn~ittcd ti1 tlrc tnrhinc-regulating device. I n place of the centrifugal governor, a so-called "hydraulic" sl~ceilgovernix can bc employed. It irr~nsi~ts nf an oil p n ~ n pdriven off tlrr, turbine rllaft. ('l~wngrs in turhin~, speed produce changes in oil pressure ~vlricl~ can he transn~ittcdto tlic turbine controller. Tlhr tr;~nsnlissionof the governor signal on sninll t~lrliinesis l ~ ydirrct, inc3anstlirol~ghlevers connected to the stcan-throttling valve. On l a ~ g c r turbines the signal is transmitted througi~;I r ~ n a l lpilot valve. Tllc llilct, v a l w is supplied with oil from ;in nil liump ~vhiclrin turn operates a pistun to open or close the steam-throttling valve or tbc various nozzle valves if automatic nozzle control is employed. I n process plants it often h~conresd ~ ~ i r n l )tloe control o u t k t prwsurc or differential pressure of pumps and compressors rat11~rthan use tlrr speed of rotation as the primary control. Irr such rases a dinplrragmoperated pressure regulator is used. It is c;et h r the required ]irwsl~rc or differential pressure and automatically oper:rtes the rtr:rni throttling valve so that the turbine ~villrotate at tbe speed necessary to p ~ ~ I u c c the desired pump or compressor discharge pressure. A standard ccntrifugal-type governor is usually included, liowver, so that it can contrul the turbine should the pressure rrgulator dtmand excessive spceds. Emergency govern~irsarc installed on all turbines. Such governors i,onsist of a ~ ~ c i g l e~:~,rntrivally it n ~ o r ~ n t cn-hclr ~ l , ii; deigned t,) swing out by centrifugal furcc at speeds IIL' 10%):rllovv normal. In bvinging out it t r i p a. dcvicc whicl~closes the luxin steanr v;rlrc and stops tile turbine. Turbine Colculutions

I n preliminary estimates and eronomic studies and for the comparism of bids it is often necessary t o cstim:~teturbine pc~.fur~nancc.P:~lcul:~tions are sitnplc. TurI!ines operate in the reverse fashion t o eunlpressars and the same principles apply. A Rankine cycle is assumed for the ideal case and an ovcrall efficiency is applied to rurrert for actual conditions. 'l'he steam a t its inlet conditions is rspanded i,sentrnpically (constant ch~triqiy)to tho fii~nlconclition. 'I'11e diffcrcnce in entli:~lpyrel)rtwntr. the

366

Motors a n d Turbines


367

tl~coreticnlivork dnnc prr lh cf ~tt~n111.Sinw .\lollit>r diagrams for steanl are readily avi~ilablc.tlli; rn1cul:ition is 111~wt~.onvenientlyand rapidly done on a Mollier diagram. \Vork where 1 1 2 HI

or

= =

=

H2 - H I Htul Ih of steam

(1)

inlet stcam enthalpy outlet steam enthalpy

H? - HI 2544

hp-hr Ib of steam

(2)

Tlw reciprocal I I eq. ~ 2 is callrd the tl~cimticaletcam rate or often the tvater rate. T h e units are 111 of steani per hp-lir. T h e actual steam rate

.-0,c

c

a 30

v

c

0" 20

I Noncondensing 2 Noncondensing

600 psi

4 Noncondensing Turbine Steam Press. 5 Noncondensing Turbine Steom Press. 6 Noncondensing Turbine Steom Press. 7 Condensing Turbine Steom Press. 8 Condensing Turbine Steam Press.

200 400 600 200 400

rn

psi psi psi psi psi

to

Rated BHP

Fig. 1613. Average efirieney of multistage turbines. [Adapted from DeLnmd Engir~erring 17a,idbouk (104i). 1)cLuvnl Strnlrl Twhine Cornpan?-. hy prt.nrission.1

can he cstiniated by tlic application of a n a l ~ p r r ~ l ~ r i overall ate turbine efficiency. Actual steam rate

=

Theoretical steam rate l'urhina efficiency

Values for estimating purposes arv givcn in Figa. 16-12 and 16-13. ' h e s e curves represent typic:~l effirit.nries at full 1,ind and present a correetion factor for obtaining thc (,Hit,ienyy at mr-half loa~i. It has been observed t h a t t n h i n ~ rontrt~llccl .~ by tllrottling exhitlit a lincar relationship between stearl1 consumi~tionin lh per hr (not unit

steam rate in I b h p - l l r i and the load in convenient unite. This straight line, ~vliiehis called the Villiam.; line, affords a sinll~lrmeans fur cstimating steam consunlj~tionfur any loading of a. given turbine when ti?-o valuei arc known. Kozzle-governing tnrt~inesdo not produce the straight line rclationsllil~. hut rather a serics of lVilli;~ms'lines of varying plolles interconnected 11y steps corresponding to each noezlc x-alre o p n i n g . A straight line relationship, h o ~ ~ c v r \\-ill r . p r d u r c cmserx-ative vaiurs of steam HOW for estimating [~urlxrses.

368


T h r propcrtir.> 111 rrl~:irlst itcam from a turhinc a r r of intered !r11en such steam is to bc used a s process steam. These properties can be conv n i r n t l y e.timatrd knon-ing thp tnrbinc cfficit3ncy by subtracting from the initial stcam enthalpy the actual energy in Btu/lb used b y the turbine in useful x o r k [112 - I H ? H I ' \ (Efficiency)]. Since t h e turbinc cxhaust pressllrr is kno7~-n,thc intersection of the corresponding constant pressure line wit11 the calculated final enthalpy mill yield the temperature of the steam and thus a complete description. N o r e conlples t ~ l r b i n can t ~ he analyzed b y similar methods. Extraction turbinc~s,for instance, ill exhibit a scries of Williams' lines for various ~ a l u e sof constant cstrnction fl01v ~ s - l ~ iacrle~ obtained b y adding the extraction flow to t,he original line for no extraction. Turbines eniploying regenerative f e d ~ v a t e rheating cycles and other similar techniques m a y bc handlcd by making heat balances around each steam user with t h e aid of a Mollier diagmm.

Motors and Turbines

369 T h e first con~monuse of gas t u r l ~ i n rin t h e process industries was a s drive, for air cimprcssora suplilying rcgenrration air to Houdry fixedbed catalytic cracking units. Hot pmducti of culilhstion from the catd y s t regeneration cycle ~ v c r eexpanricd in the gas turbine. Any surplus p m c r from the turbine m s utilized by generating clcctric povcr v i t h a small generator connected to the turbine shaft. T h e use of fixcd-bed

E X A ~ P LC LA L C U I . .d~ single ~ ~ ~ ~singe : 350 1111 IS00 rpm turbinr is to opcrare nonromlenrino ~ ~ - isteam th at. 385 psig and 520' F :nld is to rshnust a t 60 psig. a . I'reparr~ a chart shoi~-ingthe steam consumption a t any load. b. llcterniine the :ir,tnal rzhallst s t ~ a l nproperties= 1256 Inlet enthalpy H z 1115 Exhaust enthalpy (from hfollier diagram) = Total enel.gy 141 Btu/lb

From Fig. 16-12 fnll-load efficiency is 22% 2544 Actual steam rate = (141)(0.22)

iood in B r a k e Horsepowel =

82 lh/hp-hr

Full load steam consumption = (82) (360) = 28,700 W h r From Fig, 16-12. half-load factor is approx. 1.17 :. Half load rate = (82)(1.17) =- 96 lb/hp-hr (a)

Half load steam consumption

=

(96)

(g) = 16,800 lb/hr 2

h uerformance curve or 15-illiams' line is plottcd for this unit from these two points. See Fig. 16-11. ( b ) Estimated final enthalpy = 11%- (Hz - H~)(Efficiency) Intersection of 1225 enthalpy line on Mollier diagram with exhaust pressure of 60 psig corresponds to 390' F or approximately 80' F of superheat. GAS TURBINES

T h e gas turbine produces useful work b y expanding hot gases from the combustion of fuel and compressed air (see Fig. 16-15). P a r t of the energy extracted by the turbine is used t o compress t h e air for the combustion ort ti on of t h e evcle,

units d e c l i n ~ ~h ~ i. w v c r ,: ~ n d gas turljincs gr:~ciu:~Ilyd i ~ : ~ p p c a r e dfro111 1)roccis 111i1nts. As ~ilcscribetlh y Millcrl" the Houdry 11r11rr.s~ n.:li unique in it. t~daptahilityto the gas turhine sinw tlic rcgcneration t e ~ n l x m t n r e :rnd t l ~ u sthe gas tclnueri~turcto thc t u r b i ~ l c11ad to be m;iintaineil Iwlr~\\1100' F I)? :lusilinry cooling t o prevent deactivation of thc catidyst. XIterials of construction for turbine temperature v e r c not difficult to fincl. F o r t h e ordinary gas turhine cycle, Imwerer, roml~nstiontrmpcr;iturcs a r c liigli and the gases must be r o i ~ l r ds i ~ m c \ \ - l ~I~cSori. : ~ t rntcring tlic turbine. A:: high tciiil~eraturc-resistalltt111oy:: 11cca111enmrc co:ninon. not ~ :is i n u c l ~rooling n.as required and the dc.sig11 of gas turl~inesI I ~ < , ; I I I I n111r1: simple. Once again, thcrefore, gas t,urbincs nre bring used in many process plants for ccrtain applications in 1%-hichtllcy eSScct c c o n r ~ u ~ i w co~nparcrlto lnotor us stcam turbine drives. h simple gis-turbine cyclc is illuslritted in 8 i g . 16-15. 11 cu~lsisisuf a multistage turbine cxpander, associated colnbustion chambcr for t h e fuel gas, a centrifugal ecnerator. Com- a i r cornmessor, and a n elcetric ., pressed air is fed t o the colnbustion svstc:ii and t h c hot iwmhl~stioneases

370


Motors and Turbines

expanding gase.5 j11rt as in a ste:it~~ turhine produce rotation of the turbine which in torn drives t l ~ ecompressor and generator. Separate speed reducers may he used on earh shaft of thc turbine so t h a t the compressor and generator niay car11 he operated a t n l a ~ i r ~ i u nefficiency. i The stearn turtlinc has proved econumiral as a combination supplier of electric puwer and [Irocess steam and as n drive for centrifugal r o n pressurs. Procers steal11 is removed a t one portion of the cycle. 1x1 a

371

3. rtilizing waitr ga.r.5 for p r i ~ l u r t i ( ~ufn poa-er and rolnpressed air a. hfanufncturinp nitric acid; n-wte pap fro111 tlic acicl absorl)tioll colunln a t 80 psi:, is I I I Y I ~ Ltu~ 900" F hy cxchnngc n-itlr tltr convertor reaction product. an11 t h n esl~:lnilcil in ;I :,:I.< rxpanilcr tltrllinr. Air iconlpresscd for the l~rocessand electric poi^-er is generated frolll the energy thus recorerc~l. b. Regenerating catalysts; products of conil~ustiunfrom the regeneration expand in :I turbine. (li~mprwreriair an11 clrrtrir 1Ion.cr arr generated. Thern~odynamiecalculations for gay turi)inrs systeuls f o l l i w the snnlc ~xinciples outlined for stearn turbines anid colnpreisors. T h e ~ ~ r c t i c ; ~ l p o w r consumed by the air conrprf:.ssor ran h r Ijnsrd i,n iscntvupic cornpressiun. The gas turilinc,'s tlieoretic:il p i ~ w rproducti~)nis cilual t11 tile difference in cntlralpy bctwccn inlct :mil outlet gases. ~ I i l i ~II:IS ~ r givc~n '~~ the following typical efficiencies:

Compressed air to users

p C o ~ n l ~ w isentrol~ie ~~or cfficicncy Comhwtion efficiency T u r t ~ i n cefficiency

Power

Centrifugal compressor

Turbine

generator

H e further suggests us approxin~ations2 111 5% p r e , s i ~ r edrops in the mixing and combustion steps and a 1 to 3% of turbine enthalpy drop lost in operation of turt~incauxiliaries. M a n y ingenious cycles have heen d e ~ d o p c dt o increase thermal efficiencies. Thesc include generation of steanr frum tlir turbine rliscl~:irgcgases and intrndnction of this stram intu the g:im entering the cinnbu.;tion system. Nevertheless, cnel.gy calculations becmue nu trrurr diffirult siocr siuqlle energy halances around each portiou of the e q u i [ ~ ~ n c nare i alw:+ys on possiblf~. Operating tests, I i o w t ~ e r ,must l ~ emade to p r ~ ~ r i c lilat:i e tlicnnal losses nnd efficiencies.

Exhaust gas to waste or steam generation

F i g . 16-15. Simple gas turbine

cycle.

similar manner the gas turhinc has operuted economically as a comhination supplier of electric p m e r and prorcss air atid as a centrifugal conipressor ~lrive. Vhenevcr cheap gaseous fuel is availnhlc such as natural gas, producer gas, or wastc gases, such as products of rnmhustion from n process, the gar turhinr should he c~~nsidered.Some typical applications are: 1. Compressirig of natural gas a. Pipeline boaster compressors. b. Reinjection of nirtural gas into oil bearing fornmtions. 2. Supplying large amounts of process air a . Ammonia synthesis; air for production of synthesis gas. b. Nitric acid ~ n a n u f a c t u r eair ; fur oxiiiatioti of anl~iionia. c . Tonnage oxygen and n i t r u g ~ nproductiun. d . Catalyst regcn~xration; air for burning cokc from catalyst (attractive \\-hen regeneration is rondurtcd under pressure).

85 98 85 to 90

REFERENCES

-

5 . I i r : ~ i t o n ,\Y.J., S l e u n i l'tirbine 7 ' h e w y and Pioctice, 5th E X , Pitman Pul~lislii n g Co.. S e w Y d . 1948. 6 . Kent, W . , Rent's .lldia~ti.ol Euyinrcrs' IIandbuok, V o l 11, Jotin TViley B. Sons. Inc., S e n York, 1950. 7 . KrotLV. J.. Chern. ETin.. Nu. 7.123 (1951). . . 8 . Millr,r. B.. Clirm. ISrry., C. S o . 1 , 175; So 2 , 187 (1955)

372


!,,,. .~[,,t,,+ ~,,,d ( ; c , ~ ~ . , ~ ~S~;~~ wO sI I, : , IE I P , . I Y ~ C : ~ Iwmi:~,.. 1-OI.~, 1949. 10. Xminn. L . E.. -4. lir1li.1..J . 11. 1,yun;. ;ind I,. H. TFnlpi. .llndwn ' h i - h e r , Jolln \T-ile>-6- Son-. I n c . 3i.v York. 1944. 11. Shomlts. D. R., C. J . R i i ? :tnrl T. C . Jolrnron. Elccliic .lli,l~min I ? t d i i s l r y . John Kilq & Suns. Inr. S r w Y o l k 1942. 12. Killis, C. H . . :mil 11. &I. C l i : m d c ~ ~dl.., , 1izlioduclmy Electrical Engineering, D. Van S a s l r a n d Co., Inc., S e w Ywk, 1962. !I .YE.II..I ,sI,,,,,I,,,.,~,~

twr1.s .lsioeia~ion.S p w

OTHER PROCESS EQUIPMENT In the preceding chapters of this section, equipment common to all process plants has been discussed. I n addition there is other important equipment ~vhiclr the project engineer must help select ior certain processes. To make intelligent selections the project cmgineer must have some f m ~ i l i a r i t ywith the theory or c~npiricalu ~ e t l ~ oused d in design and the kind of information required by the nianufnctnrer before recommendstions can be made. Various types of prl~cessequipu~mtare dizcussrd hricfly in this clrnptcr and reierences for more intensire study are given. Information required by the vendor is listed for each typc of equipment considered in this chapter.

Q

AUTOCLAVES I

-

<

Tlrc sizing of el~cmicalreactors is the specific job of the prore% engineer. Cl~cmiralkinetic data togetl~erx i t h 11tmch scalc am1 pilot plant data arr used to determine the size, style, and shapc of a g i r m cl~emioillreactor. The reactors are then built to order. Certain processes, especially those requiring batch operation, such as some polynerization reactions, are best handled in autoclaws. The ~lem:mcl for autoclaves n.it11 attached agitators an11 heat transfer surfactt has influcnccd sercral n~anuiacturcrsto develop a cornpletc liue of suclr l~ ~ , q u i l ~ m rand n t to ofie~.n x~idcrange of standard sizes many of w l ~ i ( ,are avnllahlc f r o n ~stock. In the interest of economy, therefore, i t becomes 373

374

I


n e m s a r y to adapt one's need.< to these standard size autoclaves. T h r volunrctric rapacity uf the autoclave must he ~ e hy t the proccss mgineer t !~.ith the reaction, and since the autoclave mnnufacturer is n ~ ) familiar it is often prefcrslllc to avoid revealing rcartion date o u t d e the company. T h e autocla\-e manufacturer can and should be asked t o d e w l l ~ pthe hcnt tr:micr surface, agitator, and i ~ t h e rn~echanicalfeatures. T h e highpressure p c k i n g problems, thick-wall pressure vessel design, and fahricat i m n i c t l i ~ ~ rn-it11 l . rnrious alloy*: are all best handled by the n~anufacturer since his experience v i t h these problems is superior. Autoclaves m a y be h m l r d 11y hot r a t e r . stcam, direct firing, hot oil, D o r t h e r m , and electric iirating. Each of thcse systems, especially the direct firing, Dowtherln, and electric heating, requires considerable "know-horn.'' which autoclave ~ n ~ f i t linvr n ~acquired s througll many years { l f exlrrricnrc. I t is necessary to p l r ~ r i d ethe manufacturer ~ r i t hinformation needed for the selrction and &sign of a n agitator system: the heat transfer aystcm and the vessel itself. Xlanufacturers arc aware of t h e srcrccy nrces:ary '%-it11somc prowsses, and i t will be satisfactory under these conditions t o describe the reactiim in terms of some similar familiar fluid. Pl~yrical ~wol~cl.tics. l~oivevrr.should he reasonably accurate. .Is tccliniques of applied kinetics a r e improved, it may be possible t o conduct many reactions continuously in "pipe-line" reactorsf which have heen traditionally carried out in autoclaves as batch reactions. Information Required by Vendor

1. Ph!-sical and rhemic:~l properties

i)en.ity of wartion mix nt operating conditions. b. T'isrrlsity of rcnrtion mix a t operating conditions. c. Toxirity and flammability of rraction mix. d. Any other facts or description of material (or similar material) that it is possible to gire. c. IS autoclave is to he used for several iliffcrent rcaetions, give range of physical properties. 2. Opmating eunditions a . ~ I a r i ~ n n presure in inside autoclave. b. Mosirnnm temperature (gire time-temperature cyck or rough limits) Souic idea of rate of temperature rise is necessary for carefd pressure vessel design. c. T!pe heating preferred. d. .Jacket working presure (pressure and temperature of heating medium) r . Is cooling required? Describe cooling mrdiom. f. Ikscrihe extent of agitation required. Suggest agitator style preferred. 9 . Describe ;luton~atictemperature and presstire rontrol system. 3. Mati,riali of construction: Suggest materials based on experience with fluid to he handled 4. Miscellan~ms a. List size, number, and preferred locating of connections required b . Porr-er chnracteristicn. *Orifices are installed in the pipe to produce the necessary mixing. a.

!

~~~~~

Other Process Equipment

375

c . Is explosion-proof equiplncnt required? d . .iuziliary eqnipn~rntrcquircd. e . Loration of equipnient idesrribr).

f. Special attachments required, if any. REFERENCES

CENTRIFUGES

There a r e two primary types of rcnt,rifuges. One m a y he called n centrifuge and tlic otllcr a crntrifugirl filter. Tlic cmtriiugc, effect- >,.pnration b y causing a liquid o r solid t o move throngh a continutrus lirjrliii p h a w under the influence of centrifugal forre. I n the rentriingnl filter, the solid pllasc is supported b y a filtering medinni (e.g., perforated s c ~ c c n i and rentrifugal force causes t h c liquid t o pass tl~rouglit h e solid. The first is similar t o gravitatioiial settling and Stokes' Law can be npplirrl while the second is similar to filtratim and t h e resistance of t h e filter cake plays a n i ~ n p o r t a n role. t F o r t h e settling type machine (centrifuge) i t r a n he shown t h a t Q = 2v,Z, where Q is t h e rate of liquid flow, o, t h e mlocit,y of p a r t k l e sedimentation a n d Z is a constant for a given style a n d size machine. Ambler1 has indicated t h a t t h e performance of two centrifuges of different, size operating on t h e same system will be similar when z7, = r,?. Ilencc Q I ' Z ~ = Qz 'Z2, a n d t h i s relationship provides a means for cornpuring small a n d large scale nnit>s. Correlations, holyever, have not haen <.urnpletely satisfactory, although steady progress is being made in illis firld. T h e greatest success h a s been realized in t h c prediction of b w r i ccntrifuge performance from laboratory data. Some encouraging rcsults Ilavc been obtained \!-it11 other styles, however, particularly when the small scale unit is operat,e.ed a t a speed such t h a t it produces roughly the same centrifugal force a s ~ v i l lbe produced by t h e large unit. Centrifugal filter theory is even less advanced t h a n t h a t for centrifuges a n d tests on large scale units a r e mandatory unless t h e material t r ~11e filtered is exactly t h e same a s t h a t for sonic successfully operating unit. Even in cases for which small scale test results are not reliable for extrapolation, they a r e of value in indicating t h e nature of t h e problem and aid in planning subsequent test on larger equipncnt. On the basis of the furegoing discussiotl i t mould seem t h a t i t is essvntial t h a t t h e centrifugal manufacturer t ~ esupplied with n s n n ~ p l cof tlrc material to he prnccrsed. .I sample size of about 5 gallons for prrliluin;~ry

376



small scale v o r k is satisfactory. Later, larger samplrs may bc reqnirecl to c o n d u ~ ,large t scale tcsts a t the plant site. or it may prore clcsir:~I~le

COOLING TOWERS

Information Required by Vendor 1. Physical data

a. Complete an:rly,sis of feed tn rcntrifngal. 1. Weight per cent -olids :mil lirluidi. 2 . Cheniical composition of each cnn*lit~lent. 3. Possible variations in composition and relative amounts. b. Dnisitj- and viscosity of liquid components at operating temperature. c. Density and viscosity of ired a t operating temperatnre. d. 0per:atin: temperatnre (marimurn possible aften rlwirablc hrcsusc liig11 tlTnlxmtllre loners r i ~ r o s i t r l

q.

I

Fmzility mlcl diapr of pnrtirlri.

2 . Opimting colditiun,~ a. Pmpose of operation: olnrifi~.:~t~on, irpar:ltion, crj-stal i l r h y h t i m ~:,lid

REFERENCES 1. Ambler, Charles M.,C h e m Eng. P w g r . , 48,150 (1952). (Evnlunlion of ecntl.ifugnl pcrio~.mnnecand drscriptiun of one n ~ a n u f n c t u ~C. ~ ~ rU ~~ ~ I ~ I T I I . ) 2. Ambler, Chorles M., Nex Jewry Swtion Meeting, Am. Inat. Chcnl. Enyrs.. M a y 5, 1953. (Further craluatian techniques.) 3. Perry, J. H., Cl~ernicalh',igi?wr's Hundbook, 3rd Ed., 992-1013, hlrCra\v-Hill Book Co., Sew Bork, 1950. (Equiprnunt descr.iption.) 4 . Smith, J . C.. Ind. E n g . Chrnr. 39. 4 i 4 (1947). (Cmtt.ifu~e s~lrctiontrrliniqurs m d < i ? wiplion 01' I Y ~ ~ ~ )~ W I ~ I

T h e perfor~nanceof cooling ton.crs is based on a simultancons transfer af heat by diffusion and conrertion. l l e r k e l expressed this fact mathematically in 1925 nsing the principles of mass and heat transfer. M a n y variations of his original expression have been presented. A typical equation for a counterflow tower m a y be written as follows:

where Z

=

C,

=

height of tower in ft. heat capacity of t h e water I, = \\-atcr rate lb,/(hr) (sq f t of t o ~ v e rcross section) n = xvater surface per unit tower volume, sq f t l c u ft t = temperature of mat,er, F I / * = cnthalpy of sat,umted air a t x t t r r temperature. Utu:lb of d r y air TI = nnthalpy of main mass of air, Rt,111h of d r y air I<, = a n overall transfer cocfficicnt having t,he units Ib d r y a i r i ( h r ) (sq f t of w t c r snrfnce)

h . Gral-it!. scttlin: ratw. if nrui1:~bIe. i. hbmsivcnea- of solids.

washing, etc. b. Disposition of components and quality uE cach ph:~sc (moistnre content of c r y ~ t d s purity , of liquids, rtc.) c. Capacity (quantity per hour and per dn>-). rl. If crystals are being separated and are to he ~vashed,suggest \!-ash liquid, need for sepsmting from mother liquor, mil purity of crj-stals desired. e . Description of the proposed opcrntion of the crntrifuge in relation to thc nltirr procrss is helpful. 3. Materials of construction Cmtrifugrs are constrnctcd of certain itanilnrd niateri:ils as listed in manilfnct~lrrr'scstalogs. Possible reaetirm of thl: fwd or components of the f e d wllh :my of these materials should be noted and :~ltrrilatelnaterials anggcated. 1. hfiscellancous o. Floor space available. b. Power characteristics and type motor reqnirrd (rxplosion-proof, etc.). c. Reed for v;qor-tight centrifuge construction if mntrrials handled are t ~ ~ r ur i c fl;~mni:ihlr.

377

! I

Since i t is ordinarily impossible t o determine the d u e of a separately, the combination K,a is 4 > determined expcrimcntally b y & performance n i t m ~ ~ r r n i e n t son operating cooling to~vcr.;. T h e term h ; n contains all the empiricnl factors of design. I l l m u f a r - 2 m turers h a w obtained rcliahlc > r d u c s of K,a from perforn- _a 0 ance tests on the cooling ton-ers 5 c W they manufacture. T h e integration indirated in thc above eqnation can be done sim__t I by either graphical or nuTemperature nieriral means whcn a saturation i . I - Graphical integration oi curve of humid cnthalpy versus dtIH* - H . temperature is available. Reionthis rurvc a straight line or operating line is plotted based on the inlet a n d outlet enthalpies H I a n d H 2 as shuwn in Fig. 17.1. Values of H* - H are then readily obtainable from this plot for t h e conditions of the problem and the integration can be accomplished. This technique permits determination of K,a for a given t o v e r from

=

I

it I -

378


pcriwmancc (lntn, estiu~atiunof ton-cr performanre un(lcr varying conditiuu., un(l calvulation of t(lxcr hriglrts for \ ~ t r i c lK.,a ~ is assumed. T h r 11" - I1 term is t h r driving force and the more humid the air, the closcr tire oprrating linc mores to t h e saturation curve a n d thus the larger the ton-cr 1111i.t lie for a given duty. I Ire use of this siniplc but valuable tl~coretiralequation in design dcI E I I I ~ upon ~ accurate prediction of design values of K,a. Only cooling ton-cr ~unnufncturer::and perhal~scertain operating companies n-it11 large amounts of (lain on one ii~anufacturer'st o v c r a r c equipped to m a k r sucli predictions. I t . tl~creforc,becomes necessary to supply tllc manufacturrr ~\-itlrone'z rrquirrments and permit him t o dcsign a unit t o satisfy t h e conditil~ns of operation. Because of the magnitude of cooling tower instnllationi, ti1t.i~r~onstructionshould be rcgarrlrd a s a s u h c m t m r t and detailed specificatiuns should be written covering t h e grade of materials and x-i~rlimanshilitogetlier r i t h operating conditions.


379

b. Data on prevailing winds. c. Sketch of apace available for cooling tower indicating surrounding equipment. sizes. d. Location of nearby cooling towers. e. Elevation above sea level.

.?

Information Required by Vendor

1. T>-peof coollng tower Induced drnft because of the lesser tendency for rrcirculation of disch:~rgrd air is brcoming the most common. Forced draft, honrver, is more suitablc for highly corrosive waters since the fan and moving parts do not contact the saturxted rapors as in thc casn of the inilnred draft design. Other types are used for sprri:d :~pplic:ltions. (See referrnce belolv ) 2. Operating conrlitiun~ o. Capacity, gpm of m t r r b. Inlrt water 1cmpcr:ltnre. r . C)ut!rT ~ m t e rtelnp~~mture ilrsired. t temperature r l . Jlespn mrbient ~l-et bulb tmlperaturc. The dcsipn ~ r bulb should be selrcted on t h hasla ~ of economici :~ndshould not necessarily be the liigh<~-t\-:tlue rccurded for the arm. Onr common basis 1s the so-called .5 prr omt irct bulh This is a \wt bulb temperature d ~ i c his not, exceeded nrr~re tliarl 5 per cent of the time: elapsng between June and Sr.ptember. e . h u i l oprrntlon tune (hours) I. Noisr level of fans ,should br spec~fied. g. Acwptanrc~trstr s h ~ ~ u lbr d specified in nrmrdance with thr latest cooling e r Code for atmospheric TTater tm~-ertest procedure of thr ASME P o ~ ~ Test rimling equlpmmt. 3. 1l:rtmali of ronstruetion The type of lumber, filling, hardware, piping connections, basm, fans, and mntori. These details can ljr. developed in coopration with the manufacturer , instancr, bnt should he included in thr specific:~tirms. The term r r i i ~ ~ o o dfor is not complrtely ilrwriptive. Rrdrwrrd is gradrd in accordanrc with thr' sprciiic:itions of the California Rcdwml Associxtion and the proper grade* :nust irr s p ~ r i f i d . 4. M,kccllm~eons n. S1,:ice limitations.

REFERENCES 1. Baker, D. R., and L. T. Hart, Petruleiirn Refiner, 31, No. 10, 97-10' (1953). (Theory.! H. E.. Petroleum Enai., 22. S r , . 3 . p. C-29; S o . 1, I,. C-15; :and S o . 5. 2. Dealer. p. C-25 (1950). iDesrl.iptive.) 3. Kern. D. F.. Process Heal T1-nnsiei. PP. . . 563-6W. McGrarr-Hill Hook C o . . Smv York, 1950. (Theory. calculat~ons,and equipment deseriplions.) 4. Perry, J. H., Chemical Enginecv's Handbook, 3rd Ed.. 789-iYi, MeGmm-Hill Book Co., New York, 1950. (Charts for estimating cooling tower size and inn power.) CRUSHERS AND GRINDERS

Classification of equipment has always bcen considered a primary step in the systematic study and understanding of any ficld. Often, however, classification becomes m i r e of a problem than undcratanding. This itrue in the case of crushing a n d grillding equipment. For marly years grinding e q u i p l e n t has hcen classified in accordance with the type of product. B u t hammer mills, for instance, can hc applied successfully t o f such a s coarse, fine, and s u p t ~ f i n e . T h e production of all types r ~ product project engineer, instead, needs a descriptiun of each typc of grinder currently manufactured including information on its field of application a n d its advantages and disadvantages. Such information is f a r more helpful t h a n some ponderous attempt to classify rquipmrnt. Empiricism reigns supreme in t h e field of crushing and grinding. T!Eoretical equations for calculating power requirements a s propo:ml by Rittinger a n d Kick have proved f a r less accuratc tllan thc more recerit scmi-cmpirical correlations of Bond and Wnng.2 Although effort is hein:: made t o develop basic grinding theory, the ultimatc selcction of a crushrr or grinder for the grinding of a given material depends upon test ~ w r k or upon plant uperating data on the same 11r similar material. Since no single cmnpany manufactures all types of crushing and grinding equipment, a manufacturer should not he expectcd t o give an unbiased recommendation of thc typc equipment to employ for a certain problem It is necessary, therefore, that the cheuiical cngincer make a preliminary selection of a t least several types of grinding machines before making detailed inquiry to the n~anufncturcrs. T h e e q u i p ~ i e n tmanufacturers should then be permitted to conduct tests on the material to be crushed so t h a t thc most favornt~leoperating conditiuns can be determined for the particular type grinrl~r. Smitlr"r:is prepared a must helpful rrport t o aid t h e cngineer in s u c l ~p r c l i m i n ~ qsclections.

380


!


I

4. 1 , l . I . II,,;,cI. I ! , I . 8 . I s 1 3 1 ( r n lI.,, nl gri,,
T h e particlc size of feed and product, capacity, and the size d i ~ t r i l ~ l ~ t i o n and other physical properties of the product irlust be known bcforc i ~ t tempting preliminary ielection. This infor~nation,together v i t h morr. detailed d a t a as o u t l i n d heloy, should he furnished the manuf:~cturcrto aid in the final selection of a unit. Saluples of materials t o be groru~i~l sllould he sent l o t h e manufacturer. A five- t o twenty-fivc-pou~ids a n ~ p l c is required for niost pilot plant units. If a larger scale test is t o Le madc, a t least 100 puunds is advisablc.

opmlms.) 6 . Smith. Jdian C.. Chem. Eng.. .iB, S o . 6, 151-166 p,..tioni to aid in preliminary grinder scle~.tion.)

4. Hygroscopic, rorrosirr, infl:mmablc, tosic, etc. b. Bulk ilrnsit,y of fwd (indirat,e density -~1etemiin;itionmethod). d. Sievc analysis or particle size of deireil groduct igivr Ion-rm and up pi^ limits) e. Per ccnt moisture content (if other liouids Dresmt in the nl:iterial. rime and give percentage). f . Solrents for nlatcrid being" ground. Smcest solvent most desirable for cleaning rquipmmt. g. Abrasire properties. 2. Operating conditions a. Feed rate (minimum and maximum). b. Operating temperature (mximrun ;md minimum; list teniperntures a t ~rhichmaterial melts, decomposes, or r1ni1ergoc.ssomc othrr nnn:~ntcd chmgc) c. Can mntcrinl be ground wet'! d. Is drying permissible before grinding? e . Is heating or cooling of material :dlorvable? f. Type of clasification drsircd aftcr grinding. 3. Materials of construction Suggested materials for corrosion wsistnnce should be given. In supplying this information it should hc rimembered that thrsr, m3tcri:iii must also be resistant to abrasion and eroiiun. 4. Misccllaneons a. Poxr-cr supply. b. S l m r limitations. c. Drscription of proposed location. d. Safety precautions now in effectif matenal is hazardous.

REFERENCES 1. Bond, F. C., Trans. A I X E , 193, 484 (1952). (Theory.) 2. Bond, F. C., and Jcn-Tuug \Vang, T r a m A W L .I n s l . M h ~ i n gM e l . Engrs., 187, 871

(Theory :md cn~.rclntionsfar power czlimntion.1 3. Erickson, Henry W., C h e m . Eug. P ~ o g r . ,38, 63 (1953). (l)cscri~,lim:iml selcc-

sog-

j I

CRYSTALLIZERS

I

I

i

i i

I 1

i 1

I

(1950).

tion.)

(1952). (Description and

CLASSIFIERS T11c n ~ o s tiniportant application of classification equipmrnt is in closed circ~litgriniling where t h e ohjcct is to scparnte finisl~cd~ ~ r o i i u c~ t~ I I tliv I I 111:1tr>ri:11TT-I1ir.11 rcv~uirrv f u r t l ~ e rgrimliug. S I I ~ I a11plir:1tim* I :tw l ~ , . < t
Information Required by Vendor 1. Phyiral data a. Description of m:~teri:~l to be handled. 1. Chemical proprrties. 2 . Simil:rrit?. to othcr ~vcll-kno~~-n m;~tcrixls. 3. Size of piecrs.

381

I

A >upcrrnturated solution liiust, be formed in order trr produce r ~ y t n l i fro111:I given solution. This supcrsnturatiun can bc pro~lnccdlry waling. c ~ n p o r a l i u nrif the solrent, srtlting rlut (:ulrlition of n fi~rcign. ~ ~ l ~ . s t : ~ n r c 11-11iclic;lucrs t l ~ cni:ltcrial of interest to erystallizci. or :I coml~irl:ltionof t l w c ~r~etliod.;.Iinon-ledge of tllc solubility tempcraturc rel;~tion.slrip~ air1 greatly in t h e selection of thc general typc of cry~tnllizinge q u i l ~ m m t . h rclntively flat solubility curve indicates evaporation while a rapidly rising (with t e ~ u p e r a t u r e ) curve indicates a straight cooling type of crystallizer. Couipletc solubility d a t a for most w l l - k n o w n con~poundsliavc been published, and cxpcrimvntiil x o r k is being done in orctcr t o bcttcr undcrstanrl t h c rncrh:inism of crystal fomiation. Such information lias aidcll greatly in improving cryrtallizer design. Crystallizer operation, Iiowvvr: docs not consist merely of the formation of crystal nuclei. Simult:ineon. formation and growth of crystals is colnnion to industri:il c~ystallizcrs, and these l~rocersesare f u r t l ~ e rco~nplieatcrlhy diffusiunal resistanre.~. Tliesc several r a t e processes have also been studied but s u i t a l ~ l yacc~lr:lt(, r:~lcul:ltion of the rate is not yct posril~lc. This lack of reliilblc r a t e d a t a malics it nccessnry, vrl~winllybccnusc of the m a n y different crystallizer rlcsigns, t o design and select crybtallizers largely a n t h e basis of laboratory tests a n d performance ilata. Such test? a r e particularly important \vlicn trace impurities are suspcctrrl since crystal forliiation and g r o x t h m a y be strongly affected b y small amounts of certain impurities. Information Required by Vendors I , Ph!.sieal and d~emicalproperties a. ('hemicnl composition of feed liqlror tracc impurities

382


b. S d ~ ~ h i l i ttemperature ? relations. r . 1Tr:it (if rrystallizatiol~: sperifir hrats of sohltion, mothrr liquor :1nd rrystnl-. ie~ith;iil,y-coneel~trntion diagr:im dr~irableif nrail:ihle). d. llcn4ty of fwd :~n,l~n~othm liq~mrs. r . hiling piiints of S r d and mothrr liq~mrs. f. Tosirity or flamm:~hility, 2. Oprating conditions a . \Yri?;ht of feed liquor per unit time. b. IYeipht of crystals to he formnl. c . Fred tenipimture :~nd final de-irrd liquor temperature and crystal J-irld. d. Desired rrl-stal siar and sizc dictrihntion. (This may hr some tnlly optimum value or ma:- rlepmd on the wishes of the buyers of crystals, whethcr thrw ivi~hesa r logical ~ or not.) e . O p r a h g hours pvr day. f . Sn?- special reqniremmts for finished crystals cho~ddbe stated. 3. Xitwials of con~tructiou S11:gest lnw possible nlaterial~to rmdor. 4. hli.~cellnnrons a . Stpnm prt+s,ire :and trmper;ltllre (npproximatr cost). b. Coding water. 1 . Source. 2. Ttmpenrt~~rc. 3. :Ipprosimntc~ cost. c. Other cooling mrdia available. d. P o w r supply. REFERENCES 1. Perry. J. H.. Chrmieol Enginper's Hnndbook. 3rd Ed., MrGraw-Hill Rook Co., New Ynrk. 1850). (Throly and apparatus dcsrripiion.) 2. Tliompson. -4, Chi,,,,,. Eng., 67, S o . 10, 125 (1950) (Description and sel~ction.)

DRYERS

T h e theoretical aspects of drying h a w received particular attention in recent years, and tlle d r r e l o l ~ m e n t sresulting have aided greatly in the understanding of drying f u n d a n ~ m t a l s . T h c unique dcsign features inherent in the m a n y different typcs of dryers, however, make i t mandatury that the sclertion and final design of a dryer be based on tests made with experinlcntal dryers t h a t simulate the q m a t i o n of the plant-scale dryer. It is necessary, therefore, t h a t samples of the material to be dried be sent to the m a n u f a ~ t u r e r . T h c sizc of t h e s a n ~ p l crequired will depend upon t h e type dryer and t h e nature uf t h e test. A large sample is usually preferred. Drying theory has becn most hclpful in t h e correlat,ion of test data. T h e transfer unit roncept has heen adapted t o thc design of several dryer types, Dryer tests are requircd in such cases for thc determination of drying rates and u p t i u ~ u noperating ~ conditions. T h c manufacturer of a given typc of dryer is the moat logical p a r t y t o make the dryer tests


383

and recommend the design and size most suitahle. T h e potrntial purchaser, howcrer, must make some preliminary deci~ionson the type dryer desired. l f a r s h a l l a n d Friedman2 have prepared a n outstanding section in Perry's Chemical Enginee?.~ Hnnrlhook. They g i w a tabular classification of commrrrial dryers. Thcir detailcd d i r r u s s i ~ ~ nof s dryer types, design, selcction, and test proce~inresaid greatly in the preliminary dryer selcction. An example of dryer selcction is also given. Information Required by Vendor

1. Physical and chemical properties a . Description of material (chemicd name, rharacteristirs xhen iret and dry). b. Size, shape, and size distribution of particles. c. Density (bulk and true) of w t , commrrrially dry, and boue dry m:+terial. d. Toxicity, flammability, and corrosive nature. e . bloisture content of feed (give bas>. and methud). f. hfaximum moisture content nf pr~lrhlrt igirr :1nd mrtlmd). g. Shrinkage and decomposition tendencies of iliatrrial, if kno~vn. 2 . Oprrnting conditions a. Feed rate. b. Continuous or hatch operation. c. Honra operation per day. d. Treatment of material before and after drying. (Will some "beforetreatment," such as forming rr-rt material into pellets bc prrmissible?) e . Estimatc of probable drying time. f. Maximum drying temperatnrcs perniisible (~vhen~s-etand d v ) . g. If hot air available, rr-hat is maximum trmperatnre and hnmidity? h. Fresh air supply (temperatun, rxnge, hruwidity, xnd cle:dinrir). i . Room temperature (range) j . Feeding mechanism iby n~anufaetureror p ~ c l ~ ; i i ; edescribe). r, ic. Fuels available. 1. Steam (pressurr and trmprmturei 2. Cns (prcssnre, grarit5-, hrating value). 3. Oil (gravity, viscosity, and heating r d n r ) . 3. Materials of construetion Specify where possible in coopiration with m;~nufncturer. 4. Miscellaneous a. Space available (drscribe or r~rovidrsketch). b. Floor loading. c. Type of automatic controls desircd and ~ h furnishes. o d. ~ & r rsupply. c . Motors and starters (type ;and !rho f,~rnishrr). f. !Tho will fnrnish air filters and other xccessnrie.5 (i1,wify) REFERENCES 1. Friednrnn, S. J.. l l p a i i r < g ond I'c,rfilrrtirq, &, Yo. 2 . 96110 (18.51). (D1.ycl.srlwtie,, ,II.O(.P,~LII.P.)

384



385

subtracting from the total cost tlie estimated r:~lue of inatrrials nrccssary to make the individ~~al offering compatible n.ith the arbitrarily chosen base design. Information Required by Vendor EVAPORATORS

I n addition to the three so-called standard evaporator designs (natural-circulatio~~,forced-circulation, and falling-film typcsi tlierr a r c nunicrous spccial designs which are built t o 01-crconle certain unique problems. Tlic coniplexity of the heat transfer p r ~ ~ c e sins boiling and t h e variety of merhanical design features make t h e dcvclo]xnent of throrctical iuctliods for estimating overall heat transfcr ~ d l i c i c n t sfor evaporation ~ for approximating t h e w difficult if not inlpossihlc. A l t l i o ~ g lmethuds coefficients have hccn developed, previous experience and tests on pilot scale units represent the only reliable means for obtaining design coefficients. Here again the burden of design rests ulwn the nianufacturcr of the equipincnt. T h e average chemical engineer is f a n ~ i l i a rnit11 tlie heat and material balance calculations necessary for the design of a multiplc effect cvap
1. Phy:.ic:d and chemical proprrtics of thin and heavy liquors o . nr;rr~ptint~oi mntcrial to be e\.:iporated (ehcinicnl analysi? including in11111riti~s prr~-ntj. b. Boilin. points. c. Ileneitir. d. \~isr,ositi?s(:it several trmprmtures). e , I'm rtwt soliils. j . Frx~mingrh:~mcteriitics. y . F1nmm:ihility and toxicity. h. Nature of solids. 2. Operating conditions a. Quantity of thin liquor per unit time. b. Holm operation per day. c. Temperature of thin liquor. d. Higl~esttcmpemture that liquor mn be heated rrithout causing unfnrorable results. e . Quantit>- of solids to br srpnmtrd pcr nnit timr: or uuit nmount ui f e d 3. Materials of con?trnction In the evaporation of many mnterinls rert:~inmetals are not unduly corroded, but they contaminate the prrduct sufficiently to render their lile inadvis:~hle. The manufacturer should be given such iniormation psrticularly r i t h regard to the behavior of iron or steel. Suggestions of suitable materials should be rna-hen possible. 1. .Miscellaneous a. High pressure and exhanst steam available at site. 1. P r e w m :mil ten~poratnre. 2. .ipproximate cost. 3. Restrictions on use if any. 1. T:ltiinnte we of evaporator condm~ate. b. Cooling nater. 1. Tcnlprr;tture (m:~rirnrm~ nnd iniuimlm). 2. Sourer and drscription. 3. Restrictions on uue. c. I'orr-er supply. d . Spare nvnilnblt. (provide plot plan). e . Special equipment preierences soeh as types of pumps, drives, auxiliary equipment, and valves. REFERENCES

1. Coates, J., Ciiern. Eng. Pwgr., 6/,. 25 (1049). (Estimating required area, capncity and s t m m t.erpilmnents a i multiplc pffect evaporators.) 2. Iicl.n, D. Q., Pioceas H e n t 'Z'mn~jci, ~~~~~~~~Hill Book Co., S c w Pork, 1950. (Calculntians.) 3. I,indscy, E. E.. Chent. Eng., 60, No. 4, 22; (1953). (Evaporator types, ndruntnges and di.-ndrantag~s.1 4. Starrow, J. .A,, Ind. Chsmisl, 24, 311 (1948). (Cnl,:ulation%)

386


FILTERS Filter ~~iiinufactnrers n ~ a i n t a i n ~vell-equipped laboratories t o study r u t o m c r ~irohlcr~is and to dctcrminc cnginerring d a t a for design. T h m ever possible sarnplcs of the mnrrrial t o l ~ efiltrred slioulrl be sent to t h e tnannfacturrr. \Tit11 apprmimately 5 g d l o n s of samplc, bcncll-scalc studies can bc m:~clc\\-it11t c ~ filter t leaves ollernting under vacuum. T h e filtration eharactcristir~s elucidatrd b y thcsc tests usually can 11e interprctcd in tcr~ii; of pcriornxmce of the various filter types so t h a t a size and style of filter (.an l ~ ererommended. Leaf tests in unusual filter problems sometimes shmv need for further pilot plant st,udies. I n such casc.s larger s a ~ n p l c sarc r ~ q ~ i i111r r ~tests ~ l on actual pilot scale filters. If more con\-rnient. filter m a ~ i u f a c t u r e will r ~ make t l r c ~ csnlall scale filters a\.ailahlc ti1 tlie c u ~ t o i n e ra t the ulant site on a loan basis or for a nominal rcntnl fee. T h e majority of ur,liiliiry f i l t r a t i ~ ~problen~s, il I i o w ~ e r can , 11e resolved b y inerely supplying the w n d o r with certain pertinent d a t a as outlined belo~v.

Other

Process Equipment

387

b. Chararteristirs of elrctric porr-rr, rr-ash ~ a t e r .: i d steam nvnilnhle :it plant d r .

.lir filter. require -p?rinl rrrnsiilerntinn. Of p:~rricnlar importnnrr is ;in analysis of partirle ,size distribution of solids in the :iir or gas to hr f i l t t v i l . Sw11 :in annlysis rrquire. careful trrhniq~~ra rincr psrrirle iizri are small. Air filtrrs can be employed in r ~ m o r i ndust. ~ above :~plin,xin~ntd:-0.2 nlirrunr nhile smaller sizes i n l l r t hc handled by elertroit:ltie prwipitators. The purity of filterrd air or gas shorild hr q e i ~ f i c d .Test', wl~rre~ m s i l h are , strongly recornmrndrd brca116eof the many rnriahle- rrhich rannot br predir.ted

Information Required by Vendor 1. Physical data a. Urserintion of material to be filtered (chemical composition, of liquid

and solid induding pW). b. Per cmt cakr: forming solids in slurry. c. Density of solids. d . Density of elear liqni,l at sevpral temper:it~~res. e. Filtration temperaturc. f. Y i ~ c o s i tof ~ filtriite and slurry (:1p1xnx.) at filtration tmmp~ratnre. g. Ilcwription of solids. 1. Sm~ily,gmnular, cryst:~lline,slimy, elc., prrcentage of each t,ype. 2 . Screen analysis of dry solid. 2. Operating conditioms a. Ouantitv to be filtered ner unit time. b. Operating time per day-. c. \Thich nortion of slurrv is to be recovered lfiltrate, cake or both)? d. Cake rl'aracteristics if available. 1. Is washing required? 2. If ~wshingis rrquirrd, vhnt is minimum purity permissible? 3. Most wash liq~iidbe iiolatrd from filtrate? 4. Give cmcking tendency of cake during washing and drying. r . Uescribe most important goal of the filtration and l i t s~condarygoals. (Ez31nple: n n s i n n m filtrate rlarity.) :i. hIat,eri:~lsof const,mction ilny rsperirnces rr-ith mctnls ;ind othrr materials in handling the slurry should trr, shared rrith thr filter m:m~fuctorer. 1. Miscellaneous a. Konnal barumetric prwsure.

HEATERS AND FURNACES Design of a lieater or rracking furnace requires thorough lino\vlerlgc of hcnt transfer, fluid flo~v,and prol~ertiesof inctals m d refractories at Iligli pressures and t e n q ~ e r a t n r r s , Smue years ago tlrc inajority of t.he direct. fircd heaters were uscd t o enp11Iy heat for crudr distillation unite, and the design v a s c n q ~ i r i r a l . As the use of these heaters expanded and applications ranging from distillation tolvcr rchoilcrs to rcartors hecanic widespread, a stronger theorrtical basis f o r ~ l r r i y u v a s developed, especially in thc calrulation of both thc inrlixnt and convcl6on section heat absorption. Furnacc design has. therefore, l ~ e c o n ii~ ~ .specialty. Furnace manufacturers maintain a staff tlii~tspecializes in furnace design and ci~nrtructiun. Sonie sn1a11 f~lrnitcesrim be huilt a t tlie i'i~(.toryand shipped complete to the plant sitc, d i i l e the largcr designs r n w t be erected on the job. T h e engineer responsil~lefnr selecting n f u r r ~ a c eprofits frmn knu\vledge of f u r n a w design. Perhap:, thc nus st 11elpful paper (111 tlris sr~lijcctis that by Rickerman.:' H e pre~t,ilts:I good rle~criptioiinf lieater types and outlines in simple terms thc steps involved in c n ~ ~ i l i l ~ f ut vm w ~ I w i y n ;\ usrfol bibliography is givcn. I n the development of cracking furnaces or a n y other furnact: in wllici~

\

388


a rhcniical reartion occurs, the process engineer si~ouldrlctcrn~inetlrc zizr and length of tube required t o produce the reqnircrl reaction a t a q ~ e c i f i t d Ilcat flus. F a i r and Rase? have demonstrated the method for eurh c a l c ~ ~ l a t i o n hased on the principles of chemical kinetics. T h e furnace rlesipnrr conq~lctcsthe 17-ork h y 11roviding the ~uechanical aspect; of tile design I 1 a 4 on tire required llrat flus and tclnprratnrcs. Tlri- n.ork incl~~rlr. sclectim and location of t u l ~ e sand burners, selection of n ~ : ~ t e r i a losi constvuction and structur;d design. The a ~ i i m ~ofr ~information t required b y the n ~ i m u f a c t u r wvaries sjnlcn-hat depending on the cu.4onwr. S0111c plant> 11refcr cert:~in l ~ n r n c r designs a n d header :rrrungemcnts, for inst:irr~.e. Sncli lneft.renrc5 shonirl, to :~voiilc11stl:of ~ I I U I ' Z C ,hc c l i w l y stated during the cnrly i ~ q u i r >>tag? dr~laysa s the project proceeds. Oils for ~vlrirhgeneralized correlation^ are availnblc nccd not l ~ c- or API gmrit?- at 60' F. (Also de~wityat othcr trmpcraturcs,

if :lv~d~lhlc.) c. Tisro4ty int several tcmperatirrrsi. (1. ~1d1~rrrl:rr \wight of vapors at inlrt and outIr& I , . Cukinz r11;rmrtrrLtica of chnrgc. 2 . Oprmting conditions a. ('112rpe r:,t<,. b. Ink~ttcmpcr:itnre :mil prcwlre. c . Outlrt trrnper~tnreR I I , ~ prc-me. d. Pcr crnt rnporizrd i n inkt : ~ n doutlet. e . Stntt, ninsimnn~alloirable prcierirr drop. f . Maximum :illowablr radiant hr;it tmwfer mte. rj. F ~ ~ r n n c dut? r (BtuJhr ;ibsorboll. 11. 1Iini1111mvclocity of Horr. (if i n ~ l ~ r ~ r t : ~ ~ l t ~ i. F I I ~rompltT<~ ; 1lmcri11tion (:~n:rly~i. uf g:(,- c I w i r : ~ ~ l ~ ) . 1. IIrat content ( l o w r 11rxti11gv:~hw). 2. l'n.rsr~rr~:at iurn;~ee. 3. Tiscnsity (oil). 4. Dmc;ity. .5. Trmpcrature. j. SILWIIprwure :rt f ~ ~ r u : ~ r r . k . F u r ~ ~ a cefirirncy e ilcsired (give e s c w air on wllirll b a d ) . Rtiicieney

=

Duty - X 100 Heat libeluted by Rre!


REFERENCES I . l i r ' m I ) . Q..Pi-ocen Hcnt Ti-orialcr., M~.Grna--HillBook Cu.. S e w Yolk, 1950. 2 . T;iil. ,I. R . . :mi H. F. R a w f'hr,,,r. E u g . P;ogr., SO, 415 (1954). 3 . 10,~Ir~~m~;in. J . H.. 7'mma. A n , . S o e dl?clz. E , i g ~ . .67. 531 (1954). S w :+I-,, t ~ i t ~ l i o ~ r a at,~m h yd of t l ~ k>m+icIc.

MAiERlALS HANDLING 'Tiit> .r:trcity and high cost of l a h during World TVar I1 created a wvolution in the materials handling field. Hundred? of n w and ingcnions i l ~ v i r cwcrr introduced. and the proper aelcrtion and application of inaterials 11;wIling equipment has become more coniplex. One univcraity is non- offering a degree in materials handling cnginccring. I t is s d v i s a h k , tl~er[sior(,.t h a t thr. projcct engineer seek tlic as&:inrc of cunil~anyreprewnt:rtives trained in t h e field of materials Irandling. A general knowledge oi tlie c ~ i l n i l m ~ v n11et. t T h e printed methods for selcctii~n can rnsily i ~ c mi-intcrl~rrtcdby the occasional user. \ \ k i t lins been said ahout conveyors hold? equally \\-ell for oilirr ~n;itcrialsl~andlingc q u i p ~ n t ~ n tI. n all cases tht: purcliaser slrould s1111ply cm~lpletrinfor~n;ltion; b o u t tlit, naturc of tlie 11111tt,rialto be l~ar.~lled, it. wigl lit, tire esnct purpose of tlic l~andling.a n d tlic proliwed layout sIro\ving free spare available. T h e int'ori~intion required by a vendor of conveyors will serve a s an illustration. Information Required b y Vendors of Conveyors 1. Physirnl and cl~emienlproperties a. Size and size distrihution imasi~nunil~nmpsizes in inches) b 1loisturr content. c. ?'imlwr:~tin.r. d. Uensiry uf ~~~ntcrl;rl il~nlki u d r ~ (le~lsity). d

390


e . .ihrasiveness, chemical reactivity, stickiness, etc. f. Ability of mat~rialto withstand conveyor action. y. Corrosire nature. 2. Operating cornlitions a. Trmperature and humidity in conveyor area. b. Maximum rate material is to be handled. c . Length and location of conveyor including sketch shoving proposed path of travel. Indipate adjacent equipment. REFERENCES 1. &,oi;Irl X o . 2 of Lihi-ary of Knumiiow, Materials Handling Institute, Pittshl~wl~, Pa. (1953). (hlcthods for studying and valuating materials handling problems.) 2. Mallirk, R. \V.,and A. T. Goudr.eau. Plant Layout Plnnning and Pruclicc, John Wiles & Sons, Inr., S c ~ v1-ork, 1950. (Inelodes section on materials handling.) 3. .Uode,,r .lIute,-iols IIundlirig, 8, So. 6. 58 (1953). Pnpvra presented on couvryul. application nt Conwyor Institute, Univ, of Ill., April, 1953. 4. Mi11 and Puctoly, B, Xo. 1, 82 (1953). (Selection of monorail systems.) 5. Pallet Patteni Selection, Materials Handling Labs., Inr., 795 Boylston Street, I3oalon 16, Mass. 6. Stockcr, Harry, Xoten'aLs Handling, Prenticr-Hall, Im:., New York 1951. i . Stnihc. H. I,., Chem. Eag., 01, RTo. 4 , 195 (1954). (Report on conveyom and ric\-ntors, de~igninlo~mation,npplieation, aud election.)

MIXING EQUIPMENT T h c proper selection of t h e size a n d style mixer most suitable for a givcn service requires laboratory study. A complete description of the matcrials t o he mixcd must be given t o t h e manufacturer so t h a t synthetic mixes can be prepared. Better still a n actual sample m a y bc provided. T h c past five years havc seen rapid development of mixing theory. Following t h c principlcs of dimensional similitude, small scale rnixcrs can 11e tested undcr conditions dynamically similar t o those required for large scale opcmtion. Scale-up of power requirements, a n d impeller and t a n k size can be made with confidence. T h e prucedurc for mixers involving liquids is typical. Preliminary tests a r e niadc in a small glass beaker (approximately one q u a r t ) using a scale model of a mixer. Optimum power requiremcnts a n d impeller types and position are then selected. F o r simple mixing problems, scale-up of this information to the final plant size is possible. W i t h more complex problems intermediate scale-up t o pilot p l a n t equipment followed hy additional tests in large tanks yield more reliable d a t a on impeller diameter and power requirements.

Information Required by Vendor 1. Physical data a. Completr drscription and wmght per cent of each component in mix. b. Viscosity and dmsity of each liquid component.

Other Process Equipment c. Viscosity and density of mixture. d . Solid comlirment description. 1 . Particle sisr and distribution (sirre analysis). 2. Density of d q solids and settlrd sh~rry. 13. Settling vtlocity. 4. Xature of solids: soluhle, ~ ~ S O I I I I I I cr!-stallil~e, I~, light ill iwigl~t.c~tc. P . Voaming tenrienc>- idrwribe). 2. Operating conditions a. Purpose of mixing: dissolve solids, blend liquids, disper~ftgas i n liq~~i,ls, suspend irrlids, ctc. b. Type of agitation required (violent, intemiediatr., or mild). c. Type operation. 1. Aatrh (give typiral maximum, minimum, and normal batch sims :and time aroilable for mixing each batch). 2. Continuous (give flow rate). d. Vessel description. Supply a complete vessel drawing showing all dimensions, type heads, and operating and design conditions. 3. Materials of construction Sugpst materials most suitable for those parts of the agitator that will contact the mix. The mare possibilities given, the greater freedom thr rnanufactiirrr nil1 have in selecting the most rconomical and mechanically sound matpri;rl. 4, Miscdl:~neous a. Electrical power characteristics. b. Type motor required (splash proof, tatally enclosed, explosion proof, etc.) c. Space requirements if unusually limited. Certain special information is required for solid and paste mirrrs such as knraders and millers. This information includes the abrasive ;and shearing properties of the matcrials, a sieve analysis of the solid, quantity of liquid if any to be added, and the amount of heating or cooling required. -4 description of the purpose of the mixing, such as the dispersion of pigments, is also necrsary since this governs the type mixer and blades.

REFERENCES 1. Bautlms, R. D., Chpm. Eng. Pi-ogi..,48.211 (1952). (Mixer installaiiorl and muintpnanrp.) 2. P ~ r r y J. , H., Chemicol Engineer's Hnndbook, 3rd Ed.. 119&1231. iLlrC~.mr-Hill

Book Co., New Ywk, 1950. (Mixer t,ypes descrihcd, tables giving prefewrd mixw typps 101. variow mixing jobs.) 3. Rusbton, J. H., C h e m . E7tg. P T O ~ T47, . , 485 (1951). (Pilot plant. mixing data arid scsl~-upinwredure.) 4. Rushton, J . H.>R. D. Bout,roa, and C . W. Selheimer, in Encurloptdin n j C h c m ienl T e e h n o l o g ~(Kirk and Othm~r-~ditors).Vol 9. 133-166, Intcririmrr Enryrlupedia Iud.. New York, 1952. (Equipment description and application inrludcs solids and pastes.) 5. Rushton, J. H. and J. Y. Oldshne, C h c n ~Eng . Progr., .jB, 161 and 267 (1953). (Review and theory and spplirations.)

SEDIMENTATION EQUIPMENT

A simplc laboratory settling test in a graduated rylinder will often indicate t h a t the separation of large quantities of liquid from a slurry

392



c:rn hest he accomplished by a conil)ination of settling nnd then filtratiou T h r test n-ark needed for the proper selectim of mlimentation erpiipmt~nt. Ii~~wevcr, must go f a r hcyond such laboratury settling tests. Settling problems though seemingly simple can hecoinc very complex hecause of the many factors involved. These include the marked effect of equipment design on settling a n d t h e many physical and chemiral fartors n-hir.11 affrct settling characteristics of a given slurry. Tile observations uf Coe and Clex-enger in 1916' are valid today. Tlicy observed sex-era1 settling zones which, for a continuous t h i c k c n ~ r niay , l~c described from top to bott11111 a s a rlear zone, n zone of fced consistency. an intermediate zone, and finally a zone of compression. T h e settling rate of the niaterial representing each of these zones r a n be iletermined experimentally and the area required for each zone cnn he calculated. T h e following expression is used t o estimate required areas for cont i n u w s thickeners. This equation is simply a material balance.

AR

=

Information Required by Vendor 1. Physical and chrmical data a. Complete description of feed and analyeis, including pH. b. Settling rates if an rail able. c . Tosicit?, H:unn~ability,atid mi? utlier h;izi~rdousproperty. d . Quality mil consistme!- of proclucts desired including wight ratir~ nf liquid to solid in nnilrrHon and maximum permissible sulirl-. in clear liquid. e . 1s rlr:~rliquid to be wed? /. 1- i~r~drrflonto he used? 2. Ol~i,r:itineconditions o.

Frrd rare.

b. 01rratin? 1eliilx~t.:itIire. c. Shm~1~1 l w i t be i.,m-er~rd? (1. 011t(Ioorur i~i(loorqwr:itiou.

S(F - I ) )

P

where A

R p

F D S

area required, sq f t settling rate ft,:hr = density of liquid, lb,/au f t = weight ratio of liquid t o solid in feed = weight ratio of liquid t o solid in underflow discharge = weight of solids treated pcr unit t,ime. W h r = =

Coe and Clrrengcr2 also described a method for cstilnating the rolunw and thus t h e height of a thickener from settling t,ests made in a graduated cylinder. The rolume can be cstimated from the retention time necessary ~ I produce I the dcsired underflow consistency. Similar and n x ~ r ercliahle teats on pilot plant scale equipment have been d e r i m i , but the principles are essentially t h e same. hltliough these techniques are simple, t h e settling rates and required retention time must he determined experimentally. Such experimentation involves small scale laboratory tests followed b y pilot plant operation rln equipnient of the type selected for the particular job. I t is highly desirable to conduct these tests using a n actual saniple o i the feed rather than a synthetic one. Small quantities of a niaterial t h a t v i l l alter the properties of the suspended solids can have niarked effect on the settling characteristics (c.g., w t t i n g agents). Such materials iuight be overlooked in usual analytical procedures. Sedimcntation equipment manufacturers maintain extensive laboratories for testing c u s t ~ ~ m e r ' s samples with their equipment. I n addition they h a r e extensive files of data on operating units.

REFERENCES 1. I(row\-n. G. G. ct nl. i'nll O p e r a t i w s , John \\-ilcy & Sons. Inc.. Kpw 1-01k1950. 2. Cuc. H. S.. and G. H. Clevmgel.. 'l',.ons. Am. I i i s i . .lliriiw . l l c l . Eugrs., .Ti, 356

Piping Design

395

also used, chiefly for drainage as is the practice today. Cast iron pipe \%-as in use in the sevetlteentlr century. Some of the original cast iron pipe laid in those early years is still in use today. Lead pipe was also extensively used in ancient times. It was perhaps the first pipe made from nietal. t the turn of the t ~ v m t i e t hcentury steam p o w r n.ns ~vellalong in its ilevelop~uent. The earliest pressure piping practices were developing

PIPING DESIGN Any book i n project engineering of process plants would be incomplete vithout a chaptcr on piping. At the same t,iule it n u s t be understood that complete information on any single phase of piping u-ould in itself fill an entire book. The information included therefore is general. It is hopcd that it will create interest, and serve as a starting point for additional reading in the listed references. An attempt has been made t o cover briefly only those practices, materials, and accessories most used in piping for process plants and the several utility services generally found in all plants. I t is believed that no other single industrial product has had so much to do n~itllthe progress of the human race as does pipc. Conduits of one kind or another for t,ransporting water were ell known and used in ancient times, perhaps centuries before the beginnings of recorded history. The reciprocating steam engine was developed t o provide a means of reuloring seepage water from the mines of Cornwall, England. Aside from the development of the engine itself, therc is no doubt that much ingenuity was requircd to provide some kind of pipe which uwuld withstand the ilydr~ulieheads. Pumps or other devices for the movement of water had been in use for many hundreds of years previous to the developmcnt of the stcam pump. I n 1581, Peter Morrys, a Dutchman, installed :I watcr-driven pump for the 1,ondon Bridge n'ater Works, to increase the London water supply. This device was built almost entirely of wood. Paddle wheels located in the water of the Thames River provided power. Rotation of the paddle wheel shaft was converted to reciprocating motiou by wooden toothed gears and cranks, connected t o a series of pistons, each acting independently as a pump. M u c l ~of thc piping in these early times was h o r ~ dfrom logs or conI siniilar to barrel stavcs. This pipc g a x very strurtcd of W U U I ~ ~ Istaves good results. Various types of terra-cotta or other clay products were 394

Fig. 18-1. Piwring rvlimlriral hilkt in manr~fnrtr~reof wamles4 pipe. Strrl Institutp.)

!Smarlrss

t o meet the needs of steam power and various hydraulic operations. Impri~vementsin pipe manufacture continued, hut each manufacturer followed the requirements of his particular customers. I n contrast to the early nlcthods of pipe manufacture, pipe today is made by a nunlber of different processes and of such ~ ~ i d e lvarying y materials as carbon steel, alloy steels, brass, glass, plastics, and rubber. The several steels and alloys steels are the most cornnlon piping materials. Their manufacture into pipe is accomplished either by forming flat plate to a cylindrical shape and welding the seam using one of the several welding processes (butt, lap, resistance, fusion, and spiral] or by piercing a heated billet which is forced through a pair of revolving rolls a s shown in Fig. 18-1. This piercing operation produces a seamless pipe which is specified, because of its greater allowable stress, for a majority of process plant operations especially a t high temperature and pressure.

396

Piping Design


T l ~ ei~ietliodi. ..i~~iiI:~r 10 tlri~tL I . Siu~ t 1 1 ~ i i : ~ n n f t i r t ~of i r c.C:IIIII~W ~ tuhi:: except t h a t tubing tolrl.aniw arc marc rigid. Starting in the t~venties a number of interested consulting cnginecrs together n i t h various users' and ni;~nufnctnrrrs'enginer1.s began tlrr task of standardizing the inany codps and 11mctices then in exi-tm~,t'. T h e C d r frw P r r i s n r r 1'ipinC4" ci\-r-s a bI~orl,lwcril~iionof this n-crrk 'Tihi, ( ' ~ l c , ~:IS . ' it will lw rc,ferr!,,l to in t11i.s i,li;il)t,w. ~ 1 IN?1 : ~ l ~ ~ ~tol i:ill ul types of pil~inginstnllations. cxci.11ting erl.t;rin stwlll g('nt,r:ltillg 1)ij)illg : ~ n dpiping govcrneii 11y v a r i o n ~ITS. Go\-rrnnlcnt s1wi4ficntiuns. T h e ~ d t i m a t egoal of tile ctnun~itteci\vorking on tlic codes \\.ill he thc inclnsit~r~ of all p r a c t i c e and acceptance of tlie Code hy all gov".mlental agencies, invluding mnnieil~;~l. stat? ;111
TABLE 18-1.

Snrninal size, in.

Pipe and tubul;lr l ~ r o ( i u r t m s a y be ol~tainerlin a ~ ~ - i variety dc of sizes and ~naterials. Sinre carbon steel, or simply steel pipe: iz in more general use than the many alloys and otllcr nlctallic or plastic materials, most of the trade practicrs are b a d on steel pipe sizes, eornlnouly notell :is I.P.S. or Iron Pipe Size. Pipe is sized according to n nominal figure, n.hicli only in the large size? ithove 12 in. referr to an actual dimcnsim. Thus. 2 in. I.P.S. pipc. Ilas an outside diameter of 2.375 in. and its inside dianletcs rnny vary fro111 2.157 in. to 1.503 in. arcorcling t o the rcquired wall thicknrs;. "Pi11e" r c f w s i n to 30 in. ordinarily listcd fo? to the 24 nolliinal 11ipc sizes fro111 (See Tahlc 18-1.) I n tlrtw sizes there arc some 200 or c ; ~ r l ~ osteel. n more T-nriations in thickoras, of vllicb perhaps 100 are rarely if ever qw14ied fur process piping, or ;rrr unol~t;iinablcexce~ltby s ~ i r r i a lorder. S o m i n a l pipe sizes listed in T a l ~ l c18-1 a\)ove :'/u in. a r e the sizes ~ n w t generally used in pvocess piping. 'rlie list is incomlilc.tc; 1y2in.. 2!$ in.. 3% in.. 5 in. sizes are also ar;tilnblc. hut selrlon~used. Tlie sizes 11rlmv '/Z in. arc used in instrun~entatiunpiping. and a t times fur snlall ilmins. T h e snialler 11ipe sizes arc not nard for proccai; piping even \vlrelr flov rates permit. Kccause of their structural u-raknesa continnour s n p l ~ ~ r t or added intermediate support is required. I t is also necessary t o protect s~ilnllpipe during tlic construction period. I n addition, tlie small opening is much more suhject to closure by scale or foreign matter. It has beconle cornmon practicc to specify heavy \vnll pipe (Scliedulr 8 0 ) for all sizes below t o 2 in. in order to assure good structural stability.

Abbreviated List of Some Standard Pipe Sires

Schedule number

Outiidr diameter, in

Inside diameter, in.

TTcight. Ib, ft.

-10

80

0.405 0.405

0.269 0.215

0.245 0.314

x

40 80

0.540 0.540

0.364 0.302

0.4% 0,.i:35

?4

40 80

0.675 0.6i5

0.493 0.;(23

O..iliX

?4

40 150 160

0.8-10 0.840 0.840

O.(i22 0.5-1li 0.4M

O.R.51 1.086 1.301

9i

40 SO 160

1.050 1.050 1.0,iO

0.824 0.742 0.614

1.131 1.471 1.03i

40 80 160

131.: 1.315 1.315

1.040 0.957 0.813

2.172 2.84-1

1%

10 80 160

1.900 1.900 1.000

1.610 1.500 1.337

2.718 3.632 4.866

2

40 80 160

2.375 2.375 2.3i5

2.0li7 I .$l:3!) 1.689

3.653 5.022 7.443

3

40 80 160

3.500 3.500 3.500

3.068 2.800 2.624

-,.ah -, 10.25 14.33

4

40 80 160

4.500 4.500 4.500

4.026 3.8213 3.438

10.79 14.99 22.51

6

40 80 1 60

6.6'25 6.625 6.625

6.065 5.iIil 5.189

18.98 28.58 45.30

8

40 80 I60

8.625 8.625 8.625

7.981 7.625 6.813

28.56 43.4 74.7

96

TRADE PRACTICES Pipe Sizes

397

1

0.730

1 .ti79

I n the stainless itcclt, vast irun, and n ~ m f t ~ r r o n111ittesi:ds s there arc i n n n n ~ v r ~ b luthcr c sizes :md tliirknesss. Since t l m c ~ n a t c r i a l sare not

398

Piping Design


uscd t o the extent of carl~onsteel, rle-cril~tive inforumtion will not be included; however, the references completely ccver most of the ordiqiry materials. Tubing is nianufactured in even-numbered outside diameters x i t h various wall thickncsees and close tolerances. I t is often uscd for piping and is always specified acci~rdingt o the exact outside diameter (within tolerances). Its wall thickness is sonlctimes specified by a gage number. Tubing of the same dimen~ionsand spccifirations as pipe may be ohtained, but generally the major purtion of tubing is uianufacturcd in sizes below 2 in. diameter. Tubing is avnilahlr in a niuch greater nunihcr of varying rlianietrrs and \\-:ill t11irkne;sca than pipc sinre it has a x i d e use in conduit services other than for the conveyance of fluids. Schedule Numbers Table 18-1 is a condrnsed version of a list of nominal pipe sizes. Ouly a portiun of tlic rsiigc of thiek~icssesor weight* and nominal sizes arc included. All rolurnns are self-explan:~tory except that titled Schedult~Kunibers. The rcl~rdulcuurnber is an approximation of tlic cxpression: Schedule number

=

1000P/S

where P = internal pressure in psig S = allo~r-ahlr!\.orking stress in psi This expression is based on the a c t m l formula used for calculating required pipe thickness.

where D = outside pipe diamctcr in in. t = thickness of pipe in in C = corrosion allolmncc ill in. The schedule number is thus a rational cxpression t h a t is approximately proportional to the ratio of the working pressure to the allor\-able stress and also the ratio of the corroded thickness t o the diameter. Before the use of schedule numbers the ternis standard, extra strong, and double extra strong served l o dcsignatc pipc ti~icknesa. Sizes through 10 in, in schedule 40 arc tlic same as stnndard m i g h t and sizes through 8 in. in scliedule 80 arc the same a s the former extra strong. Double extra strong pipc sizcs hav? b c m discontinued in some sizes and schedule 160 is nscd instead. The older designations are gradually disappearing front use.

399

Materials of Construction 'There a1.c over 150 different materials .specifird hy the American Society for Testing .\luterials ( T I for use in the inanufacturc of pipe. These inrlude carhi~nstecl. alloy utccls. 2nd a vide selection of nnnferrous niaterials. The .WT\I and the ASLIE (;\nicriran Sot,iety of Xechanical Engineers)" h:srr provided an invaluable servire in prcparing detailed ~pecificationsfor thc bewildering array uf niaterials that are available. It xvould seem that steel will continue to bc the most important piping material. Tlie usual severe service conditions of prcssurc and temperature encountered in process industries makc its use mandatory in tlie majority uf 11rowsies. Plastic piping materials, horevcr, are making spectacular gains in low prersurc and low temperature scrvicer. I n the four-year period from 1950 tu 1954 the sale of plastic pipe increased i~~uui~d:: a ?car. Pulyetll~leue,i~r~lyvinylfrom ?I n~illionto 30 ~nilliul~ chloride, polystyrene, cellulose acetate butyrate, and styrene-butsdiener acrylonitrile have all hrcn used with considerahlc success for ~ ~ - a t eand many corrosive chen1ic2tls. Polyvinylchloridc and polystyrene valves and fittings wliicl~sell for less t l i m some alloy steel valves and fittings are offered by several inanufacturers. Plastic pipc can be installed with the minimum of effort. The light rreight and forming properties of plastic niake it easy t o handlc and its use should he considered whenever cconomical. It would be futile, h o w ever, t o give a cost comparison of plastic pipe since the picture is h a n g ing rapidly in this nerv industry. The enginccr should maintain an open mind and cvaluate each new develop~ncnton its merits. Tlie industry is developing rapidly and as soon as badly needcd standards arc estahlisi~cdfor plastic pipe and fittings consuniption nil1 increase trcrnendously. A riuruber of other piping materials have proved unusually valual~le for corrosive services. Thcy include rubber-lined steel, lead-lined steel. and glass pipe. Tliesc can rvithst,and higher pressures and temperatures than most plastic pipe and h a r e the advantage of years of successful applications in many services. The ASTM specifications provide thorough descriptions for each type of conventional metal piping material including the process of nlanufaeture, chemiral coniposition, tensile properties, bending properties, and required testing procedurcs. Careful reading of these specifications will aid t,he designer in selecting the lnost suitahle material for a given service. The follo\~-inggeneralizations. ~villserve as guideposts in the evaluatioli I I ~steel piping materials described by tlie ASThl.* For the many * A d a p t e d by pelmisrion, Kentucky (1947-53).

Piping Engirwering, 2.011 Tube Turns, I n c , I.onisville,

400

Piping Design


q ~ e c i a lp r d ~ l c ~in~material ~s selection, howe\-er. conipct,ent metallurgistr must hc consulted. I. Pn,i,rs; A . Open hearth and electric furnare grades are suprrior to Resemer because of the better quality control possible. B. Deoxirliz(d (or killril) carboll steels are of more uniform structure and arc brtter for rold or hot forming than open (or rimmed) steel;. C. Silicon killed steels hare higher creep strrw than aluminum killed steel?. D. Steels oxidized !\-ith both silicon and aluminum are preferred for lontemprratnrr senice. 11. Chrmical composition .4ffects corrosion resiitance, weldability, forming properties, strength, and cost .i con~pluted i s c u s s i o n ~ o ~covrr ~ l d the whole ficld of m~tallurgy. Some generalisations of value are: .4. H i ~ hcarbon and manganese. 1 . High tensile and yield points at moderate temperature. 2. Lei? weldable and less ductile. B . Silicon. 1. Increnscs rrsistance to osidntion. 2. Improve. sulmro inipaet strmgth. C. Phi~sphoro~~s and sulfur; objectionable except in small amounts. D .Molpbdenum and tungstcn; promotes high temperature or creep strmgth. E. Chromium. 1. Inhibits graphitization. 2. Produms resistance to certain corrosive agents such as sulfur compounds. 3. Strel \r-ith ehrominm and mol?Mmum combine the features of high creep rt.sistnnre with resistance to high ternprmtnrc oxidation and corrosion. F . Sickel: makes steel tough, particularly n t snbatmo~pherictemperatures. G. Nickel-clirurni~imalloys. 1. High erecp strength. 2 . Corrosim resistance to a number of agmts. 3. Colmnbiwn or titanium net as stabilizing agents in these alloys by preventinp carbide precipitation a t high temprmtlms. 4. Molyhdenun~enhances corrosion resirtance of these alloys. 111. Tensile prop~rties;a compnrison of the te~rsilestrengths and yirld points specified is an aid to the meaaurc of quality. IT. Test8; the types of tests and the requirements of the tests give evidence of the suitability of the material for a g i r w wmire. A. Hydrostatic; safeguard against defects. B. Check analysis and tensile; assurr conformance to physical and chemical specifications. C. Bending; suitability for bending operatious i n d i c a t d D . Flattening; indicates suitability for forming and checks qualit>-of srams on nelded pipe.

Table 18-2 gives a list of some of t h e types of tubular products used in process piping. This list is similar t o lists found in the Code except that it larks a tabulation of allowable s t r e s ~ r sx h i c h vary according t o tcmperiiture.

TABLE 18-2.

401

Abbreviated List of Pipe and Tubular Materials

ASTM sper~firat~on Cltin~atetensile strength 3Iaterial .\-I06 Glade .1 48,000 Seamless steel (die011 killed) 60.000 A-106 Gmde B Seamless steel (silicon killed) 48,000 A-53 Glade -1 Seamless steel A-53 Grade B 60.000 Seamless steel - boiler tubingA-83 Grade A Setln~lesssteel - restricted use A-110 Seamless stecl 45,000 h-53 Lap-irelded steel .I-53 I3utt-welded steel .i-I55 Grade C45 Electric fusion welded steel &I55 Chide C'50 Electric fusion welded steel .\-I55 Grade ('5.5 Electric fusion rveldeil steel Electric resistance welded stcel A-135 Grade A 5:lectric resistance velded steel -1-135 Grade B

1

-

Pipe cannot be specificd completely b y ASTM nun111crs alone. I L is to bc hoped t h a t a t some time in t l ~ cfuturc specifications for carbon steel 11ille m a y become more specific so t h a t a single numbcr will be sufficient for a colnplete specificati~~n..is a n illustratim note A S T I 1 A-106. This is seamless pipe specification. thus, i t is unneccssary to consider different classifications such a s butt-xelded or lap-~veldedn h e n specifying A S T M .I-106, but it is still necessary t o specify the grade. Usual carbon steel pipe specifications for process x o r k a r e ASTM A-53 or A S T N A-106, t h e latter of ~vlrichis only manuiacturcd a s seamless pipe. These two specifirations in ~ e a m l e s spipe arc crsmtially the same except ASTRI A-106 is subject to lnore rigid certification of the coml~onentsa ~ l dn i c t l ~ ~ nf d sn ~ a n u f a c t u r e . S T 3 1 A-106 is q~ecifiedfor s e ~ c l . c service conditions for ~ d ~ i ccarhon h steel is satisfactory and for piping requiring spccial bending. I t costs 4 to 7% murc tlian ASTM .i-53. A t times neither ASThI A-53 nor A-106 pipe are rcadily nv:~ilable in sizes hclon. 2 in. I n sucli cases ASTM A-83, which is a t n l ~ ~ ~specificnlar tion, is specificd whcn smaller seamless pipe is rcquired since it has propcrties similar t o both A-53 a n d A-106. M a n y process piping fabricators stock only ASTXI .I-106 This practice reduces inventory and eliminates thc possibility of installing lnn-er grade piping in high pressure service. T11cw ;ire a number of piping .pccifientions t h a t are un(lesirab1e for 1m,eess Aui,ls, but wlricl~iuay be acrtytable for utility scrrict~r,suclr a s low-pressure air, exliaust steam (15 psig and b e l o v ) , water, and lowpressure condensate. Cast iron pipe and fittings are restricted to l o n pressure and temperature scrvice by tlrc codc. Therefore, cast iron piping materials are only uscd for certain utility servires. AIL,y .tccl. nonfrrri~ri-. nn
402


Piping Design

certain services. I n lmusual or unknown scrvicrs it may he neccsiary to develup the application of these materials by lahoratory tests. I t is. of course, ncarly always possible to select alloy pipc 71-hicli will last many y a r s under corrosive conditions. The cost of alloy pipe, however, is far greater than the cost of several replacemcuts by carbon steel. Searly all processes are subject t o obsolescence. It, is obviously wasteful t o use costly materials with unlimited life in processes m.hicli are suhjrct t o frequent modifications. I n certain processes, hoirerer, it is necessary t o use alloy m:~terials t o protect product quality. The selection of materials must also be infl~lencedhy fabrication and erection coats. Therc arc many inexpensive materials which could he used, but the methr~dsof fabrication or the costs of installation may render thcir use impractical.

( h ) 90" Street Elbo~r.

PIPE JOINTS For many ycars tlie only practical n~ct,hodof joining steel pipe w\.as by connecting threaded pipe ends with coupliiig.~or other thrcnded derices such as fittings, v:dres, and unions (Fig. 18-2). Improvements in thc welding of carbon steel by oxyacetylene or other flame n-clding processes and later the shielded-arc electric welding proccss reduced labor and provided a completely sealed and niucli strongcr j o i n t . " L k t present, threaded pipe joints are usually limitcd t o pipe sizes 1% in. or 2 in. and M o w . Larger pipe is joined by flanges a t joints that may requirc dismantling. All other joints in continuous runs of pipe arc welded. The flanged joint consists of two flanges, a gasket or device serving thc same purpose, and t l ~ cnecessary 11olts or bolt-studs.

( d ) Clors

( g ) 45'

Threaded Joints

Joints in threaded stcel pipe arc made by unions and couplings. Unions serve the same purpose us flanges in the dismantling of pipe. TTeldcrl joints may he made in the smaller sizes but are usually not economical or practical. I n some services I~ack\vcl~Iing or seal welding is requirctl after the threaded joint has been madr. This is done for scvere high-pressurc services or for fluids difficult to contain such as certain gascs which diffuse t~hrouglithreaded joints. Seal welding may distort tlie fitting or accesw r y if care is not taken in the procedure. Thrcailcd joints which are t o he seal-wclded should be ma&-up witliont ~,onvcntional pipc joint lubricants or compounds since m o d of t l m r rnatcrinls afTect the welds adversely. The "Railroad" type milleablc-iron, or "Oil i~ii~lleable" union as i t is smietiult3s called, is rrtrnsivcly used for ~ I e r : tt~.llli~eraturean11 pressure services. Forged steel unions, because of t l ~ e i rgreater strength, are uacd in all process services (below 3 in.) requiring high pressures or

403

Elbow

Flp. 18-2

-I

( 8 ) 900

Elbow

( h )Tee

(1) Female Union

(i) Coupling

Screwed pipe fittings. (Courtesy oi Crnnp Cornpnny.)

temperatures. These unions have accurately machined sealing scrviccr (ground-joint) and do not rrquire gaskets (Fig. 18-2). Some ground-joint unions have a soft mctal (brass or hronzci scat ring held securely on one side of the joint facing. Unii~nsso equipped can hc taken apart and reassembled many times rrithout dcstroying their effectivencss. Composition or fiber inserts are manufactured but are unsatisfactory nlicn the joint must he disassembled a t frequent intervals because these inserts are usually damaged in the operation. The pressure and temperature ratings for small fittings are given in manufacturer's catalog~.7.'3,2Q,31,32 Flanged Joints

Standard forged steel flanges h a r e been conveniently classified as ASAt 150 lb, 300 lb, 400 lh, 600 lb, 900 lb, 1500 lb, and 2500 lb. These ratings

* Ameriran

Standard8 Bssoeiation.4

404


are nominal service pressure ratings. The 150 lh flange, fur inst:rnct.. is suitable for scrvice a t 150 psig and 500°F. The other ratings are for 800' F for raised face and 850" F for ring-type joints. Maximum serl-ice pressures a t other temperatures are given in the C o d e i q o r each flange type and material. S S T M cpccifications for forged steel flangci are A-181 fur general scrvicc, .%-lo5 for high tempcraturc m'vicr. and ;\-I82 for alloy .;tcel. Flanges arc manufactured for all the nominal pipc sizes in .several diffcrent general types suclr as ~velding-neck,slip-on, lap-joint, socket-!vclding. and threaded flanges (see Fig. 18-3). Welding-Neck

The welding-neck flange is probably the lnost widely used type. Its installation is Icss costly, requiring only a single r e l d . The rvelding-nerk is stronger than other flange types because it.; integral long-tapered hob provides d d c d ~ e i n f o ~ c c m e n lI.t is nicd [or 111ost~ e v r r el)roc~.i-.st.rvi~t,s. Slip-On

The lehs costly slip-on flangc is also ~ ~ w l d et do tllr l)il,c. Slignnient prior to welding iu greatly simplified l)ecausc the flangc slips on t r ~tllc pipe and is thereby automatically held in thc proper position. Two melds are requircd for the attachment of a slip-on flange, making installation more costly than for the welding-neck. Costs studies by pipc fabricators and construction companies, however, have inriirated that the installed costs of slip-on and ~vclding-neckflanges are equal. Slip-on flanges are reconnnended only for moderate service conditions. Lap-Joint

The la])-joint flange is uscd with a stuh. A singlc \veld joins the r;tul~ and pipe end. Lap joint flanges h a r e sonw ad\-antagc in fal~ricntion since the flange proper is free tu rutate. Tlic bolt lrolrs, tlrrrrfore, do nut need to be carefully aligned during fatxication. -1further use of lap-joint flanges is in alloy or nonferrous pil~escrviwr; or corrosive srrvices in n'llicli all mnterials in contact with the fluid 1nns1 be capable of \vithstanding the corrosive conditions. TI-it11 I:tl~-jui~~t flanges it is pussible to utilize a stub fabricated from the higher quality material required to withstand the service and a relatively incspcnsivc carbon steel flange, thus effecting a ct~nsideral~le saving. I n the process plant it is frequently desirable to diiniantle equipment for inspection or cleaning. The lap-joint flange is sometimes w e d sinc~, disassembly is somewhat simplified with the loose flanges. Alodification? of the lap-joint flange have been uscd for joints in piping m a n u f a c r u r ~ ~ ~ l fro~lrplastic or other nnnferrous materials, without sufficient bending

Piping Design

405

406


Piping Design

strmgth for flanging. In tliwe applications tlrc flange is m n e t i n ~ cron~ structed so that it. ran hr installed back of the flarr~ltwd of the llipe.

The \r-elcling of cart-iron in piping srrviccs has only limited application. under closely controlled conditions, the costs are Though it is Hence, if cast-iron Ranges are used with steel pipe, they prohibitive. are all%-aysthreaded.

The socket-\velding flange is very similar to the slil,-on flange. I t has proved popular for small-size piping operating at high premlres. r n l i k e the slip-on, t,he pipe fits into a recessed portion (socketl of the flange. The inside of the flange and pipe thus present a smootll uninterrupted surface. Threaded

Threaded flanges are used for services that rannot be welded. These inrlude cast-iron piping, certain high pressure alloy piping that cannot he conveniently heat treated after field welding, and small piping 12 in. and l ~ c l o ~ v ) K . h e n work must be done in a hazardous location and w l d i n g is not permitted, threarlrd flangrs may be used. I n general. I~i~\vever, threaded flanges are t o be avoided unless absolutely essmtial. Lens

I n high-pressure work, a joint known as tlie "lens" joint has been successfully used. The pipe ends t o be joined are rnarhined to a concave shape, and a convex ring usually of thc same material as the pipe, is placed hrtwcen these ends. Flanges are screwed loosely on each section of pipe, with the pipe protruding. When the flange bolts are tightened, compression is exerted between tlie tnw pieces of pipe and the ring or lens. Threads on the pipe and the flanges are awally very roarsc so that thc flange is not "tight" on the pipe. This joint Ira,* ~ o m eof the advantages of the lapjoint Range in that tht, flanges are not fixed in position and are not an integral part of the pipe. Cast-Iron

Two flange ratings ior cast-iron, 12.5 lb ASA and 250 lb ASA, have the same drilling (facing and bolt, hole circle) rcspertively: as the 150 lb and the 300 lb ASA stecl rating. Cast iron flanges are manufactured in accorrlance with ASTM A-126. A raised-face steel flange is never joined against a flat-faced cast-iron flange since the shoulder caused b y the raised-face portion of the stecl flange can centralize or overstress the cast-iron flange. As the strength of cast-iron in bending is limited, failure could occur by overtightening the flange bolts. The Code and manufacturers of cast-iron eqiupment, therefore, recommend that the raised face on steel flanges be ground off or that flat-faced flanges he utilized wherever steel and cast-iron eqaip:nent are joined together.

407

Flange Facings ond Gaskets

-1tight mechanical joint in piping could not be effected without some plasticit,y of the membcrs to be joined, since obviously if both faces of a joint Tverc equally unimprtwionable only perfect machining or grinding. could effect a sealed joint. I n order to close the joint without extensive niachinirlg and 1)ulirliing, gaskets are used. Thc gasket nrust he of a material \+-hie11d l u-ithstand service conditions and yet he sufficiently plautic to deform under soft eolnpression so that all interstices arc closed. raised-fare. All of the AS;\ flange classifications may he obtained or flat-faced facings male-and-female, t o n g u c - a n d - g r o ~ ~ ~ring-joint e, (bee Fig. 18-4). The n o s t common facing is tlic rsiscd-face. Th? ringjoint has a wide use in certain severe serviccs and is the niost, expeniive. There arc icvcr:~l stand:ild types of n~achiningavail:lhlc for the portion of the flange in contact with the gasket. For ordirrary services the serrated or sn~ootli-farefinish is satisfactory. may he obtained in a wide variety of n~aterialsfor practically m y type of service. Ast~estoscombined wit11 otlrrr materials is perllaps tht. I U I I S ~ common gaskcting material. Ring-type joints employ metal rings that arc softer than tlie flange material. Special Flanges

Many special typrs of flanges have been designed t o meet particular requirements of a single industry. These include certain flangcs common to oil fields2 and atnnionia fittings. The latter is a tongue-and-groove type, with oval, triangular, or square flanges. I t s a s devclopcd carly in the century for alnnmnia refrigeration c o q ~ r c s s i o nsystems and continues to be used by some portions of that industry even tlil~nglr standard tongue-and-groove or ring-type flanges vould serve equally well. Special flange? such ah tliex shr,uld 1112 aroi~ledin \lruce.-s plants. They have no particular advantages and only complicate \varcllol~sing. Bolting Practices for Flanges

Two general types of hits are used for flanged joints. The innst common is a modificaiim oi the mtlinasy cnrhon stwl m:wliine hrlt with a square or Iicxngon Iread nnd a hexagon nut. 'l'he other in the $11-called I J I~oltstud. It consists of a fully tl~readedstud with ~ T ~ 11cxagur1-headed. rn~ts. As piping pressures aud temperatures increase, carbon steel l~oltscan

408

Project Engineering of

Process

Plontr Piping Design

L

a

-

RAISED FACE

UPPED JOINT

409

no longer meet the stre% requiremcntz and alloy steel l,olt~must be used. At the present time there are four ASTM specifications for carbon steel bolts and studs, twenty for alloy steel, and twelve for nuts. Vogrin et a130 indicate in their study of bolting practices that ASTN -4-307 Grade B carbon steel bolting should be used for services to 450" F . Above 450' F alloy steel bolting materials A-261, A-354, and A-193 in a numher of different grades are recommended for temperatures up t o and above 1500°F. For low temperature services helo~i--20°F, A-320 is r e c ~ ~ ~ n mended in seven grades t o -300°F. Vogrin recommends Class 2A fit for bolts and 2B fit for nnts in nonhigh temperature bolting. For high tempcrnturc bolting, Class 7 fit for the bolt and Class 2B fit on the nut is suggested. Table 18-3 summarizes present piping bolting ,,--Tubing practice.

URGE MALE AN0 FEMALE

URGE TONGUE AN0 GROOVL

SMALL TONGUE AND GROOVE

Miscellaneous Joints 4 compression type fitting is often used for joining 1 in. and smaller strrl or nonivrrous tnbing (Fig. 18-5). I n prwess plants these fittings are primarily used for instrument tubing. There are n u m e r ~ ~ uother s methods for joining pipe, such as the solder-joint ~vhic11is naed in plumbing, the leaded joint for cast-iron piping. and thc integral flange sometimes used for cast Fig. 1 8 5 . Flnl.cd fitting. and other formed materials. The leaded hell and spigot joint for cast-iron piping is still employed ?xtensircly in inunicil~al services such as water piping, gas piping, and wxcrs. h M t e d n ~ e c h a n cal joint for cast-iron pipe is heronling popular sinrc it requires less labor for installation than the leaded joint. PIPING FITTINGS

u SMALL MALE AN0 FEMALE

Fig. 18-4. Amcncan standard flange farings. (Courtesy of Ladish Company.)

Welding Fittings I n welded piping systems now naed in nearly all process installations, butt-rr-elding fittings have been dc.vcl~ipedt o rerh~rc the necwsity for bending pipe. Welding fittings are manufactured under various trade names.i3,?5.2fi The fittings conform t o standard pipe sizes and specifications and can be obtained as tees, ells. reducers and pipe-caps (Fig. 18-61. Yearly all such fittings are seamless and have standard dimensions. The center-to-face dimension on all long radius 90" veld ells, for instance, is 1y2 times the nominal size. This standardization simplifies design and construction. An ingenious prowss is used for tht. manufacture of the various hends.

410

Project Engineering of Process plants

Piping Design

Seamless pipe cut to a predetermined length is forced over a specially designed mandrel shape so as to produce the desired bend. Careful control insures uniform wall thickness, smooth inside wall, and no rcsidual etres~es. All welding fittings are finished d l 1 beveled edges so that full penctration velds ;ire assured when joining the fitting to the pipe. Fittings are a ~ a i l a b l ein most of the same materials utilized for pipe. Each fit,ting is stamped with an idcntifying marking, and all nonalloy steel fittings are painted to prevent corri~aionin stornge. For reasons ( i f cconumy many users restrict the use of tees. Instead pipe can be carefully cut and the branch connection welded into place. This method is morc economical for small branch lines rounecting into large pipc. Costs of rtwly-made tee* and conetruction of branch connections in the field s h ~ l l l dbe compared for each ,ioh and policy outlined for their use in the piping specifications. Flanged Fittings

Cast-steel, forged-steel or alloysteel flanged fittings are produced in nearly all sizes and have the same ASA pressure and temperature classifications as flanges.7.31 Flanged fittings are used only when maintenance requires irequent disassenlbly sillre additional flanges, bolts, and g;i-lids arc expensive and suhje,.t to leaks. .kc-

41 1

412


on the pipe iteclf. Since all valves abol-e 2 in. vill nur111;llly bc flangcd. the joints a t these valves can be used for clisassembly. It is, therefore. not necessary in most cases to provide a number of ~clditionalflanged fittings unless frcqucnt disassembly is anticipated. Screwed Fittings Screwed pipe fittings are obtainable in nearly all materials and styles ( ~ i jg-21.7.1:3.29.31.32 ~ . Srrc\vcrl fnrged-strel fittings 1inl-c a v i d e llse in procesz applications zince they arc satisfactory for high trmpeiaturc operation and \\-ill p r o d e an c r t r a safety factor in cane of fire. CAST-IRON PIPE AND FITTINGS Cast-irnn pipe, valve*. anrl fittings are generally usrd fur undergr~r~rucl utility wrvircs such a . watcr, air, fuel, a n d sewers, and drains operating a t Ion- prrisurel and tcuq~eratures. X l t h ~ ~ u pc:~st-iron li plweded .tee1 a > a piping inaterial by srveral ll~tnillwl ?.car.>. ~ t : ~ n c l a r d i z a t ihas ~ ~ tnot ~ yet bcen aacour~~lished a s i t has been for strel piping and accrsrorics. Changes in t h e val.ioni codes and siec spwifications h a w had to bc d o ~ vbecause of t h e v i d e use and long life of cart iron pipe ill nruniripal installations. r> 1he codes or spccific:~tionscorering cast iron p i l ~ eand fittings include thure published l ~ yt l r Au~erican Standards A s s o c i a t i o ~ ~i.iSh),4 t h e American K a t e r K o r k s Association (AWWA) ,E t h e h n ~ c r i c a nGas Association ( A M ) and tile L-.S.Govcrnn1ent.1 1 Vntil 1922 cast-iron pipe was cast in stationary sand mol~is(pit cast). Sincc then most cast-iron p i p has been pmduced b y the centrifugal c a d ing process. I n illis process n ~ o l t e niron is introduced into spinning molds. Because of t11c centrifugal force: castings produced are denser and stronger t h a n those made b y the old pit methods. T h e SMTh q m i f i c a t i ( ~ nfor cast-iron pipe cover* pit-cast pipe only and is, therefore, obsolete. ('cntrifugally cast pipe, l~ccauseof its denser structure, need not bc ai: thick a s pit-cast t o tiithetancl a given pressllrc. Until recently userr specified cast-iron pipe on the hasis of Fcderal specification M'W-P-421 for centrifugally cast pipe. I n 1953 the ASA published specificatii~n,~ for centrifugally cast iron pipe.4 These specifications are based on the latest experimental evidence accumulated by the AWt.l, .4GA, and ASTM. They t a k e iull advantage of the s t r e n g t l ~ of centrifugally cast iron pipe a n d should be used in all specifications. Cast iron fittings may be specified as ASA or A T V A fittings. T h c -43.4 specification A 21.20 is for short-body fittings 3 in. through 12 in. These fittings requirc less laying length than the more familiar AWWA fittings. T h e AWWA ~pecificiltionfor fittings, d l i c h is still in use, covers fittings f n m 4 in. througl~60 iu. T h r .i\VTV.i type fittings a r e tllc only available l ~ c l lnntl . q ~ i g dfittings i r ~5izl.s nl~ovc12 ill.

Piping Design

413

'There arc a nulnbrr of jointi: for cazt-iron 11ipe. T h e most wirl~.l?: used in process plants a r e hell anrl spigot, nrechanical flange. cnmpression, I t h r e a l c . T h e characteristics of thesc joints are hriefly outlined i r Tahle 18-4. TABLE 18-4.

Cast-Iron Joint Types

lhwril,tim~

Rell :nn
.\lechrniical tylre

Flange

,'

' k g

I:su;~l Ikmnrks service Fluids must hl, 13ril--htrpcil end reccires .Jute twine T'n(1el.stl.niglit hliigot end to and le:ril g m m l wet so that water piping jut? re~nniw forin jniot u p to 200 espt~nderl psi. I-nderground gas piping below 10 psi Straight portion of pipe Rubber or fits into bell-shuped end rompusitinn fitted with a gl:rnd n-hieh tightens ugninst gasket

C+asl~iping Wthstanrls at moderate rihrntion :~n,l pressures. and ezpnnsiot~ .Usu n-ater piping .ibovr-grouud ASA flanges Class 25, Standard Abovevatel. linrs awl 125, and 250. Integral gaskets ground waterlines, lm--pressure part of pipe or serewxl for flatto pipe face and lowgas Aanges pressure gas

Compl.ession Plain cnd east-iron pipe Rubber coupling is held together by a coniprrssion type cuupling Thre;~cled Scl.ea-ed couplings Sone similar to steel pipe couplings

Gas, oil, nud Perniits n-nter expansiou nnil contr:irtirrll iYoncl.iticnl Threaded type compression wiste and n.;~t,erlines joint also n\.aila\>lr

C a r t - i r m jlipc for process fluids such a s gas or oil nlllst have positivv ;ittarhmcnt betr~wenjoint sections or it will not nrect Code rrrluircments. h large numher of joints are required for cart-iron piping sinre veldi in:: is not pussible. .\Iaintenance and installatim costs, thlwfore, are higher for east-iron systems. This disadvantage together ~ v i t hthe service liniitations imposed by the Code (not pernritted above 400 psi a t 300'F belon: ground and 150 psi a t 300" F above g o u n d ) restrict the use of cast-iron pipe in the process plant. VALVES Thc valve, which is the most important piping accessory, is nvnilable il: n ~ a t e r i a l sand designs of almost unlimited varicty.*~'.1~'-'~~2"~2!'~31

" Oni

l , n ~ , ~ i i ~ ; i lir.:,>. ~iim~ (.l,ll~l,illcl \.illiO1l.

tlliilll~iill~l~re~~.-i ~ ~ d v m .

414

Piping Design


Plant warehousing and maintenance are greatly facilitated, however, if thr types of valves stocked are kept t o a ~ninimum. It is t~spcrially econornical to rtan~larriiaein the smaller sizes hy selectins a on+ or twovalve design \\.hicli will satisfy a11 servirrs :inticip:~ted. Classification Valves nstd in process piping may be cl:~ssifiedas gate, globe. plug, check, Wheel and cmtrol valves. The service conSiem ditions of inany of the more common types of these have been standardized Packing as well as the face-to-face and flange Nut dimensions of flanged v a l v e s . 4 ' , l V n Glond gcneml, ho~vcvcr, rcfcrcnrr must be Packing inadc to inanufacturer's ratnlogs fur c ~ m p l e t c sprcificatims and descripStuffing tionz of a givm rulvc. Thrsc ilcsoripBox ~III~EZ tions togcthcr 15-itl1 pul~lisl~wl Bonnet and stanclanla for valves2.*' ',1".'7.2s will aid in the selccti~mof tht. inost, suitable valve for a given service. NU1

Disc

Nomenclature All gate and d o b e valves have two similar basic parts, the body and the Fig. 18-7. Valvc pmts (Conrtc~yof bonnet (Fig. 18-7). The body conCrane Company.) tains the orifice, the part ~vhichcloses the orifice, and the necessary flanges or screwed openings for connection t o the piping. Thc bonnet is the upper part of the valve joined t o and closing the body. It contains the gland, supports and guides, the stem, and valve wheel or closing device. There are three types of valve bonnets (Fig. 18-81, The screwed bonnet is the most inexpensive a s well as the least reliable. Tight sealing of the stem requires screwing the bonnet strongly against the neck nl~iclioften causes distortion of thc valve ncck. The union bonnet is designed t o provide a n easily disassemhled valve. The fluid pressure acts to seal the joint more tightly. No distortion occurs even upon repeated disassembly and reassembly. The bolted-flanged bonnet has a bolted packing gland and a large stuffing box. It is the sturdiest design and is used for most larger process gate and globe valves. I n such installations it usually has flanged ends. The importance of the method of attachment of the valve bonnet is indicated in paragraphs 309(d) and ( e ) of the C0de.4~ Body

A

41


Piping Design

Tlic valve stem r11isc.- and lo\\-crs t l ~ cplug or gntc \\-l~icl~ clo-cs the orificc. Tlic gI;11111 .i the lu~ckedjoint t l i ~ . i ~ u gn-liii.11 l~ tlri, s t c ~ i~I:IY-P*. ~ P:l~lde\>v : l l v ~ ~rrinilr : in .~iiall sizes o n k , li:lve a bellon-: tyjle att:icIilneut d i i c l i eliniinntcs tlic pucking gland.

Tlic v n l x -c:it is that portion r ~ ftlir orifice \vhirl~is rlocrl hy thc 11111g or gate. Valves may be fl~rnisheil~ i t integral h seat- or rcnewahle yeate. 1-alve trim is thc term applierl to the materials r~liicl-Iform the seat, plug or gate, and the stem. Valve ends are dcscril~rd as s c r w c d . flanged. or r ~ e l d i n g Screwed ends arc the cheapest and are more rapidly in.~tnllcdin t h small ~ sizes. They: ho\wver, always ronstitntr a potcniinl sor1rr.c of lrnkagc. Flnnged cnils ~ ~ r o v i da estrong leak-proof joint, and cvrv tl~ougli1110rr costly. tlicir reliability and superior strength makc tlicir u w almnst mandatory for I:irge process ralres. \\'?liling ends are u ~ e only ~ l for spccial installations requiring absulute insurance against leakage.

41 6

417

Gate Valves The gate valrc (Figs. 18-7 and 18-91 is the most commonly used valve. Fluid f l o w discrtly through thi! gate valve axial to tlie piping (Fig. 18-10) Tlir valve consists cwmtially of n sliding plate or gate set in grooves. The 111:itc is niovcd directly across the orifire and is closed b y means of a rhrmderl stem rotated by a hand ~rhecl. Tlie gatc m a y be 71-edgc-sl~aped SII t h a t i t n-ill seat tightly against the sides of grooves, or it may consist of two plates expanded against the sides of the grooves. Gate valves, liowever, are generally used a s block ralves for isolating equipment or lines, or in iull open or closed position serviim. They ale rarely used for throttling, for if thc valve is kept in tlic partially open position, the l~oltornof the gate becomes eroded. Throttling service is usually re5trictcd t o the more easily controlled glohe rolvc. Since the orifice is approximately concentric and the flow is axial t o the piping, gate valves Ir:~ve a lower pressure drop than glihe valves. Globe Valves T h glohe r a l r c (Fig. 18-11) is different from the gate valve in that the globe-valve orifice is arranged perpendicular to or on an angle to tllc :rxia of flo~v. Closing is acwmplislied by a disk or plug attncl~edto ;t sccni vlrich may be rotated t o opcn or close the circular iirifice. Fluid Hm~ingthrough the valve must make approximately a 270" turn t o r r a d i thc orifice (Fig. 18-10). After passing through tbe orifice, i t turn; aliotlicr 270" to re-enter the original flow line. Pressure drop through tlic glohe valve, therefore, is niucli higher than through thp gatc valvc. Glohe valves arc preferred for throttling services, and are a l m o d always used if tight shut-off is required. Because of the circular construction of the seat and plug of a globe ralve: i t may he more precisely ground or "lapped" to provide a tighter seal than the gate valve. Large size glohc r a l w s are ordinarily niorc expensive than large gate valves. M m y users purchase gluhc valres only in the small sizes, 1% in.

418


Piping Design

420


Piping Design

421

Plug Valves

T h c 111ugvnlvr. or cock (Fig. 18-12'1 as it is s o n ~ e t i m rrnllrd. ~ is tlir Its I t xvas developed froni the XT-ooden spigot. xncestor of all ralves. \\'lien the valve is open. fluid ~uutitandingfrature is d i l l its simplicity. flon-s 1,arallel t o the pipe all tlrrouglr a plug bored the same size as tlrc 1,ody r~rificc. Flow is shut-off hy rotating tlie plug 90' so thnt the orifice in t l 11iug ~ is turned past the body orifice. Certain phtg valves h:iw :r ~ c n t u r i - t y p ebody orifice so t h a t pressure drop is much lo=-er tlrau for any other type of valve. Plug valvcs nray he obtained in materials suitable for high tcniperat ~ ~ r r . they -: h a r e been usctl in services 1111 t o 1200nF. For light hyrlroc r l j o . a scrviccs. and for many corrosive services the plug c w k i. usually selectedl since i t may be niannfarturcd in nearly any t y l ~ cof ~natcri:d Th,,y ;lrc, ]rot n- conunonly used ah the gate ralx-e. Some arguu~cnts against their use for all process work arc: (1) The possibility i1f the plug '.freezing" open or clu$ed; i 2 1 no visual eridencc of tlirir i~eini:11pc11.?ncll as ~ v i t hthe rising-stem gate valre; ( 3 1 tlicy must Ilc lul~ricnte(lto ~ I J I I I pletely real in somc scrrices;* (4j in the smaller sizes more rigid s u p p r t must be provided t o operate the plug. X a n y adrersc criticisms of thrre valves, ho~vever,can hc traced to faulty maintenance. .\lodcrn plug valves l ~ a r ebeen designcd t o insure ease of movenrrnt and a r~oiitivescal. Lubricated plug cocks. for instance, employ a semisolid lubricant which is injected hydraulically. It is possible to lift tlic \.alve l'lug soine\~hatby rotating tlrr l u h ~ i c a n tinjection s c m - , and thi* ; i d o n forces thc lubricant under the valve plug. Since the plug is taprwil it is free as ~0011as it is movcd. Larger sizes of plug r a l r e s h a w a grar :ind wl~cclfor manual operation. The smaller sizes, 4 in, and helo\\-, are operalrle by a lever \vrcneh. Check Valves

u

u

Fig. 18-11, Cast steel globr v;rlrc, plug-type disk. (Conncaj- oi Cnine Cu~npany.)

fuuctions not unly as a v d \ - c but d s o :is il 90" pipin:: 11vnd. Flo\\- (mters the bottom of the w l r e , pishe. ulnrurd througl~the orifice. and t u u : 90" tu leave the valve. Since bends in piping s!.stem itre subject to greater strains than str~light-runsof pipe. :inglr r a l r o s are not. nscd rxtcnsircly. '1'11~ Y-valve (Fig. 18-101 is .imilnr lo o glnhc r a l r r in throttling r11n1.lo ;L X:I[Vv;~lve, :!cleristi~syet ~)rovi,lvsllow arc1 c~~tnl~:tr:~l,lv

C'11~~rh valves (Fig. 18-10) prevent "backing-np" of fluid in a line. i e . . revrrsal of fl

Piping Design

423

resistance to flow and is spcrified for sizes larger than 2 in. Frequent, fl(m reversals prodr~cc a "ch:ttt,cring" in .swing v a l r w whir11 can hc :~llcviat~il hy tlrc USI, of s r i n ~ vnlvcs rqiripl~c~l ~vitll:tn ni~tsiclclrvrr nnd wciglrt. A lever is :ittnched to an ~ r t t m n lrnntinuntion of tll? Iringe. A weight, the los sit ion of n.hiclr v:in l ~ crh:mgcil, is :itt:dird to the lever so the sensitivity of the valve ran be v a r i d Tn this m;lnner r h t t r r under low velocity flow renditions and ~lrockon rloiing ran 111. :~voiilril or reduced. The outside lever can also be used to aid in relcwing the disk if it becomes stuck. Control

Valves

Control valves are fundamentally similar to the glohe valve. They arc made in all the ranges and materials found in gate 11rglobc valves, but the "trim" and bodies of control Pressure valves have liieher ., nualitv. sucrifica. tions than ordinary valvcs. The diaphragm control valve is the most widely uscd. It is opened or closed by a stem attarhrd to a plate or diaphragm which forms the movable side of a chamber (Fig. 1813). The force required for movement in one direction is produced by air pressure in the chamber, and in the opposite direction by a spring. Movement of the diaphragm and thus the stem causes the valve plug t o open or close the valve orifice. The air pressure on the diaphragm is controlled by the primary eensing instrument. Control valves may be obtained either n%h double-pork or &h a single-port (see Figs. 18-13 and 18-

orifice. Governor Company.) Thc double-port valve gives a bettcr control range for larger flows. A further advantage is the small force necessary to move the valve stem. The pressure d~ffercntialacross the bottom port is opposite and approximately equal to that across the top which enables movement of the valve stem with the minimum expenditure of power.

424

425


Piping Design

Tllc single-ported valve i.5 less contly and i.5 saticfactnry for noncriticai rontml wrvircs. I t provides a tighter seal than the double-ported valve. There are several inner valve designs. The inner valve illustrated in Fig. 18-14 is designed to reach maximum capacity after only a small

from the valve-operating tiiaplir:tgni, forcing the valve stem to movc to the precise poeitiun required by the control instrument. Control valves are used for presure contrul as w l l as flow control. Many pressure controllers enlploy the fluid being cuntrolled as an actuat-

Fig. 18-14. Body of single-port control valve. Company.)

(Courtesy of Fisher Gorcrnor

movement of the valve stem. Such a characteristic is most desirable for quick open and shut service. The parabolic inner valve in Fig. 18-13 gradually increases its flow area throughout the lift of the stem, producing an excellent throttling action. V-ported inner valves of various designs produce similar desirable characteristics. Control valves in the larger sizes or in high-pressure or high-temperature services are practically always specified with m auxiliary or booster devicr called a positioner. This device continues to add or reirrwe air

ing ui~cdium. The sen3ing elmlcnt in thii t y l ~valve is located at the \.all-e and usually consids of :r dialil~rag~n or other ~iressureactuntcd device. I n pressure reducing scrvicce thc rlil,cct c~innected.diff?renti:llpressure valve is often uscd. This type control vnlve balances the t ~ v o fluid ,lrcs,mrcs, onc on e;1c11 .ill,. of :r ( Y ~ I I ~ ~ iliil~il~riipln I ~ I I wit11 a spring td wllicl~ can be adjusled to tl11, ~ l ~ ~ . s i r~liI'Sw~~~ti:il.

426

427

Piping Design


they are safety deviccs which protect hfe and property, they must be constructed of t h e finest materials for the service.

TABLE 18-5.

1. Inverted

Ilucket

Steam Trap Characteristics

Operation Steam accumulates in in\-erted bucket causing it to float by increasing the I ~ u r ~ y m cofy the bucket. Xovcment of va11.e lever attached to bwket cluses discharge valve. Entrance of n1ol.e rxlnrlerisete causes bucket to sink dosing vnlve

Features F u t , low steam loss, simple, must he pmtected from irerzing

T h e ahove descriptions include the basic t,ypes of valves manufactured. Tliprc arc. 1 i o a c ~ - c rcountless , variations of each of these types manufactured for special scrrices. A listing of miscellaneous process equipment and manufacturers in a general industrial catalog22 shows over 150 specific typca of 1-alves. E a c h of t h e w types can be obtained in scveral different materials and each can be obtained in a large number of sizes and prcssurc-temperature classifications. There a r e over twenty major manufacturers of the common types of valves exclusive of the manufact u r w s of specialty items. These manufacturers of common types of valves produce coinpctitive products, t h e specifications for vhich arc ci~ntrolledhy cithcr manufacturing standards or b y t h e various codes. One publicati1m10 enahles the engineer to compare all manufactured valvcs on a n equivalent basis.

2. Open horket

0per:ites \\-ell Bucket floats with open end up. Condensate fills bucket causing it to sink under fluctutrting and open valve. Steam pressu1.e disclrar- 1o:ids ges condensate out discharge pipe in hwket which causes bucket again to flm~tin remaining condensate

3. Piston-

Inverted bucket tmp which oprr;ttrs n pilot valve which in turn operates :I 1:wge piston valve

Gond for vwy high

MISCELLANEOUS PIPING ACCESSORIES

4. Thcnno-

Vwlve attached to hellom cwituining volatile fluid. \Vhcn steam contacts bellows, increased vapor pressure (if fluid causes expansion of bellatis and closing of discharge port

Cannot freeze. Yrr>-~ a p i d;ti7 \.enting and bigh condensate capacity

I n addition to the nccessary pipe, valvcs, a n d fittings for transporting process fluids, a number of othcr items are required, which m a y be classified a s accessories. Condensate or Steam Trap

T h e condensate t r a p , often erroneously called steam trap, is uscd in s t e m piping systems for the removal of condensate which accumulates as lipat is lost from steam. T r a p s a r e located a t low points or pockctn in steam piping, a t regular intervals in extended runs of steam piping, a t steam-driven cquipment which could be damaged b y condensate, and :it steam-hcated equipment of all types. Tlrc ideal t r a p must remove condensate a n d air from a system with negligible loss of steam and a t a rate of removal such t h a t the operating equipment will perform a t peak efficiency. I n Table 18-5 seven popular t r a p types a r e listed. 4 brief outline of the operation and distinguishing features is given. Fig. 18-16 illustrates the most widely uscd trap, the inverted bucket. It is not possible to give exact recommendations for t h e use of each type. Stearn pressures, corrosive conditions, and individual plant experience a r e important criteria fur the a~lectionof n t r a p type. T h e reputable inanufacturers are prepared to recommend the use of their traps fur services in which they will be successful. These manufart m w a should he consulted f o r assist,ance in t r a p selection. M a n y publisir

operated

static

oap:wities (up to 300,000 11)

111.)

Cannot freeze. Similar in principle to No. 4 except 5. Liquid exptmsion expansion of a liquid (oil) is used to move Cnntinur~us valve ~liscliargea t an: desired temperature 6. Ball float

As condensate collects in trap body it ciiufies a ball float connected to thr discharge valve to raise and close the vl~lvc

Discharges condensate continuously at steam tcmpernture an,] nitlrmt shock.

7. Imoulse

Onr ivorking part, a valve. .It r l r near ste:m tempel.:
Cann-! f1.eez.e. Vw>- sm:tIl and light \\-eight. High capacity to size ratio

helpful charts and design procrdurcs n h i r h are time saving and are bnserl on considerable operating experience. I n specifying t r a p s for a projert a list of all the traps is usunlly I ~ r e p a r c don a dra~r-ingor other reproducilile f o r ~ n . T h c list includrs a detailed d r a v i n g of one or more typical t r a p installations wit11 a list uf t11e nrrcssary valves and fittings for each type of inrtallation. Numb<,rr

Piping Design

428

Project Engineering of Process Plants for idcntificntion mrl ~n:itcrial,llrrrsurc : m I Row s j w i f i w t i o n ~a r r a 1 ~ 0 given. T l ~ cli.5t is w e d for (1) material take-off of all tllc snail v a l v e and fittings required for trap installations; (2) procurement operations; s n d for ( 3 ) an in.st;illntion guide. T r a p nulnhers arc used in identificatinn, both on piping drawings and d i ~ r i n gwarehousing and erection.

?..

Expansion Joints ,

.

1 l ~ cinnnufnctured expansion joint is used for tlrc reduction or elinlinati011 uf s t r ~ s s e sand for o v e r c o ~ ~ ~ excessive ing vibrntion. Exarllples ( ~ fthc t \ v < n~ m t cunlmon types, the slip-joint and thc packlcss-joint are shon-n in Fig. 18-17. Each of these joint types is madc in a variety of styles arid inatcrinls t o fit elrery need. T h e slip-joint has a stuffing hox to prev m t lenkagr; and, tl~erefore,requires more maintenance than the eorrugated linckless joint. T h e slip joint simplifies expansion calculations hcc:rurc its lcngth of travel is fixed. The ~ ~ r e s s u rtemperature, c, and movement in each expansion joint must 11r carefully inyestigated and specified. T h e specifications nluet i n ( , l ~ ~ d r clwription I I flnid! ~ nlaximum pressure, m a x i ~ n u ntemperature, ~ cokl or

Fig. 18-17. Eqmnlion joints. (0) Piston-l.ing rxp;insion joint ! i n t c ; ~ ~ . ~ lguided); ly ( b ) p;~rklrsscxpnnsiun joint. (Courtesy of Adsco Industries. I n c )

installrcl positiun, cold d i n ~ e u s i ulioi ~ ~ ,imsitiuu, hut d i t i i t ~ l s i o ~axial ~ , deflections, and estimated cycle periods frul11 hot to cold. If a numhcr of expansion jirints are to he installed, procurement is si~nl~lifitd I)? :I iI~.:twingnllirli ~ . l ~ i ~1 1\1 v1 , sv:wio~i.. t y l ~ joints required in t\vo or luol,e vicws. A t:il~ul;~tionon tile d r i ~ n i ~libts ~ g the joints by

430


Piping Design

number together with operating data. Using this drawing t h e manufaetnrer can prepare his proposal with a minimum of written information. T h e data requested from the manufacturer should include recommended joint type and material, magnitude of forces necessary to compress, extend, or cause axial movement in both hot. and cold positions, a n d

Adjustable Clevis Hnnger

Stt.ucturnl Steel Pipe Supports

Clip Ring

( b ) Pipc Shoe Pipe Shoe7

Split Ring

Pipe Clamp Guide for Pipe Shoe

Split Ring with Socket

Split Ring with Rneklc

Guide

Pipe Support lsteel) (c)

Unde~.groundClamp with Lugs

6

$+ Preferred Member

(a)

Adiustnhle Swircl Type Hanger

Adjustable Pipe Clamp

Pipe Clamp

( d ) Mcthod for Restrlet~ng Vertical

Mob ement Fig. 18-18. Pipe supports and anchors niagnit~lricof lnngituiiin;+l forrrs eaused hy internal p r c s u r c . Thcec data should he added to the expansion joint list for use in piping stress analysis. Pipe Hangers and Supports

I n earlier proresr 1)iping installations nearly all piping was hung by means of clalnps a t t a r l ~ e dto nlds or chains, to provide greater flexibility or freedom. This m c , t l ~ uof ~ l supl~ortis still used for piping installed inridc buildings. I n the inoiiwn process plant, Ilo~i-ever,most equipnicnt is lucatcd outside and piping is run on structural steel supports (Fig. 18-1%).

Pipe Roll Stand

Adjustable Roll Stnnd

Fig 18-19. Manufaetu~cdhangers and supports

Adjustable Roller Hanger

(Courtrsy of Elren Mctnl Product.

Company.) Since t h e piping is laid across t h e supports i t is simpler t o hold t h e pipe b y devices called ahocs which rest directly on the structural members. A n inexpensive and simple shoe, such a s s h m n in Fig. 18-8b, m a y bc either a tee beam or the more coiliinon split structural H or I beam. It is

432

Project Engineering of Process

Plants

Piping Design

Ilnneccssary :111
Fig. 18-20. Spring lrnnger nnd Products Company.)

typical installations. (Courtesy

of

433

By setting all pipe in any layer at a fixed B.O.P. elcmtion, practically all shoes except the guides will be the s:me height which grc:~tlysimplifier their installation. Further, a constant B.O.P. elevation fixes the position h of the horizontal structural member of the pipe support ~ ~ - h i csimplifies design and construction.

Elren Mrinl

Hangers are best suited and most often used for supporting pipc insirk huildings. Honevcr. horizontal structural memhers are used for supports inside buildings n-hen large numbers of lines are run side by side. Field fabricated shoes are used in preference t o hangers for outside installations because the shoes are easier to install and ran bc more readily protected from corrosion by painting since all surfaces are accessible. Spring hangers such as shown in Fig. 18-20 are used both indoors and outdoors on hot piping installations. Tlicy are the least expensive and most reliahle type of flrxihle pipe support available. I n designing pipe supports it is usual and good practice t o set a specifir bottom-of-pipe (B.0.P.l elevation for all pipe run a t the same relative elevation. The ~vordelevation is intentionally used since the dimension is measured from the bottom of the pipe t o grade. When shonn on drawings as 125, for instance, the number 125 indicates that the piping is 25 ft ahore nominal area grade set arbitrarily and for conrcnience a t 100 ft.

Fig. 18-21. hlanufsctu~.edline blind. (Couhsy of I I m m r Valves, Inc.)

Line Blinds T l ~ cn ~ ~ n u f a e t u r el di r ~ c - h l i ~(Fig. ~ d 18-21 ) is u s d to seal d f 3 line or. yicce of equipment. It l~ruvides:t inure pusitive :~ndreliable seal than a e o n v c ~ i t i o ~ ~valve a l and is vnluablc wl~rwportions of oprrating systems must be isolated f o r maintennncc .. putyoscs. I t is more costly but 1110r(~couvtwie~~t tllal~the c ~ n ~ e n t i o homemade ~~al l ~ :I 111rt:~l 11l;itc in the sh:il~cof :I figure spect:irlc or figure 8 bliirtl \ v l ~ i r is

434


Piping Design

8 with a hole the size of the line on one side of the 8. The line is sealed by inserting the solid portion of the plate between flanges. This is accomplished by partially unbolting and springing the flanges apart after first draining the line. With manufactured line blinds the line is sealed merely by manipulation of levers and a l~andwlleel. The spectacle plate is released and clamped as rlesired by means of a mrlvahle hub which is contrr~lledby a hand wheel-operated worm and ring gear.

equipment sucli as pumps in a group simplifies power supply and control systenir and thus reduces costs. Connecting piping, as f a r nr is poasil~le:is aln.ayr run overhead in racks above the smaller equipnient ~vhicliis located nrar grade. The primary purpose in elevating piping is to provide clearance a n ~ n n dequipment. I t is usual practice t o group nll parnllel piping in a bank a t the same elevatirm changing elevntion when dirertion is changed. I n this manner space is provided for connections t>et~vecnsucccvsivc layers as veil as for remora1 and maintenance. Care must bc cxcrcised, hon.ever, to avoid elevation changes which create pockets in lines rvhcre liquid can accumulate.

Other Accessories

There is a wide variety of additional accessories and specialty equipment used in piping. hlanufacturer's eatalogs'~31 should be studied for a cornplete description. PIPING LAYOUT AND ARRANGEMENT

I n the layout or initial arrangement of piping for the process plant the designer has six related problcms t o consider. 1. Process requirements

2. Transmission of excessive stresses from piping to equipment, and tlie transfer of vibration from equipment into the piping system 3. Economy 4. Operational accessibility 5 . Xnintenance and replacement 6. Excessive stresses in the piping system 1. Process Requirements

Except for some particular "process reasonu* the hest arrangement is not always accomplished by connecting directly from one piece of equipment to another as shown on a flow dia,grain. A study of any process plant piping installation will show that essentially all the piping is arranged t o run in definite patterns, always changing direction wit11 a 90" turn, whether the change is in the same plane or in a different plane. When hundreds of lines must be routed t o various portions of a plant, it is essential that this orderly arrangement be used. Routing each pipe in a straight line ~ v r ~ u lrreatc d a confusing and impractical arrangement. Since all equipment is suhject to snnie kind of mechanical maintenance, and inspection and cleaning, it l m s t he accessible. Safety demands that certain equipment he located a t a particular point or as distant as possible from other equipment. The simplest piping arrangement is made possible when the equipment, is locatril in parallel rnws or in some other rectangular pattern. Identical or .;iinilnr process equipment. suc11 as pumps. vwsela. or heat exrl~angcrr. is usually grouped in conrccutive rows. The location of power-driveu A pemliarity dictated by the process

435

2. Transmission of Stresses and Vibration

The transn~issionof strehaw from piping to equipment can be eliminated by tlie installation of n~anufactnredexpansion joints in such serx-ires as steam or exhaust connections t o turbine3 or other steam-dviven equipment. The possibilities of cimosion, erosiun: an(l cyclic >trcraes in 1)rocesa services, h o u w e r , often limit the w e of mect~aniralexpansion joints. Frlr these reasons the piping designer nmally attempts t r ~eliminate piping stresses on equipment i ~ y roper piping arrangement and the use of supports and anchors. There are two reawns for eliminating stresses a t piping connections. One is t o prevent the overstressing of the tlody of a machine or valve to rvhich the piping is attached and tlie other is to prevent misalignment of equipment parts causcd by differential nioren~ents. XIanufacturers of equipment will not recognize any guarantee if a failure can be traced t o external stresses. Vibration in piping is usually encountered when piping is connected t o moving machinery. Proper use of supports and hangers or rihralion dampeners will eliminate most cyclic vibration. High-frequency villration caused by high-speed niacl~inerysuch as centrifugnl cornpressors can be relieved by applying fixed supports. The correct location for these support,^ may be determined by experimental application of weights while the machine is in operation. 3. Economy

Cost considerations are often overshadowed hy process requirements. A capable layout designer, hr~rwver,xvill avoid wasteful use of fittings and supports. There are no precise rules wl~icti can be set down as each system will vary, but the best economies in piping are usually obtained by simplification of the piping specification. 4. Accessibility

Valves and other appurtenances which must be used during operation and/or which require periodic maintenance must be located in a con-

439


Piping Design

l\lanufactured cspansion joints are not extensively uscd in I1roces.C plant piping. They are used for utility piping and in process applications where piping size or space limitations would render changes in confignration impractical or costly.

costly. Several short methods of piping stress evaluation which utilize charts for the more common factors are offered.ls.31 The simplified methods, hu~vcvcr,are not completely acceptable to all designers. Even the more rigorous or formal calculations depend upon assumptions, some of which are admittedly questionable. The designcr, therefore, can only expect to err on the safe side regardless of the method used, the degree of error increasing n-ith the more simplified procedures. I t would appear that analyses which err on the safe side and yet permit the piping configuration t o remain within reasonable economic limits should be acceptable. I n order t o illustrate the variation in strcsn with configuration. the results of a calculation on an expansion U-bend are given in Table 18-6.

438

COLDSPRISCISG Forces generated by expansion are caused by movement of piping a s its dimensions change from atmospheric to operating temperatures. One method for decreasing the final intensity of stresses in the hot condition is t o cut the pipe short and spring i t into place while cold. This springing produces a tensile stress on the system which changes t o a compression stress in the expanded hot condition. Both of these stresses will have a lo~r-ervalue than t h a t which would occur if the pipe had heen cut to exact dimensions for the cold condition. This tcchniquc of installation is called cold springing. It is discussed in paragraph 620 ( e ) of the Codc nhich defines thc limit of stress rcduction to be assumed when pipe is so installed. The Code rule applies to actual erected lengtl~i.. For this reason when pipe is being shop fabricated, corrections for tempcrature differentials b e t m e n shop atmosphcrc and crcction atmospllere 111ust he made. These corrections are required when alloy ur stress-relieved pipe is used since these materials cannot ordinarily be reworked a t the point of erection. Whcn ci~ldspring is practiced, actual ficld measurements of the space for any given piece of piping should be made.

TABLE 18-6.

Case

Variation in Stress with Conflguration for an Expansion U-Bend

Length in ft L II IV

Stress, psi

Total Pipe (L 2 H ) in it

+

Design Calculations for Expansion Stresses

The piping code liar set permissible or maximum stress temperature relationships for each acceptahle pipe material specification. Chapter 3 of Section 6 of the Code composcd of paragraphs 61-20, inclusive, contains various rules, limitations, and requirements for piping stress calculations. Paragraph 620 ( a ) states in part, "Formal calculations shall be required only where reasonable doubt exists as t o the adequate flexibility of the system." Methods for analyzing stress of piping systems are not given in the Code. It functions more as a guide toward good practice and is not a complctely specific instrument which covers in dctail all possible conditiuns of piping design. The rcrponsihility for proper interpretation and application of the rules remains with the designer. The presently available comprehensive methods of piping stress analysis* are extremely rigorous and, therefore, time consuming and *One excellent method has been developed which is readily adaptable to high speed computing machines." This reference is also a good source of information on all problems oi piping flexibility.

Basis

in. Schedule 80 pipe, APML, Grade C 000" F operating temperature, 250 psig operating pressure Allowable stress = 19,300 psi hlaximuni expansion a t 70" F is 4.72 in./100 ft Maximum allowable cold spring permitted hg Code is used ( f ) Rends are 90" butt-nelding, long-radius elbom (g) For simplification guides were not considered although such n. bend would require guides (a) 6

(b) (c) (d) (e)

Case 1 shows a n S value of 20,990 psi nhich exceeds the allowed 19,300 hy 1,690 psi. Both Cases 2 and 3 are well below the allo~vahlex i t h an increase of only one ft in H for Casc 2 and an increase of line ft in both H and W for Casc 3. Casc 4 shows a decrcnse of 4,200 psi hy the addition of two ft to H only. Thc changes in pipe length cause an increase in piping matcrial cost of approsinlately $6.00 for Cases 2 and 3 and $12.00 for Case 4. The total cost for installation of t b r examplc run of piping would be very close t o

440


$2,000.00. The possible increase is less than of for 2 an113 i~ud less than 1% for 4. Since design costs are approaching $5.00 per manhour of design time (including the costs oi engineering, drafting, and 01-erheadI . little if any saving can he made hy extensive computations for siiiiplc problems such as these. Generally design organizations utilize curves for the calculation of stresses in simple t--bends so that the proper configuration can easily be determined. Reference 18 includes a tabulation giving the relative accuracy of various methods applied to tcn configurations. It is reconmended that this table he studied in detail. Refercners 2, 18. 34 are particularly recommended for those interested in the various mcthoris of stress analysis. Reference 18 is incouiplctr for ,111 crmfiguration. at this vriting, Imt, the tables of rnluer rrpeatedl>nred in c~~mputationr ~vhiehare given eliminate uiany of the simple or basic computations and :we thus vcry effective time savers. SIZING PROCESS LINES Basic Equations

Tbe overall energy balencc is basic to all fluid flow proble~ns,and it ib helpful to recall the principles of thr first law of tbermodynnmics. This Ian states that the total ainuunt of energy entering a systeru must be equal to that leaving a system. Thc expression of the first lay, neglecting surfacc, magnetic, and elci:tricnl energy: can he w i t t e n in differential iorin as follows for one pound of fluid flowing,

where V' P v u

Z g

g, Y

TV

,.

$f t o

(2) represent a pound of force and lb for

21

- dF

(for an irrevers~bleprocess such as fluid flow)

(3)

where S = ent,ropy I.' = irreversible energy losses called friction Substituting 2 and 3 in 1 t,he differential equation

is obtained which can be integrated t o give

Eq. 5 is a basic expression for the morli required t o move a unit. mass of fluid between two points. If the specific volume u is constant as can be assumed for incompressible fluids (liquids).

t:

dP becomes v(P2 - P I ) .

The sizing of limes for a process plant requires the selection of a h e size and then the calculation of t,he expected pressure drop for the proposed line. In such calculations sections of lines before and after pumps and compressors are most conveniently considered separately (suction and discharge lines). The work term then becomes zcro for the section of line being considered since the device adding work t o the system is not within the boundaries of the energy balance. The equation for pressure drop calculations then becomes

u(Pl -

The expression Pv is often called flow xork and represents the amount of erlerby required to force an element of fluid i~it,oor out of a system. l w o additional basic concepts of therrnodynan&s may be stated as follo\rs : dU'= T d S - Pdv

d y = T dS'

The velocity terms (kinetic energy) are usually very nearly the same 9 , be neglect,cd. The acceleration and the expression (uz2 - 2 1 ~ ~ ) i 2 can due to gravity in most locations is approximately equal to g,(32.17) so that g, g, is most often called unity. Hmce, assuming an incompressible fluid or an average specific volume, eq. G becomes

internal mergy per lb of fluid = Dressure: #r'sq ft = apecific volume, cu i t & = velocity, ftisec = height above a datum in ft, = accclcration due to gravity, ft sec2 = factor to convert poundals to lh of force, lb-it,'#-sec2* = heat added to system, Htuilb = vork done by system, ft-//%* =

*For convenience use

441

Piping Design

pound of mass

P?) = Zz - i l + F

(7)

~vhere~(1'1 - P2) is the "head" change in ft-lb of iorce!lh of mass or ft-#,.lb, betveen points "1" and "2". Z2 - Z1 is the difference in height betxeen points "1" and "2". The units are also ft,-#/lb since g!g, does appear although numerically it is unity. Zz - Z1 is often referred to as static pressme. F = head loss in ft-#!lh due t o friction. I t may seem to t,he reader a t this point that undue stress has been placed on the background to the simple equation for pressure drop in a

442


process line. The time is justified, however. if it serves to prevent the confusion t,hat so often results over the term "head." I t has been shown ahovr that rq. i was derived from an energy balance based on a unit mass (one lb) of fluid floving and that, the energy terms appearing in the h a 1 equation have the units of ft-lb of force per lb of mass (ft&#jlb)and not simply f t as is often mist,akenly assumed. An awareness of this fact prevents ncedless confusion especially in converting to other systems of uds. The estimation of the energy lost due to friction F is the major task in calrulating pressure drops. Experimental evidence from the studies of the drag exerted by the walls of a condnit on the fluid flowing has yielded the so-called "Fanning" equation:

where F = friction loss in ft,-#/lh .I'= proportionality constant called the coefficient of friction L = length of circular conduit in f t y, = 3 2 . l i ft-lb/(#) L) = inside diameter of pipe in f t B y means of dimensional analysis the friction factor f has been shown ~ , a dimensionless factor to be related to the Reynolds' numher, D u ~ / and called the relative roughness, r, being the depth of irregularities in the pipc. hIoodyl"as determined the relationship experimentally and the results of his work arc presented graphically in Figs. 18-23 and 18-24. These charts permit the estimation of the friction factor f , for any size pipe. I t is to be noted, however, that the data are for clean pipe since it is impossible to present in any logical manner the effects of the many types of scale that develop in process lines. Such deposits, however, can increase the ultimate in-service pressure drop over that for clean pipe as much as tenfold. For some reason that is not completely rational, the Fanning equation has been presented in a number of forms. Most of the variations can he traced to the definition of the friction factor f. I n some works it is defined such that it is one-fourth the value of f presented here. The final value of friction loss will, of course, be the same if the proper equation is used with the correct friction factors intended for that equation. Because of this confusing situation, it is best to use only friction factor charts that indicate the definition of the particular f value being plotted, otherwise a considerable error in the calculations (fourfold) may result. Since the cliarts of lloudy have been sclected as a standard hy the Hydraulic Institute, it is good practice to use these charts and thus Moody's form oi the Fanning equation.

Piping Design

ssauuanon an!wan


Piping Design

445

Losses in Fillings

0.1

0.2

Pipe Diameter D, ft 0.4 0.6 1 2 4

6

10

20 25

Eq. 8 permits calculation of friction losses in straight lcngtlis of pipe. T h e various hcnrlt;. fittings, and ralvcp a h requirr c o n s i ~ i ~ w t i o n . One of the siniple>t mctlio~lsfor esti~nntingfriction losses for valves and f i t t i n g is to add tn t h r nctual l m g t l ~of straight pipi- an alnin~nt nf ptraight pipe t h a t ill producc :I frirtirm loss iquiv:dmt to tlmt n-hi141 would occur in the fittings and ralves. h mean* of e~tim:rtingt11c-r lengths published hy the (:rani: ('innlxniys somr y w r s ago an11 n n x iin wide circulation is given in Fig. 18-25 This chart i* entirely satisfactory for the usual estimates in proccss plalit c;dculations. Fur tnore ; ~ I : I Y I ~ I I ~ I ~ iriforniation reference should he made t o thc Staltdards IIE the Hydr:ruli~. I n i t i t u t t ~ . ' V t is reawned tliat the friction loss in fittings ronsnmrs n portion of the kinetic energy of the fluid entering tlic fitting.

where

trl =

li

=

velocity of Ruid upstretm~of liLting cmpirimlly determined consinn( for thc p:~rti(.ul:ir littir~p: called the resistance cocfirient

Values of I< for various valves and fittings are give11 in t l ~ cStanilnrils the Hydraulic lnstitutc.

I I ~

Line Sizing Techniques a n d Criteria

Pipe Diameter, in. Fig. 18-24. Relstivc r u u g l m s . ASME, 66, 671 (1Y44).1

LKryrinled by pemiisaiun, L. li. Moody, l ' w r c a

The method of sizing process lines inwlves a technique familiar t o I line size is assunicd and the prcssuri2 ilrop is calculated. If cnginccrs. : the calculated pressure drop is s a t i r f a e t ~ ~ rtlie y , assumcd line size is used. The problem then becomes one of deciding ~ r . l ~ is a t a satisfactory pressure drop. If too liigli a pressure dro11 is iised, primping cilstr can hecomc excessive. If too lo\\. a drop is used, cost* of pipe, valves, and fitting; beconre too high. This suggests a n eeonmnic balance bct~vcenmatcrial costs and pumping costs. Having unit costs for these two itenis, it is a simple matter t o develop a general equation fov total cost and solve for the m i n i ~ n u mby differentiating and equati~igtu zero. Charts for determining the "economic" line size can then be constructed. M a n y sucli charts havc been presented. but sucli a n approacli rcprcsrnts a dangerous ovcr siniplification of a mucli more complex prohlcn~. JYlren it is realized tliat Inany process lines do not inrolve ~ni~ilping. p o w r costs are not nlxays well known or realistic; and most process lines represent a unique situation, i t is understandahlc that, generalizations repalding the cconmni~: size are very often 71-orthless. J l a n y operating and design firlnl: 11ave prqjared t a n d a r d s \ ~ - l i i r l ~

447

Piping Design


~ p c c i f ya l l o w b l e pressure drops or reasonable veloc~tiesas guides in the sizing of process lines. Somc typical standards are:

Pump discharge Pomp suction Steam or vapor Gravity flow of liquids

Reasonable velocity (Tube Turns Co.) d/2 4 Ft/sec One-third thc above *d in 1000 ft/min

+

-

Water lines 5-7 ftjscc * d = inside diameter of pipe in in.

.4lloaable pressure drop due to friction 2 psi/100 i t 0.5 ft#/lh per 100 ft 0.5 per cent of line pressure per 100 ft 0.2 f&#/lb per 100 ft

-

Thcse and other similar rules-of-thumh have proved helpful t o engineers for many years. They have, however, often been given thc status of natural laws and thereby caused more harm than good. Seither the reasonable velocity method nor the a l l o r \ d ~ l epressure drop can yield the exact economical pipe size for all cascs. T h e velocity method does not allow for changes in fluid densities, and the allowable prcssurc drop mctlrod does not recognize t h a t the economical pressure drop should be greater for small than for large pipes. Neither method allows for variations in material and polver costs. Despite tlicse objections, line sizing based on such standards is valid in the majority of cases. Although in many cases i t may be argued that overdesign results, i t should be realized t h a t standards after long use become such a part of an organization t h a t the overdesign t h a t results is unconsciously expected. It is impossible t o make u dctailed cconomic study of each line in a process plant in order to select the proper size nor is such a study nsnally justified. There are certain cases, ho~vevcr,particularly in the sizing of more cxpensivc alloy lincs or Iargc carhon steel lincs for which dctailcd study may he justified to aid in deciding bct~vccnt ~ possible o line sizes. A short-cut rnethod has been prescntcd21 for rapidly estimating the costs of process lines so that values for trvo possible sizes can hc comparcd rapidly. Should a large difference in cost be indicated further detnilrd study, using costs peculiar to the particular situation, will be justifieti. If the difference is small, thc larger size \ d l aut,omatically be accepted. T h e data are givcn in Tablcs 18-7, 18-8, 18-9, and 18-10 and an illustration of their use is given here. Pressure Drop in Gas a n d Vapor Lines Fig. 18-25,

Resistance of valves and fittings. (Courtesy of Crane Comi~any.)

Moat process lines which carry gases and vapors are short and do not vary enough in elevation betrvcen the terminuses to justify a coniirleration of static 11ressure i:hange u r rhanye in ,tensity. In such rases a n arerage dcnrity is assnmed based on an estinlated average pressure, and the


Piping Design

TABLE 18-7. Pipe and Fitting Prices* TABLE 18-8.

Rase price: Carbon Steel .\ST11 106 Grade .I u r equal $0.105 per pound Base \\-eights: (Based on cnrbm steel pipe)

2 3 4 6 8 10 12 14 16 18 20 24

'2.M

4.33 5.61 0.29 13.40 18.76 24.20 X.70 42.10 47.40 52.70 03.40

-, --

3.65 .i),

10.71) 18.97 28..55

40.48 53.60 55.00 03.00 71.00 iX.tj0 94.60

E'ittitrz.s 90' elhorr-, lonx :i~lils l ~ w r;idius t Tees. Sidl sizc outlet Tees. reducing outlet

180" bends, long radius Reduce1.s concentric Reducers, ercentric Lap-joint stub ends .\Iateri:d Sactws for pip? and fittings Carbon steel 4-6 per cent rhrotue. 5; per cent Aloly Stainless type 304 Stainless type 316

* Repl.intrd (1953).

by permission-Rase,

Rase 1'1.ices (Basis: 150 lb AS.4 RF Welding neck A S T l I .\-I81 (upproximately 40djlb) Size 2 3 4 6 8 10 12

5.02 10.25 11 0%) 28.55 43.40 .54.i0 65.40 7!10 82.80 93.50 104.l0 125.50

L,,jD, equiv:ila~~t length to diameter ratio 13 2.1 2.6 (12" and below) 2.1 (14" and above) 3.0 0.50 0.60 0.80 Alultiply by I 3.25 10.2 16.07

H. F., P e t ~ o l e v r n Refix<',., 82, No. 8, 141-144

Flange Prices*

Rating Factors Rating, Ib

300 600 900 1500 I

1

Cost, $

3.5 5 6.5 9 14 20 35

-.

\Idtiply by Raised Ring typc face joint 1.0 1.5 1.22 3.5 4.3t 5.01 5.5t 6.51 9.0t 9.51

--

Flange Type Factors Velding neck Slipon

Multiply by 1.0 0.65

llaterial Factors Carbon steel ASTM .I-181 4-6 gel. rent clrrome. 35 per cent hIoly (:\ST11 182 F5) Stainless type 316

hlultiply by 1 .0

3.509 5.0 g

*Reprinted by permission-Raw, H. F., Petralciini Refinpi-, Sz, Y o , 8. 141-144 (1953). i Use 4.0 for sizes 2, 3, and 4 in. only. I Usc 4.5 for sizes 2 in. and 3 in. and 5 ior 4 in S For 150 lb and 300 lh welding neck only.

450

Project Engineering of Process Plants TABLE 18-9.

Piping Design

Fabrication and Erection Costs*

Fabrication Costs hlatrrial Carbon steel All nickel and nickel allolz steels (18-8. Monel) 5 per cent chrome (no nickel) and higher steels

TABLE 18-10 (continued)

Material Factors Materials 5 per cent chrome .% - oer . cent moiv Monel Stainless steel, type 316 Cast iron (125 lh)

hlultiply carbon steel ciicts of pipe, fittings, and flanges ti!.

2.5

~~

Erection Costs Approximately equal to cost of fabricated carhon steel pipe; i.e., material cost of carbon steel pipe, fittings, and flanges plus fabrication cost. This also applies for alloy pipe installations if no field xelding is required. If field eld ding is required, the following lnultipliers are suggested for application to the cost of an equivalent carhon steel system to allow for special f i t u p and field stress relieving. Stainless steels 446 per cent chrome *Reprinted by pcmlission-Kase,

1.5 1.2

H. F., Pelruleurn Kcfiner, 52, No. 8, 141-144

(19.53).

Multiply by

1.25 2.1 1.7 (I50 lb only) 0.45

~~

Valve Type Factor Valve type Gate Glohe Check

Multiply by 1.0 1.2 1.0 for class 150 0.70 for all others

ILLUSTRATION-EST~~IATION OF h GI\.EK LLSE.* Determine the erected and dclirered cost of s &in. Schedule 40, I30 ib AS: rating (RFI, c:lrbon steel plunp discharge line which is 323 f t long and is composed uf 12 flanges, 16 meld ells, 1 ter, 1 check valve, and 2 gate vnlrrs. a. Pipe aud fittings (See Table 1&7.)

L, - equivalent length, ft TABLE 18-10.

Base price (adjusted) cost steel 150 ib O.S. and Y. gate valve 70 85 120 205 290 400 530 Rating Factors Rating, Ib

D'

Valve Prices*

hIultiply by Raised face Ring- type jolnt ~. (See Cast iron below)

325 ft pipe 325 16 ells (16) (1.3) (6) = 125 (1)2.1)(6) = 13 ft Total: Total weight: (463) Cost:

()

(8780) (0.105)

=

(463)(18.97)

=

$922

=

8780

b. Flanges (See Table 18-8.) (12)(9) = $108 c. Fabrication (See Table 18-9.) 108 Total cost flanges ancl pipe = 922 Fabrication cost = (1.0)(1030) = $1030

+

=

$1030

d. Erection costs (See Table 18-9.) Cost = 1030 1030 = $2060

+

e. Valve costs (See Table 18-10.) 2 gate valves (2)(205) = $410 1 check valve (1) (205) (1.0) = 205 $015

*Reprinted by permission-Raac, (19.53).

H. F., Prli-oleurn Refiner, 32, No. 8, 141-114

*Reprinted by pcrmission-Kahc, (1953).

H. F., Pelroleam Refiner, 32, Nu. 8, 141-144


452

IS tllis lin? ,\-we crmstructetl of Solietlulc 40. -1-1; pet. wnt ehrolne-moly wit11 :3OOii I1T.1 rhmme-moly flm~ges,the cost n.o~~ld he c:ilcul:itetl 11)- wing tlir :rpImr-

printe factr~r.;.

?.

(11~)(2..ij

+

=

z..jxo

d. 1030 10:N) = 2.0fiO r . Gateb: 12)(205) (l.i)(l.25) = 872 Chrrk: (1) (%O5)(l. i )(1.25) = 436 Tot:~l ?51O.%iO

friction p r w w r ~,lr1111 > i* ~ ~ a l r u I : ~:IS t e ~for l i ~ ~ e o ~ ~ r [ ~ r i ft -l ?u i l~~l l~~. , I~~ L IO II I I \\.11cn t h l ~ r c ~ s u drop r ~ ! ib I:lrg? ;IS i n l m g I ~ I I I . ~ ,: I ~ . S ~ I I I ) 11i :ivc'r:igc i l ~ ~ n s i ti-y not v;ilirl. TIII.1wc-snrc 1lr(,11ran Ire written nrglwtin.: static head,

Piping

Design

453

w i b c pipc. valrcs. fitting?. ! ~ n dpiping a p l m r t e n a n c e ~for car11 antici11ated type ui wuvice :mil \\-it11 piping drawings constitute n rompIetc descril~tionof tlir pil~ings?..tem. T h e first step in writing piping specifications is the preparation of a list of all the prwc-;i nncl utility fluids in tile plant. T h e list d~onlciinclurlc :I description of each fluiil. its prc,rsurc. temperature. and an? service peculiarities. Careful study of this list h s e d on a knon.lcdge of the propcrtiei of piping nlatcriak a i \\-ell a* the operating conditions n-ill rcrcal certain c;~tcgoriesur rxnge. of servicc conditions upon ~vliicli specifications can be 11nscrI. Therc ;ire t v o extreu~esin q~ccifirntionwitin:: t h a t ~ h ~ ~ be u l;rvoidrd. d h ~ e p a r a t especification ran III, ronceivahly 1%-rittcnfur I::I~II fllriil : ~ u dfor Y 111nn11erof SIIIIIII q ~ c r a t i n g1.anges. T h c s:~vingin purcl~a*e11rice>I:IIV c w r , is q ~ c n tnlany t i ~ n c sover hy thc ndiltvl c,l?ri?:il, cnginivring, :in11 construction cost- rausrd l ~ ytoo ninny sl~~,rifiratii,n?. Tile otlrcr cxtrernr i- preparing only unc or two speciiicati~~ns v i t h i n n t ~ r i a l sliatcil t h a t call n.ithst:lnd the most c r e r e operating conditions. All tile 1r.s x v t w scr\-ices will illen. of course, hr m ~ r cth8o adequnlrly s e r w d , \vliicl~ ~ v o u l dhe costly and actually ~ a s t e f u l . Sollie o p t i ~ n u nnumber ~ of categories ahout m i d x q betvcen thesr t\\-\-o extrernes Innst be found. .1 careful study must he m:rclc for ear11 project to d c t t v ~ ~ ~ it rhr ei ~optilnum. .If e n cxtril r e e k s rpcnt ,In thc l~rcl~:ll.atiim of piping .;pecifications early in thc project 1r.ill produce great savings in tinw and erluil~mcntcosts. Nomenclature

where P = psf I, = i t of pipe 1 r = I13 S C I ~ I J = insiclc dialnt:tcr in it H = 1341

1'= " I t \Vhen it is nut possihlc t o neglect t h e change in pressure causcd b y diderences in elevation a s in deep gas \\-ell-: nlure co~nplcxcquutiotls rcsult. Solutions h v e been presentcd,G.'2.'9 but the process plant wlrlun~ presents sue11 problems. PIPING SPECIFICATIONS

Carcfnl\y prepare11 pi11ing s1~tTific:1tionsLIW r q u i r m l for the s ~ ~ ~ r e ~ ~ f ~ l l cconuniic d~higrr:lnd ~ ~ n ~ t r u ( ~oft ipnr ~ ei c - sp l i i n t ~ . Specili(.i~tiun- ~ k -

.is explilincri in Chnptcr 5 it is convenient to dcsignatc I AS.1 flange l.ating< O I I the


Piping Design

v;llvc list. This list aids design-drafting since it providrs in a single compilation all pertinent data for use on the piping drawings.

piping spcrifiration and as a guide or cheek l i d for those preparing spccifiratiuns and not as a recommendation of specific items. Indeed one of the no st unfortunate practices in enginccring design is the copying of ~pecificationsused on previous projevts, hiaterials and eqnipment mllit he evaluated fur each joh and a rarefully ronsidered decision made on the basis of facts a t the t i ~ n eof design.

454

Specification Preparation I n order to more fully explain the technique of specification preparation an exanlple of a typical specification is given below. It is preceded by tlie reasoning 1%-hichusually accompanies the selection of materials and specification categories. Table 18-11 presents a summary of the fluids to be considered together v i t h their service cunditions and letter designations. TABLE 18-11.

Fluid desienation HC HR H.1 H 6

Summary of Fluids for Example Piping Specification

S c n x e and fluid Hydrocarbon Hyrb~ocarbon Hydrocarbon Hydrr~carbon Stetmr Steam. exhaust Steam, condensate Air, utility .\ir, instrument, dried Fuel, natural gas, dry Caustic Instrument piping TTater, fire protection \Tater, process cooling Water, utility Water, sanitary

Operating pressure, temperature, "F pig -

250 250

800 750 Maximum

15 240 Ambient 100 50 .\mhient 50 Ambient 50 Ambient Rltnie as line services 75 40

Ambient Ambient

The numher of specification catcgories has hecn restricted to five, 11, 3 , P, 9, and Z. This mas made possible by specifying certain items, surli as bolting, according to tlle class of fluid. Further simplificat,ion \ma acconlplislled by careful planning so that the specifications have been limited t o four types of flanges, twu types of bolts and five types of pipe. I t is a t this point t h a t the procurement sertion of an organization can be no st helpful in kceping the project engineer aware of changes in availahility of materials. Before the specification is completed the engineer should determine if the materials specified are available, otherwise t h e xill he wasted later in deciding upon substitutions. It may be desirable in wine cases t o list alternates for materials of uncertain supply. T h e example specification should not necessarily be interpreted as a recrnri~nendationof certain types of valves, fittings, or piping materials. T h e specification is written in a complete form as an illustration of a

455

Flange a n d Bolting a n d Gasket Selection 150 111 M A flanges and flanged fittings, according to .4SA BIG-5 of the Code, will be satisfactory for all the services in Tehle 18-11. except 9,HA: H B , and H C for w-hich 300 lb ASA flanges are required. F is also ~ i t h i nthe 300 lb ASA limit, which allows pressures of 340 psi and 300 psi, rrspertively, for 750 and 800" F. Raised-face flanges can he uscd for all of these services. For service H C , however: although operating a t no higher temperature and pressure than HB (300 psig and 800" F. Maximumi. ring-type-joint flanges (RT.1) will be specified since t,his srrvirr is for heater cross-overs, for wliich a t times operating temperatures m a y be morc severe. Tlie R T J flange facing (Table 16 of tlic Codc'~permits a teniperature of 850" F and a service pressure uf 300 psig Thus a safety margin of 50 psi and 50' F is provided. 150 lh .4SA flanges will be used for services A, AC, F, and C since this rating is the lowest nominal steel flange rating. AC, which is dried air for instrument services is often run in galvanized piping utilizing s c r e ~ d malleable iron fittings and flanges. I n this servicc galvanized piping will be used; however, all fittings will be forged steel and all flanges will he cast steel bcrause of the possibility of fire. For the same reasons servicc A, utility air, F, fuel, and C, caustic, will also utilize steel fittings and flanges, hut, the piping will not be galvanized. Service I N , instruments, must have tlie same specification as tlie procesi line when in contact with the process flnid. Gasket Selection Compressed asbestos ring typc gaskcts will be specified for all s c r r i r r i except S, HA, H B , and C. F o r these inore severc services corrugated iron, double jacketed, asbestos filled gaskets will be used. For HC, a ring typc joint flange facing has been specified, thus oval iron ring gaskets are required. Pipe Selection T h e thickness required for pipe in each service can be determined from thc equation presented previously and recommended by the Code [ t = ( P D / 2 S ) C ] . Reference t o Table 21 uf the Code indicates t h a t ASTM .4106 is satisfactory for services above 800' F. Tlie allowable

+

456


Piping Design

ntrrsn f o r G r a d e h a t 800" F in 9300 psi nnrl i;cIrc.il~~lc 80 p i p n.ill 11r satisfactory. Schedule 40. .ASTlI A106 is adequate for HH a n d H A F o r all other services except TI'S ( a n d where cast-iron pipr i; sprrifird in W s e r v i c ~ s )t h e lees expensive s e a m l e s . X S T l I A53 G r a d e A pip? d l be specified. F o r service \TS, sanitary w a t r r , ASTAI .I-120, whirl^ i- a 11.~11algnlvanized pipe sprrifiration, \\-ill ire ~jlecified. Pipe 2 in, anti b r l m - , fils all ~ c r v i e r rc x r e l ~ t \YS,will IIC s e a ~ ~ i l c s . S e h t ~ ~ l u80 l e .ST11 9 - 8 3 . Schedule 8 0 l ~ i p eis used in t h e smallt,r size. tu provide structural s t r e n g t i ~ . A t t h e time of rvriting ASTAl A-83. tl~ougli ~ m r crw t l y (it is m a d e t o conform t o t h e more exact tubing specifi~,;itim I was inucli easier t o obtain t h a n .ASTI1 .&-I06 or 4 4 3 . F o r s~u;tlI air piping used in instrument a i r trnnemission lines :); in. 0. I). soft annealed copper tubing a n d compression t y p e nonferrnua fittings r i l l 11e specified. Typical Piping Design Specifications

1.000 G e n r i d 1.100 Unsis of Design The de$ign, fabrication, and erection of all piping nnd ~cccisories~ h : dconfirm to prnctices specified in the Code ior Prrssure Piping AS;\ U.'3l.l-l!lji, or l:lt?-t iswe rhcrrof, and to the drawings nnd the following specific:itions. All rrfcrencca to the code herein shall be understood to refer to the above ASA Code. 1.200 Definitions The terminrhgy used throughout this specification and on the dmxings will hc in g e ~ ~ e r that a l conforming to currmt trade pr:rctires. dnc/tur. Point uherc piping is fixed is callr4 thr, xnclior point. The ~ i w i w attached to pipe or the conlplete strncturr if it serves the singlc purpose of fixin? the pipe is calleil an :~nchor. Bleed. .A small valve provided to draw off liquids. Uli~td. A plate sized to be inserted in a flxnge to isolatr n portion of n syitcrn Bloc/: T'nl~,e. h valve furnished to shut off a srpar:ite system The tcnu is loosely used x i d may be understood to mean m y valve which is wed for shutoff service rather than for throttling. B.O.P. Bottom of o~ltsideof pipe. Used for pipe $upport loc3tion. Control Valve. Any one of n number of different types of valves, remotely opcmtcd from sonw type uf instrument. Directions. The Plant Xorth direction sho~rnon plot plans and other ilr:~\~incc mill serve for orientation of equipment. Drip-Leg. A . rertieal section of pipe located in 11orizont:~lpiping to deHect and "catch" co~deniate. F I V . Field Weld. Grudient. The siiccessive drop in elevation of piping to insure gravity flow and drainage. i d . D r r i c ~contrdling the direction of piping move~~ient Hanger.. .I roil :,nil clzmp, a chain, or a spring device wrrl for snpporting pipe is called n Ixloger.

I

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I I

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i I

457

L i n r .1 pipe m n from one point tu another. The ile.ip:ition. Tine Sumhrr is a niunh<,r :111d s!-tnbol appearing on the piping drawings 1,-hirh idrntifies the pipr :icci~rdin: to sizr, proce~sfluid, :enera1 loention, and ~prrifir:it,on. P . E . Indicates plain-end. Used to differentiate between thrcadrd-rnd pipe and mill cut. A procurement term. . The dcsignatiun P.S. is used to indicate Pipe Support, which -npliurt inxy be one of the above anchors, guides, or shoes or several rtmbined to farm tlw support R o n P i Pipe f i ~ r n i ~ h rind r:~ndrm,]lot c i ~ t lrngtlis* , Shoe. Dcvire iwlcletl to or clnmpeil to :J pipr ~liir11liru\-icleproceed with f:rbricntion, i i . , receipt of the spool slicet releases all the listed >pool.. I S p u l S t i n i b e r . A mmher identif~-iug:I lliece aE fabricated pipe. S T . Strain trap. I:sunlly srhri~i:itically indirnted, but understood to n1ea11 rhr tr:ili and neces~asyvalrinp :md piping for by-p:ie;ing in nnrrgrnries. i ~ .4 pr~rfnrnted . metal shrct trmpornrily pl:icrd in n fl:inged joint to iirulect equilment iron1 foreign nvxttrr in initial operation. Permanent strainers shall also be furnished xhrrc indicated. 1.300 Line Snmbering System ,lhr: S d l o ~ ~ i nnumbering g system shall be w r d as line identification on pij~ing appe:l~.inpon How shcrts nnd piping drai~-ings The complrtr lint. nrnnber shall ronsiat of llir follon-in: components, :I? illustmtrd: 4-Ilh-101-11-The first ni~merulis thi, nominal line tizr. The HA de.ignntr,. the service; the 100, thr :ire3 nrnnber, nnd the RZ rlr-ipnatca the piping spwification npplic:rhlr. Line numbers ~ h 1.11:inge: d ( 1 ) K h ~ nsix. I.~IRII:~..; ( 2 ) n-hrn sl1rr4ic:itirm d~anges;(.3i when bmncheu leave original line; ( 4 ) n.biwi-er an additional line numbrr rrould simplify the engineering and dr:iftin:.

.

1.100 Lirte Sizes Piping shall br sized in accorrlane? with best cnginrrring ~ m o t i e efor prrsrnrr drops ronsi-tent xith proper oprrntiun of erluipmrmt. In genrrd thc Sollorrin: limit:rtion shall appl:-: 1.401 Sizm .?k in., I$!( in., 2% in., 3% in., 4% i z ~ ,5 1 1 1 , and 7 ju. ~ 1 ~ not 1 1 be wed. 1.40'2 I)rnins, m n l ~ l r and , rent lines ahnll be 7.i i n niininirun imlws o l h e r ~ i s e nuted. Drnins for hot piliing sh:rll be not iris than 1% in. nonlin:d s i x . 1 . 0 Exr.q,t for inztri~nwnt tninm~isionlinri, pillin~run on suliport shall

458

Piping Design


not be smaller than 2 in. Smaller sizes may be used for short runs less than one support space in length in special cases. 1.401 Underground lines beyond process area limit^ shall he 3 in. or larger. S a n i t a n water ( K S ) may be 2 in. minimum. Certain utility lines may be smaller, but must be considered as sprrial cases and approval secured.

1.506 Oueihead Clearance Ovcrhead lines running from vessels or other elevated equipment to steel pipe supports or to cuncretr deeprr.? shall have a minimum r.lear:ince nf 2 3 0" .~hov,. p h n t roadways, and railroad (rails). Y-CY' shall he the mininnlm piping clenr:~rrer above \ralk\vays and platforms and above grade in the immrdiate pruicsa an,:i.

1 jOO Genrral .Votes on P i p i q Design 1.501 Aboveg~mmdLines .ill process and utility lines within the process area and all yard lines outside from the process aren except ~s-nterlines, sewrr lines, :mil ccrtain designated pomp and compressor line; shall he run ahovrgruund on concrete sleepers, or overhead on structural ~ t r e lsupports.

1.507 Bent Pipe Pipe shall not be bent to a mean radias of less than five (5) times the nrrrninal pipe zize. Exceptions, when ncrrsrary, shall he accon~plishedb>- mrma u i .sIlrir.i radius welded fittings. Such special fittings shall be noted on arr;lngeirrnt drawings. .4 minimum straight run equivalent to two or mar? pip" iliametrrs should he allowed betrreen t v o adjacent pipe bends ~vhereverpwsiblr. Carbon strel pipe 1 in. and below may be cold hrnt on hrnding m;~clrinr-. .illuy pipe o r other pipe subject to cold w-orking strrssrs sh:d he considered :u spwtal :ind shall he bent arrording to specified pruceilures.

1.50'2 ilwangement of Abolteground Lines Aboveground lines running in the s a n e pl:ine shall be arranged so that the bottums of the lines, exclusivr of insulation, are a t the sanir devation. Sufficient height milst be allowed to clrar the insulatinn of insulatcd lines, and this height ahall govrrn the d c w t i o n of uniiwulated lines as w l l .

I..%% Angle T'alu~s The use of angle vnlveu shall be avoided.

1.503 i?le~,ationof Aboz,eground Lines K h r n pilring is run in parallel groups, one rlev:~tion shall be srlecterl for linrs runnitig to Plant R ~ t and h South and anothrr r:kwition for lines riinning East and West. If piping is run in "hanks" or l a y r s un pipc supports the clear dimmyinn brtwwn bottom of pipe in one layer and top-of-pipe in adjacent layer r11:ill be three times thr mminal diameter of the largest pipe in either group, plus twice the ertrnsiun of a flange beyond the outside diameter of the largpst pipr in rithcm adjacent layer. Lines shall orrlinarily change elevation whr~1thry rhunge direction, except a t the discretion of the designer in special rases and for nboveground linrs not. running in a bank of piping. The dimension of cle:~mnceslid1 he the same as that given above. The largwt pipe sizr in the hank ~11:ilInln-;iys govrrn for rlearanrrs. (Plant North is an arbitrary direction set on Plot P h n i for nrirntation prlrpmes in all ~ w r k . ) 1.504 I- hr located a h o w the oprratin: I r d 11--itlrrrutt h r use of a chain opentor or extension. Chains shall rrtend to ~ v i t h ~three n Spet I:(') of the platforms, from which the r a l r e will bc apemtrd. Ver rri rhain oprratcil v:dves, howcver, shall br kept tn a miuimum. Val\es requiring extensions, stems, or chain operators shall he noted on drawings. Keach-

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459

rods or ~xtrnsionstems, fipld fabricated, sh:~llhe prnvided for vnlre.< 1% in, heion- rathrr th;m ch:iin 5,-he&

1.509 Drains, Vents arid Test Openings Drnins shall be provided a t low points and vents a t high points. Thr drain and/or vrnt shall consist of a 6000 lb forged sted pi111. coupling iwldid into , the line, a short schrdule 160 nipple, and a 5i in. Gate V:ilrr in a c c o n l n ~ i with the line specification. I n hot process lines the drain or vrnt shnll not br lrss than 1% in. nominal pipe size. For these connections a hexagon shaped t l i r t d d steel plugX shall be madc-up into the valve. All snch plugs shall rztend :it lmst 3 in. beyond threaded portion. Teit connections ur threadrd connrctions for future use it, pil~ingor vrs.vlshall be fabricated the same a5 drains nnd vrnts n c r p t valve ma>- Ijr, omitrr
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% in. hose (manufacturd, heavy) connections for steam, air, and m t e r shall br provided a t convrnirnt points in the process area for genrwl iltility p~~rlioir... Utility lines a t vertical vrsiris are to be run nilj:~cmt to v e s d i ;ind outside oi' insulation but not outside of tower platforms. 1.511 Connections for Pressure Gages and Pressure Instruments Connrctions for pressure instruments to indicate or n ~ o r dpump dischargr preisurrs, shall he located in the discharge piping between the. pump Hnnge, nrar the pump and the first valve. Other points shall be noted on draivinga ~lli,cific;tlly. All such pressure indicating or recording points shall he nccebsihlr. Teit point;. may be accessible by ladder. Bleed-off valving fur preiwlrc inctrnmrnt:itt~~t~ an ' T h e plug consists of a piece of carbon steel hexagon bar stork tlrrmd~dwit11 ordinary pipe threads on one end. So called threaded bull-plugs often rmsh iitls.ing liglrlming, damaging Lhe pipe coupling or the thrmds.

460


Ii,d 1i1m ~1i:iIllw pmvi,lml with :L ~ I O L I I ~I11,rk P 1 1 ~ 0~ t l w s ' l :ind I d m l ~ : t l n I w : ~ t ~brtwtwi d t h r tn-o hlucke. Instrument, hlred sizes nced not folIo~!- (Ira111 a ~ r~r ndt ~ising,bnt any hleed piping for hot serrirw rhall be not less thnn '12 in. nnmin:il sizr and shall hr nrranprd so that a rod may hr drixen up t h ~ w l r r :iiui fitting. I3let.d pipinp fur hot fll~idsxliirh 111:1y i g i t r "11 expninrr t o air i h o ~ d dhr i ~ ~ p p l i ewith d :L >implr pipc
.\I1 temper:lturc il~itnimentpoints and orificr flangi. lowtioni sh:lll

1.513 Stram Traps Typical aml spi,ci:d itenm trap nwrmblie: shall he shorrn iu detnil on " S t m n Tr:ip S c h i ~ l u lL)r:ln-inK" ~ : ~ n diilrntificd by thr trxp imnrhvr. T h r +:i111 tr:111 location will bc s1iorr.n on liping dmn.ings by s y m h d and numbrr. 1.511 I?rpmxion I,onps If itrrss
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1.515 Piping at P i m p s , Compressors, a ~ l dTurbines

1.5151 P i m p s Chcck vnlrrs shall he provided in discharge lines of all erntrif~~pal piimps nptrmmu of first block valve. 1.3152 Tnnporary str;iinrra shall be hbricated from mnchine perforated in. thick for piping u p to 8 in. nominal size :?nil s h w t m ~ t : d not lrss th:m not less than $& in. thick for all sizrs above 5 in. s piping shall he so arranged that minimom clearancr 1.5153 P u ~ i ~ pand hrtiwrn projrctions of adjacent pumps or machines shall be 2' G". The niinimimi o p ~ m t i n gaide, \\-hich shnll be a t the driver end, shall be 5'0". .4clcquate cle:imnw shn11 be provided for the r i t h d r a d of reciprocating parts or parts which require horiaontal ~rithclmrrals. 1.5154 Suction and discharge piping shall be arranged in aecunlnnce ~ i t h

x6

Piping Design

46 1

t h ~"Stnn~lnrils of the Hydraulic In>titute." Watcr pumps shall be installed ~r-it11Hoarlcd sitction.~5s-hererer posihle. Otherwise, foot valves and ejector or injector -\items 41all b r provirlrd. 1.5155 Hot pipino connectione into eqnipmrnt such as pumps and turbmcs shall Ije nrrangcd and anchored to eliminate all podsible piping stre% being carried into ~irachinr. 1.5156 Piping crlnnectioni. to equipment shall not IX run h o r i ~ o n t n l luver ~ or acrws equipment. E q ~ i p m m tn111.t he left clear for reinrxd h>- e n u o or nther m:iintmanee r q ~ ~ i p m r n t Scr . 1.603. 1 S l 5 i 1.nbric:lting ;ysteni, gliind-swl, :d i m d l watrr rooling piping illall bc shm~-r-nin detail on drawings to a\-aid possible ronnection errors, lL515' Con~pressors C o m l ~ r r ~ - opipinp r clinll be :irmnped tn avoid uxccscive or cyriic vibration. Sec 1.5157 far i,ibric:~ting oil :ind o-:itt,r - p t e n ~ s . 1.,5E3 7'7irb~ws hl~rhnniciilezpnniion jointi ih:111 he j,roridwl ill a11 e z h ; ~ l w-team ~ and 1iX.r steam lines connecting t o cquiptncnt. See 1.51,R for lubricating oil and i,--aier systrmi. 1.516 S t m m Ezhniist mid C'o~iricnsutcLitips All secondnry or satomtrd stc:im piping :~nd rrhaust steam piping shall be run ~vitlra pradient. Drip-legs 11-ith rteam traps shall be provided in this piping nt all junction points and other points cnnsiderril nrrcisarl-. Steam traps shall he provided in d l vertical expansion lool~i, The discharge fro111 all steam traps shall be run t o the nearest conden~atereturn header csrrpt :IS r~otrrlon draxings. X r i n str:r~ndistributiou hmdrrs shall he run with a gr:~dient,and drip-IF:-: tr sh:111 hr prnrided for e o n d r ~ ~ w rrmoval Ste:mi ronnrrtions from ste:nu hntderq to cquil,mmt d r i r r r i rhnll he provided with a pxtr rnlvc loc;~trrlin a horizontal run at the hca
462

Piping Design


1.60'2 Changes i7r Diwcfio,i 1.0021 Change. in
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463

1.701 Field Trsting After rrrrtiun but bdnrr appliration of ininl;ltiiin, all linen shall be given a I,\-iirostntic t r 4 :is follon-s: 1.7011 Ex11 w r . r i u l ~ d piping ~ I ; I I I he tested hydrostntic:illy 3t a p r e w r r equal to twu (9tin~rsthr lowest prim:~ry-rrvicc pressnrP rating nf thr fittings, wives, and flmgcs in the line, hut in nu case less than one and n n d ~ a l ftime. thr iictn:d normal vorking 1resiure. (In certain 11ydroc:irbon and chemical processes all witer mnst be removed frun~any part of the proers y s t r m before operation. Such processes cannot be twted 11-ith xater since the romplete removal of the nater from the iyitem could not be effected \rithont ili;asirmhly thus nullifying the test. Son~rother ntwptable process Hr~idnmit he used for testing. Air may not he used since it d l also leave m t e r nr lihrirntion oil as a contaminant. Such reqnirements m w t be developed early so th:it the fluid d l be available.) 1.7012 The trst pressure must not be greater than one-half times the maxim~lmallorvshle \vorking prrsure for the pipe or as determined in acconlance vith tcsting rrquirem~ntsin the Code. 1.i013 The twl prtwiirc niust not he grratrr than the maxinnrm allonahl~~ pressure for the rwakest pirw of erplipnlrnt installed in thr line and incliiild ill the hydrostatic te-t. In ~ t w r : i l ,ru:i,im q n i p n m t such :is vessels, e x ~ h : ~ n p w , pumps, mil compressors -hall b<,isolated from pipe line hydrostatic test. When necessary for practicability, exchangers and vessels may be included with the connected piping, provided the piping test pressures are xithin the allowable cold pressure limits of the eqnipmrmt. 1.7014 The lowest hydrostatic test pressure shall be 100 psig 1.7015 The follorving equipment shall he exch~dedfrom thc g m ~ r a lhydrostatic test, bnt shall br tested with cornprersrd air ( : i d soup suds) ;it pressure rqml to the allo~vabl~ working pressnre of the rqniprnmt and linrs or equal to the maximum comprcsaed :xir prrswri., rvhidlrrer is the luwer. 1.70151 Instrument Air Lines 1.70152 .4irlinrs to Air Wotor Oprrntrd Valves 1.70153 Pressure Parts of I n s t n m m t s in GRSor Valmr Scrvice. All other pressure parts of instrnments, ho\vcrrr, rhall br whjerteil to tln: general hydrastatic test, exccpt ~ v h mtrst prrssurc c s r r d s normal working pressure, in ~ ~ h i c h case the instrumrnt shall tic isolatrd. 1.70154 Plant Air Lines 1.70155 Plant Fuel (::IS L i n ~ s 1.7016 Relief valve? d1:111 be exrlndrd from the general hydrostatic tests. Blinds shall be instnlled betwren the relief valve inlet or outlet and the section of pipe being tritrd. 1.7017 f here the test is to be made wing m;itrr or othcr Huid, all air shall be vented from the lines as Huid is zdrnittcd. 1.7015 Thr! piping and equilxnent being subjected to the hydrostatic test shall be maintained under pressure for a sufficient length of time to permit thorough inspection for leaks and defects. 1.7019 All underground pipe anchors for bell and spigot elbows and tees shsll he completed previous to testing, to avoid the possibility of I h n i n g out.

464


Piping Design

I .iOL'O Slroi, 7'catinq All Hanged, shop-iabrieated, carbon steel piping for foreign shipment shall he hydrostatically tested before shipment to trice the prrisnre corresponding to the 43.4 Hange rating of the piece being rested. All alloy or heat treated shop fabricated piping shall be tested in the same mannm whether for foreign or domestic use. Carbon steel pipe fabricatcd x~ithoutflanges will li,r sr~hjwtto ficld test only after errction, and thr shop t r d will br waived .ill shop tests shall hr p ~ r f o r m r din the preirnw of and be nitnessed by the purchaser's inspector or ilclrnated rcpresentatir-e.

1.5000 Pipe Specificatimis 1.8010 Specifiention >I Thii sperifieation dial1 :rppl\ to the follno-in: srrvicr~:

1.8016 Bolting Alloy steel holt studs, see 1.901. 1.601i Guskets Asbestos filled double-jacketed corrugated iron, except for Specs. .4 and SC sheet asbestos ring gaskets dlall bc wed. 1.80181 Gate Valves 1% in, and smallrr. 600 lb STTP forged carbon strrl screwd, in,
x6

ISOIS" Globe Vaives 1% in. :ml cmaller. 600 lb SWP forged carbon steel scren-cd, inside scrmv stem, union bonmt, 11-13% chrome stainless steel trim 1V3.1). Xote: For Sncc. .-\

2 in. and larger. 150 lb AS,

230 psi :xt 1 0 0 ~F I50 11.4 at 3 X ) ' F 100 Psi at 75OO k' (Mazirnnm) 1.8011 Pipe Seamless carbon steel, random lmgthi, P.E. for F ~ Z ~2 Sin, and hrlor, bevelled for welding 3 in. and above, conforming to ASThl Sper. -453 G r : ~ k-4, latcsl revision. 2 in. and smaller. Schrdnlc SO. (May he ASTM-A106 or -483 if -453 iunavailable.) 3 in. through 10 in. Schrdnle 40. IS012 Flatigrs in. raised face conforming Forged carbon steel, 150 lb AS$ rvrlding neck, to .4STM Sper. 8181, 1:itrst rrvision, Class I, 0.35% maximum carbon. sot^,: Uorr! of all weld neck flanges to br the smie as the I.D. of pipe vith \!-llirli nsrd

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1.8013 Fittings 1'/~ in. and smaller. Srrcrwd typr, 3000 lh CWP forged carbon stcd. 2 in. and larger. Butt~t-eldingtypc, seamless carbon .tee1 conforming to ASTM Spec. A231 and A106, lateut. revisions, Crrade -4. Inside ili;tnir~t~,rand x i l l thickness to he same as pipe with which nsrd. 2 in. and larger. Flanged t)-pr, 150 lh AS.% stanilanl cnst carbon strrl, :q6 in. raised face. Cast Steel Flanged Fittings. Do not ordinarily use. 1.8014 Unions and smaller. 2000 lh CTVP forged mrbon steel screwed, ground joint, integral steel seats. ? in. and larger. Use Hanges as apeciiied above.

1vi in.

.

IS015 Bushings and Plugs 1% in. and smaller. Steel hexagon bushings, and steel hexagon barstock plugs. Use reducers where rednetion is more t h m two sizes.

Xote: Use Gate Valves for sizes above 6 in. 1.80183 Check Valves 1% in, and maller. 600 lb STVP forged carbon steel scrcwed, horizontal, piston type, 11-13% chrome stainless steel trim (V19). Kotc: For Spec. -4 and SC, see 1.80383, 2 in. and larger. 150 lb .4Sh Standard cast carbon stecl, flanged, %G in. r a i d face, swing-type, 11-13% chrome stainless steel trim (V3). Xotr: For Spec. SC, see 1.S0383. 1.SOIS-I Plug Values

% in, Size. 2000 lb \TOG forged carhon steel, screwed, lubricated p111gu r h (T110). 1% in. :ind smaller. 300 lb WP cast c;trbon steel, screwd, wrench o p i ~ a t e d , lubricated plug cock (V58). 2 in. to 6 in. sizes. 150 ib ASA stnnd:lrd cnst carbon s t t d , H:~ngeil, % it]. raised face, wrench operated, hbricated plug cock (T54).

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1.SO"O Sprcification N l'hls spccificatim shall apply to services S, H A , H U , HC SOU lb pmcrss oil ard vapor, 2l.i lb stearn: Rating: 300 psi @ 100" F 3i5 usi (ii 500" F 300 psi 750" F 1.8021 Pipe Seanlless carbon steel, random lengths, P.E. for sizci 2 in. and below, bevelled for w41ling 3 in. and above, conforming to ASTI1 S p w :\lo0 Gr:dc. .A. 1xte.d I.~\.~.-LoI~.

1 i I : I l r S c l ~ t ~ l ~SO. dc 12 111. m d larger. ll.:ii3 i n Wall.

2 in. t o 4 in. Sizes. 300 lb .4SA standard cast carhon steel, flanged, m i 4 fare, rvrench oprrated, lubrirnted plug cock (T591

1.8022 Flanges Forged carbon steel, 300 lb ASA welding neck, $i6in. raised face, conforming to ASTM Spec. A181, latest revision. Class I, 0.33% maximum carbon, except for HC, use RTJ Flange Facing. Note: Rore of all d d neck flanges to be Fame as thc I.D. of pipe with which naed.

1.8025 Bushings and Plugs 1% in. and smnller. Srr 1.801.5. 1.8026 Bolting Alloy strcl 11olt stwls, c c 1.901.

2 in. and ~ n u ~ i l e rSame . RF nbor-e, except g:~lmnizrrl. :j in. and abo1-e. st iron, pipe, mcchamical joint in accordance ivith hS.L-:\ 21.6 or S, Class 2".

1.802i Gaskets .4sbestos Gllrd tormented iron, e r c c ~ tfor Spec. H C which shall be 90 Brinell Soft, carbon steel, octagonal, ring.

1.8032 Flariyes 150 11) AS.& standard forged carbon steel, l/lsin. wlding nrck, raised face, cxcept to be plain fare \T-hrreconnected to plain-faced cast iron ~ a l r r s fittings, , and eqnipment. Flanges shall conform to .4STM Spec. -4-181, 1ate.t revision, Class 1, 0.35% maximum carbon. For stet4 pipe only. S o t e : Rore of all veld neck Ranges to br same as the I.D. of pipe ~ i t hw11ii.h

1.8028 Valves 1.80281 Gate Vnlves 1% i n and smaller. 600 lh SWP forged carbon s t r d srrrrr.rd, i n 4 r m e w stmi, union bonnet, ll-l:i% chromr st:nnle>- steel trim (V3.3) 2 in. and larger. 3W lb AS:\ Standard Cast carlwn steel, flangnl, O.S.&Y., 11-13% chrome stainless stccl trim, % , in, misrd face (V4).

iwrd.

1.80331 Fittings. above grndc 1'4 in. and smaller. 30Cl 11, stamlurd mdleable iron, screwrtl. Galvmizrd f o r WS u p to 2 in. "11. :and larger. klr~ttweldlngtype re:rmless c:irbim strel, ci~nforniingto ASTAI S p r c A231 and AlOG, Iatwt revision, Grade -4, a t same 1.1).and thieknrss ;is pipe with which used. ? in. and larger. Flanged typr. Class 1% lb ASA standard Cast Iron.

1.8028'2 Globe Valves 1% in. and imnllrr. 600 lb S1T.P for& <.arbon strel i c r r ~ w dinsiclr screw stem, union bonnct, 11-13% chrume st;iinleii stwl trim (Y34). 2 in. and larger. 300 lh AS4 Stnnilnnl c a d cnrbon steel, flanged, O.S.&l-., $is in. raised face, 11-13% chrourr stainless steel trim (V5). S o t e : Use gate valves for sizes above 6 in.

1.80281 1'1~0 l:al~,es (V110). 1?L2 in. and smal1t.r. :300 lb 1T.P cast cnrbon stcel, s c r e w d , w e n c h operated irtbrmtrd plug cock ( V S )

in.

1.80311 Pipe Above Grnde Seamless rnrbon steel, random length^: P.E. fnr sizes 2 in. and hrlorv, berrllrd for wdding 3 in. and above, ronforniing tu .4WM Sprc. -453, Gmde :\, I;itr-t revision, fur a h o w grad^ 11% only. For 15-S wr .4STM .I-l.'O g;ilranirrd. 2 i n am1 smaller. Srhrill~le80, except for 1T.S which may b<. Schedule 40. 3 in. thnl 10 in. Schcdde 40. 12 in. thru 20 in. Or375 in. d l pipe. 24 in. and above. 0.250 in. wnll, eramleas or meld.

1.8024 linions 1% in. and smaller. 2000 lb CKF' f o r p d rxrhon steel screrred, see 1.8014. 2 in, and larger. Use flangri :id qiecificd above.

% in. Siap 2000 lb \TO(:, forged carbon strrl, z c r ~ w d Inbrimted , plug rock

1/16

Rating: 125 psi (3 150" F Note: All pipe and fittings for \VS service shall be galuniaed.

1.8023 Fittings 1% in. and smaller. Scre\ved typr, see 1.8013. 2 in. and I n r ~ r r . Ruttiidding type, Cer 1.8013. Note: Cast Steel Flanged Fittings: do not ordinarily use.

1.80283 Checli Valzws 1% in. and smaller. 600 lh SWP forged carbon stwl wrrrr-eri, horizontal, piston typr, 11-13% chrome stninlws steel trim iT.19) ? in. and larger, 900 lb. 4SA Std. rnst rarimn itrrl, Himged, N6 in. raisrd iacr, swing-type, 11-13% rhrome stainlrzs rtrrl trim (V61.

467

Piping Design


466

-

1 !

1.80332 Fittings to size required, below grndu Class 150 mrchanical joint fittings having the same laying dimcnsions as AS:! Class 125 standard flanged fittings. 1.8034 Unions 1% in. and smaller. 300 lb standard malleablr iron, screwed, ground joint, brass to iron seat. 2 in. and larger. Use flanges as specified above, or merhanicnl joints. On raqt iron pipe in acrordnnce r~-it11AS.4 A 21.11. 1.8035 Bzrshixga and Plugs Hrmgon steel bushings and hesagon steel plugs. Usr reducers where r e d u r t i o ~ ~

469


Piping Design

is mnrr than tn-n ;iaei. ?;OI(,:.ill cl~angeifrom m-t. iron to stwl ,.llnll be r(Fvrtr,cl by a fl:inped cast iron it11b piece eonnertrd to a mechanical joint.

3i n .I . a n r F :I . I I A t a n l r l s t iron r o t a : Ule either xrerl-ed or flanged as required. Note: The us? of cast iron Hanged fittings shall be kept to a minimnm.

468

I8036 Bolting Stsndard carhon stcrl square hmd machine bolts with semi-finished steel nuts for steel piping. Bolting shall be supplied rr-ith cast iron piping in accordance with AS.4 A21-11. I S 0 3 Gnshcts

x6 in. thick crmpressed n~hestos. For raised-facrd joints.

Use ring gasketfor raised-faced joints and inll face :;iikets ior phin-faced ioints. Plain composition robber gaskets shall be supplied x i t h ca-t iron pipc. 1.8038 Valves 1.50381 Gate l'olvea 1% in. and i'tnallrr. 1% ih SWP b r a s , screwed, rising -tern, inside scrcw (V47). ? in. and larger. 125 lb hS.i stnncl:~rtle:w iron, Hanged, O.S.&T., bmss trim; and s t n u (w6). 2 in. and larger. 125 lh 45.4 stand:~rilcast iron, flanged, 0.S.R-1'. (fire service donble-di-b, nonrising i t r m , bm*.~trim, m y 1 ( V I l T ) . l.S03S'! Glohe T'alws 1% in. and smaller. 250 S W P hrars, acrewed, rising iteln, m i o n bonnet (V51). 2 in. and Ltrgcr, Use gate valves. 1.80383 Check Valves 1 in. 2nd imallcr. 250 lh S W P br:w s r n w r d , horizont:ll piston type, XiAlloy sent. :ml disk (Y101) 2 in, and lnrgcr. 125 lb -1S.4 standard cast iron, flangrd, sning type, Imss trim (V25) I SO384 Fire Hl/drants Two hnsr conneetir~n,p h n t type hyilrontq ( V F ) .

1.8044 i n i o m 2 in. 1 . : I . 2W0 ib CWP forged carbon steel scre~red,ground, joint, intrgral stcel seats. R in. and hrger. Flanges :ire perrnivihlr ns sprrifird obove. 1.804.i Bi~shinysmid Plirgs in. and :mailer. Steel llr~sagonhiwliin:~, and steel 11ez:t~onIx~rstorkpin:?. Use reducers xhere reductim is more th:~n trr-o size;. 1.8046 Bolting. Carbon steel m:ichinr, hrilt.2. 1.8047 Gos1:ets.

-pi.

1.901.

?Il6 in. ron~prrswila s b r s t o ~gasket.

1.SO46 I'al13es. See 1.80:38 for f i l w Specific:ltinns. 1.8050 Specification Z This specification bhilll apply to instn~rn?iltscr\-icrs only: Instrnnlent Srrrices Rating, see Linl Scrrii.cs. 1.8051 Pipe Instrummt 1e:rrl linrs, or line? rv11ich carry f l o i d ~to and from inqtrnmrnt elements shall be the s:lrnc spr,cific:ition or l,ctlrr, than the line wrriic? fro111KII~I,II instrunlent line originntes. Srhcdnlr 160 uipplrs J u l l hr used up t o first blork valve where any danger of physic;d dam:ige to pillin: is possible. Extensive i.trnrtr~r:d support runs of small sized lines shall hr avoidcd, lalt n . 1 wi.rss:in~ ~ nlr~stbe provided. Instrument 1,iping of p r o r v s fluids meceding 25 f t most be authorized prior to installation. 1.805? T~tbing Copper t ~ h i n gih:ill he nsed for air tral~smisiion lines. .ill tribing ?hall be in. O D . 0.0X'' Kall ASTM, B68, nonar~rnirnlrokl dr:t\m, v;rcmm annealed. 1SO53 Fittings F1:irrd-type fittings shall be i~srilfor :ill cr1ppt.r tubin: lines.

1.8041 Pipe S e ; i n h s cnrbon steel conforming to :\STY1 S p c r -153, C,r:idr A, lateat reriaion, galvanizrd. .4STM-AX3 nrrcpt;lhle for 2 in. :ind .smaller. ? in. and smnller. Schedule SO. 3 in. thru 10 in. Schedule 40. 1.SO42 Flm~yes Cast iron, 125 ib -45.4 scremed, flat face, galvanized. 1.SO42 Fittings 2 in, and smaller. Srrer~edtypr. 300 lb standard malleable iron, galvanized screwed,

1.6054 Values Vidving n s r d in instrnment lead piping i11:dl be of the samc specification as the origin at in^ line specification.

1.9010 Alloy Steel Bolting Alloy steel bolting shall be provided for serriccs S, 8 , H.4, HB and HC and shnll confornl to ASThI-.41'33, Grade B7, CI:w i fit for bolt, Clnes 2B fit ior niltr, ~71thtwo (2) henry series hexagonal nut? each. S u t s shall conform to . S T 5 1 Spec. -4194, latest revision, Class 2H, oil qiwnched, hot forged. .411 other bolting shall conform t o ASTWA307 with Claw 2A fit for bolts and 213 fit for nuts, excepting bolting fumishrd by pipe vendor for 11' services, which shall meet M i - . V ' l . l l requirements.

470

Project Engineering of P r x e s s Plarls

1.9020 Clenmnp a ~ t dp a b ~ t l w 19021 After erection all lines shall b s cleaned ~ n t e r n a l l rby cirndation

Piping Design tr;

remore :ill dirt and o t h w iorwgn matter bpforr thr, plmM h ~ , e l i loperntion ~ C u r sh:ill lw taken t o t h o r o u p h l ~ clran :ilr hne.. t<, i r ; ~ c t ~ ~ a tdiaphragm eil control V ~ I . C S , hefore they are connmted, and niter ronnectlon up t o last fittine; before initniment o r valve. 1 9 0 2 :ill underground (buried) shop fabricated stecl pipe 3 ni. thru 10 ir. siae shhll have e o a t i ~ gon the outside only and v r a p p i n g applied xs follows: a. Clean by sandblasting. h .4pply one coat of bitu~nasticprimer. c. Apply first coat of bituniastic enamel. (1. Apply second coat of bitumastic rnar~iel e . Spirally xmsp one layer of 1.5 lb asbestos felt f . Spirally wrap on? la:-rr of 60 111 Krnft pnjler.

19023 ,411 underground ( h r i e t l ) steel pip<, sh;i11 have ~ n s i d eand outside c l ~ u n n iand wmpping applird o i follo\~s: Slic~cificatiosisInside (for 12 in. a i d a h o w ) n. Clean by sandbl;isting. b. Apply one coat biturnastic p n m e r . c Apply one heavy coat hitumnstic enamrl. 'ip~cificntsonsfor coating a n d wrapping uutside cjf pipr: sh:~ll he same as inr :ii n , thru I 0 in. siae as specified abo\-r, 1W22. 19030 Ftreproofing Pipe s u p p o r u carrying main steam hesdcrs o r hydrocarbons through arras subject t o fire hazards shall he fireproofed t o the point of t h e cross load beaxmy niembers. or as noted on drawings.

19040 Steam Traps Invertrd htirket-type stram traps shall be provided f a r nll srrvices e r c e l ~ i , t h w t ~llnnilling small rl,~antitiwof ~ t m mfur ir-lli?ll w i e ilnpulsr i\-jlr t m p s nlay be u a d All l u c k e t type traps s11;11I li:i\-r ir,rnrd o r exst i t r d hudies with :illuwablr~ working p r e s u r r of 600 psi m n i n n u u All other traps shnll be steel :uid h31.r sen.icc ruting a t least t x o times line pressure.

REFERENCES K o ~ P Cerbain , mnnufneturers catalogs have been included as references to de~cript r e information. The omission of othcr manufacturers' prmted information should not. he ronstrurd as a judgment ngmnst it. It would he impasabk I 0 inrludr .I complete hst of the many excellent ratahgs available. 1. American Gas .ksoriation, 420 Lexington Are., Xcw YorG. N . Y . Standanir 2. American Petroleum Institute, Standards on Pipe, Flanges and Valves i A P I d d . B, F, G-1. G-2, G-3, and L, API 600 A and If). American Petroleum Institute. D ~ n s i o nof Prorlnction, 1205 Continental Bldg, Dallas 1. Texas 3. Amwiran Society of Merhanical Engineers, 29 K e s t 39th SL.,Kew Ynrk 18. ?J Y. 4. Amernan Standards Bssociat~mspecification, Bmerican Standards Assmatmc. 70 East 49th St., i Y ~ wBork 17, h ' Y (A majority of the standards listpd below aro nppror.ed by the A S 1 and published hy the ASME I < a ) A21.1-1935 Compntntiau of srreogtk nod tbtcknesi cf Cmt-Iron PIFP. M a m d for

471

( b ) .121.61953 Cast-Iron Pipe Centrifugally Cast in Metal Molds for Water or other Liquids. (el A21.8-1953 Cast Iron Pipe--Centrifugally Cast in Sand-Lined Molds for Kater or other Liquids. id) .421.10--19.52 Sho1.t-Bodr. Cast-Iran Fittings. 3" to 12". ( c ) .A21.11-11153 illrr,hanieal Joint for Cast 11.on Prersurr Pipe and Fittings, Sperifirttion for. ( f ) B16b-1044 Class 250 Cast-Iron Flangfs and Flangcd Fittings. ig) B16.1-1948 Class 125 Cast-Icon Flanges and Flanged Fittings. ( h ) B16.3-1951 Malleable-Iron Scmred Fittings, I50 lh. (i) R16.4-1949 Csst-Iron Srrpacrl Fittings. 125 and 250 lh. i j ) R16.&1953 51ccl Pipe Flangcs and Flnugrd Fittings. ( k ) B16.+1951 Stwl Butt-llblding Fittings. ( 1 ) B 1 6 l G 1 9 3 9 Fnrc to Fnce Dimension of F c ~ o u sFlanged and WeldingEnd Valves. ( r BlG.11-196 Steel Snekel-Welding Fittings. ( n ) B16.1S1847 B i n s or Bronze S<:rencdFittings, 125 lb. (0)B16.17-1949 Brass at. I3ronsc Scrpwrri Fittings. 250 lb. ( p ) I316 19-1951 M a I l ~ a t , l ~ - I ~ .Sc~e~r.ed on Filting*, 300 lh. ( q ) B16.20--1952 Hing-Juint Gnskctr and Ct.oovus for Steel Pipe Flanges. ( 7 ) B16.21-1951 Xonmr.l;illir ( : a r k ~ t sfor Pipe Flangvs. [.*I 831.1-1951 Code for Prcsaore Piping, including s u p p l r n ~ m t ,U31.L-I855 arid B31.1.8--1'352. ( t ) B36.1 to 36.26 ASTM Iron and Stecl Plpe S1wr.ifiwtions neceptpd as American S1und;rrds. 5. .American \Tatel. TTorks .Assori;~tion,521 5th .ire.. S e w Yolk. K. 1.. Standards. 6. Clinrdinst, IT. 0 , Oil a n d G u s J u w n n l , $3, S o . 4. 79 (1945). 7. Cmnr Company Cat:zlog Y o . 53, Cranp Comlmny, Chicago 5, Illinois. 8. C r m c Company T ~ c h n i r a l Papcr No. 409, Crenr Comp;my, Chiwgo 5, Illinois. Piping Iin,iribr,ok, 4th E d , H m . . MeC~~.n~v-Hill Rook Co.. S e w 9. C I O C ~ PSabin, T. Yak 1955. 10. f i ; ~ i i i r d c u lr r i l w s , f : g o i \ . t h ~ tV:il\rs Co.. 115 \Trsf 7th St.. Los Angelrs 14, Califomin 11. F d e r ; d Sprcificntiuns, Snp't. of l)ocunrrnli, K;isl~ingtun25, D.C. 8 , 130 (1949). 12. Juffe, J., C l z e m Eng., 6fi. SCI. 13. l m l l s i ~Cwtalug KO.55. I.ntliri~Co., Cwlahy, Kismnain. 14. I,uBmheimer, Circular KO.552, 553, 555. 1.uhenhrirnm V ; k r Ca.. Cinrinn;iti 14, Ohio. 1 5 Manufactwr~.'FStandurdizatim Soriety of thr Vnlvc nnd Fitting Industry, 420 Lexington Are., S c w Yolk 17, S . B . 16, Moody, I,. F., Trri,ii. A m . Slit. M c c i i . Eiigi?... Uli. 671 (1944). 17. Sor.dstt.onr Valve Ctitalag S o . 10. Sot.dstl.orn Ttilrr D i v i s i m Rockwell Mannfarluring Company, 400 Lexington Avp., Pittrhul.gh 8. P i t . 18. Piping Engirir~rirtg,Tulhr Turn-; R ~ s e a r hStaff. Tuhr Twna. Inc.. Imiisr-illc 1, Kcntncky (1847-53). S~1.ir.siis f o l l o ~ ~ : 1.01 Codw :and SperiIikations, Snwres of Piping Drcign Info~~rniiliun. 2.01 Pipe h1;ttwinlx tmd Tllivknesses, Pip? hlntesials and tlrpir .Allonable Stresses.

3.01 l4'luiil Fluw Fluid flu^ in Pipe. 4.01 Kr]vmsiun i ~ n dI'lrrih~ltty. Intrudrwlion to thr Piping Flexibility Prohkm. 4.02 Expansion 31111 Flexibility. Z, L, U , and Expansmn li hcnds.

472


5.01 \ I ~ l r I ~.ruinti, d Joint Prcpnration for Ruttwlding. 502 Welded Joints, Wclding Rings. 6.01 Mechanical Joints. Standard Steel Pipe E'l;ingei. 6.02 bloehanicnl Jomti. Ratings of 1meric:in Stanilnl.ri Steel Pipe Flanges. 19. P o ~ t t m s n n .F. H.. J . Peti-olermi T e d . , 5, 317 (1951). 20. P o ~ ~ e Talrc ll Catalog. Powpll Vak-e Co.. K m . Po\\-ell Co., Cineinnab 22, Ohio. 21. Rase. H. F.. P~.ti.iilciit,iI
CHAPTER

19

THERMAL INSULATION

Iient,,rl.\. ~-~~~ ...... .

30. Vogrin, C. M., Frank C. G . Williams, and Julm S. Worth, . Z l ~ d e m S t d Ilnlli,~g for Piping nnd Pressure Vessels ASME Paper 52-PET-7, 7th Annual Mcctin& liansns City, Xlo. (Septcmhrr 22-24. 1952). 31. 1Volwor.lh Catalog So. 52, Walworth Company, 60 E . 42nd St., New York 17, s.Y.

Thernial insulation, propcrly applied, aswrcs effective operation of process eqniprnent and conserves valuable heat. There is always a vide ~ n r i e t yof insulating materials for a given situation and careful consideration niust he giwn to each type so that an intelligent dccision may bc ~narle. I t is not possible to rlescrihe e r w y typc of in;rilnting material. but several of tlie more frequently used typcs for process plants ~villbc clcscribed. INSULATION MATERIALS

Insulation materials can he classified into lour types: (1) fibrous (2) granular, (3) cellul;~r,and (4) reflective. I n a practical sense, sucli classifications, ho\vercr. often liare limited m l u r sinre sonle romnicrcial products consist of a enrubination of several of thwe insulating materials. Asbestos

Asbestos is a natural-occurring mineral of tlie composition 31\Zg0. 2SiO2.2H,O, a hydrated magnesium silicate. It is rock-like in its natural state but can he crushed and changed into soft, silky fibcrs. I n this state it has a texture of ~ o o and l has, thcrcfore, amazed people d o a n tl~rougli the agcs, since it does not support combustion. .Me.stos is used in many forms t o manufacture insulating matwials, rither hy itself or in combination with otlier substances. By the addition of binders it can be fashioned 473

474


into paper-like structures, either single flat layers ~ ~ i tthin l i air spares het~veenlayers, or as corrugated nshestos paper built up into lnyers. T h r relatively dead air q,aces $ewe tu decrease the cunrlucti~-ityof the finisbcd insulation. These nibcstr~spaper insulations arc efi'rctive Up t o aruurrd 300" F'; almve t h i ~temperaturt~the hiniiing n~aterialdecolu~~oses. Asbestos can be given ;I felt-like structure t ~ ycou~hininpit ~l-itlismall uarticles of some spongy, cellular material. This fclted ashcstos resists vibration and witlistandr rough handling and temperatures up to al.uunil 900" F. .ksbestns fibers are used t o strengthen higll-ten~peraturediatomaceous earth insulation and 8570 magncsia insulation. Diatomaceous Earth

Diato~naccousearth is an unusual form of silica, having a high mclting point. 2930" F , and unique properties. It is composed of minute silica skeletons of diatoms, which were microscopic plants t h a t lived millions of years ago. Large deposits occur in Califnrnia. A mixture of ashedos and diatu~naccousearth forms an escellcnt high-teml~eraturcinsulation 1600 t o 1900°F) and is mannfactured under various trade nanies. Eighty-five Per Cent Magnesia

For tcrnpcraturcs up t o aruund 600°F 85% magnesia insulation is perhaps the most popular insulating nraterial. I t is composed of 85%, magnesia and 15% asbestos. The asbestos fiber provides the reinforcing qualities necessary t o permit niolding and manufacture of pipe sections and other shapes. The so-called magnesia constituent is actually a magnesium carbonate produced from dolomitic linxstonc hy the action of carbon dioxide on slate dulomite. V7hen properly instslled, 85% magnesia maintains its excellent insulating properties for many years and is thus an economical material. It has the disadvantage of not being able to support any appreciable load. Eighty-five per cent n~agnesiainsulation is often used in combination with diatomaccuus earth insulation. h layer of diatomaceous earth insulation is placed adjacent to the hot body and is of sufficient thickness to produce a surface temperature of 600" F on its outside surface. The diatomaceous earth insulation is then covered by a layer of 85% magnesia, which has a lower thermal conductivity value and can be used in the lower temperature range below 600" F. Eighty-five per cent magnesia makes an effective insulation mat,erial because 9076 of its total \.olume is dead air space the conductivity of which is low.

Thermal lnsulotion

475

molded into hloikq by adding suitable binding ulatcrials. When a watcrproding hinder is used, an effective lov-temperature insulation can be proilueed, n-l~icliis highly moistlire-resistiir~tand rot-proof. I n this fom, it is generally called rnincral or rock cork. IIineral wool is also used for insulating hon~esand buildings. Vegetable Cork

Saturn1 eurk contains r n m y thousands of ~ c a l r ddenil-air spares. I t is light. yet strong: it ilws not aiworll vapors nor is it adversely afTectecl hy r~wtting. These propertics inake curk good for luv-temperature insulation. Expanded Polystyrene

Styrene: polymerized and molded to occlude many bubbles of air, forms a light and serviceable low-te~npcratureinsulation. It has replaced cork in illany applications. Glass Insulation

The 1mv tthrmial conductivity, nonconibustil~ility and inertness of glass are desirable fcaturrs for insulatim. Ilolten glass can he spun into fihers siriiilar to that of mineral ~\-ouland these fihers fashioned into blankets, molded pipe covering or blocks. Glass fiber insulation is normally good up to 600°F, althongh sorne special designs withstand 1000°F. Since glass cannot abrorl~v a t e r , glass fibers mol~ledinto bi~anlsserve as low-teniperature insulation v h c n p r i ~ v i r l ~xdi t h a suitable ~ ~ a r n i - s i d e v a p r seal (see helun.). Cellular glass i~rsulatingmatcrial is made of thousands of glass buhbles molded into a rigid structure of extremely light xeight. This cellular glass material ia suitable for temperatures from - 350 to f 800' F. I t is available in hlocks and in shapes for pipe coverings. Although not a glass, another insulating ~naterialis made of materials very similar t o glass, called hydruus calciuni silicate. This inaterinl is effective up to 1200°F and is ~noistureresistant. JTbm hlendrrl ~ v i t l ~ small a~nouritsof asbestos fiher, its strength is increased Thomas and Turner" have prepared a table giving the rharactcriatics of the a h i ~ r einsulating nlaterials and certain others of coninwrrial importance. This summary, reproduced in Table 19.1, is notable in its ubjectirity. l'hc use of trade nanies has been avoided. Reflective Insulation

Mineral Wool

Mincral wool is manufactured by blowing niolten silica minerals into threads. These t h r e d s can he fashioned into insulating blankets or

Heat is transferred across an air space prodnced hy two solid bodies by rncans of radiation: conrrction, and conduction. I f the width of the air space is properly chosen and the temperature drop across the air space

TABLE 19-1.

\laieriab General formr Hi~'dand.sr,"!-n,gitl~ h$llrrtus tilk I ' r w ~ r dillto p i r r i l l I,XL tnfrndrrd~ ~ l ~ t i o , I,~ I lsuperl

Diatmmous earth

Strcngth

%me to wafer

GCIIXILU ~IAI

Rmrtancc to vapor

Com~mitioo

and arcel- Errellmt i h t tensile r t r ~ w t h

Fair

Long amoslte fibers blended r i t h binderr

Prwrsed lrlto ppeinsulrtion and bluch

( h o d corwrornue and fimurd n ~ c n g t hIim ; lt"d te..,$ rtrungih

Yodeiafe

L m g ammite fibers Irlmdrd r l t h binders and dlatolnarrou~rart1i

\Inldcd and lurnled ~i," ,sr"latlo,,, srgmmts and blocks

(:od c o i n ~ m s w e Fair ~ t r m g t h limited ; nc7uralandte~~rilestc~ngth

cud eomprerrire and

Good eornpmsn~e Fnir strength: limited flexural and temilestren~th

Moderate

84% h p d r s t ~ d m a w * arum esrbonate

Moderatooompessive and tensib strength

Moderate

llincral swl fibers with asphslt hindea

Mudemlo

hlincral r w l fiben ianded

fipmral strength: lirnitcd trnsile straneth

65%

blolded and formed pipe inrulrtion, $8.. ments and blocks Formed piir

insubtion

~

w

hlud~rato I)irtomar?ous rarth hlcndrd a l t h long a.br tor fihorr

Hydrous calcium sibmte hlended with long aabestos fibers

>loldrd iornlrd "i,,~ insulation, seemmts and blorkr

snd block

iair

Moderate

Hydrow rllriuln ailirate

hlinrral cork for law temp.

d

Good

hlineral r o d lor low temp.

&&rinid blanket, ate. Moderato c u n ~ r e ~ s i u e Pair form"d lllt" pipe isanand tcllsil~strenqlh Intion, block m d l a g ~ i r w

hlineral wool (or hirhtemp.

b l ~ l d c dinto blocks u,d lagging

Polmsrane icxpandedi

B i d m d nine iusula- bloderate compressive strength: fair tmsilr tim rtrength

EIEIIIC~~~

~xcellent Polyatjrene w t h air eella

Vegctahlc cork

\folded pipp insulation. compres.iblo under blocks. lrgglng and titlight load, but dops sunport heavy loads tin$ rovers

~vod

Pair

(iranulalcd vegetable cork honded with natural pork rosin

Axbritar

Dlanketr

Fair com,xeaive stren~th

Fair

Pnor

.4abedm fiber m4osed hgarhostra cloth

Glass fiberr

Fsltodglass fibcr blan. kc1 with v r r i o u ~type8 oi lacings

%it, fiexiblo: litflp

Good

Moderate

Felted dssr fibers fabri cated with metal nmsh or 0 t h facing ~ ~

~ i ~ i t ~eod~ ~ p r e s s i v e E x r ~ l l r o t )iloderate and tensile strength: lair naxurai strength

Mineral WMI Hlr,,keta T r i l l , uariou, t y y s of lacing5 Falted inta blanket roll

ipresrre reiataoce alter

application

Hrmiler a d usrd as ininer luwc undm 85% magnesia -here operrfiur trmyrrst i i r ~r x r r d i 5idOF.

Sot ruitablr for I d s i n g under h m r y load: rwsflcrible

i.irhtrn.ht, rpri~ipni. nlld Ai\ll>lr

.%R will not rrdrt lll~rhanirnlahus"

Ihsil? shaped m d fitted: do?%,,Ofi1~pe.d on vawr barrier lor ik rnpor resistanre: inromhustihle. Bigh ie,,l,,cTatUI* li,i,it(

Should boprotrctedagainst ahranion. Dr.lgn I",rx"as&,, and contraction

Hiqh shrarine r~risfsner: high con,pressirr rtrenqth

Sot suitalh lor bridginq under heary lord; nonHnible

212

1900

32

4in

-PW

RW

056

ll5Y

002

n?i to l , 1" 11 95

70 i 3 W

0.42

O5:l

0 4 W 0.450 0.510

! d i ~ ~ e rfibers al hlended r i t h binden

Blonldr

Fell Uairfelt

TABLE 19- 1 (continued )

Characteristics of Thermal Insulation Materials* Rcri~t-

I

Thermal lnsulation


476

F u r compreseive strength

Fair

Pvor

Feltpd minerd am1

Standard denritp. very swngY: heavy deority, very fim

Little rasistsoee

Little re3i3tSiance

1W%

cattle hair

11~lonvuticwithout dsrnr~o Each installrtion must DP curton, d
IN

950

40

1000

0.50

0.65

0.35

0.45

0.26

erateimpaet; fikre respond to ,ownled rorn1,roseio~ IVilhstands erpanmon sad contraction

Soft

Excellent e n ~ e i ~ e n cl ov r

Requirw r r i c h l vawr

50 1ZW

Belm

2W

0.25

0.260

480


2. C'li~micnlproprrties a. annl!-sii. b. corrr~sirenntore. c. cfect of chemic:rlr in pipe or yesel being considered, 3. In-tallation chnrncteristies a . toxicity. b. action on akin (does it ~cmtch,etc.).

c. orer:dI n-or!ability (cutting, xhaping, ete.). INSULATION INQUIRIES AND QUOTATIONS

Tlie crcctim uf insulation is usually subcontracted to a, fir111specializing in such ~ v o r k . T h e subcontractor luust bc clloscn carly in tllc dc\-clol~mcnt of the prllject FO tdiat his plans m:1y bc dcvclol~ctlin eunjllnctiou wit11 the priuie contractor. At the tinic t h a t inquiries ar? made to tlic inrulntiou contractor the actual detailcd design of the process plant has not been developed. ITsually only tlic engineering f l o ~diagram, a plot plan, and perlial~ssereral prcliminary elcvation studies have been made. It is necessary, thercfore; t h a t the insulation contmcti~rhe supplicd 75-ith a very complcte description of the insdation requirenients on d ~ i c l rlie is to quote. Because of tlir limited amount of drawings available a t tlic time of inquiry, close cuoperat,ion betneen the insulating contractor and prime contractor is essential. An insulation inquiry should include a dcacription of the work with reference t o appropriate drawings. Complete insulation sperifications must a l w be furnished. These shuuld include not only tlrc insulation t o be used, but also thc n~ethodsof insulation perfcrred. A cleal. description of cost figures desired should be given so t h a t all q u ~ t a t i o n scan be fairly judged. A complete list of all lines t o bc insulated should be included mith the inquiry. This list sliould s h o ~ vtlre operating temperatures so t h a t the proper insulation thickness, based on thc specifications, can he selected. All otlrcr cquipmcnt, such as vesscls and exchangers, must be adequately de-rribed, or suitable drawings furnisllcd so t h a t quantity and type id insulation m a y bc selected. Portions of vessels which arc not to bc ink l clcarly indicatrd. snlatecl. sucll RF skirts and ~nanholecovers, s h ~ ~ u be In addition to l u m ~YUUI ~ prices, unit prices' should be requested fur all sizes of pipe. fittings, valves, and vessels anticipated. Close cooperation \r-it11 the vendor will uiaterially reducc the anlount of w ~ r kinv<~lveilin such :L ~ ~ r o c r ( l u r cT. h e 111lit prires for vesrcl* should be given in priw * L ( e w o s r of the incomplete derclopmmt 01 tlrc plant desigu at tire time of inquiry it is necessary to pcrlnit t h c insulation runtractor to apply for additional fees ii it is agreed by both pmtics llmt thc scope "1 thr project has cllangrd dwing llie h i g u , l r i v l o l ~ ~ ~ ~ a The n t . . nmit prices tire: oi o s ~in rvali~olingt l w :idd~liwal costa incuwed.

Thermal insulat'mn

I

48 1

per sq ft of sliell arcn :mil lirad m a . I f ciic11 v d o r quotes on tlre .-alnc hasis, the lump-sum prices can then be used with impunity in determining the lowest hid. ERECTION OF INSULATION

Tkspitr thc wide ~-:wit,tyof i n d a l i r ~ it g~ r r s , most ins111:rtion is manufactured in one or 1rrol.r of tllree i'or~us;i.e!., blocks, blank&, or inolded sectional pipe coverings. The ~iretliod*of installing these t h e e forms of insulation arc siniilar, reg:irdless of the kind of insulation heing employed 'T\\-o general rules apply tn all insulation erection. One is that surfares sl~ouldbe cleaned th(~rongtrlyhcforr insulating begins. Thc, ot11t.r i~ tlrnt, if i~lsulationis installed in rc,veral layers. ;ill joints sliould 1,s stiiggcrr(l. Tlie staggering of t'he joints minimizes the possibility of heat Fig. 9 leakage a t the joints.

Golvonized Lacing Wire Fastened Between

P l a t e Clips Spaced

at 2'-0" on Centers

Vessel H e o d

(ToD)

Galvanized Steel Bands Block insulation

9; Layer of

Finishing

C e m e n t Mixed W i t h Fimshlng

Cement

Portland Cement

Vessel Heod ( B o t t o m )

2'' Thick Gunite ( 1 Port

Sand

I

Cement 81 3 Paris

Fig. 19-1. Typical vcssrl insulation. Block and Blanket Insulation

Insulation furnished in thc form of blocks is extensirely used on vessels. h a t exchangers, and other similar equipment (Fig. 19-13. One-half i n by 0.020 in. galvanized bands are used fur securing insulation on towcrr, and heat exchangers. Insulation is held on the top and bottom heads with bands which are secured to studs or nuts welded t o the heads. T o aid in the support of the blocks, steel angles are welded around vertical vessels and spaced a t 8- or 12-ft centers. These supports are onclialf in. Icss than the thickness of the insulation. By terminating the

482


block a t both en& of tile angle and filling the space with loose mineral ~vool,an expansion joint is faihirmed (Fig. 19.2~. The r x p a n s i ~ ~joint n is corrred 1vit11 20-gage galvanizeil iron or I ~ a n l 1v:irc rlotll an11IIICSI~ wire and then finisl~edweather-tight n-it11 insul;~ting cement. Aiter the blucks hare been wired in place, wire 111esh (I-in.) is Outslde of Vessel Shell lnsulat8ng Black

Thermal Insulation

483

pasted on the pipe covering. Outdoor insulation is covered with a weather-proof jacket such as roofing paper or galvanized steel or aluminum sheeting. Valrcs and fittings are insulated \\.it11 segments of blocks or p ~ p cinsulation of the same imterial used on the straight runs of pipe. These segments are wired in place and finished n i t h a coating of insulating Steel Bcnds

Diatomaceous Eorth

Support Angle Hordwore Cloth ( 8"Wjdth)

Loose Mlnerol Wool FIII (I' Width) Note Staggerlnq

k

lnsulotlog Block Weatherproofing Plastic

Fig. 19-2. Typieal expansion joint ior block insulation. Aber Cornpmy.)

(Adapted by permission

stretched tightly around the entire vessel and laced in place. Over this wire mcsh several layers of insulating plastic (finishing cement) are applied, which is a combination of mineral wool pellets, asbestos fihers, clays, and corrosion-inhibiting materials. For outdoor installations another lnyer of 1-in, mes11 is laced in place and followcd by a final conting of weather-proofing plastic which consists of a special aspiialt emulsion. .411 openings through the insulation are made ~ ~ e a t l ~ c r - t i g h t by use of a flashing cement (e.g., fibrated cut-back asphalt). Hlanket insulation is installed in n si~nilarmanner, vxccpt, tlmt wire instcad of galvanized bands ran be used t o secure the blankets in place. Insulating plastic is applied directly over the blanket area, followed by 1-in. wire mesl~to which is applied weather-proofing 1)la~tic. Pipe Insulation

( I n Fig. 19-3 note staggering of joints.) Molded pipe insulation is fitted t o the pipe and secured by loops of wire or bands on approximately 12-in. maximunl centers. This wire should resist corrosion or high temperatures expected in the area. Irregularities which produce gaps 'here the joints butt together are filled with insulating plastic or finishing plastic. Indoor piping is finished with 6-ounce canvas jacket, which is

Fig. 19-3. Multiple-layer sectional pipe insulabion

plastic. Fittings smaller than 3 in. arc nsually insulated n i t h plastic followed by a coating of hard-finish asbestos cement. I t has been found most eronomical to omit inaul;ition of flsngcs on all but stram lines. It is so often necessary in process plants to remove sections of linee for inspection ar rcpair that it is less costly t o merely omit the insulation around flange.;. and thus avoid destroying the entire section of insulation a-hen pipe is removed. Low Temperature Insulation

The principal differencc in the erection of lowtemperature insulation is that some means of preventing water vapor iron1 entering the insulation most be devised. Sincc thc inner suriaee of the insulation is a t a lower ten~pcrnturethan the outer surface, the water vapor pressure a t the inner surface is lolwr than that a t the outer surface and thc flow of water vapor is tolVard the inside, where it freezes and causes a marked increase in thc condnotivity oi the inrulation and also caust,s its deterioration. A vapnr barrier can he installed t o utinimizc this movement of water vapor. hlatrrials which serve as vapor barriers include rapor-proofing felt. which is finished with a fibratcd asphalt sealing compound fdlor~-edby a weather-prooi jacket. Another successful vapor barrier consists of sheet aluminum fuil Imninattd betu-cen layers of Kraft paper and finished wit11 a special vapor-seal adhesive. Cork insulation is often finished with s ~ v e r a lcoats of asphalt follolved by roofing paper \vhirh is applied with additii~nalanlunnts of hot asphalt. A final laycr of w-eatl~rr-proofing cement reinforced with wire mesh is then applied over the paper.

404


T h e foregoing represents only a w r y general and brief description of insulating techniques. Insulating manufacturers and erectors put~lish cictailerl qjccifirationz ;md initructions for tile instailation of their products. These instructions a r e readily obtainable and sl~ould.of course, t E fdIo,\-ecl. REFRACTORIES

-4temperature of 1900"F is the t l ~ n s i ~ n u t nh a t a n y of tlrr insulating materials discussrd c;ln n.itl~stand. h b u v c this tempcraturc it is ncce-sary to employ r c f r a r t o ~ yniateri:ils, usunlly cast in t l ~ rform of 1)rirk.q: to c m t a i n the heat in furnaces, reactors, a n d other similar equip~ncnt. T l ~ rchoice of t h e m i a t economical refractory depcnds on a number of factors otlicr t l u n lirirc. Tlieac includc t h e pbyaic;il and chenlir.al prrycrtios listed l~elon.. Fortunately, many of tlic trst.: nrcea-ary l o ew1i1:itc ruclr propcrtirs h a r e becn stnn~lardizcd t ~ yt h e h ~ n c r i r : m Society for Tczting I\lnterials. 1. HI:-sical properties a. Specific ~.rariry. b. Poroiiry; ini1ic:ition of resist:ince to penetmtion by dn:e and gases. c. Cold strength; indicates ability to stand 1111 under adverse shipping conditions. rl. Soitening temprrature: determined by use of thr 131-rometdc wne equiralent method rhich consists of comparing tlic test c:mple in the forln oi n small cone ~ i t standard h cones of horr.n softening p i n t s . e. Load test; measures the sl~txistancervhich occ1lrr dnring thr sust:iincd :~pl~licntion of a 25 lb per aq in. load unrirr conditions of operating trn~pcr:~lnri,. Bricks, xuch as silica brick, fail abrnptly at a specific iempernturt!, ~!-l~rr~,a.? fire day bricks show a gradual failure. /. Dimension changes a t high temperatures; ASTM.Ij i n o d e s a method of determining the changes in dimensions that occur over prolonged hearing periods a t operating temperatures. This information is useful in tire design of f,rrnacri7,. y. T11errn:tl expansion; important in the ultimate planning of f ~ ~ r n adesign. cr h. Spalling; drfined ns the breaking off of iragments from thr, snrfnce of the rrfractory is an import;int property whirh most he r r m - i h r d in thr proper design of rrfr:~ctory ~ ~ n l l sThree . types oi s11:illing or1111r. rl'brrn~:il spalling is caused by thermal changes produr:rd when beating or ronling. Nagnr?ite, ehromc, nnd silica hricks ( b ~ l o ~1200" r - F) have the Ion-est reriitmw to thermal spalling of the common refractories. Mcchanieal spalling is rail-rd hy str%insplaced on the brick by mechanical means such as wcessire espansirn~. Structural spalling is caused by ch;rnges in the p11yaic:tl properties of one side of the brick compared to the other, vhich may produce q~ullingdue to unequal expansion. The ASTMS has outlined tests for determining spalling cbaracteristics of refractories. i. Thermal conductivity; this is an important property since it deteriuines the thickness of brick required for a given refractory wall. j . Permesbility: the permeability of brick to liquids ;iud giws ib itnllortmt ~n :ittack by i u ~ u eslag or during the since :i ~ ~ m b i n : ~oft ii~,~er~~al-ext(~r~lill use of the refrnctory will produce cxtrtmnely rapid fnilure.

Thermal Insulation

485

2 . Chrmical properties rr. Chemical comnnsition: ns :I q.\ ~ a l.i t rcheck of rcfractories it i! advisable to bnon- tlv rhmuiml rnnlpocitioo oi rnrh hxtrh u w l . b. Chrmical reactions ~vithrefr:~rtories; it is important to he familiar n-it11 the ilir~nibtryof rencrion; that c:ln nccw hctwrrn refr:lctoricc and iuatrrials pr?.s?nt in iurnacel. Thr tern1 -lag is n rntllrr all-incl~~iivc term n-lie11 c r r e to ilwi:n:~tc the urolt~nirnpuritie- prc.smt in :r futu:~ce,kiln, or rcartor. 'Slir renetion of thew inrporitir. wit11 the refr:letor~-hrirk nluet he mil-known anll n reir:irtor!- r n ~ ~ sbet rhown tllnt. rr-ill n-it11st:tnil we11 attack. In additim, the rr,i.trniw of the rrft.;ir.torie- t u the g:wml.d :itrnwphcrr in 1r11i1.htlir:- will be esl,wud is rqunll!- as inrlmt;~nt. C:rrbon nlnnoxidr, halogens, znd \-nriow :ici,l gase: arc known to :rffrct ct.rt:iin reiritctories ndrersely. I t is imprraon these l~ml~lrmi;, and it is further tire that i~ianniacturersbe cons~~ltrd irnportant to rraliae that certain rrfrnetory rnuteri:ils, I-hrn placed adjarrut to rach otlirr iu funning refractory rwll., ma!- react wit11 mch other und~,r oprr:iting conditions.

I?cfrnrtoric:s r a n he divided iuto 40, , I I ' I four iuain g ~ ~ o u ~ ~ ~ - a l ~ ~ m i n u - . ~ i l i c n , 'S:lm C o r h d e ' o f f %:ole 36 105 0 1200PF silica, basic, aud insulating refraeI08 @ 2 8 0 0 ° F 1oric.s. I n Table 19-2 there is rcproduced a comparison of some of \ the more important of these rcfrnetorics. T h e so-called basic refractories include magnesite, chrome, 2 24 and forstcritr. I n addition, ccr6 tnin special rcfractories such as ziliron carbide and zircmia :Ira :. l6 listrtl n.11ich prove cconon~icalunder certain rcverc conrlitions. I n Fig. 19-4, t l ~ e r m a lconduc- -6 tivitica of various refractories a r r 8 c m ~ p n r e d .It is interesting t o note + the striking diffcrcnce between tl~crnialcondnctirities of insnlating Ixick and otlier rcfractorics. o o o o o o o 0 Insulating brick is produced from , Z ~ % ~ Z" z r h v s (Table 19-31 \vhic11 a r c Meon Temoernture. "F

-

.

.

ble nlaterials are burned leaving L ' q . w, Xu. 6, 216 (1U53).1 n porous structure. Insulating hricks are extremely light in weight and linve a low thcrmal conductivity. l t ~ ~ ! ndiscuvcries t n u k e it p o s i \ ~ l et u i,ro<(occ i n d : l t i l \ g bl'icks x\-llirli witlistand temprratures up to 30003F. It is p o s i b l c thcrcforc, t o ecnll-

"

"

.ur,l!

'.,"I a,,)

OOOP OOEP DOPE OOPE OOZE-008Z OOOE 001E-OOGZ

OOZE-omz

Lull&-0062 OOOP-om

OSEE-CZEE

089-009 SLI1 O9Z CEZ

ooz

Eo=lvSL-ZL W!SZ.'OZWE

a a a aa 488


Thermal Insulation

QJ

9"

9' straight

Q Small 9' brick

2' split brick

9 " end skew

QJ

k*

lr' split brick

0%

9" rotary kiln block

Qj?

9'side skew

9" feather edge

2 w

Standard 9'x4Wx2?g clrcle brick

9' soap

9' arch

Standard 4);'x4' cupola block

Standard 4 y x Y cupola block

9" neck brick

9. key

9' wedge

Fig. 19-5. Typieel refractory brick shapes. (Courtesy of Hmbison-TVnlker Refrnct o 1 . i ~Company.) ~

ornize under certain conditions by employing insulating firchrick instead of the heavier refractory brick (firebrick) formerly used. I m r conductivity makes it possible t o use a much thinner wall and thc light weight permits much more rapid heating and cooling of a furnace. The use of the insulating firebrick, however, is limited t o situations whcrc their low mcchanical strength is not a disadvantage and their high permcahility ran be tolerated. The basic refractories are most resistant to basic slags. Fire-clay, highalumina, and silica hrick are most advantageously used in contact with siliceous slag. Operating temperature plays an important part in the ultimate selection of a refractory to resist a given atmosphere or slag eundition. Refractory brick is standardized in a number of sizes and shapes Several typical shapes are illustrated in Fig. 19-5.

Installing Brickwork

The laying of refractory brick requires the eerrices of expert brick maPous familiar with reiractury bricks. Carciul job planning huggests ordering 5 t o 107i in excess of the estiinated requirements because of the inevitable breakage which occurs during construction. The common methods of laying brick are illustrated in Fig. 19-6. Tlrc choice of method depends on the required dimensions and stabilCourse it? of thc final structure. A typical furnace 19-6. C o m m o n ~ n e t l ~ ~ l s \\all nornially requires a combination, thc most Fig. of hying h~.ivl;. common of which is alternate headers and stretchers. This arrangement pruduces a grentcr structurnl stal~ilitysince all vertical joilits are t l ~ c r c l ~ofrsct. y TIICmost complex phase of refractory brickwork is the c u n ~ t r u r t i mo f ~ w n i n g sin the walls and suspended arches (the ceiling of an enrlosure). Door widths are best kept as small a s possiblc. Suspended arclics consist, ~I are of special refractory units designed to reccivc mptnl P I I ~ I I I I ~\rllich in t11t.11 att:tclir,l 10 a11 wcrl1e;ld stwl flanlcn.urk.

Thermal Insulation


490

the surrounding air hy a combination of convection and radiation. Eacli of these processes can he expressed in terms of appropriate resistances. In general the resistance produced by the fluid and tlrc pipc wall is ncgligil,lt. cnlnparrd to that of the insulation and can he neglected. The equ a t'loll for heat flow then becomes:

TABLE 19-3. Characteristics of Typical Insulating Firebricks*

Composition, per cent

Typet Group 16

15-3i A1203 30-60 SiO2

ulus Ti02 Fero8, A I ~ . 26-38 .U203 45-61 SiOl plus TiOl, F e.A". Alk. 25-42 .i1203 45-67 Si02

Group 20

Group 23

Group 28

45-53 hl?Od 42-5'2 Si02 ~ l u Ti&. s Fe?08,Alk. 45 .&Oa 65 A190-

Others

Xormal use limit, " F.t. I600

Approx. 9-in. equiv. 115

2000

125

$/MI

Bulk density. ll~!ft.~ 21-3i

where R,

2645

R, 2300

2800

260

45-65

2900

285 480

52 69

3000

49 1

I

=

resistance of the insulation

= "surface" resistance of the insulation

The resistance of any material t o the conduction of hcat is expressed a s AXIk.4, ~vhereAX is the thickness in f t of the material in the direction of heat f l o ~k, is the conductivity [Btu/(hr) (ft) ( O F)]and A the area through xvhich the heat is flowing (sq ft). For insulation surrounding s cylinder such a s pipe insulation, the surface area %tries from inside to outside and some mean area must be determined. I t has been shorn that this mean area corresponds to the logarithmic mean of the inside (A.l~) and outside (.4z) surface areas, i.e.,

where L is the length of insulation in f t and D is the diameter in f t *Iteprinted hy pwmissioa, Korton, C. L., Jr., Chern. Eng., 60, No.6, 216, 1953. tGroup number is std. A.S.T.hl.classification, indicating normal use limit (X100) $See note under Table 192.

HEAT LOSSES THROUGH INSULATED SURFACES The calculation of licat losscs tlirougli imulated surfaces involves the suulrllation of the scvcral resistances to heat flow. I n a given situation the terminal temperatures are known. The temperature, for instance, of tlic fluid inside an insulated pipc and the room tempcrature arc known and the hcat flow can be cxpresscd in a fashion analogous to the flow- of electricity.

For spheres, this mean area can he s h o m ~to be equivalent t o the geomct,rk mean ( \ / A I A z ) of the inside and outside areas. The surface resistance is usually much less than that of the insulation and need only be estimated. I t is represented as l / ( h , h,).4z, \\-here h, is the convection coefficient and h, the radiat,ion roefficient. Values of h, for horizontal insulated pipes can he the combined coefficient h, estimated from the empirical equation,'

+

+

h, f h , where

h, where

q = heat flow in Btu/hr

AT KT

= =

total temperature drop from inside fluid t o outside air summation of all resistances

Heat flows thruupli the fluid inside the pipe by convection and by ronductiun tllrougli thc pipe \\.all and insulation. The heat then passes into

=

561 (dzOlg)(273 - At,)

dz = OD of insulation in in. At, = insulation surface temperature minus air temperature, " F h, = transfer coefficients, Btu/(hr)(sq f t ) ( " F )

+

Values for flat plates can also be calculated. The convection coefficieut for air, h., a t vertical plates can be determined from the equation h, = 0.27Ato2$ where At is the temperature difference hetmeen the air

Thermal lnsulotion


492

a n d the outaidc of the plate. T h e radiation coefficient c a n he determined from the eouation:

R,:

At,

=

-

12

150 - 70

=

8.375

=

2.2 sq ft

RI

From eq. 3,

emissirity of the plate at 7'1 TI ahsolute temperature of plate in R 1'" = absolute temperature of air in " I:

where: el

?r

Outsirle area

= =

h,

564 + h, = (8.3i5)'J"'(2T3 = 1.96 litu '(Ilr](sq i t ) ? F) - SO)

T u determine condurtirities a n d the aalucs of h , and h,, it is nvciwnry t o ;i
l'enipernture 100 200 300 400

500 600 630

85% ~1:1gnesia 0.0:i-I 0.0~s 0.0K 0.043 0.046

S o ~ u r ~ o xAssume: . 1. Outside nine wall temoerature

=

650" F.

Iiigh Timpcr~~ture (Dintomnceous earthasbe-to$)

o m 0.056 0.05s 0.060 0.061 0.0615

or. Atetnge t e m p e ~ a t u ~=e

650

+ (G50 - 300) = 600' F, assumed 500' F 2

Outer layer AT

=

(138)(1.81) = 250" F

Surface temperature

=

350 - 250

Average temperature

=

350

+

2

=

100" F, assumed 150' F

loo = 225" F. :rssurnrd 250" F

T h e relativuly small change of co:ductivity n-it11 t r ~ n l ~ c r a t ~indicateirr t h a t further c ~ l c u l a t i o n is not justified. T h e value of 138 Btu, hr is satisfactory. OPTIMUM INSULATION THICKNESS

Ensis: 1 ft of length. Brel.age area of inner layer

Theorcticnlly the determination of t h e optimnnl insultition thiclinrsis a, straigl~tfurvarilproccdurc. As t h e insulati,~ntliicknc.is is incr.cawil the costs of heat losses go down R-hilc the inxulation costs go up. T h e point a t ivl~iclrnrinimum total cost is rearhed inay he dcscribcd :1s n11 optinrum v:rlnc. M c l l i l l a n i has developed a n analytical solution for this particulnr optimum by equating the first differential of the expression for total cost to zero.

Bvernge area of outer layer

For flat surfaces

4.

Outside surface temperature

=

150" F.

494


wherc X = optimum insulation thickness in in. a = y (t - t,).11,'1,000,000 y = hours operation per year .1f = value of heat in dollars per million Utu I, = rust of insulation per sq f t per in. of thickness per year R, = surfaw resistance, (hr) (" F) (sq f t ) Rtu I;' = conductivity, B t u ' (hr) (sq ft in.) (' F ) t = temperature on hot side of insulation, " F 1, = air temperature, ' F For cylindrical surfaces (one insulating material)

Thermal lnsulotion

495

:11l fartors rrrnld l ~ rvnlmitul. r it may IIC 110ssihle to justify cv1.n t l ~ i c k ~ , r I I M ~I I V itm~civll:it11,~s. ~ ~ ~ w l i i ttlj~~oi ii~ tlw g l ~- o - ( , i ~ l lo11tiu1lu11 ~~l .1111. ~.ffvctuf \viugl v?lwity IIV 111,:itl o s s tIir1~1~ig11 i~i..uLiticm is >i rvlativc,lT -11glit 10 to 15%, if the irrsulati~mis rvcll >caIc,~l. The ~ ~ i i r / m i of t y tlir

.

-

n-here rz = outside radius of insulation, in. r l = inside radius of insulation, in. is presented in A plot of these cxpressions for various values of Fig. 10-7. Insulation manufacturers and operating compani~s have insulat,ion specifications TI-hi1.hinclude recommended thicknesses for various service conditions. Most of t,hese recommendations Tvere based on McMillan's equat,ions and xere determined in tlic late 1920's. Costs have certainly changed since t h c ~and a rc-appraisal is indicated. One further point about XclIillan's equations is that the expressions for insulation costs used in t h r development do not necessarily apply t o all insulation. [Flat surfaces:

cost per sq ft

=

bz

+C

Cylindrical surfaces: 2arzb cost per linear f t = -- (72 - 71) 12

+C

where C is a constant] Despite tliere objections, the tahlcs of recommended thicknesses rearlily available from insulation manufacturers rrprcscnt a close approxiniation to a "correct" thickncss. I n any evpnt, these thicknesses have become familiar through use, and drastic changes must be well substantiated before management r i l l agree. Surh cvidcncc is actually difficult t o produce. The effect of wind, rain, and especially suddcn changes in weather can be very adverse on the operation of fractionating units. For instance, a sudden change in weather typical of that occurring on the Gulf Coast of the trnited States ha?: often vauscd riolmt u11scts in fractionating equipwent due tr* L~ercasedheat losses through insulatiun. I n such cases if

Fig. 19-7. Eronomirnl inw1:itian thickncs. (Reprintrd hy permission, I,. B. MrMiilan. Popcr S o . 2034. .Annual Meeting oi ASRIE. S e w Vnrk, Dcc. 1926; mrtl copyright owner, Johns M n n ~ i l l eCwparatian.)

resistance is furnished hy the insulation and not the .;urfacr rcsistsnre which is all that is affected by ~vind. The loss can 11ecnme large, h o w eyer, should cracks through the insulation devrlop. Bettcr niethods of installatiun to prevent losses through cracks arid joints must be devised.

496


.kltliough the pitilation is ~ o n ~ e w l r aconfused. t 11sei.s r ~ finsulation s11o11ld not disregard the processes of objective thinking as nell- situations arise. e insulating materials, unusual locations (such as extremely cold climates), and other unique features should be examined and evaluated as 1nuc11 as possiblc on tlie basis of sound enginccring principles.

CHAPTER

20

INSULATION EFFICIENCY

Insulation efficiency is a term frequently appearing in the literature :mil in mannfacturers' catalogs. I t is ricfined 11s the difference b e t n w n the 1ie:lt l w s rllrouglr b n r ~pipe and tliat tliri~nglitlie same pipe when insulated, diridcd by tile heat lost through tire uninsulated pipe. Tables of thcsc ctliciencics are reported 11y nlanufacturcrs for v a r i m s sizes and thicknesses of insulation. T h e values are misleading, honcver, t o the casual user since they are all high and w l ~ n tappears t o be a small difference in efficiency of only 27% 196 and 911 can rcprcsent :In increase in heat loss of (96 - 94/100 -- 96) (100) = 5070. H e a t lops tables are n~nclimore useful in comparing various thicknesses and kinds of insulation.

PROCESS INSTRUMENTS

REFERENCES 1. A S T M Standards, Part 111, 298, Am. Soc. Testing M~terials.New York, 1950. 2. Grllrr, R. F., Firc-Cloy Brick, T h e i r .IInnufacturc, P m p e ~ . l i e s , ULPS,and S/?rr.ij?crrtioris, Tlnrrnu of Stnud~riisCil.eular No. 282, Washington, D.C., 1926. 3. Jnkoh, Max, nnd G. A. Hawkins, E l e m e l ~ t sof ZZcat Ti.nn.sfer and Znsi~lation, 2nd Ed., John \Tiley and Sons, Inr., New Yurk, 1950. 4. Kern, D. Q.,Process Hent Transfer, hlcGrawHill Baok Ca.: New Yark, 1950. 5. ilmitol o i .4STM Stnndnrrl,~on R e f i - n c t o q .lfntrr.inls, Am. Sor. Testing Matcrials. 1-cu' l'oli. 1948. 6. M d d a n ~ s .TI'. I?.. Heat l'ransmisaion. 3rd Ed., h.leGr.aw-Hill Baok Co., New Y o k 1953. i. hlrhlillnn. L. 8.. Neat T ~ n n s f e rthroztgh Ins~ilolionin t h Modcrate ~ nnd High l'ciiiji,'mture Fieliia, . h c v Sac. Mech. Engt.s' :mnu:d meeting, Dcc. 6 to 9, 1926. 8. M o d e m Refrtietuiu Piactice, Harbison-Wnlkr Refractories Company, Pittsburph, 1950. 9. Kol.ion. C. L., Jr., C h e m Eng. 60, 30. 6 , 216 (1953). 10. Karton. F. H., Rc/irictolzes, 31.11Ed., MrGrawHill Book Ca., New York, 1950. 11. Thmuns, R. :and TV. C. T,wner, Ch<.,n. E n R , fill, S o . 6, 221 (1953). 12. \Tilkeal G. B., Heat Insalatiun, John Wiley & Sons, Inc., Xew York, 1950.

Process industries could not exist m-ithout instruments vhich indicate. record, control, and in solnc cases anticil~iitetllc many clmnges tliat occur in a process. Even in processes wliich require nianual control, instruments tcll thc operator ~vlienlic should tnrn a r a k e or press a button. The adranccmmts in instnumcnt technology l i n w been phmo~nen:il. I n the late 1930's instrmicnts and control devices w r c relatively simple and a few standard types were used. Any engineer coulil understand and apply tlicn~for most conditions. During and since World JVar I1 change has bccn rapid and continues a t a n :wceleratcd rate, l'he greatest strider were made in the u8c of electronic equipment. The complexitie.~ of such systems and tlic rapid changes produced by the frcslily stimulated instrumcnt industry. has r q u i r c d tile creatilm of another group of si~ecialists. Some physicists, chemical engineers, n~eclianicalmginccrs. and elertrical engineers Iraw 11rwlllr instru~lientengintws tllrough self-education and training by the instrumcnt companies. l'lresc men arc c ~ u p l o p l not only by instrument companies but also by r,onstruction rind operating companies. M a n y rcl~ools of chtmirnl mgincering &er courscs in process instrumentation n.l~icl~ n-ill aid ill trniniug :i(lditio~~:ilclier11ic:il cngineers for this type of work and nil1 make others aware of the problems and techniques of instrument engineering. A11 instrument selection, npplication. and purchniing shonl~lbe dircctcri h prujeci, hy ;In i n * t r u n ~ m tenginecr. It is inlpussible fur :I ~ ~ r o r c sor 497

498


Process Instruments

engineer t o keep up with tlie latest instrument developments unless his entire attention is devoted to this field. To provide propcr instrrmientation thc instrument engineer must be thoroughly familiar ~vitliall phases of the proccss, its key characteristics, and the application or iunction of all the llrorers e q u i p ~ n m t . Conversely a general knowledge of instrumentation is helpful to the process engineer and project enginecr in initial development of the proccss. The purpose of the discussion that iollow is to sl~pplygeneral knowledge of instrumentation. Complete ~vorks on the subject are availablel,".F.s,g.'O and should be nsed for specific problems requiring more detailed understanding. Because of the rapid changes taking place, however, tlle serreral popular instrument periodicals should also be consulted.

2. Temperature; (2.01I d i d expnnsii~n;(2.021 fluid expansion; (2.03) tliernio-elwtric. 3. Pressure; (3.01 I in~lllY~oll-t~'~,c; (3.02) I1ellon.i; ~ n d(3.031 electrical and diaphragn~electronic. 4. 1,iqnid lcvel; (4.01I iliffermtinl; 14.021 Hont; (4.031 niiarcllaneous types; (4.04) risual or ninnl~al. 5. Motion; (5.01) tnclromrtric; (5.021 limit; (5.03) counting. 6. Chemical and physical ~ileasurements.

499

Control Systems

(a1 Manual, ( b ) mccliauicnl, (cj pneumatic, ( d ) hydraulic, (ej elec-

trical and electronic.

GENERAL PRINCIPLES

Flow Measurement

In order to indicate or control a proccss variahle, an instrument must be rapahle of sensing the change in the variahle. Tlie sensing part of tlle instrument may be called the primary clcnient. The instrument translates ~ means into this primary inipulsr by electrical, ~ ~ n e m n n t i Ic ,I mcriianical a visiblc indication or record. I t may : h o actuate other devices t o change proccss conditions so that the sensed variable may he returned t o some pre-determined point,. An instrument, tlierefore, is composed of some type of pr.imary sensing dcvicc in contart nitli the fluid or substance; an amplification unit, and finally tlie physical unit which indicates or records and translates tlic primary sensing ilnl~ulseinto some kind of poiyer or motion. Automation or iristrurnentation is, of course, not limited t o these basic characteristics, hut has been developed t o sense and indicate nearly all known physical or cllciiiical cliarnrteristics. Tliese include pressure, temperature, density, fluidity, riscosity, color, pH, or coniposition. It is usually unneecssary, iro\vevcr, to cuntrd precisely cacll process variable simultanconsly. Orilinwily only several key variables need be controlled to givc the desircd cnd-produet cliariteteristics.

Mechanical Flow Measurement

Tlie most, elementary form of ri~lumctric measurement consists of filling and emptying a cb;rmher of k n o w ~rolunie. This type of mcasurement is used in the proccss industries f i r taking inventory of fluids in storage tanks or vessels. Certain proccsses rrquire manual or instrument tank gaging a t regular intervals, as a cllcck on other flmv determinations. The ordinary ~lisplacenientnictcr measures liquids by alternately filling and emptying chan~berscontained vitliin its 1111ily (Fig. 20-1). The velocities and pressnre-drqx through the device are utilized to move the chambers or diaphragms and the connrcteil vitlring. Each cycle is counted by a series of numherrd gears ~ i h i r hare visiblc. Tliese mcters are relatirely inexpensirc and give long and accurate service ir-hen nsed within their capacity rangrs. us illustrated hy tlie residential water and gas meter. Thc undesirable pulsating effect of the simplest type of displaccnicnt meter is eliniinatcii in those drsigns utilizing a rocking and rotatory motion. The displacement rncter is used more frequently fnr nieasurement of total production tlian for recurding instantaneuus flow rates sincc it is essentially a totalizing device. Most displacement meters cannot operate a t lliglr pressures and temperatures. Uisplacenient mcters arc used extcnsirely in hlending and filling operations when precise volumetric measurements are r e ~ p i r c d . hIcclianieally linked displacement meters are used in the blending of costly products sueh a s lubricating oils. hutumatic shut-off meters are used in barrel filling or container filling operations.

INSTRUMENT TYPES Classification

The follo\ving list of instrumentation or control phases is convenient for discussion purposes. Primory Sensing Phoses

( 1 ) Flu\\.: (2) tenlpel.at11re: (31 presrnrc; ( 4 ) liquid level; ( 5 ) motion.

Differential Pressure Instruments

Differential pressure flow meters convert a portion of the pressure energy of a fluid t o kinetic energy. This is accomplished by placing irb

Primory Elements, Types

1. Flow; (1.01) meclianical; (1 021 d~ffcrcntial;(1 0 3 ) area. I

500

Proled Engmeering

I--

-

-

of Process Plants -

-

Process lnrtrurnentr 15~1.2 a n I,,: eq,r(wcil

ill

501

tt!rnis ul' 11, ol' fluid fion-iugpcr second as follows:

where D I= diameter of pipe in f t I)? = diameter of restriction in ft AP = prrssltrc diffcrrntial in 11) per sq ft, These e~~uations, ho11-ercr. arc hascd on iilml frictionless flow, Actually > frirtional effects consume a port,ion of the pressure rncrgy. l h c most, g energy loss due to friction has been :n convenient means of a l l o ~ ~ i nfor empirically determined const,ant called the coefficient of discharge which is the rat,io of a c t d to theorrtiral Ann.. The actual flow bhen is: r

where C Fig. 20-1. Nutating-disk displ:mement mctcr. lRpprintcd by permission, G. G. Brown, Unit Operatio,~s,Jolm Kilcy n m l Sons (1050).1

a pipc a constriction such as an orifice, venturi, or flom nozzle (Fig. 2 0 - 2 ) . If friction is neglcctcd the prcrsure drup across i u c l ~a restriction is related to the kinetic energy change ns i d o n - r :

whcrc PI = pressure upstwnm from the restriction, psf P2 = pressure a t the restriction or some predetermined point downstrt*am, psf 1 ~ 1= velocity, ft/ser, npstream 112 = velocit,y, ft/ser, a t rest,rirtion or downstream 0. = :32.li p = density of fluid flowing lh,'eu ft l?xpressing be ohtained.

UI

in terms of z ~ ?an equation for velocity a t thc point 2 can

=

coeffivient of discharge 1

=

velocity of approsrh factor

Convenient manuals such as the classic ASI\IE publication, Fluid 3 I ~ l e r spresent ,~ correlations of C for the various types of orifices, venturi meters, and flow nozzles versus the Reynolds' number through the restriction. The ratio, C ! d 1 - (D2/D1)4 is often called the flow coefficient, K. Tahles of Reynolds' numbers and corresponding values of K for different' pipe sizes and 0 2 / 0 1 ratios are p u b l i ~ h e d . ~The trial-and-error solution for flom rate or the required orifice diameter for a given flow rate and pressure different,ial is made simple hy such compilations. h Itcynolds' number is assumed and K read from the table for a given 0 2 / 0 1 ratio. The values of K do not vary greatly in t,hr range of most industrial applicat,ions and hence the solution is rapid. It is fortunate that standardization of orifice, rentnri, and flow nozzle construction was accomplished some years ago. Considerable euperimental and operating data have been accumulated and generalized correlations of C with Reynolds' number have resulted. These data make it possible t,o design and operate differential meters without any necessity for calibration provided the standards of const,ruction and installation outlineds are followed.

502


503

Process Instruments ,DOWN STRE4M TAP

11.-1.11,

m

The renturi meter (Fig. 20-20) ha? a 21" or leer angle of appronrll ~vliiclieliminates cavitation. The exit angle is 7" t o 9' so that tlie cxpansion hark to original pipe size is uniform and pressure recovery high. The small loss of energy due ti1 friction ~vhichis demonstrated by the loxipernianent pressure losses ( C 0.92 t o 0.99) is the unique feature of a renturi meter. I t is used, therefore, in systems for which high premure losses cannot be tolerated such as low pressure gas systems or water distribution systems. Pressure losses in water systems involving large f l o w increase pumping costs considerahly. I n such cases the venturi, though more expcusive than the orifice or flow nozzle, will be more economical based on orerall installation plns operating costs.

-

ORIFICEMETER Tllc orifice platr is tlie simplest, clicapcst, and most popular rcstriction for measuring flow. Orifice meters cornpriae well above 90% of inort process plant metering installatii~ns. Values of tlic disrhargc coefficient range from 0.59 t o 0.62 (see published data for tabulationsj.8 Orifice flanges with flange taps are obtainable from numerous manufacturers (Fig. 18-3). The orifice plate is held betn-een these flanges and the pressure connections are tapped into tlic flange body by the manufacturer. The taps are located so that when tlie flanges and plate are assclnblcd there is 1 in. between each t a p and the plate. Other locations of pressure taps include vena contractn and pipe taps. The tlena contractn, downstream t a p location is a t the point of minimum fluid stream cross secbion (Fig. 20-2b). This location varics with the ratio D J D , and n ~ u s tbe rnoved if the orifice size is changed. The upstream t a p is placed one pipe diameter from the orifice plate. Venn contrnctn taps are used on special installations for which manufactured orifice flanges are unohtainable or tou costly. Pipe taps are located so that the upstream t a p is 2.5 pipe diameters from the plate and the downstream tap, eight diameters. Because of the great downstream distance, a large portion of the pressure drop across the orifice has been recovered. This low pressure differential may be an advantage for high flow rates. The diffcrential measured by pipe taps represcnts, in addition to a portion of tlie original diffcrential across the orifice, frictional losses in the length of pipe hetween taps. Pipe taps should not be uscd, therefore, for viscous fluids or fluids with solids in suspension since these produce large frictiunal losses. Flashing fluids, however, are often successfully measured with pipe taps since the vapors have opportunity t o redissolve before reaching the downstream tap.

Pipe Diameters

Section Through Orifice Plote

(b)

STREAM TAP

!

1

Fig. 20-2. Differential prpssure primary e l m ~ e n t s . ( a ) Vmtori meter. (courtes>r oi Minncnpolis-Hanc.~v~llR r g d n l o r Carnp;my) ; f h ) wificr rnetcr in-lall:~tion s h m ~ i n g presauw varinlian fnd:tptril frurn Pti,irlornrrilnlr 01 Intr.,i~,,c,il,ilir,t, f o i thi. Procew Inti,usIries, b y pfnnissiun, h1innr;ipolis-Honcyrri.ll Rrgolitto~.Compzny); ( c ) flow nozzle (courtesy oi Minneapolis-Hunrywell klegulatot. Company).

$

Flange taps arc hy far the most popular type of pressure tap. Thcy are easily installed and require less space. They are satisfactory for most, types of fluids including viscous materials. The industrially important orifice platc is the sqnare-ccigc~lor sliarpedged orifice as shown in Fig. 20-2h. The rli~ilensiunalcl~arartcristirs1 1 4 this design have been very cat.efnlly stand:~~~dizcd and cspcri~lient:~l aud

504


operating data on numerous installations provide reliablc predictiou data. Any radical change in the orifice during w e such ns rounding of thc edge hy corrosion or erosion r i l l introduce serious error. For this reason urifice plates should be constructed of the best material availahlc for resisting attack by the flowing fluid. Orifice installations must be designed with care. Excessive turbulence a t points close t o the orifice will cause erroncous readings. The published discharge coefficients are based on flow which is rouglily parallel to the pipe axis. A definite am~iuntof straight unobstructed piping on either sick of tlic m-ifice is nccessary. Sprenkle" f r m l studics of various piping systems has developed rhnrts rliich give the ~nininiuniallo~l-abledistance that :I disturbance such as a pipe bcnd can he locatcd up and do\vnstrcani oi an orifice. These charts have been widely reproduced in publications of instrument lnanufacturers and should be used in preference t o sonie gencral rule-of-thun~h. If because of space requirements the orifice must be located closer t o a disturbance than the recommended minin~umdistance, straightening rallw conrposed of a nun~herof aniall tubes nestcd so as t o fill tlie entire conduit ~ n n s tbe utilized.

The flow nozzle sliown in Fig. 20-2c has characteristics intermediate between orificcs and venturi tubes. It Ims a gently roundc~lapproach but an abrupt discharge, and is morc efficient than tlic orifice but less efficient than a vcnturi meter. It costs more than an orifice, but less than a venturi. The nozzle, ~vhicliis held in place hy standard flanges, is best suited for the incasuremcnt of gases containing moisture such 3 s v e t steam. There conditions cause erosion of orifice plates but do not affect nozzles.

PRESSURE ~IEASURE~~EKT DIFFERE~TIAL Mercury-type (Fig. 20.30) or force-balance type manometers are used for measuring the differential prcvsnre produced hy orifices, vent,uri tubes, and flow nozzles. The differential pressure across tlie mercury ~nanonietercauses a change in level in both legs. The niovement of the float in the largcr dinmcter leg is transmitted by means of n~eclianie;~l linkage t o a shaft through the manometer l ~ o d yto givc an external indication. hIovenient of the sliaft nlay be uscd t o indicate, record, or control (see Fig. 2 0 - 3 a ) . Certain type8 of manometers eliminate the shaft extension through the meter body by use of a solenoid or magnet rontnined within tlie manometer body. The Imger leg wit11 the s ~ ~ i a l l edianietcr r is callc~la range tul~e. AI-

!

505

Process Instruments

111ougl1thr lotal differcntial is reprer~ntedhy tlir ~ ~ ~ o v e l n in c n lxttl~ t leg-. movement in the leg x i t h the float is a function of the total differential. The range of the instrument is increased by decreasing the diameter of the range tube. This causes more movement in the range tube than in the float tube for a given differential. Pressure inlet.

Range tube

Restriction s c r e w y

(n)

PI pa

--

Sealing bellom,

/Beam pivot

/Balance

beam

Pressure receiver

.

.

.

-

(b) Fig. 20-3. Differential prcssure-sensing drricrs. (a) Mercury manometer: ( b ) folwbalance meter. LRcprinted by permission, D. P. Eckmnn, h d u s f n n l Instriirnenlntio,~. John T i l c y and Son3 (1950)l

The mercury manolnetcr has served for many years as the principle measuring derice of differential pressure. I t is only in recent years that the force-balance or pneumatic-balance type instrument has been introduced and gained popularity (Fig. 20-3b). The force-balance manometer operates by developing a force in opposition t o the differential pressure.

506

r

,,,,

'I'llis opposing forrc is rreated hy air pressure. .4s P, increases (Fig. 20-3b) the halance hcam covers more of tlie nozzle through xvhich air is being lost. This movement increases tlie air pressure in the balancing diaphragm and causes it t o force the beam away from tlie nozzle. An c q u librium of forrcs is estahlished ivhich is represented by tlie air pressure attained in the system. This air pressure is directly proportional to thc differential pressure and can hc readily transmitted t o a recording instrument with a pneumatic hell o which ~ ~will actuatc a pen t o record or indicate the flow. Thesr merrory-lcss mctcrs arc small in size and simple t o calibrate and install. T h r y do not requirc seal pots. Unlike mercury nlai~ometer asseinblies they ran be mounted a t tlie orificc supported by a simple pipc saddle and yoke.

Area Meters Instead of maintaining a constant area restriction, and allowing the differential pressure t o vary with flow ratc, the differential pressure is maintained constant and the area a l l o w d t o vary in area meters. The most important type of area meter is the rotameter (Fig. 20-4). It consists of a tapcred tuhe and float. As the flow rate ~ i20.4, ~ Rotnmetel. , with increases thc float moves upward creating tt.nmmittcr. ( ~ o n ~ ~ t ~ i ~more ~~ area h ~for fluid ~ flow and thus rnainand Poster Company.) taining a constant differential pressure across the flnat. Using tlie same rcasoning process as in the dcvclopmcnt of eq. 3 and expressing tlie constant pressure diffcrcntial a c n ~ s sthe float in terms of the ronditions a t equilibriu~n [ A P = Tit(,, -,)/At] the following equation is obtained: MITERING
W

=

C,A2

G~ ~ C P (P I PIT',

~ r h e r eTi7 = flow, Ib,/sec (!, = rot,amet,er coefficient of dincharge

Process Instruments

I


(5)

p = pi =

V, A, .42

= = =

density of fluid density of float volume of float effective area of float annular area between float and tuhe

Since V, = Tl'l/p, (where W, = weight of float) the amount of range change produced by reducing the ~veightof the float is expressrd hy:

Eq. 6 is based on the assumption t h a t C , does not r a r y and that the fluid and cffectire float area remain tlic same. Rotamcter manuiartl~rrrs offer weight cxtensions which can be attached to standard float designs to increase the instrument range. The annular area A? varics x i t h the flow rate and is directly proportional t o the height of the float,. hlanufactnrera' data can he used to calculate height of float versus flax rate curves for rotameters, even for viscous rnatcrials. Rotameters are availablc with glass metering tubes ~ h i c hpermit visual observation of the flnat or metal rnctering tubcs with indicating extensions. Various electronic and pneumatic transmitting devices are ohtainablc for transmitting the position of the extension stem to a recorder or controller. A calibration for viscous fluids can hc predicted wit11 grcatcr accuracy for rotameters than for orifices. They arc satisfactory and inexpensive for small installations, hut are very costly for extremely large flow rates. Temperature Measuring Instrument A uvide variety of telnperature-measl~ringdevices meet the varird n e e d of temperature, range, and service. Those in use in process plants will be considered here. I n Table 20-1 a summary of usual temperature ranges for the more common instruments is givcn. Tlicac ranges are subject t o change as new developments appear. Many factors other than range, however, are considered in tile selection of a temperature dcricc. Tliesc include accuracy, speed of response, sensitivity, cost, and corrosion resistance. Manufacturers are anxious t o advise customers on the use and limitations of their equipment and should he consulted. Solid Expansion Thermometers As is well known, all materials change dimension with teinprature. I i two strips of iiietal are ~vclrlrdtugether, onc having ;I low coefficient of

508


TABLE 20-1.

Usual Industrial Ronge of Temperature Measuring Instruments (Based on manufacturer's data)

Type 1. Hiti~etallir 2. llrrcor>-ill glass 3. Fluid expansion (a) Mercury ( h ) Organic liquid (c)

509

Process Instruments

to time of tlw h i m ~ ~ t a l ldi:il i c tllcrmolnetcr described above. T h e instrurnent is made rugged by enclosing the thermometer in a metal case. Fittings make it powible t o scrcv the thern~omctcrinto a pipe or vessrl nmzle. The glass covered scale can he obtained tilted a t convenient angles. Otlrer t y l i c ~of f l ~ ~ rxlinnsion i,l instruments utilize a rlorcrl s y ~ t c m . Tlrr. expanding fluid r.zert5 a p r w w r e on a spiral pressnrc clrmcnt i s p r i n g ~ c;iusing it to uncoil. Tlii; movcll~cntis trnnamittcd to a p ~ nor p11ii1t1.r

Organic rapor-liquid

( d ) Gas

4. The~.n~ocnnple (a) Copper.-constantan

(b) Iron-ronstarrtnn

- 300 to ti00 0 to 1400 (oxidizing atm) or 1800 (redurinx :rtm) 600 to 2100 1300 to 3000

Pointer

Scale

(c) (:t11.o111el-:iI11111e1* (11) Plrttitiu~li-plnti~ium-rhodium 5. I(esid;~~irc (a) Copper (b) iYiokel ( c ) Platinum 6. Optical pyrometer 7. Radiation pyrometer 'Registered trademark of the Hoskins Corporation.

expansion (Invar, nliich is iron-nickel alloy I and the other a high coefficient of expansion (brass or nickel), the combined strip will deflect i~nclel. the influence of temperature. B y making the strips thin a large deflection can be obtained which can be used to inovc a pointer and ind'icatc tlie tenq~erature. A very popular dial thermonieter consists of n bimetallic strip ivound into a helix. One end is fastened to the casing and the other end t o :I rod connected t o a pointer. .4s the teinpcraturc changes the movement of tlie helix causes the rod and attached puinter to move. The dials are built in sizes from 1% in. to 5 in. These dial thermometers arc lugged and reasunnllly accurate (within 1% of scale) alien properly r l i ~ ~ s c n .The industrial-type rncrcury-inglass tlierniometers are the mo.!t cconuniical and convenient mrans for nonrecording temperature measurement of accessible prneess points. The bimetallic strip instrur~ientis uscd extensively for on-off control of simple devices such as air-conditioning systems. Fluid Expansion Thermometers T h e most familiar temperature measuring instruuient, the mercury-inglass tl~er~iiumeter, is designed iur l o i d l y 111ou11tt:d;~j~plirations siluilar

~vliirhmox-e across a c:~lil~ratctlscale in direct relationship x ~ i t htemperature (Fig. 20-5). T h e flnids used arc inert gases (usually nitrogen). liquids (mercury or organic liquids), and vapors (propane, metliyl ether, et,lier, or clilorobcnzene). Pressure thermometerr filled \vith liquid or gas must he compensated f o r ambient temperature changes. If the temperature along tlie capillary end a t the pressure spring is radically different from that a t the calibration point, t h e teml~eraturerradillgs d l be in error since voluinctrir expansion in these arcae d l be cli:~nge(l. Tu overwme t l ~ i seffect a bimetallic strip or a second prcssure spring. witli a capillary (witliout hul111 rruming. adinrent to the mens~iringrxpillury can 11c installrd in opposition to the l~reesure-measuring spring. This arrmgelncnt will cancel tlic ambient temperature effcct~. Vapor-fillcd s y s t e n ~ srequire O I I such compensation if tlir: liquid lcwl remains in the bulb. T h e pressure in tlic ~ y s t e n imust rorrrspond to tlic vapor pressure of the liquid a t tlie bulb regardless of ambient conditions. T h e use of fluid-expansion, pressure tliermometrre in process plants is very extenairc, l~:wticularly in temperature ranges b e t w e n 0 und 500" F. I n order t o keep tlie length of capillary to a minimum, a transmitter-type instrument may be used. This instrument is located near tlic primary element, and converts the expansion pressure impulse into an electrical or

510


I

pneumatic signal w1iic.h m a y be conducted to a rentral control house. Since tlie primary sensing device is fundamentally a pressure instrument. pressure-type instrnment elements such a s bellows and Rourdon elemmtr (helix or spiral) m a y he used a s secondary elcmcnts for indicating, recurding. and controlling. T h e pressure-thennonieter instruments are relatively inexpensive c o n pared to thermo-electric instruments. T h e vapor-filled instrument is tlle most popular of t h e three types. It is lowest in coat, requires no compensation, and has rapid res1)onse. T h e scale, hinvever, is nonlinear. Of tlie three, tlie mercury-filled thermometer is the most stable a n d sensitive.

51 1

Process Instruments

2. -4 third conductor may be introduced into one side of the circuit as in Fig. 20-6a d h o u t changing the emf produced, provided the temperature along the conductor remains constant 3. A third conductor may he introih~ccdon both sides of the circuit as in Fig. 20-Gb without changing thr rmf produrcd if the intermediate j~inctionsare at the mme temperature. IThr :~lgphmicsums of the voltages generated by a number of dissimilar conductors joined together in a circuit is a function of temperature only.)

Thermo-electric Temperature Measuring Instruments

Instrument

T3

Instrument

THERMOCOUPLES T h e thcrmocouple is the most widely used devicc for temperature measurement. Accurate potentiometers make i t possible t o employ thermocouples fur temperatures from -300' F tu 3000" F. Because of the ease by which the generated emf rnay be transmitted over large distances ti) central control r o ~ ~ mthe s , thcrmocouple instrument has proved convenient and accurate for modern process control a n d measurement purposes. As early a s 1821 it was observed t h a t if a circuit of t w o dissimilar metals was formed and the junction a t one end v a s heated (hot junction) and t h e other ends (cold junction) were attached to a potentiometer or millivoltmeter, a measurable voltage could bc obscrvcd on t h e instrument. This voltage was found t o h a w a dcfinite relationship* for each pair of riletal~ with t h e temperature difference h e t w x n the hot and cold jnnction. If the cold junction, thercforc, is maintained a t some constant temperature, the hot junction temperature can be obtained over a wide range by rncasuring tlie voltage generated. Experimental evidence and reasoning based on t h e l a m of thermodynamics have produced the following rules of practical significance to industrial thermometry. 1. The emf developed by the difference in temperature of two junctions is s independcnt of temperature gradients along homogeneous ~ v i r ~bct,wen junrtions. Heat effects alone will not produce a iwrrent in 3 homogeneous circuit.t *This relationship is not linear but roughly approximated by emi = m A t + n ( l t ) " where A T = temperature difference hetween hat and cold jnnrtion m and n = constants for pattieular thermocouple

t The wcll-known Thomson effect is used to dcseribe the emi genwated in n homogeneous wire when a tempesaturc diKermre exists betwern the terminals oi the wire. The tcmpernture distribution along the wircs, h o m ~ w r ,does not aKwt the Thamson emf. This emi tog~therwith that cansd by the diKctmm in temperature oi the two junctions makes np the total "thern~~c~uple" emf.

(b)

(a)

Fig. 20-6. Tliermocouple circuits with third conducbor

I

THERMOCOUPLE CO~IBISATIOSS.Tlic conmion thermocouple material combinations are given in Table 20-1. Each pair has particular arlvantages in degree of accuracy and range. T h e copper-constantan' thermocouple is superior in the lower temperature range. Atlove 650" F copper oxidizes rapidly. Below 2 0 0 ° F copper-conrtantan has greater accuracy t h a n iron-constantan. It produces higher emf's in its range than the platinum couple and is less costly. Because of their low cost, large mnge, and reliability when properly applied, iron-constantau thermocouples arc tlie most widely used. T h e iron, lion-ever, is subject to oxidatiun and prccsutions must he taken to prevent tlris. Clirouiel [ N i ( 9 0 % ) , Cr(l0:;: )]-Alumel [Ni(947$ j , l I n ( 3 7 ) , A1(27%), Si(lC/r ) ] mas developed b y its nlanufacturer for use in oxidizing atmos1)lierer wlicrc iron-constantan proves unurahlr. I t s most important applications are in the rangc of 1400 to 2300' F.4 A t high temperatures t h e Clrromel-Alumcl couplc is unsatisfactory in rcducing atmospheres (less than 2' oxygen). T h e platinum-platinum rhodium couple is more expensive than the base metal couples and is used in process plants primarily for temperatures above the range of other eouplcs. Platiurnn is subject t o alteration by reducing ntmosphcrcs and certain vapors, and is inl-arial~lyenclosed in gas-tight wells for protection. Commercial thcrm~,couplea i r e is manufactured tu close tolerances and will, whcn assembled, match pnblislied t l ~ c r m o c n u ~roltagcs ~le to a degree of accuracy suitablc for n ~ o r tp u q ) o s w l l a t c r i a l s of greater certified

* Cunatmtau

is a

cupper-nickel alloy (50 to

65 Cu

and 35 to 50 Ni).

512

I


accuracy ior precise work such as research can bc ohtaiued at a l~iglicrcod. TIIER\IOCOUPLE If-ELLS ASII ISSTRUJIEXTS. Industrial-ty11e t l ~ c r ~ n o couples are made in several r a y s depending on tllc type. Chrmuel-alumel and iron-constantan wires are usually tristed v i t h t ~ v oturns and m l d e d a t the ends wit11 a d-c carbon arc' using a flux sue11 as borax. The ends of copper-constantan and platinum arc not twisted but usually just fused into a round head. For platinum a carbon arc is used and for coppcrconstantan, a soldering proccdurc. The rotnniunly used \\-ires vary in size from 0.032 to 0.1285 in. in diameter. Platinun~is usually 0.02 in. in diameter.

p"

COVERHEAD

SSTD,

IRON PIPE SIZE Y R O U G H T IRON NIPPLE

-STD.

PIPE T H R E A D

L E N G T H OF IMMERSION

Fig. 20-7. Tl~r~nocouple assrmbly. (Courtesy of Minneapolis-Honey\~ellRegulator Compnny.)

-we So niany processes involve corrosi~efluids and fluids under pre.& that bare tl~ermoci~uples are scldom used. Instead the tlrermocouple is inserted into a nlanufactured x~ellwhich is provided \$-it11 fittings for mounting on a pille or pressurc vessel (Fig 20-7). Instruri~entmanufacturers offer these assenlblies conlplete with tl~crn~ocouple, two-holed veramir insulators ior the wires. ~vell,and ter~ninalilea11 x i t h cover. The most eoninlon veil materials are cnrhon steel, stainless steels, and chronliutn steels. The speed of response of a tliern~oconpleasse~nbly (well and thcrmocuuple) can bc increasd and thennocouple errms decreased by using s n ~ a l ldiameter, thin wells, and couples of lo\\- mass. The enor for tcmperature n~eitsuren~ent uf gascs can be further reduced by increasing the fl[~wrate around t l ~ cassembly and by interposing a radiation screen between the co~lduitwalls and thc tl~ertnocoupleassembly. I n all cases the thcrmoconple well nlust make gaud contact wit11 the ~vellhudy t o insure rapid response. OF EMF. The irrstrulncnts used for rccording tl~ermoMEASUREMENT couple emf's in terms of tc~npcratureand controlling processes based on the nieasrlrcd tculpcrature arc usually ~ ~ o t m i i n ~ ~ i ~ r e rcircuit.;. - t y . ~ , e Tire

t

Process Instruments

513

mnl of the tl~crtnoc~rul~le ir l~alancedagainst a known emf produced by a Ilattery across a calibrated slide mire. The battery is periodically and auton~aticallystandardized against a standard cell. A number of methods are used for halancing the thermocouple emf and thus indicating and recording the temperature hy movement of the contact on t h r ~lirlc77-irr. The iimple potentiomctcr circuit can hr i ~ ~ a l l c to perform all operations nutomatically. Cnbalance in a galvanometer may be detected by a continuous system 11-hich rnomcntarily clamps the g:~lranomett~r pointer in position and thcn moves the slide wire hy means of :I mutor until lx~lanccis r e a c h ~ d . This type was for years the standnrrl provess instrlni~ent. Norc recently, h o w v e r , high speed instruments hnsetl on electronic circuits maintain an almost instantnncous or continuous balance. I n several of thcse the galvanometer has been rcplaecd by a devicc n-l~ichconverts the d-c thermocouple current t o a-c. This is follo~vedby voltage amplification and the voltage is applicd t o the motor. These instruments are rapid, rugged, and extremely accurate. T l ~ c Icngth of a 12 in. chart can be trarerscd in one second. It has, therefore: hren posiilile to offer m r h instrunimts for measuring and recording a nu11111cr of different te~nperaturcpoints on one cl~art. The cold junction oi the therniocouple circuit is a t the instrument. R a t l m than attempt to maintain it a t a constant temperature, an autumatic cold junction compensator is provided. This compensator is n resistor in the potentiometer connected in parallel with the slidemire. T h e resistor is made of a material whnse resistance is sensitive to temperature d ~ a n g e s . The change in resistance causes a niovenient of the slidewire balance pwition so as to compcnsatc for cold junction tcnipernture cl~anges. LEADWIRES. Lead mires must be used properly if thcrmocouple mcasurements are to he accurate. Llsually it is impractical t o use the thcrmocouple xire n i a conductor from the junction all the way t o a remote recorder. I.eatl vircs which are cheaper and easier to handle are generally cunnectcd to the heavicr thernlocouple wircs a t the head of the t~l~ern~ocouplc well, and conducted to the instrument. If the temperature a t the head and the cold junction a t the instrument are the same, any suitable conductors can he used. Since these two tclnpcratures arc not usually thc same in process installations, lend wires of similar thermoelectric properties t o the tl~crn~ocouple must he employed as lead wires. Iron-constantan anti copper-constantan of snialler dianicter than thermocouple wire are used as lead wires for their respective tl~cnnocouples. The lead wire material can often he made of rejected thennocouple material sincc it must only he similar to the thern~ocouplenletal in the temperature range oi the instrument. Iron and copper-nickel alloy are used for con-


Process Instruments

nection respectively to Cltromcl slid Alumel; arlrl copper and copper-nickel alloy, to platirium and platinum-rllo(li11111. Lead wires can be insulattd in many r w y ? riqimding (in the atrnosphere. Insulation such as enamel, rubher, ashest.os, glass fiber, and eotton are on the market.

the total radiant energy coming from a hot ohject by focusing the energy with a lens on a thermopile ( a numher of thermocouples connected in srriesi. The thermopile generates an emf proportional to the radiant energy. If an object being measured approximates black body conditions mcli as a furnace flame, tlic energy transmitted is proportional to the fourth power of the ahsolute temperature of thc object. The familiar manually operated optical pyrorneter compares the intensity of monocliroinatie radiation roming from an ohject to an adjustable standard source. The radiation from the ohject and from a tungsten lamp are compared through red filters. The current to the lamp can be varicd by changing a resistance until thc two images match. The meter is calibrated for temperature in terms of the resistanec variations. o cells One type of automatic optical pyronleter utilizes t ~ photoelectric to compare the energy from the hot ohject and a carbon filament lamp. Tlie lamp currcnt is autonlatically varied to bring the two photocells into equilibrium. This current is then proportional to the temperature and can he used t o actuate a recorder. Tlie instrument is instantaneous and can rcqiond to a 200' F change in less than :& of a sccond. I t is thus valuable for measuring temperatures of moving ohjects. Tlicse high temperature pyron~etersare more familiar in stccl mills, hut they are used in chemical plants particularly for controlling rutary kilns and furnaces.

514

The resistance thermotncter, long a standard means for precise lahoratory temperature measurement, is also becoming more important as an industrial instrument. I t is competitive xvith the thermocouple in the temperature range of -300" F to 950" F. Although more costly and hulky, and slower to respond, it has greatcr sensitivity and requires no cold junction compensati~in. OUTER B R I I l o E O C ~ B R EGLLISS T U B I N G VARNISH I M P R E G N A T E D

B R A l D E O F l B R E GLASS T U B I N G VARNISH IYPREGNATEO ,MING&HIN

YlNDlNG

515

~ 5 8 E S T O SINSULATED COPPER W I R E

Fig. 20-8. Resistance thermometer assembly. (Caurtcsy of Minneal~olis-Honeynell R ~ g u l a t o rComlxmy.)

Resistance thermometry utilizes thc increasc of resistance of metals with temperature. A typical thermometer hulh as shown in Fig. 20-8 consists of a wire-wound resistor 1% in. in length. The Manganin coil connected in series is used to adjust the temperature-resistance characteristics. These bulbs are installed in wells similar to those for therrnocouples. Nickel is the most popular resistance element material since it is inexpensive and has a high change of resistance with temperature. Platinum is more accurate and can be used for higher temperatures. The resistance element is made a portion of some bridge circuit such as a Wheatstone bridge. A direct current is supplied by a battery. The change in resistance of the bulb unbalances the bridgc, and the unbalance is detected and corrected in a similar mallner to that described fur potentiometer circuits for t~hermocouples.

OPTICALA N D RADIATION PYRDMETERS Radiation or optical pyrometers are used for measuring temperature above the ranges of other mstruments. Rad~ationpyrometers measure

Pressure Measuring Instruments Bourdon-Type Gage The simple Bourdon tube and it,? modifications are the most commonly used pressure measuring devices in the process plant. The Bourdon tube as shown in Fig, 20-9 consists of a closed hollow metal tube elliptical in cross section. It is bent in a semi-circular shape, fixed a t one end and connected at that end to the pressure source. Application of a pressure higher than atmospheric causes the tube to unwind while a vacuum causes rontraction. By means of a connecting linkage and a gear and pinion, a pointer is made to move over a calihratcd scale. An approximate linear rclationsliip between pressure and scale movement exists over ranges of moderate size. The most familiar Bourdon gages are the indicating dial gagcs which are cheap, rugged, and acrurate (?I$ of 1% of scale range for industrialtype and '/2 of 1% of reading for laboratory models). They are cotnmoil in all parts of process plants, and are available in a number of ranges from 30 in. of mercury vacuum to 10,000 psi prcssnre. Laboratory test gages rapahle of measuring q i to 100,000 psi are also produced. Althuugh the simple Bourdon-tube element may be used for moving a

517


Process Instruments

pen linkagc of a recordcr in higher prcssure ranges (300 psi to 20,000 psi), spirally 11r helically ~vrappcdBourdon elements arc niorc comn~onlyused in recording instruiilcnts particularly for the loxver pressure ranges (0 psi ti1 4000 psii. The flat spiral or a helically \\.rapped eie~iicntd l produce largcr ~leflcctionsa t t h t ~irec em1 for a given pressure differential than t l ~ c aililple Hourdun tubc. Thc NOT-ementis in effect the con~binedaction of

measurements. JIetnl Lcllm!-s and diaphragms operate ~ v i t nmch l~ greater smn-itivity in t h ~ s eranges. Several 11rlIon.s ~ l e ~ n c narc t s shown in Fig. 20-10. The higl>crpressnre \ - ~ to compress it acting U I I tlic outside of tile lolv prer$ure i ~ e l l o ~tends causing a liointcr tu m > r e l'hc range of the i n ~ t r u n ~ c nist dctcrmincd I,? tlie stitl'ness of the spring n-hicli is located in tlic scaling 1iellon.s on the right. IIerc as in othrr iustrumiwts the pen nioven~entcan be linked

516

CASE MOVEMENT HOLDING SCREWS

iyzFig. 20-9. Buurrlon tnhc pt.rsan.e gage. N a m i n g Mnxn-cll and Muow, In<:.)

BOURDONTUBE POINTER TIP CONNECTING LlNK SCREWS MOVEMENT CONNECTING LlNK MOVEMENT SLIDE SCREWS HAIR SPRING SOCKET SCREWS 12 SOCKET 1 3 PIPE CONNECTION 14 DIAL PIN

"TO

POINTER

(Cuurtes,v uf .Lshcroft Gage Division uf

a number of sinqile Bourdon elenlcnts cun~icctcdin scries. This greater movemcnt is necessary for operating t h r ~ u g lauitahle i mcchanicnl linkages, electrical contacts, pneumatic systems, and recording pens on contrdlcrs and rccorders. Bourdon tube materials used are carbon stcel, stilinlcis stcel. vnriuu: cliro~iiiunisteels, bronzc, and beryllium copper. The choicc of mnteri:%l depends on tlic pressure range and fluid being measured. Bronzc tu11es arc sclccted iiiust frequently for prcssurcs bclo~v1000 psig. High prcsburcs and corrosive liquids rcquire alloy steels. For certain highly corrosive conditions it is prcferal~leto isolate ?.IE fluid from the tuhe. This is accomplished by providing a flexible diapl~ragni~ i t iiicasurcd h fluid on one side and a realing or transmission fluid (oil) on tlic other side in contact with thc Bourdon clcnient. Stcam prersurc gages can be protected from high tcn~pcraturesby interposing tuhing having m e or t ~ v ocoils between the pressure t a p :~ndtlrc gage. S t c a ~ nconrlenses in this crude atmospheric cooler and is trapped in the coils. The temperature in the gage is thereby liept bclow that of tlie steam. Bellows a n d Diaphragm lnstrumenls

I n the lower pressurc ranges, below 30 psig, and for vacuum, more sensitive elements than the Bourdon type are require0 to 11rot111crri:li:~l~lr

t o pticu~naticur clcctrical systems to affect control of a pri~cebs. Belloiw elenlents arc used in ranges from 100 in. of n-atcr t o 30 or 40 psig and a t 10 to 30 in. of mercury vacuum. For the l o m r ranges of piisitivc prcssure coum~unly et~counterctlin ~r~casuring furnace draft,s (0 t o 40 in. of water) a diaphragm clemcnt of lrntlier or lilastic material is used. It ~ u o r c sxvitli changes in diflere~~tial pressure across it and thc ~i~iivcment can he tr:ln.;fcrrt!d to :L pointer. Fur higllcr pressures up t o 5 p i g nlctallic diaphragms ( b r a s or bronze) arc used. Manometers

I n addition to the familiar laboratory type manomctcr: cliffcrcntialpressure :iier~ury ~iiano~nctcrsand the ~i~ercurylessmano~iietcrs or force-balance instruments discussed under " F l o i ~Mcters" provide relinhle measurcmcnt of prcssurc difYcrentials up to 600 in. of ~vntcr. For l o ~ v pressures one of the sex-era1 bell differential prcssure elenients is often used. T11csc cle~iicntsconsist of a bucket or bell invcrtcd in a n oil bath. One pressure t a p terminates inside the bell and the other terminates uutsiile. TIw bell tllen moves up or don-n d e p n d i u g uu chc ilifle~.ei~tial. This n~ovement is transferred t o a pen. Many other i ~ ~ a n u m e t eor r niaiiometer-like instruments are arailable, particularly for the low pressure range.

518


Electrical or Electronic Pressure Measurement

STKAISGAGE The strain gage which has heen used so successfully for stress analysis uf structural members under load, has been adapted for tlie measurement, of process pressures and as such is called a pressure transducer. The force arting on the gage changes tlie tension and thus the electrical resistance of a group of TI-ires. This change of resistance is proportional to tlie pressure applied and can be measured by a Kheatstone-bridge instrument similar t o tlic one described for resistance tliermometers. The units are built for pressure ranges of 100 to 50,000 psi. They are rugged and adaptable to process rontrol. The electriral impulse may be carried great distances t o the recording and control point.

V.icr.rnf GGER Mercury nranomrters are used extensively in tlle range from 1 mm t o 50 riim of iiierilury. .\I:iuy inrluitrial gage? for high vtacnums del~encl upon electrical or electronic action. I n the Pirani and therinocouplc gagcs changes in pressure of the surrounding atmosphere alter tlie amotint of heat loss and thus resistance of a hot wire through which current is flon.ing. The effect is pronounced below one mm of mercury pressure. I n the Pirsni gage the resistance filament is made part of a bridge circuit and the change in rcsistancc with pressure is rerordrd. The heat effects on tlre filament, produced by pressure change are measured by means of thermocouples. The tempcraturc of the filament in emtact with the vacuum being measured is compared t o that in a sealed rcference or compensating cell. The range of these gages is from 1 micron t o about 700 microns of mercury absolute. For pressures below one micron of mercury, absolute ionization gages are used. One such gage employs a triode tuhe wit,lr constant clectn~n emission. The atmospliere in the tuhe is the same as that of the vacuum being nlcr~sured. Current flow from the tube is proport,ional to the number of ions formed by e l ~ c t r o nbombardment oi gas molecules in the tube. The number of ions formed is, in turn, proportional t o the number of gas molecules in the tube which is directly proportional t o tuhe pressure. The filaments of these gages are damaged by pressures over one micron. A siliiilar gage using a permanent radium source for ion produrtion from the gas niolecnles, requires no filament and can, therefore, operate successfully in tlie range of normal atmospheric pressures down to 0.1 of a micron of mercury absolute.

Process Instruments Liquid-Level Instruments Differential-Pressure Type

1)iffercntial-11ress111.einstruluents are often u s d as liquid levei instrunlentr. One side of a manonieter, for instance. can he connected to a point a t tllr bottom of a vessel and m e a t the top ahove the liquid level. Differential pressure between tlie t ~ points o is an iniliration of the liquid level. Pressure on the lower connection includes liquid static head as well as vessel pressurc. Only one pressure conncction is needed for open tanks and that at the bottilm. This type instrument is often used for level indication of fluidized solids when a displarrment type device would not be satisfactory. I n order to avoid meclranical problems with fluids which may settle, solidify, or cause corrosion, otlier fluids such us inert gas or air may be sloti-ly injected into the vessel* a t tlic t \ differential ~ points. Tire difference in pressure of thf injccted fluid is e q l d to the stntir prewlre of the liquid. Simple Bourilon tuhe p r e ~ n r egagcs ran he uicd wit11 some fluids fur indicating liquid level by the sirlire metlii~iluf differrntial ~~ressures. Float Types

The float or displacement-type liquid lcvel indicator is probably the most corimiou liquid level instrument. This iustrurnelit consists of a buoyant float. The device is connected by piping directly t o two points in the vessel or container. Clianges in liquid level move the float. The simplest type is a ball float connected by an arm to a shaft extending through the chamber or vessel slrell (Fig. 20-11). The m i g h t of the float is adjusted hy tlic use of eouuterweiglits so that it remains in the half-submerged position throughout its range. Irr this x n y the maximum amount of liquid is displaced for all positions of the Hont and thus the maximum powcr is gmerated for both rising and falling levrla. This powcr is trnnsmitterl through a lever to a direct-connected rontrol valve and indicator or t o a pneumatic relay \vhich transmits air prcssure proportional to the lcvel to a recurder or controller. The operating range of these units is narrow (approxi~nately20-in. niaxinium lcvcl change). The displacement-type float, unlike tlie ball-float, varics in displacement depending on the level. A long cylinriricnl float is designed so that the float lrangs free a t zero or minimum lcvel and is completely or approximately submerged a t maximum level. Fig. 20-12 illustrates the *The flow of air cnn l,e eontroilrd h? n ro(nnwter

01. jipht-fwd

li~dhle~.

521

Process Instruments


of the float tinics thc length of thc float rod. Thc huoyancy of the float

nffrcts the tnngnitude i ~ fthe turning momeni. Thus by proper selection of float density, ~limensions,and length of the float arm. an instrument ran he designed for the sensitivity aud accuracy required for a given job.

2 25" DlAMCTL9 1A"LONG

~~'wATCR LlVEL

FILTERDRIPWELL

LEVEL

WATER DISPLACED WEIGHS 1 1 0

Fig. 20-12. I'rinriplcs of displacement meters. lator Cunipmy.)

W A T ~ RG~SPLACED WEIGHS 2 L B

(Caurtrsy af

hlnson-Xcilnn Rrgn-

T h e range of displacement-type floats is froin 14 in. to approximately 120 in. They are very accurate particularly on l u x density fluids. Their high sensitivity has also made them very popular for interfacial level control and measurement.

CONTROL VALVE

Miscellaneous Types

Fig. 20-11. Float-type level eontrollcr and r:tlvc. Rrgnl:itor Company.)

(Cowl.trsy oi Mason-Trilnn

basic principles by a simple demonstration. T h e variat,ion in forre on a spring scale and the moverneut of the float is illustrated for threr levels of liquid. If instead of a spring scale a torque tube as in Fig. 20-13 is used, the twisting of the tube is proportional t o the level of liquid. This movement is made t o operate a pneumatic system which transmits a proportional air pressure to a recorder, alarm, or controller. The moment acting on the torque tube is equal t o the dorrnward force

There are Inany other typcs of level ~neasuriugdevices. A diaphrugm phced in the bottom of an open tank ran IK urul tu indicntc Ievcl. T h c ~ n ( ~ v e u i e noft the diaphmgni can he balanced by LI force-l~alancepucuniatic system and the resulting air pressure used as a measure of the liquid height. T h e ~ eunits are very sensitirc nnd particularly valuable for viscous liquids whicl~ dl1 not function well in the float-tgpc instruments. Scvcral clcctronic, cl~.ctric:~l, and r;idiuli~~ri derircs are also available. ,Ll~esccnq,li,y ~ ~ l ~ i ~ t o e l c t .ccll t r i c units, gan11n:i radiation, and high frrquency alternating current. The transfer of pl~otoelectricenergy, high frequencies, and ganima mtlietion are all afft~rte(l11y intcrvcuing liquids. Suitahle scnsing tlcvice~can, t l ~ r ~ . e f n r he e , usrd t o dctcrt tlic position 0 1 a Icvcl :it d l tiuws.

.


Process Instruments

523

Visual or M a n u a l Level Gages

.4 n u ~ u l ~ t .of r vi-ual ~lrvicesa r c n~:u~rrfartureilfor iniiirating liqllill level. T h e most ~viilely uscd consists of a glass t u l ~ rronncrtr
.

Measurement of Motion Tachometric Devices

Tachometers of various kinds m a y be obtained for prnctirally any c a a s certain speed. Those for high-speed ( 7 to 10,000 rlnnl ~ n a c l i i ~ ~such turbine generators and centriiugal compressors are usually of the vihrating reed type. This t y p e instrument is used for indicating prin~arily because its indicating mcchanism has little or no force output. Other instruments utilize stroboscopic principles or a driven generating device which in turn has its emf sensed by a translating instrument t o indicate, record, or control. Nearly all high-speed machines such a s turhines are cquippcd x i t h speed-gorerning devices actuated by centrifugal force. T h e primary

Process Instruments


524

a rarcf111 ccono~nicstudy. It n-oi~ldhc un\visc, for instance, to employ a n infra-red analyzes ~ ~ d l c%: n ~lrocc-s temperature at a critical point I W I I I ~ he stati>tically (,orrelated with pr,~iluctquality. A list such as that in Tahlc 20-2 i-. subj'ct to rapid change. Eacli a ~ l dncw ones are introduced. year existing i n s t r u ~ ~ ~ rare ~ i timproved, s

PROCESS CONTROL General

S e a r l y all process-control apl~licationsfor the process plant inrolve an adjr~stmentin rate or cllangr in dirwtion of fluid f l o ~T h e elcments ui control consist of a prilnary or sensing d r r i w , a eccondary clemmt or translation device, gcncrally lcrroivn :is the instnnnent, and a tliird elenlent 1rhic11 effects thc cl~angcin strttam l~ropcrtirs. N o s t control systems utilize pneumatic systcms for operation of the third eleluent.

Limit Controls

The limit-typc dcvire is usu;~lly an elrrtrical contact ~rhicli opens or closes a t preset lilnits. Tlic no\r cilnimon electric eye as used t o C of open doors by intcrr~iptionof a heinn of light is a Y ~ I I I ~ Iillustration $1 limit ( l e ~ i c e . Thc i ~ ~ t ~ , r r ~ i l l of t i ( the i n light I m n i chnngei the out-put of a photoelectsir cell: w11icli chnngc can hc risc11 to o11er:itc micros\vitchee and in turn relays.

Batch Systems

Counting Instruments

Thc simplest type of totalizing or colmting device is t l ~ ctrip countcr. A rntcl~ctrotates a nl~mhrrcdclisk onc tooth ur int~,gcra t car11 cyrlr,. Tlie n m t r o n s e c ~ ~ t i vdisk e iv in turn niovrcl one integer for each revolution of t l ~ cfirst. Physical a n d Chemical Measurements

I n modern process p1;lnts many control laboratory functions h a r e been displaced by automatic instronients cleeigne~l to measure continuously the properties of a flii~vingprocess stream. The development of instrumental analytical tcclmiques for thc labomtory v a s iollorvcd closely by modifications o i 1nhor;rtory instrnn~entsior use a s stream analyzers \vhieh could be installed in t11c plant. Processes requiring a physical n~easurenrent or a clieniical analysis of the psiduct arc burdened \vitb a n excessirc time lag \\-l~cnoperators nmst axvait results from a control l a l ~ o r a t ~ bciore ~ r y changing conditions. Even though the initial cost limy be high the use of stream analyzers r n c l ~ a s infrarcd spectroplioto~~~ctcrs have prured profitable in poccsscs rcquiring rigid quality control. T h e continuous record eliminates time lag and prevents llroductiun ui large quantities of pru,luct ~v1:ich do not nlcct specification. A list o i some of thc instruments used to rncasure clrcmical and physical properties is given in Table 20-2. These instruments have been adapted for continuous stream analysis. Some of these instruments arc costly and in such cases tlic decision to usc tlmn most be base11 on

525

-

Bi1tc11 s y s t m control usually involvc? a simple control 1rhich \\-ill allow n certain desircd cunditim to I J ~reucl~eclin a nonflow system and continue to maintain that condition until completion of the process. .ibatch system may bc illustmtccl 11y ;I stram-jacketed kcttle filled with a fluid t o be 11r:itetl. Thc controller opens a valvc admitting steam to the kcttle jackct rdlerc i t is condenser1 giving up heat to the walls of t l ~ ckettle. T h e con(1cnsate is c~~ntinuously TI-ithdra~vnby means of a steam trap. \Vllcn the intcrnal fluid re;rches the clesircil temperature tlrc controller maint:lins thc t e m p e r a t u r ~11y o l i e n i ~ ~or g closing the steam inlet ralvc. Such systems are oftcn used in t l ~ cfood industry when a cooking process niuet continue for a n cstcn(lcd leugtl! of t i n ~ c . Tlic operator fills the kettlc and 11uts thc instrument into iq~eratiun. By the use of a timing dcvire the system can bc made to shut-off a t tlrc end of a certain period. If ten~pcratureis not, critical the same type heating can be accomplisl~ed by a jacket pressure control which r.ontrols the steam into thc jacket. Thc ronclensatc trap will ~,imtinuounly\\-itlldraw condensate, and thc jacket \rill be held a t t l ~ csame t c l q ~ c r a t a r ea s long as the prcssure is constant. Location of the primary element in n stirred kcttle is relatively unimportant since all the fluid must ultinrately reach the same temperature, a t xliich time the control will close the stcam valve until a temperature drop is sensed. Fluid-expansion type temperature controllers are most irequcnt:ly nscd in such batrll-type proccsees. T h e instrument may or may not 11c

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opening and air pressure are required t o niaintain tlie telnprrature at the control point. Clianges in t,eniper:iture cause tlic vtilvc to move tow?rd open or slint, t l n ~ sreturning the system t o its original control point. Tlie throttling action produccs a minimum of cycling. If the process load, Iioxi-ever. increases appreciably r ~ na steam heater, fur instanre, the stea~iicontrol valve opening rrquirctl to maintain the system a t the control tcinperaturc must he greater (niore steam is

535

Process Instruments

PROPORTIONAL-RESET COSTROL Reset is done autoniatirally in the proportional-reset instrument as illustrated in Fig. 20-16. Tlie throttling action is accomplished in a similar fashion as deseribcil. Tlie inner bellows is caused t o move by air pressure on the outer hellow n-lii<.li contains a liquid. When the pen niuves from tlie set point in a direction I\-liich makes the flapper move from the nozzle, tlie control valve pressure is lowred. Tlic throttling

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required). The proportional controller cannot correct for this automatically. I t , therefore, lines out a t a lower equilillriu~nteinperature a t I i c i thc corresponding valve position is adequate for maintaining constant tank temperature. This deviation or offset depends on tlie width of the proportional hand (larger for wide hands) and the magnitude of the load change. A wide hand setting produces the niininiuni cyclical action, but the greatest offset with large load rhanges. The narrow band has the opposite effect. I n order to return the instrument t o its control point tlie relationship between pen position and valve position (air pressure) must be changed so that the valve position for the new load will produce the desired temperature. This adjustment or resetting uf the pen position-air pressure relationship must be made manually and is impractical for frequent load changes.

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bellows e q ~ a n d sto lie l e d umlcr tlie lower air pressure, moving tlic inner the flapper bark to!\-ard tlic nozzlc. The liquid 11ellow to the ected by nie:tns chamber of tlie two outer hellous (left and right I is con1 /edt IS always a t of a rcstrirted passxgr. Tlir liqui,l r bl t~ a ~ n h eatr tlie n+ atniospheric pressure. That a t the @ I S iiiomentariiy below atnii~spheri(..~, tlirrcfore, passc.5 graduallv thrr~ngh to the & liquid from the causing the inner hellovs ~ I min.? I hack ton-ard the 'fhis movement mores the flapper away from the nozzle wnrl fnrtlie~l o w r s tlie valve air pressure, and the ryelt, of action just dricrihcd is rcpeateri. Tlic niovemmt of tlie pen away from the flapper will continue in tliis uianner until the control valve reaches the 11oint a t which t,he pen will

a,

m.

536


return tu its set or control lloint. Only a( this point 71-ill'the liquid prcsbures be equal in ear11 hcllun-5. This re-et action, tlicrefore, ~villmaintain the process a t the control point ~.(~g:lr~llcss uf loild fluctu a t 1011. '

PR~I'~RTIOS.AI.-RE~ET-R.~TE COSTROL R a t e actiou is accomplisl~ed hy installing an adjustable restriction between the control valve air pressure linc and the throttling bellom. It has the effcct of slon.ing up the tl~rottlingaction and thus permits the contr(11 valvr to i~vt.r-rorrcct trnqiorarily for :l drangc irl the controlle~l variable. Such action pro(lurcs a faster corrcrtion (luring thc early portiun of a n upsct periucl. I t is llarticularly valuablc for systems having large lags 11ctx~-ecnc11:rngcs in thc syrtcm and cllanges in the measured variable. T h e m t c a~.tionmay hc a d j w t ~ dto suit tlw jiro~,(wronllitions. Sollie pncu~natic control instruments can he adjusted for tlirottling, reset, and ratc (if response to suit most con~plcxprocesses. Each addition to the complexity of a n instrument, of course, increases its price. T h e least costly instrument of good quality t h a t will do the job prgperly is all that is rcquireii. If on- anii off'-contrd is satisfactory for a noncritical process strcnm, i t ~\-iluldbe u~icconomicalt o purchase a morc costly throttling controller with reset and rate action. ISSTRCMEXTAIR

Clean: dry air inust bc provided for proper operation of pneumatic systems, antl for this rcnson distribution piping s11n11ld be ecparatc from plant air systcnis. The ideal systtm has separate air coliipressors, air receivers, and sollie type i ~ f regenemtire deliydrilting unit. Plant distributim systtwls for ilistrumcnt air should hc olieratrd at 111~c.ssurcs abilve 45-50 psi so that distributio~llrcadcrs vill not hc larger than 3 in. or 4 in. nominal hise. A nsnnl pressure is fro111 75 to 85 psi. Instrument air pressure within a process :wen need not exccrd 35 to 40 psi. -4s a precautio~i a g a i n 4 moidure, n drip lcg shoi~ld bc providcd just hefore the prcssure reducer or area tilork valve. It is standard practice to provide a scparatc reducing ~:11vcv i t h a filter and drip a t each instrulrrcnt for maintaining constant air sup111y pre:;. a r e . S e a r l y :ill maintrnance problems other than mechanical n-ear r a n he eliminated if the air sul~plyis clean antl free of nloiiture. Distribution piping should 11e gnlvaniscd and instrumcnt air transmission piping s h ~ ~ u he l d s ~ n a l l~ l i a m r t c rcolipcr or :ilumimn~~ tubing, usuirlly :% in. 01) ~ n a x i ~ u u ~Fittings n. 111113 II(, I,riiss or h r o ~ i sflare-type. ~ Several manufacturers arc now pruclucing ni:~ltiple tubing assemblies, encased in flexiblc armored typc steel ronduit. T h e asrrml)lics save much time in installatiun and also protcct the s ~ n d tlr l h i n ~rluri~rgronstrurtion. Various i I 1 i ~ ~ d r u t~~ltillg. ~ i t i l ~ l ~u ll ~ l e11lu11l : t i c 1n:tri1 I qlcrntors prcfw t11csc 11iatcri:iIs tu cu1q1(~ur ~ I U I ~ I I I I I I I I .

Process Instruments

537

The ~ ~ n m ~ ~ utypc a t i rrontritl instrulllcnt is p?rhnl>s the most fool-proof of all rontrol instruments. T h e development of such instruments has curered several decadcs, and practically all the xell-known instrument manufacturers offer comparable instrunic~ntrbaecd on reliability, simplicity, ndal~tability,and opemtion. Tile instrument iniiustry is, of course. by no lncani stagnant. S e w ilrrrlopn~rntsarc ~wnstnntlyhring offrrcrl. ;in11 the instrmnent engineer mnst attempt to kcep abreast of thc whole industry rather than assumc that only certain manufncturers are capable of meeting parti~:ularapplications. Hydraulic Control

Hydr;~ulically operated controk h a w long h e m widely used in some intlnstri~s. Their use for process cnntrnl, 11o~r.n-er,ir usually limited t o olicrntiiins requiring consi(lrrah1~pun-er : m l t~t-o-pusitiontype control. The :~pplication of l~ydraulicsas a wlf-ci~ntainc(lcontrol ~ncclium ~ v a s extcndcd trcl~rendously during TYorld \Tar I1 The so-called "servo" systems, \~-hicllare uacd extensirely in airplane cnntrols utilizc hydraulic, systems for pusitive and instmtalleous action. T h e components of the hydraulic systcm are a cllsmber for storagc of hydraulic fluid, a gear or othcr type positive-displacement pump, control valves, and tlrc poner unit, xvhirh is usually a piston and cylinder. Generally cach application of hydraulic control llas all these coniponents. I t \vould be possible t o h a r e a c e n t r a l i d hydraulic p o m r systcm in vhich the fluid ~vouldbe distrihutcd to cach user, similar t o pneumatic, rystems. It can be x c n , h m e v c r , that in each case tn.0 sets of piping ~vouldbc rcquired for pressure service to the user and the return systcm to the central nnit. With tlic pneumatic sj-stem only a single suplily or conncctiun is required between instrument and power unit. Furthcrmurc, hydraulic systenis arc generally operated a t l~igherpressures than pneumatic systems and thus require hcavicr tubing. \Yhile t l m c arc a number of uses for hydraulic systems in process rontrol, the charar~teristicejust i:numerated generally indicatc tllc selection of pncumntic controls. 3-0 doubt as thc application of servo-systems hecomcs greater, the use of Iiydraulic units will incrcase. Electrical a n d Electronic Control

ELEVIXICL CONTROLLERS Thc movement of pressure in,strunicnts, potentiometers, antl other sucli i n s t r u ~ ~ i e r ~may t s be utilized to ol~eratc mercury STT-itchesor contacts placed above and hclmv t11c control point. T h e clcctric signal can thcn open or close an ele~?ricnlly o p t ~ a t c i lr a l r c (such as a solenoid valve) or position a reversible motor-operated ralx-e a t the control point. Some 1iroliortiunal : ~ n d prolii~rliot~nl-rwtcontrol instrmnents have

538


electric and electronic means for positioning an electrically operited valve. These techniques have been d e s c r i l ~ e d . f i . V T h cpotentir~mcter instrument is best adapted to this type of ciintrol. Tlic m o v r n r r ~ ~oft tiit, pen is followed by contact with a slitle v i r e resistor v i ~ i r foniis l~ a l~~idge circuit with a similar resistor in rontart n.ith t l ~ etravel of the nloti~rvalve. Suitable relays detect nnllalancc in t l ~ rI~ridge circuit ranrrd hy pen movemcnt from the control point. .\111vciumt of thc iuoti~rv a l w in the proper direction is then initiated in such a way that it ba1:inces the bridge circuit. ELECTRICALLY OPERATED VALVES Several types of electrically operated valves are manufactured. The so-called solenoid valve is perhaps more widely used than any other unit, operating motor-driven type. The solenoid valvr is a ~TVIJ-po~itiun either wide open or closcd. The solenoid valve is often used in ronjunction ~ i t pnenmatir h sy~tcm~. admitting or shutting off air-pressure t o p0n.e~units. Sdenoid valves are very useful in safety applications. If a number of pneumatic systems are fcd through a common air supply, a two-~vaysolcnoid r a l r e may be installed in the system su t h a t plant electrical failure will ciiuse the solenoid t o deenergize and open, releasing air from the system. All control valves on thc system will then assume an emergency position. The air-motor on an air operated valve can be replaced by a reversible electric miltor operating through a gear reduction tu position the valve in accordance with the signal received. Numerous models are available. SIGNALLING Electrical systems are extensively used in signalling remote process ccnditions or the opcrat,ing position of processing cqnil~rnentby means of colored lights a t a control center. Liquid level instrnments are frequently provided with contact switches lvliich indicate process liquid level hy such means. Critical electrically driven equipment can be provided with on-off indicators. The annunciator panel, an early development of low-voltage electrical signal systems is used for many of the above purposes. I t 11as the favorable characteristics of small size, low voltage, and centralization, whereas the more conventional signal lights consume much more space and installation labor. Each is usually installed as a separate unit. The annunciator panel signal system is often used in plants having involved electrical systems. Failure points are cr~nnectedt o the panel and faults are quickly located. ELECTRONIC DEVELOPMESTS Wherever mechanical movement has sufficient power to operate a microswitch or any other type of electrical switch, countless variations of

Process Instruments

539

electric control application are possible. Most of the uses of electrical systems for prucess control are in on-off services, hut the large variety of possible use? of electronirs arc only beginning to be applied t o process ctmtrol. As development proceeds undoubtedly such control methods will find a wider use. SYSTEXICOSTROL The use of electronic principles in process plant instrumentation is at present limited chiefly to conversion and amplification of 1)rimary sensing impulses, but system control by means of electronics is on the horizon. System control in contrast t o point control d l permit control of the total process. Anticipatory control innst usually bc left t o manual cl~angessince presently available instrnnients cannot function until some change occurs a t the primary element. The single exception to this is the instrument rrorking in conjunction nit11 another controller. I n some respects this may be' considered anticipatory control: however. it will he found that the number of variables u-hich can be so contrdled are very limited. I n order to 11roridc system control, all considcrrd variat~leswould have t o be sensed collectively, their relation neigbcd by a couunon instrument, and changes effected according to a pattern, either [re-determined or instrument-determined. It is only in recent ycars that such a system has proved practicable. Electronic computers will play a major role in these developments. Such "computer-control," hovrvcr, requires quantitative knowledge and expression of this kno~vledgcin such a w i y that it can he used by the machine. I t is surprising but true that quantitative knowledge has been developed for only a small nunther i ~ fsiniplc processes. Engineering judgment required in the operation uf so many plants cannot, a s yet, be reduced to a mathematical expression.

P X E ~ M AVS. T IELECTROSIC C COSTHOI. Boyd2 has drscri1)t.d the first complett. refinery n.Iiir11 n.as controlled by electronic instrnments. He has also co~uparedpneumatic control tu electrunic r o u t r d T h e n n ~ i ~ n cnif ~ ~ l signals, e for instance, instead of being convcrtrd to a pneumatic signal and transmitted in tubing t o a distant valve may be trnnsmitted after suitable electronic amplification to the valve as nn clcrtric:~l sigrr:~l. This arrnngement provides much grr:ilc~ s ~ w i i i \ . i t y . '~'III, ( ~ l i ~ t r i ~ ~ :ol~ Iii~o~t ~ d r u i i i e nair t piping not only h u l r1imin;itcs Llie difficulties caused by freezing siuiplifies ii~:l:~ll:tliu~ic moisture in air lines during cold weatlier. The installatiun described requires conwraiun uf the electric signal t o air pressure at the valve ainw motor-11rivcn control valves at this time are not a s fast as pneumatic valves and gears become excessively worn

540


nt a position corrcsl~ondingto the control point. B o y i l ~ n g g c s t s . . t l r c dcxlolnrient nf hydmnlically operated r a k e v i t h indiridual pumps .and niot~~r.; actuated 11y the electrical signal. I n this Inannpr the favorable r t ~ p o n s eeharacteri.stics of the electronic controller could be used. Control Theory

Process Instruments

541

or 11:1vc I I : ~ I . - ~ ~ I<( I, ~I ,I v~i Ie1,1\vxr~d ~e ~ t11v , ~ u t s i ~ l e Control-roo111 . cl,~,r> v i t h lock?. Exit dnors fro111tlw area ~ I ~ a n lnot i l i~r.rlin:rrilyI N 11r11vi~lcrI ill Imrli nf 1 l 1 v ~r:rnvl.lln11l~l nl.s<>I,c inrl~~ilcrl. ( ' O I I I I . I I I i o o i ~ -/1o111~1 ~i 11:1vi:clir.wliu~~:~I (11. t r ~ f f i , r i -ligl~ting. ~l I.:\;l~l,~iio~~proof f l u o r w w l t ligllting fistnrcs :l~ould l ~ ru ~ c r lif tllc crlntrol room is : n r I to I i t i I l : z r r l o n s a r c . An i n i c n ~ i t yof .XI f t - r : ~ n ~ l l r ~

Excellent tl~eoricshave been del-rioped to d c s r i b e tile nunrerous types of control s y ~ t c n ~ s At . t i n ~ c itlic ~ ~ r o j c eengineer t niay find linritcil kni~n-ledgeof t h i ~tlieor!- Iielpful in di.wxsioni of iliflicult control p r d ICIIIS wit11 instrnn~rntcnginwrr. St,veral works on control tlieory arc listed in the rcfercnci.~:mil :ire rciwnn~it~ndcil fm engineers d l 1 clrclnical ~ cngincering Ixickground. engineering I I mecli:ulical Control Centers

Pncunintic m i l clectrmic iransmission per~nitstllc ccntralization of all instruu~cnts. I\Inltimillion rloll:~rIlrocrss nniti p r ~ d n c i n glarge quantities of high q ~ l a l i t yl~rt~rluct c m n o ~ vbe ~ p c r a l d11y n f c c~x p c r i e ~ m dnle~i surronnilings of a modern ~vlio~ c l d o mneed IIIOVE from tl~il~~01nfi1rtah1e air-conditioned control room. TIIC emtrol 11ou.o IIU hecc~mcnot only the nerve renter of the process unit but also the show place. Attenti011 is given to the CII~I-cnience :is n.t!ll as alq~enr:mce of hut11 inside and outside nf the contri~lIhiiusc :is well as the panel board itwli. Instruurent ~nanniacturivshave rcsl~on~lcd to t i i s trenll m i l arc providing shapes and stylcr of inilriunmts that produce not only nrcurntc control but also an :~ttmctivccontrol parlcl. Tyllicnl conlrol 11:11ids ; ~ r cslro~vnin Fig. 20-17. The size : ~ n d:Irrangemuit of eontrd piu~vl-11:~sI I C ~ I I ( ~ I ~ a n g cconsiderd ably \vitll tllc advcnt of gr:lllllic panels (see Fig. 20-17). Tlic graphic pancl provides n simplified f k ~ wdiagram of the process. I t s utility, Irowcvsr, is more l~cnefici:rl to uninitiated than ti, cspcricnced process rs of cmtrill operators, ~ l must ~ uIcnm Lo h n u ~ vall procrss l ~ l ~ a s regardless board an.ange!nents. Tlrc rnii..t important cllangi: caused by graphic panels has heen tlre rcductio11 in instrument size, permitting subsequent rcductims in control p ~ i e Icugth l and thus control roolns. Tlic trend to aniallcr sizcs is :llm evident in instromenls not intcndcd for grapliic panel laynuts. I n arranging the contrd center for the process plant there should he xdcquatc apace hel~indthe pancl for instrument maintcnance. h m i n i ~ n u n ~ of six f t betrwen building wall and instrument is desirable. If tlrc proress is l ~ n z a r ~ l or ~ ~subject ui to fire, lnrge vindow openings should I J installrd ~ 011 thc s l ~ t ~ l t c rsi~lc. c ~ l S111:111 n.in,lons may be provided on tlic side nearcst the prure>s unit. All window glass al~ouldhe shatter11ruof or wire ~ 1 : ~ s-it. least three access opcningr or esits should h r provided in the control ruuni. Door 1lardr~-aresliould bc anti-panic type

l ) c l ~ i ~the i~l or inow is illffil~il~tlt.T l ~ cs:lnie intensity slnk11~Ihe provi~lc-~l h 111e:laing control room :Ipllenrnncc ?:In Ile llallel firc thnn terrazzo. I t is c(nnmon pmeticc for the control building to have a n office for tlre chief or shift operator, toilet facilities, a pantry equipped ~vit11a n electric refrigerator, a sink, and a hot-plate where tlic operators can Tvarm their food (shift ol~rratorsare not urnally permitted to leave the unit I . An anto~nnticallyrliillril KAtrr ~irinkingfountain is aslinlly pro\-iflc~l. A

542


locker-room is sometimes included wit11 slio\ver fncilities so that ~iperatora ran change rlothing a t the proress unit. Snmnier and ~vinter, air-ronditioned control rooms are hrco~ning ronimon, particularly in the warmer climates. If air-conditioning is provided, heating is included in the same system. Ventilation may be arcon~plishedby duct work i ~ by r fans located in tlie huiliiing wall.;. Duct ~ o r dues k not greatly increase costs and eliminatcs fan noise. For some processes the control rooul is maintainrd under a positive liressure, Intake air is rcceived from an elevated stack and noxious funics near the ground level cannot enter the room. I n general the cost of the control room is a very small part of the cost of proress equipment. Attractive control rooms are good morale builders. The slight additinnal cost of a clean and pleasant working space is indeed nell spent.

I

I

INSTRUMENTATION ENGINEERING

Instrumentation developments are continuing a t a bewildering rate. Progressive operating companies and instrument manufacturers rnaintain research divisions conccntrating on thc development of nelv trchniques, and thc instrument engineer who is responsible for the selection and pri~peroperation of instruments in a process plant must keep up with these nev developments hy attending technical meetings and reading journals. I n addition, discussions of new instrumcnt developments n i t h manufacturer's representatives is a necessity. A process plant design and construction project needs the services of a rapable and well-informed instrurncnt engineering group. At present instrumcnt engineers have various backgr~~unds such as chemical mgincering, physics, electrical engincering, mechanical engineering. and diemistry. All havc in common a n interest in precise ruachinery and electronic equipment. The organization of a n instrument cngincering group for plant design project varies in cach company. I n general, howevcr, one engineer is :issigned rcsponsihility for the instrumentation of a section of a plant or an cntire plant. This engineer begins his work early in the development of the plant design. During the process design stage the priiccss cngincer \ d l seek his advice on phascs iif design which would he greatly influenced by instrument sclection. Often the design of a chemical reactor, for instanre, can he greatly simplified by clever application of control instruments. TTlicn process design is complete and the engineering flow diagram is heing developed, all instrumentation including indicating instruments niust bc deterniincd. This is hest accomplislied by first hrginning n i t h several work conferences between the instrument engineer, project

I

Process Instruments

543

engineer, and process engineer. The project and proress cngineers must describe the process, explain the customer's thinking on instrumentation, and indirate the hudget. Kno\dcdgc of instrumentation is very helpful to the process and project engineer in such discussions. V'ith the inforniation obtained from these talks and subsequent discussions i l f critical control points, the instrument engineer is able t o determine all the variables for each process unit and decide which must be controllrd, nicasurcd, or indicnted. Based on his knowledge of the latest and best instrumentation he can detrrrninc all the instruments required for the pr(1cess unit. All of these instruments are then shown schematically on thc engineering flow diagram by means of synlbols (ecc Table 5-3'1. I*:aclr instrument is assigncd a numhcr ~vhiehis used for identification in design. purchasing, and construrtion. Instruments are then selected on the hasis of competitive bids from manufacturers. hlanufacturers' instrument drawings are used in erection as well as a limited numbcr of installation dranings madc by thc instrument department. These installatim ilrawings usudly include typical installation sketches for orifice meters, thermocouple assemblies and others. Such drawings can be used for a number of differrnt types of jubs. Henrc instrument drafting is not a very Iargc task for most projects. Dra\~-ings of tlic pancl board layout must also he made since these are designed fur cacli job using standard pancls which havc been arranged t o suit the particular conditions. Items such as orifice plates are lncatcd on piping dra~vings,but in general fcw detailcd instructions in the form of drawings arc required. Instrument installation niust he done 11y liighly skilled nien supervir;rd hy an instrument engineer. Thc dccisii~nson the various details can bc made nioet ceiinouiically during construrtiun hy the instrummt enginecrin-charge. I n this way a c o n d e r a h l c nniount of ci~stlydrafting time is a~oidcd. Successful and economical instrumentatinn of a proces. plant rlemands cooperation hetwcen the process, project, and instrunlent enginccrs It also requires a mutual understanding of tlic otlicr cngineers' field so that discussions ran proceed beyond the realm of generalities and so that cmcrete decisions can be reached. Thc projert engineer can maintain n spraking knowledge with nr\v instrument ~ l e ~ c l o p n ~ r nbyt s reading the hrief accounts dcsigned for such purposer: in journals of rhemistry and clic~nical engineering. F i ~ l l u ~ i nthe g nlure iirtailrd arrourits in q~ecializedir~strurncntatiun journals usually proves too nlucl~nf a task since tlie 11rqject engineer also ruust rrnd thr eurrcnt literature I ~ I [ ~ r o e e s s ~ cheiuical s, engineering thcurctical dcvelu~lnlents, and pruccsb cquilxiient.

54s


CHAPTER

REFERENCES 1. Brhar. M. F.. "Handbook oi Meacoremmt and Control.'' Part I1 oi 1mti.w m m t s ond datonioiion. 9:; S o . 12 (1954). 2 . Boyd D. 11.. Oil arrrl Gas Jui~,nril,63, S o . 2 i , 139 (1954). 3. R ~ . o n n G. . S. and D . 1'. Camphell, Principlrs of Serr;o,nechrrnirmr, John IYilry 8 Sons. I n e . S e x IYolk.1948. 4. Dike, Paul H.. Thcrmoelectrie Thei-murnet~y,Leeds and Sortlmip Co.. Plr~le-

21

delphia, Pa., 1954. 5. Eekman, Don:il
Honeqwll Rrgulntw Co.. Induzt~.ial Diriaion. Philad~lphia.Pa. 10. Iiajoy, M. H.. 1,td~rstrini Autonintic Controls, Prenlice-Hall. Ina., S e w Yark. 1954. 11. Sprenkie, R. E., Y'rans. A I L C ISOC. . IIILCIL.Engis., 67, 345 (1945).

PLANT UTILITIES Utilities are as indispensalile to a process plant as they are to a city and as much a part of plant planning as the design of process units. The f o l l o ~ i n gutilities will he discusscd with emphasis on dcsign:

Pri~naryutilities ( a ) Water ( b ) Fuel ( c ) Power and process steam ( d ) Storage and m o v r n ~ m tof raw mnteriak and products Secondary utilities , ( a ) LIaintenanre facilities i b ) Plant buildings (other than proccss; see Chapter 23) ( c ) Plant roadways ( d j Railroad facilities ( e ) Fire protection (see Chapter 24) ( f ) Plant seffer systems and \mstc disposal ( g j Plant air ( h ) Plant security P R I M A R Y UTILITIES

ITtilities nhirh are vital to the operation of a plant are called primary utilities. 545

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TABLE 21-2.

Process Lime-soda

2. Hot process phosphate

3. Zeolite softening

Comparison of Water-Softening Processes

Method Calcium and magnesium ions precipitated by lime and soda as C:LCOSand Mg(OH), whicharethenremoved by sedimentation.

Ileactions

+ C ~ ( O H ) =Z 2CaC03 + 2 H 2 0 2. Mg(HCO:,)2+ 2Ca(OH)? = AIg(OH)z + ZCaC03 3. MgS04 + =~ I ~ ( O+ H CaSOd ) ~ 4. RlgClz + Ca(OII)2 = Mg(OH)? + CaCL 5. CaSOa + NazC03 = C ~ C O + I SazSO. 6. CaClz + Na2C03= CaC03 + 2NaC1 1. Ca(HC03)2

+ +

+

+

Calcium and magnesium ions p1,ecipitated 1. 3Ca(HCOl)r GNaOH = 3CaC03 3NnzCOs GH?O by phosphate and hydroxyl ions as 2. 3CaCOi 2Na3POn= Cn3(l'01)I 3Nu&Ox Cas(P04)1 and Mg(OH)z. C a 3 ( P O ~ ) 23. Mg(HCOJ)2 4NaOH = Mg(OH)2 2Na2C03 2Hz0 is more insoluble than CaC03.

+

Objectionable ions removed h r replacement with other ions in the zeolite bed.

+ +

+ N:r?Ze* = CaZe + 2Nn2. Ca(HCO3)%+ HtZe = CaZe + 2H2C03

m

2.

+

m

aB

2

1. Ca++

0

zw

(sudlurn ae,,lltel

(cation exrhange)

(Ily'lrogen .e,~,,t-i

(Acids produced are neutralized by addition of alkali, raw water, or sodium zeolite-treat,ed water.) 'Ze

TABLE 21-2.

Process 1. Limc-soda

1. Hot process

phosphate

I Zeolite softening

=

Zeolite

Comparison of Water-Softening Processes (continued)

Advantages (a) Best for high hardness waters. (b) Removes iron a t same time. (c) Kemoves solids in suspension by occlrision in coagulated mass.

Disadvantages Remarks ( a ) Does not reduce hardness as Cold process lime-soda softening much as zeolite process. is conlmonly used for municipal (b) Control more difficult than systems. The water is treated a t zeolite. its pumping temperature. Hot (c) ~)issolvedsoli~lsnotdecreasedprocess softening is used for in many waters. boiler water treatment. The r m (d) Coagulants required for most ter is steamheated prior to treatefficient sedimentation. ment. The highel. temperature (212' F) increases the reaction and sedimentation, permitting use of smaller equipment.

(a) Greater insolubility of Ca3(POd)2 (a) More difficult to control than Best for boilel. water treatment. permits production of water of zeolite If water is very hard, first stage "zero" hardness. (b) Softened water can produce can be a lime-soda process. ( b ) Best for water of low hardness. deposits if pH is not properly adjusted. (a) Easy to operate and control.

( h ) Produces low hardness waters. (c) Anion exchange resins available

which in combin,~tionwith cation resins can produce demineralized water comparable to distilled rvuter. (d) Cation exchange resins produce low alkalinity aatcr. ( e ) Cstinn resins can treat high alkaline water.

(a) Turbidvatermust befiltered. (b) Treated water often corrosire. ( e ) May be more expensive than other metlrods. Each mise must t~ studid. ( d ) High alkaline nnd acid water should not he used for sodiom zeolites.

2

0

3

5-

H'

Alan? new resins available; rost studies must be made by conrpetent chemicnl engineel. and water. specialist to select the paper method of treatment. The sodium zeolites :ire rrgenec~ted periodicslly by h'aC1 brine; hydrogen zeolites, by mid.

f." f."

552


I c a t metllod fur scale prevention is thc addition of small quantities of surface active agents to the rvater. These, in effect, increase t,he solubility of salts in the n-ater by prevcnting precipitation even when thc salts arc .;upcrsetur:itrd. Corrosion inhibitors such as chromatcs or m-face actirc pl~osphate?may he addcd to prewnt rorrosion by dissolved oxygen. Thesr meth& are usunlly adequate f i r <]me-tl~roughci~oling rvnter systmm. I n circulating cooling systcms build-up of salt concentration is incritable as ivatcr is cvnporatcd in tlic cooling tower. Makc-up ~ a t c rer quired t o replarc these and other losses i4'jr including leakage and ~vinii losses) is small. The boiler water is, therefore, oftcn not diluted s u a cicntly to prevent scaling even ~vhcnsurfacc activc agents are used. Khen this occurs: a portion of the water may be removed for further softening or for sulfuric acid treatment I\-hich converts calcium carbonate t o t l ~ c more soluble calcium sulfate. This treated water is then returned t o the systcm. Many operators h a r e found it advantageous to use lime-soda or zeolite for circulating cooling water zystcms. Treated water is tlrc initial charge to t l ~ ccooling water system and all make-up x e t e r is also treated. Corrosion i~~hibitors are injected and inhibitor concentration checked daily. Demineralized water or condensate must hc used for engine jacket water cooling systems. The jacket v a t e r is cooled by air-cooled or water-cooled exchangers and re-circulated to the enginc. Corrosim inhibitors such as chromates'are used in thc closcd system. Cooling t o w r v a t e r pumping cquipmcnt should be dcsigned v i t h a 10 to 15 per cent safety factor on capacity. The pump head uiust bc mfficicnt t o circulate water through equipment and return it to cooling t o m r inlcts vl~iclr:ire usually from 30 t o 40 ft above grade. All piping must he carefully checked for pressure drop in any type of closcd circul;~. tion system. Electric n ~ o t o ror turbine-driven centrifugal pumps are used. Alternate polver sources and/or spare pumping equipment are installed because cooling ~vateris essential even during cmergcncy shut-down of the plant. Sea n-wter has been ~ l s e dsuccessfully as coding rvatcr especially in those coastal areas with fresh water shortages. Cathodic protection systems employing magnesium anodes located in the floating head and channel of exchangers prevent excessive corrosion, Deposits are minimized hy restricting cooling water temperature inrrcase b c h the point where tile calcium salts begin to precipitate. I)epo& wliicl~do accumulate can he removed by inhibited acid treatment.

I I

plant Utilities

553

SASITARY \V.Y~Y.R Sanitary r a t e r muit bc potable and free from disease-causing bacteria. In n~etropolitanareas city n-attx is usually purrlrnsed for tliis purpose. In remote Iocatior~sor in snu~lltowns a purtion of the treated ~ v a t e rf r o ~ n t l ~ cplant softening unit may be diverted for hanitary ~vatcr. Tile treated ~r-atermust be chlorinatcd to destroy bacteria and then pumped in an independent system. Periodic bacteriological tests establisl~the residual chlorine that must remain in the treated rvatcr after ten minutes to insure destruction of bacteria. The residual clil(~rincis the11 cl~eckeddaily by a simple test. Sanitary xvater system': are operated at 20 ttt 30 p i g since higher prcesures damage standard plumbing fixtures. An elevated ~vaterstorage tank is usually installed t o insure uninterrupted v a t e r supply. FIREKATER The rei~uireu~enta for fire water are intermittent, and it may bc assumed that otlicr senices will he s l ~ n tdown if necessary to proridc sufficient ivnter capacity. 21 coolirig tower basin car1 be used as a reservoir t o llrovide a rclatircly large capacity surge basin, but thc most carnuion storage for etncrgency water is the standard elevated water tank. IJnderrvritcrs-approvcd centrifugal fire pumps are uscd t o boost the rvater prcssure to 150 psig so that the prcssure a t the fire hose nozzle will be 100 to 123 psig. TKOpumps wit11 a t lcast 1000 gpm capacity each are installed. Each has a different source of power, e.g., one, electric motor and the otlrcr, gasolinc enginc. The pump should be self-priming if a suction lift is rcquirecl. Firc r a t e r headcrs must not he uscd for other purports. P r o ~ i s i o n s should he made for emergency connection of the fire w-ater s y s t m ~into the largest reservoir of n-atcr. Usually this is the ran. n-atcr supply sir~oe fire rr-ater rcquircs no treatment,. Sen ~ v a t c ror brackish v a t e r is oftcn used as fire water by plants located along coastal areas.

i 1 I

! !

i

i, I

CTILITY1 v . k ~ ~ ~ Utility n a t c r is used for miscellaneous ~vashingopcmtims such as clcaning a n operating arcx. I t should hc free from scdimpnt 11ut d w i r ~ ~ t require any otlicr treatment. Notices sliould bc posted to n-ar11 ilersonnel not to drink tliis n-atcr. Fuel Fuels arc used in process plants for open-fired heaters and renetore, r ~ l ~ ~ n - f ievaporators, rcd kilns, stcaw gencraturs. g:w turbint~s.:ltl,l i u t i ~ r ~ ~ i ~ l twu~huiticin eugit~es. Tilt. wmimnly u.wl fu?l* ::I.Y [ W ~ I . O I N I U I lirluicls. I I > ~ I U ~ : L I g w solid [II,&M',II : W ~ : d :III,I s d,,, : t t ~ ~~v::>tt, l ~,~,,,IIIV~S.

554

Project Engineering of Process Plants Plont Utilities Natural Gas

Natural gas is the most ideal fuel for the process plant. It requires no handling
0

W

I

l

l

Liquid Petroleum Fuels

A a i d e variety of fuel oils are marketed for industrial use. The U. S. Hurcau of Standards and other governmental organizations hare issued stan~lardsfor many of the common types. I n Table 21-3 the properties of some typical fuel oils are given. The heavy industrial fuels, because of their high viscosity, are delivered in &earn-heated tank cars. The fuel is stored in heated tanks and in largc installations circulated continuously between heated storage and furnace. By t,his means tlic fucl is kept a t the correct tcmperature for burning and constant pressure is maintained a t the burners so that control of firing u.ill he simple. Isolated furnaces can have combined pumping and heating units locatcd near thc point of usc. The lighter fuels such as kerosene and diesel fuel are used for internal combustion engines. Gasoline engines ar? rarely used in process plants except for certain stand-by services, but diesel engines are used extensively. Fuel storage for internal comhustion cngines is simple sincc the fuels used require no heating other than in the engine. A gravity head tank is often located near the engine and is filled intermittently from larger storage farilities. Jiqucfied petroleum gas is used extensively as a stand-by fuel in areas subject to intcrrupt,ion of natural gas supplies. Waste Products

Co~nbustihleby-products of process units may be valuable as fuels. In some cases, honever, they p r o ~ cmore costly than conventional fuels. I f , for instance, thc aaste material is a highly viscous liquid, special pumping systems will he r~quired. In othcr cases, the hy-product may contain water and corrosive materials. Finally, extensive alterations to

1; :L

0

a t

i

s

-

s

n

Plant Utilities

556


the hurner xyctem itself niay tre necessary tu supply the correct air-iuel ratio for 1,rupcr eonlhustion of the waste fuel. I f c11;rngr~sm r h n s these :Ire nrrr.ssary. it may be cheaprr to R-aste the h y - p r ~ ~ d u cint a flare or hurni~igpit. I f rpanti1ic.s of waste products Witable for w r hccomc al.xilahir I them hy mixing wit11 the regular fuel so that l~criotlically,it is best ~ I use I l ~ cfuel to tlic furnace d l he const:~ntin quality. Tlic riiost common vaste or by-product fuels are gases frotn c r x k i n g furnaces, susar canr waste (bagcssc) and \wad ~vaste. h nutnber of interesting uses of xastc products as fuels have been made. One refiner, for instance, uses the products of combustion from ;i regenerator of n catalytic cracking unit. These gases are high in carbon nionoxidc and are t~urnedin a special furnace. Coal o n d Coke

Coal ;in11 coke \\-ere standard fuels for tlic early process industries. Imt ;is oil and natural gas her:uile clicnl~crirnd 11ilx. line5 11-crc cotlstrurtcd tlie use of tlicse solid fucls 11:~sdecline
557

to the utility company and purrlrasc a large portion of the powcr and process steam generated hy the utility. I n most rases, hoxverer, proccs; steam is genelatcd hy the process plant. If tl~cseprocess stcarn rcquiretnents are high (75.000 to 100,000 lb of stcam per h r j , :111 economic study may indicate that paver should also he gcncratcil using liigli-11res.ure tl1rbine.s. Exliaust steam removed from various stagcs of the turbine*: is then used as proress steani. If electric power needs are r e r y great, such as in electrocliemica1 plants, p o m r 111ust be generated a t the plant or 11urchaseil fro111 sotr~c1:1rp hyrlroelectric project. Electrochemical plants limy consume more clert1.i~ pu\\-cr than entire municipalities, and utility companies arc often unn-illing to increase their po~veroutput so greatly for just one user. Furthermore, a plant-c~xned power gcncrnting facility rd-llen designed for large p o w r requiren~entscan be operated as efficiently and cl~caplyas a put~lic utility. I n arcaa 11al-ing Ion. cost natural gas, generators driven by internal conibustion cngiucs operating on natural gar luay p m r c lcsr costly than opcration of stenni-drivcn generators. This is cspeciallg truc ~ v l m direct current is required since I~M-speed,gas-ilri~cn engines cnn 11c directly connected to d-c generators, A s gas turl~inesarc ilnproved r w n greater economics niay he possible. An cconomic study is necessary to select clcetric generating equipment-internal-combustion engine, steam-turhinc, or gas-turbinc.' Each n111st be studied and compnrcd with the cost uf purcl~asedpower.

Power a n d Process Steam Electric Power

Electricity is the primary source of power in the process plant. I t is used for driving pumps, compressors, and other mechanical equipn~eut; for clcctrolytic processes, beating, instrument power, and lighting. Electric power may be purchased from a utility company or generated a t the plant by steam-turbine driven or internal-coiiibustion-wine driven generators. Unless a process plant is located in an isolated area. purchased porl-er is usually cheaper than that generated hy the process plant. Progressive utility companies serving industrial colnll~unities provide excellent service a t Imv rates. I n order to maintain constmt luad they also offer off-peak* power a t attractire rates. Under such conditions it is often difficult to justify the construction of a complete polim plant particularly when the same capital can be invested in n~lditionalproctw facilities that yield higher returns. Onc interesting case of niutual benefit is an agreement h e t w e n s large wc5t coast public utilit,y and several oil refiners." Tlie utility has ronstructed p o w r plants adjacent t o the refineries. The refineries sell fucl *Paver used dwing periods of low residential consumption

Any elect,ric system niust he designed by technically qualified and expcrienccd persons. I n addition t o tlie funda~nentalprinciples involved, :I wurliing knowledge of tlie Natural Electric Codel and cornplete familiarity ~ i t ~nanufacture
Project Engineering of Process Plants Plant Utilities

---

I

Instrument transformers. current and potential Power tranrtormcrr. hrgh voltage. on1 Illled P a w r t r a n r f o r m e m hich ~ o l t a g elmed burning ihqusd ~ 8 t hno" Meter and inrtrumentr

-

SCrvlce entcanre conductors Service entrance egulpment 6 circuits or less Oven 6cirru8tr Grounding Furnaces

Article 4 5 0 Article 2 3 0 . 3 8 4 Article 100. 2 3 0

- - --

.I ..t.i.r .b -7 2 0 Par. 2 3 5 1 A Par. 2 3 5 1 Alticle 2 5 0 Article 2 5 0 . 4 5 0

Air circuit breakers

Article 2 4 0

Switchboards Switches Fuse6

Article 3 8 4 Article 3 8 0 Article 2 4 0

C.p.tit0r~

I CO~~C~~C III

Generators Batteries

Article 4 6 0 Article 4 4 5 Article 4 8 0

Feeders Lightning arrerte,r Outside wiring between buildings Tranrformerr, low voltage Grounding

Article Article Article Article Article

Salefy switches

Article 3 8 0

Panelboards

Altice 384

Lighting b,anch r,rcv\,r

1

Article450 A ~ t ~ c 4l e5 0

220 280 730 450 250

Article210

Lighting tixtvrer

Aitirle 4 1 0

Busways

Azticle 3 6 4

Heavy duty receptacles

Article 2 1 0 . 4 2 2 Article 4 0 0

Por>abieaDc4hnCes

Articie 4 2 2 -

~ a c h i n elighting tranrlormcr. machine 10011

&

Motor disconnect

Arlitic 450. 6 7 0 Adele 4 3 0 Article 4 3 0

Article 4 3 0

ArlicIe 6 1 0

-

559

t l ~ cprcsent practice is to distribute por5-er a t high voltages (4,160 t o 13,800 v ) , and then transform it to lower voltages 1120, 120/208Y, 240, 480, 600, and 2400)' near the area in which it is to 11e used. High voltage .systems have lower p o w r losses. smaller conduit and rircuit breakers, and lower installatioll t,ostr, Heavy-duty svitcllgcar hest mitcd for illant didrihution systems has been standardized a t 4160 v. I t is, tl~erefore,niorc rconomical to select 4160 v for primary feeders than 2400 r Systems having capacities up to 20,000 kvaY may use 4160 v. Above this capacity 13,800 r is used. Regardless of voltage levels all distribution systems should have a grounded neutral to insure snfc operation and ease i l f maintenance. E Q C I P ~ ~ EOPERATING ST VOLTAGES.The operating voltage ree~~mmended by manufacturers of motors and other electrical equipment is given on the nameplate or in operating instructions. The ratings are sliglitly below the nominal distribution v~lltagrrin order to allou- for line losses. Typical motor ratings are given in Table 16-2 of Chapter 16. Typical voltages for lnmps are 120 for i n c a n h c e n t nnd 118. 208, 236, mid 26St for fluorescent. C o r n u l ~ . Power may be distributed through the plant by ( a ) open wiring attached to poles or strurturre, ( b l cable run in metal conduit above ground, ( c ) cable run in metal or otller types of conduit buried under ground, ( d ) cable buried directly in the soil. M e t l ~ o ~ lIn) s and ( d ) are avoided in modern plants since they are unsafe and pure a constant hazard during maintenance operations. Method ( b ) is used for cable run inside buildings and structures. Cable run underground is laid in light-wall galvanized steel or concrete-asbestos conduits. The conduit is encased in a red-colored concrete enrelope (red pigment added during mixingi t o insure ready identification of the condnit during m y future excavations. Conduit runs are located belolr. tlic frost line and spaced far enough apart to allow dissipation of heat, hIaniloles are located a t regular intervals (200 i t maximum for straight runs and 100 ft for runs n i t h bends) so that cable may be pulled through the conduit with ease. The shorter the run between pulling points the simpler the pulling operation becomes. Bends in conduit should be long radius bends and no more than one 90' bend sbould be permitted l ~ e t w e nmanholes. MAKHOLES. Manholes must he large enough to enable t ~ v omen ~ ~ 4 t h the necessary tools t o make connections and pull callle. They are con-

* 6W rolls is less frequently used than the 0t1m v o l t a g ~ sgiven. 1201208Y is R three-phnsc four-wire systmm with the fourtll wire gruund~dn ~ u t r a l . T Line to neutral on 480 v systems. .I scp:unte lighting system is not needed when lamps of thls voltage are specified.

560

Plant Utilities


itructed uf reinforced concrete, and are rectangular or ],ulygonal in shape x i t h cast-iron pre-cast concrete slab covers. The bottom may he soil or concrete, hut if the water table is near ground surface. the manhole Iiottom should be made ~vaterproof. Ladder rungs are set in the concrete sides of the manhole for access and 11~11iron-. are located opposite conduit mtrauccs for use in cahle pulling. (':lble racks are also provided. SI-STEMPROTECTIOS.The plant circuits and equipment must he prot d e d by ilerires u~hiclr open thc circuits under over-load or faulty conditions so that current will not flow. Tlie power feeders or high voltage services entering a plant are protected by m a u u ~ l l yor poweroperated switchgear and ilisronnccting (isolating) snitches (sce Fig. 21-11, Reduced voltages froin transformers feed plant circuits each of n.liich has its separate disconnect (isolating) switch and circuit-breaker. The disconnect ST!-itch is used to open a circuit so that it can he completely isolated for rel~airs. They are not oprrating .sn.itel~esdesigned for opening or closing under load. Circuit breakers are designed to open a circuit when it becomes ovcrluailed due to faulty operation or short circuit. I n this \vay all equipment in the circuit is constantly protected. ~S Electrical ecluipn~ent, EQCIPMESTFOR H A Z A R D OAREAS. ELECTRICAL transformers, and switchgear must be explosion-proof when located in l~azardousareas. Large switching cquipmcnt and t,ransformers, however, may often he located outside hazardous areas or in specially ventilated enrli~suresso that thc expense of explosion-proof construction may be avoided. Explosion-proof equipment is designed t o withstand an internal rxplosion and prcvent propagation of flame through its openings. Any flanie generated internally niust travcl through restrictions which cause extinguishing of the flame. All types of electrical equipment including telephones and drinking fountains may be obtained in explosion-proof construction. Vapor-tight equipment r ~ h i c his merely sealed t o prevent vapor penetration should never be used in place of explosion-proof equipment in hazardous areas. Steam Power a n d Process Steam

Steam is not only a source of direct power for operat,ion of pumps and turbines 11ut is also tlic most useful heating medium in a process plant. Although some plants may purchase electric power, most process plants usually produce process steam. A central boiler house can supply steam for tlie entire plant or smaller (packaged) boilers may he located near tlie area of use. It may prove economical to provide several boiler houses in large plants t o reduce

561

distribution piping costs. .icareful economic stud? sl~ouldbe niade tu ilett~ruiinethe type and number of l~oilersrequired and the must advantageous arrangement of tlie dirtribution system I n the initial stages of stcam generation, 17-ater is evaporated and is in equilibrium ~ ~ - i tthe l i boiling n-ater a t the pressure of generation. Thi: mltcr vapor is called saturated steam and any lowering of tcmperatnrc or incrcasc of pressure n-ill cause runilcnsation to begin. lloisturc in steam is undesisablc for most use:: and is liarnlful tu equipriient sucli as turbinrs: thc blades of wl~icharc eroded acrerely by ~ e steam. t I n most steam boilers, therefore, tlic saturated stcam passes through a heat exchanger called a superhcatcr which is located in a hot zone of the furnacc. The steam is heated above its saturation temperature so that, it will he sufficiently dry to provide moisture-frec steam a t all users. STEAXGI:SISRATORS .4 steam generator is composed of a furnace section d ~ i c hsupplies tlie

heat and a boiler section in which the lieat is transferred t o circulating ~ ~ - a tto e rforni stcam. Flrmnce. Fuel is l~nrncdunder or adjacent to the boiler aurl t l ~ cheat of con~buetionis transferred to the druux and tubes by radiation and conrection. Thc design of the furnace depends on tlic fuel to be used. Solid fuels such as coal are all fed to the furnace by n~echnnicnlmeans. These include the folloving: ( a ) Retort stoker; introduces fuel l~eneathburning b ~ d .

( b ) Spreader stoker; distributes coal above burning bed. (c I Traveling grate. ( d l Pulverizer; pulrerizcd coal is m i s e ~ l i t air and distributed vertically, horizontally, or tangentially into tlie cmnhustion zone. l a ) Cyclone; crushed c o d in high 7-elocity stream of hot air i-.iucs tangentially fro111burner and flows in spiral llatli. Particles form nlolten slag un wall xliich burns readily.

\\'ails of large coal furnaces arc usually xatcr cooled t o mininiiz~ undesirable clinker foruiation and decrease railiatiuu f r m l the r\-alls. 1,iquid fuels must be atomized so that the drops of fuel r ~ d lburn as con~pletelyas possil~le. A numbcr of different typcs of burncrs can be obtained using cithcr steam or mechanical atumization. I n the first t y l ~ e . stem1 flon.s througl~the nozzle with the oil, i.su::ing a t o n ~ i z a t i ~ ~Inn. tlie second type, i~toniization is produced by forcing oil at high lir(~ssurc through a spray type nozzle. Gas burners operate a t 2 t o 25 psi and are made in a number of styles. They are usually designed for altern;~tcfucls ipulverizr0 mill or oil1 i n &is- :LIICI ibil-lirwl .\ir- us \v:~trr-wohdSurnnw iv:illa :n.v :11.0 i~~.qtnlltd


Plant Utilities

563

Fire-tube Boilers. I n fire-tube boilers (Fig. 21-2) water circulation, steam formation, and separation all take place in a large horizmtal drum ( 3 to 7 f t in diameter) situated above the furnace floors so that it will receive both radiant and convective heat. Hot gases pass over the drum and then tlirougli a nuinher of tubes 12 to 4 in. in diameter) extending through the dvunr. Feed\\-ater is inaintained n h o ~ ethe top ro\\- of tubes. Fire-tube boilers are lun. in first cost and because uf tlic large capacity Crom ~ e c t i o n of hailer drum showing water circuiation.

F i g 21-3. Stmight-tnhr. hon-lirildcm type. nnler-lobe boilcr. bustion E n g i n ~ e ~ . i n p - A l p c ~ . h ~Innt c ~) .

L...---J

Fk.21-2.

Fire-tuhe boiler. (Courtesy 01 Combustion Engineering-Suyjerk~eater,Inc.)

furnaces. I n this type direct flame rontact with refractories is avoided by locating hurncrs several feet above the hearth. TYPES OF BOILERS. Boilers consist of surfaces through which heat is transferred and are rlesigrierl for circulation and separation of water and steam. Tliey may be classified gcuerally as fire-tube and water-tube types.

(Cuu~.l*syoi Com-

of the drum operate ~ v r l lunder fluctuating loads common to process plants. They arc, however, limite
564

Project

Engineering of

Process Plants

ever, can be designed fur pressures up to 2000 psig. Scctional-headers are made of forged sea~nlesstuhing capable of ~vithstandinghigh pressure?. T h e tubes in straight-tuhc boilers are expanded into the headers and a handliolc must be provided a t encli tube. \\-it11 the advent of efficient welding tecliniqucs for large drums the bent-tnhc dccign hccaulc pupu1:lr. It eliminated the necessity for hanrlhoIes an11 increased the flexibility possible in rlcrign. 1)ruln; arc n.wl in t h ( w designs to act :is headers :IS well as repar:ttnr~ for steam and m t e r . The drums range from 3 to 6 f t in diameter and have manholes ~ v l ~ i c h permit access fur tube rolling and cleaning.' Tuhcs (2 t o 2% in On) unust be bent so t h a t t h y may enter the rlrulm pcrl)mriicular t o thc h n 1 surfacc (see Fig. 21-4 I. Upper drums arc used for steam separation and the lo~vcrdrum (mud drum) scrwe as a n accuniulator of deposits formed by evaporation. T l ~ c number and nrrangcineut of drums varies with sparc rcquircmcnts :11rr1 opcrrtting conditinns. Two and thvcc dl.un1 huilcrs are most conniion altliougli four drum designs Jverc u.;c
Plant Utilities 565 . h u t h e r type uf iurced-circulatiun design overcomes these disadvantages by recirculation. K a t e r passes through a coil in which it partially ill \I.lliCI1 ~ a p o r i z c . ~Tlir . nristuae of steal11 and x i t e r disrhargps ill :I ilr1~111 ste:m is srpar:~te~lfrom the water hcforc passing tl~rouglia s u p e r l ~ e ~ t c r . TYater returns to the ! I U I ~ ) Imrti~onfor recirrnl:~tii,n,

Fig. 21-4. Circulntion pnttwn in a trpirnl bent-tnhe hoilev. lCor~rtesyof Combustion E n g i n c e r i n g - S o p e ~ ~ i ~ eInr., .~~t~ and ~ , rrprinted hy permission, C. E, Miller, .Ifcch. Eng., 78, K O . 1, 10 (1951).1

All forced circulation boilcrs have smaller tuhcs and less heat transfer surfacc for a given capacity than natural circulation. Higher floa rates and pressure drop. can he tolerated: and the higher liquid and vapor velocities producc ilettrr lieat tranbfer. Standardized and Pncknged Stemn Generators. The hoiler industry

568


Operating prcssurcs and temperatures for stcam generators vary considerably. Efficiency generally increases with a n increase in prcssurc and tculperature, but equipmcnt costs also increase accordingly. Ordinarily generating llressures and tcn~prmturesin tlrc range of 400 psig and 150" F +uperl~catarc satisfartory for a procccs plant. If stetim rcquircnlcnti for p o w r generation arc largc, higher pressure generation is usually more economical. I,o\~-er11ressurc prorest: .team is then ohtainc~lfrom thc exhaust of turbines operating the p o w r gencrators. The selection of steam generator and generating pressure depends on a study of plant requircmcnts and 011eratir.g cost^. Althuugli st can^ gcneration efficiency is of prime importance in tlrc operation of a puhlic utility pon.er plant, first cost or flcxihility may he the niost important consideration for a process plant. STI;..~ GESERITIOX.~UXILIARIES The modcrn steam generating plant requires a largc amount of auxiliary equipment. The more i~nportantitem:: are rlisrusscd belo~r.. FEEDWATER THEATISGF~CII.ITIES.The equipnient required for icedwater treating includes cl~eniicalstorage and hnndling facilities, filtcrs. x a t e r pumps, tanks for settling and storage, ulixing equiplncnt, proportioning pumps, and sludge disposal facilities. h large portion of process s t c m in somc plants is returned t o the boilcrs aftcr having been ct~ndensedin heat exchangers and other users. If the makc-up required is small, evaporators can bc used to supply distilled make-up water t o the boilers. Large powcr plants using condensing turhogencrators invariably use eraporators to replace slnall v a t e r iosscs from the system. Partial treatnxnt of the ran. Tvater is necessary t o avoid frequent descaling uf the e ~ a p o r a t o r . HEATERS).Stcam FEEDWATER HEATISO( E C ~ S ~ ~ I I ZISII E R FEEDWATER S generating plants exl~austm n e heat at Iun. l r ~ e l sof availability such a. cxhaust steani and flue gases. These niust IIC used for ~iiaxiniumfuel economy. One user of this heat supply is the fccdu-ater heater. I n addition t o conserring heatl feedvater heating reduces thermal shock on i c increases hoiler capacity. hoiler parts and in s ~ ~ ncases F e e h a t e r Ircaters usc cxhirust or live steam either on the shell side* of shell and tube heat cxchangcrs or by direct contact of steam and water in a deacrating heater. I n dearrating heaters m t e r is sprayed across baffles or trays countcrcurrent to cxhnuat steam. Tllc n-ater is heated and somc steam condensed. 811 uncondenscd stcani and noncondcnsable gases pass to a vent condenser which condcnses the stcanl and vents thc gases. Dcarmtion of f ~ c ~ l ~ v i i~nw1ss:1ry ter to reduce boiler corrosion. S o u ~ c * S < X > ~l,,~:,lt.rs ?

l,xr,, >l?:,u

"1,

th l,,hs i k .

Plant Utilities

569

power plants use shell and tube feedwater heaters fullo\\-ed by acparatc deaerators operating a t subatmospheric pressure. These vacuum deaerators reduce dissolved oxygen in the watcr to a minimum. Feedvater can he further heated by exchangcrs called economizers located in the path of Hue gasps from the boiler. The most common of these consists 11f a number of 1:-tube sections spaced closely together. Fin-tuhes arc used on many designs t o increasc heat t r a n ~ f c r . If w ~ t e r scales badly, the removable return bends can be installed on one end. FEEDVATER SURGEDRUJI. Heated fceclxatcr and rcturncd condensate arc usually accumulated in a vessel n.1iich provides a surge chamher for the feedwater. Thc deacratiug f e e d ~ a t e rhentcr can be made a part of the vessel. Such a reservoir is more nccesrary for the process plant p o n r facility ~ i t hvarying loads than for the steady loads of puhlic utility p o w r plants. BOILERFEEDWATER PUMPS. The treated and deaerated feedwatcr is taken f r i m a feedwater heater or burge cha~uberand 11unipcd into the steam generator. Feedwater pumps lnay he driven by electric motor or steani turhine. Generally turbinc drircs are more easily controlled. 1\Iultistage centrifugal pumps are uscd in nearly ail installations and a t least one spare pump is necessary. I n larger installation.; several 11umps may be used in parallcl or scries t o provide flexibility. Sufficient net positivc suction head must he provided t o prcvent vaporization regardless of arrangement. FUELSUPFLT. Storage facilities must he prorided for all types of fuels except natural gas, Manufactured gas, however, sometimes requires a gas-holder or prcssurc storage system for load surges. FORCED AXD ISDUCED D R U T EQEIPMEST. The function of the draft system is t o provide sufficient air for co~iipletecoiubustion of the fuel. Steam generators may operate on natural draft. induced draft, forccd draft, or combinations of the three. Natural draft is used for small furnaces, and the stack must he designed to dcvelop the necessary pressurr differentials.* Practically all largc steam generators, hou-ever. use forced and induced d r a f t equipment. The forccd draft system injects pri~llaryair ~i-it,hthe fuel and secondary air into the furnace a t or near the burner openings. The induccd draft systcm imposes a rcduccd prcssurc on the furnarc by rcmoving the hot Huc gases through a fan: therehy inducing primary and secondary air. Since the air-fuel ratio is critical, fire-box runditions must he closely *Head available = H ( p . - #.) 1 ~ 1 1 ~ 1 . iH l = cllirnn~yheight p. = density p. = averngc

ai o~ltsidrair, and stack-gas dmiity

570

57 1

Plant Utilities Project Engineering of Process Plants

controlled. Both the forced draft and the induced draft f a n and suitable dampers can I I ~ .wed for control. Natural draft units n ~ u s tbe controlled by dampers alone. AIR PHEHETERS. The incmiing air is frequently furced through air preheaters to exchange heat wit11 the hot fluc gases. Heat transfer surface may be thin plater or tubes. If preheaters are not used, part uf the incoming air is often conductrd through channels in the furnace refractory, sometimes the floor, so that the entering air is heated. Sool BLOWERS.All fuels deposit noncombustible dust on furnace sur. faces. The deposits are heaviest for solid fuels and are negligible for most natural gases. These deposits insulate heat transfer surfaces and reduce efficiency and must be removed. Soot blowers are locatcd so that parts of the heating surface on which soot accumulates may be cleaned. High pressure steam. air, or a mixture of .team and air passes through tubes having a series of nozzles. As the cleaner is rotated axially, soot is forced from the heating surfaces. SUPERHEATERS.Equipment motivated by steam requires dry, superheated steam in order t o operate efficiently and \vithout erosion. The efficiency of stcani generating units with capacities above 15,000 lb per hour are also improved if the steam produced is superheated. Superlicaters, therefore, are installed in most modern boilers. They may be heat exchangers exposed t o hut stack gases (convection-type) or radiant encrgy from the flame (radiant-type). As thc load on a boiler is increased, flue gas flow and temperature increase faster than steam flow, and convection-type superheater outlet ternpcrature increases. The reverse temperature effect orcurs in a radiant-type superheater, but a combination of the two gives a reasonably constant steam outlet temperature regardless of load. Superheated steam a t a particular temperature for operations such as stcani stripping is often supplied near the point of use by heating plant steam in the convection section of a direct-fired reboiler. DESUPERHEATERS. Somc evaporators for chemicals which boil a t low temperatures rcquire saturated steam. If the central steam plant produces superheated steam, saturated steam can be supplied where necessary hy means of a desuperheater. Dcsuperlieaters may be spray-type or shell and tube exchangers. In c r as condensate or feedwater is sprayed the spray-type, pure ~ ~ a t such into tlie flowing steam. Regular rooling water is used in the shell and tube design since there is not direct contact, between xvater and stcam. ISSTRUMESTATION OF STEAMPLANTS. Instrumentation for steam generation plants is relatively simple rompared t o process plant instrumentation. Controlled conditions are:

( a ) Steam prersure. ( I n certain high-pressure, high-temperature generators temperature may be as critiral or more critical than pressure. Temperature rontrnl is not ordinarily important except for large electric power generation plants.) ( b ) Air-fuel ratio. (c) Feedwater control.

The action bricfly is a s follows: Increased demand on the steam rlistrihution system causes a drop in pressure. Pressure instruments acnsc the drop and increase the fuel flon-. Air flow control is correspondingly increased by a ratio coutroller wliich increases the speed of air fans or nther controls which operate dampers. As boiler pressure drops, steam generation increases, lowring boiler water l e d which causes the feedwatcr levcl control to admit more fecdmter. The same action takes place in reverse when steam pressure increases. Feedwater in-put cannot bc controlled satisfactorily by level alune. h drop in steam prcssure nil1 increase fccd~vaterflow hccause of tlie rcdnrtion in pressurc. If water level alone controls, the feedwater input will be increased hot11 hy a steam pressure drop and a drop in feedm'ater level. For this reason differential pressure controls utilizing steal11 generator pressure and pump disrhargc prcssure are used for feeda-ater pumps. An increase or drop in steam pressure causes a controlled change in feedwater punip discharge pressurc t o maintain the same differential pressure across the feedwater level-control valve. Steam generator size and tlie type fuel influences the selection of control s systems. Solid fuels rcquire much more complicated control ~ vt ems, because of the mechanical firing equipment. Liquid and gaseous fuel systems can be controlled by changing the pressure on the fuel systenl. I n addition t o the above instrumentation, many recording and indicating instruments are necessary. D r a f t gages, temperature indicators or rzcorders, flow and pressure instruments are used extensively. Continuous analyzing equipment record the conlponcnts of flue gas for the largcr generators. X a n y power plants are being constructed out of doors similar to process units. All instruments are centralized in a control room and controls are completely automatic so that it is rarely necessary for operators to leave the control ruuni. There units arc opcrated 11y a small crew and contrast sharply with early "hand-operated" boilers.

."

STEAMDISTRIBUTION SYSTEMS The piping for steam distribution syrtcms must be carefully designrd t o insure long trouhle-free operation. The ideal steam system should supply steam continuousls with the minimum of maiutenance.

572


S I I Line yizcs for steam lincs should not hc governed by presjure drop alonc. Heat losses can be reduced by using big11 velocities, a,? augge~tcdin Table 21-5. I

TABLE 21-5.

Steam condition Satunited

Conventional Velocities for Steam Distribution Piping*

Rensonahle Service velocity f t 'min Heating 4000 to 6000 (short lines) hliscell:~neous~ 6000 to 10,000 50 nn(l up Saturated 7000 to 20.000 hIiscellsneous Superlreated 200 and up * Rcprintcd liy permission, Crane Tcrlmicul Paper S o . 1W (1042), Crane Ca., Chicago. Ill. iThc docity of deaul, in the casr oi builm Imds, should be Ioivrr than 1nl.gc tnhinc leads hecause of t h r stop-cllerk valves whicli m c necessarily instnllcd ~n tliese lini,~. A lrigli velocity tlirougli the stop-check rake would eausc an cxccsairc pressure drop d ~ i r hmay he rletrinrental to efficirnt opcrntion. Yressure, p i g 0-15

I.AYOETo r DISTRIRCTIOSSSSTTX Steam distrihution piping may be run at grade on concrete pipe "slccpcrs," (ir prefcrxl~lyaborc gradc on structural-steel or reiniorced-concrete supports. Piping run a t gradc is an obstacle and must, he run over or nnder roadways, r h i c h creates a pockct in the line where condensate can be trapped. Condensate must bc accunlulated a t predetermined points in distribution piping and a t users, and then discharged continuously by steam traps into a condcnsate system for return t o the boiler house. The return piping is most conveniently run near the main distribution piping so that, steam traps on the main line may discharge into the condensate line. If several steam systems a t different pressures are used, steam traps can be arranged t o discharge into each succceiling 1 o ~ r . epressure ~ scrrice. Condensate accumulation a t points othcr than thosc servictd by steam traps must be aroidcd by carcful arrangement of valves and piping.$ Branch lines from main headers should rise rcrtically from tlrc top of the lrcader and then run horizontally as required. Block valves can bc inrtallcd in the horizontal run of piping and condensate r i l l thcn dvain freely on either side of the valre. By-passes aronnd valres should h r located above the valve and a m a l l bleed installed between the b y p a s s ralves. 1)rip-legs arc instailed in lung horiz~mtnlruns of piping to acrnmnlatc condcnsate. They are constructed uf pipe i d pipe raps in two sizes larger than line size and are w l d c d vertically in thc run oE pipe with the inajor portion extending helon. the horizontal line. A vertical platc is installed in the drip-leg tu deflect ste:nll and moistnre into the leg. 4 s $In cold uliniates frrrring u i i.undcns;~li!trnppwl in lincs e;iuca great d i i i i r u l t i ~ ~ .

1

Plant Utilities the ~ t e n n lnrakes a 180' turn, the w t e r d r q x out. A steam trap is connect~ilt,i the hottnm of the dripleg for rnndcnsatc r e m o ~ a l . H r o c s VAI.YES. Block valves are located in all hranch lines as they I I i n l l c r SniaII i ? i i n or 1 in) I ~ ~ - - ~ i aarP s s cinstalled ~ for rrarm-a11 ~mqm-csso that a cold line may 11c~ \ - a ~ n np m l gradually bcforc admitting fall steam Rov. A \)lock r a k e is usually lwatcd at each uscr :is on added prec:~ution. Some colup;n~i~~s. Iion.cvcr, install only one l i l ~ ~ cvnlvc k at the lml~ler on exliaust stcmn lincs sincc exhaust steam is lcss dangcrous Failurc to close tlrc lieader valrc, ho~vever,will causc the discllarge of largc amounts of steam around the area. IISKLITIOS. Insulation for steam piping, especially main hcailerr, sh~nilclbe selcrted and designed for long life. E c o n ~ ~ m rtndiez ic of uptimum insulation thickness for steam lines are usually itmightfor~varclsinrc costs arc nlore clearly defined. Such atndics should be made for the lnrgr dianletrr liiit>>. Internal Combuslion Power Intcrnal combustion cnginw are uscd in thc process plant as low-speed. heavy-duty drivers of reciprocating ~ n ~ t n and p s cotnprcssors, and electrical power generators. Large reriprocating eomprcssors are generally built integral n-ith the cngine driver-the samc crank shaft is need for bi~tll p v e r and reciprocating machine (sec Chapter 15). Reciprocating pltmps arc furnishcd as separate units x i t h p o r c r transmitted through reduction gears and shafting. Fuel systems for internal combl~stionengines eliould he designed to prevent foreign material from entering the cngine. All fuel should he filtcrcd regardless of origin, and piping follm\-ing the filter shoul~lbc winferrous or stainless st,eel so t h a t scale will not be fomecl. -4 centralizecl lubricant supply \vith piped distribution for single or nlultiple nlarl~incc nlso reduces the quantity of foreign nraterials which may be introdnct.d Particulnr care should be taken ~ v i t hair-intake piping. Generally these runs are belolv grade from air-intake filter to engine manifold piping. They are not supplied by the enginr manufacturer. Since thiv piping is not readily accessible for inspection, treatment and inspection of the inride nlust be tlmougli prior t o installation. ,411 underground air-intake piping should be pickled or sand-blasted (or both), inspected on the inside (most intake piping is of sufficient size t o permit entrance), ilrln~ediately treated with some rcliablc typc uf rust inhibitor, and thcn paintcll or enameled. Aluminum metallizing, d e n carefully applied, or light stainie..,>> s.teel or nonferrous lincrs arc also used Instrumentation for internal combustion engines usnally consists of: ( o j Fuel control

574

Plont Utilities


( b j Autonmtic shut-down on cooliug water or lubricating oil failure, operablc from pressure eleu~cr~ta and teniperature elenients; audible and visible signals are required hut not necessarily sup11lird hy engine manufacturer. Storage a n d Movement of R a w Materials a n d Products

Adequate storage facilities for both ralv materials and products are essential t o the operation of a process plant. A supply of raw materials permits operation of the plant regardless of temporary procurement or delivery difficulties. Storage spacc for finished products makes it possible to fill customer's orders even in a time of plant difficulty. Liquid Storage

Vertical, cylindrical tanks are used for liquids which can be stored a t low pressures. Most such tnnkagc is constructed in accordance with American Petrolelm Institute Stnnilard 12c. Altliough this specification was developed primarily for the petri~leuniindustry, it consists of an excellent set of rulcs for alniost any type of tank. Thc stnndardization of tank construction techniques and tank appurtenances by this code aids in engineering and procurement. The National Board of Fire Underwriters and the National Fire Protection Association also publish rules for storage tank construction." (Also see Chapter 24.) The most common type of tank for storage a t atmospheric pressure is a cone-roofed tank provided with gage hatch, inspection openings, manholes, a ladder or stairway, and a vent for maintaining atmospheric pressure. For materials with low vapor prcssures the vent may be an open-type sized in accordance with tank area and pumping rate: The open vent is constructed of pipe with a large opening around the top circumference. This opening is protected from ~ ~ i nand d rain by a cap which directs flow of vapor do~vnward. Tanks for during liquids with significant vapor pressures a t atmospheric temperature (ahore 1 psia) require pressure-vacuum (conservation) vents. These vents open only when the tank pressure hecomes exceseively low or high and thus conserve valuable vapors. Floating-roof tanks are used to conserve valuable products with vapor pressures a t operating tcmpcraturc below atmospheric pressure (up t o 8 psia approximately). The roof floats on the surface of the liquid and thus eliminates vapor spacc. Thc space between the roof and tank wall is scaled by a fabric curtain coated with synthetic rubber. If flammable liquids arc stored in vented tanks, flame arrestors must he installrd in all openings except connectinns made below the liquid 'Air capacity in standard cu f t slrould be at least twire the pumping rate. Detailed venting specifications have been published?:l

575

level. As a flame arrestor a 40-mesh screen or a purchased flame arrestor may be used. The latter consists of a number of thin plates installed in a small chamber. Propagation of flame into the tank is prevented in both types through rapid dissipation of heat by the metal parts of the arrestor. Firc fr~amconnections are installed on all vented storage tanks containing flammable liquids. Large storage tank areas can be served by a central system. Since floating-roof tanks have no vapor space, they necd not be equipped with a pcrmancnt extinguishing system. Liquids with vapor pressures above atmospheric must be stored in vapor-tight tanks capahlr of withetanding internal pres.snrc. I n the pressure range b e t w e n 2-215 psig thin steel similar to that for vertical storage tanks can be used if tanks are built in the shape of spheres (30-215 psig working prcssurc) or spheroids ( 2 3 0 psig working pressure). For higher pressures, it is more economical to use a number of standard cylindrical pressure vessels of small diameter ( 3 to 6 f t ) . These arc installed horizontally and side hy side. Relief valvcs are located on each drum and manifolded into a conmoil header. Tankage for water stinage is nsually clevatcil, and, if part of the firc 1 insurance codes (see water system, is de8igned in arcorrlanrr ~ ~ 3 1fire Chapter 24). I n addition to flammable and volatile products and r a n materials, many corrosive liquids must be stored in process plants. Steel tanks lined with plastic, rubber, lead, and special brick and other ceramic materials h a r e been used successfully, particularly a t lower temperatures. At higher temperatures alloy steels, or nonferrous clad steels are necessary. Gas Storage

(iasrs are stored a t atmospbcric pressure in wet or dry-seal gas holders. The wet-seal holder is the familiar type uscd for municipal storage. Gas is admitted into a tank (holder) vhich is inverted in a water-filled tank. .4s gas enters the lioldcr. water is displaced and the holder rises. The dry-seal bolder, a morc recent development, is similar to a floating roof. The seal hetwccn the roof and t h r tank wall is ~ n a d cby a flexible s y n t h ~ t i crubber or plastic curtain, and tbc ronf rises or falls wit,l~pressure. The dry seal holder rcquires no heating roils t,o prevent freezing of water as does the wet-seal and is particularly useful for str~rageof gases that must rcmain dry. Natural gas and cvcn gaseous prnducts may be stored underground by pumping thc gas into those underground strata known to be practically impermeable to gas. High-pressure gas is stored in horizontal cylindrical pressure vessels. Gases such as N,, H,, and 0 , are shipped in gas rylindrrs designcd in accordance with Interstate Commerce Commission regulations.

576

Project Engineering of Process Plants Plant Utilities Storage of Solids

uperating unita, the same personnel may be used during operating periods for regular ninintenanre and for building special equipment. Small repair jobs can be done a t the process unit. Specially outfitted trurks and motor scooters carrying tools and siiiall parts arc 11src1 t o :~ns\\-\-er cnicrgcncy calls and for making quirk repairs. Nore extensive repairs can sometimes be liandleil Ixttcr in the sliop and niohile cranes and smaller lift trurks are wed ti1 transport the equipment ti, the ;hop. Planning of ~naintmancefa~,ilitiesis greatly facilitated by complctc spare parts lists and niaintcnrmce instructions from the manufacturer for tach ~iiect:of equipment. Tliesc can be used as a guide t o the seolic of mnintenancc work t o he expected in a plant as \wll a s an aid in planning such \T-idely varying needs as:

Solid products and ran- materials are stored in rveather tight tanks and bins ~vitlisloping liottonis or in outdoor piles. Solid products rliscl~arging from flakers or dryers are often packer1 directly in l ~ a g sand iiietal or fiher drums. These bags and drums are stored on pallets in \\-arel~r~uxs to a w i t sliipmcnt. Movement of Raw Materials and Products to Shipping Paint

.\loreiiient of liquid and gaseous ra\?- illaterials an11 products ~vithinthe plant to and from the point of shipment is done by pipeline. Transfer punilis are gr<~upedtogether to simplify polver distrihution and reill~ce labor. .I shelter is provided for transfer puinp personnel, but is not necessary for pumps. Suction and discliarge pi11ing is manifi~ldedfor greatest flexil~ility. This is done by running all piping entering the transfcr area parallel and a t one lel-el (12 in. t o 18 in. above griiundi. Transfer pun111 suction and discharge lines are run above these transfer lines and arc ccinnected t o tliem by risers. Valves arc located in the conncctiiig risers. I11 this n-ay a single discharge or auction line inn? be ~wnnectedto a nnmller of transfer lines and valves can be easily reached by the puiiil) operators. Some plants transpmt raw materials and products by pipe line. Wllen this is done local and federal regulations must be strictly followed in designing and laying the pipe. Land rriust be purchased or leased, but this land niust be selected &I1 care since the pipe line sliould not pass near residential or futurc rcsidcntial nrcas. Lines passing under high~vaysor railroads must be provided with an external pipe jacket welded to the pipe and ventrd to the atmosphere a t specified distances from the highnay or track. Evcry other possible safety precaution sliould be used. Solid materials are transported ~vithintlic plant by cr~nreyors,bucket, elerators, chutes, lift trucks, and pncu~natic systems. New materials handling equipment continues t o be introduced, and the task of moving solids is no longer a difficult hand operation.

a. personnel requirements. b. quantity and type of machine and hand tools. c. storage spare for spare parts and nml- ccquipment. d. salvage area for old equipment and parts. e . quantity and types of liandling equipment (truck*, hoists, etc.) Plant Roadways

I

I

Every process plant must have a machine shop cquippctl v i t h standard tools such as lathes, grinders, and drill presses. Large plants usually have complete shops for macliine and boiler work, pipe fabricating, inatruinent r q ~ a i relectrical , equiplnent repair, and carpentry. Since a large inct,ll:~nII,III I : h r r u r w t i w I N , ~ w ~ i n t : ~ i tfor l ~ ~r(g11:ir i! sl~u-~low :ind ~ l relmir of

Iload~vaysfor prorcss plants are designed to permit easy access to d l porti~insof the plant for inol~ilcservicing equipment, trucks, and fire fighting apparatus. Roads are located so that each pr0ce.s area is accessible from all sides. Plant roadxays are designed in accordanre ~ v i t hnsual higliway practice, and entrances froin public ro:ids ~iinst conforni t o local design methods. Reinforced concrete is used for main plaiit roads since maintenance work on con~,reteis nrgligihle. Secondary road.: may 11e niacatlani or gravel but must be designed t11l~andleloads imposed hy mcli equipment as travelling cranes. Main two-way roads should not he less than 20 f t wide. Short cntrancr roads into process areas may he narrower but must be adequate for trucks and cranes to pass into the area for servicing. Railroad Facilities

SECONDARY UTILITIES Maintenance Facilities

577

Railroad facilities are necessary for shipping and receiving materialn. Generally local railroails will provide without cost all the required spccifications and a certain amount of the ncccssary equipn~ent,such as turnouts from their system, and in some cases: t l i ~ ymay install sidings or spur tracks. Before preparing specifications or designing railroad trackage local railroad operators sliould 11e ciinsulted. There are limitations set liy local statutes or railriiad operdtors on rail size (xeight per yard), gradients, curve radii, s\r-itch design aud type, and clearances.

576

Plant Utilities Project Engineering of Process Plants

Spur tracks (sidings) and switching equipment must conform t o t h c requirements of the serving carriers. If a spur track must cross a public highway either the railroad opcratur or the plant owner must ohtain n formal permit, and foliorv the requirements for s u c l ~crossings. Railroad trackage is usually laid on ~vuodenties. Tie plates are located under each rail a t each tie, and splice bars arc uscd t o ronnect rail ends. Standard gage for C.S. railrontls is 4 ft 8% in. b c t ~ e e ninner edge of railheads. Rails, splice-bars and tie-plates for plant spur tracks can be obtained second-hand and should be used since no high speed traffic is anticipated. The rail weight for plant trackage may be 60-100 lhlyd. Rail lengths vary from 25 to 30 ft. Tie sizes are approximately 8 in. X 8 in. X 8 ft 0 in. long. Plant Sewer Systems and Waste Disposal

The primary sources of sewage and waste in a process plant are sanitary waste, prucess drains, and surface drainage. The plant sewer system no st he designed to conduct tliesc wastes to the disposal system without becoming clogged ~ v i t hsolids or filled with dangerous concentrations of explosive gases. General Considerations

Drainage systems for process plants may consist of one or more main sewer lines with branch lines from each area t o be drained. The elevation of the main sewer must be of sufficient depth to receive drainage from any area or from contemplated extensions t o tlie plant. Sewer lincs are sloped t o provide sufficient head t o produce velocities of 2% to 3 ft per sec (5 ft/sec maximum). Tliese velocities are necessary to prevent settling of solids. Contour maps of the plant area are helpful in planning the location of the main sewer so tlmt slopes can be obtained for branch lines from all areas. T o prevent clogging and to facilitate cleaning, sewer lines are run without change in direction between manboles and between a catch basin and manhole. Clean-out connections should be provided for branch lines not originating a t a catch basin. Manholes (Fig. 21-5) are located in main sewer lines a t each change of direction and a t points shout every 200 ft apart in straight lengths of pipe. Branch lines (laterals) should connect t o mains a t a manhole when possible. Manholes in hazardous areas have sealed covers with vents discharging in a nonhazardous area. Manholes through wbieh flammable materials pass should be trapped by means of a water seal t o prevent spreading of fires or explosions (Fig. 21-5).

579

Manholes are constructed of common brirk, acid-rpsisting brirk, roncrete ~ i t hbrick lining, or plain concrdc. Manhole covers, gratings, and other appurtenances are usually cast iron. Catch basins are used to collect surface or process d r ~ i n a g e . Water makes a 180' turn to leave the catch basin and t o enter the branch scwer Cover line. I n so doing sediments are trapped in the hottoin of the basin. Catch basins are ronstrurted of concrete and c have east iron slotted covers. Rcinforced concrete pipe is the ulost widely used sewer pipe. Cast iron is prefcrrcd under pared road~\-ays and Smel.,nan ,,c,lp seal foundations or other structures. Vitri- fol. i.;ol;,tingrrplosions ficd tile is used extensively for areas in ,\.hich corrosive wastc materials may enter the drainage system and lead pipe is used for strong acid wastcs. Soil pipc is used for sanitary sewers. Surface Drains

Rainfall intensity and rnn-off arc the basic data required for designing surface drainage systems. Intensity is measured in in, of water pru 11s. and may he obtained from local weather bureaus and the U.S. lkpartn~cnt of Agriculture. Rainfall intensity varies over the continental U. S.from 0.25 in. in some parts of the northvest, t o 1.50 in. in tlie mid-continent areas, 1.00 in. in some parts of the cast, and 2.25 in. d o n g the Gnlf coast. I n the same arcas in t,he northwest annual rainfall may be 40 in., while some of the arid areas of the soutlin~esthave annual rainfalls of 8 in. with intensit,ies of 0.75 in. Sincc maximum intensities are more important than averages, local weather data should he searched for the infrequent but extremely hcavy rainfalls. Run-off is the per cent of rainfall which is not absorbed by tlie soil and thus is the quantity a h i c h determines conduit size. The ~ a l n may r vary from 10070 for paved areas or roofs to zero for dry perrious soils, hIoet of the published data is based on city drainage systmms and ranges from 10 to 7576. Tliese values are used for extremely large acreagcs and are not of much use as criteria for process plants where high percentages of total area may he paved or roofed structures. It i8 p~eferahle,therefore, t o assume 100% run-off for the comparatively small areas served by a single sewer since often these areas are paved and are adjacent to roofed buildings. The run-off in paved process areas enclosed by fir pa all^ may he gove r n d hy fire hose capacity in t h a t area rather than rainfall. Both should be checked.

580

Project Engineering of Process Plonts Process Waster

Disposal of process ~vastesis often a difficult problem. State and local air and streain pollution regulations are l~ciwu~ini: morc strict ;IS poj~nlat i m gron-i in indu.;trial areas. Plant operator? are becoming more awarc of colninuuity responsibilities and usually institute nlorlern ~ ~ a s dispo.sl te wetliocls even if regulations do not apply t r ~thcm. Somc n-astes can be burned provided products of combustion do not pollute the snrrounding atrniisplicre. Others such as acid and alkaline 11-a>tecan Ile diluted and neutralized, and then discliarged into a flowing atream. All rue11 w;i;tcs tnwt lie treated and riiscllarged in a lnanncr that \!-ill be harn~lcssto strcnm lifc. l'rogrr.?ai~-cplant operators niai~rtaina careful check of strc;un llealtli. Inert ~vastesor ~vastcsinsolubls or it~lniiseiblcin v a t u can he discharged into the surface drainagp system and rcrnoiml in settling barins along ~ v i t lother ~ similar cuntaniinants prcscnt in the drainage xvater. Strong acid stren~nsor extl.enlely riangerous niuti.rial. arc l~refernl~ly discharged into special server s y s t e m for disposal in a separate trcating plant. Sanitary Wastes

Sanitary wastes must he discharged into a separate sexer systen~and treated in a sewage disposal plant or in septic tanks. Ordinarily, scptir tanks are satisfactory for the modcrate sized plant. The septic tank is a retention cliamber in rvhiclr solid ~vastesare accu~nulatedand then disintegrated by bacteria. T h e effluent is a clear liquid which may be discharged in a separate sewer or in the plant surface drainage system. Solids arc removed once a year. Tatilc 21-6 summarizes n t c r usage for various plumbing fixtures. This information is necessary in sizing sanitary s e w r lines. TABLE 21-6.

Water Usage by Plumbing Fixtures

Rased on 15 to 20 psig nzter pressure Fixture Toilet I~rinsl I.:~mtary bnsin:faucet Shower Founttin

Gallons per use

2.0-3.0 0.5-075

2.0-2.5 20-4.0 igprn rhen used) 0.5-0.i5 (guljday/person)

Disposal of Solid Wastes

Wasttt solids wlricll cannot be burned must he liauled to dun111 areas for h r i a l or be towed t o sea in dump-bottom barges and discliargecl m m y miles froln sliore.

Plant Utilities

58 1

I n some cases solids can bc disintegrated liy clie~niraltreatment, dippolred in rvater, and, after careful neutralization discharged in the plant selver. Plant Air

The ~".uwssplant's uec of colupressed air as a p o w r source for purtahle e i l u i ~ ~ ~ l continues rnt to incrcasc. .iir-driven tmls arc designed for all t y p w of \\-ark. They are si~nplcto control and may bc used in hazardous areas. A rcrr-ice air systenl, therefore, is usually installed in the modern plant. Piping is run above graclc along with process piping, and ilutlets are located in all lrroccss areas. Cuwprcsrctl air m a r he rlistrihutcd ovrr the entirc plant in a singlc system or may he sul~pliedliy scparatc comprrssnrs in each area. P l a l ~ terrvice air and instrument air (Chtrpter 20) are run in scparatc systems. 3r.rvicc air prcaturc is ii~aintainedat lo(-125 pxig, rdiile instmmcnt air pressure necd not cxcerrl 35-40 psig. Plant serricc air is soul?tinlea u 4 in euicrgencics aa R source for instrumcrit air, but it must first pass tl~rnuglr1111. instru~ncntt ~ i rdryer. ~ 1 1 for air cou~pressorinatallations are: The ~ ~ 1 ausili;tries rr. .Iil. cot~~lircsaur:vlertric n ~ o t o rrlrircn or ate;tm-ilrivcu, two-?t:~gc. rrcil1roc;iting. b. Air inrnkc filter. c. Ci~olingv a t e r for compressor jackets, int,er-coolcr and after-coiiler. 11. .Air rweivcr. e . Pressure control. Provision niust he madc a t various points in the syatem to remuve ronrlensed n~oisturc. Air rcceivcrs located a t each point of liravy lice will increase systcin volume and provide a separatim or condensation point for moisture. hloisturc m:~ybc reutovcd manually or by t r a p Traps arc preferable for systenls in liu~nidclimates. The air cumpressors for n r r n t r d Illant scrviw air s p t e n i arc tnost c ~ n venirntly lorntcd adjacent t o tlic powcc and stcam generating plant. l'olver-tiouse operators can then check compressor operation periodically. Plant Security

Prucess plants are surrounded b y fence topped with barbed wire t o prcvent entrance by unauthorized visitors and prowlers. Legal decisions which have become part of common l a x nmkc plant ovncrs rca~~onsihlr ior injury t o pcrsims r~-ithinthe boundaries of a piant cvcn though their liresencc is unautllurized.

582


Fences are constructed of galvanized steel wire and are 7 to 10 ft high. Fence posts are galvanized steel pipe set in concrete. Guard liouscs arc located at cacli gate and all plant pcrsmncl and visitors must pass through a gate house. Employees F e a r badges containing an identifying pliutogrnpli. Visitors arc i s u c d temporary badges and must be accompanied by an authorized employee. If time clocks are used for employee records, they are located in the gate house. Cniformed guards are stationed a t each gate house t o inspect persons and trucks entering and leaving the plant. Other guards are assigned to night patrol duty. I t is preferable to locatc office buildings outside the plant security area, particularly buildings for sales, engineering, and personnel divisions. Visitors can then be received in a proper and friendly manner and in plcasant surroundings, conditions which seem t o be difficult to create a t plant gate Iiouses. REFERENCES 1. Ahhott. A. L.. Notional Electrical Coda Hondbook. 7th Ed.. MeGraw-Hill I-& 1952. nook CO.. 2 . Rahhitt, 1%.E., Sewerage and Sewage Treatment, 7th Ed., John Wile? B- Sons, New York, 1952. 3. Betz. H'.H.. and L. D. Betz. Betr Handbook o f I n d u s t ~ i a lTVater Conditioning, Philadelphia, Pa., 1950. 4. C h e m . Eng., 61, No. 6, 122(1954). 5. Cook, A . L., and C. C. Cnrr, Elements of Ekclrienl Enginewing, John Wiley Q Srms. New Tork. 1954. 6. Croit, Terrell, Stram Power Plant Aaziliuries and Accessories, McGraw-Hill Bouk Co., Sew Ywk, 1946. 7. Cubhcrly. R., Chern. Eng., 67, No. 5, 140 (1950). 8, de Lat.mzi, Otto, C o n ~ b u l i o nEagineer-ing, Carnbustian Engineering-Superhrates Ca., Inr., Npa Yark, 1948. . 57, N o . 5, 129 (1950). 9. Elinson, J . It., C h e n ~Eng., 10. E~.ick.;on,Killiam H . , and N. H. Bryant, Eleeln'col Engineenn-Thoory and Prnctice, John TYilry 8- Sons, New York, 1952. , . M . , and J . C. Geyer, W a t e r Supply and Waste-Water Disposal. John 11. F ~ i r . G Wiley 6 Sons, S e w York, 1954. 12. Flow o j Fluid*, Tech. Paper No. 4M, Crane Co., Chicago, Ill., 1942. 13. Fuel Oils, 5th Ed., Commercial Standard CS12-40, National Borcau of Standtrnls, S ~ p t of . Ducuments, Knshington, D. C., 1940. 14. Gordon, D., C h e m . Xng., 67, No. 5, 119 (1950). 15. Guide ior Tank Venlino. ". It. P. 2WO American Petroleum Institute. 50 West 50th St., New Yolk, 1952. 16. H a ~ t .\V. D.. Industrial W o s t e DGnoaol for Petroleum Xefineries and Allted Plants, Kntionxl ~ r t r o l e u mIiews publishing do., Cleveland. ~ l i i u ,1947. 17. Heuman. G . TT., .Vogtirtic Control o / lndustiinl Motors, John Wiky & Sons. New York, 1954.

New

Plant Utilities

583

18. Manual on Disposal of Refinery IVaales, Vols. I , 11, and 111 (Oil, Gas and Cl~enriciils).Amcririln Petl.alrum Institute, SPWYo1.k. 1115-53. 19. M i l h . C. E.. Jfcrh. ling., 73, S o . 1 . 11 i l Q 5 l ) . 20. Pendct., H., Eleclricnl Engiarcr's H m d b o o k - l i k e t r i c I'uzoer I'olaarc, John TYiky & Sons, S e w I-wk, 1949. 21, Permutit T n t e i Conditioning L h f n B m k , Tlir Permutit Co., SlcGt.am-Hill Ucok Co., S e w York, 1946. ~d H ~ t i ~ d I w o k - P ~ ~l't,li~me. ~er 24. Snlishury, J. I<., Kent's M ~ ~ h n n iEngijleer's 12111 Ed., John Wilry B; Sons, Kew Por.k, 1950. 25. Sercms, IV. H., H . E. Degler, and J. C. Milps. Slrnm, Ail. m d Goa P ~ , w i ? . 5th Ed., John Wiley & Sons, S e w York, 1954. 26. Skrotzki. G . -4. B.. and IT. A. Vopat, Applied Encugy Cun,!eirior~.McGrarvHill Book Cu., S e w York. 1945. 27. Stoiage, Hortdling ond Csu uj Fla,nninble Liquids. SFP.4 Xo. 30-L. pp. 30-15, National Fire Protection Association. Boston. Mass., 1954.

CHAPTER

22

Foundations

585

li~tingrlore not replwcnt :I ~ysternof c l a d i c : ~ t i o n ,but arrves more as ionver~ientsnhdiyisions for the di~cursionhelow. Spread Footings

I

The footing, d ~ i c his the oldest typc of fo~~nilation. is the least expensire type if soil conditions arc fayorable. In simple terms, a spread

FOUNDATIONS Foundatione for equipment,, buildings, and steel strurtures not only must transmit the loads to the soil or piling but also fix the sup]iortr~l equipment in position. For practical purposes it may he said that a11 foundations arc constructcd of eoncrcte or reinfurced conrretc. This material is relatively incxpcnsive and may hc formed to ncarly any dcri~.cil shape while plastic. In order to attach the equipment directly to a. foundation, nnrllor-h111ts are cast in the concrete when it is poured (Fig. 22-9). After a curing period, the equipment is bolted in position. Most equipment is firmly bolted doum whether it is located on a structural stcel support whicli is in turn bolted to a foundation, or whether t,he cquipment is holted directly to the concrete foundation. Large-diametcr, flat-bottomed tanks. lion.evcr, are usually not bolted since they may be sct dirertly on ct~nrrcte slabs or on a preparcd soil surface with no attachment. I n some installations small pumps or machines and light conreyor sy9tcms are supported by plaring the equipment hase directly on the finishcrl concrete floor! and by providing expansion bolts which are drilled and set into the concrete. FOUNDATION TYPES

The most colrunon types of foundations wcrl in process plants arc spread foot,ings, mats (or raftsj, massive, and pile ioundatirms. This 584

foundation

Fig. 22-1. Sprr:t&footing i u r ;L self-sipporting tower [Rcp~.inledby permission, V. 0 . _\Iiucl~itll,Petrolci~nrKefinar, O?, Kc). 8. 101 (19431.1

footing as used in the process industries consists of a column or pedestal r;wt non nu lit hie ally with an enlarged hasc (the fouting) as s l ~ o ~ in nFig. ~ 22-1. T l x cnlal.gcd portiorr, if properly dcsigncrl, tr;~nsmitsthe i ~ n p o w l

I Project Engineering of Process Plants

Foundations

load to the soil. The more area covered hy the base of such a foundation, the less will be the unit pressure on the soil. Spread footings are usually constructed of reinforced concrete. Their bases are ideally located a t a depth not 1eps than the normal frost line or the maximum depth of appreciable soil shrinkage and expansion, whichever is the greater. The shrinkage area of many clay soils, however, mav be so deep that excavation for footings proves too costly. In such cases other types of foundations may he indicat,ed. The spread footing is used most extensively for supporting towers (Fig. 22-I), stacks, and tall structural columns. For such applications the circular footing is the idcalieed shape. Tall structures suhject the footing t o sin~ultancousforces due t o w i g h t and overturning moment produced by earthquake and wind. The unbalanced soil F i g 22-2. Distribution oi soil pl.cssure beoressures ~ r o d u c c dcan in some neath a footing subjcrt to h-ind l u a d cases cause areas of zero upu.ard pressure b e t ~ w e nsoil and footing (see Fig. 22-21. Therc is a strong tendency for the footing t o crack under surh conditions. Because of tlicir corners, square and rectangular drapes mark more easily than circular shapcs. Since it is p ~ ~ s s i h that l e the overturning moment can he in any d i r e h o n dcpcnding on the uind, tlic circular shape has the further arirantagc of providing siinilar stress distribution for any direction of overturning moment. The forming opcration for circular shapcs and the placcmcnt of rcinforcing steel, hoverer, have always provcd more costly than tbat for straight-sided shapes. Parallel rows of reinforcing steel must he cut to different lengths. The laying of steel of the same length thn~uglithe renter (radial reinforcement) is possiblc but requires too nmrh space tom-ard the rentpr. Octagonal shapes, therefore, have been widely used for such structures as tall self-supporting towers. T h e octagon requires little additional concrete and equal length reinforcing rods may be placed perpendicular to the sides. As new forming techniques are perfected, costs may change. It may, for instance, prore more economical t o have standard sizes of circular metal forms for self-supporting t,mers of various sizes. Because of the sitnple forming operation required for square footings, they rcn~ainthe niust generally used type uf spread footing. If the urer-

turning momrnt is small or negligiblc, the design is simllle. &,"are footings are used for sullporting equipn~rntand structures, esl~eciallytllose with high cross-sectional area t o height ratios.

586

Mats

D u e t o soil conditions some equipment and buildings may require a nunher of footings that h a m a combined area approximating that of the supported structure. I n surh rases it will p r o w econornical to use a flat rcinforced concrete slab covering the entire area. This slab is called a mat. M a t foundations have been successfully used with conrpressi1)le soil and when so used are rillled "floating" fuundations. h a-eight of soil is removed for the mat equal t o thc aeight of the mat plus the structure t o be supported. The entire structure will, therefore, "float" on the undisturbed subsoil. M a t foundations are oitcn used for supporting storage tanks. Thc sin~l~lest mat foundation for large flat-bottomed storage tanks tbat do not requirc anchoring is a sand pad about four in. deep. The portion of thc sand pad extending beyond the tank known as the berm should be about 5 it 0 in. It is usually protected from weathering by an asphaltic coating. The surrounding soil must he graded and pre- Fig.22-3. Ring-wall i:onptrrletion f m sloragc tank. pared fur good drainage. Perhaps the most popular mat-type foundation for large storagr tanks employs a concrete wall with a minimum width of 8 in. The tank shell rests on this reinforced concretr wall which cxtends below the frost line. Four in. of sand contained within tbe wall provides additional support (Fig. 22-3). Massive Foundations

Machinery such as reciprocating compressors, centrifuges and other similar moving equipment must be supported so that vibration and unbalanced inertia forces are dampened. Many clever methods have been developed for accomplishing this dampening. Various vibration isolators or dampeners employing absorbent materials or springs can be purchased. However, wherever possible, in the process plant heavy or massive foundations are used t o which thc machinery is firmly anchorcd. The massive foundation balances the periodic inertia forces set up by reciprocating machines as the acceleration reaches a maximum a t the ends of the stroke.

588

Foundations


The viIr:~ti,m+p r < ) ~ ~ u 11y c t ~high I si)w11 r o t a t h g 111:1~11int~ry :ire aIx> ~ I I sorbed by foundations of sufficiently high m a s . A typical mass foundation for a compressor is stmi-n in Fig. 22-4. If a numhcr of machines such as compressors are located topether as in

I

.

.

Fig. 22-4. Xlnss-type

589

Rccauic oi strmgtli limitntions m o d pile.. are h t uied as Erii,tion ~ r i ~ t l ~than e r txnrl-hearing p i l c ~ . Kaw niatcrial for n-ilud pilrs as 10ug a- 90 it v:m hc found in the forest> of Washington, Orcgou, aud S u r t l ~ e r nCalifornia, hut is hecu111i11~1e.s

I rornpt.eisnr iomidntion.

a c o ~ n l ~ r c ~I I oO IrI ~ V . 01~:i ~ , l v i ~ ~ l t aUI g ~:I > li~rgcrc1Tccti~cmass can be re:~lizc~l Ijy tying l l ~ csel~urntec o r n p r e ~ s ~blocks r into :I conmion monolithic mass.

ELEVATION

Pile Foundations

Proccrs plants nre often advantag~ouslylocated in coastal areas or along rivers. Such locations, t h ~ ~ u gconvenient h for transportation cconurnies, usually have Ion- hearing capacity soils and/or soils suhjert to excessive settlemmt under load. I n such eases thc fi~undationsdiscussed above must he supported hy piles as shown in Fig. 22-5. Piles support the loads on foundations by direct hearing on stable soil strata many feet helo~vthc surface or hy means of the shearing resistaucc creatcd by friction hctvt,en the soil and pile surface. The first type is called a point-hcaring pilc since most of the rupport is developed a t the bottom or point of thc 11ile. The second is callrtl a friction pile. Vndcr most conditions, however, such a simple classification is i n a d e q ~ ~ a t eOften . the support is ohtained by a conibinatiun of both effects.

availal~le. Concrete piles are, tlrerefore, being used more f r r ~ p c n t l yin proccss plants. Concrete is not subjcct to decay or wrrosiun* and vhen reinfurccd i. capablc of carrying large load;. Concrctc pil~,.; are either ])rc-c,;lst or cr~lul~anics n-hicli hut11 mauufncturc cast-in-place. They arc l~roduccclIJ>and drive thc pile.

Pile Types

Thc most common type of piles are pre-cast reinfurccd concrete, cast-inplace concrete, creosotcd rvi~od,structural steel meln1)ers such as H-beams, pipe, and composite wood-concrctc. Wood piles are the lowest in first cost and for this reason are widely used. Thc wnod must he thoroughly creosoted to prevent fungus growth. T o further prevent decay the top of the wood pile must be below permanent ground ~ v a t e rlevel.

Cast-in-place piles arc made by driving a corrugated or fluted sheetsteel shell us pipe into the earth to the required distance. To strengtl~cn the thin sl~clla core us mandrel is placed insidc bcfore it is drivcn into the ground. Then the core is removed and the opening filled ~ ~ iconcretc. t l ~ A number of patcnted cast-in-placc pilc designs are ax-ailahle, somc nf which arc tapered (Fig. 22-61. Tnpcred piles are preferred for soils mhicll

590


ha\-e high frirtional resistance, as s a d , since in this type of soil they produce larger shearing resistances than piles 11aving parallel aides. PIPE-COXCRETE PILES Pipe piles servc primarily as end-bearing piles. I n the casting of certain t,ypes the pipe is withdrawn as the eonrrete is hcing raliinied dom-n the pipe. A bulb or pedestal may be fortncd a t the bottr1111 of the pile to increase the load hearing area. This is accon~plishedby applying a large force on the first few feet of concrete poured.

Prevnst-concrete piles (Fig. 22-6) are made of high-strength concrete and reinforcing steel. The shorter piles can be obtained with a taper. They are used in the installations for rrhicli casting in place 1\-onld be

difficult such as locations under water. I n addition they are of great value for installatims requiring immediate use of the pile as a load hearing member. Precast and prestressed concrete pile;: are heing used for heavy industrial plants particularly if the above-grade structure is also concrete.

Sonietiines it is necessary t o use a pile that is strung and can easily penetrate the most dense suil. Steel structural shal)ra, altliougl~espcnsive, meet those requirements and are used for difficult piling operations requiring lung lengths and Iargc forces in driving whir11 ~ o u l dbreak weaker materials.

I n certain installations requiring long piles it is possible t o combine the low cost advantages of wood with the corrosion decay free qualities of concrete. The wood pile is driven first followed by a tapered cuncrete pile section which is cast in place. Several types of joints are used t o


Foundations

inillre a fir111 Imul bcl\wcn concrete and n-u~xltlierel~yescluding n-atcr and preventing bending.

:~pproximatingthe loads over each area. Soil loading can bc estimated t o aid placement of equipment within a n arca in order to spread thc loads :IF niurli a s l~otsible. T h e economics 3f equipment location involve the costs of interci~nnecting piping, arress platfrlrms. and supporting structurrs. Such studies m a y indicate t h a t the use uf piling xill be less costly than spreading the e q u i p n ~ c n to t obtain a reduction in load concentration.

592

Compressors and other henry niol-ing machinery produce horizontal forces. If the foundation must rcst on piles, it is necessary to drive a t least a vortion of the d e s a t a n anele - in order to resist t h e h o r i z ~ ~ n t forces. al Piles driven in this manner are called hatter piles and m a y he of a n y of the a h o w type%

FOUNDATION CONSTRUCTION

I'm~n~lationconstrwtion operations pritn:t~.ily arc the concern of the ~,ivilengineer. 'rhc project cnginccr, lio\vcvcr. mnrt br f a n ~ i l i a rwith t l ~ r tcr~ninology.]~rocciiurer,nrid requenre of o1wrations. Briefly, t l ~ cinstallation of illreaei ur ~ n a r s - t y p cioinirlxtious consibts of escarnting t o a firm stratum. setting the rrinforring rtrel in place, nnd pouring the initial concrctc m a t rlr spread. For111 work n-hich encloses and contains the concrcte v.hile it is still plastic. usually is not nceessary f i r the initial pours beloxv grade Icvel. I n atahlc soils thc sides of t h r rxravation a r c ~uffirientlyfirm t o form the l~eril~lieral sliapr reqnircd to contain tllp r o n c r e t ~ . T h e 1~1mp1etedp,mr is l ~ f ro11gl1 t xvith rcinforcing rod extending abol-c thc concrctc so t h a t ntlditional pours require11 to conrplctc the structnre will be w x n d y bundcd. Tlie s u p c r i m p ~ ~ ~load e i l on piled foundations is rlistrihnted to each pile hy means of a rrinforccd mnrrete pile cap, xi-hie11is rast around the tops i ~ fthe piles. This type of foundation is instnllrrl by excavating to the required pilr-r.al1 d e p t h driving t l ~ cpilcs, cutting OH' the tolls of n-otlll pilcs to nlakr thrni e v ~ m ~. c t t i the ~ ~ grcinforcing ?tee1 fur the pile cap: and ~iouringn c m r r c t c niasi n-llicli i~ the ililc c;~l>.

PII.ES MISCELLAYEOTIS A n e n w derelopment in foundation installation ~vhicli is being used s a t i s f a c t ~ ~ r i l y combines t h c chnractcristics of piling, spre:ld footings: and reinforced concrete colnmns. T h c method consi.sts of boring a holc to t h e required dcpth, then underrcaming a conical section. After boring a n d underreaming is completed t h e apparatus is ivithdra~r-n,reinTypicalsheet piling forcing steel is lowercd into place and the holc srctions. filled with concrete. If soils a r e sufficiently stable t o prcrcnt caving, t h e method is ideal. T h e upper ends of t h e cylindrical sections m a y be located below gradc, with stcel exposed for dolvelling into any reqnirrd surfacc structure. Economically, this method has advantages over both spread footings and piling, if the soil is stable. hlctal casings can he uscd in nnstable soils but a t greater expense. Another t y p e of pile valuable in construction, although not used a s a structural membcr, is t h e shcct pile. As illustrated in Fig, 22-7, these stcel shapes a r e designed to slide vertically and t o interlock. T h e y arc used a s s t n ~ n g~ v a l l sto hold hack water and shifting soils during construction.

n

SELECTING THE FOUNDATION TYPE

It is not possiblc to state conclusively t h e particular t y p e of foundation ~vhicllshould be used for a each type of project. This decision can h r made only after careful analysis of data accumulated by explr~ration of subsurfacc soil. If piling is required, cconomic studies must bc made to iietcrmine the most desirable type. Arrrangernent oi equipment over a given area t o meet process conditions is often a determining factor in selecting the type of foundation. Rough estirnates of the required spread of the footings, if the soil load hearing characteristic is known, can he determined early in t h c project, b y

593

Scheduling of Foundation Work

i

I n the irlcwi construrtion p ~ ~ ~ ~ g rall i u ui n, d c q y ~ n n doperations should hc con~pletedhefore a n y above-grudc work is starteil. T h r continuation i ~ fa t ~ ~ l ~ - c - g requipu~eut a~le has of undrrgrt~unrl v o r k after t h rrrctioo ~ Ilegun is cxtrcmcly cwtly. Opening :I t r c n c l ~ .firr i n i t a n r r . :rcrni.: ;L ronstruotio~i a r w ~ ~ r o ~ l n cI c ssafety Iiuarcl :in0 s ~ ~ i o u s l Iyi : m d i ~ , o l ~ ~ c r : ~ t i n . I , ; ~ t rcsr;~vntioli. in ;I rr~ngcstril;IW;I 11exrly aln-n>->1n11it h r ~ l u n et ~ yIi;i~iiland the, surfaw ~ o r is k d ~ i \ v c dt ~ ythe intwferen~,e. l h c rcleasc of founrlatiori rlra~\-ingsto the i:rertinn forces sllc~ulcl llc coordinated n-it11 the rrlr:rsc i l f all other undrrground x o r k srleli :IS piping. clcctrical grounding s y r t r n i ~ :mrl , electrical conduit work. ? 3

Subsurface Soil Investigations

Tlit. hmtl 1~c:iring ~ ~ l i ; ~ r : ~ r t ~ r Oi Fs ttllr i r s mil 011 n l ~ i c ha plant i~ to he erccted shuuld be explored and d c t c n ~ l i n r da t sonie early st:~gc of tlw ~ w o j w t . I n f:lct, s u r l ~ch:~~artvrirtic*. sl~oulcl 11:lvc bccn k ~ w n ~1~t~lul.e l

594


Foundations

595

purchase of the site. It is impossible to judge subsurfacc conditions by visual inspection, and competent investigation is usually most economically acconiplislicd by firms specializing in soil analysis or subsurfacc explorations. Reliable data permit foundation design and selection to proceed on a realistic basis. I n addition to the general characteristics of the underground stratum more extensive studies should be made a t the specific locations for each footing. Borings

The most reliable method for determining the characteristics of the subsurface soil is from samples of each stratum obtained from borings. Soil borings can be divided into major or decp borings, which locate the governing strata, and secondary or shallow borings, which should be made under each footing. It is sometimes possible t o utilize drilling logs from deep water wells t o determine the practical depth for the major borings. Water u-ell logs usually yield detailed data since all n a t e r bearing sands must be identified. XIajr~rhorings are made by portable truck-mounted machines. They may be drivcn onc to t ~ hundred o fcct deep or deeper if necessary. One lnetliod in a i d e use employs a fish-tail bit which moves in long vertical strokes. Wash water removes the loosencd material as in most drilling operations. As each change of soil is encountered, the bit is removed and a samplcr driven into the soil nut yet penetrated. The dry samples thus obtained are preserved in hermetically sealed jars carefully identified for laboratory investigation. B y noting the numhcr of blows a t uniform force required to drive the sampler into cacli section of strata, the compactness of the soil is ascertained. Fig. 22-8 shows a typical boring repurt. The boring oprration must bc disrontinued when rock is reached (nobed as "refusal" in Fig. 22-8). The extent and character of this rock or berlrock can bc determined from core bmings. These are obtained using rotating coring dcvices similar to those employed in the oil industry. Extensive subsurface borings are usually mandatory in areas which lmve been subject t o water encroachment, such as coastal areas, stream valleyr, and tidal flats. If the area is located in a known st,able region, not coastal or strcatri-bed, and one or two deep borings show that the section is composd of stable sedimentary formations or formations overlying rock, only a minimum amount of deep boring is necessary. Shallow cores t o locate uppermost firm stratum should be taken, however, under each major footing. These shallow cores which can he hand-driven indicate the depth of topsoil or humus, and the depth of excavation necessary to locate the bottom of the footing on the uppermost frini

I

Fig. 22-8. Test boring report. (Courtesy of Raymond Concrete Pile Company.)

stratum. The topsoil, or humus layer is never sat,isfactmy for load bearing and must all be completely removed from any area which is t o be used for foundations or is t o be covered with concrete slabs. Borings also indicate the location of subsurface m-ater. This information is of value throughout construction in enabling the erector to foresee and t o make provisions for removing water from excavations.

596

Project Engineering of Process Plants Soil Analysis

Certain soils, particularly clays, require further laboratory tests in order to more conipletely define their characteristics. Such tests include those n.11irIi determine density, moisture content,, shearing strength, particle size, plastic and liquid limit ilrloisturc content range t h a t defines the plastic state of the soil permitting identificatim of clays and silts), cocfficicnt of internal frirtion. consolidation (n~casureof the settlement of a n "unilist~~rhcil"soil sample under specified loail) pcrtue:ihility, nature. c t r l , colirsion iresistance t o clrcmicnl propertics (pH. roll~~irlwl particlc displacc~nent),and shrinkage (volunre 111ss due to derrease in moisture r m t e n t ) . These and other tests ~ v l ~ cinterpreted n by a competent soil ~ncchanicsexpert proridr accurate predictions of subsurface conditions for design purposes. It is possible to draw ssllbsurfacc soil profiles based on these data and the data oht:~incil f r i m till, boring opcr:~tion Sinre an infinite number ui' Imrings e:iririot be made n consideral~le;mount of jtdgment is required in l~rwlir+ingt h r cxtvnt oi ixch f o r ~ ~ ~ : ~am1 t i t mstratum hetween l~orinps. .\I1 engineers 11.5ing tlrese profilrs should rrme11111crthe limitations of sur!~ interpretation. K o l~rofiloe m be guar:il~tccd. Soil Bearing Copacily

Perhaps the most i m p ~ ~ r t a quantitative nt data rrsulting from the subsurfare inrestigatiun is the allowable bearing cspai,ity or press11re of t11e soil in pounds per square foot. This value is uscd in design ralculxtions as the carrying capacity of the soil. Although the value finally recorn~ n e ~ i d c by d soil experts is based partially un speculation, i t is used religiously hy the designers. I t is i~uperativc,therefore, that the ~ u o s t reliahle vnlnc lx,ssiI~lcbc obtained. 1.aboratory shear and colnpression tests often eombincd .r~ithfie111tests (see wrtion on Drsignj on critical portion? US the site are ncccssary t o obtain the most reliable bearing rapacitirs. I n r o n e cases it is f a r more flwirahle and econoluical to estat~li:l~v:~luesnut only f u r diffwcnt ,srctions of the plot but also for different types of equipment and buildings. Inztallntions subject to uccasional heavy lunds can be designed for a lower bearing value than those upon which a c m t i n u i ~ u sheavy load is impi~sed. Flexibility in establishing load rcquiremei:ts is more advantageous than establishing a single safe value for a!! conditions. D a t a for Piling

Soil analysis data rltiy indicate the necessity for piling. When piling is necessary decisions hasrd un mil analysis data can bc used to indicate the type of pile, rnaxin~umload per pile, n ~ i n i m u npiling ~ spacing, and

Foundations

597

I

1 1 l . Tlir ~ w c type l of 11ili11gto br w c ~ ld r p m l . ~~ I I X J I I the depth ti1 firm btratn, n.l:ether or not the pile d l support its load by skin friction or point bearing, the t y p ~of soil through n.11ich pile is to be driven, and the possibility of failure caused by soil or ground r a t e r conditions. If the soil chamctcristics arc extremely poor necessitating sheet piling, load bearing piling, an11 n.ater rcmovnl equil~mcnt.it i . 11~11allymore wonomical to mbcontrart all foundation n-ork, invlu~ling>ubsurface in~ n . q~rciwliaeii*kill :IS ivell :is rpeci:~l re
T l ~ cfirst field ill~c,rationin 1il:int 1:iyout is thc e m c t lo~.atiunof pro)~i>rty i ~ rboun~lnry lines, reference;, and cierations. The-c may IIC located FVOIII monunrents on : ~ ~ l j a c e nproyrties, t li~cnlhigh\vays. railroads, and other pcrmancnt ~~icasoralilc lan~bi~:irks,identifial~lt?in the field. and legally rerordt:il. The p r i n ~ ecurrtv;~ctormay be requested to [~erfornlthis xvork for the o\vnrrr or the o
598


1Sart 2nd 5 p111s 25.00 iYorth would indicate a point 558.33' r w t of, and .525.00' north of the Zero corner. Sorilr ron~istentsy*trm mc11 ;is this .~1111uld he wrrl for a project since it specifically ties certain points to the original datum. At least two permanent markers must be installed so that dimensioning may be checkcd easily. Such markers or monuments sliould he located out of the work area and should be constructed in rue11 a x a y that they cannot be easily dislocated. One siinple marker consists of a sectiun of six in. steel pipe four to six ft in length, art vrrtically in a concrete envelope, 18 in. t o 24 in. square, a i t h the upper portion projecting 6 in. tu 12 in. above grade. The pipe lnnrkcr is located so that the reference point d l fall within the diameter. A picce of 2-in. diameter brass shafting approxirnatcly 18 in. long is then located as ncnr as po.;.;il~le to renter of the point, with the top prujccting scveral in. ahove the top of the pipe. The pipe is then filled with conercte. Aftcr the concrete has set the exact point can be punch markcd on thc brass rod with the w e of n pli~nihhoh and transit. To make the marker even more permanent, the upper portion of the bar ran be tl~readcdand :i 11rasi cap provirlcd to covcr tlir tq,. The cap is very desirable n - l ~ mtlic marker is n l x to be used as :in elevation reference. Tlie arbitrary setting of a plant north, is cqually as important as elevation and dimensional references. Once the plant north has hccn set. right-angled arrangements can be used on drawings much more simply than if a true north location is used. Elevutions

Bfter dimensional references are located, plant elevation planes mrwt he set. T h e civil engineering survey report should include s referencr tc~the nearest U. S. Gcodetic (or other reliablc) survey datum. Thi. daturn can then bc used in establishing tlie elevation of the perluannt markers ~vithreferenee t o sea level. For convenience: the plant datum. however, should be estahlislied with reference t o a low point or t o tlic lowest point on the project, arbitrarily called 100.00. Thus all elrvations used in engineering the project will be 100.00 or above. The markers set for dimensional rcfcrcnce can then have an arbitrary plant elevation, which will he plus 100.00 and a t some later time may be chccked back to the local datum. Large projects are usually separated into areas. A normal area grade or ground elevation above thc plant datum must hc set for each area as early as possible so that foundation design and field xvork such as rough grading and other preliminary construction operations can proceed. Area elevations, or area grades as they are marc conimonly known, are best developed from project contour maps. The area grade generally refers to a highpoint in the area since a certain amount of sloping is

necessary for surface drainage. Aftcr the nominal area grade has been determined, liciglit of equipment above grade can be set and foundation design can bc completed. The cleration of equipn~entabove grade depends on process requirements, niaintenancc considerations, and possible operating hazards. As a typical illustration, resscls carrying fluids a t temperatures and pressures near vaporization must be elevated ahuvc pumping equipment t o give sufficient liquid head to maintain the fluid in a liquid state. Thus the type fluid, its process state and the characteristics of the pump, all nlust he considered in determining the proper elevation. All process pumps or other me,,l~anicalequipment sl~ouldbe located sufficiently abore grade to perniit operation, normal inspection, and niaintcnance from a standing position. Area grades or cquiprncnt elevations cannot be determined arbitrarily, hut must he planned ivith carc. Wliile the cleration of foundations above grade is usually set for process or n~nintrnancereasons, tlip minimum depth helow gradc of a foundation dcpends upon tlie deptli of frost penrtration or thc
Tlie largc aniount of interconnccting prefabricaterl piping requires more precise ficld engirieering and equiprnrnt locatim for process plant projects than for otl~crtypes of construction. The draftsman's accuracy in showing correct dimmsions on drawings is wasted if the field engineer n~isaligns or fails to use the same dirncnsions when locating fonndations. S h o p fabricated pipe is i~suallylirld to close tolerances (l/l in. for some work). Prefabricated piping niay require lieat treatment, or may consist of materials which eannut be reworked in the field, thus an crror in equipmcmt location of as little as y2 in. can IIC serious. Errors in anchor-bolt locations on integral foundations for major equipnlent can he even niurc serious or costly. Usually anclior-bolts for large equipment arc firmly fixed and held in place by metal or wooden templates, wl~iclireduce the l~ossil~ilitiy of crror during the pouring of concrete. Nanufacturers eonwtimes make errors in their preliminary dimensional dratving or h a r e to make cl~angcsas fabrication proceeds. For this reason the innnufacturcr nus st furnish his final prints v i t h dimensions certified t o be wrrect. Experienced erectors will not release foundation drawings for constrnction l~cforcthe manufacturer's final certified prints are received on all equipment involved. Excavation

After the site has heen cleared and graded, and locations of rquipnlcnt fuundations crtahlisl~ed,excavation can begin. Exca\.ntioii may be done by machine or by hand. hlachine excavation

600

Foundations


the choice of wl~ieh is perfornwd I)? a n u l n l ~ r rof types of cquil~nrt~nt depends 111,ontlic soil and 1lc11tliof the ~ ~ x c i ~ v a t Ti ~r cm~ ~ r I for ~ e sc x t m s i r e straight run1 of un~lergroundpipilig or conduit a r c often esravated n-itli trenching machines. T h e drag-line, ~vlii1.11is a .self-propelled crane . the iiio-t pupnlar iliachine m e t l i ~ ~ofd c s e a v a t i m iquippetl rvitl~n l n ~ c k c tis for Ileal-y c o n ~ t r u c t i ~sinre m the crane m a y also br u r c ~ lfor lifting q u i p merit during erection. Bulldozers, rrhich are simply tractors with a l~laclc i~ttaehedto the front, are extensivt~lyw e d for Ilackfilling and fur c m ['acting I I nirans ~ of othrr :rttaelinient~. Sizes and t y l w of c r r a r n t i n g end backfilling cqnil~nicntxi;.? ~\-itlitach l ~ r , l j ( ~ . t . .\larliinc ~ w a v n t i n n .I~cing1w.s co-tly tlian h:rn{l c x c a w t i ~ ~ nis, 11w1 e r e p o s i T h c Ilrocess 1)l:rlit usu;~lly consist- uf a nulrrl~cr of scpuraterl hut conge-ted arcns. It i: ord~naril?-~ i ~ u (11111rc ~ l i econumi~~irl to machine excavate 11 tr1t:rl area to the firm stratum. \vhm a numbcr of separate small frrotiugs are t o he p o u r c d than to liaurl exr:rvste raclr footing. .Iltliougl~ tliis may require wrtnin arlditional forming. tlir adrantage of a lwtter r~wrkingspare fur u n f t s m e n r e d u ~ e sfnrm building titiit, and cost of ~.eii~iorring s t w l pl:weme~it costs. Other i ~ n ~ l ~ ~ r g r o u n c l facilities such :is piping :ind piping tlirnst nuchurs. clertricnl rt~nduit;in11 grounding systems can be iustalled s i m u l t a n c ~ ~ u r l thus y , eli~ninatingpractically ell hand excavation. ~ V a t e r seepage caused by penetration 11f the vatcr-table or I I opcning of xater-bearing strata in cxramtiun 1 1 1 1 t x h n sis a cmnnon prohleni in sul~surfacropcratims. If th17 grnrral area 1i:1> d i i ~ . i c n tslopc, rvntcr iuay sonietimer be sealcrl off I I sheet ~ piling on the up~tre:im side of tire C T I , : I ~ : I ~ion. IIC uu~cleto punqt out s c q I n a n y 11i:i.inr ~ ~ s r : r r : ? t il~~~r iui~ - i s i m.~Iior~ld > :igr water or rnin v a t c r . Onc or In-(1 Ion 11oints \\.it11 ~ I I I I :rre ~ ~ prorirlc,l. I ~ A thin ( 2 in. or 3 ir1.l scid eoiit of T W I ~ concri~tt~ over the hotto111 of the. excaraterl area is often ~ f f ~ ' c t i vine stopping xvater seepage. 'l'liis method is regu!arly used in extensivta cxwvations to imllrorc working conditions and to avoid cuntaminiltiou if the ci~ncrcte. r n t t a l ) l t , TI-ater-bcaring soils c~rsand soils tlii~tare s u l ~ j c r tto caving r c q u i ~ cr s t r a safcty ~ ~ r r . r : r i ~ t i m * for tlic ~ ~ r < ~ t r cof t i ~110th l n [ ~ c r r m n e and l cquil~iiient. Errors ~ii:rrIc in esc:ix~tion 1icpt11: 11;. tlic acci~lcnt:il ;.e~iio\-:iIof ,soil ~rruundexirting fuundatiuns rcquirc careful rcfilliug. This c~perationis ternird l~nckfilling. Heavy gravel or r u l h l e concretc is so~nctimcsuscd fur this 1)ilrl~oscif tllc drptli oI hackfill is not mcebsire. If suil conditiuns a r e poor and the bearing ralne is l o ~ vtxxcessive , xveights of gruvel and conmete must be avoided. Ordinarily I~ackfilling~ v i t hw a k cmcrote is the simplcst and 11i11strcliahle practice. Bnckfilling :In :ire;i ~ v h c r ca floor slab or rvork slab is to he poured sl~oril~l al\vay.< Ilr ~,;irrfullydune and each . f ~ r surcc?iiv~.h y c r of soil s l i o ~ ~ lI)(. < l ~ ~ ~ n c l t~i i~nme p t ~ lSperifirations

601

bar.kfilling, inrluding t l ~ ct y j v of pt~r~riissil~lc l~ackfillinaterial, should 11c prepared a t the beginning ui thr! 11roject and specifically followed. Backfilling also rcfers to the filling in of excarations with soil after the foundation has been poured. L o n cost grades of sand and gravel are often uscd for this levelling of excarations If Llackfilling materiais are subject to movernent by ground water, precautions must be taken t o see t h a t they are contained. either b y the concrete work itself, by sheet piling, or by s o u ~ eimpervious soil. It is lmor ]".actice to attempt a saving in concrete by placing a footing on backfilled material or on ilisturtml soil. Drnwings ~ ~ r c p a r efor t l the i l ~ s t a l l ; ~ t iof ~ ~f n~ ~ u t ~ d a t i sliould i ~ n ; note t h a t "All footings iliall be carried t o firm and unili.;turbed s ~ ~ i l ,:rn~l " no ~ l c r i a t i o nshould be permitted without sornc import,ant justification. Grcat care must be cxcrciscd in making excavations near major footings, thougli proper scheduling of the work will eliminate the need for sue11 eurarationr. Form Building

T h e various shapes \vhirh retain t h r cmcrete vhile it is in the plastic state a r e called forms. T h e building of thcsc formi is the most rostly operation in concrete 1%-ork. Forms m a y be ronstructed of wood or metal. Metal f ~ ~ r n require ia less labor than n-ood forms! but foundation shapes must he designcd in accordance with metal form lengths and shapes. Metal fonna are sturdy a n d last for many years xvit11 rcasonsl)lc care. Wooden fornis m a y be used several times, but cleaning concretc from \voo~lforms is costly.' Finishing r e ~ i ~ e to n t a smooth a p p m r a n r c is n costly hand treatment and may be almost completely eliminated \\-it11 metal forms since the form surfaces are flat and smooth. Reinforced Concrete

Since concrete is the primary material in reinforced fouildntion e x stmction, a brief description ui its co~nl~ositiun 311d cliar:~cteristirs mnst Ile included in any dircussion on foundat.ions. Cement a n d Concrete

Concrete is composed of cement. water, and aggregates, such as sand and crushed stone or gravel. Cemrnt, a s it,$ neuie iniiicatcs, is the agent which solidifies t h e aggregates into a firm mass. Portland cement. which is used for most construction purposes. is composed of essentially four tlasie compounds: tri-calcium silicatc ( 3 C a 0 6 i O 2 ) , dicalciuni silicate *Forms rnn he oilrd before using t o incilitxtp r a n c i . r t ~ remoral. gwascs h a w proved highly S U C C ~ S S ~ for U ~ this ~ I I I ' P L I S B .

silicone

V:wious


Foundations

(2 C a O M I , ) , tri-calcium aluminatr ( 3 CaO.AI,O,), and ferrites similar to the aluminates. l'l~esematerials are produccd by ralcining the propcr cumhinations uf raw materials containing CaO. SiO,, AI,O,, and Fc. Lump:: or "clinkers" from the ceinent kiln are pulverized to f m n a dry powdery ~natcrial. When ceinent is mixed with the p~11wrfine and roarsc aggregates and water, in correct proportions, it hardens into the solid Inass known as concrete. The strength and other cl~aracteristics of cmcretc vary, depending upon the type of cement used, tlie p r q ~ ~ ~ r t i oofn cthe mixture. the kind and size of aggregates, the quantity of water used in its preparetion, and the curing process after pouring. While the ultimate strength of cmcretc may approncli 8,000 psi in compression, it? strmgth in tension is approximately one-tenth of this compressive strength. I n design, its tensile strength in tension is considered zero. I t is for this reason that another matcrial must be added to concrete, t,o provide ~ t r r n g t hill twsion or hending. Steel ~vircsor rods are embedded in the roncrcte in definite pusitions to absorb r t r e s c s or r
28 days with materials t o he used. Such crlrves nil1 indicate the best water-cement ratio and possihly thc most effective curing proccdnres. The ~vater-cementratio, as indicated above, s1111uldbc closely controlled. This ratio is cxpresscd in gal per 94 It] sack of cement and varies according to the required strength, the aggrcgatc size and type, mixing conditions. delivery conditions, and placement conditions. The range is about 4 t o 8 gal per sack. Openly storcd aggregates must be checked for water content and this water deducted froni the water to be used. This value is easily checked by drying a mcasurcd quantity of aggregate a t 2003F and weighing it. Equal quantities of undried aggregate measured and weighed thereafter will show the approximate 7,-atcr volume per cu ft. Tircre are a number of high early-strength celnents which advance the hardening process. The design or 28-day strength r i t h certain mixes, may be reached 12 and 24 l~oursafter pouring. Since thcse materials are morc expcnsivc than portland cement and since the increased rate of reartion often generates Iargc anionnts of heat ~vhich!nay require a more costly curing procedure, they are not commmly used in ordinary construction. Certain additives are arailable for increasing the density, natcr rcsistancc, surface charnctcristics, and resistance to wear of concrete. The curing procedure of freshly pourcd or exposed concretc surfaccs is also very important to the wear resistance and weathering characteristics of the finished concrete.

602

Strength of Concrete

The p1iysici1-chemical reaction between the cement and n a t e r requires a certain time t o initially sct, and further time t o harden to its design strength. I n ordcr t o standardize tcst procedures, concrete compressive strength used fur design is that stress which it will ~vithstandaftcr 28 days. The use of the 28-day time interval is the result of extensive research. Altliough concretc continues to liardcn the compressive strength curve flattens appreciably after 28 days for concrete cured in air without extraordinary curing procedurcs.5 Many factors influence concretc strength; water is pcrllaps the most important. Rcsults froni many contn~lledtests show that the compressive strength varies from a rnaximuru of 7500 psi t o a ininimum of 2700 psi a t 28 days for water-cement ratios of 4 to 8 gal per sack, respectivcly. Curing methods alsu affect strength. Concrete continuously moistcured for one year shows an increase up to 160%, of 28-day strength. The increase is 140% up to 100 days. Air curing (without moisture) produces a strength of ahout 75% of design a t 30 days. Apparently moist curing a t any time after a dry-curing period will give a sharp increase in strcngth. Curing temperature also influences strength. Seven-day strengths of 44% and 6570 of 28-day strength for curing a t 33°F and 72"F, respectively, are reported. The Portland Cement Associationj recammends that tests be run to determine cornpressivc strength curves for 7 days and

603

Specifications

Concrete strengths commonly used are 2000, 2500, 3000: and 3750 psi after 28 days. Spccificatiun of strength in effect sets the water-ccment ratio w.hich must be uscd since this ratio determines tlie 28-day strength. Ordinarily suppliers of ready-mix concretc are familiar with this mctliod of specification and will supply concrete t o meet or better the specifications. I n urdcr to cl~cckthe concretc strengtl~,samples are taken from each delivered inix by a testing laboratory in prepared cartons 6 in. diameter by 12 in. These cylinders are preserved under controlled conditions and tested in compression, until failure, after 7-, 14-, and 28-day intervals. For certain types of work it is desirable to spccify n~inimumsacks I I celncnt pcr cubic yard of concrete, and nmximum gallons of water pcr sack of cement. Thc slur~iptest which is described in detail in 4STX Designation C 143-39 is often used as a consistency check tcst while concrete is being poured. Tlic American Society for Testing Materials has prepared a number of teats for evaluating cement, ronwete. and aggregates. Three tcsts are tlie basis for all carefully prepared concretc specifications. The Portland

~

604


Foundations

Cenrent A~.ociation~h:is issued suggested concrctc specifications 21s ell as 1iter:rturc on tlic proper use of 110th ]il:~in and rcinforceil concretc. Reinforcing Steel

The liasic strcngtli material used in concrete is steel in the form of roil?: bars, and stecl wire fal~rics.' The most conrmo~ireinforcing ~natcrinlis the round steel rod or has. ~ o n n n o nliar 51ircificationa arc: for billet bara. -4STlI Al5-SOT; rail bars, ASTAI .416-SOT; cold drawn steel ~vire: A S T N .482-34; and ~veldcdsteel wirc fabric. .\ST31 A1 85-37. Thc *(Icnlled deformcd bar 11as forged or rolled surface extrusion.i. For climcnsions of deiormation~.see .\ST11 A30.5-SOT. At present only deformed bars arc used and their sizes are sliecifiecl hy nmnlier ( n i ~ size) t a(,cording to I-.5. 1)cliartment of Connnercc Sinlplificil Practice Rerolnlncn~l:itiol~ R-26. The bar number refers approximately to thc numher of in. diameter incrcmcnts up to KO. 8 hnr n-hicl~is 1 in. Only three square har sizes are listed in the recom~nendedstandard, starting a t 1 in.. d ~ i c l i is S o . 9; 1 5 in., S o . 10; and 1 % in., KO. 11. The smallest bur is a S o . 2, % in. round. Tlris bar is furnished plain or undcf~irnrcd:md is sometimes called pencil rod. I t is used for miscellaneous functions sncl~ as ft~rm-ticshut is ordinarily not used for reinforcement. Strength or stress limits for reinforcing steel vary from 14,000 psi t o 30,000 psi depending upon thc design requirements and the s t t d usc~i. The usual sjiecifieati~inis 18,000 or 20,000 psi. The various atrcngtl~smay he found in the above named .\ST11 specifications. Another c~ininronrcinfurcing material is know1 as wclilerl ~viref:iIiri~,. This ~naterialconsists of steel wire m l d e d together to form a scrcclr-likc fabric. The spacing and gage nrust hc sliecificd according to connnerci:~I practice. A 6 X 6-10/lO, mesh indicates gage wire on 6 in. squares.

!,

Pouring Concrete

After tlrc forms arc built and the reinforcing steel is in place, the concrete can he poured to form tlrc foundation. Concrete lnay be nlixctl a t the point of pour or elwvlrcrc. For :I large lirojcct :I ccntral mixing lilanr may be prnvidcrl: n.hcrc :ill c~m.rt:teis miscd, :rnd t l i e ~c ~o n v ~ y c dti1 t l ~ c various puints of use by lrantl "buggies" or by trucks. Ready-mix concretc is alsu extensively nscd when it is available. Tlris type concretc is sold ready-mixcd by mixing cnmpanies and is delivered by specially designed trucks to tlrc point of pow on the project. The pouring of cuncrete is a relatively simple procedure. The plastic mass nrust be poured or shovelled into the forms. For large pours (several hundred cubic yards) or pours covcring a l u g e area metal chutes arc usimlly prnvi~lcd to cunvcy tlw w t nrnss to the proper plnec. Largi. buckcts are ~onietimcsused, holding from me-half to tiw cuhic ynrils of

605

n .c;trricd r,nnrri,t~. T l ~ ceimcrete is poure(1 in the linckct wlricl~.in t ~ ~ r is hy a clan? to tlie necessary point. Chutes must be high enough to pprnrit the concrete to flow ~ i t hease. I n certain types of n-ork a system of conrcying chutes or pipes may be provided. Once the pouring of concrete for any massive slah is started, such as for a large foundation, it must not be stopped for any length of time. A stoppage ~ o u l dpermit partial setting (solidifying). The successive ponr would then not bond properly and a clt.a\-age plane might be produced. \Vl~envery large pours are contenrplatcd arrangements nrnst be nrad? t o ininre continuity of all operations, mixing. conveying, and placing. .is the concrete is poured into the f o r m it is continuously proilileil l ~ y hand wit11 x ~ ~ o ~ paddles len or poles so that it fll1~Wintu all tlrc contoul.of tlie forms. Pneumatic vibrators are also used continuously during the pour. TTater mnet never be addcd after the concrete is poured. The degree nf fluidity cannot he ar11itr:rrily chnngerl by ndrling n i t e r .sinre this ill cllange the specified ~vatcr-ccnientratio newssary for the required concrete strength. There are, ho~vercr,ievixd additives sold nlrich will lower tlie viscosity of the concrete ~vithoutr q u i r i n g an increase in tlw T\-atcr-cementratio. Curing of Concrete Foundations

I n order t o derel~ipmaximum strength frcsh concrete must he protected from loss of rvatcr by evaporation and from exccssivcly low or high temperatures. This is especially true in the first 7 to 10 days. Concrete can be kept moist by sprinkling, covcring x i t h water, applying muisture resistant seal coats, and by using moisture-retaining covers sucl~ ;re burlap or ci~ttoncloth. Air around concrete should lie maintained a t 70°F or ahore for a t least 3
606


Foundations

200°FI, tlie cracking tenilency also increases. I t is. tlicrcfore, necessary to gu:1rd ag:rin?t rxceseively hip11 teinperdtures during hot 71-eather 11y shading tlic concrete from the direct rays uf the sun and using cooled inixing ~ v a t w .

from a distance of about 3 ft. The douhle-acting halnlner aids the force of gravity by supplying energy on the downward stroke. Drop hammers are often used for driving light piles. These are simple devices employing ~vincliesand hoists to lift a ram and then permit it to fall again. The driving of piles is judged by skilled operators on the basis of the inches of penetration for each blox. They arc usually driven t o a predetermined resistance iueasured as the numher of bloxs required for the final inch of penetration. The last blow in turn is related empirically to the safe load that the pile may bear. The penetration of piles thruugh denre strata can be aided greatly hy the loosening action of a strong stream of water near the tip of the pile. This process is called jetting.

The Finished Foundation

After the concrete is cured, the forms are carefully removed to avoid injuring the surfaces. l'rojcctiune are reiiiored by rhippiiig. Holes may he repaired 11y chipping out to produce a t least n 1 in. deep rcct;lngular area. The chipped area is then filled with successive layers of in.

607

FOUNDATION PLANNING AND ARRANGEMENT General Practices

Fig. 22-9. Typical nnchar S o . 2, 111 (1947).1

bolts. LRcprintd

by prrrnibrion. Gco. Stevens, Puuxr, 81.

thick concrete. Compressor and pump fuundations must be left rough a t the top after pouring so that grout ill adhrre to the foundation when the machine is installed. During and after the completion of the foundation all anchor bolts should be carefully protected from damage and bending. For large machinery such as compressors, removable bolts (Fig. 22-9A) are preferred. >lachines can then he skidded into position ~vllilethe bolts are removed, and broken bolts can be replaced easily. Piling

When piles are required they are driven by a hammer supported on vertical leads bung on an ordinary crane or a machine made specifically for pile driving. The hammer is driven by a single-acting or doubleacting steam or air reciprocating engine. The single-acting engine lifts the ram (3000 to 5000 lb) and allows it to fall by gravity onto tlie pile

The layout and preliminary design of f~~undations starts with the arrangenlent of the major process equillulcnt. Pllmps, colllpressors, vessels, heat exchangers, or uther cquipmcnt located essentially a t grade, are set on separate raised concrete sections. The base of the equipment or top of concrete is always elevated a t least six inches above non~inal area grade. I n general, all niajor equipment ~vlietherhoused in an enclosure or located in the open, has a separate or independent foundation. An independent foundation is one that is unattached to the floor or x o r k area slab and extends to tlie depth required to transmit the load to a firm stratum when using spread founiiations, or ti) a pile-cap in the case of piled fuuntlntions. Steel colunin Imse; of structures or structural steel >upports for equipment (Figs. 2 2 - 1 , 4 and 51 arc set on reinforced concrete pedestals, exten(ling ahuve :irca. grade and provided with anchor 1)olts rast in place. The steel structure like other equipment muit he securely fixed iu pi~sitii~n.The scparate concrete pedestals s u p p ~ ~ r t i nthe g coluli~ns extend to ii~dcpenrlent~ p r e a dfuotings or t o a pile cap. Equipment Drawings

Since equipment varies in dimeniiuns, and foundations cannot be designed until riimcnsimal data are known, tlir various ~nanufactmers Impare drawings showing the dimensions of their equipment necessary for installation. The rnnnufncturcr also utilizes these drawings for securing approvals from the purchaser. T1iu.s a series of transmittals takes place as descrihrd in (:hapter 9. I k p m d i n g upun the type of cquipnimt. several montlis may rlapsc froni the time of onler placelncnt and receipt of the ~ i i a n n f ; l ~ - t ~ ~d;it:i r e r ' or s vcrrdor prints. Vendor prints are the only reliable source of dilucnsional data and

608


::ccurattt dimensions are necessary f11r tlic preparation of all inr;tallatioli drawings including foundatirln dra~vings. 3Innufacturers must. thercfor~,. certify thc correctness of tlie dimensions on the drawings thcy f w n i ~ l t . These prints are known as Certified Vendor Prints and gnarantee in effret that the equipmcnt \rill bc furnished in accordance ~ v i t lthe ~ dimensiorl sho5~-non the draxing. Although the lower portion of foundatinns conrtituting massive pads may be poured, the upper or final portions. n-hirh contain the anchor bolts and conform to the shape of the equiptn~~nt (,annot be poured lintil this certified dimensional data is rccci\-cyl. I'll,, lack of vendor print6 can delay construction as seriorlsly as the delay in delivery of the cqnipment itself. Economics

As in most design and planning for plant c~rnstrnction.econornirs is important. The follol~-ingcost factors must be considered. Concrete Costs

Cuncretc in its mixed state, ready for ponring or placcmrmt in a form, :r relatively cheap inaterid costing from $5.00 to $15.00 per 1.11 yrl. lhese costs, up to tlic point of pouring, depend on: ( 1 ) quantity; (2) methorl of mixing; and (3) mix specification, in that order. Thcsc are tlie costs only thrl~ughthe niixing phase. Finnl cost of concrctc n.11rk; however, is considerably higher, ranging from $40.00 for simple poln-s t o $200.00 per en y d for conlplex pours. This increase is duc to: (41 nmterial and labor for form building; ( 5 ) matcrial and labor for bending and placement of rcinforcing stcel; (6) lahor for plncemcnt in the forms, including vibration; ( 7 ) labor and matcrial for curing prowdure; (81 labor for form stripping; (9) labor and material for cement finishing. I n items 4 through 9, labor is the governing factor varying from 5 0 v to 809, of thc total costs. Thc labor costs of form building d l usl~ally exceed all others. Cost of concrete foundations seldo~u exceeds $65 per cu yd based on 1954 labo~,rods. App~.oxi~nately 60% is for Inhor. This figure ~ l l ~ n ~ l r l not, bc used intliscriniinately for all foundation vork. Tlrc ro.~tper rll yd for large mats cmsisting of many hundrcds of en yd of concretc ~j-itll little or no forming ill be much belolv $65. Otllcr factors affecting concrete labor costs are labor productivity in thc area, climatic conditions. working conditions, and type of n-ork. 1;:

?.

to the p i n t of pollr at a fixr~lprirr. Gcncrnlly thc delivcrerl price of rc;trt>--mirr,l concrctc !!'ill Llc fairly rlosr to the ro.st of plant-mixed eoncrete ~ r l ~ cthe n requirements do not exceed 4000 or 5000 cu yd. I n coniparing the two the cost of plant-mixed concrete should inrlude costs of the niixing equipment on a rental basis, material handling a t the mixer, and conrrete transportation over thc johsite. If concrrtr is to br mixrd at, tlic site: provisions must bc made for dry storagc of ccmcnt, aggrcgate storage. and a water supply. I n cold climates provisions must be m::dp for heating ~ r n t c rand nsunlly aggregate. Thus if the amount of concrete r c q u i r ~ dis not n c e s ~ i v c it , is i~r'nallymore ~ ~ e ~ n o ~ l to ~ i rpur:%l clr;lse concrete mixed an11 Itarc it delivered to the forms. Forms a n d Dimensioning

Since the major costs in foundation construction are labor costs for form building, simplification of concrcte shapes and thus fornl n-ork slioulrl reduce costs. Thus all possihlc changes in snrface whi<>hmight he 111adi' to cffect small economies in concrete volume should be avoillcd. Flat panels ;iw less espensive t o form than protrusions, offsets. or any change in fi~rnlsurface. The uac of metal forn1s for all flat surfaces conserves both form ~nnterialand labor since thcsc iorms may be erected in about 1 4 the time require11 for roode en forms and may be re-used as soon as renlovccl. Furthermore, thc concrete surface nil1 require little or no finishing since metal forms leave a snlootl~and clean surface. hl(1dular metal forms can be uscd for practically all types of concrete work, but the dimensions of the foundation must conform to the form sizes available. Costs \rill he rcduced if dimensions of foundations are based iln standard hnnber sizes or standard metal forms. Fractions of inches should be avoided unless required for anchor bolt dimensions. Stondardizafion

Furt11t.r economies ran bc obtained by standardizing certain types of projects require a nunibcr of squ:~re pcdcstalu for f ~ ~ u n d a t i m sMost . supporting structural stccl columns used for pipe supports. B y setting onc stnndard sine for these pedestals and standard anclior bolt sizcs based on tlic se\.erest serviec, costs of design, drafting, field cngineering, and iorin building are all greatly reduccd. FOUNDATION DESIGN

Ready-Mixed versus Site-Mixed Concrete

Certain other basic costs, such as thc source of concretc materials,

sometimes seriously affect foundatiori and other concrete 111:lterial costs. purcli:ts?d rv;r,ly-nristyl. ('1lllrTi~tt~ Illay hc mistvl ;:t the johsitc 111. m:ly I n nr7nrly all domestic industrial areas ready-mixed conercte is delivered

Design Basis a n d Soil Mechanics

A foundation consists of the concrete mass, the reinforcing rod, and the surrounding soil. Since tlic man-made portion of the foundation murt be supported and surrounded by the subsurface soil, it is impossible t o

610


select a foundation type and to design it for a givcn application ~ v i t l ~ o u t careful considcrntion nf soil mechanics. Became of thc large variety of suhsurfacc conditions peculiar to earl^ m a . a designer must rely on judgment hased on experience in that area. For this reason it llas i)r~.omecommon practice t o engagc local foundati~in engineering consultants to aid in the soil analysis and testing program as well as in decisions necessary for foundation selection and dcsign. Foundatim drsign is cnipirical in nlany respects. This is particularly true if the fo~indationniust rest on clay, sand, or silt. Load tests made a t the jol~sitcare nccessary for any such soil with questionable suliporting capacity. Tliesc tests when properly made subject the subsurface strata to conditions similar t o thosc anticipated for thc plant equipment. Load tests are made by applying weights (sand, rock. $tee11 t o a platform resting on test piles or hearing platcs, if piling is not contemplated. The bearing plates shonld rest on the soil a t the same lcvcl planned for thc footings. As the load is applicd, settlc~nrntnhserretl for each load increnlcnt is recorded. These tests may a t times prove rostl>,. Iiut nevertlieless should be made wlicn reromnicndcd by ~:omjrctcntsoil experts. Load test information togethcr with soil analysis &a providc tl~c! only sound basis for design in questionable soils. Settlement a n d Foundation Failure

Two important factors must bc considered in the dcsign of each foundation. First a foundation must be designed so that the soil ur rock upon which it is resting supports both the load imposed by the foundation and the equipment bcing carried by it. Wind loads and other cxternal forces must be considered also. The single inost important factor in this phase of design is thc bearing capacity of the soil or rock. I f the hearing capacity is exceeded the soil or rock will give xvay and the foundation ill collapse into the ground. It is possible, Iiowever, to construct a foundation that will not exceed the bearing capacity of a certain soil, but that will settle into the ground. If this scttlernent hecomes excessive it can cause cracking of the foundation, particularly if the settlement is uneven, and prnduces undue strain on structures which are supported by the foundation. Differential settlement between multiplc footings supporting a singlc structure can cause difficulty since concrete columns begin to crack when the diffrrential settlement exceeds :!/, in. Steel and brick can withstand grcater am~)unts, but all are adversely affected.

Foundations

61 1

The following brief description of design considerations for varioo> types of lirwess plant f o u n d a t i ~ ~ nrvill s proviile a superficial kno\vle~lgc n.hir.ll. ~vlienproperly w e d , n-ill aid the project engineer in understallding the problems of the foundation engineer. Soils a n d Design

As already emphasized, tlic character of the underlying soil or rock must he an in1l)ortant factor in foundation design. Each type requires a diffcrcnt basis for design. I t will usually be found. for instance, that the soil pressure permitted for maximum allowable settlement for s:md is less than required for bearing capacity failure.' Hence, the allol\-a11lc settlement usually governs the dcsign of foundations in sand. The rvidtll of a sprcad footing or a mat located in sand influ~ncesthe a l l o ~ r a l ~ hearing le capacity of tlic soil (the \$-ides the footings the greater the capacity1 Clays, on the other hand, do not cxliibit such incrcascs in allo~~-able or safc capacity ~ v i t hwidth. Furtlier, it cannot he statrd definitely whether settlement or bearing capacity ill control foundation design for clays. Both must he chrckcd. After the foundation is designed for a clay soil. a prediction of the settlcment bascd on laboratory cunrdidation tests must bc made. I n clays and silts, t,he only reliable method for determining the safc load on pilcs is by means uf pile load tests. Empirical safe-load pile formulas should he used only ~vlienprcvious experience %vit,hthe sanle soil conditions has indicated reliability of the formulas. Design Calculations

Onre tlrc allowable safe soil pressure or allowable bearing rapacity is determined by a conlbination of soil tcsts and judgment, actual design of the cuncrcte portion of the foundation can proceed. I n imlust~.ialpracticc standard computation procedure forms arc 11s11311y preliared for specific designs. The arrangcnlent of thcse forms follo\v.; the logical steps in the c~nnputation. Since foundations arc concerned v i mnrily ~vitli~veigllt)all 15-eights are tatiulated. The kip or 1000 11) unit is employed by nrod ,designers. Althougli standard forms are used by many organizations the priire~lures r a r y \\-idcly. l l a n y of these tcclmiques havc been published and those common to process plant practice are included in the references,Y.4.B.i.8.'J.1 0

Spread Footings Design Procedures

No attempt d l be made here to outline or recommend design techniques because foundations, due t o the empiricism involved, must he designed and selected by experts in that field,

h simple ralculation yields the area required for a concentrically l~inded spread footing. when the depth of placement of the footing and thi, I X ~ C snil pressure ior settlcment or the allowable bearing capacity i m given. * T h c usual safety factor for bearing capacity is 3.0.

61 4

Project Engineering of Process Plants that phase of the design v4l not he discussed, and the thickness will be assomed to he 2 it. The wight of the foundation and tower r d l be calculated as f o l l o ~ s : Area of 6 f t octagon = Volume of top course = Area of base (octagnn) (a) = Volume of base = Total volume = Weight of concrete = Volume of earth fill (4 f t - I St) X (151 sq We~ghtof ealth fill Keight [IS empty toxel

*Kc = 30,000

= =

Foundations

This loading is satisfactory. as the soil will safely support 2000 psf. Thc minimum soil loading due to dead load before internnls, ladders, piping, and liquid are added is: 125.i00 lb = 830 psf 151

0.828d2 = 0.828 X 6' = 29.8 sq f t 4 f t X 29.8 = 119.2 en ft 0.828 X 13.5" 151 sq ft 2 f t X 151 = 302 cu ft 119.2 302 = 421.2 cu ft 421.2 cn it X 150 lb/cu f t = 63,000 lb

This is the dead load under the w x s t stability condition, and since it is greater than the orerturning stress ( 8 %= 803), the soil hrlrw the foundation will alrvays be under compression a t all points, thus indicating that the fourrilntion is stable.* Usually it is found that the first assumption of foundation size is not correct. in which case another assumption is made, and the calculations repeated.

+

St - 29.8 sq f t )

=

363 cu ft

363 cu it X 90 lh/cu ft 30,000 lb

=

32,700 ih

T h e calculations shown in t h e above example d o nnt complete the design of the foundation. Next, t h e various stresses in t h e foundation must be calculated to be sure t h a t they are helox t h e allor~able. Permissible stresses for design a r e recorded.4.8,Q Theac stresses include diagonal tension produced by the upward action of t h e soil. This is a n eccentric reaction which tends to break t h e foundation along a diagonal starting a t the foot of the pedestal and on the l e e ~ r a r dside. T h e foundation must also resist t h e tendency to shear along t h e bottom l e e ~ r a r ~edge l of the pedestal. T h e shearing loud is produccd hy the dcad load and the ~ ~ - i n d load and in its calculation allowance must be made for t h e load-carrying capacity of the soil. Other stresses include t h e bending produccd b y the upward reaction of the soil which must be resisted b y the reinforcing stccl, bond stress between concrete a n d steel (must not bc excessive or steel will not act with full strength), and hearing stresses a t t h e hase of tower. These and m a n y other considerations must he carefully analyzed before a foundation can be completely designed. Much judgment and many assumptions are necessary. Only experienced designers should attempt the design of t h e more complex foundations.

+ 63,000 + 32,700 = 125,700 lh

*KOn111 be as follows:

TI7

=

a

=

S, =

Insulation, platforms, piping. etc. Water required to fill the tower (4 f t diam) (50 it high) Total (TI',) 125,700 48,500 = 174,200 lb 151 sq ft, and from eq. 1

+

=

9,000 1b

=

39,500 lb 48,500 lb

=

174,200 lh 151 sq f t = 1155 psf = maximum dead load on soil

Allowing 3 in. for the thickness of the insulation, the effective diameter of the tower exposed to the action of the mind is 4.5 ft. 1wind velocity of 100 mph is equal to 25 psf of projected area [PC= 0.0025(100)2].

Therefore

P, = 25 psf Do = 4.5 it H = 54 ft P , = 25 X 4.5 X 54 Height of foundation = 6 ft

=

6080 #

Mats

1 From eq. 2

s , = z00.000 ft-# -- 803 psf

248.5 = maximum soil load due to overturning moment.

'The total n~aximun~ soil load (toe pressure) can be calculated from eq. 3, as foil<,,, 5 :

+

S = 115.5 803 = 1958 psf !wight of towrr and iaundntion. 1V. = weight of nppurtcnances and water necessary to fill tower for pressure test.

'Ii't

=

615

I I

T h e design of m a t s is influenced b y t h e type of soil. Because of t h e large area of a m a t the soil loading in sands is usually coriaiderably heinnthe allowable hearing capacity. Soft materials such a s clays, l~oi\-cvcr, have low bearing values. I n such cases excavation to a greater depth will uncover strata capable of greater load bearing capacity. T h e eccentric loadings produced b y wind on the equipment ordinarily supported by large mats a r e never a s great a s for unsupported t m e r s . B u t t,hese loadings and thc stresses produced tlierchy should he rhrrked. More commonly, however, the eccentric loadings causcd by difrcrential settlement of large mats which support tanks r a n produce stresses sufficient t o crack the foundation.

*h-S2

-

+27 #psi mininrunr soil loading. Positive sign indicates eomprcssion.

616

Foundations


' r n n k ~heing supportrd by ring xalls filled n.iil~smcl must h ~ c:11x,f11lly . designed. The ring rail must be so proportioned that the soil pressure? under the tank bottom are equal a t the base of the nall. Because of the tremendous weights carried in storage tanks it is essential that thc eharactcristics of the soil under thc entire tank area be knmm accurately. ( h l y tht-n ran supportr he designed which u-ill not undergo r1ifferenti:d settling. Massive Foundations

No satisfactory metlml has hecn developed for designing massive foundations to resist kinetic rcartion of m ~ ~ c h i n e r y .Equipment manufacturers are prepared to provirlc r a l n e for t l ~ runbalanced forres an11 vibration produced by their machinery. Experirnre'O has shown that the total mass of equipment plus concrete foundation should be cqual t o 15 t o 20 times the disturbing force for reciprocating equipment. Specific recommendations for each type of equipment s h o ~ ~ lhe r l oht,ainerl. Hcavy foundations must, of course, be checked carefully for soil loading. Piling may be necessary for massive foundations tnore often than for other types. Piles

The stresres in the pile cap must be determined in the same manner as for spread footings. The a l l o ~ a h l eload on each pile can he determincrl by an empirical formula, as mentioned above, but load tests arc preferable if doubt exists. Smaller Equipment

Foundations for smaller equipment such as pumps. filters, and dryers &reoften poured in the form of rectangular solids \vith straight s i ~ l r sand no offsets. The periphery of the support must conform to the periplrcry of the equipment and the foundation base must he extended t o firm stratum. Small process equipment usually has a low mass-area ratio and thus unit soil loading is invariably below the hearing capacity because of the large foundation area. Reinforcing stcrl is rarely rcquireil in these installations unless it is needed to insure secure attnrhmmt of consecutive concrete pours. I t mould, of course, be possible to undercut the base of the foundation since tbe large area is not needed for support. I n such cases, ho~~evel.. tension is created in the foundation and reinforcing steel is required. The added cost of the steel and additional form work usually offsets any saving in concrete. Xumcrous excellent articles and lrandbuoks have been publislledl,?," in addition to standard texts on foundatim design which out-

e.7.".",10

617

line dcsign procedr~rc~.The clarity and li~gical l~rcsentation.; in t11csc I.rferenccs, lio~verer,may cause the novicc to consider foundation design sinrple. As in any specialty field, handhouks, codes, and papers have hem written to reduce the routine of design. Inlplicit in all of these Ircscntationsl ho~vcver,is the assumption that an experienced designer ;L heginner under the supervision of an experienced inan d l use them vitll the judgment necessary for safe design. .I 11lant is certainly no 11ettrr than its physical foundation. 111~.on*i~lered "rnrings" on foundations can cause mucl~necdlws expmsc and unintisfactary plant operation. REFERENCES 1. A.C.I. I3tiilding Code (ACI

318-51). m e r i c a u Conercte Instilute, Delrmt,

1951. 2. Bolmg. In.ing. P c i d a u m Refiner, SO, So. 4 . 126 (1951). 3. C o n c r t c Pi1i.s. Povtland Ccmrnt Associ;ttion. Chicago, 1951. 4. C.E.S.I. Ihaign Ifandbook, 1st Ed.. Concrete KeinIol.cing Stcel I t ~ r t i t u t r . iition. Chiwgo. 1052. 6 . Fork.,~C. H . .. P e t r o l e i ~ mKcfiner, . . SO. S o . 3. 81 (1951) 7. Fwk. C . H . , Pclrule~intRefiner, S t , T o . 11. 145 (1962). 8. Marslmll, V. 0.>Pt.lioleun~R e f i m i , 2, KO.8. 101 (1943). !). Rcircforecd Coats-etc Design H a n d b o o k . American Concrrtc Inslitnte, Detroit,

1948. - 10. Steven. Georgr. Pon.ri-, PI, XI,. 2. 111 (1947). 1 1 Stibsoil l a w s t i a n t i o m fur Poundatio7~s,Cat. 04, Raymond Cunrrrte Pile Cu.,

usually masonry structures x i t h flat roofs which are supported by the walls and partitions. \Vlien several floors are required, thc strurturc framing may be either steel or rcinforccd concrete with thrx roof and exterior walls above the first floor supportcd from this framing. The lightest possible materials are used for csteriur ~vallsin order to w d w r the dead load, and insulation is used t o provide weather protection instead of many layers of brick and masonry. I n milder climates, simple steel-framed structures are used for lrousing mechanical equip~lent. LIetallic or corrugated asbestos-cement siding and gabled roofs corered witli the same materials are generally satisfactory for single-story structures. Flat roofs are illore common for multistory buildings. Some of the more common huildings in proccsr plants include huildings for housing process equipment, office buildings, change houses, cnfcteria and recreation center, medical facilities, laboratories, and shops and wareIiouses.

STRUCTURES AND BUILDINGS

Buildings for Process Equipment

The modern process plant is located almost entirely out of doors and contrasts sharply with the totally enclosed plant of a decade ago. Now only instrument control centers, critical machinery, and operations requiring cmtrolled atmospheres are enclosed by buildings. Automatic control instruments, and weather-proof and explosion-prmf motors h a r e enal~ledthis striking change to take place. Today t,he most irrlposing structures in a process plant are the large unenclosed structural steel skeletons which are used t o support equipment that is operated from the c o n h r t of an air-conditioned control room by means of automatic instrumcntation. Thcre are three typcs of structures for process plants: ( a ) the totally enclosed structure, the conventional industrial or commercial building; ( b ) the partially enclosed structure which is a simple t,ype of roofed shelter; and ( c ) the unenclosed structure which is a n unshcltered structural support. TOTALLY ENCLOSED STRUCTURES

619

Structures and Buildings

I

-BUILDINGS

The types uf huildings usually found in process plants are relatively simple ones, similar to thc mill huildings used in heavy industrial plants, with the exception that process plant buildings arc generally of rnuch liglrtcr cunstruction. Single-story structures in the colder climates of the United States are 61 8

In cold climates some culnpanies h a r e found it advantageous t o locate process units in buildings, hut the necessity for euclosuree in any climate is rapidly diminishing. Some pieces of cquipsncnt, however, must be enclosed regardless of climatic conditions. Tlrese include: (11 certain heavy mechanical apparatus such as electrical polr-er generating macliiucry, (2) small hatch or kettle processes, (3) processes or lnecl~anical equipment handling solid materials which must be protccted from the xcather, (4) packaging equipment, (5) certain types of mechanical filters. (61 major or master control panels; and (7) any equiprrlcnt or process which requires constant operating at,tention. I n warm climates buildings for some of thcsc items vill be opcn-sided a t points ~vliercwiml will not interfcrc wit11 the proccas. Those 1)uil~ling; \vllich are completely enclosed such as control rooms will be airconditioned. Office Buildings

I n designing officc buildings the most effective studies can be made hy making cut-outs of desks, chairs, file cahinets, and office uiachines. Tarinus arrangenlcnts of these cut-outs can be made on a plan view of tire proposed office space. Heat and ventilation, lighting, traffic, and office equipment requirements can also he studied in thi: manner. Good office equipment arranged in such a way that it causes inefficiency or constant annoyance t o the staff is of little value. If, for cxamplc, several persons must work together in a room, the seating arrangement should provide as much privacy as possible. Two persons sllould never

-

620



Iw wntwl so t11ey 1lnl.t f;rw enell irthcr. Rrg:rriIlr~s( i f pcr~rmnlity.s11rl1 arrangements lead to problems. I n general, separation of each individual even if only by glass semi-partitions is better than group arrangements. The proper floor upon ~vhichto locate a given group must be given ~ a l . e f u lronsidrration. Assumc t h a t a n mginewing department and a purchasing i l q ~ a r t m r n tare to bc housed in a tvo-storied structurt,. Loration of these t ~ departments o in the same building is functional since in any organization n-here engineering anil purchasing is p e r f ~ ~ r m ead consirlcrablc anlount of rollal~orwtionr i l l bc n r c r s a r y . T h e next question is I ~ h i c hdepartn~cntshoul~lbe located on t l ~ rg r o ~ ~ nflr~or. d Purrhasing department personnel are usually more active in ilmling with outside firnis than any other department except sale.-, and n steady flov of representatives from other firms r a n always Ile rinticipated. I t folluas then that the purchasing department sl~ouldbe on the ground floor to facilitate the reception of salrsmen and visitors. Change Houses

Tire design of employee change l~ouseeis rrlativcly simple. A count must be made of employees undcr various ~ v o r k cla~sifications,and personnel in clean types of jobs separated from heavy maintcmnnce workers. Foremen and supervisors are also often provided with sepilratc space. Generally each employee is provided v i t h two lockers, one for work clothes and one for ordinary clothing; ho\~-ever,many different arrangements are made depending upon company policies. The problenl of ventilation is hest solved by using single rather than back-to-back arrangement of lockers. This permits the lockers t o air from but11 back and front altl~oughrequiring more floor space. Ceiling lieiglits for change houses should not be less than 12 ft t o permit better natural air circulation. Slmver r o o m .slrould he provided with d o m and completely partitioncd from other parts of the building t o reduce l ~ u n ~ i d i tas y niuch as possible. Lighting nray be kept to 25 foot-candles for extreme economy. Careful design of circuits, horever, can provide better lighting a t little addition:d cost. I n larger plants there are free laundry facilities for outer clotl~ing (coveralls etc.), and these are operated hy the locker room attendant. T h e existence of such facilities removes any excuse for continued uneleanliness. Heating may be by forced hot-air circulation in the colder cliniates or by ceiling and wall radiators or unit heaters. Generally it is desirable to provide sonle means of forced air c i r c u l a t i ~ ~for n year-round ventilation in all climates.

62 1

Cafeteria a n d Recreation Center

(:aietcrias for industrial plants may be rquipl~ciln-ith r,o~npletekitr111.11 facilitirs or may be dcsignril for -1iort-oril~~r~vmking n-it11 cmril~lt~tr dinner. fur~~islred by eatcring scrricc.. IIotrl crluipment cul>l~lylrr~uses arc lrelpful in the planning of complite kilclien facilities and r i l l usually prepare a list of rc~cilmlllcndedcqili~llnent. Adequate storage ellace sl~ouldbe l~rovi~lril fur rnnned goods. 1111lk nlllst Ill, i n l i l t goods: and regetables: and refrigcratio~li n ;hlli-in l i;r~,ilitil:~ for meat storage. Tllc cafeteria counter 1s 11:u;ill!- rlcsigncil as :I uuit to suit tlrc specific lr~cationand service. Tr:iffic must he studied ti] aroiil mngcstion. T h e total space requirrd for t:il]les can 11c ~ ~ s t i m a t chy d TITOviding irmn 10 to 1,; q f t pcr prr.iin; I~or~--rwr, tlic best proccdu~cis to lay out foul.-person tables. If largcr t:il~lcs arc crcr .;uhstituteii, nrorc persons I I I : ~IIC ~ :i:co~~l~~l~~il:itcil. Cozts for rccreation f:rr,ilities may 1,c rrcliicc~li1>- coml~iningthe recrcation arca ~ i t l tl l ~ rplant r:lictcria. Thib nrr:ingrnimt ofirrs ni:lny 11o.ssibilities. I t pro;.ides morc spare if large g r i ~ u l ) s o fpcrs~~nncl ur visiti~~': are to he entertained ; ~ n di t enal~lesbetter sen-i1.e if food is to be ~ ~ r o v i i l e ~ l for these occasions. .\Io~-:~ble partitionh n-hirh fold into thc 1\.nll ran bc used fur isolation of ccrtaitl areas. One part ( l f the cOlll~lin:itil~llToolll iin11 lil~rnry can bcromc R l i l ~ r i ~ rury ri,a~ling~ I I I I I I Irquipl~edn-it11 ~11elv1.s tal)lcr. Wnll spncc i l l ~ n o t l ~ 11:irt e r may he nrr;~nge(lfor milring ] ~ i r l t ~ ~ ~ , l , projection. Fol~lingchairs can Ile l~ru\-i,le(li ~ n dstored il\vay 1\-11rn not In use. 1,avatory farilitics ~cl~ould 11e ~ ) r ~ \ - i i l:irljaccnt c~I to tllc kil<:11~11 fur ci~fctcria help and h g r r f:iditics ( 3 to 10 ~II".>IJII.~ each IIINI(::mil ~ I ' I I I : ~ I L . I located conveniently for pewonnel being served. The design of heating. ventilating. and air-conilitii:ming servircs ivill rlel~endupon the company's policies. If an ;air-con~litimingsyitcnr iproperly dcsignctl and the structure has h e m adequately insul;~tcilt l ~ v operating costs will llc rcl:rti;,cly lo\,-. \Tit11 ln'oper zone control rvlif~l~, areas may be isol;ited, tlierehy reducing the load. I n 11-arm and l~inniil cliuiates air-conditioning is a neccsiity. The ro~nl~in:iti<,n cafeteria and rrcrcation cmtt:r rcyrcsrnts t l ~ cmininlunl in facilities i i ~ ~vorkcr r cimvenicnce ill the proccss industries. I\lan!plants provide country-club style recreation buil~ling;, slvimniing 11o11l>. libraries, and sports equiln~lent. Each coulpany n~ust,decide the extent of recreation facilities necessary for its particular situation. Plants located in large inetrupolitan areas do not requirc as nlucli as plants located in remote areas. Medical Facilities

Pl:~nt size and 1111,:1tioriarc the l~rin~;ir!. con;ider;~timx in ilrt~wnininp tho type of medic:il f:icilities n1wl171l. Pl:~nt.- 1,wxtcml I I W ~ ~,itic>~vit11

622


liospital facilities can use ambulance service, and provisibn need only be n u d e for tempurary bed patients. Kaiting rooms, examination rooms. and uffiees for tlie physician and nurse are required, ho~verer. A comhination examination and surgery roo111 is sometimes provided if tbe nearest hospital is one or two hours a v a y . Operating roilins require anesthesia facilities, special lighting, liospitalt,ype lavatories, sterile containers, and sterilizers. All e q u i p e n t must be grounded to prevent cxplusii~ns. Grounded types of floor tile are available for this purpose. An analytical medical laboratory is necessary if extensive pliysical examinations are contemplated. Xedical supply firms will reconimend tbe equipment necessary for routine cxaminatii~ns. Process Plant Laboratories

1.aborati1ries for tlie process plant may be designed as Control Laboratories, General Plant Laboratories, and Researcli Laboratories. Control Loboralories

I n niany plants simple control tests may be 1)erfornied in the operating area. Usually n sink with water, air. and other liquid connecti~~ns d l suffice. The extent of apllaratus provided varier with the function. General Plan1 Loboratories

I n addition to the actual lahoratory work rooms required for General Plant I.aboratories, space may bc provided for a chief cl~einist,assistant, cl~cn~ists, shift chemists, library, file room, supply and store rooms, and locker and slimvcr roonis. Isolated and air-conditioned space is sometimes necessary for analytical equipnient such as rpectropl~oto~~~eters. In roille cases lead shielding limy he needed fur floors, walls, doors, and ceilings of rooms housing m11io:xtive materials. Arrangenicnts for tlie gcncral analytical laboratory equipment follow conventional patterns. A number of firms specialize in custom-built Iallorntory bcnches and related equipment,, and it is more economical t o purchase equipment from theni. The furniture, though standard in design, is unitized and can be arranged to suit almost any situation. Propcr ventilation for the lahoratory is usually a problem which requires eoneiderable study. All office, technical, and clerical personnel and facilities not related to actual analytical work sliould be located togcther in one end of the building or on a separate floor. If a choice of floors is pmsible all such personnel and facilities should he located on the ground flour. If the Iaburatory is air-con~liti~~ned the two gericriil areas, office and analytical, should be on separate recirculation systeins. An alternate


623

arrangement could he reciroulation in tllc offire area and v m t i r ~ gor 100C : , I Y I I I ~ S C\v;~stes ~ c11n1~(1 air. The make-u11 in the analytical a w a . T l l i ~of aniount of air circulation can l,e rcducerl if opernti~~ns e v ~ ~ l r i nnosio~ls g or disagreeable iurnen arc. crmd~~ctcd in hoods. 1,ighting for the analytical arcas of the 1abor;rtnr~-sholllll be of higli foot-candle intensity (75 t o 1001. Fixture selection dcpmds on tlie typrs of laboratory m-ark. I n more hazardous areas all lighting may have t o be vapor- or explosion-proof. Research Laboratories

Process plant research laboratories must be flcxible in design and layout since the operations performed in any one area may change. Research it: often conveniently divided into bench scale and pilot plant research. The bench scale operations are best conducted in two-man laboratories eomplete with hoods and all utilities. Special racks for assembling tall glassware such as laboratory distillation colurnns are required, and convmicnt desks and files in the laboratory are necessary for each rcscirrclrer. Pilot plant facilities may bc located outdoors or inside light prefabricated buildings. Buildings and structures shuuld be ennstructed with the knowledge that change in such facilities is inevitable. Safety precautions should not be neglected, holverer, just because the existing equipment is known t o be temporary. I n designing researcb facilities, every attempt sliould be made t o provide working conditions conducive to creative thinking. This implies comfortable, quiet, and pleasing surroundings. Conference rooms and adequate library facilities are essential. Shops a n d Warehouses

Sbops and varchouses are no longer ugly, dark, and dirty places in in a process which t o work. Modern mcchanieal shops and ~varel~nnsc~s plant arc designed t o provide the maximum in wnrkcr comfort and thus worker efficiency. hIaeliines are usually painted pastel shades which are easy on the eyes and enable more rapid location of knohs and pusl?-1)nttons. Better illuniination together with well-designed painting scl~cmesassure a minimum of eyestrain. Kew shops in w m n climates are being furnished v i t h crmplcte airconditioning even in the areas used fur \velding. Tlit: increased costs are apparently offset by greater worker efficiency. Anyone involved in the design of s l ~ i ~ or p s ~i-arehoust'sshould thoroughly study the needs for the particular plant. If pos.sible, the slinp or I n r e house foreman sliould aid in all the planning stages.

624



625

Economics in Building Construction

I n planning buildings for process plants, the designer is often confronted xith attempts hy management t o reduce costs. Procccs equipment costs arr nwnlly fixed. and ~~-1ien total estimates lnust lie reduced, it is a common proccrlnre to attempt savings in buildings or huilrling facilities. In grneral savings effrctrd hy rednction of building sizel or hy limitation of i'arilities sucll a; lighting. heating, ventilation, and lavatories only result in poor employee morale. Building costs. ho\\-ever, ran be reduced hy the w e nf new and l~etter nxttcria1.s. IYlrile the rl~aracteristicsof tlie hasic or fnnilamrntnl materink , masonry have not rhangcil of con-trurtir~ns11r11;IS con~,rete,s t ~ c l and :qy~recial~ly in tlie last seveml decades many hundreds of new matcriala or new uses for existing niaterials have heen developed n-hieh reduce labor msts. The cost of exterior ~valls,for instance, may be greatly reduced by using light metallic panels instead of masonry. xot only is there saving in labor cost but also in time. Light panels ~ v i t hfixed insulation n u ~ yhi! t v r t e d in day? ~vhilcit takes Iveeks or months for a ~naeonrywall. l\lany sinlilar economies can he effected by alert tmgineering organizations. PARTIALLY ENCLOSED STRUCTURES - SHELTERS

Sonic process equipment, such as large process pumps and compressors, need not he rncloserl in a tluilding hut do require prrltection from minfall and snolv so that maintenanre of the eqnipnient may he done in a sheltered area. Tlic vnrions parts of conipressors must he handled hy mechanical means i ~ h e ndieassenil~ledhrcnusr of their great ~veiglit. The sheltering structure, t l w t ~ f o ~~e n, n s tprovide support for overhead crnnes or monorails. Compressor piping is also large and ~ n n s tbe supported. Although compressor shelters art, not nc~wsarilydcsigncd to ~vithstandhorizontal forces iron1 piping. it is connnon pmctiw to design the major structural menihers to carry the dead loads of cmnceting piping. Other shelters that arc romnion in process plants include those for loading racks, barrel storage, and salvaged equipment storage. UNENCLOSED STRUCTURES

- OUTDOOR

PROCESS UNITS

In most areas of the U.S.. particularly south of latitude 40°, it is common practice to install tlie major portion of the process or opernting equipment without shelter (Fig. 2'3-1). Shelters of some kind lnust he provided for operating personnel, but improvements in instrumentation permit all major instrnmeuts to he located in a control center. This not only provi~lesa shelter for operators but also enables them t o observe the process froni a single location.

flamn~;~ble :nid cs1,lo~iveT7apors are rare in outdoor 11l:mts. Fur these rrasons, 11vxr1yall l~rowasp\:\nts, l ~ : ~ r t i c ~ ~ l aTVIII'K r l y cIi111:ttic~ ~ o n < l i t i o n . ~ :ire l ~ u lwvcre, :wc clc>iynctl Till. uut,loor instiillntiun of mu>t pruccss equipment. Punqw, nlotors, n l d rrtl~crcqnilnnt.nt 1l:lve Iiem drsignrd t o operate satisfnrtorily x$-hcn rxl~cwcito ; i l l ly]ics of \vr:itllcr. '1'11~ ; i d ~ l i t i ~ ~costs nal fur auv11 \ \ - c a t l l c ~ ~ l ~ ~isu ui~rqligilllc, l i ~ ~ ~ 111 C ~ I I I I ) : L ~ 1~0. -Lllikli~lg UII COSS.

626


Types of Equipment Supports

Unenclosed equipment d i i c h mnst he elevated above gradc may be supported hy either structurill steel or reinforced concrete. Structural steel is less expensive p:rrticularly for multi-story structures, but rcinforccd concrete columns have thc advantage of requiring little or no maintenance since they are unaffected by many of the corrosive vapors common to process plants. I n addition, concrete n-ill not fail when subjected t o fire Thilc steel must be protected by the application of a concrete coating. When "fireproofing" is necessary, therefore, reinforced concretc structures may prove the more desirable, especially for single lerel structures (10 ft t o 15 ft ahove grade). General Considerations in Planning Equipment Structures Arrangement

I n addition to supporting elcvatcd equipment, space and access must be provided a t the elevated level for operating inspection and for maintenancc. Heat-exchangc~sand other equipment subjcct t o dismantling will require more space than simple chambers or vessels. Any equipment d-hich must bc opened or disconnected periodically must be arranged for disassembly in placc or for ren~ovaland lowering t o grade, and equipmcnt a t lower levcls must be arranged t o avoid a n y interference during this operation. The structurc nus st also be dcsigned for the forces encountered n71icn lowering of equiprncnt is in progress. Wherever heavy equipmcnt or its parts are dismantled or lifted, hoisting apparatus is providcd. Gantry-type cranes are sometimes installed if many pieces of heavy equipment subject to dismantling are grouped togethcr. A monorail with trolley is provided for isolated pieces of equipment. A portable air, electric, or manual hoist can then be attached t o the trolley when required for lifting. Modular or fixed spacing of columns, as used for office or other multistory building structurcr, is seldom practical for structures designed for the process plant. Instead, tbe w i g h t and the desircd arrangement of equipment should govcm the column arrangement. Main structure columns, of course, must be locatcd on common centerlines t o simplify design and improve stability. When a number of floors are planned, floor spacing should hc made cqual if possible to simplify general design and stair arrangements, and t o improve stability. Floors

Concrete slab fl~iorsare installed when maintcnancc operations for elevated equipment arc extensive, or when operating personnel must spend


627

considerable time on the opc~,;itilrgfloor. Stct.1 plat? or ,nratin: floo1.s arc used for arcas requiring only occasicnial attenti~ln. Grating is preferred to steel plate in areas in which snow orcurr. since sno~r-arcun~ulateson steel plate and crcatcs a hazard. Grating also requires a minin~unlof cleaning and reduces the w i g h t of thc structurc, an importnnt factor for tall structurcs subject to high wind loads. Attachments

All equipment must bc securcly holtcd t o the supporting members. Horizontal cyli~~drical vessels, drums, and hcat-exchangers arc usually supported a t two points only. These suppiirts arc ta-o tramverse s11oe.i welded t o the equipment. Equipment ~~-11ich changes dimension under operating conditions is arranged so that une end is frcc to movc in a guided direction. Largc vertical toiwrs located in a structure ur uhove gradc arc usually supported a t the lower end. Lugs welded to thc pcrip11ery are used for sn~allercquipmmt. Since lieat rx(~11:mger~ h a ~ ~VIIIOYe able heads a t both cuds, they must a l r ~ a y sbe supported along thc length of the rquil~nicntso that the lieads may be rcniovcd. Intcrconnecting piping for hot equi1xnent must he restrained und,/or guided so that strcsses caused hy changes in ter~~pcrature, either in the piping or the cquipment, are controlled or al~sorbedhy the supporting structure rather than t l ~ cequipment. Since many of thcsc streases cannot be calculated beforc all piping dcsign is completed, it is common practice to overdesign structures for process cquipmcnt rather than delay thc final dcsign of structural steel. -4nd further) since ncnrly all processes are subject t o modification, it is usually more economical to design major mernbcrs slightly heavier than rcquirml rattier than design ior the ahsdute minimum as in commercial building practice. BASIS FOR DESIGN OF STEEL STRUCTURES

The detailed design of stccl structures must follow the practices outlined by the American Institute of Steel Construction.8 and reinforced concrete structures those of the .4mcrican Concrctc Institute.',7 Either of these codes may be amended according to the requircmcnts for the particular type of plant,. Specifications vhich must be dcvcloped as a basis for design include the following:

I. Structures thirty it in height or above 1. Weight of equipment. (a) Empty; ( b ) operating or filled with prorejs fluid; (c) testing (fillrd nith m t e r or other trcting Huid). 2. Wind loads; use niasinium ;\ntiripted vind and calc~dnttlui~dfor each of the three conditions above under itern 1.


~

~

fonmda 20 p?f for Type 11 6. S t r i ~ c t ~steel ~~rl

7. Kcini'orwd steel ironcrcte)

..\reording to AISC According to .\CI

111ailditim to tlicsc, specifications for the particular installation must, include n unnibcr of qwcific r ~ i l ~ ~ i r e m esni t~sn i l a rt o those illustrated in tlic folloxvi~igq~ecificationb, All li:rrngrnl~llsrliould be numbered fur later i~lmtifirntiunor rcvisiun. Inl-olvrd general statcnient:: in spccifications oftcn lead to misunderstan~ling.which usually rcsult in aclditional costs. Any statcnlcnt sh,xiId 1 1 ~ .cra~uineilti1 lie sure thc exnct meaning is understood by both i ' a l ~ r i o i t ~and i r customer.

IV. Misrcllaneous rrqi~irenlents 1. If locd building codes require increased design rqnirements such incrmsnl \.:dues shall form thr b : ~ kfor h i g n . T h e n local code requiren~mtsare less than the req~~irrments hrrein or rvonlil permit lighter designs, the requirenrenti herein ?hall govern 2 . Clearances. n . Railroad clearances. S o structure, nor equipment of any kind shall be permanently located rithin a rectangle seventeen (17) f t wide b>-

629

Iwnly-1~vo( 2 2 ) it high, ihr wnivrline of n-hie11 i; the r,cnlerline t l ~ ~ r:iilroad tmck, and the h ~ i g h tof which rectangle is measurrd from the top of the railroad rails. (Sote: Alan? states hare statutes rr-hich fis railroad clearaners. The-e dimensions conform to most requirements.) h. Eleetriral p o m r line clearances. The minimmn overhead clearance for olwn wiring carried on str11ct11ra1supports or entering buildings, or run ~djncrntto structnres above rondxays or milmy track rails ?hall he t~rpntyeight (28j ft. The minimum horizontd elearanec f r o ~ n~tnlrtnresshall be ten 110) f t . TViring entering bi~ilrlingsor nm inside the :~horelimits ih:~ll he corlosed in conduit. r . Pipine rle:~r.~nrcs.Piping run or~rhendon strnctuml supports or otherwi-r -1i:dl clo:~rro:ld\\-nys or railronrl rails by not less th:m twenty-five 1%) f t froor highest point of road crown or t o p of r:~ilrun
T h e use of stcel a s a supporting framework for clcvatpd structures is probably faniiliar t o ewryone. N a n y decades ago certain shapes v e r c developed which would give maximmn strength with minimum weight. Design formulas were proposed based on these shapes, and tabulations of properties w r e made so that the structural steel designers' task is much simplified. I n general, the common "rolled" structural steel shapes, such its beams, coluii~ns,channels. and angles, sutlice for nearly all types of heavy structural design. \Vith the advent of electrical arc ~veldingand its general acceptance in

63 1



industry, other special and light shapes are built, such as the well-known bar joist, (Fig. 23-2) used as a supporting member. Many other types of r\.cidc~ilplate or builtul~sl~apcsarc used in the manufacture of prefabricated, rigid frame steel structures.

bearing alloys. In most cases either these materials are more costly than carbon steel or the required fabrication processes arc inore costly. Alloy and nonferrous materials have been used economirally, however, when corrosion or weight problems exist. Aluminum and its alloys have been used to good advantage for exterior panels and window frames, and stainless steel structures are often used in particularly corrosiw atmospheres because of the rapid disintegration of other less expensive materials. Stainless steels also have greater strength than carbon steel, and some reduction in weight for a given design is possible.

630

REFERENCES "I"BEAM

"W"BEAM 'Wide Flonge' O e i i g n a t o n : 14 W 3 0 ( 14";30;)

Designation: 15145 05":45$1

CHANNEL

ANGLE

oe3ignotion:L 4 " 4

DeSignotion: I0 U 20

110": 2 0 +I

t in

Mo

nr

B A R JOIST

Fig 23-2. Commonly used structural shapes.

Common structural members are shown in Fig. 23-2. Each section is manufactured in a number of different sizes. For instance, "equal-leg" angles may be obtained from 1 in. by 1 in. up to 8 in. by 8 in. in a number of thicknesses totaling 80 different sizes and weights. About 120 different sizes and weights are available in unequal-leg angles. Standard manufacturing practices and the properties of various carbon-steel structural sections are given by the AISC8 and manufacturer's catalogs. I n addition to carbon-steel as a structural framing material many other materials are available, such as the various stainless steels, aluminum, aluminum alloys, magnesium, magnesium alloys, and the many copper

1. Building Code Requirements for Reinforced Concrete (ACI-51), American Concrete Institute, D ~ t r o i t Mieh., , 1951. 2. Carrier, W. H., R. E . Cherre, and W. A. Grant, Modern Air Conditioning, Heat and Ventilating, 2nd Ed., Pitmsn Publishing Corp, Keti York, 1950. 3. Dunham. C. W.. Plannina Industrial Structures. 1st Ed.. MeGrati-HIII Book Ca., S e w Yark, 1948. 4. Gay. .. C. M.. and H. Parker. Materials and Methods of Architecti~inl Constmetion, 2nd Ed., John W i k y & Sons. Ten York, 1943. 5. Ketchurn, hl. S., T h e Design 01 Steel Mill Buildir~gs,5th Ed., McGr;irr.-Hill Book Co., Kew York, 1932. 6 . Procedure Handbook of Are A'elding, Design and Pmctice, 9th Ed., Lincoln Electric Co., Cleveland, Ohio, 1950. 7. Reese, R . C., C R S I Handbook, Conwetc Reinforcing Steel Instihtte, 1st Ed., Chicago, Ill., 1952. 8. Steel Construction Manual, 5th Ed., American Institute of &el Construet,ion. New York, 1952. 9. Stoddard, R. P., Brick St~mctures, 11th Ed., MrGraw-Hill Rook Co., S e w York, 1946. 10. Suthcrland, H., and H. L. Bowman, Structural Theory, 4th Ed., John Wilry & Sons. New York, 1950.

Safety in Plant Design

SAFETY PLANT DESIGN Safety must he a paramount consideration in t h e design of a process plant. T h c mass US steel t h a t is fasl~ionedinto a plant will ulti~nately be operated by human beings d i o s e health and well-being must he protected. Disregard of safety in t h e design of a )prure,ss plant is comparable t o criminal negligence. Each drsign cnginrrr shoulcl feel a responsibility I he willing for providing a safe design H e slioulcl ask l ~ i ~ n s e l "IYould f: t o operate this equipment as it is 110n. designed?" If t h e a n s w x is "no" or if the "yes" is ~ v c a k ,the rctuons for the uncrrtainty a l ~ i ~ u lhe d found :1nd corrcctcd. T h c designer should. 71-hcuevrr possil~le.iliscuss his d c i i q ~vitlioperating men and the 11lnnt safety cngiucera. Thesc inen are keenly ; w a r e of safety and d l have many good suggestions. HAZARDS IN PROCESS PLANTS

T h e 11:lz:rrds to bc considered in thc design of any process plant can hc grouped ruugl~lyinto three major categories: flamt~iahleaud e q ~ l u r i v e , hygienic, and mechanical. X majority of chemical processes are potentially dangerous because flanmable and cxplusire nlaterials are produced. T h e design of equip~nentfor s u c l ~plants ~ i l u s tbe dictated by characteristics of t h e materials being processed. One's memory on t h e combustion characteristics or explosive limits of materials should never be trusted. Careful investigation of thcse charactrristies of the materials t o be l~aullledin the plant should precede d l dcsigu calculutions. 632

633

A n u n i l m of cliemiral pruduct;; constitute ilrfinitf h c a l t l ~1iaza1.d~.Prolonged breathing and/or skin contact over a long period of time of suc11 materials a s benzene and carbon tetrachloride can cause permancnt impairment of Iicalth or even death. It is surprising t h a t many scientifically trained people are u n a v a r e of the hazards to health presented b y some common chemicals. Although there are excellent references on industrial toxicology ~ v h i c hcan be used as guides: all hut the most cornlnon chemicals sliould be referred to a trained industrial toxicologist for study hefore liandling techniques are devised. Mechanical hazards include all the hazards created b y inoving equipmcnt and arrangement of equil~nientand structures. Thcsc classifications are s i ~ m e ~ v l i aarbitrary t and overlap, but they serve t o en~phasieethe primary hazards in process plants t h a t create or a r e capable of creating unsafe vorking conditions. accident prevention proCareful design combined with ~vell-l~lanned grams have produced amazing safety records. 3Iannfacti1rcrs of tctrnethyl lead, for instance, xvere faced with a n unusual health probleni due to t h e poisonous naturc of the raw materials and product. Rcnlizing this problem even before the dcsign of t l ~ cplant ~ v a si ~ e g u ncreated a n a v a r c ness t h a t influenced all design decisions. T h e result has been an enviable record of safe operation. Sources of Information

M a n y safe practices are no more t h a n application of common sense. T h e problem is t o rccognizc unsafe situations before they a r c incorporated in plant design. Basically, this involves determination of the hazards that exist. I n additiot~t o many books on safety a n d industrial liygiene,'~2~"".'".'Vliere arc a number of handbooks, codes, and similar publications b y numerous agencies interested in safcty and fire prevention which are l ~ e l p f u lin defining potential hazards. A selection of these is given below: I. Fire and explosions 1 N*'ntionalFire Protection Sssocintion; GO Rntterymnrch Street, Bastoll 10, blass.; a nonprofit technical and educational organization; publishes: a. Standards: widely ndopted throughont U.S..I. as basis for construction. Following summtiries of standards arc :~v:dable. (i) Sational Fire Codes for Flammat~leLiquids, Gases, Chemicals mil Explosives. (ii) Rational Fire Codes for the Frel-ention of Dust Explosions. (iiii National Fire Codeg for Building Courrruction and Equipment (i1.i Rational Firr Code; for ~ . x t i n ~ u i u h iand n ~ S l a m Equipment. ( v ) Rntidnal Elrctricid Code. b. Quartrrly of thc Sntional Firc Protecti~n.4ssoeiation: up-to-ilntr information on fix-: ~ n dfire prevention. c. SFPA Ilnu~lbuolrof Firc Protection: a handy reference work.

634



2. National Board of Fire Undervriters, 85 John Street, Ncrv York 7, New York: an educational, factual and engineering organization supported by the c u ~ ~ stock ~ t d fir? insurance compwni~spublishes: a. Stnndanla for fire protection many of which are based on NFPA standards. h. R ~ ~ e a r creports. h c. Special reports on unusual disasters. (Most of this information is sent free of charge upon request on company stationery. Advice and counsel on certain phases of fire protection problems not nox covered by codes or st:lnrl:irils r a n he ohtained.) 3. Other insurauce organizations: The Factory Insurance Associaton, 555 .4sylum Street, IIartford 2, Conn.; Amociated Factow Mutual Fire Insurance Cmn~inny,18-1 High Street, Boston 10, Mass. These also operate research laboratories and publish standards. 4. Frderal Agencies, Washington, D.C. n. 1. U S . Bureau of Mines-research reports and recommendations, minerals, dusts, and oils. b. U.S. Dept. of Bgriculture; dust explosions and fires. c. U.S. Drpt of Labor, Division of Labor Standards; safe practices recommended for various industries. d . N:ition:d Bureau of Standards; fire hazards and fire resistance research. P. ITS. Pnhlic Health Service; industrial hygiene publications. 5 . National Snfrty Council, 20 N. Wacker Drive, Chicago, Ill.; mainly safety education. Research work conducted-advice available (nonprofit). 6. Cndermitcrs Laboratories, Inc., 207 E. Ohio Street, Chicago 11, Ill.; (nonprofit). T~wtsequipment (electrical, fire protection, etc.) to insure safety. Lists of tested and approved equipment issued annually with hi-monthly supplrments. 7 . L:iws; federal, state, and local laws relating to fire protection and buildings. Many refer to various provisions of the NFPA codes. 8. Insurance companies and local and state fire prevention bureaus can provide valuable advice. 9. Amcricnn Petroleum Institute, 50 W. 50th Street, New York, N.Y.; publishes bulletins on Fire Protection in Refineries. 11. Industrial hygiene 1. M:umfscturing Chrmists' Association; publishes chemical safety data sheet for thc safe handling and use of many chrmicals. 2 . Nation:il Safety Council; publishes health and safe practices pamphlets relatire to the handling of various chcmirals. 3. m e r i c a n Industrial Hygiene Bssociation; publishes technical quarterly on in~I~lstrial hygiene. 4. U S . Bureau of Mines, Washington, D.C.; dusts and toxic vapors. 5. Atomic Energy Commission, Washingbon, D.C.; radioactive materials. 6. Mellon Institute, Industrial Hygiene Foundation, Pittsburgh, Pa.; research. 7 . Division of Industrial Hygiene, U S . Public Health Service, Washington, D.C.; publications of various typrs and advice. 8. American Medical Association, Committee on Physical Agents of a Hazardous Nat.ure. 9. Chemical companies; publiuh information on the safe handling of their own products. Producers of tetraethyl-lead, for instance, recommend and furnish complete design for equipment handling the ethyl fluid. 10. Sax, N. I., Handbook of Dangerow Maten&, Reinhold Publishing

635

Corp., N.Y. (1951); gives hazardous properties, treatment, and antidotes; also sueerstions for safe handling of numerous toxic materials of commerce. 111. &hanical 1. Equipment manufacturers; will recommend safe installation procedures. 2 . U.S. Department of Labor, Division of Labor Standards; publications on safe nractices and recommendations for industry. 3 Xat~onalSafety Councd; safe practices, recommendations, presented in pamphlets. 4. Codes for constrnct~onof vessels, tanks, piping, electrical equipment: a. ASME and API-ASME Codes for Unfired Pressure. b . ASME Boiler Construction Code. c. American Standards Association Code for Pressure Piping. d. API Standard No. 12C and 12E for Storage Tanks. e . National Electrical Code. 5. Liability insurance companies; publish helpful data rrhich aid in the design of safe plants. PLANT LAYOUT

T h e safety record of a plant depends partially upon the arrangement of thc various units and the location of equipment within thoac units. F o r tliis reason alonc zafcty considerations should permeate even t h e early planning stages o f plant design. Topography a n d Weather

I n selecting a site topography a n d meteorological phenomena should be carefully considered. Hilly areas present certain inherent hazards. Overflowing tanks or vessel failures can send thousands of gallons of flammable materials into surrounding areas. If the area is hilly, these materials can reach a wider arca a n d if ignited cause a rapid spread of fire. Prevailing ir-inds should be considcred in t h e layout of a plant so t h a t flammable and toxic gases can bc properly dissipated n i t h o u t endangering t h e lives or comfort of plant personnel or peoplc in the surrounding areas. T h e occurrence of sucli n e a t h e r phenomena a s inversions should be analyzed. T h e atniospheric temperature normally decreases with altitude. During periods of inversion t h e reverse is true. I n such situations the loner atmosphere rcniains stagnant, and smoke and noxious vapors hang over the earth's surface and create extreme health hazards. T h e DeA'ora, Pennsylvania disaster in which a number of peoplc died was caused by such a condition. Any area t h a t has frequent inversions lasting more than three t o four days should be rejected a s a possible site for a process plant. Division of Plant into Units

T h e operating unitr of a p r o w s plant should he srparatrd not only for more efficient operation and ninintcnence hut also for safety reasons. By

638


2 . Proride a snificirnt number of m;inholes and hantlholes for inspectio~l and nrnintmance, and orient to permit easy access. 3. Avoid screnwl nipples for small nozzles. Use 6OOO lb couplings. 4. Xozzles above 1% in. should be Hanged. For high pressure, use flange6 nozzles for all sizes. 5 . Careful inspertion during and nftcr fabrication; a competent inspector can m w h to prewnt vessel failures. a , Inspection of materials. b. Inspection of mrkmanship (especially quality of welds). c. Witnessing of radiographing and stress relieving. 6. Atmoqheric storage tanks should be provided vith ndeqnate vents for breathing (the taking in or dischzrging of rapor as the pressure in the tank inerrases or derreasm dlir to change in temperature or liquid level). a. L-re vacuum-prenw~rebreather valves (consrrration vents) b. Use floating-rnof tanks for volatile liquids. c. Connect rapor spaces of gas-tight tanks to a single tank serving as a gas holder. Providc relief d v e s for all tanks, holvcrrr. i . Automatic tnt:illy enrlosed tank level gages prrfcrred; manual gage hatchrs whjret opemtor to needless hazards. B. IIrat eschangers 1. If both inlet and outlet of exchanger require block valves, pn~viderelief ralrr: on cold slde to prevent excessive thermal cxp;~nsion h l m y exploiion;i h:ive orcurred becausr of eurh expansion. 2. Sufficient drains should be provided for maintenance. 3. Each Huid space of an errhanger should be given an individual test. 4. If units are to be stacked, they must, be st:ickcd during the testing process. 6. If mixture of shell and tube Huids constitutes a hamrd, extreme care in design and w o r k m a ~ h i pmust be excrcisrd. C. Moving equipment (pumps, etc.) 1. Provide guards a t all couplings, belts, and chain drives. 2. Providr a r l ~ q x l t espace betx~.een units for safe and convenient servicing. 3. .\utornatic overload, overspeed, or other devices are good invrstments on machinery such as compressors. 4. Proteetire devices such as strainers on pumps and liquid knockout drnmi for compressors are essential to safe operation. D . Piping 1. Abore-ground process lines are prcferrcd. These may be elevated or placed at ground level on sleepers. Buried lines constit~~te a hazard since leaks are not readily detected. 2. If lines are installed in trmches, fire stops and drains mnst be prmided at regular intervals. 3. .\rrunmment of ninine~.nnd rslves is imnortant to safe oueration a. Large ralvrs in particular must be readily accessible from platforms. 7 ft 0 in, is thr maximum distance from centerline to illatform Annroximatrlv .. level. .4bove this chain operators are used. b. Use double-block valves for hazardous equipment which must be removed while remainder of unit continues to operate. A small tell-tale valve in between double blocks indicates leakage. c. Arrange long yard lines to avoid congestion so that in case of fire any portion c:m be isolated from the renlainder by closing a block valve. d. Ilcadroom for overhead lines should be np~~roximately 15 ft 0 in. abovc roads; 13 St 6 in. above platform; 9 ft 0 in, above grade. If a line must be

..


639

located belorr 6 it 6 in., locate considrrahly below and provide a walkr\-ay over it. e . Fuel supply valves for furnaces should be in a remote location. /. Emergency dump ~ s l v e sshould be located at a safe distance from the equipment to he dumped and preferahl5- behind a heavy wall or building. g. Install valves discharging into open tanks so rhat operator can operate without undue exposure to vapors or splashing. 4. Check valves leak; and if such leaking is intolerable, provide a blork valve in addition to the check valve. 5 . Avoid angle valves. 6. For structural reasons avoid pipe smaller than 1 in. fnr overhead line.. 7. Drains for low points and vents for high points should be pro~ided. Use 3/4 in. or larger sizes. 8. Water lines, rspecially fire lines, should be looped. 9. Loop stf,am lines and provide block valres so steam can be provided from scrrml directions in case of failure of one portion of the system. 10. Separate sewer sj-stems may bc nccrisory for ccrtain haznrdous materials. Venting of such sl-stems must be carefully planned. 11. Firr stops are necesary in all snrfacr drainage sy-temp to prevent spread of fire. 12. Lines should be pressure tested prior to operation. Care mnst be taken to avoid overstressing certain pieces of equipment or fcmmlations during hydrostatic trsts. E . Electrical ~quipmentand grounding The safe installation and design of electrical equipment is carcfully out,lined by the National Electrical Code. The problenl requires the, attention of c o u ~ petrnt electrical engineers. They must be supplied with information on the hnzanls in rach part of the plant. 1. Means for remote shut-down of opcrating eqnipment in addition to locally mounted starters is desirable. 2. Critical items such :IS ST\-itchgearnnd tr;lnsformers should be loeatid ;is remotel)- as liractimble from o p ~ r n t i uunits. ~ 3. Identify nnderground ronduit by inclndine :I dye in tho concrete for the casing. 1. Protert rwerhead rond,~itfrom expourr to excrssive hrat. 5 . Provide emrrgency power supplies. 6. All portions of the plmt must be adequntely lighted so that operators cml avoid bodily injuries from b u m p or falls. 7 . Static electricity and lightning constitute real hazards to safe procrw plant, operation. Xeither can be pre\.ented b r ~ tprotrrtion is posiibk. Watch for static electricity :~rcun~nlation and diir.h:~rgesin the folln~~ing situations: a. Moving niachincry (belts, conveyors, etc.). b . Flowing fluids or dust. c. Human beings. d. Lightning. Protection is arrrmlplirhcd by propcr grounding of all equipment in arras whew static electricity is antieip;iterl. When all n~etalequipmmt wsts on concrete foundations, for instance, grounding must be installed. Instructions for proper prouncling of equipment are given in Handbook of Fire Protection,R the Sationnl Electrical Codes, and various govcmnlmt pr~blicationsg (See also sources of information).

640


F. Strr~cturalsteel 1. Protect from failure due to fire b!- corrring with concrete to the main support level or by providing cmergencl- nnter sprays for cooling steel in event of fire. '2 .ivoid interfermces of structural steel n-it11 piping :ind equipment. Interferences are sometimes remedied in the field hy removing or "cutting-out" portions of steel, thereby reducing the -trengtli of thc structure. :i.Platforms shoald be provided :it all operxtinn or inipectiun areas with a ? it G in. minimum vidth. 3 it to 3 f t 6 in. i.< prcferrnl in maintenance armaround manholes. 4. Stairways are prrfrrul~lcto h d r l m ~:ind at 1c;wt t ~ are c required for larger units. Use gentlr slope, 45' or lwa, and nidths of 3 St 0 in. or more. 5 . Snfrt>-a g e s arc rcquirrd for I:dd~.r-owr 15 to 20 it. 6. Handrail? are rcq~iirrdn r o ~ m lall pl;itiorms anrl stairwrys. 7. Tor plates ( G in. high) nronnd the etlgcs of platforms are necesrar!- to protect personnel froni falling objects. G. B~iilding~ 1. Finlprooi crmrtruction is essential in hazarduus nrcni. 2 , l'nlris abrol~~tely nrwz.;sr\- prorcis eqr~ipnient sho~~lrl not hr Iio~wril. Operation of outdoor plants is much safer. 3. P n r d r explosion door? to handle ;my porsiblc expli~iionsthat may occnr. 4. Provide automatic sprinklvr systems \\-lien practical. 5 . .it 11,iist t\rn exits are rcquirecl. 11. Imdation 1. I n d a t e all hot linrs ivith \I-hie11 personnel may comc in rontaet. Approrifor protection of personnel. mntely 1 in. to 1% in. of 85% m:~gnesiais :r~lrqu;~tc Nore, of co~irie,may be requird for heat conserr~tion. Detailed specificntion~ are ;rvailnblc from insulation rnnnufncturers. 2 . Inrulatr portions of critical instrument leads and electrical conduit in areas of rsresire heat or areas hen! fire is probable. VENTILATION


641

vxprrssed ns u p p r r aml Ion-cr lin~its. T h e 111rwrlimit r ~ p r r s c n t sthe 1ra.t amount of the mntcrial 11-hirlr d l sustain flame propagation when mixed with air, and the upper limit represents the greatest amount. These limits of flammahility a s determined experimentally are affected b y the typc of testing apparatus used. Extremely small apparatus in particuInr p o c h ~ r e snarrow limit3 of flammability, and rcsults from such equil). ~ caution. T h e flammability limits for mixtures rnent shoul,l he I I 1~-itl1 of several romhustihle gases am1 air ran bc estimated from a n equation d i i r h h n been verified espcrimentally:

I,",

where

=

100 Ca C ' + - + +C:,. 14 1,z I.3

..

limit of flammability of mixture. Mole % (upper or lower) I,R= limits of flammability (upper or lo\~-er)for gases 1, 2 , L1, IJ2, a n d 3, mole % (c.g., moles of g a d m o l e of gas plus air) C,, CZ.CR = mole C ; on air and inert free basis of gases 1, 2, and 3

L,

=

T h e units of this expression arc consistent since tbc summation of

C / L terms has units of moles of air plus n~olesof combustihlc per mole of rornbustible. Required Ventilation Rate

Knowmg tlic rate of release of hazardous vapor and t h e allolvahlr concentration of contaniinatc in a n e n c l o ~ n r c ,thc nrininiunr fresh air rate can he calculated from a simple material halance.

When process equipment must be located inrloi~rs,ventilation becomes major problem. Both toxicity and flammability of a material must hc ronridered in design of a ventilation sy.stcnl.

:I

Toxic Concentrations

Alatcrials such as aniline, the lialog~ns,hydrogen fluoridr, and phosgcnr are toxic in concentration? ;ii Ion. a s 5 parts per million. ~vliereastoxic concentrations of sucb familiar inatcrials a s ammonia, l~eiizcnc,cblorof o r q hydrogcn sulfide and carbon tetrachloride range from 20 to 100 parts per million. M a x i m u n ~allowable ronrentrations of various chcnricals bave been pnblished a s tahles.2 T h e user of sucb tables should he cautioned, I~owever,tbat rcsc:u.t,l~ on tuxic p r o l ~ w t i c ~ soni~' ,f n~i~tcrii~lr is incon~plete,and, ah new infor~ilationbeeoules available, t l ~ evalues o l allowable concent,rations m a y bc revised either upward or downnxnd. Limits of Flammability

Information on flammability limits of gases and vapors and metl~otlsof estimation have bccn p u b l i ~ h c d . " . " ~ ~ jT h e limits of flmnmnbility are

moles of c o n t a m i n a k entering enclosure per unit time moles of fresh air per unit time I,.., = lo\ver flammability limit or toxic limit ~vhicheveris smaller, mule t', contaminate per mole of air plus contaminate

n.hrrc r,.

=

r

=

T h c practice of expressing rcntilating capacity in air cliangee per hour sbould be avoided. If 15 air changes pcr hour provrs the correct air rate for one installation, i t does not follow that tl~i::samc rate vill prodnre satisfactory results in a n enclosure of smaller size. Air changes

=

rlir rate, cu ft! hour Enclosure volume cu f t/change

Local Ventilation

General romn ventilation can be supplemented by localized ventilation over t h e equipment from which offending vapors are being emitted. Sucb

642



local units are arranged as exhaust systems, and consist of hoods designed to catch the maximum amount of vapor or dust without interfering with the operation or servicing of the equipment. Hoods can be ]~laccdo r r r filters, a t pump packing glands, around crushing and grinding operations, and a t other similar installations. Positive Air Pressure

It is often desirable to maintain a higher air pressure in a hazardous area than in the surrounding rooms or the outdoors. T h e electrical equipment, for instance, which cannot be designed for explosion-proof operation can be installed in a hazardous area by p l a c ~ n gi t in a room under positive air pressure. Inert Gas Purge

T h e use of inert, gas is another valuable aid to ventilation. Inert gas is manufactured hy burning fuel gases in conrentiunal furnaces or, preferably, specially designed inert gas generators. T h e gas can be uscd t o purge tanks and wssels of toxic and flammable vapors before purging with air so t h a t men may enter the vessel. Men have died after entering inefficiently purged equipment,. Every process plant which handles toxic or flammable materials must be equipped with inert gas generators or air or steam eductors for removing the toxic vapors and flammable vapors from tanks and vessels which must be entered by personnel. Ventilation for Comfort

I n addition t o removing flammable or toxic materials generated in enclosed areas, ventilation and conditioning of the air in operating buildings is also important to workers' comfort and morale. It may be considered safe for men to v o r k under hot and humid or extremely cold conditions, but the worker's efficiency and dexterity are reduced under such conditions and accidents may develop merely because of fatigue, discomfort, or low morale. Design of Ventilating Systems

I n process plants extreme care should be exercised in locating inlet and exhaust ducts t o avoid short-circuiting of fresh air (entrance of fresh air into exhaust ducts). T h e degree of mixing of the toxic or flammable gas with the room air must be known in order to decide upon location of exhaust openings. If possible, vapors removed from rooms sl~ouldbe treated before releasing to the surrounding atmosphere. Centrifugal or cyclone separators, spray or packed columns, air filters, and electrostatic precipitators can

642

render exhaust gases less ohjectiounble. I n any event, the gases should be discharged from the building in t h same ~ dirertim as the prevailing r i n d . Rerolving-type roof ventilators permit such a discharge ever. with variable winds. PRESSURE-RELIEVING DEVICES

I t is impracticable to design proress equipment for every possible condition that may arise through abnormal situ:~tions. Fortunately, however, abnormal situations can be liandlecl by the use of preasure-rclierir:b TABLE 24-2.

Conditions Requiring Relieving Devices

Comhtion Failure of cooling a i ~ t e rsupply to fractionating tower

Design Basis Vapor equivalent to maximum total overhead rate

Failure of fractionating tower reflux

BIaximum possible flow equivalent to total overhead rate

Entrance of foreign highly volatile matel.itll

Calculate vapor flow based on instautaneous vaporization

Exposure to fire 1. Calculate heat input on hasis of PAW data which in equation form becomes approximately: log q = (0.796) log S - 1.7

where q

=

S

=

heat input to vessel in millions of Btu per hour surface area exposed to flame in sq f t

2. Pse for exposed surface area

Hol.izonta1vessels One-half cylindriless than 20 ft in cal surface plus dim1 area of heads Horizontal vpssels All alea up to 20 ft more than 20 ft ahove ground in d ~ a m Vertical vessels less than 20 ft high

All rircumferential area plus bottom head

Vertical vessels Lower 20 ft of ares greater than 20 ft high For insulated vessels (2 in. fi~cpron' insulation or above) reduce eslculateZ input by 20 C:,

644

Project Engineering of Process Plontr TABLE 24-2.

Conditions Requiring Relieving Devices (continued)

Crrndition Cxposu~.eto fire (continued)

Design H:& 3. Cdcul:~ten p o r s genemted

sherc Ii' II

= =

It) lrr vapors latent heat

(Alternate method)

Safety in Plont Design

645

Discharge Rates of Relief Valves a n d Rupture Disks

T l ~ erare of dkrhargc for a relief valve or rupturc disk is calculated Tlie vapor formula is derived ;i.s*uniing a n ideal gas, adiabatic expan.sion: a value of 1.001 for t11c r;>tio of sllecific heats, and vapor flowing a t the acoustic velocity. Higher valucs of -prcific heat ratio r i l l give a lover discharge r a t e ; a n d , tl~eri.fore) tlrc 5implified formula given below is ronservative. Tlie io1~111l;ifor liqniiis is based on the siniplc o ~ i f i c eequation. l\Innufacturrrs furnisli handy cliartr and tables xhich facilitate thc calculations of rclicf I-ulvc m i l ruptwi. (1i.k -iact;. 11y the iollo\\-ing iorniulas for vapors and liquids.

1)ischnlgc rtttos of relief valves a n d rupture disks Tse r l / S = 22.000 This nlternate n~ctliodis far irwrr. 1';LlY conserv:~tive than the nicthod. Other metliods give intwmediate values.

Closed valves

Amount of fluid leaving vessel undel. normal oprrating conditions

A P C

=

,ll

=

=

7' = coefficient of thernxrl cxpansion. I ,'T p = heat supplied to fluid C , = heat capacity 11' = Iblhr

where B

The~.mnlexpansion of confined gases

Exenssire heat loads during :rbnormal operation

area of orifice, sq in.

= upstream pressure, psia

nozzle coefficient, 0.97 for relicf v:~lves 1 a~~curnulation), 0.81 for rupt,ure disks (consult m a n ~ ~ f n c t u r c r ) molecular \\wight al)solntc upstream temperature, F

=

Calculate incrcase in volume using Gas Laws

Vapor gelrerated 11)-addit,ional h w t in1111t

devices sucli a s relief valves or rupturc disks. Tlie ilcsign of prrssurerelieving systems requires careful study. I n a badly planned system, too many or too few arc installed or tliosc installed are not well pl:~ced. Sylvander and Iiatz14 have prepared a n excellent diacussim oil the design and construction of prewure-relieving systems. Some typical applications for relieving deviccs are given in Table 24-2, ~ v i t hsuggested design Lasis for each applicatiun. This talrle is b a d ill 11wrt on tlic n-urk of S y l ~ n n d c r;mtl I
Q = 38.1C

Q

=

A C

=

S.G.

=

=

S.G.

liquid capacity in gpm orifice area, sq. in. coefficient of dischnrgr. 0.40 for relief valves (10:'; tion), 0.61 for rupturc disks specific gravity

accumolit-

Relief a n d Blow-down Discharge Systems

Tlir 11ropcr disposal of inatprial:: ~ l i i ~ ~ l i a r ghy e d automatir relieving y blo~x--rlin~n valve. is ;In iniportant p l ~ a s e ilevices i r n ~ ; ~ n u a l lol~eriitcd of ~ j l a n td c t y . Xelicf valves which are located on top of high fractionntirig t o w r s can oitcn be vented to the atmosphere. Such atmospheric venting, lloxcver, is not always possible when large quantities of flamlnable vapors or liquids must be discharged a t a safe distance from t h e 11lnnt for disposal. T h e discharges of relief valves and blow-down valves c;rn be i n i ~ n i f o l d into ~ ~ i it single discharge line connected t o t h e disposal ,ection ( a t~urningpit, flare stack, or a quench tower).

648



Water a s a Fire Extinguishing Agent Water continues t o be the major firc fighting agent, and its uses expanded after the introduction of water fog nozzles and sprinkler systems. A steady stream of vater on a flammable liquid often does more harm than good, hut the nee of a fog or mist of water which tends t o smothrr Ihr firc in addition to producing ;I cooling effrct has provcd extremrl>sucressiol. The great depentlcncc upon ~ ~ a t as e r a firc fighting agent suggests the r a r e i d planning of fire water distribution ~ y s t e m s . Such a system inl-ari:hly requires fire pumps to boost the normal water pressure to the liig1ic.r pressures rerlnired for the fire hose and sprinkler systems. Fire p u m p must he carefully selected and have an alternate drive t o insure opcration w d e r the most adverse conditions. A typical dual drive fire pump i. equipped with an electric motor and a gasoline engine drive. The gasoline engine is used during polver failure. Other Extinguishing Agents Another common method of extinguishing fires quickly in confined areas is by s~notheringthe fire. This can be done hy the use of foal11 or inert gases such as carbon dioxide. St,eam smothering is also valuablc and is pnrticularly useful in extinguishing small fires around furnaces. Emergency Valving Main shut-off valves for lines carrying flammable materials should be located so they can be operated in case of firc. It, may be preferable in some fires to simply stop the flow of flanmlable matcrial and allov. that already escaped to burn. This avoids large concentrations of explosive gas and vapor. Portable Extinguishers I n addition to the permanent installations of fire hydrants, automatic sprinkler systems, and automatic carbon dioxide extinguishing systems. portable fire extinguishers should be supplied thrnnghout a proccss plant since a small fire can often be extinguished with ease by the rapid use oi :in extinguisher. Most large fires begin as very minor conflagrations, and immediate attention t o a small fire will often prevent a disaster. Selecting Fire Extinguishing Equipment The project engineer should be cautious in using handy fire extinguishing tables designed to indicate the exact extinguishing method for various types of flammable material. They give general suggestions and are not intcnried to be specific for all situations. These tables can he a helpful guide, hut advice of authorized agencies should be obtained.

649

When a n e x plant is being designed all niatcrials which constitute a fire l m n r d in the operation of the plant should he carefully studied. Case histories of prcviuus fires for similar plants should be ohtained so t h a t fire extingnishing equipment can be intelligently selected and placed. The Sational Board of Fire Vnderwiters, The National Fire Protection ASROciation, The Associated Factory I\lutual Insurance Agenoy, and other such groups d l sul~plyreliable information of this type. Plant Alarm System .4n alarm system should he installed in all process plants so that persomiel can he alerted in case of fire. I n most plants the alarm system ran he manual: although in some process areas normally requiring little attentiun, automatic alarm is prefer:ible. REFERENCES

Ywk, 1047. 3. Buvgcrs, hi. J.. and R. V. Wliecier. J . Chern. Soc., !I!/, 2013 (1911). 4. Uoggiin. J. J.. Client. Eng., 68, KO.6 , 125 (1951). 6. Fiii. Pirdeciiu,i in Rcfiwiiea, 3rd Ed., .American Prtrolr~om I n h t o t e , X e w

-

~

10th l < d . S:~lionalFitc P~.otrrtiunI s s o r . . Boston. 1048. 9. .Yrilioani Biircau o f Standards H a n d b o o k H.jO. Supt, of Documents, Washington. D.C., 1945. 10. \.afinnol Fire Codes, S;ltioni~iFire Protrrtion s i o r i s t i o n . Boston (1945). 11. Petty, Frank A . I,idusti.iol H y g u v x aud Tozirology, Interscience Puhlishcr.~, Inr., S e w Y w h , 1948. 12. Keigclutli, R . J . , S a f e l y u n d Ecmoniy i n H e n w C o n s t w c f i o n , hlcG~.a~r-Hill Book Cn., S e w Y u k 1933. 13. Hol,inson, C. S.. Ezplusio,ir, l ' h c w A ~ ~ i l u n t mid y I)esfxetii,c,tcsa, XlrCrarrH11l Hook Co., X e w Y o I . ~1941. . 14. Syl\mdrl.. 3 . F:.. :ind U . I,. I<:ctz. ? ' I K Dcriyn mid C o , i s l ~ . i ~ c f i oonj Pi.rsrri,c I { c l i ~ i i , ~ ,Sysfui,,r. g Engr s : I Inst.. Bdlctin S o . 31, Unir. of Michlgon I ' r m .\cbal. h l i d . . 1018. 15. Tliwntan, IV. %I,,Phil. J l u g . , 33, 140 (1917).

CONSTRUCTION

THE PLANT

design work is complete, construction may begin. At this point most of the responsibility shifts to the construction superintendent. The project engineer, however, must maintain active interest in the construction operatiom in order to interpret where~er necessary the intent of the drsign engineers and art as liaison between the construction forces and the enginerring design groups. Such work requires some knowledge of construction methods.

A

FTER

CONSTRUCTION Wlicn construction begins the work of the project engineer is rsscntiall~ finished and rompletion of the project dcpends 1111 t l ~ cconstruction ilel~art~ u c n t . The project engineer, however, cannot bc complaisant abont t l ~ c tecliui~~ues and problems of construction. On the contrary he must bc st1 well scliuoled in thc inetlrods of ronstruction t h a t he can forrsw and avert possible difficulties in construction vhile the plant is still in design >tages. T o understand the problems of construction thc proicct engineer should I ~ n wsomc understan~lingof construction planning. l;tl~or,and labor relntions, and :ictual ~,onstructiin~ ollerations. CONSTRUCTION PLANNING

Ileaign drawing> and spccificati~~na give thc construction d r l ~ a r t n ~ c n t rlctniled infomlation a l x ~ u td ~ a ist t11 be built, hut the?: do not presrribc thc uictl~odsof erertion. Long before actu;il erection begins, therefore, the cunstruction superintendent and his staff study prelinlinary engineering data and scale tnodels of thc plant to be erected. I n this way the most advantageous location for derricks and hoisting equipment can be chosen; major conetruction equipment can be selected, and the most practical con~tnlctionn~etliodsdetermined for each major piece of e q u i p nicut. Such preliniin;iry planning in the office always results 111 loxcr construction costs. 653

654


1

CONSTRUCTION PERSONNEL

The field or construction organizatiirn has two general clarsifirations of personnel, clerical persinme1 fur the field office and the craftsmen who perform the actual construction work. Tbe routine office operation. lor a construction job consist of local purchasing, receiving, and accounting operations, preparation of a weekly payroll, and maintennnce of daily labor cost records for each portion of the project. T h e executix-e persunnel for a construction project consists of a field project manager or superintendent, or both for large projects, assistant superintendents, gencriil and iubioremcn, and a n office manager. The key field i q a n i z a t i o n usually consists of from three t o five general supervisors including the superintendent. Office operations require from eight to fifteen c l e r i 4 workers. The i ~ i l l o ~ i norganization g is typical of one nliii,li could be used on a large project costing ten million dollars or more. 1. Field project ni:mager 2. Superintendent 3. .issistiint superintendent 3.1. Field engineer (civil)

4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.2 4.13 4.14 4.15

4.0 Field General foreman Area foremen I'iping superintendent Pipriitter forcmen Carpenter foreman Iron worker foreman Boilermaker foreman Bricklayer foreman Cement masonr). forern:in Electrician foreman Machinist foreman Painter foreman Asbestos worker foreman Sheet metal worker, foreman Rodman. reinforcing steel workers, foreman.

5.01 5.03 5.03 5.04 5.05 5.06 5.07 5.08 5.09

5.0 Office Officr: manager

Chief accountant Chief payroll clerk Buyer Warehouseman Rccciving rlerk Timc clerks Secretaries and strnographers Typist, svitchbonnl operators

Engineering groups sometimes work a t the jobsitr, hut they are usually separated from t l ~ cconstruction operations and are not considered here. T h e titles under 4.0 are also classifications of union labor. Organized labor requires a pnrtirular craft for each type of work. When the work of a given craft is completed thosc workers are rlischarged, but most crafts on process plant projects are used during t l ~ eentire project. The greater portion of construction work is performed by organized

1

I

Construction

labor. T h e construct,ion worker is essentially an itinerant worker and is employed permanently only when ire becomes a supervisor. Construction employee labor organizations make agreements with the contractor which fix the construction wx-ker's wage, hours: overtime rntes. and working conditions. I n general the union controls the employee, his employtnent. and his s1)ecific ~ v o r kas well as tbe area lahor practices. Unions constantly seek improvement in working conditions, n-age ratee and length of employment. The length of e~iiployrnerrtis incrensed by strictly limiting the functions ui each craft SO that morc types of rviirkers must be retained throughout the project. Most of the priiblenis x i t h construction labor arise from this practice which oftcn causes one craft, whuse n o r k is slack t o arbitrarily take over the work of another craft. h dispute results which is called a jurisdictional dispute. Jurisdictional Disputes a n d Labor Relations

T h e jurisdictional ilispute iii a disxgreiment hetween two or more crafts over which craft shall perform certain functions or parts of the work. T h e reasonable solution t o sucli questiuns ~ o u l dseem tu be mutual agreements betrwen tlic sevcml labor organizations n-ithont. employer participation. T h e employer is not necessarily interested in whether one craft or another perforn~san operation unless erection costs are increased or quality of work impaired. Regardless of his neutrality, the contractor may find himself in a dilemma when trying to choose between two crafts for a certain job. T h e craft not favored may "walk-off" or the dispute may induce a "slowdown" of otber v o r k . Some of tbese difficulties can be averted by agreements on division of work with the national offices of the various craft unions. I n any discussion of labor problems i t must he remembered t h a t the construetion laborer performs tbe most difficult typcs of work. Furthermore, he has no job security, and must attcrnpt to earn higher Tvages than regularly employed personnel. As underst:~ndingincreases liet~veenlabor, management, and labor leaders many of the iiroblcm~sucli as jurisdictional disputes will be more satisfactorily resolved. Construction Labor Distribution

T h e scope of work and type of project governs the types of craftsmen required on a project. T h e following work distribution is typical of a process involving fluids. T h e manhour distributions slion-n vary considerably rvith each project. T h e project illustrated is one nliicli is to be erected in 12 months. All foundations are spread-type and no piling is used. T h e total cost of the project, material, labor, engineering, procurement, fee and profit amounts

656


Construction

657

to 64.200.000 of n.hich 63.150.000 inrlr~dcsmaterial. e q u i p e n t , fee. and profit. T h e remainder. $1,050,000 is for construction costs, erection labor primarily.

ern1 foremen reccive 25$ per hour over t o p foreman's rate. There a r e approximately 300 different classifications of organized labor used in constrnction operations. M a n y of t h e classifications slightly overlap. Those s h o v n are most common for process plant installations.

Craftsman Distribution

klnximnm Craftsmen a t ]oh peak Craft designation P I,

B ('

ti

I

Craftsmen Pipefitter 1,ahrxer 13oiIer1~ker ('aq~nter I'lectriciun Ironworker

=

3.50

hlnxin~omused

3Ianhours

135

115.000 68.000 51,000 44,000 37,000 35,000 350.000

-53

30 45 3.5 45

Subtotal

M

Xiscellaneous crafts. clerical, and super!-ihion

40

50,000

Total -100,000 Craftsman Distribution by Month

XIonth

1000 nrnnhrmrs per month

l i u m l w of Men Used

C B ~~

P

I,

R

p~~

I

Subtotal

I

TABLE 25-1.

C~.aftsnran

I

1

!

I

Construction Labor Rates 1954-1955 Southwest Area U. S.

1. Painters 2. Tean~sters

\Yarehousemen 3. Lahorers 4. Ckmcnt finishers Thew r m f t m ~ e n(nos. 1-4) rereire time-and-one-half for overtime except for Sondn~-and any autho~.izedlrolidny which are paid a t double time. 5. Electricians 3.00 1:; Benefit fund, DO.Oi5,'lrr health, and welfare These craftsmen (So. 5) receive time-and-one-half for hours from 4 3 0 P31 to 10:00 PA1 Monday through Friday. 1 1 hours past 10:00 P31, Saturday, Sunday, :mrl holidays me l,aid a t dr,nljle time. If personnel are called from home after w u ~ . k i nhours ~ the)- 1,eceire IIOUIIIP time from home to home, i.e.. they n1.e paid for travel time as well as work. 6. 7. 8. 9. 10. 11. 12. 13. 11.

1rona.orkers 2.90 (Reinfo~ing)rodmen 2.65 Carpenters 2.625 Millwights 2.8i5 Operating engineers 1.975-2.75 Hear? cranes, tractors, derricks 2.75 Oilers 1.975 2.975 Health and welfare $O.Oij Roilermnkers .Isbestos workers 3.0625 Health and welfnre $0,075 3.10 Pipefitters 3:15 Bricklayers These craftsmen (nos. 6-14) receive double time for all overtime.

1.5. Sheetmetal workers

T h e columns indicating subtotal and total are peak requirements rather than averages. T h e total of c m f t s m m pcr month constantly fluctuates because of thc discharging of some personnel, changes in the work, ndvcrsc weather conditions, and off-schedule equipment delivery. T h e Sotali shown, if constantly a t work, would exceed t h e manhour level hy 10%. Labor Rates

T h e typical rates listed in Table 25-1 a r e so-called '.Journeyman" rates. Foremen receive from 1 2 % ~to 256 per hour over journeymen a n d gen-

Rateihr 2.50 -2.75 1.615-1.70 1.70 1.60 -1.80 2.625

2.85

These craftsmen (no. 15) receive tinre-;ind-one-IraIf for the first three hours over any regular working day and for tire first four hours on Saturday. All other overtime is paid 3t double rate. CONSTRUCTION OPERATIONS

Every project engineer should accrpt the first opportunity t o observe the erection o i a process plant from start to finish. An understanding of the many complex operations can be developed only hy actual obserration. T h e erection of a plant m w t procee~lwit11 the minimum of delay and a visitor t o a project is invariably impressed by t h e spirit o i action that, pcrvades the jubaite.

660

Project

Engineering cf

Process Plants

4

l ~ c k f i l li? II:~:IIIYI ~ Y U I I I[lit, : I ~ ~< i]o>>il~lc and ready for tbe installation of underground facilities. Installation of Underground Facilities As ditches are completed, pipe fitters hegin the task of installing underground piping, and electricians, underground conduit and cable. Thc nictliod of pipc installation varies with the type. Re11 anil spipi~t cast-iron pipe as used for x a t c r , process sewers, and drains is laid on ? I sand cushion to insure cuntinuons support. Tlie joints are pavkcii n-it11 plain or t a r - s a t u r a t d jute anil carefully caulked ~ i t n~olten h I t d . Aftvr t l ~ cjoints are niadc-up, firm soil is packed aronnd the lower lialf o f tl~i. pipe and ns tlir ditch is lmckfillcd tlie soil is tamped. .\Icclianical joint cast-iron pipe, niost often nseri for water, is laid in n similar manner except making u p of joints requires only the setting in place of a gasket and tightening of bolts. Cement,-ashestos crrnbination pipe can bc 1 1 4 instead of en-t-iron for some services. A collar and heavy rubber ring compose the joint which can he rnade u p in one-tcntli the time reqi~ire(lfor ltw~ledjoints. Vitrified tile is usnally uscrl [or sanitary sc\vr.rs mi11 wrrosive pruce?t fluid drains. T h e joints arc sealed ~ v i t h neat* cement or corrosion resistant mastic. Ungnlvanized carbon stccl pipe to lie installed undergn~unriis first coated and ~ r a p p e d . After the wcklcr:: complete tlicir work i t is clcaned and coated with rust-rcsisting paint and then bitumastic. and finally it, is >mapped with tarred felt or t,arred glass fiber blanket. If the quantit,y of pipe t o 11a wrapped is large, it is done by a nincliine \\-hidl moves along tlie ditch an11 wraps and l o ~ e r ; .the j ~ i l ~into c the ditc11. .4lI u n d c r g r ~ ~ u njoints d not t l i r r n d t ~ lin l~oltriiarc protected against Ienkage and xvatrr hainnicr 11y incans of concrctv :rnrholc. Tlic tanipcil soil alonc nronnd n joint is not sufficient to overcome strains introdured by sudden pretmrP surges. Electrical Conduit Ftcel condnit is rut, tlirmded, and bent with tools siniilnr to thnsr used hy pipe fitter.;. Bccawe of the thin \T-allsand light weight, l~ow?vcr. Iiandling and fa1)ric:tting is very siniple. After cutting :ind threading. sharl) edges arc coniplctely r e n ~ o v e ~since l they m n damage the val)lo insulation during cable pulling. Tlie conduit is tlrcn lowered iiilo thc ditch and joined together by couplings. Cable is pulled through the conduit between nlanirules by air-driven ~vinchesor by hand, using a lubricant to reduce frictim. T o avoid injury to the cable, pulling tension is carefully cbecked by spring scales when pulling tension is believed high. *Cement ith hoot nggwgnte.

Construction

661

.As r:rl,le is installrd the insulation is tcstcrl l ~ yan i n - t r ~ ~ ~ i i c\~-birll nt applies high roltage across the insulation and indicntrs tile re.sistanee of thc insulation. This testing is supervised by a competent electrical engineer, as is all electrical equipment testing and installation. Red-col~redconcrete is poured around the condnit and after i t sets, the ditch is hackfilled and tamped. The red culor is plainly visible and acts as n warning to vorkers v h e n excavations are mnrlc around it. The only other nn~lcrgroundelectrical ~ v o r kprneccrling at this time is the installation of grounding systems and cathodir protection. Bare grounding cable: either eolid or stranded c q ~ p e r .is laid di~,e~:tly in the griinnd and brought to the surface a t prcdeterniined points for connection to equipment. Insolated wire used for cathodic protection is connected electrically to the undcrground pipe t o he protected and hrought t o the surface for attachment to the cathodic protection system.

I

Foundation Construction Foundations are puured as soon as underground piping and conduit I\-ork in till, ilnnirdintr area IIM h e m complrte~l. 1.awer foundations rcquirc several p n ~ w:lnd ~ u r kun a tingle ir~undutiunnlay 1;lst a week 01' more. The details of these operation:: arc descril~edin CI~alltcr22. Oncc a concrete pour has 11cgun it must he contiuued uninterrupted. Hence tlir nlajur effort of the construction forces and supervision is directed toward the pouring operations. Erection of Guyed Derrick A fi,unri:iti~mis also constructed for the guyed derrirk d i i e h must I J ~ installed next so tliat equipment inay he lifted in place. The r r e h o n o i a guyed derrick is a nlajor ol~er:~tion often requiring some 3000 mauliours of construction labor. T l ~ e(ierrick (Fig. 2;-l) consists of a v t ~ t i c a l structural stccl mast, a boom, and a hoisting engine. T h e iiiast is often 200 i t or more in height am1 is held in position by 6 or 8 guy c:~l]lr. extending radially from its top to ground where each guy is seeurt~ly attached to a ,'deadnlan." A "deadman" is &: liea\~ylength of 11ilr I~uriecl ~lerpeniliculnrto the direction of pull anti cncnsed in concrete. T h e boom is pin connected t o the niast near its bottom. At the lover end of the mast is a hall-and-socket joint, the bass of whicli is supported by and securely bolted t o a concrete foundation poured for the derrick. Tlie upper end of the boom is raised or lowered by heavy cables running through a set of blocks on the boom and mast, and on to the hoisting engine. Another cable and set of blocks is extended from the boom t o the load for vertical lifting. .i n.liec1-like contrivance is provided :tt tlic lover end of the mast so tliat inast and boom may be rotwtrd. T h e load

664

665


Construction

held by steel mire slings. A crawler crane, a guyed derrick (Fig. 25-l), gin poles (Fig. 25-2). various portable truck mounted cranes, and even chain l~oistsnlay he used for the lifting, depending on tlie load. Large equipment n-Iiich is to bc located at or near ground l e d can often be skidded over wood or pipe rollers to the desired position. In

Any Inrgr p~efahrirntrrlreswl n.11icIl i . to he in-t:~llril rcrtirally is unloaded from truck or freight car so that lifting equipment can operate from directly above the point of attachment. The lift niust be as nearly

Fig. 25-1. Guy dcrrirk (right) and crawler crane (Icft) at construction site. (Courtesy of M. W. Kellogg Company.) Note guy wires.

such cases tlie equipment is protected a t its base by wooden beams called skids. Short lifts of large equipment can be made, when necessary, by the use of 1ie;~vyduty jacks. The lifting of heavy equipment is probably the most interesting phase of the construction operation. It requires highly skilled operating engineery and helpers. Tile lifting :tnd 11recise placing of a 200-ton piccc of equipment, for instance, requires strong nerves and a great deal of cunfidencc. The hoist operator controls his derrick with the aid of hand signals from a helper standing near the load. These signals, as well as all j~hascsof crane operation, have been standiirdized by the Anlerican Stantlards Azwcintionl since ~nisintrrpretatiol~ may prove costly and dangerous. Uuring l ~ i glifts evrn ,seasoi~rdcunstructim workers stop to ~ ~ a t and c h admire the work of the dcrricli operatur.

Fig. 26-2. Gin-poles being used t o erect a 360-ton distillation tower. h1. W. Iicllogg Company.)

(Courtesy of

.Tole: Bottom of tower rests on sled which was p u l l ~ don rollws starting with the

\cis such that the lifting cables t o s c r in a horizontal position. The specd of remnined ret.tical. The illustration shows the tor%-erhanging in a n almost vertical position just before the sled was rsmored and the tower placed on its foundation.

vertical as possible since hoisting equipment cannot withstand high horizontal forces. Vesscls fabricated on the jobsite are usually built n~ithinthe effective radius of the fixed lifting apparatus. Equipment may be provided with lifting lugs for attachment of hoisting apparatus or special slings may be wrapped around the equipment.

666

Project Engineering of Process Plants Lifting lugs, which arc welded on the vessel, siniplify the ~ t t a c h n l e n tof hoisting cables. They add t o the cost of the vessel, ho~vever,and make insulation of the vesscl more difficult. In gcneral nearly all types of cylindrical cquipmcnt are lifted v i t h braided steel wire slings. Vcrtical ressels are lifted directly above their fc~undationsand the slight degree of slope in the vessel caused by the sling aids in starting the anchor bolts into the vessel base. Anchor hillti for large vessels are usually provided with special threaded cone-shaped caps n.hich protect the threads as well a s guide the bolt into position. Steel plate shims are placcd a t each space bctween anchor bolts so that ~ r h e nthe vessel is set donm on its bolts it will be essentially level. Bolt nuts are tightened after the vessel is cheeked with a n instrument (transit) for perpendicularity. After the vessel is satisfactorily located, nuts are tightened and the anchor bolt sleeves and base ring are grouted with concrete. O t l ~ c rlarge equipment such as machines are handled in much the same manner. Even though machines may weigh several liundrcd tons they arc not usually so unwieldy as extremely long and heavy vessels. l\lachines are carefully aligned and leveled during the bolting i~peration, and grouting-in of large machines is usually done only after a manufacturer's representative has checked the machine for proper alignment and level. When bolting and grouting is completely supervised by the manufacturer's representative, the supervision is a condition of the manufacturer's guarantee.

Installation of Piping

The erection of above-ground piping begins after major equipment is installed and continues throughout the construction period. The majority of process plant piping is connected by flanges and wclds. Thc rarious picces are fabricated in a shop and delivered t o the site or fabricated in a field shop a t the jobsite. I n either case the methods are similar. The pipe is cut t o the proper lengths by means of a cutting machine or an oxyacetylene cutting torch. A piping piece or assembly n-hioh may, f i n instance, consist of a straight length with a 90" bend attached and two nozzles in different planes is set up on a work table or on trestles. The setup is carefully aligned and then tack welded. The tack-ivelded assembly is checked dimensionally and final welding is done usually hy the electric-arc process. h full-pcnetration weld free from slag and cracks must be made. It is economical t o do as much of the welding as possible on the ground since the pipe may be rotated on rollers and welding may be donc with little or no movement of the w l d i n g electrode. After welding, each piece is checked for alignment and weld quality.

Construction

667

Slight misalignment can be corrected by pulling into place by suitahle machinery while the assembly is held stationary. Screwed piping is fabricated a t thc johsitc and as much as possihle a t ground lcrcl. Threading and cutting tools, many of them power opcrated, are part of a pipcfitter's standard etlnipment. The fitter cuts, threads, and partially fits the pipe on a bench about 3 ft !vide by 12 ft long. Cutting oil is used dnring the threading operation to prevent excessive heat and help in the penetration of the metal. Tllrends are ~ n a d ein accmdance v i t h standard lengths recommended by tlic codes. They are thorouglrly clcaned before making up joints. A jointing compound which serres as a lubricant and filler is placed on thc threads. Various compounds are used for different operating temperature ranges and fluid conditions. Screiring of threaded joints is donc slowly to prevent binding caused by excessive heat. Pipe assemblies and sections of straight runs of pipe are lifted intll position by means i ~ fchain hoists or slings attached t o cranes. Tlrv several pieces are then aligned. Flangc faces are thoroughly cleilncil," gaskets applied and the bi~ltstightencd. 'hghtening of bolts is clone in such a x a y that the tension is erln;d on opposite bi~lts. If field n-el& arc to be made, aligning clamps arc used. Expensive items such as valves must be handled \vith care. They arc well supported a t all times during erection and their faces pri~tcctcdfrom injury. A safe adequate work area is necessary for the pipefitters who install orerlicad piping. Scaffolding must be strong and roomy since it is n i ~ t possible f i n pipefittcrs to align heavy piping ii-it11 great accurncy n-he!? t,heir own bodily safety is in jeopardy or when forced t o assumc eutrem~ly uncomfortable positions. As piping is completed, it is nashed or pickled, pressure-tested, cleaned, painted, and insulated. The painting of insulated pipe depends on process conditions. I n general all carbon-steel piping, whether left bare or insulated, is treated with a rust inhibitor after thorough cleaning. Pipe Idenlificalion

Each separate piece of shop-fabricated piping is given a piece nun~bcr or spool number on the original piping design dravings. These numhcrs are used as irlcntifying numbers and are painted and stamped with a steel dic on the fabricated pipc. T h e original design drav.ings are thcn used as erection drawings. A color code is oftcn used for identification on extensive projects haring a number of process units w.hich utilize larger sizes of piping, Mark, piece, or spool numbers must still be assigned to identify the pieces. If

* Ring-type

joints muat he cluaned exceylionally ell to insure a tight seal.

668


>el-era1q ~ a m t units e are being fabricated, color can be >elected for each unit su that pilling in the storage pard can be easily aeparated I\-itliuut finding tlic inark nunnbcr. The color coding ib applied l i e u e a c l ~end tlie piece and cumpletely circles tlic pipe in a band sufficiently a i d e to be $ten irom 3 reasonable diatancc. Rnndom pipe delivered to a jobsite is also color coded 13-hen receiwd. This code should be deaigned to indicate the size and type uf pipe iseaniless, alloy). llucli of tlie random pipe purchased must oiten he stored for screral niontlns. Only certain mills carefully identify pipe, l ~ n tthe original identificatiun may be lost or defaced ii it cxistcd Color m:nrkin: ran be quickly ilimc as pipe is being unluaded and will save much time ;IS the job proceeds. Insulation

iliter cleaning, pipe is pressure-tested and then insulated. Insulation is done by a aubcontr:tctor specializing in this n-ork. Tlnc.
Construction

669

r,ffort, involving rl~cmiral,merl~nnicul, clcctriral. and rivil engineers. draitsn~ncn,stenographers, accuuntante, buyers, i.raftsmt.n, and office hnys, .4.q one leave? tine plant sit? on this final day t x o people will probahly he busily ronfrrring: the project engineer and t h r construction superintmrient. These two men h a w done more than any t o a r m a s ~ ~ c c e s p f ~ ~ l npwating plant. T h r projrrt cngincer has direrterl thc projrrt .;inre tlrlc%rlj- prmr-r clchign. IIc Ira. Iwrn a gnori r~r,q:tnizrr nnd n rompctmt cnginccr c a l ~ : ~ l ~oil r ,do:~ling~1-irI1p ~ p l cof n-irldy ~lifierentt~ackgroimls. Tlie slightly hamssctl louking gcntieman \\-l~onithe 11n1jectcnginwr is congratulating is tire con.!t~.r~?tionsi~l~erintt.n~lrlit. n.ho ! d l sliortly move to :I rnen- n s s i p u ~ c n t . Hecause of his intrliigcncr. high niccl~;mir:~l a l i t i t o d ~and ~ good judgment, he Inas not unly hren allle to construct tlnr ~ h n ;tI . onlrlirrcil l)y the engi~uwiiigilmxings, l ~ u talso has correcte
Buildings

Office Luildings. change houses, warehouses, and machine shop buildings are cwctrd at :illy time (luring tlie project as men bcc,~line available. Process buildings ; m i slnelters are erected after major cquipnnent and large piping are installed.

S e w l-ork, 1%4. 3. Hossnngcl, IV. E.. IIonrtBook oi Rigging,

Final Stages of Construction

After all tlie major equipmeut is in place, sriiall equipment which n i u ~ t lie supported by the larger allparatus is inslidled. Fragile irnatc1.ia1.ssnrI1 as instruments, electrical apparatus, and small piping are also iristnlled in the final stages in order to minimize possibility of d:lm:rgc. T h e last veeks o i a construction project are husy on?.. Equilirn~ntii pressure-tested. Operating tests of equipment are made. T l ~ c-it? is <,leaned and put in order. T e n ~ p i ~ r a rbuildings y are removed, arid many official visitors arrive to inbpect tlie plant. The contractor's and the cu~tomer'sengineers n-110 began working on the design of the plant a year or two before can a t last see t h e t m ~ g i h l i ~ proof of their efforts. M a n y portions of the design could he improved and criticism of some portions of the plant can easily be made. B u t as the construction equipment is moved from the site and the contractor's operators conduct the acceptance test of the equipment and dcnionstratc that the quantity and quality of the product can be produced with e : w . adverse criticism seems in;ippropriate. The plant now ready to operate is a tribute t o a tremendous ~ I ' U U ~ I

Co., S e n Yatk, 1931.

l\IeGmn-Hill Rook Co., Yew l'ork,

INDEX Above ground lines. 458 hrrrptnnce order, 131 Accessul.iw for. piping, 426434 Accounting procedure of eontrnetor, 164 Acetylene gas wclding, 189 Actual gases, compressor calculations for, 339

Additives i o ~concrete. . 603 Afiinity laws, as applied to centrifugal pumps, 280 Air, design of instrument air system, i""" 7R

design of plant service air systrm, 581 Air chamhrrs far reeiptm:ating pumps, 256

Air changes, ealeulation of, 641 Air conditioning, costs of, 1617 design of iacilities. 621-623 in control rooms, 542 Air-cooled cxrhangcrs, 215. 223 Air line service and plant location, 12 .kit.-motor valve, 538 Air preheaters. 570 .2larm systcms, 649 Alignment oi pumps, 294 .illoy pil,~, pffprt of variuus mctak on phyzirai prapcrtips. 400 .kltcrnillirrg-ct1r1.e11trnolors, 352 Alumina-siliis refiavtories, 485

American Bureau of Shipping Rules for Clearification and Construction oi Steel Tpscelr. 198 .Itn~riran Concrete Institute, design plxrtiws of, 627 hmrriran Instituts af Steel Construction, design prartiws of, 627 American Petroleum Imtitute; Specifications for Oil Storage Tanka, 198

Amcrican Standards Asaociation, Code for Premure Piping, 396 flnnge classification, 403 Amee facinez. " , 408 spcrifieatians for centrifugally cast-iron pipe, 412 Anchor bolts, 606. 666 Anchors (and supports), marking on drawinas, 111

..

Anglr-type

reelproeatmg

campreasor,

301304 .In& values, 418,420 .lnnual rctorn, 54 API-.ASME Code for Unfired Pressure Vessels, 195, 198 41.c welding, 189 Atca eleration, 598

Index

673

['wlfcii~igiil r o n ~ p r e ~ w t ~design s. ralrnlation ior, 343 diaphragms for, 315 ~ I t i w sior, 317-318 efficiency of. 333 impeller typcs, 31W14 ia-line Rrrnneement oi, 315

565 h i t rffiei~ncypoint ( B E P ) , 2i9, 284 3%. 401 Ilid vompnrisans, 127 sprcifications. 101. pipe, 399 I{ill of lndmg, 128 Atmospheric 1ernper;rtnt.c. rnaximon~nad Billing procedure o i rontl.arfw. 164 nrinimtim, ior design, 2 i Bimelallie strip, 508 Atomization of liquid ioels. 561 Hirmingham K i r r Gage (BIVG), 225 Attachments ior equipment. 627 I h n k e t insulntion. erection of. 481 A u t , o r l a r ~373-3i4 , lllnnkel a r d e ~ s123 . k i g n ui. 374 BIwd. ilefinition oi. 456 .intomntic zprinklel. sytems. 640 Bl~nrl.Minition of. 456 .lntom:itic s t w m v d i c cut-off type for linc. 43-34 reriprocnting CUIIIJ,I~CSIOI~I. 307 I I Black dingrsm. 65 Auxiliary piping fol. pumps. 296 Block insulntiun, wwtion of. 481 A\-wage tempcmturr, iol. brat transicr Block m l r e , &finition oi. 456 cnlculntions, 237 Blo& valvre i m stmm. 5i3 \ V W A specification iol. cast-iron pipv. Hhr--,lu\vn systrms, 645-646 412 Blurv-down d l - e l , 645 HIov-c~.r.iumpmison with compressors, 315 ,hives ior. 317-318 ~rgulntiunoi. 318 Blue-printing. 116 Body of vu1i.e. 414 Boiler ierdxster, 549 Hack filling, 6 W 0 1 Boiler ieedeater pump*, 569 Back pwssure, reeonlmended fur atean Boilers, drums fol., 564 cylinder of reciprocating pumps, rypes oi. 562-571 261 Boiling corfficienta. 235 Bacteriological rests on water. 553 Bolt stud. ior flanprs. 407 Baffle spacing. minimum ior errhnngew. Bultr.,l-flanged bonnet ralve, 414-415 224 Bolting, for flanges, 407, 410 Balancing drum for eentl.iiugal comuf equipmeut. 62i pwsor, 317 oi strncturd stpel, 662,663 Ball bearing& a n centrifugal pnmps, 275 Ualts and nuts, recommended t3-pes for on motors, 358 vnrious services. 409-410 Ball-float level indicator, 519 Bonnet of valve; 414 Hall valves, 254-255 Horings ior soil tests, 594-595 Base plates for centrifugal pumps, 277 Bottom of pipe ( B O P . ) , definitiou of, Bnric refractories, 485 456 Basis oi design, 55 wtting of ele\.atrun ui, 433433 Bateh system eontr.ol. 525 tkjumlnry line loc:~tion.59i Bxttcr pilec. 5Y2 Uowdou tulw hlti Bearing c;ipwlly. ; ~ l l ~ w ~ i l596 ,le, Buurclon-typi g;ige, 51b516 f o r soil, 596, 612

Ihl&linp oi I I I F C S ~ I N i<.->cli,203. 201 Building w & i . 628 Building 11r:in-iop 101 13t1ililing*.design <,i.325, 61Fr621 d w g u o i ~ U II ) S O W ~ S C ( I I I I I ) I I I C ~ I ~610 . rwvlmn oi. 654 668 loc:lllm uf minicuiz? irnz;~r~is. 636637

~n~ullislapr. 311 performnnrr curvrc for. 336337 rrgnlatinn oi. 318 wlrction of impflier. ~ i z eand s p e d , 337438 h t i t srnls iur. 31b317 trl.minolo&~ for. 310311 (!cntriiognl filter, 375 Cvntl.iiuga1 gavwnoi., 365 (:mtl.iillgnl pumps. affinity laws for, 280 nuriliary piping for. 296 b:wr plates for. 277 Imuings. 2i4. 275 raleulation of NPSH for. 288 ensings oi. 268 L U c ~ v t i :h~ . ~ g of, n 621 i.liemid, 266-268 C . ik I'.. 126 cl;tssifimtiun oi, 263 I t t fat. hmt IIBOS~PI. r.orrcction8 to performance curves oi, ralrul;itians. 237 285-287 C;inc~II:ttionr . l ; ~ ~ w134. s . 135 ~:ooplingfor. 2i7 C:ipxity, ni,tunl of i.rripmi:lting pumps, douhle-suction. 270 2.57 estimating eKect of speed and impcller theorcliwl ior i.wiproc:iting ptlnrps. 256 diameter on periormsnre of. 281% vwintion in. inr ~mtriiue:il ~ ~ ~ r n p s . 289 281. 283 general service of, 266 Cnl.Ron dccl pipr, spwificution ior. 401 glmd oil piping ior. 296 Cx~.-loxlingronlp:lny. 11 Irorsepur~rand cffirirncy of. 278 C;lrry-nlls. 659 hot oil, 266 Cti.inps (rcntrifugnl ln1mp), ciriulnl., 269 in~lwllwtypcs, 265 difilsion. 269 install;ltion of, 293 rnollntinp oi. 269 rnwlinoieal seals for, 276. 2i7 voltttc, 269 rniiltislngt,, 272 CusL-in-lllare conmrte p i l e , 589, 5gg NPSH, 287 C;lrt-imn fittings. 112 opcrnting points ior, 289 Cast-iron flnner. 406 opewition in parnllrl of, 289 Cast-iron joints, typcs of. 413 openition in wries of, 289 C:m-imn pilie, dcwriplion mxl use of, packing for, 276 402. 112 periormance currps iol. 27%280 installatim~oi.660 process type, 266 Catch basins, 579 radial impeller typrs. 271 Catliodi? protection, inetalintion of. 661 )range oi service for., 263 Cavitation in rmlrifugnl pumps. 288 rotation of, 268 Ccment, 601 sliait and shaft sleeve ior, 275 Cement-asbestos pipe, installation 01, yingle-stage, 272 660 single-suction, 270 Cont~~.-packed plunger pump, 251 specific specd of. 284-285 Centriiugnl roniprosors, and axial blowstuffine bar ior. 27.5 ~

~

~

r,m. 3llX32V

bearings fur. 317

674

Index

Centrifuges. p~rformanceof. 375 trsts of, 375 Crt.tifird prints, description of, 109 f i x wntrifugnl pumps. 277 u e in foundation ilrpign. 60R Chain opcmtors. usr of. 458 Chambrrs of Commerce, aid in site selection of. 17 iniomration :
Compr.?ssed Air and Gas Institute, terminoiogy for centrifngnl campl'i'swv hy. 3 1 W l l Cum~wssibilityf:i,:tor. 34S341 i h i l for. 340 Compr~ssionratios, typiral. 339 Comprei.ion tcsts for soil, 596 Conlprrssion theory, 326330 Cornpl.rsaion-type fitting. 409 Coui~~rcssive strength of c o n r r ~ t c ,602603 Corrqressor cffieicncirs, 331, 333 Comp~.cssorhorscpox~et.,calrul;ition of. 33 1 Comprcmxs. see type Colnpressors, accecsot.ies far, 322 rosL of maintenance for, 322 cylinders far. 304-305 for plant air, 581 foundations for. 587-588 inslnllafiun of. 325 piping at. 461 pistons for. 304305 vnlws forl 304-306 selrrting tj-pc oi, 32W22 Concrete, costs of, 608 curing of, 60W03, 605, 606 pouring of. 6 0 M 0 5 rcinforecd, 601 repair oi. 606 ~ t t . m g t hof, 602403 Uec in p i l ~ of. s 589 Cmrrele foundations, curing of, 605, 606 Candenwte. piping ior, 572 Condrnsatc linps, typical rulps for, 461 Zcnd~nsatetraps, w e Steam traps Eondensation nxw, 235 :'oud~nsers, 220 L'ondcnsing rorfficirnts. 232 : k n d r ~ i t559 , lonc-roofpd tank, 574 lonferencc leadrr, 137 lonfwenrc notw, 137 ~ o n f r r ~ n c e136, s . 137 Ionfidential information on flow dingrams, 79 :onstruction, final stages of, 668 ot.gnnivation for, 654 personnel for, 654 ulnnnine- of., 653 preliminary data. for conett.uetion planning, 3 2 4 2 steps in, 88 ~onstt~uetiondepartment, planning by, 653 ~onstruction interferences, anticipation of, 34

675

Index

Correspondence, volnmc of. 139 Ccmrosion allowanre iar w s a ~ l s ,210 Corrosion data, 58 Corrosive fluids. pnmping of, 277 Cor.rouion inhihitars. 552 Cost ~ i t i n l ~ trests ? ~ , of. 47 precision of. 4 i rauid mrthods ior, 47 tybrs of. 46 :ost-plus contract, typical exsnlple of,

Consrruction labor, distribution of. 655 man hour requir~ments,94 on ioreign johs. 41 mtcs, 657 Construction ofire build in^. 658 Contingcnries fol. estimate?. 47 Continuuus system control. 531 Contracts, bnscs for. 159 ranrrllntion oi. 166, I79 definition of tprms in. 173 163 . . . finm oi. 162 !~,st-plwwitli fixr&iee contrxrts. 161 typrs oi, 160. 161.162 losts, estimation oi for piping. 447452 Contrart buying. 122 Intmr. 54. 170. 657 Cantt.artor and custorn~r, division of slip-on rrrrue welding n w k flanges, 404 work. 2 !olmt~rflow1-1 pxchanger, 216 Cuntmctor, definition of. 2 hunting instrummts, 524 frmctiou oi. I56 !ouplings, far rentrifugal pump, 277 selection of. 157 lneliing joints by, 402 Contt.ol centers. 540 tlsr of on \-essels. 192 Control Laboratories. drsign of. 622 :meking furnscrii. design of. 387388 Cun~soloi prowasr-, 525, 31-5-42 :raitsmnn, ninnhonr distribution, 656 Control of turhinca, 364 h n r . cmwlpr typr. 664 Contt.al psnrls, 105,540-541 gani~.\--typr.626 Control point of nn insfnment. 534 self-propellrd. 600 Control room, design of. 540-542 hss-fins, 216 Contiol tlieol.y, 540 hsr;flow. in heat rxchnngris, 232 Control vnlres, air ptrsawe of, 533 pwssure drop in, 239 &finition of, 456 h s l r c r s a n d grinders, descl.iption description of, 423425 38W81 danhlc-port,. 423 selection of, 379 sinele-nort. 424 test of, 380 Contkll& volume pumps, 261, 262 :~.~-~twilizrrr, drscription of, 381 Convection roeIiieient, for horizontal dpsinn and selertion of, 381 pipes. 491 trsts oi. 381 Conveyors, 389390 t plant lotnCoalinr hetmern stagps 101. c~ntnfngitl :ultur;d iaeilities, ~ f f e c on tion, 17 mmprcssors. 315 l u r t m w r , definition of. 2 Cooling s y s t ~ m s ,circulating. 552 Inioots. WP OE in plot planning. 82 Cooling t o ~ c r s design , o f , 377-378 Syclr for gas turbines, 369 Cooling w a t w 549 .,y!inders, for reciprocating eompl'essor5. Cupper-constantan tlrern~ououplc. 511 R -M Cork insulation, 483 Cylindcr liners, 254 Corrected mean tempwat,ure differmrr, "lindrr sizrs, deaignntion of for recip23i Carrrspondmre, and d~.awings,trnnsnlittin^ for f o r ~ i g njobs. 40 drslgn inrtrucrion. 143 Detdm-ight !onda on vessels, 203 forms. 141, 148 Deneraling h c a t ~ r s568 . instruetion letters. 141 Dearration (11 h o i l ~ rwater, 549 interofice, 140 Delivery date, 91, 127 k t t r r s of intent. 146147 Dclirery t i m ~ sfor ~ q a i p m e n t ,91 rrierno iorms. 141 Den Harlog iormuln, 196 owner-rontmctor. 144 Density measurement, 529 Desien data. 59 Design draiting. 103 manhour requiwnents. 94

-

-

~

678

Index

Fabricator's drawings far vessels, 211 Fannine enuation. 442 Fans, 3f8 ' F.A.S., 126 Feedwater, heaters for. 568 surge drums for. 569 treating farilities for. 568 Field roil. 350 Field-iahrientrd pipc, typical rules for. 461 F i ~ l dfabrication of vessels, 195 Figurc 8 blind, 433434 Filing and distt.ihution of vendor-prints, 108 Filing, systems of, 151 Filter photometers. 527 Filters, tpsts of, 386 Fin effirienry. 250 Fin tnhes. 215 Fire extinguishing equipment, 648449 selection oi, 648 Fire foam connertions for tora age tnnks 57s Fil.cproofing of steel, 626 Firc pumps, 553 Fires, iniurrrlation on prevention, 633 Fire-t,uhe boilera, 563 Firewalls, 637 Fi1.e water, 553 Fittings, cast-iron, 412 energy losscs in, 445 flanged, 411 pr-ssure drop in, 445 ratings far, 403 screwed, 412 welding type of. 4011.411 Five-step clearance control, 308-309 Fircd capital costs, 50 Fixed price contracts, 161 Fixed-tube sheets, 221 Flitrne arrestors, for storage tanks, 574 Flammability limits, 6 4 W esleuliltion of for mixtures, 641 Flange and hoking, selection of, 455 Flange facings, 407 American standard, 408 flat-faced, 407 male-and-female, 407 Flange fittings, 411 Flange prices, estimation of, 449 Flange taps for orifices 502 Flange types, 405 Flanged joints. 403109 E'langcs, 4 w w rompanion for pumps, 296 ratings for, 404 special types of, 407

Index

'lapper for pneumatic ron(1.01.533 lare darks. design of, 646 'lashing cement, 482 'lat heads. 190 'lexible couplings, 277 'loating head. pull-through type o f , 221 split-ring type of, 221 'loating-roof tnnks, 574 'loat-type level controller. 519, 520 'load conditions, design for, 28 'law diagrams. block, 65 engineering, 67 gmphir, 67 proecss. 65 schematic, 64 Vow measurement, mechaniral, 499 ;low nuzzle., 503.504 , k i d expansion thermometer, 509 C0.B.. 126 ?areehalanee type of manometerrl 504506 k c c d eirrolntion boilers, 564 Coreign projwtr, 35-42 'orm work for foundations, 693 ~ o l m conferences, d 137 hrming operations for. spread footings, 586

Terms, building of, 601 economies of. 609 ?orwarcling agpnts, 36,37 Fouling factors, 236 Foundations, con~ttuetionof, 593, 661 design of, 6 0 H 1 7 ~ x a m p l edesign of. 613415 for compressors, 325 for pumps. 294 for small pqoipment, 616 layout of, 607 scheduling of w o r t for, 593 selection of type of, 592-593 types of, 584 Four-cycle engines for compressor drives, 302 'Free Air" unloadcrs, 308 Freight forwarders, 36 Freight planning, rnovcment within foreign rountry, 38 Freight rates, 9 and plant location, 10 Friction factor, 44%443 Froat line, design for, 28 location of conduit runs with resprct to, 559 location of foundation with respect to. 586 Fuel oils, 31. 554, 555 h e l sources, 30

Fuels and plant location, 14-15 Fuels for prorrss plants, 53-556 Fundamental research. 43 Furnaces, 387388 &sign of, 387 types oi for boilcr~,561 F. F., definition of, 456

679

Guidc i o r pipe. 430, 456 Guidc vanes for crntnfug;d romprrssors, 314 Guyed (derrick, 661-664

Hnicpm;. 215 H:md~ailr.640 Hnngcrs, ddinition of. 456 Gage glasses. 523 I for pipe, 43M33 Galvanizd hands for insulation, 482 Hnzsnfaas areas. electrical equipmrnt Galvanizing on structural steel, 114 ior. 560 Gantiy-type cranes, 626 Hazardous cquipmcnt. minimum spacing Gss burners, 561 for, 636 Gas d i e ~ ~for l s rwipromting compresmr, Hnznrdou.; locations, for reciprocating 301304 vomprewora, 310 Gas engines for reriprorating C O ~ I ~ I P S S O ~S:~tion:d , Elwtrir Code, definition of, 301-304 357358 Gas storage tnnks, 575 H;ia:~rdain pnxrzr plants, 632435 Gas turbines, 3 6 M 7 1 Hrtrd. ralculation of h o r s r p o n ~ rand psi npplirations of, 370,371 from, 288 cycle ior, 3 6 M 7 0 dcfinition ui, 272 efficiencies oi, 371 of rentriiugsl pump, 278,288 use of on wntrift~gnlramptmsors and variation in, for centri1ug:d pumps. hloneru, 317 281,283 Gaskets, for fltinges, 407 Head room. recommended mlues, 638 delrrtion of, 455 Headers for fire water. 553 Gate valves, 417,418 Heads for r-easels, selection of, 190 installation of in pump piping, 295 spinning of, 190 Gear pumps, 290 types of 190, 191 Grncral files, 152 Hest ~xrhangcrs, drsign of, 226, 241, General serviec pumps, 266 242 Geometrically similar pumps, 281 fabrication of, 224 Gin poles, 66W65 nomenclature, and p u t s for. 221, 222 Glands for valves, 414 safety rules in design of. 638 Glnnd oil piping for pumps, 296 shell size of. 224 Glnss insulation, 475 specification sheet for. 240 Glam pipe, 399 tuhe lengths for, 224 Glohr r d v m , 417420 typrs of, 214-220 Governors, for steam turbines, 365 Hext losses. through insulated surfaces, throttling type of for reciprocating 4m93 compressors, 307 bhrough insulation. ux:mipir ralcul:iG~.adient,definition of, 456 tion of, 492-493 Grnphir diagram, 67 H a r t transier resetweh, 1Tnivet.sity of Graphic panels, 54b541 Delaware. 231 Grating, use of, in out~doarstrwturra. 62i Heatmi, see Furnaces Grid plates, 193 H ~ a t i n gand ventilating farilities, design Grinders. see C~.ushersand gt.inder.s of, 621 Grounding, 639 Hrating, costs o f , I 6 1 7 Grounding systems, installation of, 661 Hravy equipment, erectiorr of. 663466 Ground joint unions, 403 H ~ a v ymachincry, planning iw, 39 Grout, 606 Hcight of roaling tower, ilet~rminwtion Grouting, 666 of. 377 Guamntee clause, 129 Helical Eon stage of a tnrhine, 361 G u a r ~ n t e c dmaximom contracts. 162 Helical pumps, 291 Guarantees, 181 IIor.~aontnllift check valvp. 419 Gua1.d~ and guardhouses for process Horizontnlly split casings iut. centrifugal plants, 582 pump, 269

i

~

~

680

Tn4;1llntion. d~.orrineifor, 106 of mrnprrcwn, 325 of ptlmps. 293 Inslruclmn Iettws. 141 I n i t r w t i o n ~to vmdarr. 134 Instinimmt nil.. defign of system. 536 In.3twnrent dhitinp. 105, 115 I n - l w n ~ ~ n l n t i ncnginwring. n 512-543 I ~ ~ - l r ~ ~ n ~ ~ for ~ n liwntl.iiue;tl ; ~ t ~ o n . cmalpvr,ior?. 321 for intwnal r o n h ; t i o n engiow. 573 iot. ~.rriplwi.:ttingrumprr-sots. 3'24 3fig iw s t r : p ~ h~n t r . 570-571 .Housing, far I : h m mi iuwign jol,., 42 on flow di:tgr;trn.;. 71 Human relations, n e ~ db , ~~lnilwclm.~rrntnirig;ii cronomir.;~lthickncra of, 495 cornpl.rssol.s, 337-338 effieicnry of, 4116 Impeller types. for centrifug:d rompresrrildion of. 481484.668 sors, 312314 i:wtow in rr:%luntionof. 470-480 backward cwrcd. 313 1o1.pel.sonn?l protwtion. 640 forwsni rurr-erl. 313 fat. s t < ~ : ~piping, rn 5i3 for centrifugal pnn~ps.265 h m t lass through. 490-4'13 Impolse turbinr. 361,362 inquiries and qnotatiims for. 480 Indwtion motors, cdaulntion of nctunl ,inckets im. 483 sprrd, 353 optimum thirkncss of. 494496 drsmiption of, 352 safety rulcs in drsign oi. 640 use o f , on reriprorating eompwssor. selection of. 479 301 iyprs of, 473-458 Indimtot. horzepo~pr,259 Insur;m~.efor ronitmrtion Inlmr 42 Induvtrial Comn~issions.nid in site selec1ntprroast;il canal. 12 lion by, 17 Internal combustion puwe1.5i3 Industrial hygicne, inionnation on. 614 Internd gear pump. 290 Inert gas purges, 642 Intwoffire e o r r ~ s p o n d e n w140 Infrared photometer. 525, 527 Interoffire Ipttpr. 140 In-line arrangement of renldugal romIntrrstnte Commerce Commission. 11 prersws, 315.316 In\-ersions, rffect of on plant location and Inquiries, for insulation, 484 layout, 635 forms for, 124 Inverted bucket tmp, 428 minimum number of, 124 Invoice. 128 parts of. 124.240-241 Iron-eonstantan thermocouple. 511 Inside film corffieient. 227 Isentropic compression, rercrsiblc, 328 Inspection, of equipmmt. 124, 131 Isentropic rsciency, 333 of vessels, 195 ior rpntriiugal compressor, chart for. 335 Inspeetol.. duties of. 131 I s e n t t q i c head for centrifugal rompresrepurta hy, 131 sam 336 Instability, conditions for in foundations, Isentropic horsepower, from enlhalpy 613 diagrams. 332

68 1

Index

Index Isothermal cornpreicion. reversihlr. 328 Iaotl~ermalefficiency, 33J Itenl numhers. on f l o ~ ddi;~g~.:mi. 68

Hal-s~power. mlcrhtion of lor ronrpl.Pisors, 331 (we olro WolA of rornpreasion) for centrifugal pumps. 278 for motors, standard ratings of. 358 for reciprocating pnnips, 259 Hose connections, 459 Hot oil pumps, 266.267 Hot prorws phosphate. coftming of. 551 Hotel facilities, effect on pl:~nt locntion. 17 Haudry prowr-, ose of gas twhinrs in.

J;icki, henvy dilly. 664 Joints. fat. pipe. 402 staggering of f m insul;ition, 182-483 lypes uf cart-iron pipe. 413 Joristlictional diapute~.655 Iirrusene as a fuel. 554 Krttle-type rpbuilw. 219 liingihwy-typr hearing, 101. rcnlriiugal compl-c-sol-.317 for centliiugal purrilw. 275 Iinorhout d~.unlc,323. 647 Iiraft paper. 483

~

Labor, and plant lwntian, I 5 elreck list for cunat~.nvtionplanning of.

"RR

-

I.iit rheek ~ s l w421 . I.ifting lug?, 6 6 x 6 6 Light Itydrocarhonr, ptmping of. 277 1,iglricr;~gec h r g e . 37 1,ighting. 620. 623 Lime-soda softening proeei?. 551 I.i,nit rontrals. 524 Limits of fla&mahility. 610-641 I.inc blinds. 433434 Linr nulnhers, 71. 457 I.inr sizes, determinatiun of. 410U32

Lmm drawing s h e ~ t s116 . 1,jungstrom turbine; 362 Liquefied pctl.olrum gas :a. :Liurl. 31. 554 Liquid eylindel.~for rreip~.oratingpunll~s,

--7x7

Liquid hot.sepo~cr,calculations o f , 259 Liqui&le~rlinsttum~nts,519-523 Liquid storage, 574 Lad teats un soil. 610 1,aulr. nlluwahlr for i t t . ~ l ~ t ~628 ir~i, J.ocnl flood or tidr mndition.., drsign c m sklerationa fol., 28 Locatiun of sul,surince water, 595 1,ocumotire boilci, 566 Lag mean tcmpwntnl~cdiffer~uw.236 Longitudinal hnRi~.218 Longitudinal fin&,215, 216 Longitodinal stresses; 1'96 Imw point, ~ ~ s t a b l i s l m ~of. m t 598 1 . o ~temperature insulation, vwution oi. 4% 1x1,shipn~ents,11 1.ubricntion of rrntl.iingnl compwsml., 317 of plug r a l i - a . 421 of rcripl~orntingeonipl.escor. 3 0 6 3 0 i Lump-rum or fixed-price contlxcta, 161

costs of. 54, 170. 655 distribution of, on constrrwtion jobs, 655 on ioreign jabs, 41 unwst of, 16 U.S. expatriatrs. 41 Labor market studies. 15 Lahor organizations, 655 Labor liractirps. 655 Lahm ~ x t e s656 , on constn~ctionjobs. 657 Labor relations. 655 Lahoratorics. design ui. 622 Labyrinths, for eentl.iiugal caulpressom, 316 Ladders. 194 Lantern ring, 275 Lap-joint flanges: 404, Large equipment, plmning for. 391 Large pressurc rcssels, rnaxinlorn sizes. 40 1.avatory facilities, design of. 621 blnrhinc bolts fol. flanges. 40i Layout, for steam distribution ~ y a l e m , hlrrliinc shops, 576 .&'I? 3l:whintr)-, ioundations for, 687-588 of rquipment. 637 J1:tintcnnure costs for ronrprussul.a. 322 of formdation, 607 Maintrnnnec ieeilities in prows- plant*, of office equipment, 619-620 ,576 of piping. 103,434-440 Manlroles, electrir:al, 55S560 of trimsfel. pump syarem. 576 ior senem, 578, 559 I.CL shipments, 10 Manhours, distribution on eansrruction Imul ruhs for thermocauples, 513 job of, 656 Luascd nirc services, 150 r.equir.ements for engineet.ing, drafting, Lens flange, 406 and construction of, 92 I.rttcr of intmt. 146 .\lmimiwtrrs, bell typc, 517 I.<.llel.i, re i. ( 1 ~ 1 1 ~ ~ s ~ ~ o ~ a l r n e e i,rw l d : t ~ w 604-5C6 I,uvri g;~grs,5'231 n,,w,,ry, 504-~zIxi

682

Mamlal rontrol. 531 hlamlfacturrr'i rlrn~<-ings and data, 106 Manufacturing costs. pitimation of, 52 Marine freight carriers, 37 Markers. prrmanent, for conrtmetion site, 598 Marshall and Steven index, 52 Mass ratios, for m a s i r e foundations, 616 for reciprocal rompressor foundations, 325 Massive foundations. 587488 design of, 616 Mnstcr plot plan. 8 M 2 coordinates on, 597 example of, 81 factors influencing, 82 Mat foundations, drseription of, 587 drsign of, 615 Material and energy balance. 55 Materials handling equipment, 389390 selcetian of, 389 Materials of constlrlction, for cenlt.iiugal pumps, 278 for exchanger tubcs, 225 for pipe, 399400 for pump casings, 268 for rceiproeating pumps, 250 for structural shapes. 6 3 W 1 for vesarls, 209 selection ofl 57 Mean cBeetire prrssure ( M E P ) , 260 Mean tenrpertiture difference. 236 corrceted, 237 Mechanical control. 532 Mt.rlrmird design, and safety, 637-640 of YVSSPI. 210 Mechanirnl efficienry, definition of, for eompt.cssors, 333 of rrriprorating pumps, 25S260 Mechaniral expansion joints, schedules of, 111 Mechanical flow diaggmm, 67 Merlmnical joint, 409 Mechanical seals. 275-277 for centrifugal compresion, 317 Merhnnieal specific~tions,101 Medical farilities, design of. 621422 Memo iormr, 141 3lcl.cury-in-glass t,hcr.mometer, 508 Mercury-type rnanom~trl-s,504406 Mcridion.al stress, 196 Mineral nvol inculation. 174 Mixed flow lnrpellm, 265 Mixers, sekctkn oi, 390 tests of, 390 Mixing equipment, 390 Mixing plants, for concrete, 604

One-two exelranger, 218 Opcn impellcrs. 265. 271 Opcn motor, 355 Operating company, 2 O p ~ r s t i n gIwbol.. 15. 18 Operating points of centrifr~gal pumps 289 Operating tests of rquipn~ent.668 Optical pyrometers. 514-515 Orientstiun uf nozzles. 210. 211 Orifier m ~ t e r sSM-503 . e q u a t ~ a nfox flow rate fol 501 Or~firr-trpcbnfflrs, 221 Or.sst, automatic, 526 0 . 5 . and I' (outsidp stem and yokc). definition of. 416 Outdoor r q u i p m ~ n tlacntion. adrantages of, 625 Outdoor procew units, 624429 Outline drawing for vcssels, 112 Ontsidr r o ~ f f i c i e nfor t ~ ahell-and-tube exrhmgers, 231 Outsid? film corficient, for double-pipe exrhnngcr, 229 fur rxtmdrd surface. 229 Outside stem and voke r d r~, ~415 .-~ Overall hcnt transfer eaeffiri~nta, calculation of, 227 estimating of, 244-246 Owr.hmd rosts. 54 Ore~.lrcsdrlrarmrc for piping, typical, 459 Orcrbime payments to labor, 171 Ore~.turninplond for cylindrical towpr.

Aanolithic mass, 5% .lonthly tirnc chart. 100 .loody friction fartor chart. 443 dotor-driwn reciprocating compressor, 299 dotor ratings, 358 dotors, 3 4 W 6 1 alternating-current. 352355 =drives for centrifugal compresaors,317 classification by N.Eb1.A. of, 35M56 cost comparison of, 35%367 direct-current, 3 5 M 5 1 elementary principles of, 349, 350 selection of, 359 standards for, 349 typical applications of, 360 rlovemcnt of raw materinls and products, 576 Multicylindcr compressor, 300 Multistage blowers. 314416 \fultistaec centrifurrnl romnressor. 311 \lultistage centrifugal pumps, 272 Multistage compressors, 314316, 338 Multistage steam turbiu~s.362-363 Vational Electtic Code, 349 Yntianal Electric hf~nufaet,Urer~ Amariation (N.E.M.A.). . . 349 Vatural gas, design of pipclinc connections, 30 plant pressure of, 31 use of in process plants, 30. 554 S e t uositirr suction head ( N P S H ) , 287, 288 Nipples, use of a n vessels. 192 Koise abatement, 14 Yominal pipe siws, 396 Yozzlcs, nr~~angmmmton ccntrifngal pumps of, 269 control of stenm turhinea by, 364. 365 details of, 211 for process wssels, I92 orientat,ion of, 210,211 reinfol.remmt of standard-lmgth, 192 Nussdt equation, 227, 232-233 Nulaling-disk displacement metel., 500 Nuts, w r Bolts and nuts Orrnn frright rates, 36 Octagonnl iootings, design of, 613415 Office buildings, dcsign of. 619-620 OH-prak power, 556 Off-the-slrelf materials, procurement of, 123 Oil-field boiler, 566 Oil mall~ahleunion. 402 Oil seal for centrifugal compressors, 316

683

Index

Index

612 ...

0, wturning moment. 5%

-

Parknge-type stenm generators, 211, 565 Paekcd stuffing box, 275 Packing, fat. ecntrifugnl pump, 276 for export, 37,38 for reripmating eompwssor, 304 for reciprocating pumps, 254-255 for turbines, 364 see also Shaft wals Packing gland on 1-1 rxrhnnger, 217 Packing list, 128 Packlcss expansion joint, 429 Psrklcss valves. 416 Painting of pipe. 470 Parallel centrifugal pump operat,ion, 289 Patcnt protertion, 130 Pedestals for centrifugal pumps, watercooled, 270 Perforated platcs. 193 Performenre curves, estimation of, 282 for centrifugal compressors, 336337

Pcrformnnce curves, for centrifugal pumps. 275280 ior riscous liquids, e w r w i m n to, 28.287 Pwiphwal ~n,mps.2111 P w i r d ~ ~ r velocity, al drsign vnlvr foy renLdug;tl c o n ~ p ~ ~ e s s338 oi. ui wnlrifugal pump. 283 I'wmits, 35 Pr~aonuel dialribuliun. typical, 95. 96 Personnel mornlc. 154 pH miler, 530 Photoelectric cell, 524 Piece marks on structuul steel. 662 Pieee numbers far pipe, 667 Pile drivers, W 0 i Pilrs, east-in-place conl.rete, 589 dt.iring of, 606607.658 penetration of, 607 types of, m 5 9 2 Pilot light for flare stark, 646 Pilot plant facilities, design of. 623 Pilot plant, use of. 43 Pin-fins. 216 h p c , .iSThl speclfiratmns for, 399, 401 contmg of, 470 design codes far, $96 fittings for, 4091113 history of, 394 identifirntion of. 667 iointa for. 402 &nr~fwrture of. 395 plastic, 399 required thickness of, 398 schedule number. for, 398 selection of. 455 sizes of, 396 steel, 399 t. m s 395 . ~ of. 3 p c and fitt,ing prices, estimation of, 448 'ipe bmding, 459 'ipe-cap. 409, 411 'ipc coils, 223 3' ~pe-concretepilcs, 590 'ipe fittings, screwed, 403 'ine foundations. 588 'ibc hangers, 4 3 k 3 3 'ipe insulation. woction of, 482 'ipe shoe, 430 'ipe supports, 43M33 design of, 432433 fire proofing of. 470 indication on drawings, 111 'ipe taps for orifices, 502 'ipe wall resistance to heat transfer, 235 'ipe mall temperature, calculation of, 238 'ipelines and plant location, 13 ~

684

Index

Index

I'ipine, nrcww~.irsfor. 126-134 ~rh;mgpsin dirrction oi, 434,462 rlearanrer r r q u i r ~ dfor. 629 rstimating installmi roits of. 447-452 mpansion oi. 436440 iahvirstion of s r r e w d piping. 667 for romprewx installations, 325 ior pumps. 294-2% ior rclici r;tlrcs. 64G-647 for stcnm di&hution. 571-573 insta1l:~tionof. 666 lii\-mt iind a m n g ~ ~ r i e n o ft , 431-440 lifting of. 667 mFrty m1i.s in design ior. 638 -Imp-inlricuted or field-inhl.icntrd, 110 $>zingof. 440152 sperificntionu ior. 462-470 testing of. 464-465 Piping costs. uee oi in linr ~iainp,447 Piping derign, 103 Piping dr:r~r.ings.checking of. 103 rrwthodi for. 110 .,.;dt,s for. 110 l'il,ing mutwitil 1i;ting 01. t A - O N , 112 I'ining ~ . q m m ~ t i t t i oon n flow di:rgrnms,

70 Piping spceifimlions. typicid crarnple of,

466470 Piping stresses. 436 Pirani gage, 518 Piston pump, 251-253 Piston-ring expansion joint, 429 Piston rods, 254 Piston spepds r~rommended,for reoiprocsting pumps, 257-258 for rrriproiating compwssor, 304305 Pistons, for ~wipl.ocatingpumps, 251-253 Pitrli, minimum for cxchnnger tubes, 224 Plnnt nil.. 581 Plnnt datnm, 598 Plnnr dmign, steps in, 88 Plnnt lahol.:~tori~a. deaign of, 622 P l m t layout. see Master plot p l ~ n and iafcty. 635 Plnnl location. inrtors in, community, 17 fuel :ind ~ U W P14 I., labor, 15 noise d ~ n t e r n m t 14 . proress watrrl 13 raw materials, 9 transportation sic freisht, 12 railroad it.cight. 10 trucking. 11 tiastr diqornl, 14 nwtel.. 12 vtwthrr, 16

685

P h t 1w:ilion ztwlirs, inbnrmntion for

19-24 Plant north, wtting o f , 598 Plnnt s e r n c r alr .sy.tem, drsign oi, 581 Plant .?ile. scr o h Planl location proredurr for selrrtion of.8 Plnnt tcw.ain studies, 28 Plant wastes. ~~~~.31 Plnitic. uw in rh~micnlpwnpF, 266-268 Pl;tstir pipc, 399 Plates f o ~ shells. . wual sims of. 189 P l n t i o l m ~ ,dimcnrionr of.640 ~

couple, 511 Plot plan, see Master and unit plot plans Plug cock, 421 Plug valves, 421,422 Plumhing fixtwes, water usngr of, 580 Plungrr Dump, 251-253 P1ungr1.s for rccip~.ocnting pumps, 251-

253 Pn~uninliceont~.ol.532 prupoition:tl. 534 pl.qwrtiontrl i.ri.et. 536 ~ , r o p o ~ . t i o n a l - r c ~ ~ t -536 t.at~, Polyphmc induction motors, 354 Polystymnc insulation. 475 Polybropic compression co?fficient, 331 Polytropie cffirieney. 333335 t o isentropic c f i c i ~ n c y(01. ~.rntriiug:~l eonrpl.essor.. ronversion of. 334 Portnblc extingnislic~.~. 648 Potmtiometer ri~.roit Em t.lre~~moaouplc mmi, 513 l'out~ingof conrrele. 604.605 Powrl. msts, study of. 15 l'uwc~.data ior design, 29 Powel. distribution, 559 I'owcr shovels, 659 Pmndtl number, 227 Precast-conerrte piles, 590 P~.eliminarydesign, 158 P~.essul.cdrop, a l l o ~ a h l cfor prorese linpr.

447 in gas and vapor lines, 447 in h a t exchangers, 238 in proccsj lines, equi~tions for, 441,

442 Pressure gages, 515616 connections for, 459 P~.rssure-lnensn~.i~ig instmments, 515518 Prrssur.e r~gulaiorfor steam turhinr control, 365 P~wsire-relievingdcvires. 643446 Prrssut.t.-rart~umvents. 574 Ptwstwsard concrete piles, 591

7~

~

.~~

Pre\-ailing winds, rffect on plnnt layout for coolng mater, 552 ior fire, 553 of. 635 Prirri;, discussion oi, 134 foundations for, 294 installation of, 293 re-negotiation of, 134 Pi.ocesi cantl.ol, 525.531442 piping for. 294-295,460 Prore% desien, safetv factors for. 231 - , data ior. 59 p r o r e d u r ~ior, ~ 55-58 tank ~ ~ R " s ~ P576 I. Purchase wdcr, guarantfe clause in. 129 1'1.ocess development, 44 P I . O ~ Pengineer. W 56.57 ! inrpretion claoze in. 129 and project mgineer, rehtion hetreen, lnhor el;wses in, 130 patent p1,oteetion in. 130 58 Ploccss engineering, 43-63 I aunlitr . . rlnuse in. l2Y mnnhoor lequil.cments for. 93 shipping inatructiuns in. 130 standard notes on, 130 Procesn evnluntion, 45 Prorrss flow dingranre, 58,65 suhrontl.artor clnuars in. 130 Process iniomation on engineering Born Purchasing, see n1.w P~.ocn~.ernent Purchasing agent,. 122 d i a g m m ~69 , I'roeess lines, sizing ai, 44W52 Purrhesing methorlr, 122 I'cwceis mtrnns. . . 266.267 Ptmerss sprcificntions, ior pnmps. 292 iiunnlily rliscounts. 126 i2nrndi towws. 646 use of. 101.157 Prorou. - i t r ~ i ~ l557, l, 560 "Quickie" mtimatcs. 51 1'mi.r~-\r;~te.;.d i q m d of, 580 Qnotaiioni. 125-128 Process 5mtev. 548 mmpmisoo of. 127 P~.acul.rnlent. cnginwring participation contcnts oi. 125 rvointion of fol. heat erc1l:mgerr. 246 in. 122 m:~nliourrcquirerncnts iol., 94 lor inmhtion. 480 ~m'liulin:~sy ,l:it:~lot.. 32 ~ ~ u r c i ~ : ~ r r r - vpractices i ~ ~ ~ ~ l for. o t ~ 134 R ; d i ; ~ lbearing un rmtt.iiugal pump. 274 Pruco~wmr~ntDepartment. orgnnizwlion Ha0i;il impeller-. closed, 2il :and operittion oi, 121 (01. rmtriing:tl ronrprwsor. 311 P1.or.uretnent ~netliotls,122 opcn. 271 I'ro~lurtionDepnrlmcnt, 109 z r l n i - d o s d 271 wuri-opm. 271 Project m g i n ~ ~tind r . ~ i o ~ w w m c n135 t, coop~~.:ttion oi with inslrument engiH;dialion corffirirnt fur 1m~ieont:Jpipes, 491-192 nrrr. 543 d~finitiunof. 1 lladiation pylomrtws. 511-515 rlrnics of, 2 4 Rndiogl.apliing of ~ c s i c l s 194 . Rnil~.,,:idele:usncez. 628 Project engineering, nranhour requiwRnil~~onrl facilitiri irr process planis. 577 m m t i lot.. 93 Project pstirnotr. 3 R~ill.ond.liipwnt and plnnt. location. 10 Projrct files. 153 R:drond qlurs in ptmwss plants. &sign Plwjert mnn:lgPI.. definition of, 1 d,577-578.659 I'mjert organizeition, 3 Rnilt.m&rypc m n n , 402 Project schedule, 85 Rainiirll, fur design. 27 Proportional cant~.ol,533 Xaininll intmsity, ioc. design oi surface Proposal, by eontl.uetors. 158, 169 dvsins. 5i9 P~~,posals. see Quotations Raised-inre flwngr facing, 407 Puhlie trxnsportatim, effect on plnnt Random pipe. definilion of. 157 l o c h o n of. 17 R:tnkine cycle, 365 Pumps, S I P t)pr of pump Raw maiel.ials and plnnt location, 9 Pump casings, 268 Rencrion turljine, 361,362 P u r q housc. 293 Kendy-misrd eonrl.ete, costs of romPump selection chart. 249 jiaicd with site-mixed canercte, Pumps, alignment of, 294 608

i

686

Index

Rcnrly-mixed concrete, use of, 604 Reboilerr, 210 Reciprocating campl.czsars. 297310 angle-type, 301-304 cle&nce pockets of, 308 design calculations for. 343-3413 <&irimcies of, 336335 enginr-driven, 301 fisr-s1t.p cleerance control for. 308 lubrication ofl 306-307 motw-drir-cn, 299 parts of. 304306 regulation of, 307 t y p oi, ~ 29~304 selection of drives for, 308710 steam-d~.ivenduplex, 298 suetion ralvr unloatl~rsfor, 308 tut.hine-driven. 301 two-slngr, 201) Rwiprorating pumps, actual rapacity of, 2.57

air chnmher.s for, 256 applirstion oi. 249 rlnssifimtiou of. 250 rv1iuilpt.s fa!.. 253 flangrr for. 256 rnatwinls of construction ior. 250 merhnnical efficirncy of. 259-260 parking ior, 254-255 parts oi. 253 piston and plungcr tvper of. 251-253 piston rods for, 254 recommenricd piston speeds for, 257258 airing of. 256 thcor~tiealcapacity of, 256 valves forl 254 r a ~ u m ~ t r ~fficiency ie for, 257 Rccrpation renter, design of, 621 Recreation facilities, effect on plant loentiun oil 18 Reducer, 409.411 Re-cntry nozzle. 361 Ref~t.encelocation. 597 ReflwAive insulation, 475, 479 R ~ i r n c t o r n e t ~ r528 r, Refractories, 484-490 selection of, 484485 types 06 485 Reirartory brirk, characteristics of, 4 8 6 AX7

inatnllatian of, 489 typical shapes of, 48-89 Refrigeration. principles of, 347 Refusal, 591 Regulation, of centrifugal and axial compressors and blo~vet.~. 318

Index

Regulation, of reciprorating compressor. 307 Beinforced concrete, 601 Reinforced concrete struvtuwr. csrction of. 662 R<.infol.ringstpel, ior ronewte. 604 sperifieatiuns for, 604 Relative humidity, for design, 27 Relntire roughness of pipe. 444 Kelnlse for fabriration, 113 Rdief valves. description of. 425 design basis. 643444 discharge rntes of. 645 discharge systems far, 645446 in pump piping, 295 piping for, 646-647 Relieving dcriees, conditions requiring. 64.L644 ~ - .-Research Ixboratot~ies,derign of, 623 Reset, 535 Resistanec of vslrcs and fittings. 446 Resistance thermomcter, 514 assentbly of. 514 ranee of.,~~ 514 Return on investment, 55 Reynolds numbcr, 227, 280, 285, 442, 501 ior rentriiugal pumps, 285 for orifire me& 501 Ridgway's approximation of compressor xwrk, 342 Rigging techniques. 663 Right-angle comprPsor, 302, 303 Ring-joint flange racing, 407 King-wall foundation, 587 Riveting of st,ruetnml steel, 662, 663 Rivets, detecting faulty, 663 Roads, sniety hazards rrcated by. 636 Roadways, in pmeess plants, 577. 659 suggested width of, 577 Roller ~xpander.225 Kpm effect of on centrifugal compr.essor performance. 337 Rotameters, desc~.iptionof, 506 effect of changing float weight on, 507 floa equation for, 506 Rotary cornpressom and blowers. 318 Rotary-liquid piston compressor, 319. 320 Rotary pumps, 290 Rotation, of ecntriiugal pump, 268 of induction motors. 354 Routing fluids in shell-and-tub? cxchangers, 242 Ron-off. for design of surface drains, 579 Rupture disks, design basis for, 643-644 disehnrgc rntes of. 645

-

Safely cages, 640 Safety factors, for pumps. 291 for pressurc ~es.-els.208 for reboiler design, 220 for soil-bearing capacity, 611 use of; 55 Safety haaards, in plant design, 632-635 information on mechanical, 635 Sanitarv wastes. disnosal of, 580 Sanitary water, 553Scaffolding,667 Scale, in boilers, 549 in cooling-water systems, 549 prevention of, 552 Scales for drawings, 100, 115 Schedule numbers of pipe, 398 Schedule preparation. 90 Schedule sheet, 86,87 Scheduling departments, 100 Scheduling drafting manhours. 99 Scheduling foundstion work. 593 Schematic drarving of an eiertrieal system, 558 Sohematic flow diagrams, 55, 64 Suope of work, changes in, 4 Screwed bonnet valve, 414, 415 Screwed fittings, 412 See, water, use of for cooling, 552 Seal ail pump for centrifugal compres sors, 324 Seal oil systems, 276 Sealing liquid, 275 Sealing oil, 276 Seamless pipe, 395 Seat of valve, 417 Secretarial help, 151 Sectional pipe inmletion, 483 Security for process plants, 581 Sedimentation cquipment, 391392 Sedimentation tests, 392 Segmental b d e s , 221 Selection, of insulation, 479 of pipe materials, 402 of pump types, chart for, 249 of pumps, 291 Seli-supporting towrrs. design o i footings for, 612-615 Senii-closed impellers, 271 Semi-open impellers, 265.271 Seriee-wound motor, 351 Service connections for IIUSP, 459 "Servo" wstem, 537 Set prassure, of relief vah s i . 647 Settlement of foundations, 610 Sewer systems, 578 S m w s , dcaign of, 578 manhole for, 579

687

jewers, slope of lines for, 578 ihaft ior centrifugal pump. 275 B a f t seals for centrifugal compr?ssors, 316 ;haft sleeves for centriiugal pump, 275 ihaft work, 327 Sharp-edged orifice, 503 ihpar tests for soil. 596 $hearing load in foundations, 615 Sheet piling, 592 Ihell-nnd-tube heat exchangers, 216220 shell plates, 189 Shell-side pressure drop, 239 ihellers, for eonstmction, 658 for process equipment, 624 ihielded are welding, 188 Shipment of products, 576 Shipper, 37 Shipping, costs oi. 36 instructions for, 130 Shipping lengths, for piping. 462 fur vessels, 40 Shoes, definition of, 457 fat. supporting equipment, 627 Shop drawings, description of, 107 far structural steel, 113 for vessels, 211 Shop-fabricated pipe, practices far, 110, 111

typirid rules for, 461 Shop iabrieation, of pipe. 666, 667 o i ICPSCIS,195 Shop testing of pipe; 464 Shopping facilities, effect on plant lorn. tion, 17 Shops, design of, 623 Shurt-cut mcthods of heat exchanger design, 243 Shunt-wxmd motor, 351 Sipdcr and Tale equation, 228 Signals, standard for derrick operntiaus, 664 Signaling, elcetricd systems far, 538 Silica refraetorics. 485 Similarity of flow, 280 Simplex pump. 251 Single-phase induction motor. 354 Single-stage hlowrrs, 314 Single-stage cmlrifugal pumps, 272 Single-suction centriiugal pnmpa, 270 Site, sac Pliml site and plant loration p~.cparationof. 658 irlcrtion of. I8 Sizing str:tnt rylindexs for purups, 261 Skidding I;trpe equipment, 664 Skil.ts, 194 Slab floors, 626

688

Index

Sliding-vanr type comprcsror, 318 Slings irn liiting nylindneal equipment 666 Slip. of elcclxic motors, 353 of rcripmeating pumps. 257 of rater? p u m p 290 Slip-on flanges, 404 Slump teat far ronwetc. 603 Snlotht?riag gl:ind on ecntniugnl polnp. 276 Snow conditions fut. dcuign, 27 rinow load, 628 Yorket-rvrlding flmgc. 406 Soil. annlysir of. 596597 bearing riiparitp oi. 6% d c r t oi un ioun
I

689

lndex

Slfing hanger. 432 Spur tracks in pmews plants, . 5 i i L j i 8 Square-edged orifice, 503 S q i m e iaotings. 586 Square pitch, J !% Squirrel-cage motor, 352353 Stages, caleulntion of number. for centtiiugnl compresor, 343 Stairways, slope of, 640 Stalling prcsure of reciprocating pumps. 295 ---

Standard instrument symbols, 71 Stundanl notes on purchase order, 128 Stund;
.

( Stuffing box paekmg, for reeiproeatmp, examnlr ralculatmns for. 368 pumps, 254 rste oi steam for.366 Sohrontraetor. in purchase orders. 130 ptenrn ronsumption o f , 366368 use on centrifugal compwsrars and Suhcooling in condensers. 235 Y~~I~s,lriar.i. mil inrestigntions. 5W b l o w ~ r rof. 317 ' Su/~sorf:wr~ W R ~ I T . loration o f . 595 us? on rccipl.ornting r n m p l - t ~ r ,cii. ~ . 301 ! Swtion headers for pumps. 295 Steel taper pilps. 590 Suction piping ior pumps. 294-295 Steel structurps. basis for desizn oi, 627; Stllwrlirnlvi;. conwetion tylir of. 570 629 Stem oi mlvc. 114 Step-control for r e r i p l . o c h ~ gcornprossors. 308 Storage, location oi. 31 of raw r n a t e d s and prodwt*. Q 4 oi solids. 576 Stomge tanks, foundations f m . 587 St,raight-tube, box-headw-typ~ water Surge d r r ~ r r w i oiwil,tiwit~ing 1.011111111~tube boiler. 563 .or.. 3a3 Strain gagc. 518 S~n11lucnuctc~.iali,linndling of. 181 Strainer ior p~rmps.295 S ~ i n xd ~ w k\ : ~ l \ c ,41:). . $21 Stwam nnalyiis, 524 Stwarnline flow, 228 Stress, allowable, for structures, 628 walking, 199, 201, 208 design enlenlations tor. 438440 due to dead weight wind loads. 203 in ioondatione, 615 in piping, 435.436 limits oi for reinfor.cinr steel. 604 ~~~

~~

!

I

~

~

., .. ...

on sphrrc under. inlermrl press11r.r. 197 variation with configuletion of piping. 439 Stress relicring of vrssels. 194 Sttueturnl clenrnnrca, 520 Sttuctural design. 103 Stl.uctural details. 113 Structural drawings. 113 Strnetnml shapes, commonly used typw of, 630 design formulas ial.. 629 mntprials used i o r 630 Structural stcel. detail dtwvines .. ni., 101 erection oi, 662 rnnrking oi, 662 piles of. 591 safety rulrs in design far, 690 Strurtures, basis for design oi, 627-629 partially enclosed. 624 totally anclosed. 61&824 unenclosed, 624429 Stuh end for lap joint. 401 Stu! halt !or flanges, 407

Tnhulatinn of h i d . 127. 128 Tnehomctc~~s. 523 Tnngentinl stlasws. 11% Txnk g:rging. 499 T;~nk-.dwign u i iminhtions for. 616 dorsgr of, 5il-575 T:N o~.dil~ani.t.i, effwt on pI:mt loration. 1 R1

Tclrgramr, 149 Telrphane. use oi, 151 Tclrtrnr. .. 148. 150 Ternperntul.~nmawring instruments. 507-515 nsud industrial rang
690

Index

Temporary buildings, 658 T r m i n n l companies, 11 Terms oi L>ayment,125 Test curve for centriiugi pnnlp. 2i!) Twting of pipu. firld. 463 shop, 461 T ~ s t - :of rqoil,mcnt. sce typr o i equipment Theoretical work of compression. 327 Thet.nul uc~ndurtivitymeter, 530 Thermal eonduetirities, of t.eirartol.y and insulating fire hriuk, 485 of thermal insttlntorr, 479 Thernmconplp rircuita, 511 Tlirmocouple combinations, 511 Th~rmocuuple errors, minimizing of, 512 Thrt~nououplewells, 512 Tl~ennoeo~qiles, range oi, 510 Thcnno-rlcctrie trmpcrtature mr;~auring inztt.ummts, 510-515 Therrnu-syphon r~tmilers,2111, 220 Thermometers, solid mpnniion type oi, 507 fluid expansion in, 508-510 Thicktnrl.~.*stirnation of requityd area and volume for, 392 test3 oi, 392 Thickness calculation, ior pipe, 398 ior vessels, 199,201, 205 Thick-walled vessels, 201 Thin-walled vessels, definition oi, 196 Threaded flange. 406 Threndcd pipe joints, 402 Throttling hellows, 533 Throttling, eont1.01 of stemn turbinrr;, 364, 365 Thrust hearings on ccntriiugd pumps, 27G271. 274 Ti& :wditians, for design, 28 Titrimetrrs, $27 Toe plates, 640 Ton of reiriget~tion,347 Tanguc-nnd-groove flange facing. 407 Tool room. for eonstrurtian, 658 Topug~.aphy,eNert on plant saipt?, 635 Top-suction, top-disrharge centrifugal pllmps. 269 Tornado frequency, ioi design, 27 Totally mclosctl motors. 356 Tower hasc plates. 211 Tower, self-supporting, 585 Toxie chemicals, iniorrnation on, 634 Toxic concentrations of chemirals, typical. 640 Toxic fluids, pumping oi, 277 Trade terms, 126

T~xuafet.pumps, 5i6 Tran-mittnl letters, 142, 148 Transrcrse fins, 215 Triangular pitch, 225 Trickle coolers, 223 Trombone coolers. 223 Truck shipments and plant location, I1 Tube hundlr: nssrnibly oi. 224 Tubing, 398 Tuhula~.exchanger, Manuiartnring :Issociation Standards ior. 223-224 Turbine drirps. ior imtriiugal compres sow and blowrrs, 317 , Iurbine pumps. 291 Torbinea. 361-371 piping at, 461 arw also types stcwm classification oi, 361 Tnrhtiirnre at orifice. 504 Turbdcnt flow. 228 T w - c y r l r rngines for camprrssor drives. 302 Two-font. cxulnmg*rs, 218 Ttru-lnipcller blowers, 319 Two-position control, 532. 533 Two-wt>eel turbine, 361 Typing, on drawings, 117

.

Ultimate st,rrngth of concrete. 602 Ultraviolet photometer, 527 Unbsltinrcd iorrrs. effect oi, on foundation design, 616 Underground iaeilities. instnllntion of. 660 Untlet.gronnd lines, 458 Union bonnet valve, 415 I:nions, iar labor. 655 i m pipe, 402 1-ntt plot plans, drscription of. 82-84 steps in preparation of, 84 G.S. Grodetic suwey datum, 398 Vtillty companies, porrlrsse of power from, 15 ... t,tlLt:. water. 563 IJtilitirs. see type lowtiun o i generating pk.'.? to minimize hazards fat.. 636 primary, 54.5 U-tohes. 221 !'-angle rompr.esmr, 302, 305 Vacuum fquipment selrrtion chart, 323 Vacuom gages. 518 Vacuum pumps, 322 Valves, 413426 :wrrssihility of, 435 classification ai, 414

69 1

Index Yalres. clectrirally operated, 538 rrrrcrgenry. 648 estimation of prices ior, 450 flow characteristics ior, 418-419 list? ior, 453 loration oi, 458.638 namenclntu~.efor, 414 parts of. 414 reciprocating pump typcs of. 254 seat for. 417 symhols for pipes and. 70 trim for, 417 Vapor hat.riers for all insolation. 483 Vapor-filled thermometw 509 Vegetable cork insulation. 475 Velocity-compounded tnrhine, 302 Vrlority diagr;
Vessels, saiety ~ u l r sin rlcagn ior tanks and, 637, 638 skptch 01,206. 210 Vibration in piping, 435 isolntian of. 587 Viscosity i,orrertion curve? for rentrifugd pump perfurnlancc. 286 Viscous fluids. pumping oi. hy rotary pumps, 291 Vitrified tilr, installation of. 660 Voltape rztings for motors, suggestrd, 359 Voltages. typival, for equipmml. 559 for power distribution. 557 Volumrtrir pffici~nry, for rrriprocating rumpressors, 332 with nrttinl gases. 341 ior rwiprocntmg pumps. 257 Volute-type multistage c r n t d u g a l pomp, 272. 273 \\:nrchouses, design of. 623 iol. eon~tnwtion.658 \\:nstc rlispoanl, 14.5XO-581 I\-tisto-brat hoillws, 566 IVaste products, as fnels. 554. 556 IVatcr, as a fire extinguishing agent, ,548 - -~~

rornrnon inpuritirs in. 546548 information on. far ilcsign. 28 sources of, 548 t~rnpornrysupply of. iol. constrnrtion, 659 \Vrrter-heitring strata, 600 \Vnter-cement ratio. 602,605 Rntrr-cuuled txaring housings, 275 \Vatpi liot~s~powcr. 259 \Tatel. jacket. 276 \Yater-proof motor. 356 Water secmee. 600 . \V:ttcr-softening proeesrra, comparison oi, 548.55W51 \Vater sources. and plant location, 13 investigation of, I4 Wat~r-tuhchoilrrs, 563 \Taler transportation nnrl plant location, 12 Ratcr usage of plumbing fixtures. 580 \Vaternaya, 12 \Vrat.ing rings, advantages of. 272 for casing, 272 ior impeller, 272 on centriiugal pumps, 271-272 Kcather, data iot. ronstructiun pro~crts, 26 pNwt on plant location, 16 effect on plant safety, 635

-

are. 18.8

iaoll3-. 189 of wa-el-. 188 of stntrtrli-al steel. 663 Wclding r.fli~.icneies,allowable, 2 M Welding fillinpi, 409 \Velding neck flanges, 404 \Velds. detwling faults in, F63 Wet-seal gas Iroldel., 3 5 Weymouth'r equation, 452 Williams plot ior steam turhinrs, 36i368, 369 Wind, iol. dehign purpoars, direction of, 2i orertirrnillg nroment produced by, 586 pressure oi, 613

iol dcrigu, 2 i Wing r.slot~s.254-255 \Virinp diapmms, 114 \Vood-composite pile. 590 \Voud, use of, in pilrs. 589 Work; calculation oi. for cumprcssors. 327, 346 for pumps, 259. 278 for str;uu tnrhinr;, 366 iar rnultistsgr i.omprriso~..330 PI. stage for ccntriinenl cornpveisor. 338 \Vork of eomprei~ion,h;iwI on irlu:il gar law. 3 2 9 3 3 0 ex:~mulrcalculation of. 345-348

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