5,PIP!NG HANDBOOK Reprinted from HYDROCARBON PROCESSTNG . Gulf Publishing Company
.
01968
.
$1 .25
PIPING HANDBOOK TABLE OF CONTENTS
Page No.
STRESS ANALYSIS
4
A Simplified Computer Program For Pipe Expansion Loop Design Piping Design Method Beats Computer Symmetrical Piping Arrangement Solves Two-Phase Flow Distribution Problems LAYOUT Plant Layout And Piping Design For Minimum Cost Systems What lnformation ls Essential For Good Piping Design How To Design Yard Piping . Locate Tower Nozzles Quickly Piping Of Pressure Relieving Devices MATERIALS U.S. vs British And European Piping Specifications Which Material For Process Plant Piping?
5
10 20 24 25 34 39
.
49 59 66 67 73 80
EXPANSION
Find Best Pipe Expansion Loop Quickly Expansion Joints: How To Select And Maintain Them Spring Pipe Hanger Design Simplified Piping Tierod Design Made Simple THERMOWELLS Procedures For The Piping Designer Soecifications ., . . lnstallation And Specifications Selection Of Thermowell lnsertion Lengths PRESSURE DROP AND VIBRATION Simplified Utility Loop Balancing . . Piping Design Stops Pulsation Flow Find Line Pressure Drop By Nomograph New Approach To Pipe Reactions STEAM TRACING New Guide To Steam Tracing Design .
.
81
88 94 96 100 101
105
.
111
120 121
125 131
133
.
138
.139
3
SS ANALYSIS
A Simplified Compufer Program for Pipe Expansion Loop Design
Using a single input card with terms and measurements common to any drafting room, computer computation and analysis has 5:1 time advantage over manual methods W. W. Shul!, and G. N. Bogel, Jr. The Dow Chemical Co.. Ilouston
A conputnn
pRoGRAM has been
written that will de-
sign piping expansion loops with less cost and with less elapsed time than ,existing rnanual methods. It requires a single input card containing measurements common to any drafting room.
Mqnuol l,lethod. A previous articlel recornurends a manual method for piping loop design except for critical lines (those with high or low operating temperatures and pressures andfor force sensitive connected equipment) and except for piping which conveys hazardous or flamnrable materials. These exclusions eliminate application of the author's semi-graphical methodl from most of the piping in a petrochemical plant and require that the piping designer both understand and have access to process data. Even if process data were available, the hours required to segregate the hazardous senice and critical piping for solution by a stress consultant or specialist and the queue hours for the attention of the stress consultant or specialist are additional factors which the authors omitted.
The authors' make the claim that, for non-excluded piping, their graphical approximations are obtained in a fraction of the time it takes to prepare the data for computer analysis. Readers will have to guess at the engineering and clock times used by the authors in arriving at their conclusions. In our trial runs, assembling of data took the same time and computation and analysis of results from computer and hand calculations had a five to one time advantage in favor of the computer, besides having the ability to better understand the effect of the various alternates. It is probable that the computer programs available to the authorst did have a complicated input for solution to simple problems; and considering only over-all time lapse, their claim is often true for an answer to any one single problem which happens to fit a manual method which the designer uses with sufficient frequency to main-
tain his speed and accuracy. Effective use of computer programs also requires user familiarity with their input requirements and their output capability. This learning eflort is less than the eflort of learning any equivalent manual method. Moreover. one rnan can examine pipe layouts for a plant, input the loops on a computer program input form, and get answers for one to several hundred problems within 24 hours, and in some offices within the hour. Well planned piping design jobs seldom need answers faster than 24 hours; but, under planned conditions, the computer results can be rnade available within minutes. Resislonce ?o Computer Use. It has been our experience that people who resist using the computer as a tool for the routine as well as the difficult tasks in design may be described in two groups. The first group thinks that computer answers are either beyond question or are not subject to parametric study of input variables or modifi-
cation based on engineering judgment. This group
has
5
A
SIMPLIFIED COMPUTER PROGRAM FOR
..
.
S AND B ENGINEERTNG SEPVICES PIPE LOOP OESIGN PROCRAX PLANE'2 TO 6 PIPE IEXAERS PIPE LOOP DESIO {AINLINE -_sINGLE rITH I TO 5 ELAOiS OR BENOS OF SAXE BENO RADIUS ilAY T967' HOUSTON TEIASI ANO G.N.AOGEL' BY T.I.SHULL IRITTEN OESIGN AND PRL]GRA{ USFS FORNULAS ANO T BLES PPES€ilTEO IN TIPIPING PFOVTO€NCEI RHOOE ISLANDT THE GRINNELL COXPANYIINC't ENGINEERINGI' 196f,. usA. SECOND EOtTION. OF CRINNELL PROCEOUPE AS DETAIL€O ON PAGES 52t5f ALL SUBS FILOI ANY f,EiAER' NY XEXBER AND €NDING IITH INPUT STAFTING IITH (TELD€O) IHICH ARE ANALYZED FOR EACH XEXAEF HAS T'O JOINIS
105
too
IHE LO.EST ANO HIGHESI JOINI NUXBERS ARE CONSIDEREO IO tsE THE LOCATION OF IHE TNNER{OST PAIR OF GUIDES OR THE LOCAION OF ANCHORS IF IHE lNPUT LENCIH TOUISIDE OF GUIOES' I 5 ZEKO. iHE EXCEPTTON IO THIS RULE TS FOR TIO XETBEF ISINGLE ELBOI' INCREIENT ONE f,EMBERS LENCTH FOR IBICH THE PROGRAI TILL JOINIS TO PROVIOE THE NECESSARY FLEXTBILTTY' l2ltrY(12,,R(12) r2 );Y( r2l.xL( r2r,r( l2l,rxl 6),x( c.rf,xoN o(6) t6(6).vl r.s( r2t.Rxt t2),sT( t2), AAI 20 ) COTXON SIPTPI. TLA IXKTSAETAI XBARtYtsAR! XLP!YLPTPXYTP I XTPI Yt IMAX ICT' !FST{AXTDEMT ILEN!ALTsI IFX! FY t CONSIX!CONSIYTOA'THX COHXON TLNCTXOFY.OLNG 5),OXl 5l rAST (5' rBR'srtAXrKBD coxf, oN tEx(5, t TRY( 5),BXl 5l.AY( J!K'N.KXAi COIXON KPFI TKSTI(FNDIKFSI!KLOOPt OOUBLE PRECISION PIPEIO t.JI X OIRECTION = OST TO.ENTROIO Y(J) = DST to CENTROID Y DIRECTIoN II IJI: LFNGIB OF SEGXENI R(J) = X DIST FROY CENTFOIO 5(J) = Y OISI FROB CENTROIO PXY = PROO OF INIER I A ABOUI X PIX = COU OF IdTERIA ARoUT Y PtY xof, oF INIERIA = CT = ExPANSION AT TEHP XLGTYLG = t ANO Y DIST FND FOINT TO END POINT PI P1PE IOXENI OF TNTERIA = PIPF SECT TON XODULUS Sf,P =
RESULTS: 'OHPUTER FOR PAOBLEM P.52:
to2
lOa
O2a
I
0?5
I O7
l06 23 2a 26
3t J2
ll
I
lo
ttt at2 ttJ tr5 C
I
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to
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t20 121
tla t22 c l4i
tro
2 A 3 = 9IA2 PSI XAX.BEND STRESS RET.JOINTS SIREsS IS AT JOTNT 2 = A723 PSI GREATEST JOINI Fr. XBAR=34.62'YBAR=9.59 INERTIA OF PIPE=2\?. lX=9395. lY=2135'. tXY=I0446. sEaTloN HoDULUS=19.43
(ONT RL:2
lor
I
lo2, t 0t
fa CENTROIO OF STFAIGHT LtNE IN PLANE OF PROJECTION - COLN EoN r A = LENGTH B= x OR Y DISI COLNlarB, = A*A ( TO AXISE0NS OF aEND!X=DI5T CENIRDTO OF BEND XK=FLEx.FACT'R=RADIUS aR coaNo(xKrRrxt= t.57axxrx c XL=LENGTH PROD. OF INIEFIA LINE PARALLEL TO AN AXIS EON6 C Y PLNXY(xL!x.Yr= xL t r: C PROO OF INTENIA AEND NEG IHEN AXIS I RADIAL OR ARC < ( +R +x' Y xKI r.57 xK +.lf7rFaRrR. PENON(xKrR.x!Yl= RADTAL AND AFC C PROD OF INTERIA EEND POS iHEN AXIS ' 4a ( pBNOp(XK!R,r,y)= + iKal.57tR*XrY XXr.r37*R+R*R MOMENI OF INTERIA ST L'NE tN PLANE OF PROJ PARALLEL TO AXIS X C ( PLMILNIxLTY) = XL aY:Y 5l C MOU OF INI SI LTNE PERPENDICULAR TO AXTS Y ppxtLN(iL,xl 52 ( XL+X1X = iL*xllxL/I2.. Y IDB OF tNT BEND FROM AItS C p!taN (xxrRrxt xK tR tx.x l.s7! < = xK +to.r49aRrR+Rl. 55 THK= THICXNESS IALL DA = ACTUAL OTA. PIPE SECIION NOOULUs C ) DA+oa_2.4( DA.THK T+2.a(rHK.THKl s!( oA. rHKr sxx )=0. 25loarsMx*( 57 AEND F = RADIUS OF PIPE XLAX . LAMBAOA 5A +.2s) iL^{l THK. R. DA)=THK+R/l ( cA_rHK I *(DA-THxl XLA = LAMNADA C FLFX. FA'TDA FF ( xL A l= I .65/ xL A FACTORT AETAS' FOF IELDED ELBOIS OR BENDS' STRESS INIENSIFICAIION C O. 6667 EEIAs( xLA l=0. 9/xLA*t OIPE CROSS 5ECTION!L ICTAL AR-A C I PAREAI DATIH('=3. I4 I 6IIHK:(OA_TBK plpE ioH oF lNr 65 c PMINTI OA'THK I=3. L 4I6*I DA-IHK)'+O3TIHK/4. C XBAR DISTANCE B=tsEND RAOIUS v= vAFIAELE D l5 DISI C NON-ZEEN ENIPY IN CDL 7A PRINTS VALUES TN CO{{ON C XPRI--A SHOYS LAST OF PIPE LODP5 USING ENIRY IN CI]L. 79 C LPRT--NON-ZERO EXPECT A NEt HEAOER CARD' HEADER CAFD ANO PR'GRAil TILL C STRESS A5 PtOF IEilBER LENGTH IS VARIED FOR OESIGN C NPPI_-PFINIS FEFIT 1 FOP STNESS EACB.5 PROALEqS. ENIER IN COL. AO DIGIT C DIGIT 2 FOR STRE5S EACH I. FEEII C FEEI! ETC' DIGTT 3 FOR SIREsS EACH I.5 C A AO IN X OR Y DIRECTION OUISIDE THE SECIION OI5IAN'E C 6UIOE INOICAIES x=Ol 'D3'D5 o=x l=Y DIHECTIoNS . C OEFINED FY Ol-D6 9 A 72 FROM PAGE T€5I DAIA FROM GFINNELL SIJCOlO EDITION PAGE 52. C 1CT JI1 c A6 F5.O Fs.O Fs.O F5.O Fs.O Fs.O F5.O F5.O F5.O F5.O F5.O rtF4.IIF4-IlF4. GUIOEVARYLVARYA PRT D5 06 03 ALiST CT tsND D DT D2 C tD DIA TH( {0. 24. 12. 14. 17675 996.50, cP.52R1O.75.50 A. 2 lO.l4oOO 12. lO. 17675 996.50.40. cP.5201o.75.50 FT-LB END HOMFNIS=24f64'-23970 ANsiER5: ANCHoRS x=2795rY:lA67LB5. CP.52RGRINNELL 2 3 = 9O3OPS] t IOA'=29672 MAi.HE'TD STRESS EET. JOINI FOR PROBLE{ P.52: C ' 2 PtPE tS AI JOINI 6REATESI STRAIcHT {ANUAL-GRAPHICAL: C = a7l4 Pst !BAR=3a.63!YBAR=9.6oFT. INEPIIA oF PIPE=212. c lx=941s. lY=21i69' lxY=lO4s7. sEcTloN MOOULUS=39.43 C C C c C c
lor to! lo:l to2z IOal
c
(f,r r r5) rRITE aA RE-aD (rtl29,
5J
(r, r30l icITE NPACETAA DO tOr J=rt 132 oo tor AlJl=0.0 READ I I TKDIRI YFIIE IRITE
J=r53r2ll tAFAOtD!kFSr!FSTMAx.
l-Pipe expansion loop program. Note: Subroutines not included in the program listing solve step-by-step ments in the mainline program listing. The comment statements reveal all the basic thought and method. Fig.
thE manual method illustrated in Lit. Cited 2, pages 52 and 53, using the functions duplicated as comment state-
little knowledge of the difficulty of progran'ring a computer to satisfy every possible need or whim of the user. Its members reject the computer as a tool when the program's logic requires flexibility in the user's notion of input and output content. The second group has some experience rvith either programing or using the computer; yet, its members over6
estimate the difficulty of communication r.vith the computer. Both groups deter the economical emplo1'msn1 of computers and thus restrain the development of the engineering sciences from the precomputer art of applying empirical relationships to approximate solutions for -nvhich exact theoretical solutions exist. Fortunateln membership in either of these groups need not be perrnanent!
Pf,OBLE
T ACTITAL
LOOP
lDEl'lTlFlCA-
ilot
rlU_
0wsl0E
c
ALLOY-
PIPE
IELE sTncss
PIPE
(PSt,
DITUETER Ir[cr{Esl
X I D El,lTlF lC AT lOil ,1/tC, ,4 , t , ,
.?a,aat+.cnt, ,tF€
FACIOff
Itotu3
FIBST
sE00ilD
OF PIPE
LOOP
r.ooP
t FOUNil
LOP
LOOP
ltax.
strTlt
FIFTII
LUn
L
LooP
SEEIETT
AT
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ltnurEJ,
IETGTII IFEET}
llIERs-01
lrilcHEsl
TAIND
LEUOTN
IFEETI
LEXGrll ITEEI)
IErt6TE (FEETI
LEI'IGIH IFEEN
LEXGTH
(FEEN
.=
DE
lBu I ax-
i=
IET L.
BF /0|'lD iIJIDE
Er a*E
t
6 7
I
2
1
fr
2
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al
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at
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5
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o
A
e
TYPICAL LOOP LAYOUT START AT ANY MEMBER,AND STOP AT ANY MEMBER TO DEFINE LOOP GEOMETRY - EETWEEN ANCHORS OR GUIOES
A
Fig.
2-lnput
+ C = ENTRY IN NET LENGTH
card with data for problem shown on Fig. 5.
The Progrom. A computer Program in FORTRAN IV was written (Fig. 1), just to see if it could be done, to solve expansion Ioop design based on a published manual method.2 The program does not require manual inter-
not less than the sum of bend radii (expressed in feet) incorporated in the particular member.
o The number of
a member whose length the program allel the
'-'i1"
ex-
eto
allow solve
upon consultants. If the loop as input has too great an anchor force or too great a stress, the program provides the required flexibitity by increasing the length of a designated member of the loop within user input limits. The Iocations of guides normally are not altered because guides usually are mounted on supports whose locations are subject to controls other than piping flexibility.
Input Data. The entries for an individual piping loop r"qri." a single card (Fig. 2-80 letters or digits maximum) containing the following information:
. o
PiPe loop identification name or number. Outside diameter of the pipe and the wall thickness . There are no limitations on diameter or thick-
l;:n"r) o An allowable
stress range at bend and terminal joints based upon code or connected equipment limitation (pounds/square inch).
o A value of C obtained from the following equation: ^ Expansion, in.,/100 ft. (E")
r-@
or from Literature Cited 2, page 9. This value combines the lineal therrnal expansion in inches from 70o F to the operating temperature with the tensile modrrlus of elasticity at 70o F (pounds/inch). o Radii of bends (inches)-a single bend radius is applied to all bends. o Lengths between corners of the loop members within the innermost pair of guides (feet). A "corner" is defined as the intersection of the center line extensions of straight pipe members (however short) which connect to a 90" bend or square elbow. The input length must be
hold anchors and move guides.
o The maximum permitted anchor force (pounds) X or Y direction of this limitation. o The piping length ( most pair of guides and axis of this additional
and
the
contributes force because of thermal expansion. An additional header card precedes a grouP of pipe loop entries. This card contains any desired alphabetic or
numeric descriptive data desired in the output printout (job title, user's name, accounting information, etc.).
Whol The Progrom Solves. The program is capable of expansion to handle many possibilities of piping loop
for PurPoses of this documeltation for the following frequently used single-plane loop types which have no external loads or restraints between
design but implemented
anchors except guides:
o
U-shaped loop with unequal or equal legs plus up tangent members of unequal or equal length. (Terms correspond with Literature Cited 2 terms for U-shaped examples.)
to
trrzo
o U-bend expansion loops similar to above. IJse our term "legs" instead of the Literature Cited 2 term "tangents" for the expansion U-bend examples in Literature Cited 2.
o Simple two member loop with one elbow. o Z-shaped expansion loop. o Hooked Z-shaped with up to one tangent
rnember.
Progrom Tesis. The program has been tested with book problems' (Fig. 3) and with the examples from the 7
PIPE LDOP rnFNt-
,
FlPE n D
rNcHEs
IALL THtak-
ALLOI qTRFsS
qI_rnrNT
JOINT
.
)>
--E-
A020.
6330.
962-
63A0,
ANcHoR F0RCE IN X-DIREcTION
2 HAS GREATEST STRESS
MOMENT AT JOINT
ANCHOR FORCE LIXIT
.=Nn-
I -Y ,=v
nlo
PouNDs FoRcE
-E6b>
COORDINATE OFFSET FEET .r I .ll-uI_1,f.-_THRU Y-AXIS X_AXIS
LENGTH OF sUM DF MEABERS F' rrrn qtrH--Dl=D6 LENG.IHS FEFT FEET
--
D- IHICH xaY vAeV
!!!tsES- -EEEI- -EEEI- -EEqf- -EEEI- -EEEI- -EEE.M: EEE! qlqE
l-lellEs -_e5!_ --__---
75O-......_o
SE
RADIUS LENGTHS OF ME{AERS (TO CENTER OF CORNERSI nA n2 nd n< oF FFNn Dl Df
FACTOR C a nFG-F
7426. =
ANcHoR FoRCF IN Y-DIRFCTION=
2a03.
MAXIMUM STRESS IS IN BEND LENGTH OUTSIOE r I O,|I AErEF{ rpiHiB ' ^Hp IN POUNDS/SO. INCH
_J5_{EXBEF rl
JoINT
MO{ENT AT
DIAGRAM OF PTPE LOOP
I =
L4LOz.-
147O.
AXIS DISTANCE FEET
a
AX I S
=
"I_J6_ J7
ll - --L-Lq-ottrrrr
| o-ooo MEMEER O4
MFMBER D2
ffEL
-.+
|
D5__J
_J9__MEMRER
r
o_
|
LOOP O. K. FROM STRESS STANDPOINT
Fig.
PIPE LOOP
PIPE
TALL
3-Test
FACTOK C
I|.OI
problem based on book2 input data.
PAOIUS
LENGTHS OF MEMBERS (TO CFNTER OF CORNERS)
j.o9B
JOINT
l6la7.
2154f,.
l30aa.
lm
X_DIRECTI ON -
I2N6.
1NO IN POUNDS/SO.INCH
7
LENGTH OUISIOE !@
AXIS OISTANCE FEET
MOMENT AT JOINT
LotP
o.
ANCHOR FORCE IN Y-DIRECTION=
MAXTMUM STRESS TS IN EEND
DtaGRAM 0F PIPE
MOMENT AT JOINI.
o-
I tq6.
ANCHOR FORCE IN
5 HA5 GREAIEST STRESS
lMo-a-@lo4Lp4
24642.
LENGTH OF SUM OF MEMBERS COORDINATE OFFSET FEET PATH. J+-THPU J I FtLF LENGTHS -D.!=s. -JONIX_AXIS Y_AXT5 FEET
IO =
J'
+
l. ro.o@ Er
leooo rEL D2
VEMEEi
MEMtsER
/ l2.ooo FEET - - - -- -A€G-INNIN5-:]Jl---::4EUBER-oJ:=:-:r+=lcuIDE =
J3
.
D4
I
I
I
|
I
F#T-
JrL=-
-I J9____MEMBER D5___JrO_l I OIIP OVERSTRESSEO
Fig.
8
L_-
4-1"r,
o.o
EtBU N-E
. l--
--
THIS
ANCHOR FORCE LIf,IT
!NS!ES- -EEE!- -EEEI- -EEEI- -EEEI- -EEEI- -EEE! !S! EEEI qgOE eQ!.Nqs
lrlclEs rNe,BES __PS!_
7t96.
D- IHICH
problem based on Haque/Starczewskil input data.
FEET
AX
IS
FoRcE
PIPE
LOOP
PIPE
ALLOI
TALL
J!-C!ES I-NCHE5
t!Pu'
OgL6.6fs
rtrH w^ovrNc IITH VARYING YIT{ vAqvINA IITH VARYING !u+wYl!r: IITH VARYING
O.'r0
xFMqFa I Fil.TH = HE{BER LENGTH = {EMBS I ENGrts = MEMBER LENGTB = l.MHFo LE.Mg xEHtsER LENGTH =
6473. JOINT
-'5Oo.
eToFss STRESS STREq( STRESS
I< IS rq IS s| STRESS IS
FEET.
12044.
19443.
6 HAS GREATEST STRESS
LENGTH OF EL'rlo ptIB
d.ooa
35s.0
FFEY. FEET' FFFrFEETr
LENGTHS OF MEMBERS (TO CENTER OF CoRNERSI
RAOIUS
SUM OF MEMDERS COORDINAIE OFFSET FEET ot_DA til.-rs< Jot{ItL t THRU FEET X-AXIS Y-AXTS
a.OO
a.OO 12.^O
I aq/ea IU - aM.Hno FnorFc LBS/SO.IN.r ANCHOR FORCES FnR.FS LA<'sO.IN.^Ncpno LAS/SO.IN.. ANCHOR FORCES pq"qr' LBS/so.IN.r ANCHoR FORCES
'a^^126276. 3lS223251.
21960,
A.^0
r2.OO
r.:Ao30O79.
21960.
1944a.
ANCHOR FORCE IN X-OIRECTION
UOVENT AT JOINT I aE. FOOr-POTJMIS
D- THICH
ANcHoR FoRcE LIHTT
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--eS.!.- -------
a-6 a.s o O 9.5 rOlO.s
1456t.
FACTOR C
12044.
y-6ro = X-DIR.= y_DIor_ X-DIR.= : X-DIR.=
14561.
Jl!
-u
6473.
I045.
=
O.O
2
,^A9.. la3l.. '5ra.,. 1434.. 12a6.€ lr57.r
IN BENO LENGTH OUTSIOE , sl!'s 6 N0 LOOp IN POUNDS/SO. INCH FEET
e2OO.e
-O.
y-DIR.=
-O.
o.
-O -O. _o.
JP o.
AXIS DISTANCE
FEET
,rotu__
LOOP
t
w-DIp y-DlR.= v_DtF._ Y-DIR.=
ANCHOR FORCE IN Y-DIRECTIoN=
MAXTMUN STRESS IS
DIAGRAM OF PIPE
4.5O
EgUNgS-FoRcE
MOMENT AT JOINT
Ar5-
AX
T
S
IO =
-^r.oo JI I I
I
! l.ooo Ef MEMBER D4
,l a
tz.ooo FEEr
ar u[Ytrac_:_I__---8ff8tre CUTDE
^t
)2_l
J3
I
I
I
I
tt |
l2.Qio FFEr
_J9_____MEMBER
o. o
FEET
Jll
D5___J I O_ |
LOOP O. K. FRO! 5TRESS STANDPOTNT
Fig.
S-Test problem
based on Haque/Starczewskil input data.
About Ihe qa.rthors
'Wrr,lr,lrr \1r. Snur-r, is u, r,iril cnginecr utith tlte Cor.poro,ta Enginer:.ring antl C onstruc tion Sertices of The Dou Cltenticol Co., HotLstott. He cletelops qualitA tnctltods of ck:sign problem sctlu-
tions f or ci.-il, ntcclta.nicrLl, an.cl :--esscl disciplines. Mr. Sltull holtls a, B.S. clegree in nkc/l.anisa1 engineering front Lottisionct Stote Uni.uersitu rtnd, Itcts don.e gradu.ote toork at Tulane, tlLe Lini-
,:l "(
uersity of Ho.ttston, and Georgle lVasltingtotr Uniuersity. He lm,s pS ,LJ(.al s c:t:perience in tlrc Dotu Engirtcering Dr:pttttltt.emt in ci.-il ancl mcchanicctl engineering dr:si11tt. Hc is q, nttutttr:r of ASCE NSPZ', and ACI.
G. N. Bocrr,, Jn. is a seuiol" engineer
in the Corporate Engincering and Construction Seruices of The Dous Chemicol Co., Houston. His utork inrolr-es chentical engineering, systems dnalAsis f or effecti"-e use of coinpllters in design engineering, liaison f or lrcat erclTan!.ler tlesign practices and metltods witlt Heo,t Transf er Researclt, Inc. Mr. Bogel ltolcls a B.S. degree in chetnical enoineeri,ng -J|I L from Teras A.&M. Uni"*ersity. He h,ns wollced Lil.ptocess det:eloptnent, pilot ancl production plant supert:ision, pyocess and mccltanicctl design, and, project engineering. He is a metnber of AIChE, ACS, ACM, TSPE, NSPE, Process Heat Exchu,nger Society, rntd the National S ociety f or O ceo,nogro,pltu.
Haquc/Starcze$.slii article (Figs. ,l ancl 5). In general, the agreement rvith answers gir-en b,v our program asree u.ith the problems and examples \rithin + 2 perccnt. Extrerle care \,vas necessary to make sure the problems r'r'ere the same and that the results u,ere identifiable. For the exarnple given at the botton'r of Page 204 in the I{aqLrc,/Starczervski article, our stress using long radius bencls and con-rputed intensification factor is in agreement, but onr anchor force is lorver than tlte square corner solution bv a factor of tu o. The anchor force for our square corner solution of the sartre probleln agrees r.vith the force from the computer program mentioned in the Haque/Starczeu,ski article and is nine percent lo',ver than their graphical method. Square Corner Technique. The use by inclustry of the square corner technique with its conselvative answers (sometines by a factor of two or more) is difficult to understand because it tends to indicate problems rvhere there are none and results in tvasting investment and operating capital for unnecessary expansion loops. Note: The mainline program (Fig. 1) with its sanple output (Fig. 3) represents original u,.ork and is in no case endorsed by our emplo),er or based on any program cllrrently in use in our ofTice.
1Ha.gu9, FI; "Pipinq
prrrer.'' 2
Providence,
)'-n",Jll?"r",t*n -3. 16. No.
r\,rethod Bcars com-
March l9ti7.
serond edirion, 1963. Grinncll Co.,
Index!.ng Terms: Coefficients-6, Computers-10, Design-8, Diameter-6. Expan-
sions-6, L^engrh-6, Loops-9, Pipine-9. program,-i0, Radiui-6, Sr.*.F.-i,
9
Piping Design Method Beats Computer
Symmetrical, U-type PiPing looPs can be analyzed for flexibilitY using this new graPhical method.
lt
can be done faster than the time required to prePare the data
for computer analysis M. S. Hoque, Engineering Consultant, EMMCON, London and J. Storczewski, Woodall Duckham, Ltd', Crawley, England
ple easy to follow method is used and no extr'aordinary mathematical knowledge is required. In structural design, the imposed force on the system piping is specified and the deflection by the design, the deflection is given rigorimposed deflection is determi accuous methods available which demand intricacies computational involved their racy, but the attention of an engineering mathematician or an ex-
the solution'of 'lJ' type symmetrical expansion loops. It procluces results reasonably accurate in almost a fraction of the time it takes to Prepare the data for computer analysis.
The total deflection in a piping system is usually known' For example, if the pipe length of a symmetrical loop is 50 ft., i.e. 'U' length betrveen anchor points, the thermal expansion 4 inch per 100 ft. of lincar length, then the total deflection : 50/100(4) : 2 inches. The height and width of the loop are generally detennined by the space available. Oncc the shape of the loop is decided by the layout engineer, forces, moments, and stresses can easily be found using the graphs presented in this article. It is suggested that the use of precise and analytical methods and also comPuter analysis shor.rld be limited to only critical and hazardous lines. Critical lines are those involved with high or low operating temperatures and pressures and/or the type of equiprnent to which they are Connected. Hazardous lines are those concerned l'r'ith the nature of fluid being conveyed, highlf inflammable etc. Therefore, designers should segregate all critical and hazardous lines rvhich demand the attention of a piping stress consultant or specialist. For simpler, noncritical lines an approxirnate calculation method is permitted by the Code for Pressure Piping ASA B31'1. The Starczewski/Haque stored energl'method is an approrimate solution and the analvsis produces safe results.
Allowqble Stress. It is recommended that the allor,r'able stress range S.1; rvhere
: I ( 1.25 ,Sc + 0.25 Sr, ) : allorvable stress (S value ) in cold condition S,, : allorvable stress (S value) in the hot condition
perienced pipe stress analYst.
S,r
to use method is the only answer. One that would even win over the total time involved to solve a problem on a comPuter, and at the sarire time produce acceptable results and also satisfy the requirements of the Code for Pressure Piping ASA 831.1 or British Standard Specification 3351-1961. The authors present a method which can be used for
S"
A
to
less time consuming, easy
stress
obtained bv this method should be compared by the code
S" and S,, are to be taken from tables in the applicable tions of the code
sec-
f :
IJse
stress-range reduction factor
for cyclic conditions.
a value of 1.0 for one cycle pcr day or ASA 831.1.
less. Consult
2.0 1.8
r.6
1.4 t.2 r.0 0.8 0.6 0.4
0.2
SCALE P ?o 30
40 50 t00
Weight and other sustained external loadings shall not
200
exceed Sa.
300
400
500 a 5
Pipe supports qnd restrqints are not considered in the flexibility calculation. It is assumed that the supports which have not been considered in the analysis should be located and designed so as not to interfere with the flexibility of the system. The reactions computed by this method shall not exceed the limits which the attached equipment can safely sustain. Equipment such as. pumps, hrrbines and similar strain sensitive machines should receive the manufacturer's approval; and the piping system should be designed flexible enough to comply with their recommendations.
The following data apply to all sample problems, unless otherwise stated.
PipeSize:3in.
:
40
Operating Temperature : 8600 F E : Young's Modulus (cold) : 27.9 (10") psi. Thermal Expansion : 7.37 in. per 100 ft. 1 : Moment of Inertia : 3.02 ina. Z : Section Modulus : 1.724 trf .
i:
Stress intensification factor : Carbon Steel
:
1.78
Material Code
:
Se
Allowable Stress
:
2p00 3p00 4,000
5p00 rop00
Fig. l-Force graph (above) and moment graph (right) for SAMPLE PROBTE'VIS
Schedule
rp00
Power Piping
:
U-typ" pipe expansion loops.
Somple Problem l. For a simple 'IJ' type expansion loop as shown in Fig. 3, check maximum stress in the loop, and if the calculated stress is much less than the allowable, suggest a loop which will produce a maximum to or near Sa. Space does not permit the modification of 11, but G can be modified. Given: 3 inch carbon steel line, Sch. 40, thermal expansion 2 in. per 100 ft., temp. 325oF. Data:, I : 3.02 h.n; Z : 1.724 in.3; i : 1.78. Allowable Stress Sr : 18,000 psi (Power Piping). stress equal
Solution: 16,800 psi.
Solution: Use Figures L and 2.
B- w10 :_:1 'H10
ll
2.0 t.8
1.2 r.0 0.8 0.6 0.4
t.6
0.2
SCALE B
G10 o:7.-ro-1 6o
-
z.
Total thermal
expansion:+
(100)
:2
50.u00 ,) Td inches.
=
and a and other nomenclature have no con-
too,ooo E
nections with similar symbols used in piping design books. These are used in this article just as symbols.
= o =
Note: B
ut
Step 1. Determine Force Fe using Fig. 1 (Force graph).
Entei scale p with F : t then move vertically upwards to the curye a : 1, and now move horizontally to the right to the line 8o : 2 and then vertically move down tJthe line FI : 10 ft. and horizontally from this point to scale Fal I and read the value Faf I : 38The Force Fa : 38(I) : 38(3.02) : 114.76. SaY Fa : 115 lb. Step 2. Determine maximum moment in the bend using Fig. 1 (Moment graph). Enter B scale with 13 : l. Move to curve d : 1 and then horizontally on right to H : 70 ft. and vertically down to line F1 : 115 lb. From this point go horizontally to the moment scale to rcad BM, (Bending Moment) : 6,300 lb.-in.
Step 3. Calculate the maximum stress
in the bend.
U{ .S, : Expansion stress : ,, : ,S,
I
:
8,000 psi.
S,
(
63oo ,r.rr) r.72+',
S.
-
6.52opsi.
500,000
The system is acceptable. The calculated Stress is than the allowable stress. Step 4. Determine the flexible loop, rvhich duce a stress of 8,000 psi. Use Fig. Stress ratio
will
less
pro-
2.
.s. 18.000 1_l_b,5zu sE _-2.i'6
Find, y : 0.475 from Fig. 2 when a : 1 and F : 1' New y :0.475 (stress ratio) :0.475 (2.76) :1.312. Enter Fig. 2 with new y : 1.312, move to 13 : l, then travel vertically dorrnrvards to read ne\v d : 0.25. Since a :
G
i:0.25,
G:
0.25 (11)
:
0.25 ( 10)
-
2.5/ft.
Somple Problem 3. See Fig.
PIPING DESIGN METHOD BEATS COMPUTER
oW4 ' H 10 :0.4 GO A:-: :0 H10-
T
I H
l'-n
uo
t.0
E
P
5.
0.9
O: G/H
0.8
B=w/tt
0.7
7.37 : 100 (55) :
4.05 in.
From Fig. 1, by interpolation, FalI :270. :. F.q. : 270 (I) : 270 (3.02) : 815 tbs. By computer Fe:6421bs.
s06 u) 0.5
at)
H
0.4
6
0.3
F
Somple Problem oW4
F
p:-: '_H10 GO H10
z.
trJ
0.?
= = >-
4.
-
See
:0 in.
Find force from Fig. l, FalI :' Fe - 20 (I) :20 (3.02) By computet Ft : 46.0 lbs.
t23456789 a=G/H
Fig. 2-Variation of bending mometrt and stress with beta and alpha.
.6.
0.4
oo: l-it100 (4) :0.295
0.09 0.08 0.07 0.06 0.05
Fig
: :
20. 60.40lbs.
From the above three cases, it is obvious that the result by this method compared with computer analysis indicate safe and reasonably accurate values; and
for these
shapes,
this method wins over computer analysis including data preparation time.
p:Y: .H
t,b/
-
lo, tr
-
Somple Problem 5. See Fig. to.
6:_:w10 H r0 :
The suggested loop will have the following dimensions: H
-
l0 f.t.,W
-
10ft., G
-
2.5
This new loop will produce a
ft.,and
stress
:
U-
100
BM: 6300 lb.-in. - 2.76 BM (Stress ratio) - 6,300 (2.76) - 17,400 lb.-in. 17'4oo BM New stress ,, (1'78):lB,000Psi. Z ,): ,12a
3:u
Calculated
ratio
,:(+)
-4/to_
0.4
a:l_/c \I :8,/10-0.8 \H/ U,
:
t-al
100
(55) :4.05 in. (Thermal expansion of 'U')
From Fig. I find FalI : l2O. Fe - 120(I) : 120(3.02) : 362lbs. "' Computer result : 252 lbs. Kellogg graphical : 368 lbs. Fa : Force of pipe on anchor or nozzle, caused by
thermal expansion.
7
-
.31
loo -r55,-4.05in.
Find from Fig. 1, F^lI : 78. : 78 (I) : 7A (3.02) : 236 ]bs.
F.E
M1
-
Stress
Somple Problem 2. Calculation of forces at the nozzles, see Fig. 4.
I
a:- G10 H - --:1 10
ft.
18,000 psi.
Check stress: Stress
7.
12,000 lbs, in.
in the bend.
qil So- M;!z '' -- ':::? 7.12+
(t.78) S,i :
16,800
psi. Sr (
The reactions and
:
12,400 psi.
S,r
stresses
are within the allou,able
Iimits. The svstem is therefore adequately flexible. Economic Loop Design. If the anchor forces are not the factors which dictate the design, then the loop can be quickly determined by the use of this method which will produce maximum moments and stresses equal to its allowable limits. No trial and error method is needed. By using Fig. 2 a great deal of labor can be saved. This also eliminates a large amount of mathematical computations and reduces the chances of errors to a negligible degree. The graph is self-explanatory and results are sufficiently accurate for most engineering purposes. The following example illustrates how Fig. 2 can be used efficiently.
t3
If
the calculation, based on either the Starczewski/Haque
method or an analytical method, indicates that the moments and stresses exceed the allowable limits, then Fig. 2 can be used to predict the guide distance "G" which would enable the shape to become flexible enough and to yield moments and stresses equal to the allowable limits. U
Sompte Probtem 6. A loop which has the ratio a : GIH :3 and p : IrylH: 5, and the solution indicates the Bending Moment : 50,000 lbs. in. and Expansion Stress : 30,000 psi. This exceeds allowable limits.
oo'
Fig. 3-Simple U-type expansion loop for Example
l.
Allowable BM :25,000Ibs. in.
Allowable Sr : 15,000 psi' Determine, U-tyP" symmetrical expansion loop to yield
the maximum moment and stress equal to the allowable limits.
Solution, Step 1. Determine from Fig. 2 when a : 3 and p : 5. FolLw the arrows and read value of 1 : O.l7 which is the moment and stress factor on the left hand vertical scale. Since the allowable stress Sr : 15,000 psi. and the calculated expansion stress SB : 30,000 psi' then the ratio : 15,000/30,000 : 0.5. Therefore, corrected y : 0.17 (0.S; : g.g8t. It is assumed that F : W lu : 5 remains unchanged'
Fig. 4-Calculation of forces on nozzle, Sample Problem 2'
G:0
Step 2. Determine new d.
Enter in Fig. 2 the corrected y : 0.085 on the vertical scale from the left hand side of the graph, and move horizontally to the right to the curve F : 5 then move vertically down to the e scale and read the new ot : 5.7. Now summarize the new values as follows:
a:
Fig.'A-Figure for Sample Problem
3.
5.7
B:5
Expansion stress Sa : 15,000 Psi. Bending Moment BM :50,000 (0.5) the allowable moment.
Fig. 6-Figure for Sample Problem 4.
:
25,000, equals
Step 3. Determine the distance of the guide 'G'. New a :5.7 : GIH when 11 remains as before. Therefore, the distance of the guide G : 5.7 (H) . II the 'G' is increased to 5.7 (H) then the new shape will yield a stress of 15,000 psi. which is equal to allowable stress.
.rc'J U=55i
Bosis For Method. This method assumes that the energy is stored in a system because of bending, which is caused
by the deflection due to the thermal condition of
l*-u=,0'
Fig. 7-Figure for Sample Problem 5.
the
piping material. (1)
where, F : Force and X : Distance travelled force in the direction of the force 'F'.
by
It is accepted that when a piping system-is subjected to deflection it stores energy, and that the
Also: Interndl energl' stored by the system is by'
caused
Energy stored
: tY! J2
Again:
stored energy must be equal to the work done upon the piPe'
The work done by a force upon a piping
y? system : (2)
t4
e Compressive stresses o Tensile stresses o Bending moment.
the
PIPING DESIGN METHOD BEATS COMPUTER
Deflections 81, 82 and 8s are produced by elements
.
Lab, Rae and. cd respectively. The system is confined between
Le: Ra : f-i
lzl
E,
ts-
Teft hand side anchor
right hand side anchor.
o That the whole
R1
Fig. &-Basis for the method starts with this piping layout.
I
I
q.
That the system is treated with square corners intersystem
is composed of straight elements of
pipe of uniform size and thickness.
-l
o That the thermal
expansion of a given element is absorbed by the elements orientated perpendicular to the direction of the deflection.
I
'i-1
Fig.
system lies in one plane.
sections.
That the Go
anchor points.
The following conditions apply in derivation:
---t
Lq
2
9-The loop deforms from the cold to the hot
position.
o That the effect of dead weight, wind etc. are neglected. o That the clearance between guides and pipe is nil. o That the compressive stresses within the element are neglected.
[,--1
o That the flLxibility of the elbow
caused
by an oval
shape is neglected.
The three deflections in the horizontal plane are: 81
Fr
l.-Gf
are shown.
I
*
8,
: 8o:
total deflection
portion of the system, see Fig. 9. The loop will deform from a cold condition to a hot condition, when the system is subjected to the operating
---i
Fig. 10-The forces and moments acting on the Fig.
8,
The total deflection 66 must be absorbed by the system contained between the points a and fo which is tJle flexible
+ l.--G6-------*j f--0.------!
+
in Fig. 9. Fr : thrust acting on the loop at the point ,a,,
temperature, as shown loop
Fig.
Mo:
bend'ng moment acting on the loop at the point
'a',
If
see
Figure
10.
the energy stored by compressive and tensile stresses are neglected then the total energy stored will be due to
it is evident that the slope at the point must be horizontal.
bending moment only. See Figs. B, 9 and 10.
IIence the change in the slope between point point Gs is equal to zero.
Energy due to Bending Moment
But d0 :
:
BM
:
M
I+
EI d*
(4)
Therefore, the equation will be transformed as follows:
o: Fo and Go-
Mo:
ll o'1"":o
and
(6)
G1
M6
-
X
- Me- FEU)
e)
Slope and Bending Moment. The general relationship BM, is as follows:
(s)
(a)
Fa6o/2:l-Znr)n f U, a* I G"
and (Gr)
i.
dt: M,!: EI
(8)
Therefore the total slope change between point a and
point Go is: (5A)
Thermal stresses in symmetrical expansion loops are
derived as follows:
F
a
Go
between slope and
fMzdx :Jzn
2
i.e
Bending moment, BM at point X
ur,:l*!ru:l+W) Deflection taken by the shape between equal to 8o/2
From Fig. 9
(3)
see
10.
X:
ll+l'" Pipe Iength
in
(s)
general,
r5
.:llr#):". llr-#,
*,),
Go:
But the change in slope between a and.
ll*+* *)*,"
* Q
*{*"*o) +M,(H) -L#L * Y* f +H+ w1 fu, r+twtl *"1.
- elnw)l:o
T):r"l;*-) T H2+H(w\ I M,:Fo f H,+H(wt I Lzrdffit ):'"tdc +TiTT) H *W M-- F,'" "2(G+H)+w
(10)
Now refer Equation 1 to 5a, Further, 'oouo
:
;*{ll -; o""f:' +ll w.- rot) *7'"*ll ,*"-'outo'f*""| (II)
oruo: 4
EI
3o
2Fo
EI 2
#
: r,
3o
FoH2
*r)' ("" * " *[)
{rr ", (r-ffi
{,,
+ w),
: ,o * rr'{ 212(G+H)+w) (H
+
H2
1 -L2 -)-Hl
cH
,
+2
w t6
tl/
_
-L
\,
I'
H 3
I-
W
'2
+al4l2P
(#)'
Force, Moment, and Stress. The follou'ing units apply
Moment of inertia of the pipe : 1 (in.n) Total thermal expansion between anchor points is in
inches.
W
LLL,)
Height of the loop : Il (ft.) Width of the loop : W (ft.) Distance of first grride : G (ft.)
't-H
+
I 3 , 2
r+28+p'
4aa4l29
a : G/H.
I
(13)
in the formula below: Modulus of elasticity : E (psi.) Resisting force : F, : F" (lbs.)
t1/
Section modulus
H
of pipe
: Z
Stress intensification factor
+) . r*'(+
and,
(F * L)\
t +2 p + p,
rl
w H
60
F - I,Y/H
r,,
14/)2
+ ' (#)' I
-(+)
where
2(G+H)+W
4(G+H)+2tr
:"[-f, *
--
(FoH, + FaHW)*
zz\ I c+H+w/z - T(G+hl l, - H, 3 Tl +w-l ttr@+h+wF
HW -3-2
Er
- FoH r#T,
where
h : tRlr'
(in.') for the bend
: i:
0.9
lh
See code for pressure piping ASA 831.1.
Then the force
is
(12) B
1
2
4
+2p +
4
+ 2B
I ,,-,
The maimum stress can therefore be in a system either
PIPING DESIGN METHOD BEATS COMPUTER
at bend b or at the bend c. It is suggested that the moment at point b and point c be calculated, then take the largest moment of the two to calculate the expansion stress SE in the loop. Fig. ll-For round corners, tte width, height, and guide distances
s,,
M -_
(i)
( 1e)
must be modified.
Loop Restroinls qnd Supporls. Design engineers should make certain that the loop between the two guides is made to function without any environmental obstructions or restraints. Also that the system is fully supPorted and no branch connections are made within the flexible portion of the loop. It is not recommended to induce any external loading upon the loop. The designers should avoid locating rigid sections, such as large valves etc., within the loop. A good practice is to locate valves and other rigid sections near the guide or between the anchor and the guide. Fig. l2-Loop designations for round corners.
Fig. l3-Symmetrical loop with guide G distance from bend.
Line Size Limits. This method provides engineers with reactions and stresses that are reasonably accurate for pipe up to 6 inches in diameter. Lines above 6 inches in diameter can be safely analyzed by this method. However, the authqrs would like to point out that the results thus obtained will be on the conservative side. Therefore, where the system is dictated by the space, reactions and stresses or economic limitations, a precise analysis should be made. Round Corners. Solutions to loops having round corners can be solved as follows:
Fig. l4-Symmetrical loop with guide very near to the
o If the square corner solution gives reactions
and
stresses, which exceed acceptable limits,
bend.
o If
the radius of the bend is more than 1.5 pipe diam-
eters,
o If
.
Fig.
l5-A
the line is above six inches in diameter,
Refer Figr,rres 11 and 12. Use Equations 20, 21,22, and 23, to modify the width (W) , height (I1), and guide distance (G) respectively. Use Figs. I and 2 to determine forces and moments. Assumption:
two-plane loop configuration.
: I{: R
radius of all the bends which must be the same. height of the loop which must be equal on both sides.
n'^
Er s^ l3456H3 I
" t_ 1
I
Is
p , Z
L+2tt+t2 4a*4*2F
From equation (10) the following forroula
Mo: FoH
l
:
distance
both
)
of the
1-rB
' Fo
It T; )-, +-O
:
F^
(lbs.-ft.
t
W:u+1.57R(K/3) H-h+t.s7R(K/3) H-h+1.57R(K/6) C:e*1.57R(K/6)
(15)
is derived.
(
K:1.65/h -flexibility factor, K)
16)
(17)
rf R)
' - r2..' ; i: thickness of pipe; r: pipe: R: radius of the bend, rvhere h
M": Mo- Fr(H) (lbs.-ft.)
guides which must be equal on
sides.
H+W 2(G+H) +W
Note that Fo
ln
(lbs.
G
(20) (21)
(22) I
1,
2q\
(24)
mean radius ol
Note: For force calculation use modified Height (H) of the loop. For moment calculation use original Height (II) of the
general: Stress
:
M /Z
( 1B)
ioop'.
t7
For Figs. 13, t4, and 15,
g:G_R.
u:
W
-
2R;
h: H -
Fwi
2R;
Symmetrical Loop. Refer to Figs. 12 and 13. Modify W, H, and G as follows:
For W, use Equation Eor H, use Equation For G, use Equation
20.
Fig.
21.
lLA
U.loop configuration
with equal
23.
legs.
Symmetrical Loop. Refer to Fig. 14. Note that the guide is very near the bend. For W, use Equation 20. For H, use Equation 21. Since the guide is at or near the bend, G:0. Two-Plane Loop. Refer to Fig.
15.
For W, use Equation 20. For H, use Equation 21. For G, use Equation 23. U-Loop With Equal Legs. Refer to Fig'
16.
u:W-2R. h:H-R. For W, use Equation 20. For 11, use Equation 22. G :0. Two-Pliane Loo,p
Fig. 17-A twb-plane loop configuration with the Y leg longer than fitting to fitting.
With Y-Leg Longer Than Fitting
to Fitting.
w:W-2R hr: Ht - 2R hr: H, - 2R g:G_R For W, use Equation
H:.: Ht *
20.
Hz.
For G, use Equation 23.
Fig. 18-A two-plane loop with equal
legs.
Two-Plane Loop With Equal Legs. u: IU - 2R. hr: H, - R.
Hr: H, -
2R.
For W, use Equation 20. For IIr, use Equation 22. For H2, use Equation 21. H: Hr]- Hr. G :0.
U-Loop with Equal Legs and Single Tangent. Refer to Fig. 19 and solve the same as Fig. 16. Grophicol vs. Computer Solufions. The following exto illustrate the results obtained by this method and by the computer. amples are given
Example. Given: 4 in. pipe, schedule 40; radius of bend : 0.5 ft.; operating temperature : 3500 F.; mate-
rial : ASTM 106 GR. B; thermal
expansion
:
2.26
in./100 ft.; allowable stress : 22,500 psi.; code : Power Piping; moment of inertia : I : 7.23 (in.a); section modulus : Z' : 3.22 (n.3); stress intensification tac-
tor:i:1.95.
t8
Fig. 19-A UJoop corfiguration with equal legs and
single
tangent.
a:GfH : 12110 : 1.2;B : WIH : B/10 : 0.8; 8o : (2.261100) (180) : 4.06 in. From Fig. 1, Force Graph, FII : r : 86 Force : r(I) :86(7.23) : 620 From Fig. 1, Moment Graph, BM : 27,100 lb.lin. stress
: +#
(1.95)
:
16,450 psi.
PIPING DESIGN METHOD BEATS COMPUTER
.
ized staff members to spend their valuable time only on the analysis of critical and hazardous lines. Alsq it will help site engineers design and incorporate a loop in a rack piping system, or in a long transmission line, without seek-
.
ing help from the design office. Furthe4 the method will help project engineers estimate piping flexibility in the proposal stage of the project. Symbols used:
,s/
E
I Z F
Allowable Stress (psi.) Modulus of Elasticity (psi.) Moment of Inertia (in.u) Section Modulus (in.3) Force (lbs.) Force component in the direction of
Fig. 20-An example configuration calculated by the graphical
Fx
and computer methods.
M Moment (lb./ft.) i Stress intensification
axis.
factor.
21-A square corner configuration calculated by graphical and computer methods. Fig.
About the quthors M. S. HIQUB is an engineering consultant
Moment Max. stress at bi:nd, at guide psi. Ib./in.
Method
Force, lbs.
Graphical
620
27,100
Computer
6t7
2
7,000
Remarks square corner
16,450
solution
t6,47s
.t;?.?;,:to"*
Example. Given: 6 in. pipe, schedule 40.
All other data
as
in example above.
Z: From Fig. 1, Force Graph, r : 8o :
4.06 in.,
I :
28.1,
8.50, 86,
i:
2.27
r(I) :
86(28.1)
:
2,410 lbs.
From Fig. 1, Moment Graph BM : Stress : 90,200 18.5(2.27) : 24,550
90,200 lb. in.
Force, Moment lbs. lb./in.
Stress,
Graphical
2,4tO
90,200
Computer
2,179
90,500
21,550 20,122
Method
psi.
Remarks sq. corner soln. sq. corner soln
as
so
ciated.with
CO
N,
L ondon.
He also has fi,ae years fi,eld eupet'ience on construction jobs
in Ind:ia.
J. St-q.nczowsKr 'is an engineet'wi,th Woodall-Duckham, Ltd,, Crawley, England. He o,ttended the Polislt Techruical College in England and completed a B.Sc, mecltanical course at London Urvioersity. He has done graduate work in
fluid dgnamics, mathematics,
and
Mr. Starczeu.tski has in heat enchanger de-
nuclear energA. had, enperience
sign, pressure aessel design,
In conclusion, the authors feel that the introduction of this time saving piping flexibility analysis method will help piping design engineers solve most of the simpler configurations. This will allow consultants and highly special-
EMM
He specializes in pipe stress analysi,s, piping lo,gout, and fleribilitg analgsi,s i,n th,e lal1out stage. Mr. Haque receiued a diploma in mechanical and electrical engineet"ing from Dehri Technical Institute of India. He is an o,ssociate nzember of ASME, Institute of Engineering Designers, Institute of Plant Engineers, Associate Fellou; of the Institute of Petroleum, and Associate of the Institute of Fuel. He has had 16 gears enperience as a senior designer and piping analyst usith such, firms as Wellman Smith Ou;en Eng. Co., Mattheu Hall & Co., Ltd., McKee Head Wrightson, Ltd., and Constructors Joh.n Brou.tn, Ltd., all in London.
u-telding
equipment dea elopment, special pu,t'pose machine design and, other process equi,pment design. He h,as uorked, u.titlt, such firms as Constructors John Brown, Ltd., and, Caird & Raynet", Ltd,. both in London,
T9
Symmetrical Piping Arrangement Solves Two-Phase Flow Distribution Problems
The secret to two-phase distribution in branched piping systems is strict adherence to symmetrical piping and an evenly dispersed liquid flow pattern Fig. l-Shows slug flow; G:0.0085 lblsec;
L:
Fig. 2-Shows plug flow; G:0.00421 lb,/sec;
L:0.38
0.38 lb,/sec.*
John L. Greene The Fluor Corp., Ltd., Houston
A rnequrNT ENcrNEEnrNc problem is
designing
branched piping systems for flow distribution, mist or dispersed flow, and an over-all low pressure drop. Controlling flow patterns, liquid distribution, flow distribution, and optimizing pressure drop need to be considered.
Recognizing flow polterns in two-phase flow is the first part of the problem.1,3 In a two-phase system, when gas flows at various rates, demonstrative types of flow patterns are developed. In general, these flows are described as bubble, plug, stratified, wavy, slug, annular, and spray, mist, or dispersed. Slug formation, plug flow, wavy flow, and stratified flow are shown in Figures l, 2, 3. and 4, respectively. For this discussion, slug flow is defined as a mixture of liquid and gas that has a varying density with respect to time. Therefore, the term slug flow will also include plug flow and will border on annular
Fig. 3-Shows wave florv; G
:
lblsec.*
:
0.38 lb,/sec.*
0.0081 lblsec;
L :0.38 lb/
0.0083 tblsec; L
and bubble flow. fn engineering design the flow pattern must be determined in every two-phase application. fn a service where pressure fluctuations cannot be tolerated, there can be no slug formation. For example, slug flow downstream of a
distillation column will cause pressure fluctuations and of catalytic reactors
unstable operation, or downstream it can cause catalyst attrition.
sec.'
Liquid Distribution. When two phases flow through the same pipe, the gas flows faster than the liquid. In a
* Water and air at atmospheric conditions and in a 2-inch OD horizontal pipe.'
20
Fig. 4-Shows stratffied flow; G
:
(I)
ll ,'=T,' PARALLEL TO HEADER (POOR)
ELBOW PERPENDICULAR (2) ELBOW
TO
HEADER (GOOD)
(3) TEE 8 CAP TO HEADER (ACoEPTABLE)
Fig. S-Shows liquid distribution into a header: (1) elbow perpendicular to header (good); (2) elbow parallel to header
(poor); (3) tee and cap to header (acceptable).
The problem of two-phase flow distribution in manifold piping arrangements is frequently encountered in large plants, particularly around air coolers, parallel exchangers, etc.
The simplest solution to flow distribution is to provide a block valve in each branch line. From the standpoints of valve and of pressure drop costs this is often unattractive. Therefore, the pressure drops through the system must be depended upon to distribute the flow. As is shown in Figure 6, if valves are not provided in each branch line of two-phase flow, then the layout should be symmetrical. For comparison the preferred layouts for single-phase flow are shown in Figure 7. The selection depends upon the importance and duty of each service. Friction loss in the fittings was determined by using Bernoulli's Theorem
(Velocity head method) and velocity head coefficients from the literature.5,6 To determine the pressure drop in two-phase flow when there is less gas by weight than Iiquid, two-phase flow correlations should be used.2 (I) THBEE
PASS
(2) TWO PASS
Fis. &-Shows symmetrical piping in two-phase flow: (1) three pass
and (2) two
pass.
Applicotions. Savings can be realized in optimum overdesign of heaters, heat exchangers, etc. In large systems horsepower usage from pumps and compressors can be reduced.
With this knowledge of how to minimize pressure losses in manifolds, plot plans can be laid out more efficiently. The preferred piping layout creates fewer plot plan changes and shorter pipe runs.
(I)
GOOD
FiS. two buti
DISTRIBUTION (2) FAIR
DISTRIEUTION (3) POOR
DISTRIBUTION
Iayouts for single-pass flow in d distribution, (2) fair distri-
smooth turn the iiquid has a tendency to follow the outside wall. The elbow or turn should be perpendicular to the manifold, as is shown in Figure 5. If thii is not possible, a tee and cap or a mixing length after the turn may
be
used.
Slug flow causes pressure fluctuations in the system. Elimination of slug flow helps stabilize the unit. Slug flow can also cause major problems such as catalyst attrition. Therefore, catalyst life can be increased. Minimizing pressure drops and equalizing liquid and flow distribution will increase yields and decrease capital and operating cost.
Exomple Problem. Distribution into and out of a 16section air cooler with 5.3 pounds per square inch pressure drop (16-6' nozzles) and with the following flow:
LIQUID Flow lb/hr. Specific Gravity @ Temperature & Pressure
Temperature oF Viscositl, Cp.
IN
OUT
484,000
652,000
0.670
0.678
277
150
0.310
0.412
IN
OUT
The liquid must be distributed into heat exchangers, coolers and other types of equiprnent. Often it is necessary to rotate an elbow to the shell of an exchanger in order to distribute the liquid on the baffling ,.r.a.rg"ment. Tees and caps or mixing'lengths are also used on the inlets to heat exchangers. On the outlet, liquid distribution is not usually important. The severity of the operation and the duty (size of heat release) of the service as selected to provide liquid distribution are determined by an economic balance. Therefore, each case must be looked at individually.
Three cases r,vill be considered to determine the best piping layout. Economics prevents putting valves in each of the 16 sections.
Flow distribution in monifold piping systems is a function of pressure losses through each lateral system.
Cqse. l. One header with 16 ]aterals on the inlet and outlet is shorvn in Figure B.
air
VAPOR Flow lb/hr. Molecular weight Viscosity Cp.
533,000 8.49 0.01132
365.000 5.99 0.0099
2t
ST RATI FI ED
Flow Pattern. From Baker's1,2 two-phase flow correlations the type of flow is determined aIter each lateral take-ofl and is shown in Figure 8. The flow patterns go from mist to annular to slug to stratified flow. This flow pattern change is not acceptable.
8 SECTIONS Fig. 8-Shows single 24-irch headers with 6-inch laterals (example problem-Case I). 16-6.. LATERALS SPACED AT
Pressure Drop. The pressure drop calculations are a trial and error procedure to determine the exact distribu-
tion. Using Bernoulli's Theorem and velocity head coefficients from the literature5,6,7 the initial pressure and flow distributions (assuming equal distribution) are as follows for the first and sixteenth pass:
o First Branch cooler
o
System: AP1
:
10.46 psi
Fig. 9-Shows tapered (24 x 8-inch) headers with 6-inch laterals (example problem-Case
II).
including
loss
Sixteenth Branch System. APro
cooler loss .'. Percent flow not distributed
:
:
8.24 psi including
4.89 percent
On a service with a large duty this 4.89 percent of maldistribution of flow is not acceptable. Case I is not a good system.
Cose ll. One tapered header with 16 laterals on the inlet and outlet is shown in Figure 9.
Flow Pattern. From Baker's1'2 two-phase flow correlations the type of flow is determined to be in mist flow the total length of the header on both the inlet and the outlet. Pressure Drop. The pressure losses were calculated the same way as Case I only the expansion and contraction losses were considered.
' First Branch System: aP,:1i.86 psi
including
cooler loss
Sixteenth Branch System: APre : 9.55 psi including cooler loss .'. Percent flow not distributed : 4.64 percent
o
Fig. l0-Shows
semi-symmetrical manifold piping layout
(example problem-Case
Cose
III).
lil. A semi-symmetrical manifold
piping system
is
shown in Figure 10.
Flow Patterns: AII of the piping is designed so that only mist flow is encountered. All turns into headers have to be rotated corectly so that the liquid is evenly distributed. Pressure Drop. The pressure losses were calculated
as
in Case I.
o First Branch cooler
On a service with a large duty this 4.64 percent of maldistribution of flow is not acceptable. There is 8.73 percent rnore pressure drop than in Case I and the tapered header is expensive. Case II is not a good system.
System: AP,
: 9.34 psi including
loss
o Fourth Branch System: APr:9.97 psi cooler
Percent flow not distributed
In
Case
III
including
loss
:
1.96 percent
the florv is in the dispersed legion throughout
the system. The flou, distribution is the best that can economically justified. This is good piping la.vout.
be
LITERATURE CITED
Indqirrg Tere: Ctrmputations-l0, Design-4,8, Distribution-7, Fluid Flow-4,7,
22
Layout-4,6. Liquid Phase-5, Piping-9, Vapor Phase-5.
NOTES
23
LAYOUT
Plont Loyout qnd Piping Design for i,tinimum Cost Systems Afier process ond equipment ronditions ore sel, plont loyout con be the lorgest single cost sover in HPI plonts. Line sizes ond pressure drops depend on pipe lengrh ond configurotion. Use these guides io moximum plping system economy Robert Kern, The M. W. Kellogg Co., New York PrprNc EcoNoMy is closely related to three areas of plant design: o Equipment layout o Piping design a. Line sizing and flow slntems b. Piping layout, and o Piping details These areas are interdependent; without an economical
engineer is the process flow diagram (PFD). This has to be evaluated for an economical plant arrangement. From a layout standpoint, three types of lines can be distinguished.
Main Process Flow Lines. First, lines which represent the main process flow. Such streams pass through furnaces, reactors and dryers, then they continue as tower bottom and feed inlet to the next tower, often with exchangers and pumps between them. These lines will be the shortest if towers are arranged in process flow sequence as close to each other as equipment sizes and access space permits. With smaller interconnecting lines, towers can be located further apart without much increase in piping cost il other economies can thus be realized. For example: the grouping of condensers between two towers can result in a shortening of cooling water lines; a conrmon steam line can be designed for grouped reboilers. Grouped condensers and reflux drums
will permit a
common supporting structure. Figure 1 an example of alternative tower arrangements. Many configurations are possible and justified if shortening of these process lines is the ultimate result. Process flow is not always a simple straight through flow but can split into two or three streams, as is oftL done with a number of distillation columns. Subsidiary circuits to process flow must also be considered such as the refrigeration circuits in ammonia or ethylene units. shows
Plonl Loyout qnd Piping Economy. Plant layout can in refinery and petrochemical plant design, after process and equipment design be the biggest single cost saver
posibilities have been exhausted. Savings can be rcalized not only in piping but also in the cost of pumping compression and utility cost. Often a layout can eliminate equipment (for example, pumps with well arranged standbys).
The most important document issued to the layout
are generally large diameter lines and should have preference over the first group which are wually smaller process lines.
Feed and Product Lines. The
third group of lines
are
25
an optirnum location for minimum Prp-"--ttlt' For ex-
PLANT LAYOUT AND PIPING DESIGN
-'.,
changer, drum, and pump locations the following general classifications can be n ade:
Exchongers. Exchangers which are next to towers use short pipe runs. These are thermosyphon reboilers and condensers' Short reboiler and overhead lines are essential for both economy and reliable oPeration'
o
Exchangers which should be close to other process equipment. For example, exchangers in closed pump circrits srch as some reflux circuits. In the case of a bottom-draw-off-exchanger-pump, flow exchangers should be close to the tower or drum to give short suction lines'
o
Fig. 1-Alternative tower arrangements can shorten
main
process flow lines.
runs.
o
Exchangers located between Process equipment -and the unit li-it .ut be located at one end of the plant' Such exchangers are, for example, product coolers'
MAII{TEMI'CE ROAI)
Drums.
.
Drum location when it must be next to a tower or exchanger. For example, when a tower bottom flows by grarriiy into a collecii.rig d.rrm, the drum should be under or next to the tower. A reflux drum should be next to the condenser. Compressor suction drums and knock-out drums should be close to the comPressor'
. Most process
and utility drums serve as seParators, drums and should be arranged in reflux trrd ,..rrg" process
flow sequence.
Storage drums or tanks, Iocated within a unit usuaHy are given secondary consideration and are located as space permits mostly at the peripheries of the unit'
o
Fig. 2-Exchanger location for minimum pipe runs'
Pumps.
o
Pumps have one general rule:
below their point of
the feed. lines and the usually small diameter product Iines. These lines can be minimized if they start at equipment close to that battery limit where feed and pro'duct lines terminate.
ments.
Location For Minimum Pipe Runs. For plant layout, in addition to tower sequence, every equipment item has
26
put them
close
to and
suction.
So far, our discussion has dealt w'ith the bases of economical process unit piping, rvithout mentioning specifications, site information and project design data' construction, oPeration, and maintenance. Specifications describe the client's requirements or con' tlactor companies standards for all sections of plant dey concern econofil)" malnand sPecial requirements. ign should read them. Detailed discussion here is unnecessary.
Site and Project Desrgn Data. The unit has to be
located on a given site. Soil conditions, existing
access
roads, pipe lines, connections to the unit, even prevailing
wind can have its affect on the economy of the plant and piping layout.
Construction. A plant arrangement should also be diswith the Construction Department. They know available crane and construction clearances, access width and location requirements, and difficult construction points. Expense can rise rapidly with poor access to equipment or difficult-to-erect piping. In some cases, increased structural and piping cost to facilitate construction is more than oflset by the saving in construction cost. cussed
Operation and Maintenance. An engineering company's reputation can be enhanced or injured after a plant has been built and operated. Beside performance and production costs, the plant layout and piping design can influence maintenance and, operating costs. It is essential to have road access to exchanger'bundle removal, tower tray removal, to pumps, catalyst loading and removal, crane access to compressors, etc. It is advisable to study plant and piping layout from this standpoint.
more extensively. Several towers car, be lined up fairly close to each other on one side of the yard providing common interconnecting platforms. Piping economy is usually sacrificed for convenient access to manholes, valving and instmments on the towers. F.xchangers can a.lso be grouped on the other side of the yard and a common gantry crane provided for convenient maintenance. In such cases, tower overhead and other process lines to exchangers cross the yard, increasing pipe length and the number of fittings.
In the case of piled foundations, the plot arrangement should also be discussed with a structural expert. Often by regrouping equipment, a number of piles can be saved, which can often more than pay for increased pip-
ing cost. Economy-of Ycrrd Piping. The main arterial system of a plant is the yard piping. It is here where long,process lines are located interconnecting distant equiprnent, and lines entering and leaving the unit. Also, utility headers are located in the yard supplying steam, air, gas, and water to process equipment. Here are located all relief and blow down headers. Often instrument lines and electrical supply conduits are also supported on the yard
access
Also, it is essential to have convenient and adequate to points of operations and instrument adjustment. Grouped, lined up manifolds and functional locations of control valves help to maintain economy of operation. It is here where all details of piping design gains much
Figure 4, shows those critical dimensions which will influence piping cost from a yard piping layout standpoint. These dimensions depend on the over-all plant layout and should be carefully considered when the plot
importance.
is arranged.
In short, economical design is provided by good access to the unit as a whole and to points of operation and
maintenance. Beside this, it should be rgmembered that roads and access space spread the unit apart and adds to the length and cost of piping.
The Plot Plon. Figure 3 shows an estimate plan of the feed gas compressor area of a 200,000 long tons per year ethylene unit. Main pipe runs are also shown. This area (and the whole plot plan) has been developed with the principles outlined so far. It is an "In-Line-Layout" with equipment in process flow sequence. The large diameter gas lines directly interconnect process equipment. On the complete plot plan, equipment (including compressors) are arranged on both sides of a central yard in process flow sequence. Pumps are located at their point of suction and are lined up under the yard. To every line of equipment, a parallel road is arranged for convenient construction and maintenance access. For economical plot arrangements, many equipment groupings can be adopted. Two obvious groupings are: furnaces and reactors. Small furnaces, however, are often placed in several locations as process flow dictates. For safety and economy, these furnaces should be located at the periphery of the process unit.
Another often employed equipment grouping is housed is achieved here by the common building and maintenance facilities; also, by the operacompressors. Economy
tion of the grouped compressors. On Figure 3, the feed gas compressor has been separated from the refrigeration compressors. Saving in piping and construction cost justified two compressor houses. Also, centrifugal compressors require less attention from operating personnel. Some layout systems use similar equipment groupings
steel.
Dimension
A is the total
length of the yard and
is
goverened by the amount and size of equipment, structures and buildings arranged along both sides of the yard. If, with good layout practices, the same amount and size of equipment can be arranged on a shorter yard length,
yard piping cost can be considerably reduced. Equipment in pairs, stacked exchangers, exchangers under elevated drums, drums or exchangers supported on towers, two vessels combined into one, closely located towers with common platforms, drums supported on exchangers, process equipment located under the yard are only a few examples which help shorten the yard length. These arrangements, of course, shorten not only process lines interconnecting equipment directly or in the yard, but also shorten those lines which pass through this area and
utility
headers serving this area. Equipment not associated with but arranged along the yard increase yard piping cost unnecessarily. A control house located along the yard, for example, will increase yard piping cost because all lines must pass by without really being associated with the relatively long control house.
The careful selection of dimension B and C (Figure 4) can minimize pipe length between the yard and process equipment and pipe length interconnecting equipment on opposite sides of the yard. Not more than necessary yard height (Dimension D and E) will minimize vertical pipe runs. When changing direction, change elevation is an old rule in piping design. This happens with all lines connecting to yard piping. Ilowever, some large diameter Iines can make a flat turn when entering at the edge of the yard. So far, process plant layout has been developed. In
the following a classification is presented for the most
27
FROM FURNACE
i
-l
___-______==_ PROCESS EQUI PMENT
>'--
I I
---
Fig. 3-Part of ethylene utrit Plot plan showing direct routing of piping'
LIiIES WITH BOTH E]IDS HIGHER THATI TOP YARO EANK I-OCATED O}I THE HIGHER LEVEI.
LII{ES WITH ONE EI{D EELOW AIIID OTHER EiID ABOVE YARD CAII
BE
FLAT.BE}ID AT ED6E OF YARD.FOR LARGE LI}IES
LOCATED ON EITHER
YARD ELEVATIOiI
ETO PIPI}IG
P0ssrELE
EL. lO0'
CONTROL,VALVES
ALTERNATE PUiTP SUCTIOil
PUMPS
Fig.
28
ACCESS 10
+-1r,"al
VALVES
G PSOCESS LI}'IES Y'ITH BOTH ENDS LOWEF THAN rOU YINO AANT lgg 1-oCATEO ON THE LOWER LEVEL
cross'scction of yard piping showing geueral pipe runs'
-
common equipment elevations, also highlighting the comparative cost involved. LIOUID NEAfi -EotLtNG po[{T
Cost ond Equipment Elevqlions. Towers, drums and exchangers can be elevated for the following reasons:
-(l-}1ffi EQUIPITEiII ELEVAITOT
r
D VYITH 2 ORSE I ELEOY
STRAIGHT RUII
rD flTH '60)
With choose a
denser
is
floor can and construction, maintenance and operation access improved. Vertical pumps usually give a minimum height from grade to equipment because their suction inlet nozzle is below grade. If for some reason equipment is elevated higher than the required NPSH, a reduction in line size and pump differential is often possible.
o Thermosyphon Reboiler Circuits. The driving force in a reboiler circuit is the static head difference between the head of the liquid draw-off line, and that of the liquid-vapor mixture in the return Iine minus friction
loss. For horizontal reboilers at grade, an increase in driving force requires greater elevation of the tower or drum. Line sizes can be reduced because higher friction loss can be allowed. By decreasing the vertical legs of reboiler qipil-S the driving force will also decrease, consequently,
the line size of the system will have to be increised io provide lower friction losses.
o Liquid FIow Measurement. The requirement of accurate liquid flow measurement can also elevate process equipment (see Figure 5). If liquid is near the boiling point, a static head is required in the front of.the conl trol valve to overcome pipe friction losses and avoid flushing in the line. Minimum equipment elevation, orifice range and minimum line size will result if the orifice is as close_ to the equipment as possible, and up to the control valve the piping has only one elbow.
Fig.
LPut
control valve close to process equipment for econ.
omy and reliability of operation.
o Gravity FIow. Requirements often elevate process equipment. The-size and elevation of associated equipment; size and arrangement of interconnecting piping; clearances for structural membersl headroom and access to valves and instruments will influence the final elevation of process equipment.
. Grade Location. The most economical and common location of process equipment is at grade. Supporting structures and platforms are not required. Construction is easy. Most valves and instruments can be made accessible from grade. Operation and maintenance is convenient.
-
Elevated equipment
with
associated structures, plat-
forms, handling beams etc., means cost increase. irr-.e*reral design areas. In layout and design, the first attempt should be to eliminate structures, extra supporting columns and extra platforms. Smaller equipment can be supported on towers, on yard columns, or structures for larger equipment. The second attempt can be to combine two or three qrripment. Some equiple over-all plant layout, be more than a possible
Piping Design for Leqst Cost A pRocr.ss lrxrl should he cbsignecl for a milrirnurn of or.er-all (ost, \\.hic[r is not neccssarily a nrinimrutr of PiPing cost (or a nrininrurn cost in other r:quiprnent grorr;rs) . This can be achievcd [rr, a t.losel), coorclinatecl
over-lrll clesign and accurate cost conrl;arisoir betrveen ternatir.e soltrtions.
ol_
Economy of Piping Design. Line sizes give a readily available basis for comparison. Ifowever, accurate cost depends on weight, type of material, insuiation and construction. Consequently, pipe lines for economical comparison are better represented with an in-place dollar figure per unit length, than with line size, schedule and material alone. Special attention should be given to alloy
lines, high pressure piping, and large diameter of carbon steel piping. For rough comparison, irr-placc piping cost is about double carbon steel piping ruatt:rial ..rri., " At an early stage of plant layorrt. line sizes at.e not available. Two items of process data from the process
FIow Diagram (PFD) S size cornllarison: flou,inC
for rough line
Irressurc differ_ ences betrveen t\{'o vessels lr.r florv quanti_ ties or higher available ces for fiiction losses will result in smaller diameter lines. For suction and discharge to pumps, only quantities should be compared
for the feel of line size. For line size calculations, The M. W. Kellogg Co. uses economical pressure drops. This is a most direct approach
29
stlaiglrt luns oI piping. there is a rnuch highel than ivith a pitot tube. straight ru., of pipe wit
PLANT TAYOUT AND PIPING DESIGN
that rifice
orter Pitot
tube.
Reboiler Piping. Two types of thermosyphon reboilers are used: vertical ar-rd horizontal' A vertical reboiler has very little piping and its length determines the height of the torver skirt. Supports at grade are sa.r'ed but supPorts on the tou'er have to be Fig.
l-The
hydraulic slide rule is used for fast florv calcula-
tions.
added.
Many tolvers have a bottorn drau'-ofl pump, and NPSH r-equirements usually elevate the torver higher tt," reboiler's miuirnum. This increases the than that "f the vertical legs, also the driving force in in static hcacls the circuit. With the increasecl torver lieight, it is rtorth-
rvhile to check the reboiler circuit for reducing the liquid
flow conditions exist.
general rules rvhen estiassociated fittings' and rnating or ialculating line sizes Valves and check valves are generally line size' Maximurn control valve size is line size' In most cascs, control valves are one size smaller than line size' When a larger pressure clrop is available, control l'alves can be trvo or ihree sizes snraller than line size' Sometin'res it is feasible to coDrPaIe piping cost and
It is helpful to know a few
and the return line size. Symmetrical piping arrangement betu'cen the drarv-ofl and reboiler inlef nozzlcs, similarly betrveen the reboiler outlet and return connection on the tower, is preferred for equal flow in the reboiler circuit' Nonsymmetrical arrangements may also be accepted for a rnore economical or mole flexible PiPing design.
Overheqd Lines. Scveral variations exist for overhead reflux circuits. A condenser can be eievated above the reflux drum. The reflux drum can be elevated but the condenscr is at grade' Thcse arlangenlents can be adjaccnt or so-eruhat remote from ttre torver' The sin-iplest
overhead line is shorvn on Fig' 2, sketch A' Littlc pressure drop is usually ar''ailable in these lines and longer overhcacl fnes rvith more elborvs quicklr' result
in increised line size (see sketch B)' valve assembly.
Orifice Runs. Because of metering accuracl'' olifice
straigl-rt runs. can be madc straight runs cs and .shorter
About the outhor
gineer.
30
CONDEN SER
REFLUX DRUI,4
SKETCi]
SKETCH 8
A
SKETCH
C
D
LINE
THE SIIIPLES'i OVERHEAD
SKETCH
REI\4OTE CONDENSER LOCATION INCREASES PIPING CONFIGURATION AFFECTS PRESSURE DROP AND LENGTH,NUIIBER 0F FITTINGS AND PIPE DIAMETER. STATIC HEAD BACK PRESSURE (Dll\ilENSlON X).
tINi
Fig, 2-Typical overhead piping arrangements.
for a direct gas flowg and equipment in the circuit should be in process flow sequence. Because of the ever present vibration problems at
The yearly utility cost per unit pressure drop can be calculated. Multiplied by the time of amortization (number of years) gives the cost of utilities for the period of capital payout. Pipe cost plus utility cost gives the total cost of compression for the calculated period and process
as much as possible
reciprocating compressors, pipe supports have a very important role in piping design. Supports independent of any other foundation or structure is almost mandatory. Pipe systems "nailed down" close to grade is a much preferred arrangement. If badly desighed compressor piping has to be corrected after startup of the plant it can become very expensive. Compressors are used in process plants for transporting gases. With constant gas inlet and outlet conditions, the compressor size and cost on one hand and the cost of driving force on the other depends on the volume of gas compressed; the compression ratio between inlet and outlet pressure; (and temperatures: and material of construction). Pressure differential is composed of friction loases in equipment (furnace, exchangers, and reactors), control devices, and piping. Consequently, plant Iayout and piping design has an effect on the compressor's driving cost; and sometimes on its size.
TABLE I
-Alloy
The example on Table 1 is a tabulation for comparing sizes, pressure drops, alloy piping cost and utility cost for a portion of a centrifugal compressor circuit. This example shows that for a two-year payout time, a l2-inclr line is the most economical. For five years, any line'from 12 to 16 inches is economical, and a 16-inch line should be selected. For 10 years, a 16-inch line will be the most
line
economical.
For maintaining these calculated economies, line sizes at least, with a good preliminary
should be calculated, layout.
Optimum pressure drops and sizes can be established
for all equipment groups in the compressor circuit.2
Table 1 assumed that the compressor works well within its capacity and pressure range. fn border line cases, the cost difference between the price of smaller or larger compressor will also enter an over-all cost comparison.
The selection of an optimum pipe size is also more
involved. With increased line sizes, the cost increases but pressure drop and utility cost
conditions.
of piping
Pump Gircuits. Centrifugal pumps are used in
decreases.
Pipe Size Selection for Vqrious poyout Times PAYOUT TIME WITH YEARLY UTILITY COST OF
I pst ap :
gS50
l0 YearE
Llne Slze
ap psl 9.75
10"
Total Cost col. 3 &
Uttltty Cost
$
$
,1
Total Cost
col.3&6
Uttltty Cost
$
s
process
PTANT LAYOUT
AND PIPING
larger than the preisure drops iconomical pr-rn header are otle pump nozzle.3
DESIGN
gives unit will give ds to the than the
Reqcfor Piping. In connection with reactor-furnace piping it should be remembered that it is usually the most expensive alloy piping in a process unit (because of high temperatures and pressure) and it is olten part of a compressor circuit. PI.AIFOR',I
and reactor design. IJnder such circumstances, piping lavout economy depends on the ingenuity of the designer, who can scrutinize his layout and eliminate every unnecessary fitting, flange, and field weld, establish optimum equipmeni locations and interconnect a piping system with a minimum of pipe length and fittings. Fig. 3 shows some extensive valving in reactor piping
oRooo
5 E
r[J
o
LE VAT ION
Fig. LPiping and valving between reactor and
furnaces'
units for transporting liquid. Sizes are established as for compressors. Piping and over-all economy for very large notecl for com-u"hir,"t can be sinrilarll' evaluated as not be justimight calculations pressors. Time consuming pumPs. average than smaller with fied Very small pumPs, in-line or vertical Pumps, are usually adjacent to thiir suction vessel. With many PumPs taking srction from the same vessel (crude Iractionator, for exible with onlY four ample) adjacen dium or large sized o, si* prr-pr. T It is advantageous u. .oud p.r*p., and
d to all tlre PumPs
Lconomical
in the plant for convenient operation and maintenance' This is achieved r'r'ith an "In-Line" plot layout' Too
many dead ended access roads between process equipment will lengthen the Yard bank' Suction piping should be designed without loops or pockets. Tho sultion line is generally one or two sizes
and gives an idea how much piping and valving cost can be saved. with line size reduction. It pays to recalculate and check line pressure drops with an exact piping layout. It also pays to investigate the pressure drop distribution in the entire compressor circuit' Decreased pressure drop in other equipment groups (exchangers, lrlr.r""r, reactors) can help in decreasing alloy line and associated valve sizes and still hold the over-all pressure differential constant. With large expensive piping, the smallest detail can run into thousands of dollars. Here is where care in detailed design pays large dividends. Details of piping design have been discussed in several articles of HvoxocARBoN Pnocrssrwc eNo Pernor-EUM RETINT:n.a-10
last remark to the reader. Piping economy is extremely complex. About each paragraph heading in this article an entirely separate report could be written. IIowever, for writing technical reasons, ideas in this report have been simplified, classified, itemized and organized what is believed in a logical sequence. In their application, these principles are not so orderly and cannot be separated. Many factors influence an optimum solution and design ideas have to be related simultaneously. The more penetrating an analysis becomes, the more likely it will lead to a most economical piping design solution'
A
ACKNO\\'I.EDGMENT to \t'. J. H' Baker and Mr' O' H' Hoegthe suigestions and hclp rcceivcd -during- the prcp:ration^ of the
The author
TABLE
2-Economico! Unit Pressure Drops for Pump Dischorge Line Sizing
expresses his thanks
lo" -uir,..ipt a.d
U".g
to*
M.- J. Lundgrcn for the
design shown on Figurc 3'
LITERATURE CITED
Ap pst Per 100 Ft.
l Mendel, O. Chemical Etgiteeritg' Vol. 68, \{ay 15, 1961' P' 190' , i.t.i*ir, F. W. HydrccZrbon iocessing €l Petroletm Refircr, YoL 43' 6, June 1964, P. 153. No. ";'g.l;", n. u. g Happel, J. Chemical Etgiteeritg, Vol' 60, No' 1, Jan 1953. P.180.
'"; S"rd], V. L. and Romain, D- H1'drocarbon Processitg I Petroleum Re' No.6, June 1964, P. 116' finer,Yol.43, '"iil"l.k"it, L. R. i"irnl"r* Ii"fit"t, Yol' 39, No' 7,.Julv 1960' P' -127' -.
7. w. Hvdrn"otbot Processing I Pettoleun Reftet' Yol' 44' 1965. P. 153. n- l'lriiltuu [cIaer, Vol. 37' No. 3, March 1958, P' 136' Pctrnlcu,r Il,f,ner, Vot. 39. No' 2, Februarv.1960' P' 137' 'fttriltuu "ii;;;; R. n.6n.'. vot.39. No' 12, Dcc. 1960, P' 139'- -R: -i. "-K;;;: .-f Hldrocatbotr !'rtressing I Peuoleum Refiter' YoL '10' DIo' 5'
"ih;;;:
2. Febrorv No. ";'xi." Optimum Friction Losses For Extended Payout Tiine
32
25,7
"rri, P, May 1961,
195.
NOTES
33
ANALYT|CAL
s€cTtoN
PPOJECT
DESlON
DITA
Fig.
l-Piping Division
organization and flow of information.
Whot lnformqtion ls Essentiql for Good piping Design? Three moior source documents ore essenriol for good piping design: Engineering Flow Diogroms, Nomenclolure, Equipment Elevotions
R. W. Judson, The M. W. Kellogg Co., New York
Trre PrprNa ANar-vrrcer, ENoTNBBn is the key information center for the piping designer. He produces three major piping source documents (Engineering Flow Diagrarns, Nomenclature and Equipment Elevations). Therefore he must realize that when he puts down a symbol or writes a note on his flow sheets, he gives specific in-
structions to the piping designer. These instructions must be clear, logical, concise and necessary. A.y extraneous information which does not pertain to the operability of the design itself does not belong on the flow sheet, because it limits the designer's concePt of the arrangement ho is able to provide. Essentially tfie Engineering FIow Diagrams must contain a schematic representation of the lines themselves. They must incorporate all arrangements critical to the operability of the hydraulic design. Further,
34
each and every piece of control or indicating hardware must be incorporated. Some information essential to layout and production design does not appear on the flow diagrams. In essence, this information consists of equipment elevations, pipe
wall thicknesses, and insulation specifications which are required for the individual line. This information is provided to the designer in the equipment elevation summary and on the nomenclature. Every line incorporated on the engineering flow diagram is identified and any emergency or special conditions which relate to this line are tagged with the same identification number and spelled out in the nomenclature or in the elevation information. Basically this co-ordination between the three source documents results in a detailed identification of every line on the Engineering Flow Diagrams. Without it a chaotic arrangement of information would exist with no logical system available for finding the information required.
To fully understand the requirements imposed on the detailed design, it is necessary to understand what information is required of the Piping Division, the scope of the information they receive, and how much information they actually place on tho flow diagrams themselves. The piping designer must have enough information to design accurately and yet not be hampered by too much infor-
P/P/N6 D/V/S/ON
,2QODUC7/ON
SECTlON
PLOT
i
LA4OUT
/IlZTEQ/AL CEQU/S/7/OM/NG
STUD/ES
Fr'BP/CAT/ON
to4-C CONSTzUCT/ON Fig. 2-Portion of typical Process Flow Diagram.
mation, which would restrict his optimization piping arrangements.
of
the
Flow of lnformqtion. To understand any major break-
vision itself.
equipment
Engineer on each ncru project ic docunrents rvhich pror.ide hirn turn out his three rnajor piping diagranls' r'tolllenclatures and
erevations).
Process data sheets supplement the PFD ancl give physical data related to process equiprnent; (vapo. liquid proportions of tower trays, physical data, safety
factors for pumps, detailed furnace florv conditions, etc.). From the fnstrument Division: The process Control Diagram (PCD) shows the instrumentation of the plant. See
Fig.
Fig. L-Portion of typical Process Control Diagram.
give detailed design requirements concerning piping design, valving, safety, operation and maintenance.
o
Specifications which give minimum wall thickness, schedule and insulation requirements.
o
Specifications which glve a clearly marked print of
3.
From the Specification Group; Specifications which
35
ESSENTIALS FOR
GOOD PIPING DESIGN
..
.
PFD showing special piping materials (glass lined piping alloy piping, high pressure piping, corrosion allowances, etc.)
From Project Engineering: Engineering design data which gives specific requirements for all utility and auxiliary syslems which are normally not shown on the PFD' Applicorion. With this information in his possession, the Piping Analytical Engineer analyzes the entire process design and expands this design on his Engineering Flow Diagrams. In addition he designs the necessary utility and auxiliary systems which are required to support the process flow.
In fulfilling this responsibility, the engineer decides on the necessary valving to fulfill the specifications and process requirements, includes all instruments dictated by the PCD, sizes all lines, and insures realistic pressure drops. He further indicates on evefy line the material specification and the specification break points. To suit these specifications he determines wall thickness, and schematically represents an accurate picture of the number oI lines required which may have been a single flow line on the process flow sheet. Fig. 4 is an example of a developed engineering flow diagram for the same area that was depicted on the process flow diagranr in Fig' 2 and process control diagram in Fig. 3. Loyoui. All the information designed and specified by the Piping Analytical Engineer is contained in the three basic source documents. These are then transmitted within the Piping Division to the Layout Section and the Production Section. The Plant Layout Section analyzes its arrangement of equipment on the plot with the engineer's design as a basic guideline and further performs layout studies of the critical areas as indicated on the flow sheets. The Production Section receives the plot plan, layout studies and the source documents from the Piping Analytical Section, and proceeds to design the individual key plans of areas and isometrics of individual lines. Once this has been completed, eve4r piece of material is taken off the isometrics and transmitted to the Material Control Section which writes the material requisitions, issues the isometrics to the shop (where job fabrication is necessary) and arranges with procurement for the shipment of material to the construction site. Here the isometrics, flow sheets and nomenclature are used as a road map in the fabrication and erection of the piping system.
Flow Diogrom Symbols. Since the engineering flow diagrams are the source document for all production work to be done at later stages of the job, the symbols which are contained in these flow diagrams must convey a distinct, accurate, and concise description of the requirements established by the engineer. The Engineering Flow Diagram sl,rnbols are the key working tool for the piping design function. Since every firm engaged in the process industry operates through a flow sheet as a base document, each has adopted a different method of maintaining their own piping symbols. Thus, 'we will not go into any extensive listing of symbols. (Fig. 5 is 36
a list of some of the r.najol t1'pical symbols as used in the illustrations) . It can be noted from an investigation of the sample engineering flow diagrams that the major symbols included are those for piping and valves. The only fitting symbols which generally appear on an engineering flow
diagram are the symbols for reducers, which indicate a change in line size, and the symbol of a cap, which indicates a header where the Engineer has decided a deadend is allowable. Instrumentation, being an essential part of the chemical process, is fairly well defined in basic sgnbol language. The reader is referred to the "Basic Instrumentation S),rnbols RP5" of the Instrument Society of America. The syrnbols recommended in this publication are generally accepted for notation on the engineering flow diagrams. These instrumentation spnbols must show if the instrument would actually control an automatic
control valve in the process stream. Thus, we can see the need for showing the location of the instrumentation' The critical locations are indicated on the engineering flow diagrams as required. The board mounting instruments are generally so indicated that key operating information can be readily available to the personnel in the control house. flardware and Instrumentation. In essence, flow sheet syrnbols fall into two major categories' The first being tLe symbols for the hardware iterns such as regular valves (gate, globe, check, plug, lubricated plug, etc-) and special valves (control valves or relief valves). The second classification, the instrumentation sr'mbols, falls into three categories: temperature, pressure, and flow indicators. Properly used and properly indicated on the flow sheets, these symbols can tell the entire control and hardware arrangement requirements for the plant. Engineering Flow Diograms. From the information entering his section, the Piping Analytical Engineer puts together a set of Engineering Flow Diagrams- In compiling these diagrams he duplicates the flow requirements of the process as indicated on the PFD and converts a single process flow diagram into from 5 to 10 engineering flow diagrams which are Process-oriented. The processoriented engineering flow diagrams are separated fron.r the auxiliary and utility systems by both a numbered sequence of drarvings and by mantler of presentation. f'he process diagrams are in schematic form showing actual arrangenlents and denoting special considerations such as gravity flow wherever necessary. Whereas, the auxiliary and utility flow diagrarrs are laid out acconding to plot plan arrangement. In addition to the information found on the process flow sheet, these process-oriented engineering flow diagrams contain the start-up conditions required by the unit, the normal operating conditions and considerations for shutdown. They further specify the valving and piping necessary for the pump sparing arrangements. The exchanger arrangement, i.e., number of shells, number of shell and tube inlet and outlet connections, is also shown schematically on the flow sheets. Any critical arrangements of piping where the Engineer has to specify the exact arrangement in order to obtain proper operation should also be shown.
The auxiliary and utility flow diagrams on the other
hand have no preliminary design but are designed completely by the Piping Analytical Engineer. His basis of design is simply supporting the process flow stream itself and his auxiliary and
utility sptems must meet this requirement. Ilere tho engineer must be more conscious of physical layout as his auxiliary and utility header sizes are a direct function of flow quantity as the various pieces of equipment are fed.
lot-E
The entire set of process, auxiliary and utility flow diagrams, constitute major source documents from which the piping designer details his design of the over-all plant.
Nomenclqiure. As previously stated, of the design data presented on
some
the engineering flow diagrams must be recorded in the nomenclature. Each and every line tagged with a number on the flow sheet must be Iisted in numerical order in the nomenclature. On the average size job there are approximately 1500 lines under consideration. This presents a tedious task for the Piping Analytical Engineer, but is information which is absolutely necessary downstream in the Production Section where the pipe is actually being designed. The nomenclature itself includes the sizes of the line, the specification which dictates its ma-
,o tot.F
l I
t
terial of construction, the wall thick$h and the flowing media in the ; line. In addition, the nomenclature i I provides a road map consisting of the -a Engineering Flow Diagram number and the equipment or line number at Fig. 4-Portion of typical Engineering Flow Dagram. both terminals for every line. The routing of the line is given in the direction of flow in a lished by the Piping Analytical Section give the Designer detailed information restricting or freeing his design. AII main pieces of equipment have their elevation set and critical circuits pointed out (for instance, where gravity flow is necessary). This gravity flow requirement, for example, might require the location of the condenser to be above or below the reflux drum with which it is For many of these items listed above there is no source associated. This type of information ddfinitely restricts other than the nomenclature itselt and for all items the the designer and is one of his primary considerations in only document tieing all requirements together to the commencing his design. proper re system. This entire system Some of the major elevation requirements center has an that it limits the Designet's around: isometr important for many reasons, but mainly for clarity. The nomenclature also becomes o Pump NPSH which sets fractionator tower elevathe over-all cross reference index betwen the flow sheets tions based on the bottoms line conditions going to the for the schematic representation of the hydraulic desigrr pump. The bottoms line is normally associated with an and the isometrics which are the hardware representation eqilibrium liquid. If there is not enough head pressure of the piping arrangements. Thus, the nomenclature to offset the friction in the lines, the pump will receive seryes as the overall map identifying the various pieces a liquid vapor mixture resulting in cavitation. of piping associated with their respective lines. o Reboiler circuits which again may set tower elevaEquipment Elevotions. Equipment elevations as estabtions. A thermosyphon reboiler requires enough liquid l
ness,
I
a
37
ESSENTIALS FOR
GOOD PIPING
Flow Diogrqms qnd Piping Design. Once the designer all the information, in final design quality, he proceeds to actually run individual lines and specify their exact location. The designer has received the schematic flow sheets, the equipment elevations and nomenclature. He now knows what lines are critical, which piece of equipment has definite elevation requirements and the size, schedule, t)?e of material and all technical information about the lines he has to run. At this time, he has also received a final plot plan which locates in
DESIGN
has received
P/PE L/NE /NSTPUMENT LlNE
+ -+ {
6A7E VALVE,
6LO6E VALVE
& @
C/./ECE VALVE CONTPOL VALVE
plan view every piece of equipment.
PEL/EF VALVE WELO AAP
+ <>
With all this information at hand, the designer sketches the most economical arrangement of piping without interfering with lines he has run already or lines he intends to run. He proceeds from the larger size lines and the most expensive alloys down to the less expensive, smaller carbon steel lines. With this priority in mind he completes his over-all layout and begins to draw individual isomet-
PEDUCEP
//NE s/zE oc/FlcE EUN /N€PEASED &/F/CE zUN /.|YPE STPAINEQ
?
C e 4 5
/NS7qUUEN
7 LOC/4LLY
AIOUNTED
lNS TPUMENT EOAPD AIOUNTED
AIOTOP DC.VEN PIJMP TUPE/NE DQ/U€N PU*IP
o
aNtr Br'T7EPY Lt l/7 /5O LB, P@CESS SPEC/F/CA7/ON
tPt 3Pt
5OO
LE, PPOCESS SP€6/F/6AT/ON
.
Fig. .LEngineering Flow Diagram symbols.
static head to provide driving force so that the reboiler will work properly. This head determiaes-thrcirculation ratio and the amount of vapor returned to the tower, thereby setting the entire tower gradient. Reboiler circuits in conjunction with pump NPSH consideration set the tower elevation.
o A flashing liquid must have enough static head to oflset the friction loss in the lines, and the total loss through an orifice. In this case the vessel from which the liquid is being drawn and the location of the orifice flange itself must be specified, either by definite elevation or by a relative elevation.
rics of each and every line. As the isometric is drawn, the material required for this line is summarized. This summary is then compiled and entered on requisition sheets. The designer, as he is summarizing tJre material, further indicates whether there is a shop or field fabrication requir6ment. This is one of the major breaks in the summarization and requisition compilation. On the shop fabricated material the designer indicates the breakpoints for the shop such that the shop will cut and bevel or provide mating flanges so the fabrication can then be assembled in the field. The drawings, material, nomenclature, and the flow sheets are all then sent to the field, where the field construction force accePts the design information, finds the proper pieces of piping and assembles them to the design isometrics. This completes the job. Jhe_efficiency with which the entire system works de- pends upon ihErn-itiation phase, that phase lying in the hands of the Piping Analytical Engineer. Every change the engineer makes from his base design is compounded tenfold downstrearn as so many other operations depend on his design. The Analytical design is the "Bible" and must be correct the first time. The correctness, thorough. ness, and efficiency of the design released by the Analytical Engineer determines the effiicency of the piping design and influences, significantly, the efficiency and quality of JL JL the final over-all plant.
o Gravity flow which determines the relative elevations of related pieces of equipmen! and most probably would determine the exact elevations of the pieces of equipment themselves.
it
can be seen that the equipment elevations as specified by the Analytical Engineer determine the critical arrangements in the vertical direction for the Piping Designer. Once-these elevations have been taken into consideration by the designe,r, he is then free to arrange the other equipment, which is not involved with the critical
Thus,
in the mdst economical arrangement he can visualize. Therefore, it becomes extremely important for circuits,
the Analytical Engineer to specify every elevation which
is critical, but not to overspecify to the point where he is restricting economical design.
38
About ihe quthor R-q.v W. JuosoN is Piping Diuision engineer utith The M. W. Kellogg Co., New York. X[r. Judson is responsible lor plant lagout, and arualytical and producti.on de-
sign of piping systems f or all petroleum and cltemical plants built by the company
in tlrc trTestenr,
Hemispltere, He joined
Kellogg i,n 1957 and u.tas f pro.iect inanager. He holds
ormerly a a degree 'in
ciuil engineet"ing from the Uniuersity of Michigan, He is a registered p,r'ofessional engi,neer in the State of Neus York and is a member of AICLE.
How to Design Yard Piping Use this method to quickly and systematically
design yard piping and save piping costs
Roberl Kern New York City
MINIMUM COST YARD pfpfNC is a direct result of precise engineering design. This method shows how to save piping dollars and gives a step-by-step evaluation procedure. fmportant sections are:
o IIow to evaluate flow diagrams and other data o IIow to analyze yard piping design o IIow to economize yard piping. Examples of yard piping design hightlight all these factors and show details of the best yard piping at mini-
mum
cost.
control and switch house; location of utility and process lines entering and leaving unit limits; main pipe runs 'outside the unit; Iocation of storage tanks relative to process units; also blending, loading, filling station, and cooling tower locationl and site grade level variations.
Plot Plan. The relationship between plant units, equipment, buildings and yard piping is shown on the plot plan. Position of incoming and outgoing lines can be seen. Major structures, Iocation of buildings and all equipment is shown. Roads crossing the yard or located under the yard steel are indicated.
The main arterial system of a plant is in the yard piping. It is here where long process lines are located interconnecting distant equipment, and lines entering and leaving the unit. Also, utility headers are located in the yard supplying steam, air, gas and water to process equipment. Ilere are located all relief and blow down headers. Often instrument lines and electrical supply conduit are also supported on the yard steel.
Flow Diagrams. Process flow diagrams show essential process lines interconnecting process equipment, Mechanical flow diagrams (developed from process flow diagrams) indicate the complete flow systems necessary for plant operation; also, pipe sizes, valving, manifolds, all piping details and instrumentation. Utility flow diagrams show the number and size of water, steam, condensate, gas, air, etc. headers, also all equipment supplied by these headers with necessary valving and piping
lnformqtion Required. Data
details.
essential
for yard piping
design are:
Specifications. Usually, only a few items included in the job specifications affect yard piping design. Such items are: minimum headroom over roads, under overhead pipe lines, or steel beamsl access, headroom and handling requirements to equipment arranged under the yard; ladder, catwalk and platform requirements to valves, relief valves, orifice flanges and instruments Iocated in the yard; details affecting piping and structures, operating and safety requirements.
Project desrgn data and site maps give required or existing conditions inside'and outside the unit limits. These are: required location of cooling water mains, below or above grade; required locatioh of furnaces,
Figure 1 shows a plot plan and process flow diagram. With this two drawings an assessment can be made regarding which portions of process lines will be located in the yard and which lines will interconnect directly nozzles on adjacent or nearby process equipment. Heavy lines on the flow diagram indicate piping assumed to be located in the yard. These lines are also shown on the plot plan to give a visual idea of yard space requirement. A mechanical flow diagram is similarly evaluated. Greater number of lines can be drawn on the plot which gives a more accurate estimate of required yard width. In addition to process lines, utility flow diagrams will show individual service lines and utility headers. Utility mains generally run the whole length of the yard. These
39
Ftow diauavn and Vlol planohow\ngryoeae linee in *te yard
I
a
,r)
[r
tl
h a
$l\
di!
+e
Pl
q
fl[
\
0
I
trtr
s#
PPoc€ts LIN€ S
(, d
conrRil
FIGURE l-The first step in yard piping design is careful
ta \
\
rir
/'tof 40
HoU.tE
PUN
study of plot plan and flow diagram. Notice that the heary lines on the flow diagram have been located in the yard piping rack.
Various yerd ViVing errangements
A.
oEAo ENo tARo. AttD /FAyE
o{E
B. ,lrR.ltGflf ntuu€ Y*?O.I/NES c4rl €ilr€R 4ilO ttlyE M4 Et t oF lw vtPO.
uNEs EilrER
€ilo 0P yARo,
I
-1
t_l
1
I
I
c
t-sttapeo yieo- uttgir qN lEAttE MPru 4il0
€7451
#
ENrGe
7,{E
PtOf
ffi r-l
lilo
LElrc av
7//PEe
sDes oF ruE
,Utli
l-l L_l _J
E, u-"uaii
lND t€AyE
I l'i!i:
--.--
YAR,, L/il€c au tNr€P ttt php s/Et 0F r,tE PCor
I
o
|-l Li
U
n
il
Li
--G,
ar*ra ysiD P{trile I lxRy t4&€ ?//€Hpra
Puiln
2-In these typical yard piping arrangements, notice how a complex piping arrangement can be broken down into a combination of several of the more simple arrangements. FIGLiRE
E
co,qerulnal/
OF
f |uo 7-stAEo yARO,
41
GeneYal Vipe line €wanqewtenf {'
on e onb)level yaYd IETWUNES
k4ttto
PpcEts th(Et
RMS'
alttly
t/AtE5
LINIS
HEAYY UilES .(cootttv? MrER,
,TN'^.F"
cmlrls. IN€S
s
I5 \
/Nr.rrQa4Eil| l,tN€t
tN€.t WtrH EXPANS.ar{ LOOPS. HaTTES| 4ilo lAPG€sr L/NE oaf,toE/ cotoe'r
GPOAP
L/Ne NS/DE:.
FIGURE 3-Important points in this typical line position arrangement of yard piping are: healy lines over columns, utility lines near the center, and horizontal expansion loops with hot lines on the outside of the loops.
lines should also be taken into account for estimating additional space requirement.
How to Anotyze Yord Piping. The plant layout
de-
termines the main yard piping runs. Figure 2 shows yard piping layouts resulting from various plant arrange-
ments. Smaller plants have usually the simplest yard piping as shown on sketch A and B. On sketch A process and utility lines enter and leave the same end of the plot. Sketch B is a frequently adopted layout often with
utility lines entering at one end and process lines at the opposite end of the yard, Layout conditions sometimes result in an Z shaped yard as shown on sketch C. Larger plants will have a more involved yard piping'as shown on sketch D, E, and F. Sketch G shows yard piping arrangernent of a very large plant. This layout can be considered as the combination of several simpler yard piping arrangements. Of course, the shape of yard is not chosen when doing plant layout. The yard is the result of over-all
42
plant arrangement, site conditions, customer's requirement and above all plant economy. Some pipe lines arranged in the yard need special consideration. Consequently, the designer must also know what type of lines are arranged in the yard. These lines are classified as follows: Process lines:
(a) which interconnect
nozzles on proc-
more than 20 feet apart (closer process equipment can be directly interconnected with pipe lines) ; (b) product lines rvhich run from vessels, exchangers or more often from pumps to the unit limits, to storage or header arrangement outside the plant; (c) crude or other charge lines which enter the unit and usually run in the yard before connecting to exchangers, furnaces or to other process equipment, e.g., holding drums or booster pumps. ess equipment
Relief line headers, individual relief lines, blow dorvn lines and flare lines should be self-draining from all relief valve outlets to the knock-out drum, flare stack
Spacing ol yard Viping Table I - ?iVe linee witho uf Planqee NO\E: t. rHls rAaulAr/o/t ls 6AsED oN rtE F ot
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ARE /N UNES LlSTED HTRE UsE BOTTO|4 Fl6UR€S
EAb 2-?ipe lineo witlnFlang.* or tineeize valvee (up toaOrbe rafing).., N)fE, l.rqls
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2.
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D=
C+x+y -
!^ ro
rAauLAr€D yAl(/€,t:
?*?rJ'+xry, 4204
FIGURE 4-Use this chart
for determining line spacing in
yard piping racks for
bare
lines with and without flanges and insulated lines. tArEpAt T//ERtlAt r'/0/E/.1Etv/$ GAp 4CCoRbNGty.
tr 1aac€ilr flfts, F* xc,tt/yE
UTERAL hot/€tv€Nr /ila?ElsE
43
Tynol e-ro*-eedion of yerd
SKETCH JHOil/T/G
Typ/cAt P/ArFa?Hs 0N v4QO ,tr€EL,
U//E WIH O,yt
6Et0u 4//0 2r/tR ASOY€ YARD L/A/E
ilITH SOTH
EilO' HIiIIER THN .OP YARD EANK AlTTRNATE
YIY^' *0")---
l/NE
fv0.r
Hlrt 00/// UWFR fHA,t/
Mfrotl y4p9 6111p
FIGURE S-Typical cross-section of yard piping showing critical dimensions which affect piping cost, Notice ment for platforms for access to valves in the upper right hand corner.
or to a point at the plant limit. A pocketed relief line system is more expensive, because usually an extra con-
pot is required with instruments, valves and To eliminate pockets some relief line headers must be placed at a higher elevation above the main densate
pumps.
yard usually on a tee support on the extended yard column. However, on some noncondensing gas systems selfdrainage is not so essential. Relief lines can be in great numbers with some large diameters and occasionally
high temperatures.
Utility lines in the yard can be put in two groups: (a) utility headers serving equipment in the whole plant. Such lines are: low and high pressure steam lines, steam condensate, plant air, and instrument air lines. If requested cooling water and hot return, service and fire water can also be arranged in the yard. (b) Utility lines
or two equipment items or a group of similar equipment (furnaces, compressors) in the plant. Such lines are: boiler feed water, fire steam, compressor starting air, various fuel oil lines, lubricating oil, cooling oil, fuel gas, inert gas, and chemical treating lines. serving individually one
44
tJre arrange-
Steam headers should drain to the steam separator for more effective condensate collection. Branch connections to steam l-readers usually connect to the top to avoid excessive condensate drainage to equipment.
Instruurent lines and electrical cables are often supported in the 1.ard and extra space should be provided for them. The best instrument line arrangement eliminates almost all elevation changes betu,een the plant and the control room. This can be easily achier.ed rvhen instrument lines are supported outside the yard column on a suitable elevation.
All these lines have been listed in detail to emphasize the large number of process and utility lines rvhich are usually located in the yard. Now, hor.v to arrange these pipe lines in the yard?
Line Location. Figure 3 shou.s one level yar-d piping. Regardless of service, hearry lines (very large diameter lines, large lines full of liquid) are placed over or near the yard columns. (Centrally loaded column and re-
duced bending moment on the beam
will result in a light structural
de-
siga.) Next to these lines are placed
all process lines and relief lines. Utility lines are in the center portion of the yard. A general sequence of utility lines is also shown on Figure 3. Under position in the yard depends on the number and size of branch connections. If the majority of similar size branches connect to the header from the right, it is more economical to place it in the right half of the yard. It is advantageous, from a suPPort standpoint, to group hot lines requiring expansion loops as shown in Figure 3. Loops elevated horizontally
47o5
Fl
7l.5FZ
LThis is a typical elevation for yard piping intersection. Notice that the 14-foot elevation of the lateral rack permits turning up or down at the inter-
FIGURE section.
over the yard is the most common adopted design, having the hottest and largest diameter line outside. Line guides, Iine stops, and anchor points are usually also required along a hot line somewhere in the yard.
Pipe expansion forces, at some of these points, will affect yard sup-
port
design.
Those process lines which interconnect eiluipment on the same side
of the yard should be near the edges of the yard bank; lines which inter. connect equipment located on both sides of the yard should be closer to the utility lines and can be placed FIGURE 7-In sketch A, a flat turn is more economical if line sequence can be Sketch B shows the need for an elevation change either side of the yard. Position of kept the same in both directions. when line sequence changes after the turn. product lines is influenced by their routing after leaving the plant limit. Right (left) turning lines should be Generally those process lines should be located in the on the right (left) hand side of the yard. Utility lines top bank which interconnect two nozzles elevated higher serving individually one or two equipment items should than the top yard bank. Process lines with one end lower be on the same side of the yard as the equipment to than the bottom yard elevation can run either in the which they connect. top or the bottom bank. If both ends of a process line If, because of the large number of lines, two yard lower are than the bottom yard elevation the line should bank elevations are required, generally all utiliry lines be located in the bottom bank. are placed in the top bank and all process lines in the bottom bank. Obviously, exceptions always can be made The elevation of a line can also be influenced by to the elevation of individual utility or process lines. valves and instruments in the line. Often a more conLine sequence arrangement will be similar to the se- venient access platforrn can be provided for valves arquence already discussed for the one level yard. Line ranged in the top yard bank. The preferred location of spacing in the yard is shown and explained on Figure 4. lines with orifice runs is near the edge of the yard with Yard in Elevation. Figure 5 shows tlpical yard sec- orifice flanges taeat a yard column for more convenient tion with main elevations. Elevation of yard piping is portable ladder access. determined by the highest requirement of the following: The sketch on Figure 5, upper right corner, shows (a) headroom over a main road; (b) headroom for ac- platform and walkway arrangements to valves, relief cess to equipment under the yard, and.; (c) headroom valves and in the yard. irstruments located
under lines interconnecting the yard and equipment outside the yard. The size of steel beam supporting yard piping should also be taken into account when consider-
or two slots are required along the yard usually over
ing headroom.
the pump discharge nozzle for process, steam and other
When pumps are affanged under the yard often one
45
utility lines connecting Irom the yard to the pumps and drivers. Economy of Yord Piping. Pipe economy depends primarily on the length of lines arranged in the yard. Fittings, valves and instruments are relatively few in the yard compared to pipe length. Figure 5 also shows those critical dimensions which will influence piping cost from a yard piping layout standpoint. These dimensions depend . on the over-all plant layout and should be carefully considered when the plot is arranged. Dimension A is the total length of yard and is governed by the number and size of equipment, structures and buildings arranged along both sides of the yard. On an average, about 10 feet of yard length is required per process equipment (exchanger, drum, tower, unhoused compressors, etc.) A control house located along the yard, for example, will increase yard piping cost because all lines must pass by without really being associated
with the relatively long control house. It with good layout practices, the same number and size of equipment can be arranged on a shorter yard length, yard piping cost can be considerably reduced. A 7- to 8-foot average length Per process'equipment is not unusual in a well arranged plant. Equipment in pairs, stacked exchangers, exchangers under elevated drums, drums or exchangers supported on towers, two vessels combined into one, closely located towers with common platforms, drums supported on exchangers, process equipment located under the yard are only a few examples which help shortening the yard. These arrangements, of course, shorten not only process lines interconnecting equipment directly or in the yard, but also shorten those lines which pass through this area and utility headers serving this area. The careful selection of dimension B and C (Figure
5)
can minimize pipe length between the yard and process equipment and pipe length interconnecting equip-
ment on opposite sides of the yard. C is usually 6 to 7 feet. Not more than necessary yard height (Dimension D and E) will minimize vertical pipe lengths. When changing direction change elevation-is an old
rule in piping design. This happens with all lines connecting to yard piping. Ilowever, some large diameter lines can make a flat turn when entering the yard. Such
About the Author Robert Kern studied mechanical engineering at the Royal Joseph Technical University, Budapest, Hungary, where
he received his engineering degree in 1946. He left Hungary in 1948 and w€nt to England where he joined an intemational engineering - construction firm to work in plant layout, piping design and design coordination. Kern has been in the United States since March 1958.
lines should be placed at the edge of the yard. Any other spot will block excessive space in the yard. Figure 6 shows commonly used elevations for main yard heights at a yard piping intersection. Note that the 14-foot elevation of the lateral yard perrrits turning up or down at the intersection. It is important to elevate lateral pipe banks between the two elevations of main yard.
Elevation difference between main yard bank and laterally connecting pipe lines is about 2 to 2/2 f.eet. This gives an elevation diflerence of 4 to 5 feet between two main yard banks. If a building (control house, pump house) is located under the yard main piping elevations will be higher than without a building. Clearances in the building, pitching of the roof, steel structures and pipe line clearances will affect the height of the yard. Elevation difference is not required if a flat turn can be made within the'yard. Line sequence in this case must be identical before and after the turn as shown on Figure 7, sketch A. Ilowever, varying line sequence in the two directions introduces an elevation difference and an additional elbow in each line as shown on Figure 7, sketch B.
Ycrd Piping Supports. The width of yard is influenced by two conditions: (a) the number of lines, instrument, electrical lines and space for future lines in the yard, or (b) space requirement for equipment arranged under the yard. The number of lines can be estimated by marking up the yard on a print of the plot plan, with the help of flow diagrams, showing all lines located in the yard. Adding the number of lines (rr) ,p to 18 inches diameter in the densest section of the yard the total width (W, ft) will be as follows:
Wt:(f XnXS) +A(feet) Where f : safety factor-(f : 1.5 if the lines have
been laid out on the plot with the help of process flow diagrams. f : 1.2 if the lines have been laid out with the help of fully detailed mechanical flow diagrams). S in feet is the estimated average spacing between lines, usually S : 1 foot. If lines in the yard are smaller than 10 inches the value of S : 0.75 foot.
A in
feet is the additional width required:
(a) for
lines larger than 18 inches, (b) for future lines, (c) for instrument lines (about 2 to 3 feet) and sometimes, (d) for electrical cables (about 2 to 3 feet) if these are also supported on the yard steel, e for one or two slots for
pump discharge and driver utility lines (about
18
inches or 3 feet).
The total width of yard W1 can be between 20 and If W is bigger than 30 feet usually tt/z or 2 yard banls will be required. The upper limit of yard steel span is 32 feet. Space requirement for. equipment plus access below the yard can also influence the width of yard' For a single row of pumps and 8 to 10 feet access to the pumps about 20 to 24 f.eet yard span is required depend60 feet.
TyVlal yqrd piVing eu??orfe
Wifh auailable ffal wi d+1.1 amd divueneions of ?par4
ror
LlYt+ltAEtc moru il/2
ht
FEc.r
,t ltloar I Aff :ttntsvEZ I zumty€i|
htnEuttous hl Fer
Als
/0
/o
OF
AeHncl
20-2*
.t
38'12
?8-3z,
f
3C- 42
2o-2*
?
r? -47
4S-ds
2o -27
{0-44
le -12
28-s2
9{- 63
c/-
zg-32
zo- 24 2c-s2
-t+
2E
Jo-
sl
6?
WtirCa
I
Uo
I ?
/
3
rt
6
2
4
tr)
/t
7
(c)
2
.r
k-t
r (r) i r
sterc,
LFrom these data, total available width of these typical yard piping support bents can be determined. FTGURE
ing on the length of the pumps. fn case of a double will be required. typical yard steel Ie yard width to e table of dimensions. This tabulation can be used for selecting a type of yard support after the total required width fias been
estimated. The most commonly used yard piping zup ports are Types 2, 3, 4 and 5. _ fn almost all plants spacing between yard support
bents is about 16 to 20 feet. Neverless consideiation should be given to (a) line sizes: smaller lines have to be more frequently supported than large diameter lines; (b) liquid filled lines require a shorter span than gas
47
Yard ?t?in g
o v1 wi th e*chan 1un cli
ger gl ru clure
€tEailo(
LooK/NG
^/oP.H
.4 ^aott
9-In this example of yard piping layout, notice how the elevations have been governed by headroom requrrements over the North-Souih road. This elevation also sets the height of the first platform of the exchanger supporting structure. FIGURE
lines; (c) Iine temperature: very hot lines span shorter distances than cold ones of same size and wall thickness; (d) insulation: heavily insulated small diameter Iines with cold temperatures must be supported at relatively short intervals; (e) Space requirement for equipment at grade and under the yard can sometimes also influence the spacing between yard bents.
All lines from the exchanger structure to the yard dropped along the east side of the structure. A siot has been left open in the yard adjacent to the exchanger structure for lines r,r''hich connect to the lower northsouth yard or to pumps below the yard. Process lines turning into the east-west yard from the exchanger
Exomple. Figure 9 shows a yard piping junction with an adjacent exchanger supporting structure. The yard elevations have been governed by headroom requirement over the north-south access road. The top of northsouth yard set also the height of the first platform of the exchanger supporting structure because lines had to cross below the first platform to the top bank of the north-south yard.
vation.
48
structure have been arranged on the highest yard eleA number of vertical reflux clrums have been arranged
on the first level of exchanger structure. A1l
suction lines to pumps turn horizontally below the lower northsouth yard bank. This, of course, is an unnsual example but it illustrates the necessity of choosing carefully yard elevations L! and an over-all system of design. 1+ 1+
Locate Tower Nozzles Quickly Same time and detail work Iocating tower internals and nozzles by using these charts and tables.
Brion D. Wookey Kellogg International Corporaiion London, England
THE PHYSICAL interpretation of process requirements inside
'ovarhoad condo.t.,
-
S€. Fig,5
S.e Fig. 6
r\-rI Rettur tz/e/ t2"
See
a tower
is frequently more exacting than the exterior piping. Often the location of an internal part fixes within strict physical limits the location of tower nozzles, instruments, piping and steelwork. Consequentln the f reedom which the Iayout man usually enjoys in the initial stages of design can be severely restricted. He may be forced to switch his attention from the overall layout to tedious, large scale setting out of tower internal details. This is a lengthy but essential part of his work, done to avoid internal and external interferences coupled with poorly designed piping. Much time and detail work in setting out tower internals can be saved by using the tabulations and graphs
Fi! 3
presented here. iec Ft?. 4
Tower lnlernqls Figure 1 shows a typical process vessel sketch. Dimensions and details are developed by the process vessel designer. Vapor and liquid flows deter-
mine tower dimensions. Tower
throughput and working pressure are important factors in choosing an economical shell diameter. The number of trays are determined
by the Rabo//cr ,lafurn.
,?.cyc/c
FIGURE l-Typical
vessel sketch as developed
by the
process engineer.
degree
of
fractionation re-
quired. Usually the tray diameter and spacing are so chosen that entrainment does not exceed 5-10 percent.
The depth of the liquid in the tower bottom and consequently the length of shell beneath the bottom trapout boot is controlled largely by the required holding time for the tower bottom product. The vapor space beneath the bottgm tray is influenced by the reboiler circuit, when provided. Reboiler draw 49
Locafe Tower Nozzles Quickly . . .
aoHriFLO^,
RLet
(*reli!r rrcrt)
FT B'Et
SC6L
(fiL.feRr{hTC
1nF'3)
r
-liir-
FIGURE 3-(Above) Manhole locations for single flow trays.
FIGURE 2-(Left) Reboiler drawoff nozzle locations.
(a)
(b)
off quantities and the density of the vapor/liquid mixture in the return line governs both nozzle and trapout boot sizes. Vapor quantities to the bottom tray and liquid quantities from the bottom tray carr be calculated by means of heat balance around the reboiler.
Tray
spacing
is
occasionally in-
creased to permit access from outside,
via manholes, to important internal If the tower is in very "dirty"
piping.
service the minimum tray spacing is considerably influenced by the distance required to locate a manhole at every ffay f.or cleaning and maintenance.
The distance above the top tray is usually sized to accommodate reflux inlet piping, vapor outlet piping and the provisions of a top manhole for lnspection of the critical head-to-shell weld, and tray installation. The pressure vessel designer (acting between the process and layout engineer) engineers the physical details of the tower. Arrangements of tower 50
internals are discussed in the followalternative possibilities are
cost of the tower, but this is usually more than offset by saving through explored for arranging process nozzle better tower piping. The remaining connections. segments of 90" lyg impractical -vo drawoff conneclocations for reboiler Nozzles ond Piping Economy tions for obvious practical reasons. Figure 2 shows typical reboiler The reboiler return line connection drawoff connections for a single presents no problem as it can be loflow tray. This connection, often one cated beneath the trapout boot and of the largest nozzles on the tower, can be orientated anywhere on the can be very influential in arranging circumference of the tower. the orientation of trays. The simplest Figure 3 shows the arrangement of and most economical location for re- typical single flow trays within a boiler drawoff connections is shown tower shell. Access is frequently on sketch (a) . Alternative locations needed to specific trays by using shell may be placed within the angular manholes or handholes. These are in limit of 2ao. This angle, of course, addition to drawoff and reflux condepends on the size of the reboiler nections with their associated internal draw-off nozzle and. the width of piping. The arcs bo shown on Figure trap-out boot at the tray downflow, 3 give the angular limits in which a dimension "h". shell manhole or handhole can be In the interest of more economical placed. external piping arrangement, the nozFigrre 4 shows the arrangement of zle arrangernent shown on Sketch (b) typical double flow trays. Here, the can be used within the angular limits possible areas for shell manhole locaof 1800. This arrangement adds to the tion are restricted to the four seg-
ing and
tl'*. (ivrt 'r.iill ".n*]l Illo*rarrel
[
?
rrEta (oo .'r.ilr)
J
?\ ;,/
AeCt
(ererl:no1s;
FIGURE 4-Manhole locations for double flow trays.
(a)
(b)
FIGURE 5-Typical internal reflux piping.
ments co, Manholes and handholes are not' usually placed in either the downflow or seal-pot section of trays. Process connections are not located in the downflow sections of trays, unless specifically required by the process. Generally where internal piping is arranged ovet a tray a manhole is also provided. Reflux nozzles are provided
with internal pipes which discharge the liquid into the seal pot of the tray below. This internal is diagrammatically shown by the process vessel designer as in Figure 1. The obvious and cheapest physical interpretation is as shown in Figure 5a. Ilowever, if the tray orientation has already been fixed within prescribed limits by other factors, this nozzle location may be in a
very undesirable position for good piping arrangement. This problem can be overcome as shown in b, but
(.)
(b)
FIGURE 6-Two types of overhead piping arrangements.
the designer must take care that the horizontal leg of the internal pipe clears the tops of the bubble caps or weir dams. Ife must make sure that the internal pipe itself can be fabricated for easy removal through a manhole or can be fabricated inside the tower shell. The vapor outlet nozzle (Figure 6) can be located at the top of the head (a), or it can be located in the shell with an internal pipe bend leading
(") (b)
FIGURE 7-Distribution piping arrangements.
5l
handling of such piping within the tower so that no obstruction is encountered when removing other in-
Locate Tower Nozzles Quickly . . . BSCKGROU}.ID GR,ID SCCLE to
to
to
+
lo
ternals. :e
u
Accessibility, whether internal or external, is very important and is often not given enough consideration. A balance must be made between the external accessibility of connections from ladders and platforms and internal accessibility from shell manholes, handholes or removable sections of trays. For example, a shell manhole opening must not be obstructed by internal
piping unless that piping is removable through the manholes or can be slung clear from an internal hitching point. In either case, the break flange bolts must be accessible from the manhole. The consideration of the design of even simple internals illustrate these five steps which can be applied in the
of all internal piping: l. Analyze the functions of the inter-
design
nals.
2. Determine the desirable location of the shell connections relative to external requirements (piping, platforms)
.
3. Determine the desirable orientation of trays to suit all internal requirements.
A.Lay out the internal piping
re-
quired to satisfy the prefered loca-
tion of the shell nozzle and the preferred tray orientation, and if necessary adjust these to make a
VESSEL DIRI{ETER9. FIGURE B-Grid for internal lavout sketches.
toward the center of the head
(b). j"b and gives complete
freedom
of
These alternative arrangements allow orientation of the shell nozzle if the the piping designer more flexibility in distributor is above the top tray. If it
workable arrangement. 5. Determine the practical physical design of the internal piping relative to cost, removal and/or han-
dling together with internal and locating the overhead line, and ar- is located as shown in Figure 1 the external accessibility. ranging platforms to the top manhole, orientation would then be governed All of these considerations must be vent and instrument connections. by the tray downflows. This alterna- made early in the design as they bear Figure 6a shows not only a simple tive is only possible where space per- directly on the external arrangement outlet connection but allows the bist mits dimension "1." of a tower. The examples shown are for vapor outlets, simple cases of internal design that access through the manhole. Figure t distributors and occrir very frequently. Orthodox 6b shows quite common internal pipst be designed to methods of large scale layouts require ing, and it has the advantage of makions as bubble caps, much time and labor. Even more time ing blinding of the vapor outlet nozzle accessible from the platform which weir dams, downflow and tray sup- is expended with more complicated serves the top manhole. The vessel ports. At the same time they must ful- and unusual cases. vent connection can also be piped to fill the process requirements for their Grophs ond Chofis for be accessible from the same p^laiform. location, as well as the physical reQuick Design quirements of fabrication to enable This arrangement eliminates the need
for a small platform above the top head withdrawal through the shell manaround the vapor outlet nozzle for holes. blind, instrument and vent Access ts Figure 7 shows a double cross disIf withdrawal is impossible, and intribution pipe. In arrangement (a) the ternal piping must be fabricated inshell nozzle orientation is restricted to side the tower, adequate arrangements 2xco.Arrangement (b) doesthesame must be provided for removal and
access.
52
Tower infernol toyout grid, shown
tmporront 'il::H"*t* r [:::*tl;;:tlJfii:: overlays,
a portion of any tower
of
specified diameter can be traced, freehand, and the internal tray, manhole ot nozzTe can be sketched in to scale.
yessel diome ters
'o
-t
n|
:r'q -3 .s; |l -rt "ob rli
s i-3
-E
si
i :: i
5-O
c'-c'
\(r.
cl ii
ot s'-cf cl EI
i-6'
o .s
o q
z'-o" €o
t
!-6
o
(,
co
.{
t-o
!
6
o' polnl
tongenc'1
6'
l1o' l'-6' 2'-o' 2'-6" 3'-o" 3'-6o tl-o' centerlinc ol vcssel to loce
4'-6"
of ftongc of nozzlc. *
sb"
5'-6'
o olo"
With the help of the radial grid, correct relative orientations can be made.
*.@
nozzle stohdout should bc
cnter chort horo
meosured from
nside ol
y.ssel to foce of llohge ot lhc p.c.d. ol llongc bolt holcs neoresl vcssel shell. viz:
Hillside connections are another tedious job. These connections are often
used for temperature points in tray seal pots. When seal pot width prevents sufficient thermowell immersion,
a hillside connection is the only solution. The correct dimension from the center line of the tower to the face of flange of the hillside connection must allow for bolt withdrawal. This is usually found by setting out to scale ald measuring the required dimensron.
FIGURE 9-Use this chart for determining the centerline of vessel to face of flange dimension for hillside connections.
Fig-rre 9 can be used for a quick solution of the problem. It can be used for all sizes of hillside connections in horizontal and vertical vessels. The example shown on the chaft cites an 8-inch 300-pound RF hillside nozzle located 12 inches from the point of tangency of a 5-foot diameter vessel. (See Figure 9.) The standard nozzle standout which allows for bolt
53
l-fflini6lum Nozzle Spocing-lnches
TABLE
(All Dimensions Are to the Neorest /1")
Nozzle Size
%
Mlnimum Center Llne to Center Llne Dlmenslon-Flanges GovernlnE l0 1 2 2tz 3 3% 4 5 6 8 L% r% % 22%
22% 23%
23'
,L1,
25122
26'
27% 24
27
2t% 2t14 2t3Z 22
20..
lglz
\8r.
t8%.
19
t9,
2i1,
20st
27tZ
21y
2211
23%
18.
t7%
t7%
t7%
18
L9' r8)
20
77
L8%
19,
79l/t
20
20)4.
,1L
22% 23%
t6%
16y,
16az
l7
17>4
18
T8'
tE94
7s%
20
21%
9rr,
14' L4% 15 13' 73' t3tz
t5%
75,,
lSxt
16%
t6%
77
t7'
18
t8,
20
2th
14%
74%
t4%
15
tsyl
lSxz
t61Z
6Ya
171t
t894 20
13
t31Z
74
L4'
vnl
75%
16
L2%
123/a
11
17)4
.
16..
),582
74
12
t2
12%
L2y.
8
roy
roVa
11
Lr/t
77y.
6
912
AL
e%
10
to, t0,
5
8y
8s.
I
9'
Q1z
931
1
I
8'
Etl
8%
s%
LO%
7rl
7at
8
EY
I 8,
s%
3%
8%
9LZ
e%
10.
182
7%
r0% tOrz
Lb. Max. RatinE)
t2
t4
l6
29'
3011
3l3t
26lt
2794
29
30,
371t
50
,t
25'
26y,
ny
29
42
46
-20
24
2512
26r)
38
40
44
.18
42
.ro
io
40
1,1
2ra,
a+Y4
3832
t2
28%
30xl
32%
36%
.r0
2Lxl
26%
2881
30,
3LaZ
22xZ
21N 26al
28'
32%
.8 .6 ,1
24
36
,1 1,
30
3+
tTtz t8y.
27Yl
28% 3081
23)4
2631
7911
25' 23' 27'
t21Z
7294
131/:
t9tl 2tt
l1
tt>4
72
75'
tTtz
t0,
11
13
8'
20,
2111,
23y
11
t2
74t 13,
t6%
IO
t51Z
77%
7s%
20%
22N
25' 27' 3ty 2+' 26t 30,,
LO
LOy
24
7'
711
7Ve
8%
8y
o
o1,
7
7%
7'
7al
8
8'
9'
2
6%
6y'
6%
7
7%
7
7%
I 8'
o
ou
10
v
A3/
16
t2r/
r494
76%
l83l
20
22
11
t2h
t4%
L6r/+
18r/t
t9y.
27y 23'
702
LI'
t3y.
75%
L7'
19
6'
AI,
6%
7'
5%
6/t
6%
7t
7X
a
t4
17
tTtz
5' 5'
6
6
6'
4
5%
6
6'
7
7y
8y
ox/
1ttl
13%
752
17
5xz
6
332
4
5%
5%
oYt
7
7y
8r/:
9y 1tlz
73%
t5%
t7
74.
5t
5y
%.
A82
3' 3' 3'
3
%
%
3xl
3' 3' trz
l0
3%
29!,
3
27
25
tqu 21, t9 2t 19 2\
23% 27y
2
oYl
5
5y.
6%
6%
7%
8%
e%
o
6
ELl
7
li
e%
3%
5
5' 5'
6r,
7
8
t3, t5y 76% 188) tl% 121, t51Z t6yl tStl sx tt% 13, t5% t6, BY
212
3
4
5
6
I
6
3%
71%
E
10
t2
t4
5
30
311
r>6
24
t1,
6%
t%.
20
34%
1
7
ttl,.
1E
tStl t4
2%.
12,
(300
16
26
lrz 1.%
22%
264)
20% 22)\
2614
20az
20% 1E
1
ny wy 20
24
%
Nozzle Slze
Mlnlmum Center Llue To Center Llne Dlmenslon-Relnforclng Pads Gorernlng
TABLE
!-fllinimrrm Nozzle Spocing-lnches
FIGURE lG.-Minimum certer line to center line dimension fiot tozzle flanges and reinforcing pads caD be determined from
these
tables.
withdrawal and a nominal thickness of insulation is required behind the flange bolt hole nearest vesel shell. Enter the chart at the vessel diameter, and follow the curve until it meets the horizontal line giving the distance
of the top bolt hole from the point of tangency (i.e. l"-U' to nozzle centerline phts 6f-inch pitch circle 'radius of bolt circle). Move along this line the number of divisions equal to the standard nozzle standout (in this case, 11 inches)'and drop vertically to the bottom of the chart where the
of vessel to face of. nozzle flange dimension can be read off (3 feet 3 inches).
centerline
ffinimum found
noT.zle spocing can be
in two quick
reading tables
(Figure 10) which give minimum allowable nozzle spacir,gs along a vessel
shell
for any combination of
nozzle sizes up to 24-inch diameter. This enables relative nozzle elevations to be
54
established on a tower if the nozzles are on the same orientation.
They can also be used for nozzles on the top and bottom of horizontal drums. The figures for flange clearances have been calculated on 300pound flangEs as 150-pound and 300pound flanges are the most commonly
used ratings. It however, larger flanges have to be used, clearance dimensions should be separately determined and tabulated.
The table in Figure 10 also allows for both reinforcing pads (Table II) and flange clearances (Table I) governing. For all normal minimum spacing, the larger figure obtained from the two factors should govern, but in particularly tight cases a common reinforcing pad can be used. For example the linear clearance is required between the centerlines of an 8-inch x 300-pound nozzle and' a 3inch x 300-pound no le. Enter Table I at 8 inches in the left hand vertical
column and move horizontally until the vertical column under the 3-inch figure is reached. The figure here (l2t/a-inches) is the minimum center-
line to centerline dimension between II at 3 inches in the right hand vertical column and move horizontally until the vertical column above the 8-inch figure is reached. This figure (14/a inches) is the minimum centerline to centerline
flanges. Enter Table
dimension between reinforcing pads, and in this example will govern unless a common reinforcing pad is used.
Angulor nozzle spqcing is the final problem to be dealt with here e.g., the determination of the minimum angular spacing for nozzles at the same or adjacent elevations in a slender tower. This occupies countless hours of work in making large scale setting out sketches. Where angular room is limited because of the small diameter of a tower or for reasons of
Yi't ,'ld
4= oF!
e
=-eB
/\ \/
oj FIGURE ll-Minimum clearance between govern.
nozzles when flanges
"$.\
FIGURE l2-(Right) Minimum clearance between uozzles when reinforcing pads govern.
accessibility, every inch is important, and clearances between nozzles must be kept to a practical minimum. The minimum angular distance between the centerlines of any two nozzles
in a cylindrical
vessel shell is de-
termined by one of three factors: 1.
A minimum practical clearance between flanges.
2.
A minimum practical clearance between reinforcing pads.
3.
A minimum practical clearance
between nozzle necks at the inside face of the shell. The linear distance for (1) is measured along a chord of a circle 1 foot 6 inches greater in diameter than that of the vessel under consideration. This assumes a nozzle standout of 9 inches (see Figure 11)
all
nozzles over
4 inches. However, it
cannot be automatically assumed that nozzles of 4-inch diameter and under the flanges govern, or that for
for all
all
nozzles over 4-inch diameter the pads govern, as in a small diameter vessel, the minimum clearance re-
quired between nozzle necks as in a small diameter vessel, the minimum clearance required between nozzle necks at the point of entry into the shell may override both considerations; viz. ao in Figure 13 is less than ao in Figures 11 and 12. Even if this is not so, because of the sharp convergence of nozzles in small diameter vessels, the reinforcing pad requirements can govern even when the pad itself is smaller in diameter than the
nozAe flange.
.
The linear distances for (2) and (3) are measured along a chord of a circle equal to the diameter of the vessel under consideration (see
flange diameter (plus clearance) for
Figurt
12 and 13).
Considering 300-pound nozzles, the
maximum reinforcing pad diameter (plus clearance) exceeds that of the
When the angular distance between
two nozzles must be an absolute minimum, factor 2 above is discounted, as a combined reinforcing pad can be used. This should be the exception
rather than the rule, as combined reinforcing pads (or pads of smaller diameter than twice the nozzle diame-
ter)
are often thicker than the vessel
shell thickness, requiring special plate for this small item. There are, therefore, two alternative CASCS:
Case 1. Normal minimum condi-
tions assuming separate reinforcing pads. Case 2. Absolute minimum conditions assuming a combined reinforcing pad. For each of these cases, only two of the three factors have to be considered. For Case 1, these will be factors (1) and (2), and for Case 2,factors
(1) and (3) . The total minimum ciearance dimensions for factors ( 1) and (2) l% flange + t/2-inch (for 150-pound
through 900-pound flanges) and /2 pad * l-inch respectively] are tabulated in Figure 14, but those shown for factor (3) do not include the minimum clearance between the O. D. of nozzle necks which can only be determined when the shell thickness of the vessel is known, i.e.
If t = shell d
:
thickness
in
inches
outside diameter of nozzle neck
55
Nozzle Size
Neck
-;
%
s.: +
+
2t.
io.f
to Figure 14 gives a table which 2t must be added when known. This table assumes nozzles fabricated from pipe and flanges. If forged weld-
ing necks are used,+ can be obtained from a manufacturer's catalogue.
Consider the three triangles outlined
in Figure 71, 12 and 13. The angle ao in each triangle is the clearance angle for the particular factor illustrated.
Notice that this angle will vary directly with the linear clearance dimension (x) required for the r:ozzle in question and will eeual sin-l -a . As the length of the hypotenuse, (y) remains constant for each vessel diameter under consideration, a gra;ph of "clearance dimension" (x) against t'clearance angle" ao can be drawn for any diameter of vessel. This has been done on the accompanying graph Figure 15 for vessels with a range of diameters from 1 foot to 10 feet in 6-inch increments. The linear distance for the two factors to be considered for the required conditions sho.uld be entered on the graph at the appropriate place, and
56
300 Lb.
400 Ltt
23
294
+
'41 600 Lb.
900
2l1a
2)11o
2\1la
211\s
3
Lb.
Nozzle Slze %
lio
%
7tl
1
t1/\6
Lr9{o
2%
2r916
2t1\a
2)5,1a
371a
t%
%
I'A
2117u
3%
3%
3%
3%
r%
3910
39'ie
39la
4
rrz
2
then the linear distance for factor
Lb.
ils
rll
vessel shell.
150
711a
%
FIGURE l3-Minimum clearatrce between Dozzle necks at the poiDt of entry into the
HALF FLANGE DIA.
PAD _+1 a
2
% t
191o
2'l4e
3%
o "/4
:l%
oY4
4%
2
l11a
311
4
1%
1%
4%
51,\a
2%
5%
3
I%
4
4%
46h
4ra
4%
311
2
411
1%
5
5
5
+
2%
5
5
5%
5%
5r(
6%
4
5
231
6
5%
6
6
7
7%
5
6
3l{a
7
6
6%
6%
7%
ll
6
8
4st\o
I
7%
8
8
8%
e%
E
10
5%
11
8%
9%
e%
t01l
\11,4
10
t2
63,4
13
10
tosz
70%
\ltl
12%
12
t4
7
15
tl
12
t2
t23
13]
71
16
8
t7
12%
t31Z
\3%
t4
743,1
16
1E
I
l9
'13
t41l
14rr4
tStA
l6
1E
20
10
2l
l41r'tr
t5%
75%
t6rl
t7%
20
72
25
t6%
tE%
181Z
19
21
J/2
Insulatlon Note: The figures tabulated above and io Figure 10 are for uninsulated nozzles. For
insulated nozzles where clearance between insulation is required add the thickness of irsulation to the figure obtained for flange clearance dimensions oaly. All figures in inches.
FIGURE l4-Total minimum nozzles. Thess figures are
clearance between nozzle flanges assuming pipe is for
for uninsulated
nozzles.
For insulated nozzles where clearance
between insulation is required add the th'ickness of insulation to the figure obtained for flange clearance dimensions only.
the minimum clearance angle for each nozzle determined as shown in the following example.
Example 1. It is required to find the minimum angular spacing between a 6-inch x 300-pound R. F. rrozile and an B-inch x 300-pound
R. F. nozzle at the same elevation in a tower 2-foot inside diameter and with a shell thickness of three-eighths inch. A combined reinforcing pad is to be used, as absolute minimum conditions are required. The factors to be considered are:
hand edge of the graph and project horizontally until they meet the curve of .D:3 feet 6 inches. Drop vertically from these points and read off the clearance angle required for each flange, i.e.22/zo for the B-inch flange, and 19o for the 6-inch flange. Again using the table in Figure 14 read off the clearance dimension for an 8-inch nozzle neck (4s/6 inches) and for a 6-inch nozzle neck (3fi6 inches). Add to these figr-rres 2t (%inch) i.e. 5rl inches and 4r/16 inches.
1. Clearance between flanges.
These clearance figures are measured along a chord of a circle equal to that of the tower i.e. (2 feet) . Enter these
2.Cleatance between nozzle necks at the inside face of the shell. Using the table in Figure 74 read'
dimensions at the left hand edge of the graph and project horizontally until they meet the curve of D : 2
off the
clearance dimension
for
an
x 300-pound flange (8 inches) and for a 6-inch x 300-pound flange (6sl inches). 8-inch
These clearance figures are measured along a chord of a circle 1 foot 6 inches greater in diameter than that of the tower (i.e. 3 feet 6 inches diameter.) Enter these dimensions
at the left
feet. Drop vertically from these points and read off the clearance angle required for each neck, i.e. 25o for the 8-inch neck and t9z/ao for the 6-inch neck.
The total angle for this latter consideration is greater than that for the
first consideration (+4y4" against +t/r"). Therefore, the practical min-
a
e o @E
F
q
,E
@
=
o
O
tr o N N
tr E
I
='
o 6E
I
@
'g
E F go
o
oZ .r
ba
I k
(n
bo
tr -o
Y<
4o
Et
P.,
:9N gE EZ e=
lo-
I
ro
ri
.E@ _E-@-
=L?
a &
=a h
g
j
o o
= E
:
oogS :6O T riBEs -g>
E c
3-i:E a6= 3 t o.^E g-iF?
e
3
+O o
=EE3 BRS
NSS
SRS-Re@F
@6s
urnu,rurl!- (alq01 ur0/l) saqsul ul elzzoN
n9y=9o@ts@
l0l
6+DN-O
o
uorsuauJl0 stuo/0e13
57
Figure
Locate Tower Nozzles Quickly . . .
16 illustrates normal minimum
conditions assuming separate reinforcing pads, the same procedure can be applied to absolute minimum conditions with a minimum clearance between flanges and a combined reinforcing pad. Figure 15 can be devdoped for vessels over 10 foot diameter, and it can be used for many other purposes than that just described. For instance, angular clearances between vertical lines and platform brackets on towers can be easily determined, once the radial distances from the tower centerline and the linear clearance dimensions are known.
Example 3. Enter the linear clearance dimension (c) from Figure 17
ELEVATION VATION SHOWING PADS ONLY ONLY FIGURE 16-Normal minimum clearance assuming
imum angular spacing for these nozzles will be 45o. Exarnple 2. When determining the minimum angular location for nozzles which are staggered along the vessel shell as shown in Figure 16, the minimum centerline to centerline dimension (x) can be read from the table of data for longitudinal nozzle spacing, Figure 10. (This is accurate enough for all practical purposes al-
PLAN separate reinforcing pads.
though the theoretical distance is a curved surface). Dimension (V) ir set by the designer, and thus the dimension (z) can be calculated. This figure can measured along
then be entered on the graph and the
minimum angle obtained as for "in line" nozzles. This angle, however, will be the complete angle between the nozzle centerlines as shown in the plan view of Figure 16. Although
on the graph (Figure 15) and move horizontally to the curve which gives D equal to twice the radial distance from the tower centerline (r) from this intersection move vertically to the required clearance angle. This application of Figure 15 can be of great assistance to checkers of piping layouts where there are large numbers of similar angular clearances to be investigated. This procedure can be followed for many other instances which arise on layout studies and piping drawings where angular clearances are required and when only linear clearances are known. ACKNOWLEDGMENT The author expresses his thauks to The Kellogg Interr:ational Corluation for permissim to publish this article.
About rhe Aufhor
Brian D. Wookey is a planning engineer for Kellogg International Corp., London, where his duties involve design coordination, vessel design, and plant layout. Wookey received his technical education from the West Ham College of Technology (gained Higher National Certificate and Endorsements). He received his mechanical engineering apprenticeship with Associate Lead Mfs. London, and has been with Kellogg since
FIGURE l7-Method of using Figure 15 to deterrnine angular verticle lines and platform brackets,
58
clearances between
1951
.
Piping of Pressure Relieving Devices Pressure safety valves and safety discs must 'fail safe.' Engineered approaches to piping and support design are essential for reliability
L. R. Driskell
nozzle
Chemical Plants Division, Blaw-Knox Company, Pittsburgh, Pa.
THE MOST important design factor ,about pressure relieving devices is the underlying principle of intrinsic safety. They must "fail safe" or not at all. Therefore, the solution to problems in pressure relief piping must be based on sound design practices. Because failure is intolerable, simplicity and directness of design should be encouraged as a mea,ns to reliability. There are at least four good reasons why the installation of pressure safety valves and discs should be engineered with care: (1) The inlet and outlet piping can reduce the capacity of the device below a safe value. (2) The operation of the device may be adversely affected to the point where the opening or closing
pressure is altered. In the case of safety valves,* premature leaking or "simmering" may occur at pressures Iess than the set pressure or chattering may occur after the valve opens. (3) The reaction thrust at the time the device starts to discharge can cause mechanical failure of the piping. (4) Good design saves maintenance dollars.
order to operate satisfactorily, a safety
should
It
be directly on the vessel
* For sake of brevitv. the term "safetv valve" will be used throuehout this artiele to describe rclief valves, safety valves, and safety-reliel valves.
unobstructed flow between the vessel and the valve. Safety valves protecting piping systems should of course
$e mounted in a similar manner. The device may never be installed on a fitting having a smaller inside diameter than the safety valve inlet
o Stiflen the nozzle
may be connected as
in Figure
1.
Pressure Drop. The pressure drop between the vessel and safety valve
inlet flange should not be so large that the valve is "starved" or chattering will result. Sylvander and Katz' suggest the following limitations:
o The pressure drop due to friction should not exceed 1 percent of the accumulated relieving pressure.
o The pressure drop due to velocity head loss should not exceed 2 percent of the accumulated relieving pressure.
Some safety valve manufacturers suggest a maximum total pressure drop of 2 percent of set pressure. fn the absence of test data, it is recommended that this more conservative
limit be
used.
on a blowdown of 4 percent. Within limits, if the blowdown setting is increased, the pressure drop may be increased proportionately. Remember however that pressure lost in the inlet piping must be taken into con-
sideration when sizing the safety
valve.
with
gusset
plates.
.
a long welding neck ncgzle cut to proper length. This wiiin
IJse
provide added stiffness, w-ithout sacrifice of intennal area, since the long welding nedk rwzzl,e h,as a greater section rnodulus than does the same nomirral sire pipe.
connection. Horizontal vessel nozzles, when used for safety valve mounting,
These recommendations are based
Sofety Vqlve lnlel Piping. In valve must be mounted vertically.
or on a short connection fit-
ting that provides direct and
Overstressed Fiping. It is important that the inlet piping or mounting nozzle on the vessel not be overstressed. The rea,etiorn force at t[.re time of valve opening, along with the forces transmitted from the discharge piping must be considered. To rninimize stra.in f,rorn tlhese sources, keep the inlet piping as short as possible. Considel these remedies for troublesonae situations:
.
IJse an oversized nozzle and re. ducer.
o Orient line-mounted valves to discharge in a direction parallel to
the line upon which they
are
mounted. This method is useful
rvhen the thrust would overtorque the main upon which the valve is mounted, or ca.Lrlse excessive deflection. The lever arm and consequently the moment may be reduced by this method. Also bracing is handled more simply. Safety disc-safety val'".e combinations may occur where the disc out-
let is Iarger than the safety valve inlet. This arrangement (using a reducer) is satisfactory as lbrrg as the assembly is strong enotrsh mechanically.
Block Valves.
Locked-open or
sealed-open block ra.h,rs,
times specified
ale
some-
in relief lines for
maintenance purposes. These valves should be full area gate or plug type. Gate valves should be of the
risins-stem type. The wedge disc should be so connected to the stem, tha,t disengagement is highly improb-
59
Piping of Pressure Relieving Devices . . . able. The valve should be located so that the gate moves horizontally. Plug valves should be constructed
that the direction of opening
so
is
readily visible and unmistakable. Where three-way valves are employed to direct the flow to or from alternate safety relief devices, the valve selected must provide full-area opening at all valve positions. The transflow valve is of this type. Where block valves of this style are used on both inlet and outlet piping, they must be so connected that it is impossible to operate one valve without simultaneously operating the other. The only exception allowed is when the valves are locked or sealed
in
position. The ken
in this case,
must be held by a responsible supervisor.
Low temperature service, below 32o E, may cause atmospheric moisture to condense on the valve seat and freeze. One method which will prevent this is to install the safety with an uninsulated vertical inlet line. This line must be sufficiently lor.rg to cteate a dead space which is adequate to insulate the safety device from the low process operating temperatures. The valve device
must not be allowed to reach a temperature below the dew point of the atmosphere. Consider the fact that
a small leak may exist through
a
safety valve seat. If the warming section of inlet piping does not pro-
protection against it may be necessary to heat the valve by steam tracing or other appropriate means. The designer is
vide sufficient freezing,
cautioned that when the inlet line is lengthened it is usually necessary to brace the line to prevent overstress-
ing by the large bending moments which occur at the time of discharge.
Plugging tendencies in the inlet piping due to coking, salting, congealing, etc., may demand special designs. Consider heating, insulating,
Balanced bellows valves operate practically independent of backpressure up to pressures as high as B0 percent of the inlet pressure. They are limited principally by the mechanical strength of the valve and bellows as established by the manu-
facturer's rating. Of course it must be recognized that the above limitations are exclusive of the effect of back-pressure on valve capacity. If the drop across
the valve orifice falls below the critical pressure ratio the valve
capacity must be calculated on the
of sub-sonic flow.
purging, flushing or blanketing the
basis
device, whichever is suitable. Figure
Piping Guide. Various factors determine the type of discharge piping
2 shows one type of seal which is useful to isolate the valve from the process fluid.
Sofety Vqlve Dischorge Piping. The back-pressure permitted on a safety valve depends on several factors. One of these is the valve's backpressure rating. This is not necessarily the same as the ASA rating of the
outlet flange, but must be obtained from the manufacturer. Conventional safety valves discharging either
to atmosphere or to any other constant pressure cannot tolerate a build-up or rise in back-pressure greater than 10 percent of the net spring setting (spring set pressure with discharge at atmospheric pressure). Even though the back-pressure is constant it must always be at least 5 psi lower than the pressure at which the valve is set to open.
arrangement that should be used. Table 1 is a guide to the selection
of a
suitable design based on considerations which are frequently involved. Hazardous Fluids. Figure 3 should
not be used on hazardous fluids unless the valve is at a considerably higher elevation than the surrounding equipment and the discharge
can be directed away from such equipment. The possible need for a bird screen should be considered. When hazardous fluids are discharged from valves installed as in Figure 4, the terminal point should be at least 10 feet above any walkways which are within a 25 foot radius.
Drain Hole Plug. The safety valve
drain hole plug (Figure 4) should be removed in those services where liquid could gather at the valve discharge. This includes services where condensate may form or where rain or snow may enter the discharge pipe and collect as a liquid in the line. If the plug is removed, the
lnlet piping design . . .
drain hole must be piped for safe if the fluid is hazardous or il the location of the hole is such that sudden discharge through the opening might endanger personnel. If the pipe is not warm enough to melt any snow which may enter it, disposal
a cover must be provided. This may be either a lid as shown in Figure 10
or a light plastic bag fastened around the end of the pipe. Metal covers
J+' ,^oa
u-J \
FIGURE l-Horizontal when used
Flashing liquids, wherein much of
rocrDswPmr
vessel nozzles,
for safety valve mounting,
can be connected t\is wa].
60
in some sizes are also avail-
able commercially.
f-rq
FIGURE 2-Valve can be isolated from process fluid this way.
the liquid is vaporized on relieving, should not be emptied to a sewer or
other ground location without
Table 1 - Design Guide for Discharge Piping UMBER Valve Outdoors Non-Hazardous Serrice -(a)
,{ir
or Gas.
3,(b)
Liquid-,.,--..--..
l(b)
5
Steam or Vapor Disoharge Pipc Sizc to 1". . .
6
.
-l 4
llazardous Service (a) Closed svstem (Lo vcnt sta(k burriirrg stark or s.rul,l,er).... Opcn s1'stem ([o atmnsplrere)
I I
............. ...1 LiquiC--rdt........ . .....1 Cas -.,1,
3, 5
8
FIGURE
3, 1
I
v;;';i,;,;i::::.... . ...1 r.+,c
3-For air or gas service.
5
3,1,6
FIGURE 5-For liquid
I
service.
Low Temperature Service At or below ambient-design discharge pipe so that now or ice cannot accu mulate at any point in the line wbere the temperature may be at or below freezing. Use Figure 3, if possible. Where necessary Figure 4 may be used with &
at
coYer,
Below 32" F-locate safety valve to avoid need lor discharge pipinq, if possitle. Discharge opening and exposed spring must be proteeted lrom the weather. A housing or local heatiug may be required. The discharge, i[ properly designed, may be sealed with a lorv viscosity oiI and covered with plastic to prevent the entrance of moisture. Note s:
(a) []emmablc or toxic
fluids arc considered baz-
ardous.
(b)
Dischargc pipe nol requircd iI outlet over 7 leet rbove walkway andl'or dircctcd away lrom personnel. (c) Carry dischargc outdoors to a safe eleva[iort. (d) Carn to an appropriate drain. (e) Poirrt oI discharge musb lie safe for fire.
FIGURE 4--For air, gas or
steam
servlce.
FIGURE
LONG MDIUS ELBOW
6-For
steam or vapor
PROVIDE HORIZONTAL RUN HERE IF NECESSARY BECAUSE OF EXPANSION
DMIN TO MANIFOLD
ENTRANCE ANG LED
TO REDUCE
FIGURE 7-For steam or vapor
PURC[
TO
ELEVATION
\rrrano*ou
serY-
ice to 3 inch pipe.
'
AS INERT
PROCESS FLLTD/
lvlANrFoLD
FIGURE B-Closed system for hazardous service.
FIGURE 9-Open system for pyropnorrc gases.
6t
Table 2-Safety Disc Piping rlcuf,f,
NUM8EB
Si4h
Y \l
SAFI CLE{P^NG
Dire
12
t3, t4 IT
(a)
I
I 5--_J
-ltGa, l--p^r.8.
tllaEr trd
ro0
rxd.r6.,
t{
Parl,s of assembly 100 lbs. or less lor ease of
haqdline.
(b)
Parts of assembly exceed 100 lbs. and require mechanical Iilting. (c) Vent stack through roof.
FIGURE 12-For lightweight assembly.
lG-A cap like this will protect discharge pipe from being plugged FIGURE with
//.
/_
sT ACK
INDEPENDENTLY SUPPORTE
snow.
HOOK
D
OR
DRAW EOLT
(sEE FIG, 18)
FIGURE
ll-Piping must be ade-
FIGURE 13-For heavy
to prevent sway or vlbration while the valve is discharging.
short stack
proper protection for personnel. The vapor will propel the liquid at high
fully aligned
quately anchored
velocity and may spatter passersby with the hot liquid.
Piping Supports.
Safety valves,
although they may not be included under the heading of "delicate instrumentsr" are nonetheless instruments. They are required to measure pressure witbin three percent and to perform a specific control function. Excessive strain on the valve body adversely affects its ability to measure and control. Supports for discharge piping should be designed to keep the load on the valve to a minimum. In high temperature service, high loads will cause permanent distortion of the valve because of creep in the metal. Even at low temperatures, valve distortion will cause the valve to leak at pressures lovrer than the set pressure and result in faulty operation. The discharge piping should be
62
assembly with
FIGURE l4-For heavy long stack.
supported free of the valve and careso that the forces act-
ing on the valve will be at a minimum when the equipment is under normal operating conditions. Expansion joints or long radius bends of proper design and cold spring should
assembly with
up fittings. In no
case may the crosssectional area of the discharge pipe be less than that of the valve outlet.
Discharge Manifolds. The design of discharge manifolds or vent systems with multiple safety valves in-
excessive
volves numerous factors which have not been considered here. Optimum
The major stresses to which the discharge pipe is subjected are usually due to thermal expansion and discharge reaction forces. The sudden release of a compressible
design will depend upon an overall economic study of the system composed of vessels, safety valves, and discharge prprng. Increasing certain vessel design pressures or changing certain safety valves to the balanced bellows type may decrease the dis-
be provided to prevent strain.
multi-directional discharge pipe produces an impact load
fluid into a
and bourdon effect at each change
of direction. The piping must be adequately anchored to prevent sway or vibration while the valve is discharging (Figures 1 and 11). Pressure loss in the discharge piping should be minimized by running the line as directly as possible. IJse
long-radius bends and avoid close-
charge piping cost significantly. A study of this type is rather complex and is beyond the scope of this article.
Piping For SofeIy Discs. Some of the problems associated with the installation of the safety disc are similar to those of the safety valve; some are entirely different. For instance,
Design Guide [Ergi-ldlallM4 . rlftlE l:Da € rB7
,,/.vN
'llE
l0d M^l. lNct_ F6-
FIGURE l7-Closed
\
system.
.,., ,o ,r,.
L
t- 7_l lLHook detail
FIGURE 1tr-Double disc with light-
FIGURE lLDouble disc with
weight assembly.
assembly.
similar).
the use of block valves in conjunction with a safety disc calls for the
smaller than the pipe size of the disc receptacle. If an arrangement of this type is desirable, the pipe diam-
effective orifice area of a safeiy valve of the same pipe size. Consequently, the pressure loss in the piping will be of greater importance in the case
same design practices recommended
heavy
for the safety valve. Protection against plugged inlets, freezing, drainage of the outlet and handling of flashing liqriids requires similar
eter must be calculated on the basis
treatment. Stack covers must be pro-
however, must have an area which is at least equal to that of the receptacle in order to comply with the
vided. Since the safety disc has no moving parts it is not as sensitive to overstressing as is the safety valve. IIowever, care must be used in bolting up the assembly so that the diaphragm is not reduced in cross-section or
damaged in any other way by high or uneven flange pressure. Outlet Piping. The size of outlet piping required for a safety disc is
not necessarily the same as the disc receptacle size. Discs are frequently sized on the basis of pressure requirements r:ather than capacity requirements. In such cases it is possible
for the outlet piping to
be
of the relief capacity requirements and the maximum allowable upstream pressure. The inlet piping,
ASME
code.
Pressure Drop. The pressure drop allowed through the inlet and discharge lines is unlimited as long as the capacity of the line is adequate for the relief requirements. That is, at the required flow rate the vessel pressure must not exceed the maximum allowable accumulated pressure. fn sizing a safety disc, it is
usually assumed that the entrance loss at the nozzle is the governing restriction insofar as capacity is concerned. Thus the effective orifice area is considerably larger than the
FIGURE
(Draw-bolt
of the disc. It is advisable to check the effect of line pressure drop on any safety disc installation rvith a low rupture pressure or a long discharge line.
The allowable pressure
loss
through the discharge pipe, exclusive of the entrance loss, may be determined as follows: P
(
P^rn
where, P, : Accumulated relieving pressure, psia
P :
Pressure inside relief pipe
near the vessel, psia
rc : Critical pressure ratio for sonic velocity
2 \ - /\s1/
k/(k-1)
63
Piping of Pressure Relieving Devices . (See values
k:
If
of r" tabulated
below)
ratio of specific heats
P exceeds P,r"
it becomes
neces-
sary to size the safety disc based on subsonic flow. Back Pressure. The pressure limitations referred to above apply only
to built-up pressure necessary to expel the fluid through the discharge piping after the disc has ruptured. Back-pressure which is present before the disc ruptures is another matter, since it affects the rupture
If
the back-pressure is constant, the rupture pressure must be specified based on the difference between the maximum safe vessel pressure and the back-pressure. If the back-pressure is variable as is the pressure.
case when several
pressure relief
devices discharge into a common header, it cannot be allowed to increase by more than 10 percent of the maximum allowable working pressure. Discharge to pressures less than atmospheric is acceptable, but the disc rating may not be increased to compensate for the added pressure difference because failure of the
vacuum would prevent the disc from rupturing at the pressure specified
by the vessel code. Of course if the equipment being protected is not covered by the vessel code, the limitations cited are not mandatory. The ASA Code for Petroleum Refinery Piping, for instance, permits temporary conditions of overpressure.
(")
forces:
internal pressure, (b) dead weight of piping, (c) thermal expansion or contraction of either the discharge line or the equipment upon which the valve is mounted, and (d) the bending moment caused by the reaction thrust at the discharge.
All of
these stresses except the latter are common to practically every problem.in piping stress analysis and will not be covered here. The magnitude of the reaction force resulting from the instantaneous release of a compressible fluid may be calculated from the two simple for-
F,
Piping Guide. Table 2 is a guide to various types of piping designs recommended
for safety
discs.
Reqction Forces. The total
stress
imposed on a safety valve or its piping is caused by the sum of these
64
is possible for air to be re-
: (k+ 0.2) AP1
For a safety disc . F, : 0.63 (k + 0.2)
:
for
1.4
design.
Calculation of the reaction force for liquid service demonstrates that this force is negligible. Ilowever, since it is usually possible to trap air or gas in any pressure system it is recommended that
k:
7.4 be used
in the above formulas
a basis of piping design for liquid service. Ifere are values of k which can be safely used for common fluids: as
Fluids Air
and diatomic
gases
Steam
k
r"
1.4 1.3
0.53 0.55
1.3 1.67
0.55 0.49
NH3' CO2' CH' and SO, Vapors Helium, Argon
Vqcuum Breqkers. Vacuum breakers are used on pressure vessels to prevent their collapse should the internal pressure be allowed below that of the atmosphere. Their installation offers few problems. They shoutd be installed with a minimum of pipe since the pressure drop limitations are invariably stringent. Bird screens
For a safety valve
AP1
Where:
Fi : Reaction force, lbs. A : Area of value orifice or disc,
are usually required.
sq. in.
Pr : Inlet pressure at time of opening, psia (set pressure plus 14.7)
k : Ratio of specific heats,
L. R. Driskell is the principal instrument engineer for the Blaw-Knox Co., Chemical Plants Division, Pittsburgh. The Instrument Department, which he heads, is not only responsible for all instrumentation but establishes
the
de-
sign pressure and temperature ratings
of all
pressure equipment, vessels,
piping and
designs
the safety relief
The admission of air to processes may be more
some
hazardous
than the collapse of the vessel. The problem cannot be overcome by merely supplying the vessel with inert gas through a pressure reducing
ce/cu
About the Author
Disc Replacement. The considera-
necessaxy.
k
mulas given below.
tions involved in the design of a safety disc installation are similar to those which were discussed under safety valves. In addition, the design features of the piping should reflect the need for periodic disc replacement. Changing a disc should be an operation which is quick, easy, and as safe as possible. Access platforms should be provided where
If it
lieved from the system under special conditions, use a minimum value of
sys-
valve. Neither the reducing valve nor the source of gas is sufficiently reli-
able. The best solution is to design full vacuum. If a number of vessels are involved it may be economical to connect them to an inert gas system which floats on a the vessel for
gas holder. All valves should be Iocked open and the gas holder should be equipped with a low level alarm. Another method which has been used on very large vessels is to provide two separate sources of
Driskell has been with Blaw-
inert gas. These independent pressurizing systems are then each equipped
the instrument and pressure vessel field for 20 years, having previously been
with alarms to warn the operator when safety depends upon a single
associated
system.
Final Control Elements Committee of the Instrument Society of America.
LITERATURE CITED lSylvander, N. E., and Katz, D. L., The Design and Constructiot of Pressure Relieoinp Systems, Univ. oI Mich. Press, (Apr. 19,+8). ,API RP 52O, Recontnendtd Proctice lor the Design and Construttion ol l'rctsure-Relieoine
tems.
Knox for 12 years. He has worked in
with E, I. du Pont de Nemours & Co., Inc., and J. E. Segram & Sons, Inc. He is also chairman of the
This committee is responsible for all technical activity of the society with respect
to
safety discs.
pressure safety valves and
Systens s
in Rcfircritt, tSr:pt.
1955).
ASME Boiler and Pressure Vesel Code
tion VIII, (1959). t'o it'
,i,,"'ir"ronTi
.
P i pi n
g
H an
d boo
k'
Sec-
McGraw-
NOTES
65
MATERIALS
British qnd Europeqn Piping Specificotions
U.S. Ys.
U.S., British, Germon, French, ond Swedish srondqrds ore compored
Steelmoking Process ond Piping Specs. ASA 831.3
for steel pipe commonly used in process plont pressure service
other hand, both API 5L and ASTM A53 permit undeoxidized Bessemer steel. fn using these specifications, therefore, it is necessary to clearly state any limitations of steelmaking practice that may be felt desirable to en-
J. F. Loncqster, Kellogg International and W. B. Hoyt, The M. W. Kellogg
specifically limits steelmaking processes to electric furnace. or deoxidized Acid Bessemer steel. On the
open hearth
Corp., London, Co., New York
IN nreNv TNSTANoES, it is possible to find European standard piping specifications which may be substituted for ASTM standards. This can be done without any appreciable change in the quality of the material being purchased. Diflerences in steelmaking and tubemaking methods exist, but may generally be accepted subject to certain qualifications. The standards that are considered to be comparable to ASTM specifications are listed, with an indication of the limitations within which the list
is
applicable.
Comporisons for the Averoge Engineer. In selecting a suitable piping specification for refinery or process plant
it is rare that the average engineer needs more than a superficial understanding of what the specifications cover. Provided the chemical composition is of the desired type, the strength characteristics and dimensions are known, the purchaser relies on the specification title and scope to testify that the pipe will be suitable for the intended service. This reliance is justified, because national specifications have been prepared by groups of experts who have extensive knowledge of the production and usage of the pipe. For this average engineer, the comparison tables in this paper will be sufficient to advise which foreign specifications are comparable to the more familiar ASTM and API specifications. It is the intent of this paper to discuss some of the more important differences and to indicate where such diflerences may limit the selection of foreign specifications for piping designed on the assumption that IJ.S. materials and standards are used. The specifications tabulated herein are limited to pipe such as is commonly employed in process plants for pressure applications. The discussion applies equally to all tubular products for pressure containment, but the specifications available are too numerous for listing here. service,
sure adequate quality. European pioducers have made considerable efforts to improve the quality of Thomas steel (also called Basic
steel) since World War II, particularly in Belgium. Thus, it is now possible on a regular basis to produce Thomas steel having maximum sulfur and phos-
BesSemer
phorus contents of 0.05 percent and a maximum nitrogen content of 0.009 percent. Since the nitrogen content of open hearth and electric furnace steel lies typically in the range 0.003 percent to 0.012 percent there is no metallurgical reason to regard such an improved Thomas steel as technically inferior. To obtain the optimum of
price, quality and availability, therefore, Thomas steel (which is permitted by most of the European pipe specifications) may be regarded as acceptable to the ASA 831.3 Code if it is fully killed, or if it meets the composition limits stated above. In the table of equivalents (Table 9) such a requirement is included as Note 1. Generally speaking, the improvement of old, and the continued multiplication of new, steelmaking techniques means that specifying the type of steelmaking furnace or converter is no longer of much value as a means of defining the end product. In the future, specification writing will need to depend more on a definition of the required mechanical properties and chemical composition-particrrlarly nitrogen and residual elements such as chromium, nickel and molybdenum-rather than on limiting the permissible means of making the steels.
Deoxidotion Proclice. So far as deoxidation is
concemed, carbon steel may be divided into three categories:
rimming steel, killed and semikilled steel. Rimming steel is often used for fumace welded pipe. The low carbon skin of skelp rolled out from a rimmed ingot is particularly good for pressure welding and the finished pipe has good corrosion resistance on both inside and outside surfaces. Seamless pipe made from rimming
for non-corrosive service. National standards for carbon steel pipe used at higher
steel is, however, only acceptable
67
l-$eqmtsss Cqrbon Steel Pipe for Normql lufis5-About
IABLE
Standard
Irance Germany
GAPA\-D 11] A 37C
0pen bearth or electrjc
DIN
Electric furnace,
1629
hearth or
veilerAq 35 UNI 663
Sredeo
sIS
|
n,,
Sircs
lllax. l
lMax.
l-.-.
'r,
lrlslo,r,"' Ma*. Si
psi
(
1233-05
-l-.
Stre.ss psl
Maximum
A.lBr
52.500
furnace
St. 35
Italy
*c"-
SteelmaIing Practice
psi Ulfimote Strength
MECEANICAL PROPERTIES (Minimum)
CHENIICAL COMPOSITION % Countrv
5O,OOO
1i
Heat Treetment
Recommended Temperature oF
Cold-drawn pipe to
661
be normalized open oxygeo con-
0.1
I
005
005
3 1,000
None-gcnerallJ,hob drawn
Not specified
Killed steel, process un-
50 000
0.17
specified.
0.10
-0.5
005
0.05
to
Cr 0,2
30,000
50.000
30,000
50,000
2t
Non
Cu 0,3
e
J,
CoLdrlrawn pipe lo be heat treabcd
1,07t
N u009
0.10
DI\:101)
(See
D,
t
,07+-
D
United Kingdom
BS.360r
IIFS
22
CDS 22
ASTM A 53 seamles
Opeu hearth, electric fuDace or oxygeD coDYer-
021
0.70
005
0,05
\fax
30,000
ter.
Cold
4i 2D
50,000
ot-
Type S, Gr. A:
0.048
30,000
n,,l
Opeo heuth, bmic oxygen, acid Besemer or electric furnace.
48,000
3,i0 (See BS,335I)
None
1.09b
1
,00
100
(See
ASA 831,3)
(See
ASA B3t.3)
t
+ --
D
E.S.A.
API 5L Lioe pip seamless
Grade
A:
Open hearth, electric furnace or bmic
0.22
0.90
0.01
0.05
30,000
Max.
48 000
None
I 100
oxygeD.
'A:
Dietaoce between inside surfaces oI tube.
I B: Distaoce belween platens of press.
| [or
acid Bessemer prodes.
l-$sqmtgss Cqrbon Sleel Pipe Suitoble for Higher Temperotures qnd pyg55rr1s5-About
IABTE
60,000 psi Ultimote Strength
MECEANICAL PROPERTIf,S
Cortry Frence
Stendard
Stcelmalirg Process
GAPAYE 421 A 42 C (Si-killed)
DIN sr
1629 45.4
elecLric
Iurnace
idation Ptactice
(Minimum)
CHEMICAL COTIPOSITION %
Deox-
c-t-
P
s
I o,h;-
Max. M" I Si Mex. Max I
M"*.
Yield Stuess psi
Iiilled steel
Open hearhh, electric
I{illed
furnace or oxygen conYerter
steel
0.22
0..10
l\{ rn.
0.10
o.rE
0.05
Cr 0.3
ta
37,000
Flatten ng Test Stress psr
Bi
60,000
5t
6 1,000
1_07r
0.35
ture
oF
662
Nol specified
t .07 + --
t)
DIN sr
171751 45.8
Not speciEed
I(illed
022
steel
0.15
ll
in.
0.
l0
005
to
005
N 0.0I0 for
37,000
6J,000
1.07t
basic Besor
semer
0.35
t
Or con-
.07
verter
Sweden
Tem pera.
Nornalize
Germaoy
Italy
Marimum H€at Treatment
Aq 45 UNI 663 D (Si 0.1/6 nio.)
Not speci6ed
sIS
Not specified
1435-05
Itilled steel
Killed
0.22
steel
0.60 Nl
in.
0.t0
0.05
0.05
to
0,{0
Cr 0.2 Cu 0.3 N 0.009
Normalizc, anneal or rluench and temper
tJZ
\,'5
in2
+ -t)
34 000
64!000
37,000
64,000
1t
spp116",1
Colddrawn pipe to
1.05t
i
s37
be heat treated
.05+ D
Uoited Kirgdom
8S.3602 HFS 27 (Si-killed)
Opeo hearth, electric furnace or basic oxy-
Iiilled
025
0.30 0.70
to 0.8i
0.29
0.
to
sleel
gen.
ot0
0.(E
005
36,000
60.000
Colddrawn pipe to
6h
3D
be heat treated
or-
!i50 .See BS
.335r)
4
u.s.A.
ASTM A106 Grade B
Opeu hearth, electric furnace or basic oxygeD
Iiilled steel
030
to
l0
0.0.1{
005
35,000
60,000
I .07
'A:
Distance betweeu inside surfaces oI
tube.
t B: Distance between platens of
press.
cal service,
but for normal duties, the deoxidation practice is not normally specified. Nevertheless, most seamless pipe is
such material to be supplied. Although responsible manufacturers would not iupply rimmeJ ,"u^l"r, pipe for
68
+ -n
be beat treated
1
I0L)
(See -{SA B3 1.3)
I Similar to DIN 1629 Clas 4, but with guaratrteed elevated teEperature propertis.
temperatures and pressures commonly require killed steel,
either killed or semikilled, except where specially ordered. An exception to this rule is Germany, where rimmed seamless pipe is a commercial product and where both DIN 1629 St 35 and DIN 17175 St 35.8 would permit
ColdJrawn pipe to
1.07b
M rn.
1.06
for
it
seamless
s. Table
is wise to specifically pipe when ordering
9 includes such a require-
Pipe-moking. In many respects the tube-n.raking methin Europe are the same as those used in the United States. There are some diflerences, however. Flash butt welding of line pipe is unknown in Europe. ods used
More important: electric resistance weldecl pipe, which in quite large diameters in the United States, is sometimes available only in the form of small diarneter tube on the other side of the Atlantic. ERW pipe ordered in Europe may be delivered as fusion welded if it is a large size, and fusion welded pipe may or may not be an acceptable alternative. Spiral butt welded pipe is finding increasing use in Europe. This product must not be confused with spiral welded pipe to ASTM A211, which may be lap or lockseam jointed. The European material (as specified, for example, in B5.3601 SFW) is a double submerged arc welded pipe which, manufactured with adequate quality control, has been applied successfully to refinery offsite can be obtained
About ihe quthors J. F. LaNcasron fs a mo,terials consultant with Kellogg International Corp,, London. He is the metallurgi,st
t"esponsible f or selection of matec'ials used in oil refi,nery and petrochemi,cal
engineering, Mr. Lancaster holds a B. Eng. degree from, Lberpool Uniaersity, is a fellow in the Institution of Metallurgfsfs, is o, member of the Institute of Weld,ing, the lron and Steel Institute, and the Institute of
llletals. He utorked u;ith the Royal Engineers and u_tas a metallurgist at A.P.V. Co. before ioi.ning Kellogg in 1957.
duties.
It is always worth while to pay attention to the quality of welded pipe by quoting the correct specification and by adequate shop inspection. API 5L and ASTM A155 require electric fusion welds to be double side welds, as do DIN 1626 Blatt 3 and Blatt 4 and B5.3601 SFW (Spiral weld). ASTM 4134, DIN 1626 Blatt 1 and Blatt 2 and 85.3601 EFW, on the other hand, permit single side rvelds. The quality control measures called for in the specifications permitting single side we.lds do not guarantee freedom from defects, so that they are not suitable for the more severe duties.
Gorbon qnd Gorbon-Mongonese Steei Pipe. Tables 1-4 list United States and European specifications for seamless and welded carbon and carbon-manganese steel pipe. Each table is intended to comprise material that is equivalent in tensile strength and similar in over-all characteristics. There is a general difference in character between most Continental European carbon steels, on the one hand, and British and United States steels on the other. Con-
tinental specifications indicate a slightly lower level of carbon content and higher yield to ultimate strength ratio for quality carbon steels. This tendency has been influenced by an increasing use of yield strength as a basis for design in Continental countries and a desire to achieve optimum weldability. In general, the Continental tendency is to achieve the required tensile properties through slightly higher manganese and lower carbon content than the corresponding American and British material. Improved yield to ultimate ratio is frequently obtained by aluminum treatrnent. Whereas British and American carbon steels may be semi-
killed, silicon killed or silicon/aluminum killed, there is a tendency in Continental European practice (particularly in Germany) to produce either fully killed aluminumtreated steel or rimming quality. Such differences in deoxidation practice (which are applicable to both plate and pipe) may have an effect on the properties of carbon steel. Aluminum treatment, for example, combined with the appropriate rolling technique, can reduce the grain size and thus improve the notch-ductility as well as increase the yield strength for any given ultimate strength. It has also been suggested that by fixing free nitrogen as aluminum niride this deoxidation practice may reduce the creep streng*r of carbon steel. The elevated temperature properties of steels produced in different countries may not be identical and, in particular, the ASTM values for creep properties may be not applicable to some European steels.
W. B. Hoyr is the chief materials engineer with The M. W. Kellogg Co., New York. He is a staff consultant to the Design Engineering Department on materials. Mr. Hoyt attended, the Junior College of Connecticutt and, Brooklgn Polytechnic Institute. He has been uith Kellogg for 32 gears. He is a, member of the ASME Comruittee on Code for Boilers and Pressute Vessels, chuirman of ASTM Committee A-7, Subsection 11, Steels for Eoilers and, Pressure Vessels. He is a membet of ASTM, ASME, AWS, NACE, RESA, and, ASM.
The need to specify deoxidation and steelmaking techniques more closely for carbon steel plate material is now recog'nized to some degree in standard specifications. The most sophisticated example of this trend is 85.1501 : 1964 (Plate Steels for Pressure Vessels) which comprises a number of grades in which the deoddation practice (e.g. killed or semikilled) is specified, together with the deoxidant used. Grain refining additions are also covered by this standard. The Ge.rman DIN 17100 for structural steel plate (specified for welded pipe to DIN 1626) lists the disignations U (rimming), R (killed or semikilled) and RR (Specially killed). For quality grades the purchaser may specify the deoxidation practice according to these desig-
nations.
The recent ASTM standards for carbon steel plate ASTM A515 and A'516 do not attempt to define d6oxidation practice, but rely on control of chemical composition and inherent (austenite) grain size to achieve ihe required properties. ASTM ,4,515 is intended for elevated temperature use and specifies coarse grained steel with silicon between 0.15 percent and 0.30 percent, while .4'516, for atmospheric and lower temperature service, requires fine grain and controls both manganese and silicon contents. ASTM ,4.524 is a pipe specification covering fine grained stee.l similar to the plate specification 4516. The specification for killed steel pipe for elevated temperature se.rvice, A106, on the other hand, does not contain any requirement for coarse grain and would not prohibit the supply of an aluminum-killed fine grain steel. It is possible that, in countries where aluminum treatment is the ru.Ie, steel ordered to ASTM specifications may also be aluminum-treated, with potentially Iower elevated temperature properties. A conservative practice for critical piping operating at elevated temperature is to use tlre nationally-accepted design stresses of the country of pur-
69
3-Welded Cqrbon Steel pipe for Normq! Duties_About
TABTE
CouEtry Germany
Plate Spccification
Stendard
DIN
1626
Blatt
DIN ];
3
](](]
CHTMICAL COMPOSITION %
IIql ll eldiog Process
SteelmaIirg Process IiilJed or rimoring stecl:
TreatmeDt
an.r
process
After l{elding
C
Ilar.
Double-side lusion neld or any type of prsure weld
No! rquired
0.17
Electric resistance weld
Requ ired
0,l7
Nln
\r
P
S
Mar.
Otbcr
Max
Mar.
005
0.05
005
005
006
0.06
0.05
005
(including buti weJd).
sls
Sreden
sls
1233-06
IiilLed steel
1233
-0.5
0.
r0
to 0.10
BW 22
ER}I Unitrd Eiugdom
o
22
EI,'\Y
Not speci6ed
Continuous furnace butt
\ot
Open bcsrth, elec[ric furnace or oxygeD conlerter.
Illeclric resistance rreld
Not required
Open bearth, electric fur-
Electric fusion rreJd (single
Nol required
006
006
0.06
006
0,0J5
0.0rii0
nace or oxygen cooYerter.
j
reid
required
Open bearth, eleel,ric [urnace or orygetr conyerter.
Spiral seam double-side electr:'c Iusion reld-
Not required
Butt red
0pen herrth, electric fur-
Co[tinuous furnace butt
Not required
cl,
q
of
ox),gen coDverter
0.30
weld.
to 0.60
1
Acid Bessemer
Electric qeld or sub-
I
070
or douLrle side)
SFl\'
nsce
020
0.il
0.30,/0.60
uerged arc weld Grade
Open hearth, electric furnaco or lrasic oxlgen,
lllectric resislance *eld
Typc F l'urnace-welded
Open hearth, electrie Iur-
Continuous furnacc bull
submerged arc rreld, ble side.
or Cou-
Not required
021
0.90
0
0
0t
0.065
005
Dax.
a
nace, acid-ox5' gen-stearn,
Not required
0.08
rveld.
or Uasic ox1'gen. ,{cid Ressenrcr Type E Grade A-IIRW
0 13
Open hearth, basic ox1'gen.
lilectric resistance reld,
Not required
Operr hearth, basic or1'gen or electric frrrrrace
Electric fusion (automatic,
Not required
0,05
U.S.A.
Fusion welded Plate
A2{5 Grade B
Pioe I 6'aod over. dia.
sinsle or double side).
025
A283 Grade B
001
0.05
(Acid) 0 oii Basic)
005
0 A285 Grade B
0.20
080
0.1
see spec.
FBQ: 0,0
1
Flange: 0.05
ERW 30'and under Grade A
Fusion relded Pim and ovcr Grade
i
4'
0pen bearth, breic oxygen or electric furnace,
Electric rmistaace selded
Not required
Open heartL, basic oxlgen or electric furnace-
Fllectric fusion (automatic,
Not requircd
aingle or double eide).
0.30
0,05
006
rl-0
0.05
1
to 1.00
'A;
Distance betreen inside surfacee of tube.
I B:
Diataoce betreen plateDs of pres.
chase whenever these are lorver than the ASA 831.3 values (Note 4 of the table of equivalents) . In other words, the list of equivalents for carbon steel holds good up to 650o F, but above this temperature special consideration
must be given to material according to the country in which the piping is bought. The country in which the piping is erected will also influence material selection: in France, Germany, Holland and Italy stearn piping comes under the jurisdiction of the local Code authorities, who are not so liberal as ASA in the upper temperature limit permitted for carbon steel. In any event, u'here reduced
70
i
Aa
limitetl,by ASA BBl.3:1962.
design stresses
for carbon steel are in force, it
becomes
economic to change to alloy at a lower temperature than would be the case with ASA B31.3. The argument set out above applies with greater force, if anything, to plate-and therefore to large diameter welded pipe.
Ferritic Steel
for Low Temperqture Duties. British
and German standards offer carbon and nickel steel for use at subzero temperature. The British steels are impact tested carbon steel (down to -5Bo F) and 3/2 percent
Cr 0.2 Cu 0.3 N 0.009
a Cr-Cu-Al steel. Similar to the situation in Europe, the nickel steels are available in the United States, but the procurement of all the needed piping components in one grade of steel is frequently so difficult that the use of a stainless steel may be preferred. steels and
5O,OOO psi
Ultimqfe Strength
MECHANICAL PROPERTIES (llinimum) Maximum
FLATTENIi-G TEST Yicld Stress psi 30,000
Bi
Ultinate Stress psi
Temperature "F
t.09t
48 000
llaterial:
572
t
.ull
+D
2D \Ye!d; 31,000
50,000
\ot
50 000
Marerial: 5t D
weld. 30,000
50,000
58 000
It
7s2
required
200 (BS.3351)
-
2D or
850
--2 300
Mrlcriol:3t rrd.
45 000
Meterial:0.6D
weldr 30.000
50,000
30 000
48 000
400
3D
-4 llaterial:
weld.
400
D
-
1100
(ERI9 onlv)
2D
_
15,000
1\'eld'
3D
llaterial: 30,000
50 000
30 000
48,000
llaterial: \\'eld
'
100
I 0.6D
D'
1
100
--3
2D
-3 30 000
49,000
300
l;,000
50,000
300
27,000
50.000
300
3u,000
18.000
D Matcrial:
Weld:
1
100
-
2D
-3 30.000
48,000
temperatures over
for carbon will apply. steel also presents problems.
85.3604 does not include the alloy at all. French, German and Swedish standards do have this type of steel, but the minimum molybdenum content is specified as 0.25 percent, as againsg 0.44 percent for Grade Pl of ASTM 4335. Where carbon molybdenum steel is used as a hydrogen resistant material, this diflerence may be significant. For hydrogen service the French, German and Swedish car-
bon-molybdenum steels are not equivalent to the Ameri-
3 25 000
operating at
1,0000 F the considerations already outlined steel pipe operating at elevated temperature
Carbon-molybdenum
BBND TEST: Matcrial: 2t rad. Weld: 3t rad.
25 000
of any consequence is that German and Swedish standards call for normalized and tempered pipe and list ,higher yield and ultimate strength figures than the ASTM specifications, which permit pipe to be annealed or normalized and tempered. The creep rupture properties reported for German steels are lower than those given in ASTM publications at tempeatures over about 1,0000 F. Thus in selecting European equivalents for ASTM chrome-moly grades
BEND TE$T:
Wd& St rrd. 58,000
Low Alloy Sleel for Etevoted Temperoture Service. The chromium molybdenum steels currently listqd by European specifications are almost identical with the corresponding ASTM composition. The only difference
300
nickel steel, both virtually identical with similar ASTM grades. German materials are impact tested carbon steel and 5 percent nickel alloy, and are standardized in Vereine Deutsche Eisenhuttenleute Stahl-Eisen Werkstoffblatt 680. In practice, 3/z percent nickel steel is equally
available in Germany-or rather, equally unavailable. Indeed, nickel alloy is difficult to procure anywhere in Western Europe and, for short delivery, it is often necessary to substitute austenitic chromium nickel steel. ASTM A333 covers six grades of impact tested pipe: two grades are carbon-manganese steel tested at -50o F and the other grades are 2/4, 3/z and 9 percent nickel
can.
For strength, the low-molybdenum German steel 15 Mo 3 is, like the chromium-molybdenum grades, reported to be lowe.r than Grade Pl over 1,0000 F. On the other hand, the minimum specified yield strength is within the scatter band for the ASTM material. Corrosion qnd Heqr Resisting Steels. Generally speaking, the common grades of austenitic chromium nickel steel are readily available in Europe. European specifications (85.3605 in particular) list a number of compositions that are identical with ASTM stainless steels and includes the H grades, which are 0.03 percent to 0.10 percent carbon steels intended for high ternperature duties. Extra low carbon steel is also in better supply in the United Kingdom than was the case at one time. The latter material is also available in Continental Europe. Dimensions qnd folerqnces. Standard dimensions for pipe are given in 85.3601-5 for seamless and rvelded carbon and alloy steel pipe, in DIN 2448 (seamless pipe) and in DIN 2458 (welded pipe) . All these standard sizes have been written to fall in line with I.S.O. Recommendation R64, which gives outside diameters only. Up to an outside diameter of 5/z in. ISO R64 follows ISO R7, and above this dimension follows ASA B2.1: 1945 and API 5L. Wall thicknesses for the British standards include some of the commonly used schedule sizes, as do the two German standards, However, the German standard wall thickness is less than the API standard weight (schedule 40), so that to specify schedule 40 pipe to DIN 2448 it is necessary to select one of the special wall thicknesses given in that standard. In this way a fairly good match for API rstandard weight pipe may be obtained. but
7l
TABLE
4-Welded Cqrbon
Steel Pipe Suitqble for Higher Temperotures qnd pys55rrys5-About
60,000 psi Ultimcrte Strength
NTECHANICAL PROPERTIES (Minimum)
CEEMiCAL COMPOSITIO!{ Plate
Coutrtrr
Staodatd
DIN 1626 Blait 4
Germany
Steel Process
Welding
Killed, rim-
Dbl. side elec fusn weld or
Spec-
DIN
sr
17100 12-2
C
Heat Treaa
Process
miDg stcel, atry process
elec rest
100/6 destruct
Mr
Max.
NR
si
o25
P
s
Max
Max.
0.06
0.05
70
PlrttoirI for
Yield
Other Msx.
Stress psi
Stress psi
37.000
60 000
a.
Mar. Temp "F
B' Material: 1.07r
weld
tot-
t
.07+-
t6t-
rDg
D
2L
Weld:
sIS
Swedeo
1435-06
sls
Killed
1435
elect. resist
steel
Reqd
0.22
0.6
weld
0.10
0.05
Cr 0.2
0.05
0u 0.3 N 0.009
to
EID.
0.10
United Kingdom
BS.3602
EFW 28S
u.s..{.
ASTM A,551
Open hearth, elect. furo.,
Dbl- side elec. fusiou weld,
or Oz convtr Silicon killed
radio-
spot
KC 60 Class 2S
0.10
to
to
1.20
0.35
0.80
0.15
005
Ni
0.05
0.30
Not equr4J
33;
36.000
62,500
BEND TEST:
s50
Cr 0.25 Mo 0.10
2t radius on weld
Stres reliel over fun
0.2{
Eax.
See spec.
32,000
60 000
to
wall
Distance between platens oI press.
1 As
r00
BEND TEST: 2t radius oo
0.30
weld
uotr destruct uot reqd.
t B;
A: Distance betweeo iuside surfaces ol tube
0.60
61,000
Cu 0.20
ual or auto. fusion weld,
kifl
'
0.25
Rotl
graphed
Dbt.sidemu-
Open beartb, elect. ftrm., or Oz couvtr. Si.
A 201 Gr. B
Pin. by Eot
-
37,000
limited by AS.{ B31.3:
1962. g Class i requires sLress
relie[ and 100/, radiography of weld*
fABtE f,-(q1l6n-Molybdenum qnd Chromium-Molybdenum Alloy Steel Pipe for Elevqted Temperoture Duties
ilIECHANICAL PROPERTIES
CHENIICAL COMPOSITION 70 C
Altoy C 0.3
-\to.....
Standard
IIax
tr{o
si
AFNOR 15 D 3 GAPA\ E
0.20
0.50/0.80
0.15l0.35
Country France
Ni
Maximum
(Minimum)
S
Yietd
Ultimatr
and
Mo
P
Stre.ss psl
Stress
Cr
0.30 mar.
0.25/0.35
0.01
3S,000
62 500
ps:
Heat Treatmeot Annealed
ard
C
\
Germany
DIN
Swedeo
sls
):1I0.....
U.S.A.
\lo,
Cr ,rl
I Cr
fi \{0..
trZ Cr !,i \1o
2V Ct 1Mo.
6Crl!\{o.., eCrl]Io
72
17175 15
Mo 3
or
Recommended Temperaturc "F
normalized
97;
bempered
0.20
0.50/0.80
0.15/0.35
0.25/0.35
0.0
1
41,000
6{ 000
Normalized
0.20
0.40l0.80
0.15l0.35
0.25/0.50
004
41,000
64 000
Normalized and teupered
AST\1 A335 Grade Pl
020
0.30/0.80
0.10/0.50
0.44l0.65
0
041
30,000
55,000
Annealed or normalized and tempered
t100
Fraoce
AFNOR 15 CD 2.05 GAP.{VE 222
0.18
0.50/0.00
0.50 max.
0.40/0.65
0.45/0.60
0.03
39.750
61,000
Ncrmaljzed and teoperer
1022
u.s.A.
ASTNI 4335 Grade P2
o20
0.3c/0.6r
0.10/0.30
0.50/0 81
0 4110 65
004
30,000
55 000
Annealed or noroalized and tempered
Ir00
Germany
DIN
0.18
0.40/0.70
0.15l0.35
0.70/'1.00
0.40/0.50
001
42,500
61,000
\ormalized aod teupcrer
Swedeo
sIS 2216-05
(I15
0.40l0.90
0.15l0.35
0.70/1.10
0.40/0.70
001
12 500
61.000
\ormalized and temperer
United Kingdom
85.3604 HF 620 or CD 62(
015
a.40/0.70
0.10/0.35
0.70l1.10
0.45,/0.65
005
33 600
60,500
\ormalized
t200
U.S.A.
ASTM A335 Grade Pl2
015
0.30/0.61
0.50 max.
0.80/1.25
0.44/0.65
0.04
30,000
60,000
-\nnealed or normalized and tempered
1200
I'rance
AI'NOR
0.r5
0.30/0.60
0.50/1.00
I.0c/1.50
0.{5/0.65
0.03
30 000
61,000
Annealed
10ri;
50,000
71,000
\orroalized and
29
12{5
17175 13
CrMo 44
10 CD 5-05 GAPAYE 222
United I(ingdom
8S.360{ HF
II.SiA.
ASTI{
France
I or CD
l
312 96S
963
remperer
0,15
0,30/0.60
0.50/1.00
r.00/1.50
0.15l0.65
0.01
33,600
60,500
Normalized
1200
c.t5
0
30/0 6u
0.50/1.00
1.00/1.50
0.1{/0.65
0.03
30,000
60,000
.\nnealed or normalized and tempered
12(10
AFNOR 1O CD 9-10 GAPAVE 222
0.15
0.30/0.70
2.0/2.5
0.90/1.10
0.03
30,000
60,000
Alnealed
1
Germany
DIN
o15
0.40l0.60
0.15l0.50
2.0/2-5
0.90/1.10
0.0{
3S.300
6{,000
Normalized and temperet
1022
Sweden
sIS 221845
Gl5
0.30/0.60
0.15/0.50
2.0/2.5
0.00/1.10
0,0.1
38,300
6.1,000
Normalizetl and temperer
1076
Uoited Kingdom
8S.3604 EF 622 or CD 62i
0.15
u40/0,70
0.50 max
2.0/2.5
0.90/1.20
001
33.600
60.500
Anuealed
1200
12,500
73 500
Normalized ard temperec
30.000
6C,000
Annealed or norualized and tempered
1200
62
62
A335 Grade P11
17175 10 CrMoO 10
II.S.A.
ASTM A335 Grade P22
United Kingdom
85.3601
U.S.A.
ASTM A335 Grade
France
AFNOR Z 10 CD GAPAVE 222
IIF
625 or
.0.50
mu.
0.15
0.30/0.60
0.50 max
t.90/2.6
CD 62i
0.15
0.40/0.70
0.50 max
Pi
0.1
5
0.30/0.60
0.50 max
0.15
0.30/0.60
9
11,
c.87/ r.13
003
4.00/6.00
0.15/',0.6,t
0,0.1
30,000
00 000
Not specified
1200
4.00/6.00
0.{s/0.65
003
30 000
60 000
Annealed or normalized and tempered
r200
0.25/1.00
8.0/10.0
0.90/1. l0
003
30.000
00 000
Annealed
I 157
Ewedeu
sIS 2203-05
0.12
0.3clo.6c
0.50/0.80
8.0/10_0
0.80/1.20
003
18 000
i8,000
\orrnalized aod temperer
7202
U.S.A.
ASTM A335 Grade P0
0.15
0.30/0.60
0.25/1,00
8.0/10.0
0.90/1.10
o03
30 000
6C 000
Annealed or normalized
I 200
TABTE
s-Corbon qnd Low Alloy Sieel Pipe for Low Temperolure Dulies. CHE}IICAL COMPOSITION %
Ultimate Stress pst
CouEtry
vDEb
Geruouy
680
TT St
35
N impact tested
I(illed, normal, opn hrtb elec furn Oz
0.40
to
to
coDvtr
0.60
0.35
030
015
to
DVM
0.50
0.35
zverzge
Eh 650 12 Ni t9
udtd
t\
50,000
0.10
0.035
0.05
83:3603 HFS or CDS: 27 LT 50
Kingdom
Q&T
5 kgm/cm2
85,000
min.
ft. lb. min. average 15 It. lb. min, Chu-
As-ro.l or
,r"r*
15 ft. lb. min. aYerage 10 It.
Norm. &
:
Ib. mioimum
20
60.000
Noru
pvv 0,04
P, 0.,f5
ASTM A333 Grade I
15 fh.
JJ,UUU
eyerage 10 ft.
S: 0.06
,rJ*
Open hearth, elect furn
Temp.
Norm.
lb. Din.
or
Ib. minimum
Norm, &Temp.
15 ft. Ib. min. average l0 It.
Norm.
Ib
ol Norm.
oinimum
& Temp.
Open hearth,
9Ni
ASTI{ A333 Grade
lb. minimum
-320
8
. According to AD-Merkblatt W. 10. Ia practice Germu cebotr sttrl t lfith the addition of no 6ller metal in the welding operation..
TABLE
Norm, or Norm,
15 ft. lb, miu. average 10 ft.
eJecl
furn
pipe
my
be obtained impact Cested
at -50'C for ue dowr to this
i
25
&Temp,
o &T
ft. lb. miD.
dbt,
temperature.
/-ps5ignqtion of Corrosion-Resislqni Austentic Chromium-Nickel Alloy
Stee! Used
for Piping
Germany
Nomiaal Conposition
C 19 Cr 10 Ni..-.-.--..-..,..O03 oax C 19 Cr 10 Ni..,..... Titanium-stabilized 18 Cr 11 Ni..- -....... Colmbim+tabilized 18 Cr 11 Ni.......... 0.08% Eax
18
Cr 12 Ni 2% Mo.
Extra low 18
$
12
erbon
18
Cr 12 Ni 2%Mo
.{ISI Tl'p"
rrYerkstofi
Italy
304
x8cN1910
304L
x3cN191l
Jlh
x8cNT18 10 x 8 cNNb 18 11 x8cNDtT12
Designation
X5CrNi189
Sweden
4301
801
10
CrNiTi
18
s22 Ti
4641 1550
X 5 CrNiMo
18 10
4101
X 5 CrNiMo
18 12
4436 4404
2338
822 Nb 845
or 4435
845L
\r811Mo.................,,..,.
TABTE
Utritod Kitrgdom
801L
I X 10 CrNiNb 18 I X
X 2 OrNiMo 18 10
316L
number
846
$-!s5ignqtions of Heql-Resistqnl Auslenitic Chromium-Nickel Alloy
Steels Used for Piping
GERMANY AISI Nominal Composition 0.04/0.10 0.04/0.10 0.04/0.10 0.04/0.10 23
Cr
12
C 19 Cr .10 Ni....... C Titanium*tabilized t8/8....,.. C Colmbiu+tabilized 18/8... . . C 18 G t2 Ni 2rl Mo,.-...-,-.., Ni,....
Tvpe
It{ly
Werkstoff numbcr
CrNiSi 18
4878
Sweden
304H
United Kitrgdom 811
X
321H
12
9
832
Ti
832 Nb
317H 316H
855
309
x20cN2412
310
x25CN2520
in most cases, be outside the limits of the DIN standard. In practice, pipe may be obtained to schedule sizes without difficulty in Europe, so that it is not usually necessary to apply local standards. Tolerances are genefally similar to or within ASTM requirements for the standards under consideration. double-extra-strong would,
Designation
X
12 CrNi 25 2l
4845
236t
805
Toble of Equivolents. Table 9 (next page) "British, French, German, Italian and Swedish Equivalents to ASTM Specifications" has been compiled based on the considerations outlined above. European grades have been selected to give equal or greater strength than ASTN{,
and to show equivalent corrosion
resistance.
73
g-British,
TABTE IIAIERIAL
French, Germon, ltqlion ond swedish Equivolents
U.S. SPECIPICATION Seamless
Grade A Grade B
BRITISH BS.360l t{l'S 22 or CDS 22 HFS 27 or CDS 27
FRENCII
GERM.{r-
DI\
GAPA\-E 41I
A37
A]2
to AsrM
C C
IT.{LI.{N
Notc3
1629
Sr 35
st
Specificolions
15
Aq 35 UNI 663C Aq 45 UNI 663C
sIs 1233{5
sls
1.13{-05
Aq 35 UNI 663C Aq 15 UNI 663C
sls sls
1233{5
Electric resistance welded Grade A Grade B
Carbon sreel
linc
pi1rc
El""t.l"
f,r.t-
welded Grade A Grade B
Furne:e butt welded
8S.3601
ERW 22 ERW 27 BS 3601 (Double welded
EF\4 :2 Et'\\- 27
z
Carbon steel boiler tube,
semles
Servlce
plpe
1626
I
8S.3601 BW 22
DIN
1626 3 St
Btatt GAPAYE
A37C .4.
]II
Fusion r elded
31-2
Sr 37-2
3l-2 Furnace buttrrelded
DIN
1629 35 15
st sr
12 C
1434-05
t2 3{
Electric resistance welded Grade A Grade B
BS 3601
Furnace butt welded
8S.3601 BW 22
ASTM A83
tsS,305!lrl or
DIN
ERW 22 ERW 27
1626
Blatt
3
St 34-21 Electric reslstaDce st 37-2l welded
DIN
1626 Blabt 3 St 3{-2 tr'urnace butt lrelded
2
GAPAVE 211
A37 C
Silicon-killed calbon steel pipe,for high teuperature
Eletric
DI\
Btath
Blatt 3 St
Grade A Grade B
F .a
1625
Blatt 3 St 3{-2i Electric resistance Blatt 4 St 37-21 welded
Seamless
Carbon steel pipe
DIN
fusion rvelded steel
ASTM AI06 Grade A Grade B Grade C
BS.3602 HFS 23 HFS 27 HFS 35
ASTM AI31
B,q.3601
GAPAVE 12I
A37C
Aq 35 Aq 45
A]2C A{8C Et'\\
DIN
1626
Illatt
[]ectril
2
U}lI U)iI
663C 663C
firsion
wclded
ELectric resistance welded
ASTM A135 Grade A Grade B
8S.3601 ERW 22 ERW 27
Electric Iusiou rrelded 6teel fit)e
ASTM A 139 Grade A Grade B
BS.3601 EFW 22
E-lectric-fusion welded pipe tor hrgh temperature
ASTM A 155
steel pipe
Clas
c45
Eervlce
EFW
Dt\
DIN
1626 Btatt 3 mit Abnahmezeugnis C st 34-2
st st
85.3602 UEW 2S
KC 55
KC KC KC
60 65 70
AST-\I A312 TP 30] TP 30]H TP 3(]1L TP 3IO TP 316 TP 316H TP 3I6L TP 3I7 TP 321 TP 321II TP 3]7 TP 3{7H
Austenitic stailless steel plpe
ASTM Grade
-{333 I 1 |
BS 3602
i.--t3 :**-,.,.r" for for alloy pipe elevated temneratube serviie
EFW 23-\
st 52-3 si 52-3
DESIGT-.lTIOli
8S.3605 Grade 801 Grade 8 I 1 Grade 801L Grade 805 Grade 845 Grade 855 Grade 845I Grade 846 Grade 822 Ti Grade 832 Ti Grade 822 Nb Grade 832 Nb
I
F
X
l5o6
\2Cr\i 189 \ 15 Cr\iSi 25 20 \ 5 Crlii.\Io 18 t0
18tl
AENOR
222 15 D 3
er'\bn
rs
5
riol
X
2
iiri
\
10
Cr-\i\Io
wsN
DESIGNATION
0437 5637
SEW 680 TT St 41
.,
10
Ni
liEcNl0
r
\
10
siS'iadd-bz
e'cx'id ri
sis zi;z-oz
2t cN
x:.c:\:.rr-
r2
sIS 2361-02 sIs 2313{2
.\ 8 CNT t8
r0
sis zdiz-bC
25 2{t
18 l0
Cr\iTi 13 I X 10 br\i-\b ls e
isso
8S.3603 2Z LT 50
Cr\i l3 tr
1301
{101/1136
sIS 2353{2
\
8'C\Nb'13 u
z-o;
Pr1
AF-\OR l0 CD
5-05
P22
AINOR 10 cD 9-10
Mo 3 WSN 5123 16 lto 5
DIN i7i75
ra
siS zsii-b,
1-l
DtN ul75 l5
co
Pr2
37-2 42-2
Si 42-2 Si-killed St 42-2 Sikilled
GAPA\'E P1 P2
3
27
2
c50 c55
1626 tslarr
St 31-21 Iliectric resisranrc St 37-2l welded
sIS.2912-05
bruo
DIN 1;175 10 Cr-\lo
11
I
10
sIS
22 16-05
sIS
2213-05
P5
.{FNOR Z 10 CD
P1)
3003
Aluoinum alloy prpe
5151
z
F @
H|2
9
DIN
DI\ DI\
II1 t2
6061 T6
1716 -\1 1716 Al 1716
lln
\Ig
.\l \Is
Ft0 3 FIS
Si
I F3l
composition requirements:
mar, \ 0.000[
mar.
for design in crirical applications. f1': "I\-etded seants Lo be 0on
74
for design in criiical applications.
with
paras. 11.5 aod
ll.6
ol
Which ltoteriql for Process Plqnt Piping? Here ore reminders ol whot nof fo do in specifying piping moterial lor refinery and petrochemicol plant service
83 1)
Dr. Cqrl H. Samons, American Oil Co., Whiting, Ind. RBrrNnn.n oR pETRocHEMTcAL rLANT piping is the Iargest single construction item, representing about 15 percent of the equipment and material cost. However, DON'T expect to have a wide selection of materials. Carbon steel, the low-alloy steels containing up to 9 per-
cent chromium with 0.5
for Pressure Piping (ASA gives engineering requirements for designing and constructing safe piping systems. But, you also know that it does not decrease the need for competent engineering judgment, particularly with respect to pipe materials. This judgment usually comes only from direct experience. However, a review of some of the significant metallurgical and process factors which influence materials selection may be helpfLrl, not to tell you what you should do, but rather to remind you what you should not do. The temptation to spend a little more for pipe to avoid possible trouble is great. But, DON'T select a more expensive material than actually is required unless you know that it has been used successfully before or you are fully aware of all the additional problems that could arise. Otherwise you may be "master-minding yourself into trouble." rleer, you know that the Code
or 1.0 perceirt
molybdenum,
the straight chromium ferritic stainless steels (400 series), and the chromium-nickel austenitic stainless steels (300 series), are about the only ones which have been used successfully.
Nevertheless, materials selection for process pipe is not as simple as this might suggest. As an experienced engi-
Fig.
l-Brittle
'
Cqrbon Steel. Carbon steel is the most common pipe material, but DON'T look down on it simply because it is relatively inexpensive. There are other reasons why the
fracture of steel pipe.
75
WHICH MATERIAL FOR PROCESS PIPING?
..
significant only below -20o F. DON'T be misled. Unless
.
some simple precautions are taken, much steel pipe also is subject to brittle failure at ambient or even higher temperatures. You can see this easily if you try to bend run-of-themill ste.el pipe made to well-recognized specifications.
With some lots, you may have little trouble; but DON'T get overconfident. With the next lot, bought to the same specification and often from the same mill, rejections may run alarmingly high.
Fig. 2-Inside surface of joint in steel pipe with high-tempera-aiid tur-e hydrogen 611aa[ slown by deep etchingl Note that only portions of circumference are attacked. process industries use it so widely. One of its big advantages is how close it comes to being foolproof-most
of the time. But, DON'T forget either, that steel" is a generic term, not
of specification grade.
"carbon
a specific one, even if it
is
Specificotions. Many steel specifications actually cover a wide range of properties because only maximum analysis limits and minimum properties are given. Maximum or minimum specification values are just that. You usually get pipe reasonably close to the specification value but your only guarantee is tllat the pipe will meet the specification, not necessarily the way you choose to interpret the specification. And the very time that you are counting on specific properties will be the time you don't get what you expect. To be sure you get the steel you want, select a specification with maximum and minimum values for both chemistry and properties. Some of the newer specifiations do this, some do not.
Britle Fqiture.
Below some limiting temperature, steel pipe is notch sensitive and can crack at lower-than-yieldpoint stress with little or no deformation or adsorption of energy2 (see Fig. 1). Hence, DON'T use any cjrbon steel pipe at temperatures even as low as 0o F unless the service is completely nonhazardous or you have specific evidence that a particular lot of pipe is resistant to brittle failure at the service temperature. Bessemer steel pipe is perfectly satisfactory for many applications but DON'T use it where unexpected brittle failure would be disastrous. And DON'T confuse modern basic-oxygen steel
with
bessemer steel. Although the basic-oxygen process resembles the bessemer process, bessemer steel contains
more phosphorus and probably more nitrogen. This increases the tendency to brittle fracture at ambient and lower temperatures. IJnfortunately, for many years construction codes allowed the same design stress from -20o F to 6500 F. This implied, although not intentionally, that brittle fracture was
76
ERW-Pipe. If run-of-the-mill pipe inconsistencies disturb you, and they should, inquire about ERW (electrical resistance welded) carbon steel pipe. This has more consistent properties than the usual steel pipe. You should be able to buy ERW-pipe for essentially the same price as pipe meeting your old specifications. It is made from fine-grain, fully aluminum-killed (0.02 percent minimum residual), basic-oxygen steel containing 0.08 to 0.15 percent carbon, 0.27 to 0.63 percent manganese, 0.05 percent max. sulfur, and 0.035 percent max. phosphorus. In the usual normalized condition, it has a minimum teruiie strength of 40,000 psi, a minimum yield strength of 30,000 psi, and a minimum elongation of 40 percent in two inches. Low-temperature impact strengths have been good, although not guaranteed, down to -50o F. The combination of low carbon content and high manganeseto-carbon ratio increases resistance to cracking and brittle fracture but still provides adequate control of mechanical properties so maximum values need not be specified. DON'T have qualms because ERW-pipe is made from strip. Rolling deforms strip to a greater extent and more uniformly than the wall of most seamless pipe is deformed. Strip can be made with both surfaces clean. It can be inspected readily. These features give you confidence in both the inner and outer surfaces and the uniformity-of-thickness of welded pipe. With selected carbon steel strip, modern automatic fusion welding pre duces reliable longitudinal seams, and a normalizing heat treatment after welding removes all evidence of weld structure.
Gentrifugolly-Cosl Pipe. As wall thickness both
increases,
pipe become increasingly diffi. cult to fabricate. Ifowever, DON'T become alarmed if you need heavier pipe. Modern centrifugally-cast steel pipe is a common product, and simple heat treatment develops a suitable metallurgical structure. Although pipe is cast in lengths shorter than you may be used to, these seamless and welded
can be butt-welded together into any lengths you want.
High-Temperqlure Hydrogen Attock. As service temperature increases above atmospheric, the likelihood of brittle fracture decreases, so carbon steel still may be the best material to use. But DON'T forget the pipe selected must resist process deterioration, and DON'T think that deterioration means only corrosion. For example, if process atmospheres contain more than 100 psig partial pressure of hydrogen, watch out, you may be headed for trouble (see Figure 2). As a competent refinery engineer you know about Nelson's hydrogen attack curves.3 But,
DON'T think you can always save money by
keeping design temperatures low enough so carbon steel pipe can be used safely. There are many possible traps. For example, as catalyst deteriorates, DON'T be surprised if operating pressures or temperatures rise more than you expect.
If
they do, reactor outlet piping, in particular, could be
subject to hydrogen attack.
DON'T panic,
However,
because hydrogen atmoIf you use Nelson's curves
spheres can be handled sa'fely.
intelligently, they will help you choose the proper steel to withstand most process conditions, particularly at high hydrogen partial pressures. But, even though these curves are quite well established, DON'T select even a low-alloy steel whose limiting-resistance curve is too close to operating conditions. Operators may become careless in controlling temperatures as alloy content increases. Incidentally, although molybdenum additions improve elevatedtemperature strength, and resistance to hydrogen attack, their primary function is to retard the temper embrittlement of low- and intermediate-chromium steels (up to 10 percent chromium) during Iong exposure to process
d U o z o
r?5
F
o
_-
ll,:3
loo
\
E
o o ui t-
\' 5()
E
\.
zo 625
\_
--tkrpn
o
G
E
o
|
l)
o
4
cRuoE orLs -------r---
6
8
rO
CHROMIUM,O/.
Fig 3-Efiect of chromium content on various sulfide corrosion rates.a
temperatures.
Welding Problems With Cr-Mo Pipe. Also, DON'T
Some engineers consider austenitic stainless steels so resistant to hydrogen attack that no precautions are necessary. Stainless steels do resist high-temperature hydrogen attack, but DON'T select them with the belief that hydrogen will not pass through them. .It will, in the
use even low-chromium steel pipe unless you are willing to pay for more careful welding and post-weld heat treatments. At a given hardness, low-alloy chromium-molybdenum steels have somewhat more ductility than carbon steels. Ilowever, because they air harden so much, they usually require post-weld heat treatments to toughen the
if you use an austenitic stainless steel to line or to clad a low-alloy base, be sure that the base metal will resist hydrogen attack. Alsq be sure that the bond between the two layers is metallurgically tight. If it isn't, diffusing hydrogen atoms, after passing through the stainless steel, will combine to form molecular hydrogen at the interface and will build up a pressure essentially equal to the process hydrogen partial pressure. It doesn't take much of a disc,ontinuity in the bond to allow molecular hydrogen to form, so DON'T count on any of the usual . inspection methods for detection, even ultraatomic form. Thus,
sonics.
Corrosion. In petroleum refineries, process streams containing hydrogen frequently contain hydrogen sulfide also. This causes sirlfidic corrosion. You know from experience that increasing the chromium content of a steel increases its resistance to cgrrosion by high-sulfur cmdesa (see Figure 3). Ilowever, DON'T jump to the conclusion that chromium alloying always improves resistance to sulfidic corrosion. It does so if the operation is dirty, as it usually is in crude streams. Or if the corrodants are elemental sulfur or sulfur compounds that do not decompose to release hydrogen sulfide. This increased resistance to sulfur corrosion depends on formation of a protective scale. With such scales, the corrosion rate is parabolic; that is,
it
decreases
If
weld metal and heat-affected zone. This heat treatnent complicates field welding. DON'T always be subservient
to convention,
because
intelligent materials selection should decrease sorne of these welding complications.T For example, when carbon steel pipe is welded to a higher alloy, such as 5-Cr, /r-Mo steel, some engineers require weld metal corresponding to the higher alloy and a post-weld heat treatment. However, DON'T you think carbon steel weld metal should be equally satisfactory? And then a post-weld heat treatment might not be necessary. Such joints clearly have to be in a process zone where carbon steel is acceptable. Frequently, the very engineers who insist on post-weld heat-treatment with carbon steel or low-alloy weld metals would be willing to omit the post-weld heat treatment if an austenitic stainless steel electrode, particularly Type 309 (25-Cr, 12-Ni) were used. Ironically, their reasoning that the hardened, heat-a^ffected zone of the 5-Cr steel would have ductile, austenitic stainless steel weld metal on one side of it and ductile, 5-Cr steel parent metal on the other, is equally valid in the rejected case where the weld metal is carbon steel.
Higher Alloys. If low-or intermediate-chromium
steel
pipe won't resist corrosion adequately in refinery streams
with exposure time.
you'll have to use aluminum-coatings8 or high-chromium
it
ferritic (Type a00) or austenitic (Type 300) stainless steels.e DON'T try to justify anything more expensive; it's almost impossible. And, when trying to choose between these possibilities, look at the over-all picture, DON'T even bother about corrosion resistance; they
the operation is clean, as
usually is when hydrogen
is present, the iron sulfide corrosion product is not protective.s,8 Under these conditions, the corrosion rate is linear and does not decrease with time, and chromium additions are not beneficial. Carbon steel and 9 percent chromium steel corrode at substantially the same rate and a 5 percent chromium steel may corrode even faster tharr the other two. So DON'T waste your money by picking a chromium content higher than you need to resist hydrogen attack.
don't differ that much. As a matter of fact they also may differ less in cost than you might expect, too.
Aluminum Cootings resist sulfidic corrosion well, but DON'T expect them to be perfect and DON'T expect
77
WHICH MATERIAT FOR PROCESS PIPING?
.
.
far the most continuous aluminized coating; unfortunately, it is also the thickest, and because both surfaces of the pipe usually are coated, it is difficult caiorizing, gives by
to weld.
Stoinless Steels are well advertised and may look very good in short-time field trials or in laboratory tests. But, DON'T expect them to get you out of trouble automatically, and DON'T specify them unless you know their many disabilities. They have been most successful at operating temperatures lower or higher than most of those in petroleum refining. If you accept the advertising claims simply because stainless steels cost five or six times more than carbon or low-alloy steels, you may be heading for
Fig. 4-The aluminized backing ring in aluminized pipe is on the upstream side.
real trouble. DON'T expect plain 11- to 13 percent chromium ferritic stainless steel pipe (Type 410) to be much of an improvement over 9-Cr, l-Mo steel. It has only borderline corrosion resistance. Tlpe 410 welds also air harden and require post-weld heat treatment. DON'T put this alloy, or any of tho lower alloys, into service if the hardness is above Rockwell C22; it is likely to hydrogen stresscrack. The aluminum-containing grade (Type 405) is completely ferritic up to the melting point so it doesn't
harden on welding. Ifowever, it develops extremely coarse grains adjacent to the fusion line, which lon'er ductility. DON'T use ferritic stainless steels containing more than 16 percent chromium in the 7500 F to 1,0000 F temperature zone. They invariably embrittle, because of precipitation of a chromium-rich constituent.ll Even the 11- to 13 percent chromium alloy sometimes seems to embrittle
in this way, for
reasons not clear. IJnfortunately, this is
a common temperature zone for many refinery and chemical plant processes. Furthermore, DON'T use these ferritic stainless steels above 1,0000 F, either; they will embrittle for a somewhat different reason, because of the
formation of an iron-chromium intermetallic compound called sigma phase.12
Austenitic stainless steels resist oxidation by either oxygen-bearing or sulfur-bearing process streams. But, DON'T expect austenitic stainless steel pipe to be foolproof simply because it has corrosion resistance. Many Fig. 1-,Stress-corrosion cracks in stainless steel pipe.
them to stay on unless they have reacted with the base to form an iron-aluminum alloy layer.8,ro Simple sprayed coatings won't do. This alloying reaction requires melting the aluminum. But, DON'T go too far above the melting point or the brittle reaction product becomes excessively thick and tends to spall. Also, DON'T expect to be too huppy with aluminum-coated pipe if the aluminized surface has to be welded; the weld probably will embrittle and may crack. In addition, if butt welds are used for pipe joints, a low-alloy chromium-molybdenum weld metal will be susceptible to corrosion. One alternative is to use austenitic stainless steel weld metal. Another is to use aluminum-coated backing rings to protect the weld root against corrosion (see Fig. 4). Neither of these steel
has been completely satisfactory.
Hot-dipping produces a good aluminized coating but 10 to 12 feet is the longest pipe that can be handled. Because even these lengths have to be dipped from each end, there may be a poor coating in the overlap region. High-temperature aluminizing, known as alonizing or
78
plant operators are too optimistic and feel that tight temperature controls aren't necessary with austenitic stainless steels. If temperatures climb too high, even these steels will oxidize and sulfidize significantly.G Relatively short-time tests indicate that austenitic stainat all temperatures. But, DON'T expect this conclusion to be valid for steels exposed to thousands of hours at process temperatures. Long exposures between, roughly, 8000 F and 1,6000 F precipitate chromium carbide and sigma phase in many stainless steels. This causes a significant loss in atmospherictemperature ductility; ductility at higher temperatures is affected less. less steels are ductile
Slress-Corrosion Crqcking. The greatest problems witJl austenitic stainless steel piping usually arise when the unit is off stream rather than when it is operating. You have to anticipate such problems and take the necessary steps to avoid them if you want to use stainless steels. Chlorides, and caustics under some conditions, can cause any austenitic stainless steel pipe to crack transgranularlyrs
(see Fig. 5). Plain-chromium stainless steels do not crack in chloride solutions, but they usually pit badly enough to be only moderately satisfactory. Strictly speaking chloride stress-corrosion cracking will not occur unless there is contact with an aqueous solution of suitable chloride concentration, a favorable temperature, and strain or residual stress. Ifowever, DON'T be lulled into an unrealistic sense of security by this complexity, as these requirements may be met rather'unpredictably. For example, the small amount of chlorides in most external pipe insulations can be leached out by exposure to weather and become concentrated at the pipe wall.la Temperature may be difficult to measure, let al,one control, especially during startup or shutdown when gradients exist. And residual stresses usually are present in a relatively low yield strength material like annealed stainless steel pipe. A pipe bumped in shipment, or sprung or cold bent in fitting can have all the stress needed. In fact, circumferential weld shrinkage alone, particularly in heavy-wall pipe, may create complex bending stresses at the joint. Post-weld heat treatments should relieve many of these stresses, but, if there is much restraint, the subsequent cooling can reintroduce harmful stresses. DON,T overlook the fact, either, that the much higher thermal expansion and contraction of the austenitic stainless steels may introduce unexpected restraint stresses as well as being troublesome in piping layouts. When the normal carbon (0.08 per.cent maximum) grades of austenitic stainless steel pipe are used in the temperature range of B00o F to 1,5000 F, chromium carbides precipitate in the grain boundaries. This sensitizes the material and makes it susceptible to intergranular corrosion in many acid media. So long as the unit stays on stream there is no real deterioration from this precipitate, except some loss in ductility. In fact, if the material stays at these temperatures for a long enbugh time (the necessary time decreases as the temperature increases to approximately 1,6500 F), it will heal itself and lose its sensitivity to inter-granular corrosion. Nevertheless, DON'T count on this long-time exposure. Something, if only a check to be sure everything is working properly, generally shuts down initial mns of a new unit prema-
turely. Sensitized material also is susceptible to intergranular stress-corrosion cracking in the polythionic acids formed by the reaction of iron sulfide, air, and moisture.l5 Any type of stress-corrosion cracking is troublesome because it seldom is noticed until the unit is being brought back on stream. Then it is invariably attributed to some-
thing that happened during the startup. Shutdown costs may be increased still further by futile attempts to weldrepair the leaks. With cracking like this, weld shrinkage
will
open
up another crack as rapidly as one lea-k is
repaired.
DON'T expect the extra low-carbon (L grades), the chemically-stabilized (Types 347 or 321), or the controlled-ferritelG (centrifugally-cast, usually) varieties of austenitic stainless steels to solve these potential cracking problems. They may help, but success is unpredictable. For example, in the low-carbon types some carbide precipitation still can occur toward tho low side of the B00o F to 1,5000 F temperature range. This may be enough to sensitize the structure to intergranular corrosion. The higher the carbon content the greater the danger. The
About lhe quthor Dn. Cmr, H. Snrrlrts is assistant director of Resea,q'ch and Deaelopment, Amer'ica,n Oil Co., Whiting, Ind. He holds the Ch.E. degree from Rensselaer Polytechnic Institute and recei,aed luis M.S. anil Ph.D, d,egrees in metallw'gg from Yale Uniuet'si,ty. Dr. Samans has held positions in the Resea?,ch Dept. of Cha,se Brass & Copper Co., as instructor at Lehi.gh and, Rensselaer, and as
chemically-stabilized types (containing columbium-tantalum, or titanium) are excellent if carbide precipitation occurs during welding and if subsequent service is near atmospheric temperature (at least below 7000 F) . Then,
only randomly-distributed columbium, tantalum, or titanium carbides precipitate during cooling. However, if service is between 8000 F and 1,0000 F for long times, the carbon left in solution, even after the stabilized carbides form during post-weld cooling, precipitates conventionally as chromium carbide at grain boundaries. Here again, if there is enough precipitation at any. one location, and if these grain-boundary particles are properly spaced, sensitization still can occur. In the controlled-ferrite grades, the ferrite won't crack, although it may embrittle or corrode selectively in some media, but the austenitic matrix is subject to all the disabilities mentioned above. The higher-nickel stainless steels offer some hope. But, these alloys are expensive and they may not have adequate resistance to either stress-corrosion cracking or sulfidic corrosion if conditions are severe. There is no certain way of preventing transgranular
(chloride) stress cracking and the only real solution to intergranular (polythionic acid) stress cracking is to heat-treat the piping, including welds, in order to precipitate as much carbon in a stabilized, nonsensitizing form as possible before service. Even then, DON'T forget to caution the operators to open equipment as infrequently as possible, to Ieave it open as short a time as possible, and to keep it either dry and blanketed with inert gas or flooded with an alkaline solution when it is off stream. LITERATURE CITED 1 ASA 831.3-1966, "Petroleum Refinery Piping," The Amer. Sc. of Mech. Engs., New York, 1966. or Engireering. Sttuctures"' John w,ev
o'.lill"i;I
S;;'?ilX]"Sf lavior
Nelson, G. A., Hydrocarbon Processing, 45, 201 (1966). Dravnieks, A., and Couper, A, 5., Corrosion, 18,, 2911 (1962). sDravnieks, A., ud Samans, C. H., Prc. A.P,I.37, 100 (1957). oSorrell, G., Corrosion, 14, 15t (1958). 7 Bland, J., Weld. Jour. Res. Suppl. 35, 1815 (1956). ETisinai, G. F., aud Samns, C. H., Proc. A.P.I.,39,92 (1959). oAlessendria, A. V., and Jaggad, N., Proc. A.P.I.,,lO, 1,10 (1960). l0Dravnieks, A., and Smam, C. H., Prrc. A.P.I.,37, 100 (1957). 3 a
A. l. Metal Progress,66,722 (lgH\. A. and Hawkm, M. F., Trans. A.I.M.E.,200,607 ulfoar, T. J., P,, Corroion, 19, 331t (1963). 11
Lena, 12Lena,
(1954).
LAshbaugh, ti,l. G., Materiak Prolection,,l, 18 (1965).
rrDravnieks, A., and
Suau, C. H., Proc. A.P.I.,37,
100 (1957).
M, G., Brck, F, H. md Flmers, J. W., Metal Progress 80, ^-'u.Eg!!e"", (1961). 99 C|. H.," M e tottic Mate riats it Etshe eths ;' "I\e "*f,:,U;.t*:t.ft"Yffi."d,
79
EXPANSION
Find Best Pipe Expansion Loop Quickly If your piping flexibility calculations
represent
little more than an expansion loop juggling act, check this new one-try method
George L. Ellison,
Thompson's lndustriol
Drofting Service, Boton Rouge,
Lo.
Most methods for solving expansion-flexibility problems
fall into two categories, the rigorous and the sornewhat Iess rigorous. The rigorous methods are time consuming and often are too involved or complicated for the man who does not have time to become an ex?ert in this branch. It may also be found that the time spent on numerous problems, the expense incurred, and even the
t. I
r ! It
'
nature of the problem itself does not justify such rigorous calculations. The less rigorous, simpler methods are usually designed to conserve time and eflort, but often fall into much criticism concerning their accuracy. Regardless of the method used there is an inherent weakness in the results. This weakness can be illustrated best by looking at a lr,ypical procedure. First, a proposed piping configuration is drawn up. Then one proceeds to
calculate the moments and other things that may be required by the particular method. Last, the maximum pipe stress and the thrust on the anchors is calculated. As can readily be seen, the thrust and stress (the main considerations), are controlled entirely by the piping configuration. As the piping configuration is arbitrary, this often results in excessive stresses or thrust. When this happens the designer must revise his piping configuration and start over with a little more assurance that the second
or a later try will produce results that are within the desired limitations. As these calculations are spmewhat tedious and "hit or miss," a designer will often lengthen the piping configuration in such a way as to cause the system to have an unnecessary length in order to have assurance that excessive thrusts and stresses will not occur. This causes added expense for pipe. In some cases, this will cause added pressure drop through the pipe which must be offset by using larger pumps and more power.
Using this new method, t-he maximum stress and
a
desired thrust are selected first. This is most desirable because it eliminates further concern about these two main considerations. Lastly, the piping configuration is selected in such a way that it can be adjusted with little effort to give the desired total moment for the stress and thrust selected. Thus, problems are solved in one operation with the best possible results. The method is partially graphical and of the complete system concept so as to minimize laborious calculations, yet it has as its basis the rigorous mathematical concepts which will be readily recognized by structural, mechanical and piping designers.
How the Method Works. This method assumes that the moment of inertia is constant throughout the pipe in the
piping configuration, that the flattening of pipe bends
8t
FIND BEST PIPE EXPANSION LOOP QUICKLY.
.
This method is theoreticat but it may be used as cor_ rect, subject to the limitations stated above. The deriva_
.
Anchor
CONDITIONS
i
The. complete system and semigraphical concepts have .been thoroughly
EIGURE
l-Piping
configuration and conditions for Example 1.
time tested. They were presented as far back as 1930.'z They since have been uied as standard or recommended procedure by numerous manufacturing firms and engineering handbooks.
This new method is unique in that it uses second moments. The determination of these second moments is similar to the determination of the moment of inertia oj 1"y structural shape with respect to an axis. In particular, it is analogous to the determination of the moient of inertia of an extremely short beams of arbitrary configuration, with a compressive load on its flanges ihat is parallel in line of action to the neutral axis of ihe beam. FIGURE long side. All
Rod
2-The
expansion loop l, can't be taken off the
Exomple
l.
tions shown
1. Assume a
!s
:
7,500 psi.
may
preferably one that conforms to f,is stand'ard anchoring system).
3. Calculate
d .9 4' e =40
f
60,000 (.125)
choose, _but,
l3'
=
:
T:750 lbs.,(This figure.may be.any one the designer
Moment Arms
=lJ 0
max.
2. Assume a Maximum Thrust:
0'
c
and condi-
Maximum Stress: S
k=J75'
o
configr_rration
1. Find the most econornical configuration to meet these conditions.
Solufion
3 93'
5
a piping
=2.5' Cornei Siretch Out=t.5?(25') =39J'
All Corners
lz=
Assume
in Figure
"b": (IJse Equation l.
See
and derivation)
r u: sp: 6TD : =l*gj1gfl_:10.r 6 (750) (6.625)
=9.4
FIGU-R! 3--Proposed configuration for Example I caluculation of neutral axis. -
list of Equations
and
4. Compute
Ac: (Use Equation 10.
closely by some a method, which con
List of Equations)
33.5 (6.90'l
and derivation)
,,, l}t 6.
varying of wall th
See
_ -a: 2.31 in. ac: 1b0 -100-l 5. Compute M': (Use Equation 2. See List of Equations Da
during expansion or contraction will be negligible and that all anihor points are 100 percent fixed. It should be noted that systems having a combination of higJr expansion facto$, low tensile strength and extremely high temperatures should be examined more
(e) :
rt.
_ Ac E I : (2.31) (24,200,000) (40.49) -178T @:1,750ft.3
Draw an assumed piping configuration and calculate the neutral axis position:
the system which Ilowever, few systems require such an examination.
Tors be
not
render
section Piping.l
82
systems
will
designer to
,yi:KT::
3 for the proposed configuration and calculation of the neutral axis distance (n).
o See Figure
Ailr
C.G.
FIGURE LAssumed of gravity for elbows.
center
-ffi
lr = 2-5' lz
=
r,27'
5.0'
lr=50'
.
Note all lengths in Figure 3 are true and all moment arms are to be perpendicular to a line drawn through the anchor points.
o
For layout purposes the center of gravity of bend may be assumed as shown for extremely long radius bends.
7.
in
k
=16
15
=21.0'
Ir
= 3,93' = 3,93'
h
5' ;r
lc = 393'
FIGURE 5-New moment arms are drawn.
each
Figure 4 except
Calculate radius of gyration of the configuration about the neutral axis based on (M): (Use Equation 4 from List of Equations)
{H:4.7rt. ":{+: . Calculate approximate radius of gyration (M'):
TABLE
l-ltomenl
{Y : {-ffi- r.rr,. Cqlculqtion Form
.
0)
I
Sect.
I
2,5
2,0
(r')2
0)
4.0
t2
from List of Equations) (0.4)
s3.5 . Al:CAx:T:0.9ft. . Compute Kf (actual): (Use Equation 6 from List
: K * Ax: 4.7 + 0.4: 5.1 ft. L': (Use Equation 11 from List of Equa-
K'
.
Compute tions)
: 61.8 + 4(0.9) ,- 65.4 ft. adjusted (M') to see how closely it
L':L* o Check
2NAl
168.0
0.8
168.8
2.0
4.0
1,3
JO.O
1.7
382
4,4
19.1
4.1
16.8
840
8.1
92.1
16.5
7.8
60.9
4.0
16.0
254 0
83.7
2t-0
9.5
90.2
4.0
16.0
336,0
157.8
Note that, with respect to significant figures, this is as close to the desired M' as we can get with the
in
tJris example.
Anchor
50'
403.8 1030.6
Rarlius 1.57 R
Corner
R
2
do
do
do
do
2.5
3.S
:
Ms
D:
Mc Per Cor.
:C+D
R3
(D
0)2
r (:D,
156
53
28.1
109.7
do
03
01
04
do
2.7
do
72
I
do
204 4
51
I
202
,15 R3
112 0
3i9
Mc Total
M
c:
*
Mc
:
1030.6
+
319.1
-
1349.7
cuft.
agrees
with the required (M') : (Use Equation 3 from List of Equations) M'(adj.) : L' (K')2: 65.4 (5't;z - 1700 cubic feet
:A*B
r
672
Length
of
Equations)
Exomple 2. Assume a piping configuration and condi-
0),
Ms
-4.7):0.6ft.
Al: Assume a Ax based on above ,Ax (approx.); try Ax : 0.+ ft. then: (Use Equation 9
Ms Per Sect.
h.l,
4
(5.3
exceeded by this change.
I (l)2
(ii,
-K) -
by adding 2Al to the length of the expansion loop and check to see that "b" is not
5.0
2
on K and K'
9. Change configuration
for Exomple I
Lealth
Lenfth
(K' (approx.)
Compute
figures used
B:
Lergth
(based
Ax of 0.4 ft. checks
based on
(Use Equation 5 from List of Equations)
K' (approx.):
:
Ax (approx.)
Adjust Configuration:
.
Ax
o Calculate approximate
(approx.) above):
Draw new moment arms G) (."" Figure 5) perpendicular to the neutral axis and extending to the center of gravity of each of the components, and the equivalent lengths (l') of each component. Note that new comPonents were made wherever the neutral axis crossed any section, with the exception of bends. The difference in moment by considering a bend as two components is in general negligible. Measure each component (l), eachmoment arm (l) and each equivalent length (l') from the layout, place in the appropriate column of the "Moment CalculationForm" (Table 1) and calculate moment (M).
B.
! 40'
1
EXAMPTE II Pipe . .
Mbment
Anchor
CONDITIONS l2"sch.160pipe
of Inertia.
...781.3
Max. Temp.
.
in.r
.750o F
j:: :: . .: :: . :: : ::::: :: :l3oJ* pipe. .6.4 in. n" : : -: : : : : : : : : : : :: : : : : : :36;3#H
of
.51.0 ft. FIGURE LPiping configuration and conditions'for'example 2.
83
FIND BEST PIPE EXPANSION LOOP QUICKLY.
.
max.
2. Assume
:
(l),
r al),
t2
28 1
807.0
131
179.8
5260 0
1970.0
211
596 0
11.0
141.8
3500 0
1260 0
80
20
40
768 0
61J0.0
30
18.1
t7.7
,IJ
96.0
r766.0
4rJ0 0
5
196
188
354.0
8.1
70.5
1382 0
578.0
1960 0
6
210
4-8
23,0
2J8
615.2
i770.0
16.0
14,816.0
Length
(l')
293
3
:
60,000 (.125)
7,500 psi.
Thrust:
T: 3. Calculate
l=
Radius R
Corner
o": A#[:
3.26 in.
C:
Lenqth
1.57 R
6.0 2
(
7230 0 4700 0 61
13.0
2246 0
37 -15s.0
4. Compute Ac: (Equation 10)
M':
:A*B
1)
(7500) (781.3',| b:ffi:83'oft'
5. Compute
98
D
Ms Per Sect.
\{s Total
925 lbs.
"b": (Equation
(r),
(l'),
Letrgth I
2
Maximum Stress:
r
Length 0)
Sect
Solulion S
2
B:
tions shown in Figure 6. Find the most economical configuration to meet these conditions. \
1. Assume
2-Moment Cqlculqtion Form for Exomple
fABLE
.
2
R3
(t)
r6.0
269
(
t),
D:
l\Ic Per Cor
| 0)2
15 R3
:C+D
6800.0
320
683: 0 5 191,0
do
do
do
24,1
581.0
5160 0
do
do
do
do
19.4
376 5
3510 0
do
trIc Totat
(Equation 2) It'I
3.26\ ( 24.550-000 ) (781.3)
:
N'Is
35;2,0 I5,SPrl.0
* IIc :
37155
*
15896
:
53,051 cu.
ft.
M':ffi:39'loocu'ft'
Draw assumed configuration and locate neutral
6.
o Calculate
axis
(See Figure 7).
7.Draw and measure l, l'and Figure B and Table 2.)
i
and compute
(M).
K' (apprbx.) (
See
o Calculate
K:
Rod.=
6.0"
(Equation 4)
Corner Stretch Out=157(6)=9.4'
Corners
lc
=
.
9-4'
:
cAx
( 5t\ (-2.2\ : --;o:
_2.2
f.t.
K' (actual) : (Equation 6) : : 16.5 1,. K, K -| A* : (18.7
Compute
Lengths
-2.2)
lr = 54.0' lz = 8.0' ls = 38.0' lc = 24,O' lr
= 29.3' lz = 24.?'
Moment Arms
o = 26.5' b = 56.0' c = 30.2' d = 2.5' e = 55.0' f . 52.5'
s=
16.0 rt.
Then:
al All
: !T : \i-+#:
Ax (approx.): (Equation 7) Ax (approx.) : (K'-K) : (16.0- 18.7): ft. -2.7 o Compute Al: (Equation 9) Assume Ax: trv Ax : ft' -2'2
":{+: {#:ra.7rt. All
5)
o Calculate
Adjustment:
B.
K' (approx.): (Equation
lr = 80' lr = 18.4'
ls.
19,6'
ls = 240' l? = 9.4' ts 9.4' lE = 9.4'
'
8.0'
I
-,-
l33, iz= ll.9' 1=T-q'
iz= 2?.7' ir = 9.9' s.+'
t. iu.24.8'
iz. 269' is= ?4.1'
o= lro*
lzb +lsc +lod+ lc (e+f+g) lt +12+13 +14+3lc
is
=
19.4'
Anchor Line
l'
1432 + 448 +1150 +60 + 1087 152.2
-
4t77
= ?8.4' tz = ?4.4'
l'3. _ 27.4,
152.2
FIGURE 7-Proposed configuration for Example 2 ard location of neutral axis.
84
I
2.0'
= l?.7' r;. l8.s'
l'q
t,6
.
4.8'
FIGURE
&-New mometrt arms drawn for Example
2.
L': (Equation 11) :l l' + 2NAI : 752.2 + 4(-2.2) :
o Compute
143.4 f.t,
o Checked adjusted (M') to see how closely it agrees with the required (M') : M'(adj.) ,- L' (K')2 : 143.4 ( 16.5)'?: 39,080 cubic feet 9. Change the configuration by subtracting 2Al from the length of the expansion loop. In this case, "b"' does not require a further check.
25'
Exomple 3. Assume a piping configirration and condiin Figure 9. Find the most economical configuration to meet these conditions. tions shown
Solution 1. Assume
2. Assume
EXA'I'IPLE III CONDITIONS
Maximum Stress: g
11av.:60,000 (.125) :7,500
pipe.. ....,..12u X-Stg.pipe .. . .361.5 in.l Mbment of Inertia . .750 "F Max. Ternp. . . .70 'F Fab. Temp-, .......680 oF At .......... i':.:1 .':::. : :::::: :'.'.'. .'.:3aa,s?o,ooo p.s.i.
psi.
Thrust:
T:925 3. Calculate
30'
l5'
lbs.
"b":
,;'
(7500) (361.5) .b:-o'ffi:38'3ft'
::::::::: .: :: :::::: :::fl:ffir.'"i
FIGURE 9-Piping configuration and conditions for example 5. Compute
4. Compute Ac:
o":E#4:2.64in.
3.
M':
*':W:14,650cu'ft'
I
I PLA N
____111:
ELEV
I
lrn = 14.9' lzx = 13.l' Note. Poro I le
i
Lenqth
Line
lat
I
= l0O'
. 6.0" lsx' l9' bt'= A'l
l+x lzx
=
"
tr (lrxl +lz
150'
lrv.
O 0'
lzv= 6
O'
40o' rS.O' = 5.0' ta = tOO' ls = 7.85' = 7.85' lz= 7.85' r,
l:
lnv= 3 5' lev = ll0 lzv = D.3'
(hi) t
13
(11x)
t h lkx
ir = 50'
tr =
iz = 8.2'
=
i. = g.O' tr = t3.0' i. . rf S' 15'
15
) +15
6.2'
h,lO2'
(l:r) +t (tax )+lr(tr
x)
ltrl2tllrla.lsrlarl7
.
F=
r5,0'
v=
;-' FIGURE
lLPiping
(40x0) r (l 5 x6)+(5)(1e.5)+(10)(3.5) + 7 85 ( 1.6 +l
1.0
+
10.
3)-?7a,
40115+5+10+3(785)
configuration and new axis calculations.
85
FIND BEST PIPE EXPANSION LOOP QUICKLY.
.
and equivalent lengths (l'). Place these lengths in the appropriate column of the Moment Calculation Form and calculate the moment (M) (See Table 3).
.
7.
Adjust Configuration: o Calculate
K:
{+:{=s--:B.oft. ": o Calculate K' (approx.):
Length ond/or
: {+-:
K'(approx.)
I# ll-Piping
FIGURE
configuration used
to derive equations
Draw assumed piping configuration and calculate the neutral axis position (See Figure 10). o This problem involves a three plane system which complicates the relatively simple method that was used in the two plane problems of Example I and 2. It may be greatly simplified by using a few of the more simple tools of descriptive geometry. They are: ( 1) the transfer of points, which should require no explanation here, (2) the true length of a line and (3) the point view of a line.
6.
Explanation. The true, length of a line may be found by projecting a view of the system with the fold line parallel to the line drawn between the anchors or with the projection lines perpendicular to the line between the anchors. The point uieut of a line may be found by projecting a view containing a true length line across a fold
line that is drawn perpendicular to the true length line or with the projection lines parallel to the true length lines. o Project the trire length line view (Figure 10) and the point view of the line view. o Erect a convenient pair of perpendicular coordinate axes and calculate the center of gravity, which will also be a point view of the neutral axis parallel to the point view of the line between the anchors. o Layout moment arms (l) and equivalent lengths (l'). . Measure component lengths (l), moment arms (i), TABLE
3-filoment
Golculotion Form
for
Exomple 3
B:
Len'gth
Length
Sect.
I
0')
I
400
6,0
360
2
15.0
ob
5.0
1.7
100
4
(l ),
| (t')2
Length ri)
t2
5.0
25.0
1000 0
120 0
1120.0
423
8.2
67.2
1010.0
530
1063.0
2.9
9.0
81 0
405 0
1-2
406.2
109
130
169 0
1690.0
9.1
c:
1.57 R
R3
Length 0)
(l)
3
l 0),
.15 Ra
7.85
t25 0
13.5
t82.2
911.0
1&8
do
do
do
6.2
384
do
do
do
t0.2
104.4
rlius R
5,0
Mc Total
86
:
1690.1 4,288.3
Ra
M
:A+B
r rr-),
Mr Totsl
Corner
Ms Per Ser
(t)2
Me * Mo :
D:
Mc Per Cor
:C+D oro a
192.0
do
210,8
0
do
540 8
522
r.681.4
4,288.9:+ 1681.4 :
6,969.7 cu.
ft.
.
{1o436:560:,r.tu.
Calculate Ax (approx.):
- (K'-K): (12.5-8.0):4.5[t. AI: Assume Ax: Ax = 3.3 ft.
Ax (approx.)
.
Compute
Then:
.
Compute
K'
K' : o Compute
L'
(actual): K
*
Ax
:
8.0
+
3.3
:
I1.3 ft.
L':
:L + 2NAI :
o Check adjusted
93.6
+
4(5.0)
:
113.6
ft.
(M):
L' (K')'- (113.6) (11.3)'9: 14,500cubicfeet. B. Change configuration by adding 2Al to the length of the expansion loop and recheck "b."
M:
Derivqtion of Equotions Derivqtion of Equotion I. The basic, flexural equation seryes as the basis for Equation 1, i.e.:
stress
s:-+!-
(r)
(Where S : stress at extreme fiber, M : moment due to the force applied to the section, b : distance to extreme fiber and I : moment of inertia of the sect.) Consider thb general piping configuration of Figure 11. Imagine it to be a beam whose length is the same as the diameter of the pipe (D). To this beam is applied a uniform distributed load of T lbs. acting on a line through the anchors. At various times and under various stress conditions all of the load may be shifted to one end of
About the Author George L. Ellison is a design draftsman with Thompson's Industrial Drafting Service, Baton Rouge, La. He designs 1lressure valves, oil field
equipmcnt, piping, structures and other related equipment. In 1951 he started in the industry rrith J. B. Beaird Co. as a pressure vessel draftsman and designer of L.P.G. systenls. Later at Delta Tank Mfg. Co. in 1956, he did the mechanical
design work on high pressure-
temperature vessels and piping, structure, general layout, heating and controls for the company's gas dehydrator and hydrocarbon recov-
ery unit. Mr. Ellison is presently Ellison completing his work on a degree in mechanical neering at Louisiana State University.
engi-
this beam, (that is to say, one edge of the pipe). From any convenient beam tablesra it is seen that the moment (M) for a beam under the above conditions is:
M:-+-
Q)
D are as above.) Since the distance "b" is measured in feet and must be
(Where M, T and
converted to inches, ( 1) becomes;
(
_
12Mb
(3)
I
On combining (2) and (3), s
_
6TDb
(4)
I
IJpon rearranging (4);
FIGURE
12-
IR'? is a second moment of this section.
List of Symbols
SI
b-1rr-...Equationl Derivoiion of Equolion 2. This equation has as its basis
*S max.
: Maximum allowable system.
:
(l)
Youngs Modulus or the modulus of elasticity, T : thrust, A : area that thrust is applied to, I : length of rnember to be used and Ac: change in length of (l).
Where E
Rearrange (1) as follows; AcEA r:_ ---T,
(2)
Square the radius of gyration (R) of the section to be used and add it to each side of equation (2) thus; AcEAR2
in any part of
the
Piping Codel or it may be safely assumed to be approximately 72/z percent of the tensile strength o{ the material used in the cold condition.
the formula for Youngs Modulus, i.e.;
o_ Stress :_ T/A L: Lc/l struir,
stress (psi)
This can be set by the applicable part of the
T: Thrust, taken on a line between anchors (Ibs.). Ac: Change in the equivalent length of pipe between
anchors (in.). *E : Ypungs Modulus or modulus of elasticity (in psi). *f : Moment of inertia of the pipe used (ina).
M:
Second moments of all sections of the configuration with respect to the neutral axis before adjustment (cu. ft.).
b: Maximum
permissible, perpendicular distance from
(3)
the neutral axis to the farthermost fiber of the configuration (ft.).
Since AR'zis simply the moment of inertia of the pipe, (3) may be restated as;
*D: Outside diameter of the pipe used (in.). L: Total true length of the piping configuration (ft.). K: Radius of gyration of the total system before adjust-
T
p,
- -4$IT&)
Noting Figure 12, lR'z is a second moment of this section about its center line. Thus, if the left hand side is generalized to lK'z for use with respect to any axis, (4) becomes:
O:EI
M:IK2n,.-: - ---i-
(5)
Since (M) will be in cubic feet, it must be converted to cubic inches thus; AcEI M:17rr...Equation2
.
b: ur, AcEI M'- Urr,
(ft')
(2)
(cu. ft.)
(3)
*: {*
rn.r
: {f
,n.,
K'(approx.)
(+)
L' :
A_djust-ed
: *e:
Distance between anchors (ft.
Da
total length of piping configuration or
(L + 2N^l) (in ft.).
Expansion perature.
in
)
.
inches per 100 feet at maximum tem-
*.For these values refer to the Piping Codel or any other good, convenient engrncerlng or plplDg handbook. LITERATURE CITE,D
K':KfAx(ft.) Ax (approx.) : (K'(approx.) Al (approx.) : CAx (approx.)-K) (ft.) al: CAx (ft.) ac ^^_ -
(1)
(cu. ft.)
M' (adj.) : L' (K')2
or (K-l- Ax) (in ft.). Ax: The adjusting distance between K and K' (in ft.). M': Second moments of all sections of the configuration with_respect to the neutral axis to which (M) must be adjusted (in cu. ft.). Al:Proportional equivalent of Ax (in ft.). C: Proportionality factor for the configuration. N: The number of members crossed by the neutral axis must be adjusted to
including bends.
List of Equations SmaxI
ment (ft.). K' : Radius of gyration of the total system that (K)
Da(e)
,6 (in.) L':L + 2NAl (ft.) ,
(s)
(ft.)
(6) (7) (B)
u,i"ffr:
ff} ff".i:j"o s**:rr3i
,[::ny*.T'rr'lfr.
Method for Determining .by"jA_Gr-ap-hig C. T. Mitchell; published
(ratest edition); pub-
Expaosion Stresses
in pipe Lines,,,
in A.S.M.E. Tiansactions (tS3O). -
,. ] "f-jShlcage Cold-Fomed Steel Design Muual,, (1956 edition); published by The America Iron and Steel Inititute. a "Steel Construction Manual" (latest edition); published by T'he American Institute of Steel Construction.'
(s) (10) (11)
Key Words for lndexing Design
Expansion
Drawing
Loops
Flexible
Pipi"S
87
FIGURE l-This Texos refinery uses both slip-type exponsion loints ond doubleoffset U-bends to obsorb pipe line exponsion ond controction. See next poge {or other
of exponsion ioints.
Expansion Joints How to Select and Maintain Thenn If you are confused about all the t1'pes of expansion joints, here's a method of selecting and maintaining the right one for the job.
Philadelphia
caused by a rise in the temperatule of the pipe. There ars also instances where means for absorbing pipe con-
LARGE NUMBERS of pipe lines conveying steam, hot Iiquids and other fluids for refining and petrochemical processing must be fitted with some means to absorb expansion
traction must be provided, if the line is installed at a temperature higher than the rninimum experienced in operation. Positive control of pipe expansion and contraction is absolutely necessary if dangerously large or de-
K. 5. Roberls Yarnall-Waring Company
88
structive forces at the anchors and other restraints are to be avoided. Three proven means for absorbing pipe expansion and contraction are popular in refineries and petrochemical plants today. These are: (1) expansion bends, (2) corrugated- or bellows-type expansion joints, and (3) slip-type expansion joints. This
Expansion Joints
FIGURE 3-Simplified sketch showin9 o hinge-type corrugoted expon-
sion ioint suitoble for
refinery
piping systems.
FIGURE,t-Single-end ond pocked
double-end glo nd-
slip-type exponsion joints
use conventionol
osbestos
rubber ond duck ring pocking.
FIGURE 2-Simplified
sketch showing o typicol corrugoted-type exponsion,
ioint suitoble for
refinery
piping systems.
article discusses the relative merits of each, and the important factors in application to modern piping systems in refining and petrochemical plants. Expansion Bends-These are made
in several different
shapes, depending
on the amount of space available, size of the pipe, expansion or contraction to be absorbed, and the temperature and pressure of the fluid flowing
through the pipe.
In
general, the
more intricate the bend configuration, the greater the expansion that can be absorbed for a given stress in the pipe. The common types of expansion bends used today are either fabricated or built-up. Fabricated bends may be simple U, double-offset U (Figure 1),
circle,
or
single offset
IJ.
Creased
to some extent, have become less popular in
bends, though once used
recent years. Built-up bends are made in a number of configurations from
welding elbows. Expansion bends require no routine maintenance if they are uninsulated. If the bend is insulated or fitted with
a drip trap, or both, routine inspection if the insulation and trap is required.
All expansion
bends, whether fabri-
cated or not, require more installation space than either corrugated or sliptype expansion joints (Figure 1).This is often an important consideration in crowded refinery areas, but can
usually be overlooked on tank farms
and other locations where a large amount of space is available. Expan-
sion bends are usually mounted vertically (Figure 1), or horizontally,
depending on the amount available.
of
space
The first cost of a fabricated expansion bend may exceed the first cost of a bellows or slip-type expansion joint. A built-up expansion bend usually costs less than a fabricated bend or either type of expansion joint, unless a large amount of labor is required to build the bend.
Corrugated Joints-These j oint
s
consist of one or more corrugations in
a metal suitable for the temperature and pressure in the pipe (Figure 2). Typical materials used for corrugated joints include copper, stainless steel, or Inconel in the bellows and castiron or cast-steel end flanges, or steel welding nipples.
The corrugated joint, when well designed and constructed, has advantages where the installation is
of the joint is difficult or impossible. Corinaccessible and maintenance
rugated joints do not require maintenance in the form of repacking or lubrication. Ifowever, the selection of a corrugated joint must take into careful consideration the extent and frequency of the cycles (degree and number of expansions and contrac-
tions) of operation anticipated in the fife of the installation. Otherwise, the joint may fail prematurely due to overstressing ths corrugations or bellows.
There are other advantages of the corrugated type. When made of stainless steel they can be used at temperatures beyond the range of slip joints; the latter are limited by packing and lubrication considerations. Stainless steel corrugated joints are excellent for handling corrosive fluids
or fluids which must not be subject to cohtamination. In very large sizes (over 30 inches) corrugated joints are easier to fabri-
cate, transport, and install than slip joints. They are often used in large ducts and manifolds, particularly for high-temperature exhaust systems and other refinery applications. They are also useful when the piping is subject
to lateral and angular misalignment, well as axial motion, although here again it is important to select and install the joint properly so that the corrugations will not be overstressed. rn recent years corrugated expansion joints have been used increasingly as hinge, universal and gimbal joints. These are specialized applieations of the bellows principle which have definite advantages for certain tlpes of installations. One of the most useful is the hinge joint, Figure 3, as
which, when circumstances permit, can be used to absorb expansion without the need for anchors.
Slip-Type Joints-In spite of the
versatility of the corrugated joint outlined above, the slip joint (Figure 4) has certain advantages which make it
the choice for many refinery and petrochemical installations. When well designed it is a rugged, dependable, and economical means of absorbing expa"nsion and contraction.
It
is particularly useful in steam and hot-water transmission lines where
the expansions and contractions are frequent and of large magnitude- Slip joints contain no highly-stressed flexing element subject to failure after a finite number of cycles.
Slip joints require a nominal 89
amount of maintenance in the form of packing and lubrication. The exact amount of maintenance required depends largely on the operating conditions, i.e., temperature, pressure, expansion or contraction absorbed and
by the manufacturer. The numerical value of this traverse specified
should always exceed the computed
expansion of the pipe (i.e. the required traverse). Thus, with a 20inch expansion a joint with a total traverse of 24 inches is usually chooen.
frequency of operation. Probably the
most objectionable feaiure of slip joints in the past has been the necessity for periodic repacking of the stuffing box, which entailed shutting down the line and considerable labor.
In one uniqug and well established design-the gun-packed joint (Figure 5) packing can be inserted into the stuffing box at any time with full
FIGURE 5-Single-end gun-pocked type slip exponsion joint. This is olso built with double ends.
temperature and pressure on the line.
This eliminates any shutdown and to a mini-
reduces maintenance time mum.
nature of the fluid, presetting, expan-
Slip joints fitted with a sliding member at only one end are known
ports.
as single-end joints. When sliding members are used at both ends, the joint can absorb twice the expansion of a single-end joint and is known as a double-end joint.
Where repacking under pressure is not a consideration, conventional gland-packed joints (Figure 4) rnay be used. These resemble gun-packed joints but have conventional asbestos or rubber and duck ring packing.
Cast-iron glands are generally used, while the body and sleeve are wrought steel. The sleeve is polished and chromium-plated. Gun-packed joints are of all-steel
construction, the sliding sleeve being
sion, anchors, alignment, and supA number of these factors aJe
discussed below.
Traverse-This is the distance, expressed in inches, that the joint or bend must contract in order to absorb the expansion of the pipe served by the particular joint or bend. The required traverse is numerically equal to the distance the pipe expands over its full temperature range. Ths lowest temperature that will be encountered is as important as the maximum temperature. This means that if the expansion tables available start at 70 F. (as some of them do) and the line is to be installed outdoors where winter temperatures can drop as low as 20 F. below zero, traverse must be provided
made of polished seamless steel with a layer of hard chrornium plating.
to cover the additional 90 F. range below the reference temperature of
the stuffing box.
bend is the maximum safe movement
The sleeve is guided internally and externally for correct alignment in
70 F.
The traverse of the joint or
the
Packing, in joints of the type in Figure 5, is forced into the stuffing box by the jack action of a wrenchoperated plunger threaded in a cyl-
inder, as shown in Figure 6. The packing .can be fed into the joint while the line is under pressure. The packing used is a semiplastic. heatresistant, high-grade, Iong-fi6er asbestos, combined with an inert filler and impregnated with high fire-test mineral oil. It is furnished in small slugs for easy insertion in the packing gun.
Joint ond Bend Selection-When choosing any t)?e of expansion joint or bend it is essential that a number of important factors be considered. These include the required traverse, operating temperature and pressure,
90
Presetting-Where traverse in both directions is expected, it is essential, when actually placing the joint, to preset it for the temperature of the pipe at the time of installation. With slip-type joints, the sleeve should be pushed in from its fully extended position a distance equal to or slightly greater than the distance the pipe will contract in going from the installation temperature down to the minimum temperature. For the example cited above, if the installation temperature is 70 F., the sleeve should be preset enough to accommodate 90
F. of contraction---or approximately one inch if the pipe is 100 feet long. Bellows joints are sometirnes furnished in mid-position (halfway between the fully compressed and fully extended
positions
of the unit) to cover such with all designs the
conditions, but
manufacturer's'installation instructions should be followed carefully. The following actual case is an example of how important contraction can be. Expansion joints were installed, fully extended, in a pipe line in a tunnel where the temperature was close to 100 F. The line was well supported and rigidly anchored to the tunnel wall with through bolts and backing plates. In accordance with good practice, the system was given a hydrostatic pressure test prior to putting it into steam service. Ifowever, the hydrostatic test water came from a deep well at a temperature between 40 and 50 F., and the pipe contracted with unfortunate results. The pipe anchors were literally pulled out of the wall. Obviousln the trouble in this case was not that the anchors were inadequate but that no provision had been made for contraction of the pipe.
Pipe Expa"nsion-Figure 7 shows the expansion of steel pipe for any temperature up to 700 F. For conFIGURE 6-Wrench-operoted plunger
for feed-
ing plostic pocking to o gun-pocked type exponsion joint.
venience, one scale also provides the saturation temperatures for various steam pressures. Given the tempera-
ExpansionJoints... SATURATEO STEATI PRESSURE v c0-rcHEs
xERcuRY
Ooa
tfitsmt-rolt
ro 25 $Er@
OO ?CA
Smt H m@
Occasionally installations have been observed where an expansion joint was anchored by only one of its two legs or by an inadequate number of anchor bolts. While this can be done safely under certain favorable condi-
tions, U
4 E
o F
U U
d
9
a
E E o U
o
S
=
= 2 o 2 A U
it is not generally
recom-
mended. Such procedures have resulted in damage to the expansion joint or to the piping, either from the excessive loading on the secured leg or from the inadequate number of anchor bolts. Trouble of this sort is not the fault of the joint, but of the manner of installation. As a rule an expansion joint, like any other fitting, should be anchored with the full number of bolts provided for in the base.
2
EXPANSION OF STEEL PIPE
Bending moments caused by offsets source of
in the piping are another
trouble. Offsets are often necessary to get around obstacles in the line of the pipe, or to shift its axis a few feet up or down or sideways. The net effect is to create a bending moment TEMPERATURE RANGE IN DEGREES FAXREIHEIT on the pipe and elbows that is proFIGURE 7-{hort for quickly determining lineor exponsion of steel pipe for vorious steom portional to the thrusts at the elbows pressures ond temperotures. and to the length of the offset. If the expansion in the offset leg is relatively ture range and pipe length involved, straight run of pipe without an ex- small, an additional expansion joint the to{al traverse and amount of pre- pansion joint or other device to ab- may not be required, and diagonal setting can be readily determined. ft sorb the expansion between them. bracing of the elbows to provide Anchor design is particularly im- rigidity may suffice. Ilowever, every should be noted that when the minimum temperature is below 0 F., the portant with high pressures and large project must be checked carefully betemperature range used in determin- pipe sizes because of the high thrusts cause frequently it is necessary to ing expansion must be increased ac- that develop at end anchors. End anchor both elbows to prevent excordingly. Values taken from the anchors are so called because they cessive bending stresses in the pipe. curve include a safety factor of 10 occur at terminal points and at The importance of analyzing and percent over the actual pipe expan- changes in direction of the pipe. At properly providing for anchor loads sion to provide for discrepancies in these points, the pressure acting on is graphically illustrated in the folinstallation and unforeseen tempera- the inside area of the pipe would lowing actual case. A large steam line tend, if unrestrained by anchors, to in a tunnel had a right-angle offset ture extremes. Anchors-Anchors are important pull an expansion j-oint apart. Thus, of several feet. One elbow was conin any piping system, but there are end anchors must absorb this pressure nected to the body of a slip-type exsome special considerations necessary reaction as well as the forces required pansion joint which was very solidly when expansion joints or bends are to activate the expansion joint and anchored. The other elbow was lightly to overcome friction in supports and braced by an I-beam that was not used. In general, anchors are installed to stabilize the piping at certain vital guides. Intermediate anchors, on the properly aligned with the run of the points, such as valves or other equip- other hand, are subject to only the pipe. This brace was not strong ment, junctions of two or more pipes, latter forces. The curves in Figure B enough and it eventually collapsed. and terminal points. With expansion illustrate the comparative magnitude The full end-anchor load then acted joints, anchors also serve to divide the of end and intermediate anchor loads on the offset and created a large system into sections, so that each joint for slip-type expansion joints, and moment at the other elbow and the absorbs only the expansion in its own they also provide reasonably accurate expansion joint adjacent to it. anchor load figures for various pipe section. This may seem plementary, Although the joint anchorage was but it is frequently overlooked. There sizes and pressures. Values for corru- more than adequate for its normal are numerous instances where two gated joints are comparable, except loading, it could not support this adjoints are installed in the same section that end anchor loads are somewhat ditional stress. The anchor bolts were without intermediate anchors with higher in the larger pipe sizes because the result that one joint becomes of the larger area in the bellows. In- all sheared or dislodged from their its overloaded and subject to damage termediate anchor loads are some- concrete foundations; and, but for joint probaexpansion limit stops, the what lower because bellows require while the other one is underloaded. The converse of this is that two an- less force to actuate them than do slip bly would have separated. Because of its rugged construction, it withstood chors should never be placed in a joints.
9t
the abnormally high stresses imposed upon it and prevented further damage to the system. This case demonstrates the potential force of a moment; and, even more important, it shows how serious the effects of a failure in one part of ths system carr be to other parts of the system. Pipe Aligpment-Except
for
load is the vector sum of the thrusts in the two legs, or 21,000 pounds acting along an axis 45 degrees from the pif'e axes (dotted arrows, Figure 9). Maximum, contraction loads in the reverse direction consist of friction only and amount to 8000 pounds along the solid arrows with an.11,300 pound resultant. Note: Anchor loads with corrugated joints will be somewhat higher or louter depending on pipe size, pressure, etc. Consult manufacturer's in-
some
specialized applications of the corru-
gated type, expansion joints
=
and
bends require. good pipe alignment to
perform satisfactorily. Guides serve two important pur?oses. First, when installed near an expansion joint they prevent cocking of the sleeve in a slip-type joint, or distortion and possible buckling of a corrugated-type joint, or an expansion bend. Second, guides are usually necessary in long spans to prevent the pipe from buckling as the pipe expands. Ths tendency to buckle increases as the pipe becomes smaller in diameter, longer, or both; hence, the need for guides is greatest with long spans of relatively small pipe. Table 1 gives recommended spacing of guides from expansion joints and also between guides for various pipe sizes. Prpe Supports-Table 1 also provides generally recommended spacing
of
supports for steel pipe filled with water. The importance of adequate support is well recognized. However, it should be pointed out that supports must be designed to withstand the thrust resulting from motion of the pipe over the supports as well as the* vertical load due to gravity. Failure to provide for this thrust has resulted in failure of the supports in some installations.
System Design-Figure 9 shows a typical refinery piping system using slip joints, consisting of 8 inch steel pipe with a total length of 770 feet. It carries steam at 125 psig, with 25 F. suporheat. The procedure for finding traverses, anchor loads, and guide and support locations is as follows:
TRA\IERSES: Saturation temperature for 125 psig. steam is 355 F. Recommended Spocing
structions.
FTGURE
8:An# i:'":'i
i,'I11"",."a,o,"
ona
end onchors used with slip ond other types
of
exponsion joints.
(Figure i). Add 25 F. for a total temperature range (assuming minimum temperature to be 0 F.) of 380 F. Expansion for this range is '3.4 inches per 100 feet, from Figure 7. . Span AB : 140 feet; expansion :
(l+0) (3.4) 1100:4.8
inches. A single-
end joint with an 8-inch traverse is suitable at Point A. Span BC is 90 feet long and has an expansion of 3.1 inches when figured as above. Ilence,
the joint C is single-end with 4-inch traverse. The span CE is 430 feet long with 14.7 inches of expansion.
A
joint with an 8 inch at each end is suitable at D,
double-end
traverse
the approximate mid-point. Span EF
is 110 feet long with 3.7 inches of exfor which a single-end 4 inch traverse joint will be adequate. pansion,
ANCHOR LOADS: fntermediate anchors at A, D, and F are subject to possible maximum loads of 8000 pounds in both directions. These values are obtained from Figure
8 for 8-inch pipe. The contraction loads equal the expansion loads but are in the opposite direction. End anchors at B, C, and E have possible maximum axial loads of 15,000 pounds in each leg (solid arrows, Figurs 9). The resultant anchor
TABI.E I for Pipe Allgnment Guides ond Supporis, in
Feet
Nominal Pipe Size, Ioches...., Distance between guide and expansion
6161717181
8le
11112113114115116118
151r0122125130135145 11112113114115116118
92
I
SUPPORTS AND GUIDES: FTom Table 1, assuming the joints are the internally-externally guided type, install alignment guides not more ihan 18 feet from slip end of each joint and at intervals of 45 feet, more or less, along each span. Also, from Table 1, the pipe should be supported at intervals of about 18 feet and wherever concentrated loading exists due to valves and fittings.
lnslollqtion-Having designed the the expansion joints, it is advisable to observe the system and selected
following points at the time of installation. Align the expansion joint carefully with the pipe span so that motion of the sleeve (or bellows) is axiat
and lateral thrust on the joints is
minimized. Also, for the same purposes, be sure that guides adjacent to
the joint are properly located and aligned. When installing expansion joints with anchor bases, uss ihe full number of bolts provided for and tighten the nuts securely. This is particularly important at end ancliors. If the temperature of the pipe at the time of installation is appreiiably higher than the minimum temperature designed for, expansion joints should be preset to allow for contraction. To do this, the sleeve of a slipjoint should be pushed in from its fully extended position a distance at least equal to the distance the pipe will contract in going from instillation temperature down to minimum temperature. Corrugated joints are sometimes furnished in mid-position to cover such conditions, but with all designs of joints and bends the manufacturers' instruction should be carefully followed.
lnitiol Operction-When the sys10
10
11
12
L2
70
22 80
25
60
00
1Li
26 110
20
21
22
25
26
20
tem is first energized, expansion joints should be checked for leakage or any other signs of improper operation.
Usually joints which are properly
joints will vary according to a variety
of factors such as
ANCHOEED
sIrl4LE-EN[)
stallation.
JorNT
Ai.CrlopEt)
S(N4LE-END
Conventionally packed joints are kept tight by taking up on the gland nuts from time to time. Eventualln
Al\)C}IORED
Dou6le,.epo
JcxNf
AlrC.{ocED ELBoW GUrDE
r L ^
UNIO.ICIiOQEO
SINGLE-ENO JOTNT
ANCHOEEO FIGURE
9-Typicol refinery piping
GrlOry
I \
system using slip loints to obsorb the exponsion ond controction.
constructed and installed will need no attention for the first few weeks. I{owever, it is quite normal for the packing to require some attention after a month or so in service. In a conventional gland-packed joint this con-sists of tightening the gland nuts evenly until signs of leakage dis-
times a year. One shot (strokg of pump-gun lever) in each fitting will usually suffice to maintain optimum packing quality. Only in rare cases of relatively high pressure and temperature should it be necessary to increase
appear.
the sleevs and g1and. Always use the lubricant recommended bv the manufacturer of the joint.
In the gun-packed type, the addition of only a few plugs of plastic
packing (depending on size of joint) is necessary. Once this initial adjustment period has passed a regular maintenance schedule should be established, the frequency of which will depend on the operating conditions (steam pressure and temperature) and the type of joint used.
Lubricqlion-Good maintenance of expansion joints is primarily a matter of keeping the packing tight to prevent leakage and lubricated to keep sleeve friction low. Though not recommended, most joints will operate in a dry, unlubricated condition, but the stresses in the pipe, fittings, and anchors will be considerably reduced by a nominal amount of the correct lubricant. Furthermore, lubrication helps retain the sealing qualities of the packing, in the conventional as well as the gun-packed type. fn the better designs, alemite-type fittings are provided on the body of the expansion joint, through which lubricant can be added to the stuffing box with a lever-operated gun. Fittings are usually the hydraulic or button-head type and have built-in check valves to prevent blow back from the pressure in the stuffing-box. In the average case, gun-packed joints on continuous service need lubrication no more than two or three
this rate. Excessive lubrication
is
shown by oil being extruded between
Pocking-Packing requirements of
conventionally packed
expansion
S. ROBERTS received his
B.S. degree
in
of course, steam must be shut off and the stuffing box overhauled; i.e., the gland pulled back, old packing removed, and fresh packing installed. Packing rings should be carefully measured and cut to fit the stuffing box snugly. Rings should be installed with ends staggered so as to minimize the possibility of leakage from one ring to the next. ft is most important that the gland be tightened evenly so that cocking is eliminated (no binding on the sleeve) and packing pressure is uniform around the sleeve circumference.
The great advantage of the grrnpacked expansion joint is that it does not require overhauling. The cost and inconvenience of shutting down the system is completely eliminated. Leaks are sealed simply by forcing small plugs of a specially prepared plastic packing into the stuffing box by turning a threaded plunger with a short
wrench. This feature is shown in Figure 6. In normal service, packing needs to be inserted in gun-packed joints only two to four times a year. Experience varies considerably, depending on service conditions, and some installations have required no more than one packing addition per year. The amount of packing inserted varies from one or two plugs to several
Meet the Aulhor
K.
service pressure,
and temperature, traverse, frequency of expansions and contractions, design of joint, and alignment of in-
engineering from
Hartford College, Hartford, Pa. in 1942. His professional experience includes being a field engineer with the U. S. Coast and Geodetic Survey, Washington D. C. from lg47 to 1948; and a cost engineer with GeneralShea-Morrison, fnc., contractors for the Hungry Horse Dam in Montana from 1948-49. Roberts is presently a mechanical engineer for Yarnall-Waring Co., Philadelphia, Pu., where his duties include the design and application of expansion joints and other products.
plugs per packing gun, the number of guns per joint varying from one to 12, depending on the size of the joint. As a rule it is wise to establish a
regular schedule of packing and lubrication maintenance, the .nature and frequency of which can best be determined by experiencs in the par-
ticular installation. Refinery and petrochemical piping systems provide many opportunities for wise use of all the available means to absorb pipe expansion. The ultimate choice of the method to be used lies with the designer of the piping system. The pointers outlined in this article should be useful to all designers, operators, and supervisors who must choose, use and maintain devices for absorbing pipe line expansions and contractions. ##
93
Spring Honger Pipe Supporl
PLAN
Use scale plan of piping
ELEVATION
(left) and elevation (right) to simplify hanger
design.
Spring Pipe Hanger Design Simplified By using a scale plan piping drawing, the Iocation and weight of piping components can be greatly simplified Wqrren E. Doyle, Las Vegas, Nev. weights of the flanges ar A and F to points the weight of pipe C-D to fall at D. given to the location and weight of various components of a piping system. The results are well within tha fimits that are correctible by adjustment at the time the supports are installed.
Sample Design Procedure. Problem. Determine the load required to be supported by a constant-support located at point-D of the piping system shown in the figr.rre.
Assume: 1. The unsupported pipe between A-C and D-F is saje and not overstressed. 2. Piping system between A and F is adequately flexible provided the total vertical movement is shared by
A-C
and D-F. 3. Pipe weighs 100 lbs. per ft.
sider B-C to be one continuous pipe even though it is interrupted by a valve. Include the weight of flanges and bolts connecting to a valve as part of the valve. Add the
94
A and F and
2. Layout the piping system to scale and draw workin plan between the points of support. A-CD and
lines
CD-F.
3. Transpose the weights of the components from their center.of gravity to the work-lines, at right angles to the work-lines, such as the weight of pipe A-B, rvhtse center of gravity is at G to fall at H, the weight of the valve to fall at K and the weight of B-C to fill at J.
4. Calculate the loads at A, D and F considering that the transposed weights at H, J, L and M ar.e loads fall_ ing on simple beams whose ends are at A and C. and D and F.
5. Determine total r.veight of the system frorn the figure and knorr.n inlormation:
A-B: B-C:
[: J-
Valve: K: C-D: D-E: L: E-F: \{: Flange @A: Flange @B: Total
400 700
500 1 500 800 200 100 100
4300 lbs.
6. Determine the following dimensions by scaling the plan in the figure:
C-K:
D-L: D-M: : D -F
1.5
c-J :
3.0
C-H: C-A:
7.O
8.0
2. Install all appurtenances which attach to the pipe being supported, including but not limited to: insulation, valves, instruments and branch pipes.
3.85 8.0 8.25
Calculation: 1. Take moments about C to find the load at A: (r s X 500)_* (3 X 700) * (7 X 400) roo
o: A
_
l
8.0
(7so
+
21qo 8.0
+
28oo)
loo
:8o6
rbs.
8.25
* roo:667 :
total system load minus
: 4300- 806 -
-
2827 lbs. (answer)
667
5. Where the load indicator fails to mbve from the
rbs.
3. Find load @ D: D the loads at A and F. D
the screw-device provided as a part of the hanger. In some cases this device is a turnbuckle in the pipe-hanger 4. Load all spring-supports approximately at the same time until the pipe has raised approximately 1/16-inch above each temporary support. Readjustment will be required since some unloading will be required of those spring-supports which are first to lift their pipes.
.:W*,oo (3o8oJ-l600)
3. When the pijring is completely installed, leak-tested and cleaned, the spring-supports are ready to be installed, loaded and adjusted. Load the spring-hanger by turning rod.
f
2. Take moments about D to find load at F:
-F:
constant-supports may be installed temporarily, provided the pipe is not permitted to deflect the spring.
(-)
Select a support from a manufacturerrs catalog. One spring support suitable for this application has a nominal rating of 2900 lbs. and a load-range of 2030 to 4060 lbs. over its working deflection range, which tends to justify the short-cut method described herein.
!nslqllqti,on Procedure 1. Install piping on temporary supports where shown on the drawings. These temporary supports may be of any description consistent with good field-practice and which does not interfere with installation of other piping. The
top-most part of the scale during the loading-operation, or where the load-indicator in its final location, relative
to the ends of the scale, does not allow for the expected operational movement of the pipe, or when the loadindicator moVes to the bottom of the scale without raising the pipe, the spring is inadequate and shall be
to replace a spring-supPort is very were designed by any of the accepted procedures or by the procedure described herein. replaced. The need
unlikely
if it
6. After the piping system is completely installed on spring-supports, make a punch mark on the support scale at the load indicator and then, when specified, make
adjustment for the weight of the fluid in the pipe. Adjustments are usually made only for liquids and are not made for gases and vapors. Liquid hydrogen is one exception because of its light weight (+.+3 lb.lft.3 ) and may be neglected the same as a gas or vapor.
7. Where compensate
. About the Author Warren E, Doyle is the resident engineer at the Nuclear Rocket Development Station near Mercury, Nev. IIis companl. is AETRON. Div. Aerojet-General Corp. Mr. Doyle's drrtics ere to give engineering sup-
port to the Space Nuclear Propulsion Office, a joint ADC-NASA Agencl', for the construction of a nuclear rocket engine test facility for the NERVA engine. He has studied at the Llniversity of Minnesota and Indiana University. Prior r,, jni11i11q ,\ETRO\ lrc sr. e projr:tt cnginccr rvith Air Ploducts and Chemicals, Inc., on liquid hyclrogen
f)ovle
it is desired to load the spring-supports for the liquid-load proceed as follows:
to
Calculate the load imposed on each support by the liquid alone, using the method given in the example above.
o Adjust each constant support so that it lifts the additional weight designated for it. The amount of this rveight is usually arbitrarily set at 50 percent of calcr.rlated liquid-load. This will make the prestress in the pipe about equal to the stress during operation and is about half of that u,hich '"vould result if the springsr-rpport rl.ere adjusted for the full liquid-load. The
additional load can be measured on the load
scale
betrreen the punch-mark mentioned above, and the load-indicator.
production facilities and nuclear re-
actor testing facilities. lIe rvas also associated rvith Danicl, X{ann, Johnson and Mendenhall, Architects and Enginecrs, as a mcchanical design group leader. He is a registerecl professional enginccr, a member of the National Socicty of Professional Engincers and the American Instilutc of Aeronautics and Astronautics.
CAIJTIOII! Before disconnecling a pipe line or rerroving any part of a piping system that tends to change the rreight on a spring-support, provide a fixed tempo-
lall
support for the pipcline belore removing the spring-
support. Failure
to do this may result in the
causing excess deflection and stress
in the pipe
spring
## 95
Piping Tierod Design Made Simple Most piping designers recognize the need to provide tierods around pipe joints. What are design requirements? Here they are-simplified Worren E. Doyle, Guided Missiles Range Div., Pan American World Airways, Inc., Mercury, Nw. TrsB.oos ARE usED to restrain the anchor force producod by the particular group of pipe-joints which tend
to pull apart when
subjected to internal pressure. Figures 7, 2, and 3 show typical installations of tierods around such joints. The structural failures shown in Figures 4 and 5 graphically demonstrate the consequence of having an inadequate anchor system around an expansion (These joints failed under test pressure, whereas, they should have been able to withstand rp to 2/z tmes
joint.
this pressure without failing.) The technology governing the need for tierods, and their design is quite fundamental, yet, tho absence of tierods where they should be used, is one of the most frequent hazards in existing piping systems. The object of this article is to show the conditions where tierods are required to make a piping system safe, and provide the tools to simplify the design of tierods and other anchor systems.
There can be other conditions which add to the longitudinal (anchor) force produced by internal pressure, but the force resulting from theso conditions is relatively small,
tE.
and usually disregarded in the design of tierods; e.g., the longitudinal component of the centrifugal force caused by a change-in-direction of a pipe flowing water at 50,000 gpm in a 30-inch pipe, is equal to the longitudinal force produced by an internal pressure of only 6 psi. It is unlikely that the sum of this pressure and the operating pressure, would ever exceed the design conditions of a piping system. A condition where tierods in a long-vertical run-of-pipe support a dead load, should be examined for the effect of the dead load on the design conditions of
the tierods. The longitudinal force in a pipe joint, caused by internal pressure is,
P-Ap
(1)
,{: effective area of the pipe joint, and .1, : pressure in the pipe, The effective area of a sleeve coupling, or bell and spigot-type joint is considered to be the area of a circle having a diameter equal to the outside diameter of the pipe. The effective area of convoluted expansion joints is determined by pressure tests, which are made by the manufacturer and published in his catalogs. The eflective areas given in Table 1 are representative of the product of several manufacturers. where
Design Procedure. 1. Determine the longitudinal force ( 1) , using the effective area from Table 1 and the specified test pressure, ot L/2times the working pressure of the pipe line, whichever is greater. Add to this force, any other longitudinal force in the joint, to obtain the Total Longitudinal Design
in the pipe-joint from Equation
Force.
2. With this design force, enter Table 2 and select the
,
ta,
I
Fig. l-Tierods around a slide-joint in a pump discharge pipe.
96
Fig. 2-Expansion joint wittr factory installed tierods.
Fig. 3-Tierods around an expansion joint in vacuum service.
Fig. 4-Overstress failure in a gimbaled expansion joint.
Fig. 1-Overstress failure in a hinged expansion joint.
number and size of tierods most suited to the operating conditions. The joints which are required to have a hinge
3. Enter Table 3 with the size of the tierod selected, which determines the size of the tierod anchor required. The required section modulus of the anchor, given in the second column, has been determined using an allowable fiber stress of 10,000 psi and a distance of 3/2 inches from the rod to the pipe, which is adequate'for all joints in corunon use. The structural member size and shape given in the third column is merely a suggestion, other structr,rral rnembers may be used provided their section modulus
is adequate. Table4 is provided to give data for the design of tierods to suit conditions other than those given in Table 3.
Design Notes. Steel for tierods should be selected to have an ultimate strength of 40,000 psi, or more. o Tierods should have national-course threads and at least two nuts on each end. o Sufficient weld-metal should be used to develop the full strength of the tierod anchor where it connects to
l-Efiective Areqs of
500 .. 1,000...
% IZ
1,500. 2,000
,4
4,500,
5,000
.
6,000.
7,000 , . 8,000 . . 9,000, . .
10.000, . 12.000. .
.
(1) The recommended choice of tie-rods is \\'ithin the heavy lines. a2) l'he size of tie-rods is based on a tensile strength of bolts giYen in Table 4.
fABLE
!.. t]. li lo.,
t.l.
Iri
13
15
20 29
.4+ .56 .70 1.06
58 90 L28
135 180
20.. 30.
51
L54
.
Ita..
.
Structuml & Shape (2)
Member Slze
In.
4 .
tl
Anchor Selection Tqble
.09 .15
3
4..
3-fierod
Convoluted Expanslou .I olnts 1
200
97 231 289
254 314 452
424
702
871
r Areas representative of the product of several manufacturers.
5E3
RODS
3,000 . 3,500 .. 4,000 .,
Pipe Jolnts
SUp-Jolota
TIE
slt
2,500 ..
Rod Size
Nomlnal Plpe Stze
Selection Dotq
NUMBER OF
Force, P Lbs,
the pipe. Whe.re an expansion joint is used in a vacuum line, or lvhere any other compressive force is required to be TABLE
2-Tierod
Longltudlnal
action should have two tierods.
o
TABLE
r.47 1.93 2.42 3.10 3.70 4.50 6.10 8.00
2 xr)4x sl6L 2 xllx )4L 2 x71,5xl4L 2)4x7)4x )4L sAaL
2)4x2x
3 x2 r )4,L 3 x2 xsAaL 3x2x3xrlU 4x2x4xlU 4x2x4r)y',U 4x2x4x 5l6U
(1) Based on an allowable fiber stress of 10"000 psi. (z) Ottrer shapes may be used if their section modulus is adequate'
97
PIPING TIEROD DESIGN MADE SIMPLE . TABLE
4-flerod
.049 .077
16
.1
.027 .045 .068 .093
10
.150 .196
13
72
.248
10
.307 .442 .691
l1
I
8 7
.785 .994 L.227 1.485 1.767
6 6 5
2.405 3.142
4%
.
Design Doro
20 18 74
.
.126 .162 .202
.302 .419 .551 ,693 .890 1.054
7.294
t.745 2.300
270 450 680 930
t,260 t,620
(o)
HTNGED ExpANSroN-JorNT
2,O20
3,020 4,1 90 5,510 6,930 8.890 10,540 12,940 17,450 23,000
SPACER
sleeve should be placed over each distance between the anchors, with t in the free condition, as shown in
.
Thg design details of tierods around an expansion joint tllat the required function o] the expan_ sion joint is not jeopardized. fn certain cases it is necessary to specify a particular gap betryeen the tierod anchor and the tie.rod stop. See Figure 7 f.or typical tierod design detail. shall be such
(a)
Exr,ANSloN-JorNT "TMBALED Fig. L-Gimbaled and hinged expa.sion joint detail.
@
(D "
A2P
where
P:
3l total longitudinal design force
joint,
(2)
in the
rrrnoo trrRoo ANcHoR
@ erer rrrue srrrve @ COUPLING -
expansion
Fig. 7-Typical tierod design detail.
and
f - allowable shear stress. Where the force is appreciable, the pin connection
About the quthor WnnnnN E. Doyr,p is a faciti,tg engineer at the Nuclear Rocket Deuelopment Station near Mercu,r'y, Neu. His com,panE i,s Pan American Wo,t'ld, Airuags, support serui,ce contracto,r, fo,r, the station. Ml,.
DoEle has
should be designed to place the pin in double shear, as shorvn in Figure 6. The structural failures shou-n in Figures 4 and 5 undoubtedly would not have occurred i-f the pins had been in double shear. The maximum stress in the gimbal ring occurs at the pin connections, rvhere the bending rnoment,
M: whcre
P: total joint,
Minnesota
8
(3)
longitudinal design force in the expansion and
: outside diameter of the gimbal ring. This equation takes into consideration the fact that the ring is not an ideal beam- and is intended to give a con/
has held, utith Air associatecl
and Xlendenh.all, Architects and Engiresident
Heisa
National
-ic'un In-
selvative design. The tension bar at the pin connection should be designed to be stronger than the pin. The holes for the pins should be drilled and reamed to
a Class 3 (medium) fit
98
PI
J)- JL
1+ 1+
NOTES
99
HERMOWELLS
g"
Thermowell Design For Process Piping Pqrt l: Procedures For the Piping Designer Part 2z Installation and Specifications Part 3: Selection of Thermowell lnsertion Lengths John A. illqsek, Philadelphia DesrcNrNo pRocEss piping with thermowells properly located so they will project inside the pipe to give accurate temperature readings with good speed and response requires important engineering considerations.'This will often present a perplexing problem to the new designer because this design work must be done without knowing the length of the thermowell, especially in the early fl35orern uooLEFS design siages of a project. The inexperienced piping dethe situation. signer will unfortunately find this Parts 1 and 2 of this article will provide sufficient information for the design and installation of the threaded
type thermowells in piping. Part 3 will show how to seiect the proper insertion and immersion lengths of thermowells for most pipe configurations and pipe sizes. When the design work of a project is started it usually has to be done under pressure to meet drawing completion dates. These schedules impose an additional burden to the designer unfamiliar with thermowells. Practically, there is no time for training or consulting available instructors. Sometimes the designer may be able to obtain the desired information on how to install thermowells. At other times he will not get assistance so he must do the best he can. He has learned from experience that to ask
Iines, regardless of size. This will create a problem for the piping checker who will have to redesign sections of the piping to install the thermowells properly. Most engineering design offices have a piping depart-
FIGURE
Fetp Cutrr-er
l-Flow
sheet showing temperature instruments re-
quired and sensing points.
pend on ho- *u.y experienced piping designers are assigned to the project. Some engineering offices may have elaborate instrurnentation standards to which the piping designer can refer and follow in this design work. Other drafting rooms may not have any such standards, thus leaving it up to the individual piping designer to work out what he may think best. To an experienced designer this is no problem.
Flow Sheets qnd Temperoture Points. AII refinery and chemical plant design work is guided by flow sheets.
instrumentation designers working with this department will make the required instrument drawings covering
the project. Since thermowell connections are for instruments that must be installed in the piping by the piping designers,
On other occasions each department may function independently with the result that instrument and thermo*"^ll .o.rrr""tions may or may not receive the attention they should from the piping deaprtment. Much will de-
These present the diagrammatic arrangement of the process equipment and piping. The flow sheets of a process become the main working reference for the piping designer. Tho temperature points, with their index numbers, will be found and will require the installation of thermowells in piping. The temperature index numbers assigned to each point are designated by conventional symbols such as Tf, (Temperature Indicator),
TH, TIC, TC, TRC, TR, TIA, TRCA, TT ANd TW
followed by the number assigned to each of the points.l In Figure 1, a partial process layout from a Process flow sheet illustrates where the typical temperature instruments'have been actually assigned, and later used in designing the process pping. Only the temPerature points have been shown. The other instruments have been omitted to emphasize the installation of the thermo-
rot
(l-l .'r--:n .r1 3 -,-
(.)
(c)
(6)
(l)
(f) (h) (i)
(e,\
FIGURE
2-For process piping 3-inch and larger, typical thermowell locatio-ns. Instillati6n details: therm"obulb"(g),
thermocouple
wells in the piping. The flow sheets will give the pipe line size and the prylng specification reference to use. In
pipe that may be shown on florv sheets into rvhich thermowells are installed is a pipe reducer betrveen trvo flanges. Such a connection may be used betrveen t\\.o heat exchanger nozzles as shown in Figure 2c.
this case we will assume that the l-inch pipe thread thermowell complies with the specification for the job. An identifying process reference line number may also be given to each line; giving the piping designer the necessary data needed
to proceed with this work.
Piping foyout. The plot plan of the project will usually in thl process afea with the elevations. The equipment connecting nozzles required in connecting the process piping with the pumps, vessels and exchangers will be found on the respective equipment drawinp. The pping designer will layout the piping to suit the general piping arrangement, clear the obstructions, and run the piping from one piece of equipment to another. The piping must be run in the space provided, without interfering with structural steel platforms and other piping. Sufficient space must be provided for the valves, flanges, instrument connections and for the installation of thermowells. Thermowells must be accessible from the grade, floor or platform. fn the case of a dial thermometer, the face must be easily seen. Piping will often have to be diverted from the shortest possible course with the addition of extra fittings to install thermowells. Possibly the shortest piece of locate the equipment
ro2
and dial thermometers
(j) (k)
(l).
When two different process lines conr.erge into a pipe tee and then flow into one line it is necessanr to get a good representative temperature. This pipe line must extend not less than 10 pipe diameters to obtain a good mixing before the flow reaches the thermorvell. An erample of this is shorvn in Figure 2. Thermowells for Lorge Size Pipe. Thermorvells can be installed with ease in process pipe lines 3 inches and larser. Every effort should be made to install the thernowell connection in a welding pipe elbow. The connection should be made b1, rvelding a l-inch, type 6000 lb. or other size forged steel elbow adapter in the heel of the pipe elbow (see Figure 2). If this is done the thermowells with the longest required insertion length can be installed u'ithout running into interferences inside the piping. The pipe should, of course, be laid out so the thermorvell rvill be accessible from the grade or platform. Since most thennowells must be removed for inspection during a plant shutdown they must be located within the pipefitter's reach, preferably without resorting to the use of ladders. This will often require an additional proc-
Coxootr
(cnrtr
r-
To
?trc,l
!r.x'-
u\ FIGURE 3-Small ess
process pipe lines,
fi
to 2-itch, swaged up to accommodate thermowells.
pipe elbow in the line. This precaution will be ap-
preciated by the maintenance department and by those who have to service the equipment. Some
of the typical piping layouts that can be
used
are shown in Figures 2a to 2e. Only the pipe elbow has been used in each of these details for installing thermowell connections. These are for dial thermometers, thermocouples and thermobulbs. Such arrangements are necessary whe,n the 3-inch and 4-inch and larger process lines are used. It is often possible to install dial thermometers and thermocouple well assemblies on a 45-degree angle by using an elbow adapter as a lateral connection as shown in Figures 2h and 2k. Thermowell connections
can be installed perpendicular to the pipe wall with a forged steel thread adapter. This arrangement can be applied best on 4-inch and larger pipe as shown in Figures 2i and 21.
Thermowells for Smoll Pipe Lines. Installation of thermowells in small sized process lines f-inch to 2-inch requires special consideration. Because the lines are small, the thermowells cannot be installed directly into the process piping; this would restrict the flow in the line. The pipe is enlarged to overcome this or swaged up with a2/z-inch pipe elbow to accommodate the f -inch elbow adapter connection for the thermowell. Thermowells with 6-inch insertion lengths or longer can thus be installed. Longer length thermowells required for long thermobulbs furnished with the instrument or process requirements can have the 2/z-inch outlet of the pipe elbow extended with a 2t/z-inch pipe spool piece, to accommodate these wells.
In Figure 3 four typical piping arrangements
are
shown to be used in installing thermowells. When the enlarged sections must be provided with a 2f-inch spool piece, the minimum length should be at least 12 inches.
Note that the Figure 3 details are accessible so the thermowells can, be taken out and inspected and reinstalled
during plant shutdowns. Providing for an indicating dial thermometer, the swaged up section should be located to be seen from the grade, floor or platform. At times it may be necessary to install two thermowells together in the same pipe section for the same service. Such installations may require an indicating thermometer and another thermowell for a temperature transmitter thermobulb. The 2/z-inch enlarged pipe elbow with the spool piece can provide for these duplex installations. These sections should be made up to enhance streamline flow. The fittings should be assembled to prevent the residue in the florving product from accumulating inside the pipe and around the thermowell which would present a temperature Iag to the operating instrument. The swaged up section could give the arrangement an awkward appearance, thus every eflort should be made to blend this piping with the surrounding equipment. In Figure 3a, this 2t/z-inch section is installed in the vertical, with a thermometer at the bottom, and the thermobulb at the top. The vertically installed thermowell may be required if a thermal-fluid is to be placed inside the well to increase the thermal transmission through the well to obtain a quicker temperature response, to the instrument. In Figure 3b, the 2fi-inch section is installed with two l-inch elbow adapters in the horizontal with one connection for the indicating thermometer and the other for a duplex thermowell containing a thermocouple and a zfi-inch diameter thermobulb for a temperature transmitter. If vibration is likely td be transmitted in the piping, the transmitter should not be supported from the process piping but instead mounted on a building column, wall or from a floor pedestal. In Figure 3c, two 211-inch pipe elbows are installed together with a pipe spool piece at the lower end to increase its length for the installation of a thermowell with a thermobulb. The other elbow adapter holds a dial thermometer in a 6-inch long thermowell. In Figure 3d,
t03
THERMOWELL DESIGN FOR PROCESS PIPING
-a
.1'
FIGURE 4-Three types of l-inch con-
nections
for
thermowells
installed
on
welding pipe elbows: (a) regular pipe coupling that should not be used, (b) improvised connection made with a boss,
(c) 6,000 lb. forged steel elbow adapter provides best thermowell connection at lowest installed cost.
a single 2t/z-inch pipe elbow is installed with
suitablc
pipe reducers to fit the small size process line. The l-inch elbow adapter holds a 6-inch long well with a thermocouple (T/C). The T/C head is connected with an electrical conduit that carries the circuit to the temperature recorder on the control panel.
ThermoWell Pipe Elbow Connections. Most themowells for process work will require a l-inch pipe thread connection, for its installation, in process piping. It has been observed that in some engineering offices a f-inch, 3000 lb. or 6000 lb. forged steel screwed end (F.S.S.E.) pipe coupling will be specified for the installation in a pipe welding elbow. This continues'from the time when there was nothing better. If the designer would check this, he would find that the pipe coupling cannot be installed, in pipe elbows. This is shown in Figure 4a. This is often done by designers new in this work who are under the erroneous impression that this makes for a cheap installation.
The piping fabricators are well aware of this, and inwill provide a steel boss lf-inch in diameter by 4 inches long, drilled and tapped for a f-inch pipe stead
l04
thread. This boss is then n,elded into the pipe elborv as shown in Figure 4b. It is a more erpensive operation than using an elbow adapter. The best and cheapest installation for a 1-inch thermowell is to rveld a 1-inch type 6000 lb. F.S.S.E. elborv adapter in the heel of a welding pipe elborv as shou.n in Figure 4c. The elbow adapter is shaped for u'elding and gives a streamline florv service and appearance. It rvill
prevent unnecessarv flow turbulence in comparision to a "boss installation." mentioned above. During some refinery inspections it has been noticed that rvhen bosses are installed in pipe elbows, for mounting thermou'ells
on hot oil serr.ices, considerable erosion would actuallv take place inside the elborv, in the welding area, because of the flow turbulence. It is therefore recommended that for all threaded tvpe thermowells installed in piping whether 3A-, 1-, or l/a-inch, an elbow adapter rated at 6000 lbs. (F.S.S.E.) type shall be welded on all pipe lines requiring a thermowell connection. LITERATURE CITED
rlnstruentatioD FIow Plan Symbols, Iutruent Pittsbugh,
Pa,
Sciety of Amerie,
Thermowell Design For Process Piping Part 1: Procedures For the Piping Designer Port 2: lnstqllotion ond Specificotions Part 3: Selection of Thermowell lnsertion Lengths John A. Mqsek, Philadelphia Thermowell connections for temperature sensing devices, specified by the instrument department, are designed by the piping department and installed by the
piping fabricator. This divided responsibility produces an often neglected design detail. Part I of this series described how the piping designer can properly design thermowell connections by using information on the flow sheet to locate the thermowells on the piping drawings.
in most cases because the pipe branch is permanently installed in the pipe connection and will remain in place throughout the plant's existence. be satisfactory
It
also described design consideration pipe sizes 3-inches and over as well as
for thermowells in for small size pipe. This part will describe detailed installation procedures and specification details.
Fittings For Thermowell Connections. The piping for a refinery or chemical plant will often give the allowable sizes permitted for screwed pipe specifications
branch connections. For usual piping services, the 2000 lb. or 3000 lb. F.S.S.E. fitting will be specified This will
Thermowell requirements differ from the screwed pipe branch connection in that the threaded thermowell must be removed occasionally for inspection, especially during plant shutdown, and then replaced. This will require perfect pipe threads for the thermowell connections. If the t/, l, or ltf-inch F.S.S.E. type fitting rated at 6000 lbs. such as a thread adapter, elbow adapter or pipe coupling is welded in the process piping or equipment, good threads can be assured.
Pipe welden differ
in their
welding technique;
some
can do a better job than others. If a s/, l, or l/a-inch F.S.S.E. 6000 lb. rated thread adapter or elbow adapter is installed there is a better chance that the pipe threads
and connections will be free from warping. The fitting will more than likely take overheating which will prevent stress concentrations in the pipe threads. It may happen that during one of the thermowell in-
For
T.c.
I
rrira?ar'-l (c) Tf'pical
thermmouple u'ells
Jxenmotourre Hero
I'PItt ilrfrLr,3'Loi6
/r.r*lffill
ril.PT lf-,.Dre,
To lH6Tiliexa.
(a) Typical dial bimetallic thermometer
TrrRxotol!
,'i, +t,t
rr
-(d) _Double bore well
ell
head
Jlcerrt LExctr Ta Surr :zo4"Eors For
Tlermocoutrt
L .31s" B o*, Fo^
.!Jr "! r a.THErhoruLl
with bore lor thermobulb and thermmouple including
i'tol"D,^. I ii ro't t+-l
i',ro
(b) Typiel thcrmowells for thcrmobulbs roburbs with filled niled
sysrem system
ll
['tii'"r"*$.;l1T3n'111j$,f:l['#"#::.i?.ilft'ud'd
FIGURE 1-Typical thermowell types for
r,/c
thermouerr,
process piping.
r05
THERMOWELL DESIGN FOR PROCESS PIPING
...
Pipe Threod Size For Thermowells. Thermowells can usually be obtained in pipe thread sizes of /z-inch as a special type, rvhile z/- and l-inch are the usual available stock carrying sizes and the lt/a-inch is a special size.
in the /2-inch size are used where on the equipment will only allow a /z-inch connection to be made for either a thermometer or thermoThermowells
space
couple assembly.
l'x,r.r.
The zfi-inch size thermowell is generally
tl*:: f
Nlrial.G.pa.r
FIGURE LThermobulb installations: (a) Special union fitting-use with caution, (b) Cormgated sleeve, (c) thermal liquids.
spection periods the pipe threads may require retapping.
A 6000 lb. rated fitting will also have sufficient metal to permit retapping in the future. If this is done it may be necessary to replace the thermowell with another well, one with a long tapered pipe threads io fit into the enlarged retaped connection. Thermowell manufacturers can provide such wells on special order.
There are seemingly unrelated reasons for using the 6000 lb. thread adapter, elbow adapter and pipe couplings for thermowell connections. Prefabricated pipe bends are often shipped to the plant site in long haul trucks or in freight cars. While these pipe bends are in transit they will get some heavy jolts. A 6000 lb. rated fitting is more likely to lvithstand darnage under these connections. When the piping is being erected, the pipe fitters will often use the l-inch thermowell connection fitting as an erection lug. A pipe nipple may be screwed in temporarily and used as a ladder rung to support a pipefitter's foot. A 6000 Ib. fitting will usually sustain such mishan-
3/, l, and l/a-inch, F.S.S.E.,
dling. Thermowells are provided in piping with the assumption that they will be used under normal flow velocity service. Sometimes unexpected high flow velocity may be encountered. A l-inch, 6000 lb. F.S.S.E. connection with
its extra rigidity will provide a better mounting connection for the thermowell and prevent it from vibrating and to withstand these disturbances.
ro6
selected
where process operating service pressures and tbmperatures are in the low range. They are used for mounting thermometers, thermobulb in thermowells and thermo. couple assemblies. These are a few dollars cheaper than the next larger size thermowell. When a z/a-inch thermowell is to be used, the pipe designer is cautioned not to use the conventional %inch full pipe coupling for mounting thermowells. If the z/a-inch full coupling is welded on equipment, the narrowness of the inside of the coupling where the two pipe threads meet may prevent therrnowell insertion. If a z/' inch type 6000 lb. thread adapter or elbow adapter, u'ere
instead welded on the piping this will make for a better installation. The l-inch size thermowell is the one usually selected for most process services. A typical selection of the thermowells is shown in Figure 5. They should be used when the l-inch pipe thread connection conforms with the piping specifications for the project. Sometimes they can be used on process services that operate at fairly high pressures and temperatures, as high as 750o F. The l-inch connection for these thermowells should be made with a F.S.S.E. type 6000 lb. fitting. When process pressures are
very high, approaching the super-pressure range, the threaded connection should not be used. The specifications in such cases will usually call for a flanged nozzle connection with a special type of ball ground joint for the thermowell. In some refineries, the l-inch threaded thermowell is used only on steam pressures, 400o F. and Iower, on water and air services. For hydrcarbon services, a ball ground joint thermowell that fits in a flanged nozzle, made to fit the joint, is often used. There are other special adapter type thermowells used by refineries.
Chemical and petrochemical units have been designed using piping specifications which allow for the installation of l-inch pipe connections for all the l-inch threaded type thermowells used throughout the unit. This ap-
plies to the process piping and the l-inch pipe thread connection that is also specified drums . for
for use on vessels
and
the threaded type thermowell. Normalll, type nozzle connections are specified for vessels
flange including those used for thermowells. Apparently the engineering departments of these companies have found
that in their processes the l-inch threaded thermowells will give satisfactory service. These processes usually operate in the low pressure and temperature range, and
the products are noncorrosive making threaded thermorvells acceptable.
The l/a-inch thermowell,
because
of its large
size
Prtr Nl??L1 \.lrr.Or[Nri. TilT \.ilrr l!Lo! n SL'Dr FrT f oi Tir lHtlio{Err--,
Rrgurer UJrrorrr
Nrer FLara! C^r Dt Dir!Lro Arr
SirrL
Jrt 5ot,o 5urpoirrtt Ero 0r Tcr l'prr. Traril.waLL Erf airr.* 7i.Ja.rr Ixr. 1ir .5lO" 0irrrcc O?arria. L.rta 5?rcr lt ErD, CouxT.R 6oRE a"', i',li"l'0rrrs 0a.r{.t ID .5lo'Olt,fri'a Dr..1rupurrL.
Trtrro PloYuur 'Irrr Am Il'
B
^r{.,.LDto
c-t", ti' or \L" -6oaof Ptan
't\N
I
, I
fo 5urr,---7
!,EY
Fol
I
ulrn
of pipe elbow with internal support for
thermowell
lcstlht'!lt. lSo".PtrarTrrrf/c, Lf0[.Prtre'[rrr T/crBor rrt'D'..(l.tio+).
Errrrr.r0 Vrrw 0r TrrlmourrLL
Hr.rr Tttr,xocoulr-c,
,
FIGURE 7-Orifice flange adapted for installing a T/C well and assembly.
thread, can be provided with a thicker tapered wall construction which starts at the bottom of the threads and is shown in Figure 5a. They are used for higher pressure, temperature and velocity steam services, becausc of its sturdy construction.
Moterio! For Thermowells. It is customary, when the piping and vessels are of carbon steel, to order the thermowells in stainless steel, AISI type 304 or AISI type 316 for greater protection. The AISI type 316 is often specified for refinery and chemical plant services and preferred when process pressures and temPeratures oPerate in the higher range. The thermowell manufacturers usually provide recommended materials selection list or chart in their catalog. This can serve as a guide in the selection of the right service material required for various process fluids. Special material recommendations can be obtained from the thermowell manufacturer by specifying the service and fluid in which the thermowell will be submerged. The threaded type thermowell connection is not recommended to be made of the same material as the special alloy of the equipment, this could cause galling of the thermowell pipe threads. In such cases it is customary to provide l/z-inch flange nozzles in the process piping and flange type thermowells are installed. It is important when selecting the thermowcll material that the composition will prevent an electrolytic action between the well, piping or vessel.
Thermobulbs Without Thermowells. The catalogs and service manuals for some of the instrument comPanies show recommendations for the installation of temperature transmitter thermobulbs; being installed without thermowells similar to Figure 6a. A compressiotr union fitting with gasket and packing gland permits the thermobulb to be inserted through this fitting and made
tight at the capillary tubing. This type of installation should not be emPloyed as a general practice. It may sometimes be used wbere a Doncorrosive pressure
Elevalion and section o[ process pipe shou'ing details support for thermorrcll.
FIGURE
8-An
installing for installing
inaernal
internal pipe supporting bracket for a long
thermowell.
,".uite exists, and no flow velocity to cause movement to the thermobulb that is suspended from the frail capillary tubing. It is regrettable that illustrations of these have been reproduced in several recent
process
instrumentation books.
While therc may be a slight increase in tl-re temPerature response, this may prove negligible compared to the disadvantages that may be encountered later. One inconvenience is that the process containing the thermobulb must be shutdown and drained each time the bulb is inspected.
A service man for one of the companies told the writer that he has had to answer many service calls on the complair,t that their temPcrature transmitter would not operate. After driving all day to get to some out of the way location, he would inspect the temperature transmitter which was usually in satisfactory condition; the next step was to inspect the thermobulb. After the process was shut down and the line drained, he would open up the compression union. At this point when he would withdraw the capillary tubing, he would often find no thermobulb at its end. This had been corroded and was carried away with the process flow in the line. In other cases, the bulb was still intact; however, the flow velocity imposed forces on the thermobulb inducing stresses in the capillary tubing. A small crack would eventually develop and cause the thermal fluid under pressure to leak out thus ruining the temperature transmitter. Installing these thermobulbs in thermowells would have pfevented this trouble. Often the user of the instrument does not realize the benefits that can be derived by installing thermowells as shown in Figure 6b and 6c. Reducing Log. A thermowell is required to Protect the thermal element of a thermometer or temperature transmitter thermobulb from corrosion, erosion, and to give
t07
THERA,TOWELL
DESIGN FOR PROCESS PIPING
.
length
T"Z"ltt,urrocs Flexo;
a metal to metal contact throughout the of the sensitive thermobulb. In some cases, two
insuring
.
Tc Dottor.r oF ELrrrD
Trir ecrr is 0 Fr,cw DiFlrc,roa. Dlrrr- A{r Tol For TrEi,rour ur, I ilt,?, T. Crrrr.
sleeves are used on both sides of the bulb. The corrugations in the sleeve itself provide a metallic path between
the well and the bulb on opposite side. The advantage of using a sleeve is that it can be applied to thermowells installed in a vertical, horizontal, or in an upsidedown position.
The standard type thermowells manufactured EorTom Srre 0r
{-tgo*
n,f. F.5,BrtHD
Cenllrr\ Turrxe
FuRile
To lrt
Dr-rxo Fuc. Drtuurp
s.
rr r.
t T^er:o,
and
supplied are provided with the following bulb diameter to well bore relationship. The dimensions listed in catalogs are usually given as (/a-inch bulb fits into a 0.260inch bore) ; sft-inch into 0.385-inch); (/2-inch into 0.510-inch) ; (9/16-inch into 0.572-inch) ; s/s-inch into 0.635-inch); (11/16-inch into 0.707-inch) ; (s/-inch into 0.760-inch) .and (t/g-inch into 0.885-inch). It is generally assumed that thermal liquids and metallic filings will be used when the thermowell bore is excessive, a condition encountered when an existing well must be used, or a crude well is made up in the field to be used in an existing process cannot compare with a thermowell manufactured to close bore tolerances as those listed above.
f,revr tr ox FIGURE 9-Thermowell protected with angle iron
deflector.
When thermowells are installed, in a vertical position in piping and. equipment, various substances are used to increase the heat transmission and temperature response is by using mercury (See Figure 6c) . Mercury is -one probably the best, from a thermal consideration. Mercury must not be used when the process operating temperature approaches its boiling point (3750 C or 6740 F). Both the thermowell and bulb should be made of steel or ferrous alloy. A brass thermowell or bulb immersed in mercury would be destroyed by amalgamation. Some authorities question having exposed mercury in a room, whose vapors could mix with the room atmosphere, claiming this can create a toxic hazard to some people.
A mixture of oil and graphite is better than graphite for use on higher operating temperatures. Ottrer sub-
,=tf;:=='.11$ I.t
t'..l4iy
i
IIGURE l0-(u) (b) Use shut-off valve and
Pipe plug stops small leaks in thermowell, pipe nipple for large thermowell
leaks.
to permit jts removal without interrupting the process. The use of the thermowell will unavoidably introduce a temperature time Iag to the
it
adequate support;
in temperature in the process and response to the temperature relayed to the instrument. This is caused py the transmission of the heat through the changes
thiclcness
of the metal well, the invitable dead air
space
between the well and bulb.
One manufacturer solved this problem by producing a corrugated sleeve and this is shown on Figr_rre 6b. This sleeve provides a metal to metal contact between the bulb and the thermowell by means of a very thin (.005-inch) corrugated aluminum sleeeve.
The
to8
sleeve forces
the bulb to one side of the well
stances used in vertical thermowells are: glycerine, naphthalene, oils and various types of greases, and proprietary heat transfer fluids. Oil evapcrates in time, breaking down as it ages, filling the inside of the well with wax and dirt. The thermal liquids should immerse only the length of the thermobulb. Thermowells should not be filled entirely to the top of the well, this would increase the unwanted heat transmission resulting in greater lag and lower temperature readings at the instrument.
Thermowells in a horizontal position can be filled with graphite, carbon, metallic dust slrch ,ui copper, aluminum or clean iron filings or a corrugated aluminum sheath to reduce the insulating properties of the air gap. Solder is sometimes used between the thermobulb and the thermowell (tin, +2Oo F, lead, 6000 F).
Additionol fhermq! Logs. There are other normal thermal lags, in addition to temperature lags in thermowells, which will vary with different process flow services. For instance, the lag will be small in water, Ionger in oil and quite long in air. The lag in superheated steam will be much longer than for wet or satu-
nated steam, for the same velocity thermowell.
or the flow past
the
Pipe Flonge Used for (T/C) Well Assembly. Special types of thermocouple (T/C) wells can often be designed and installed in process piping to better advantage than the conventional cantilever type thermowell. One such arrangement is shown in Figure 7 which utilizes an orifice'flange for mounting the T/C well. This T/CC well is /z-inch in diameter. Half of the extended length is a solid extension which fits into the opposite flange orifice opening that has been counter-bored to 0.510-inch diameter. The solid end of the T/C well holds the entire well securely in place regardless of the flow velocity. The slight expansion that may exist between the parts will slide in the flange openings. The active other half of the T/C well is drilled to hold either a /s-inch or /a-inch O.D. pencil type T/C assembly. The hot junction extends into the center of the process pipe flow area. This T/C assembly is shown in Figure 7 and is connected to the T/C head. The entire well and assembly must be designed special for each flange and ordered with the drawing from the thermo-
tt tl
_ii
G)
I
L--- -:---
FIGURE' ll-Extend platforms for inacccssible thermorvell asscmblies.
well manufacturer.
If an orifice flange is not available for this puryose, the regular pipe welding neck flange can be drilled, bored and taped as shown in Figure / providing the flange is l/s-inch thick but preferably thicker. \..Jer-pEo
of Long Thermowells. When temperature control instruments are provided with very Iong thermobulbs they must be installed in suitable ther-
Supporfing The End mowells.
An example of such is shown in Figure
8.
Thermowells 15-inch to 24-inch in length, if installed and held in place only by the pipe thread connection, could cause the well to vibrate with the flow velocity. Eventually the well could bend and lead to a possible fracture. Some self-acting types of temperature controllers often require long thermowells. When they are installed in piping they should be provided- with some internal means
of supporting and in stabilizing the end. In Figure 8, such a supporting arrangement is shown. When an instrument is ordered requiring an extra long well, the instrument department should prepare a sketch similar to Figure 8 and submit it to the piping department to be incorporated on the process piping drawing.
Protecting Thermowell With Deflector. In some process pipe lines the flowing product rnay carry a mixture of entrained solids. Such an installation is shown in Figure 9 which also requires a long thermowell. This process line will require a 4-inch flange nozzle made at the outlet of the main pipeline tee, on which the welding neck flange is installed.
A 4-inch blind flange is drilled and tapped for the l-inch thermowell. To protect the thelmowell from the flow velocity, a 2x2xsft-inch angle iron flow deflector is welded to the bottom of the flange. This angle iron flow deflector is installed ahead of the well and in this way takes the shock and diverts the flowing product in the pipe, thus protecting the thermowell from bending or becoming damaged by erosion. The blind flange
Drnme.rens
t
FIGURE l2-Locate back welded thermowells near pipe flanges.
supporting
the thermowell provides an easy arrange-
ment for inspection of .the inside of the process pipeline.
When Thermowells Leok in Service. When a thermowell does develop a leak in service, it will be necessary to isolate this thermowell and stop the leak without shutting down the plant. When the leak is small, the instrument
in the thermowell may be removed and a /z-inch or f-inch pipe plug screwed in the thermowell opening and tightened in place as shown in Figure 10a. This will take care of the situation until the next plant shutdown when the well may be replaced.
There may be other cases when the eroded part of the thermowell will let go under operating pressure resulting in a very large leak. It will be impossible to screw in a plug to stop this leak and it must be han-
t09
THERMOWELL DESIGN FOR PROCESS PIPING
design of piping in the drafting room. Sometimes thermowells with their assemblies may have to be installed unavoidably in the process piping, heaters and vessels
.
where Lhey will be completely inaccessible. When this becomes known to the piping designer he should cbtain mark
This . The
to reach and service tt" tnllffl*ell without difficuly. An example of this is shown in Figure 12. To neglect such details or leave it for someone else to pick up later may mean that it will be overlooked. The- plant may be built with no easy means of getting to these thermowells except to build a scaffold or by using a ladder, cach time ihe the.mo*ell must be serviced, Such omissions have sometimes been responsible for accidents and injury to the instrument mainlenance men who must service these thermowells under adverse circumstances.
FIGURE l3-Locate thermowell downstream of pressure
gage
connection.
dled differently. During these emergencies, a tfu-inch shut-off valve and pipe nipple assembly must be obtained and used. The valve is left in an open position so that the process fluid can leek out while the assembly is being screwed in the well opening, as shown in Figure llb. When the nipple has been screwed in tight, the valve is shut off and the Ieakage stopped. This will hold until future repairs can be made. Hof Oil Leoks. One of the real hazards in oil refineries is to have a thermowell leak in hot oil services. When a leak occurs the vapors will flash into a flame on coming in contact with the atmosphere, creating a dangerous situation. When an operator sees something like this happen he will immediately rush for a steam hose and will direct the live steam on the leaking thermowell assembly; in this way he can put out the fire and
keep it from reigniting.
Another operator will obtain a /2-inch valve rvith nipple as shown in Figure 11b, with the valve in an open position. When the thermowell has been cleared oi its T,/C assembly, with the steam continually being directed on the well to prevent valve assembly will be When the pipe nipple is shut-off thus preventin$ gency. The well replacement will be made in the next plant shutdown. When a thermowell is brokcn off in l.rot oil servicc, due possibly to imbrittlement oi other causes creating a very large leak, there is only one thing to do thatthat is to shut down the plant. It is for these reasons that thermowell inspections become an important responsibility during plan shutdown periods.
Provide For Accessibility. Accessibility to the thermo-
rvells and their assemblies becomes very important in their installation, mainteilance and especiaily during emergencies. The time to provide for this is during the
no
Bqck Welding fhermowells. Threaded type thermowells when installed on process piping for some services may have to be back welded. This is often done on high pressure steam, hydrocarbon, acid, or caustic lines and on other service pipelines carrying toxic prodrrcts. Thermowell back welding at the threads will prevent its removal for inspection. When back welding is necessary, it is a good practice to locate and install the thermowell
section to be removed. Sometimes the adjacent pipe bend can be designed to be removed without too much difficulty. This facilitates gerting to the other pipe flange with the thermowell so it can be inspected. When a refinery turnaround takes place, the inspection of all thermowells receives important considerafion. They are carefully examined and the stem is gaged with
a caliper. The opposite side of the
checked by reaching inside the pipe
feeling the thermowell stem
for
thermowell is with the hand and
evidence
of
possible
erosion.
Pressure Goge And Thermowell Conneclions. The flow sheet of a process will often show a pressure gage and thermowell connection that must be installed in the same piping. It is considered good practice to install the pressure gage connection ahead of the thermowell, as shown in Figure 14. Since the thermowell will create a flow turbulence in the direction of the flow this could have an effect on the pressure gage connection. On some critical processes re
on which a pressure gage conn this too is located near a pipe two pipe diameters away from the face of the flange. This puts the connection where it can be examined and inspected from the inside of the pipe, for possible erosion.
Thermowell Design for Process Piping Part
1: Procedures
for the Piping Designer
Part 2: lnstallation and Specifications
Port 3: Selection of Thermowel! lnsertion Lengths John A. tlosek, Philadelphia TrrBnr ARE Two METlroDs that can be pursued when providing for thermowells during the design of process piping. One is to design the process piping and to provide the necessary l-inch thermowell coFrnections in the piping or for the enlarged pipe sectio-nF wherever they are required; later, the thermowell insertion lengths are selected from the completed drawing to s'uit each connection, depending upon the piping and configuration. The other method is to decide in advance what thermowell insertion lengths to use for all the thermowells. This will apply to the dial thermometers, thermobulbs, resistance bulbs and thermocouples. The design of the process piping will then have to be made to accommodate the assigned thermowell insertion lengths. The thermowells handled in this way will usually have 9 inch, 12 inch, 15
inch or longer insertion lengths. When the thermowells are in the longer range, this will be advantageous in that complete immersion will be assured. There will be a better chance that the thermal element will project adequately inside the piping to be completely immersed in the process flow. This is one way of designing for thermowells in piping to enchance better temperature resPonse and thereby reduce lag to the temperature instrument. The other advantage of this method is that it will also reduce the number of types of thermowells that have to be ordered. It confines the types that have to be carried in stock at the plant where they will be used for future maintenance work, to a minimum. When the piping designer knows in advance what thermowell insertion lengths are preferred he will be in a better position to
gl
8n r!-
FIGURE l4-(above) Thermowell connections made with l-inch, 6,(X)0 lb. elbow adapter installed ot 2/z to l2-inch pipe weld
l.ryl E Dbor Adapt.! c.!!.rllil r!or. r.ldlq lll c.nt.r1l!. latd .pa !1p. s.)d vt!h dalcl.rl b.tY.cE r.ld. lo dlt.
elbows.
FIGURE lL(right) Thermowell connections made with l-inch, 600 lb. el6ow adapter installed at weld line of 2 to lO-inch welding elbow.
lll
Each piping detail confoins cr scole Use it lo selecl lhermowell lenglh
5aalr lN'
0A
t
.
on ihe centerline ol the thermowell,
by spolting eftective flow dreo. degree angle. The well perpendicular to the pipe will naturally be in the turbulent flow section of the pipe. Of course, it will not always be possible to do this because of the piping arrangement and direction of the process flow. If the thermowell is long enough, with complete insertion and immersion this will enhance quicker 1emperature response and reduce lag to the instrument. Since o the thermoweli may protrude the piping so they will be paral atforms. If this is not done, workmen carrying tools on their shoulders may accidently knock off the head of a dial thermometer. An operator in an emergency rush could become injured by bumping into a T/C head that may stick out in the aisle. Capillary tubing should not dangle from the well but be attached and strpported with |xlx/s-inch angle iron or placed inside conduit. In Tables I to +, lists are given
of the various types of thermowells that apply to the details in Figures lt to 27. These are recommended for use either for dial thermom-
eters, temperature transmitter thermobulbs and for thermocouples. The proper insertion lengths for special
tclt r!3t lr'orC
F.-6= (0r Lertorn
ro Surr)
sc"u8
Ir
rmEDt
8tf, lrDlr I
FIGURE lLElbow adapter installed on 2-inch reducing elbow for
I
and l/z-irtch piocess piping.
provide for their installation, in the process piping. This will save time and will enable him to complete the drawhg sooner. In Figures 14 to 27 many piping details are shown that will suggest to the piping designer the various schemes that can be used. The important feature of these details is that each has been provided with a scale, in inches, shown on the center line run of the thermowell. This will enable the irxtrumentation engineer to select a thermowell by examining the scale. He will be able to
Oi LtN:ri T6
(\)
5urT
SCM IN INCIIS s{ lEU I
spot the active eflective flow area where the thermal element of the instrument will be located, preferably in the turbulence zone.
When the thermowell is installed perpendicular or at a 45-degree angle to the pipe wall, the tip of the thermowell should be at or near the center line of the pipe. Thermowells and their connections should point counter flow to the flow in the process line. This should apply to thermowells installed on pipe elbows and those ot a 45-
It2
a
u
(c,) Zr'. ,,.. qq{r{6!FrNr Wnrx Two '
-i2RBoueLLa MulI B(,{iraLLiD To:rra:a.
FIGURE l7-Thermowell connection f.or t/a to 2-inch piping tg 2/2-inch with l-inch 6,000'lb. elbow afaptei installed in elbow.
:waCg.d_up
TABTE
l-Thermowells with l-lnch Pipe Threod, Giving lmmersion ond Ordering lengths
Flfl. l4-f -1n., 6000 lb. elbow fl8. l5-l-1n,, 6000 lb. elbow Il9. l9-f-1r., 9999 !F. Fl8. l7-l-1n., 6000 lb. "!F"* elbow
adapter sdspter adapter adapter
lnstalled on lnstalled at lnstalled on tnstalted
mowell
,thermowell std tr/zn procees tlnes
on
2, procbisilnes
Thermowells
for thermobulbe Immerslon length Etart8 wlth dlmen-
Flg, no. of plpe detall followed try reference to the Bpectfic nomlnal plpe elze Inches
Inches
)4
Fig,
Indlcatlng dlal thermometer wlth t/.n dla. blmet^lllc stem Dlal thermometer Dlal thermometer Immerelon length slon glyen below. wtth yz" plpe lmmerelon lengttl wtth rl" plpe of thermowell Check wlth the thread of thermowell thread scale shown on fIE, zi-iiJrt-lo. wtl add the length s."-l.a"Ge No lnsulatlon Stem orderlng extenslon requlred for the leng,ths lengthg thermobulb. See glYen below glven below S"" S'". aete for determln"a"1" ""t" lng ordedng length
2t4
Inches
fnches
Inchee
Inches
Thermmouple well
IiiE-r-"oo
length
orderlDg,
fnchee
Plus Bulb
6
Plus Bulb
6
8%
5 6 8
Plus Bulb
8
15
71%
10
Plus Bulb
t0
70%
5
71%
13
Plus Bulb
12
10%
15
t7%
I5
Plus Bulb
72
t2
10>4
15
1\t4
18
Plus Bulb
12
6
4%
9
5%
2t4 PIus Bulb
3%
Fi,e.75-2rl
6
4%
9
5%
4% Plus Bulb
6
15
6
4%
I
5>4
4% Plus Bulb
6
7%
t2
8%
4)Z Plus Bulb
8
t2
'10t4
15
tr14
714 Plus Bulb
lo
6
4t4
9
5t4
Fis. 14-3
6
4%
I
5%
Fip- l4
9
7%
12
14 6 Fie. l4-8 Fig. 14 10 Fis.14 12 Fie. 15 2
I
7%
12 12
Fig,
Fig.
3
Fig. 15--4 f lg. lb--b
Fie, 15-E
2
to14
5
r1>4
714 Plus Bulb
72
Fig.
l5
I0
12
10%
]E
t4%
10)4 Plus Bulb
72
Fig.
16 a, b
6
Lrz
d
6
LU
5%
Fig. 17 a, b
6
4>4
Fig. 17
6
4%
I I I
Fig, )6 c,
c
TABTE
4%
5>4
5%
4 4 4
Plus Bulb
6
Plus Bulb
6
Plus Bulb
6
l-lhsvmqwells with 'l -lnch Pipe Threod, Giving tmmersion qnd Ordering lengths
l8-l-ln.,
thread adaDter
I
oa
2t ,
Zrht.
l. it tll 4"-45 plpe ofisets tn 2il to 12" Droceas
D
Thermowelle
for thermobulbe
Flg. no. of plpe detall followed by reference to the speclfc nomlnal plpe slze Inches
lengthg
Blven below
Inches
Fig. lEa-2 B-is.
Iodlcatlng dlal thernrometer wlth y1" illa. blmetnlllc Btem Dlal thermometer Dlal ttrermometer Immerslon length wlth t/zil DtDe Immerslon lenEth wtth r/ ptpe of thermowell thread of thermowell thread Stem orderlng N" l*rl*b" Stem orderlng extenalon
3
raf-2ri
4rz
Thermocouple
lenEthg Elven helow
See scale
thermobulb. See scale for determln-
Inertlon
Inches
fnches
7% 7%
t2
6
4%
I
5%
4Ll 9
Fig. 18d-4
Fig. 18e-2
I""h*
wrtllTlltioo
slon glYen below. Check wlth the scale ehown on flg. Add tbe length
I I I
6
t8b-2)i
Fig. 1Ec
See ecale
Immer8lon lenEth
requlred for the
lng orderlng lenEth Inches
5ti
well
Inches 4%
4" PIus Bulb
4t4
5%
4//Plus Bulb
6
8%
4'Plus Bulb
5%
6 6
6
4y
I
5%
Plus Bulb
6
Fig. 18g-3
I
714
9
5%
5'
Plus Bulb
8
Fie. 1Eh- 4
12
10rl
12
8%
6/ PIus Bulb
8
Fi,s.
Fig. 19-2 Fis. Fie. Fig.
19 19 19
4
l rA*
lrl*
2rZ
4
111*
6
4
trl*
6
4
6
4rz
6
5lz
2 to 6 For Bulb
4t1
5%
2 to 8 For Bulb
6
5%
2 to 10 For Bulb
6
5%
2 to 12 For Bulb
8
Fig, 19-6
6
4%
6
4%
Fig, 19-10
19
r14*
3
Fie. 19-8 Fig.
6
12
6
4rl
I I I
I
7%
o
and
orderlng length
t4* 1U*
3r4*+
3ll*+
NOT
+ The 2)4o sensitive element oI the bimetallic thermometer is immersed ooly 7!l' in the flowing stream within tlre line. Use u'hen indicating temperature is of secondary importance. ** Select another piping arrangement so a longer thermorvell rvith more immersion can be installed.
II3
4 Prr:
(I)
.r
lo" Pr,
E
lotl
!
ral1 rhlch6i.es 1:ryf, s6 for Schedul. 8C Dl!6. Plpo
,':il
s{'-
sc^!! IN IlicHts SI! TELS 2
/' ,
.ir2
1L6,M Ib, ElboY ldept.! 1. ln.lall.d on ..n!.tllr. af, v.lA1B.1tov tsa.n! !o c.n!.!11D. oi ul. $[I IX s lfir
IXCES 2
12"
FIGURE l&-Thermowell connection installed oa 2,2/2, 3, and 4.in-ch piping, 45-degree ofisets using l.inch, 6,000'lb. clbow adapters.
Prrr
FIGURE lLThermowell connections perpendicular to pipe
wall.
thermowells can be determined from the scale, slrorvn on each of the figures. In this way, other thermowell lcngths can also be verified for their insertion and immersion.
Piping Detoils. Figure 15: The long radius welding pipe bend. The point of maximum flow turbulence is at the end of the elbow where the weld line occurs. Every effort should be made to utilize the quarter pipe bend or welding pipe elbow for locating thermowells and their connections.
Figure 16: The welding pipe elbow has the thermowell l-inch elbow adapter connection near the welding line. The point of flow turbulence is at the center line. This arrangement is used when accessibility ancl observation of the dial therrnometer make this arrangement
sAr Ili I):!=5 @TEU3
desirable.
Figure 17: Two reducing type quarter pipe bends are to make up a 2-inch swaged-up pipe section in an l/2-inch or smaller process line for the installation of
used
thermowells.
Fignre 18:
The 2/2-inch welding pipe
used for swaging up a section
elbows are
of the piping. This applies
to t/4- to 2-inch process line thermowells. By installing a pipe spool piece between the pipe elbows and welding f-inch elbow adapter on both elbows, two temperature instruments can be handled for the same service.
il4
FIGURE 2G-Thermowell connection installed 45-degrees to pipe wall oa 2r/z to l2-inch pipe using l-inch, 6,000 t6. eito*
adapter.
TABTE
3-Thermowells with l -lnch Pipe Threod, Giving lmmersion ond Ordering lengths
Thermowells
for thermobulbs
I^-.*flG-e.t
Indlcatlng dlat thermoDeter slth %" dta. blmetallic stem
starts wlth dlmenslon Clven below. Check wlth the
scale shown on
flg.
sdd the length requlred for the
FlA. no. of plpe detall followed by referencc to the speclfic
thermobulb, See scale for determln-
Inches
Inchee
nomlnal plpe elze
roe3rjlal:lirqleth
V Fie.
20
3
Fie,20 Fie. 20 Fig. 20 Fie. 20
6 S
Fig.
I I I
5%
2 to
5%
2 to 6 For Bulb
4%
8%
2 to 7% For B\lb
6
12
8r/,
2 to 10r/6 For Bulb 2 to 16 For Bulb
l0
2 ro 16 For Bulb
10
I
7t4
I
7rl
\2
r0%
12
12
t0rl
r5
5Yz
3
c Fie,22-2rl Fig, 22a, b,
t'lP. z6-J
23 4 F\e.24 111 Fie.24 2 Fie.21 2\l Fig.24 3 Fie.21 4
Fig.
+%
12
21c
4
Inches
5%
I0
b-3
orderlng lenEth
6
t%
Fig.21a,
well
Insertlon and
l+
4%
Fig,20-4
Thermrcouple
rz*
4ft
For Bulb
2 to 4% For Bullt
4%
8
4%
6
4%
I
4
t%*
6
5%
6
4%
I
8%
2 to 6 F'or Bulb
4%
I
7rl
t2
8%
7 Plus Bulb
8
t2
10rl
15
L|%
8 Plus Bulb
8
72
.10%
15
rt t4
9 Plus Bulb
10
7%
)2
8%
7 Plus Bulb
8
I
7%
t2
8%
7 Plus Bulb
8
I
7%
12
8%
E l']lus Bulb
12
12
10%
t5
tltl
9I'lus Bulb
t2
13%
18
)4t4
ll
12
l5
4%
Plus Ilulb
NOTE: perature is oi secondary importance.
Figure 19: Vel with short offsets
the arra
and providing nectiron. This lr's{Gil ?,tG l5E.l'!i
3'Loflq.
(c) Honrzoxreu
can be Provided gree piPe elbows for the well cona dial thermomand assembly. When a thermowell
eter or 'f/C well with a long inscrtion length tlermobulb is required, a pipe spool piece can be welded between the 45-degree elbows. In ihis rvay! the longest type thermowell can be installed with a minimum of pressure drop rvith a good streamlinc florv in the process piping' Figure 20: Thermowells can be installed PerPendicular to the proccss pipe line; however, this becomes practical on 4 inches and larger pipe lines. When the process lines are smallcr, it will be necessary to s\\'age uP the thermowell section to 4 inches. The l-inch thread adapter connection is welded on the piping. See Figure 27 fot
I I
Prt
other arrangemcnts.
Figure
2l: lnstalling thermowells on a
45-degree
a l-inch elbow adapter as a lateral, is a good arrangement when it is desirable to place a angle by welding.on
sc[!
IN Ixcus
SI! T[L' ]
Vrnttcar-
PtPe Ruu'
FIGURE 2l-Thermowell connection installed on 3'inch swaged up pipe section using l-inch,6,000 lb. thread adapter Iot 1/4 2, 2/r-inch process piping.
it
can be easily seen. Somctimes this may provide a means of installing a thermowell that was intended to be perpendicular to the line but was too long
tliermometer so
by a fraction of an inch. This thermowell can thus be installed on a 45-degree angle and made to suit the installation.
tt5
THERMOWELL DESIGN FOR PROCESS PIPING.
..
?iT.r
J
4"
Te. SCIT IN II:'hTS SE TED I
fgt Sttrrrrvg Tf,EtHo ELtMti lirrpr Trr Trarnolllu 5rouro PRoJEat BEyo{o Tr. Tra lr]rrp Lrrz. THt! !rrLtH
scrr.E IN Itrcms 3I! !8t! g
THE
IEE
Lai6T, 0f TF! Trrr
FIGURE 22-Thermowell connection installed on a 4-inch
FIGURE 23-Thermowell connection installed in back of.2/2, 3, and 4-inch pipe tees with a l.inch,6,000 lb. thread.daptli.
Figure 22: When small sized pr-ocess lines have to be to three inches, the arrangements shown and their adaptation in several positions can be used. Figure 23: This 4-inch swaged-up pipe section with reducers can be connected into smail iizid process pipe
lines where short thermowells can be installed,
:",uq:q up pipe-scctio-n using a l-inch, 6,000 lb. elbow adapter Ior l/z to 3-inch piping.
for dial T/C assemblies. Figure 24: The back of a process pipe tee can occasionally be used for the installation of thermowells. This takes care of the branch of the process piping into
swaged up
TABTE
thermometers and
4-Jhsnn6wells with l -!nch Pipe Threod, Giving tmmersion ond Ordering lengrhs
ilt'.l=i: Tft:ffif:lllfil[llfifl ll;Hf""3:1.:'ffjii:*eilffi9
3obi,lfl".En".t",".I,.tEi trnEs and prpe rensths to surt requrrements
Thermowelle for thermobulbs
FlE. no. of plpe detall followed by reference to the epeclfic nomlnal plpe slze Inches
sill.oEe lenEtbg glven below
S.*1.
Inchee
Inchee
"rd*t"( lenAths glyen below Inches
rale I".h""
See
Immersio.n length slon glven below. Check wlth the scale shown on flg.
add the length requlred for the
thermobulb.
See
scale for determlninE ordering length
Inches
Thermocouple *ell Insertlon and orderlng length Inches
F're.25a-lr6
b
+%
5%
3
Fis.25b-2
6
+%
5%
4 Plus Bulh
FiE.25b-2r6
6
+%
I
5rh
4 Plus Bulb
6
Fig.25*714
9
7%
12
8%
5 Plus Bulb
6
Fig.25c-2 Fie.25c-2%
I
7t4
12
8%
6 Plu
Bulb
8
t2
10%
12
E%
7 Plus Brrlb
r2
10%
l5
11rZ
8 Plus Bulb
Fig. 25c-B Fig. 26
It6
Indtcatlng dlal thermometer wlth y{, dla. blmetalllc stem Dlal thermometer Dlal tlrermometer Immerslon leneth wlth rl, ptpe Immerelon lenpth wlth r/2, ptpe of thermowell thread of thermowell threed 2" lnsulatlon wlth N" fr*rtrtfsIm extenalon
As Noted Above.
Plus Bulb
s
4% 6
10
TABLE
s-Evoluollng Thermowell ln3lollotlon Arrong.monlt llg.27, For Usc Wlrh femperoture lntlrumenlr
.N,.5IzE
Shown ln
t{'x
lilsr^LLiaro{ Nooiorl
{rc Gtre lo"fr""
TxETMowELL
Best tenp. speed ol tesponse is reted es No. I end lollors
2
3
1
Ideutifyin! the 2-ir, thermorell conncction shown in Fi(.
b
c
d
5
6
rs rhown
a
f
,
6In.
In.
Sinto 6
Yes
Yes
6 in. or Longer
3into
Yes 6
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
No
No
n
bcREUED
Il;ff
I
+
Ealad trai
2{
Scneweo
Teel lr Ltles,
Yes
Yes
Ye
Yes
Yes
Yes
Dru. Foa
in.
No
No
No
No
Fr qp'
r50t
Dial thermoueter
Yes
Yes
Yes
No
No
No
ThermocoupJe on center line ol pipe
Yes
Yes
Yes
Yes
Yes
Yes
_litrrorrrr
Tee. Tre 3"-300* irqc, TEt is 9Howt.. Foi 0THER FLqD. TE 3i U!r DrnExjroi!5tsort A!oYf,
$M IX INCES sm lEL! {
Brrpo Ernrte f Ta r r ro For
t'PrpE TiafaD
lH
Lrx:r \ Arrp lxro Ar t{
Yes
3into 4
Yw
in.
5r.
0F
Yes
Yes
in. or
Longer
Thermobulb 3 In.
in.
Yes
Thermocouple on center line of pipe
No
Yes
Yes
Dial thermometer
No
3
Dial theroometer
6
No
io.
Thermmouple on center litre of pipe. Thermobulb 4
6inor Longer
Of PIFE LINC Hsno
^ tt )"/-1P u I Et,
ti, t|'nno
Scltrtrp
27
Thermobulb
l'H:r
Dltrtro I' l{,P'
Foi ErrirA Ar
lNlraarrxq DrAL TnrlMourrrr , A TrtiFocou?La OR FoR A TrMptt^aoit TRAtrFllrar TxraMoDU!8.
lNriALL^rro{ 0r Txrar"lowrrus
tl" rEE
Nort:
Ttsz 5ct!r Nor.o 0{ € 0F Prrric l5 li U{Cl{tl nrD ir lJe(D hDlTErxtrrN4
tho h
l" Pr?g 8^rr Coursrtrror
I'TrrcrDhLEr
lr li',
Z', 2i'AHD 3'-l5otAltD3OOlFLtl(Eg
ltrt'
FIGURE 2Llnstallation of thermowells in 11, 2,2/2, 3.inch, 150-lb. and 300 lb. flanged tees.
Crtcrrla 'Irc
anid
'lir
iMMERrtoi LrNqai 0r
Trt Txrrvoutur Fro. TH€ Eolron otliE
iill
1" PrPr TFiE^D.
''liri
'THt 5Eisiarva P.i1 0r TiE Tx!iFoWrLL 5iouLD PnoJtcl
ul
iNsrpa THa PtPE
BErorD TNE a ot
Trr t4ologrrq Prpt. Tit THEaMAL ELtillxt li THE !IELL Sroulg 5E Loarrr! ld TBE Srrzrq Frov.
zl'a
eL
Norr: M^at Prlt Nrttrt Larrlsr 1o \irro!
0f ?ltl
iutl THrimoutr- lMqrlrrrx:'
Ll{at'
+.TEE SO& Itr INCES sm rEr 3
FIGURE 2,f,,-Thermowells installed at outlet ol l/2 to 4-ich welding pipe tees with either l-inch thread adapter or f-inch half coupling,6,000 lb. rating.
which a thermowell has to be installed. When using this arrangement the thermowell must project inside the pipe with sufficient insertion length so the thermal element will be in the flowing product of the line. Figure 25: This is an alternate arrangement for the pipe elborv. The pipe tee is arranged to enable a Possible future branch connection. It is important that the thermowell insertion length projects beyond the dead space and is in the flowing product of the line.
FIGURE 26-Pipe ofisets with screwed end fittings. N.P.T. thermowells of all ture controller bulbs, ther mometers.
Figure 26: When screwd pipe a,nd fittings are sPd: 6ect for use in prrcess piPing' the threaded tee and screwed fittings tan be arranged with a reducing pipg bushing for the thermowell connection. These enla;ged sectior;
in the
screwed pipittg strould be big enough to
assure unrestricted flow inside the line where the thermo-
well is installed.
Figure 27: When a straight run of piping -with scre;ed fittings requires thermowell, the run of the piping
tt7
THERMOWELL DESIGN FOR PROCESS PIPING . .
.
by radiation to the surrounding atmospherc. The iesult of all this will lcad to a slightly lower temperature inside the stem of the thermou'ell that contains the thermal element at its bottom. The larger the operating remperature diflerence betu,'een the process temperature and the atmosphere tlte greater the heat flow,. This will invariably cause a slighth Iower temperature inside the thermowell stem. All this will ultimately be reflected in the temperatlrre indication. either on a dial thermometer operating through its bimetallic element, on the temperature transmitter througir its thermobulb or the thermocouple in the interior tip ot the well stem, that transmits the temperature to the rccorder on the control panel. There will be a temperatlrre dilference at a given moment between the operating prc" ess temperature and the tentperature indicatccl or recorded on the instrument. The fact is that it takes rir*e t,-r heat and cool the thermowell stem with its tl-rernr:l eltment inside the rvell-this is referred to as a timt lag. The effect of temperature lag can be reducecl 1l.r' ,:ocd engineering design of the therrnowell and bv pror,idinlq a good location for its mounting conncction in rlte nroce...,
4-rx, Prpe
for Thermowell Connectioris
Nomenclature
(a) l-inch Elbow Adapter, 6,000 lb. ratrng.
(b) 1-inch specially
designed nozzle
connection, welded to suit. (c) l-inch l.lbow Adapter as a lateral connectron,
(d) l-inch Thread Adapter, 6,000 rating.
tlrermometer or a T/C assembly. Some of this heat will likewise be passed on by conducrion to the exposed parts of the well extension and assembly and will be dissipated
lb.
piping.
Vcry short thernrou,ells inadvertentlv locared in pipin: areas where the florving medium mav be stagnant or )ag. Reducing the:e ed of response to the to improve the speeci
tion and
3-ru, Pree
(e) f-inch Flange Nozzle or l-inch
socket weld flange nozzle made with a f-inch Sch. B0 pipe nipple. Flange drilled and tapped for Thermowell. Use detail (f) in preference to this. (f) l/z-inch Flange Nozzle. Blind flange is drilled and tapped for Thermo-
I Wr.r PR.!rrr L,rl. air -.. ix.LLtr aia 3.r{. !..r'rr il) i(x.,r! etTriluA.rr u'
well. IJse this detail rather than (e).
Eftective Length of Thermol Elemen? DETATL
Llae Slzc 3.Inch Pige 4-Inch Pipe. 6-Inch Pipe
FIGURE
27{omposite
arrangement showing six typical cgn be installed"in 3, 4, and,6linch piicess piping (see Table 5). w.ays thermowells
can be made with"an offset as shown. This is another way of giving the thermowell adequate consideration. Thermowells ond Speed of Response. All thermowells l.rave characteristics similar to a heat exchanger; that is, they either absorb or gi'".e up hcat. They rvill be affectecl by both conduction and radiation. The heat flow will pass from the hot or cold temperature of the process medium to the thermowell stem. This transmitted heat will also travel along the length of the well and pass through and beyond the t/a- or l-inch mounting pipe tlrread connection, to the uninsulated upper well extension. The heat passed from the process u'ill continue to move outside to the accessory parts screwed into the tftor s/-inch thermowell opening, which may be a dial
lt8
immersion
length of the thermowell in the process piping. The thermal element must likewise be at the tip inside the rvell stem. Figure 27 shows a composite arrangement of six rvays thermowells can be installed in piping. The best possible thermowcll connection is the I-inch elborv adap-
ter installed in the heel of tire pipe elbow. TI-rcse ar.c shown in Figure 27, 3-inch(a), 4-inch(a) and 6-inch(a). The advantage of this arrangement over the others is that it can provide for all thermowell Iengths that mav be required for most temperature instruments. When thc tl'rerrnowell is long enough this will to an extent. minimize the heat conduction and radiation losses to the outside because the thermal element rvill be completelr. submer€Jed and arvay from its mounting connection. In this way the over-all speed of response rvill be irnpror.ed. In Figure 27, the 6-inch(a) detail will naturailv have a better speed of response than in the smaller 3-inch(a)
process pipe line.
The thermorvell arrangements shown in Figur.e 27 pr.esent other methods that can be used in makinq the f -incir connections in process piping. There are aclr.antages ancl some disadvantages regarding each of the schemes shou,n. All of the types may have to be used from one tirne or othcr, depending on the process conditions encounterecl and the piping confisuration involved. In order to cvaluate each of the thermo*'ell details shown, these are sunt-
marized and appraised in Table 5. This table presenrs an analysis shorvins the active, effective thermal lengths inside the pipe and horv they cornpare in speecl of response, and to what instruments they are best applied: also sho*'s it is n ol practical to use certain well ui.u.rq"ments
for temperature
instrurnents.
NOTES
rt9
PFIE
RE DROP AND VI BRATION
Sirnplified Utility Loop Balancing
Utility distribution
systems require periodic checks on flow and pressure drops in the loop mains. This method reduces the calculation time from days to minutes B. Wesl and A. J. Newton Poll,rner Corp., Ltd., Sarnia, Canada
IJrrr-rw DrsrRrBUTroN srrsrEMs for refineries and chernical plants are becoming larger and more complex. Usually these svstems are looped, so that the utility supply to any unit is not dependent on one path through the system. As a result, complicated piping networks are built up. A major plant expansion will normally include a study of the utility distribution systems, to determine the efiec[ of the load increase, and to indicate where expansion is required. These studies when performed by hand are very time consuming and prone to error because of the large number of repetitive steps involved. The repetitive nature of the calculations naturally leads to the use of a computer method of evaluation. Computer prograrns 2,3,6,7, B have been written to solve this type of problem. The following is a description of the network analysis program developed at Poll,rner Corp.
lnformqtion Required. It is decided to examine one of the plant utility distribution systems. The object of the study is to determine the effectiveness of the system under present and future loads. The effectiveness might be determined by comparing required pressures at various points in the system to the predicted pressures. It could also be determined by comparing the predicted fluid velocity in the pipes to the maximum allowable fluid
to find the correct flows is
procedure used
relatively
simple but tedious to solve by hand. The calculation procedure can be.broken up into stePs.
1. Collect Data. Pipe diameters, pipe equivalent lengths (i.e. including length for fittings.), system configuration and average fluid properties.
2. Estimate Flows in the Network. The flow rate of fluid in all the pipes in the system is estimated. The only criterion for this estimate is that the chosen flows must be consistent with the over-all masS balance. It is preferable, however, to make reasonable estimates, as this will reduce the length of the calculation.
3. Calculate the Pressure Drop in the Pipes. Any standard pressure drop calculation is used. In the computer program, the Polymer standard procedure is used.
ir:t
, ,
:,
r
I
I
il
*
Vr
1 ,
J
'rE
|
rll
,.,:
F r: r
lt
1
il
ttt t tr)
Yz.Yl r-t
r:.i
F
J
ESTIMATE I,
t!
q
Fi.:r ,
!
r4
:tii : :i, EiT ri:F I lr I L' I I I
,,
I
ir
ra
l:t
.F,
velocity.
This information can be provided by determining the flows and pressure drops in the pipes of the system. The
Fig. 1-Simplified computer flow diagram.
t2r
SIMPLIFIED UTII-ITY LOOP BALANCING
..
.
- 4. Check to Find if the Loops Balance. Each loop is examined individually. The algebraic sum of the pressure drops in the loop pipes is found. If this is zero, the loop is in balance. If this sum is not zero, an adjustment must be made to correct the flow rates in the loop, to give balance. Each loop is checked and corrections made to the estimated flows
if
necessary.
5. Return to Step 3. Steps 3 arrd 4 are repeated until all the loops in the system balance.
The above procedure is applicable to both hand or computer solution. Hand calculations make use of various approximations because a detailed calculation would take too long. Computer solutions may be made rieorous by reducing the number of approximations.
Equation 2 ancl 4 ciln be ;rut in thc form:
,' 'I'lre value of Equation 5 is l]uter prosr':,rnr t
quate.
rstant for a qiren systenl.
\-\
!t
- 1.75 1og R -
rr.rr,.r,.
+
and
1
(:;)
kn (s.G.) |
,,
(l)
,"(3')
(2)
122
6.
l-tr : lt f,/
r.'
5.76 log
I'l
1.75 log
-
R
1 1i-'l lc,c
-R
l
I'
-!2.5 lnI+t-
0.761n
R-0207 (lnll
,.
Tlre corrcct cstimatc of f gives Fl' : O. To soh'e Equation 7. a value of )' is chosen arcl I J' caiculated. If FY is not zcro, e corrtctiorr is rracle to tire initial value of Y. This correction is lound br a1;p1rcr:tr,.,, of the Neu,ton-li.alplrson techniclue.l
Y,-\',
,
E
and
d(FY ) dY
,/\
+
1.03
(3)
FY
n'( P' \ ,pp.or.h., ,"ro. 'elocities \P./
i
Whcre
:X*l*,",+-," (#)]
(f 200ft) or 1ow
--
FY:1.03
is
Compressible Fluids.
For long pipes
-
5
or
Noncompressible Fluids. The relationship between inlet
!,, - !,,
R)'?
gir.es:
Y
Pressure Drop Equotions
_
2l
tt,-_-lttc ]f '_ _ _Re t' 2Y8 l
The basic relationships used for analyzing the loops are the equations for flow of fluids in pipes.
p_
excel)r
7t1
-. ,:{,
Datum temperature is 50o F.
or pr_
-
i' \
Substituting the follorving into Equation
properties are for the average temperature and pressure of the fluid in the system,
!,- ?,-(+)
1.10 (log
R_Re(;,)J
Isothermal flow for compressible fluids,
and outlet pressures
r5;brc*(R'
lt'
o Fluid
.
in the cor in the pip|s
equation usccl essurc drolts
l--=ru3
The assumptions inherent in the following theory are:
o The pipes are rough,
^
Friction Foclor. In Equation 5 all the tcnrs
The relationships used for pressure drop calculations in our program are simplified and reflect certain assumptions stated below. The degree of sophistication used to calculate the pressure drops is very much dependent upon the individuals' needs. For our requirements we have found the flow formulas presented here to be ade-
/o.\ (;:, )
the friction lactor. are input data lrredeterrninecl lol tlr, s,vstem under study. The friction factors can be reacl r.,.o a chart if the calculation is done by hand. Thc conrll,-rrr-l solution reclLrires an analvtical expression lor frictir,: factor. .\n cxprcssion developed by Dukler' from f Icrocir'. friction factor chart and used in t]re program is sho,,r:
BASIS FOR CO'YIPUIER CATCULATIONS
.
'r (F , t'o,t (;t; ..
t,
1 03
-\
/
r\ ) ) +250 rtnlt') 1
)-+
-Oi6 (tnft) -0207
1.7+ )-Y
0.+1+
_
On
tt.
(lil ]l)
'I'his proccclurc is repcated until iound lronr I'.
F)' is zcro ther i
r.
Boloncing loop Flows. 'l-lrc prcssure drops in all t]it, 1;ipes alc calculatcd bascd on tlre initial cstirnatcs of {lorr
rates. The algebraic sum of the pressure drops is found for each closed path or loop taking the clockwise flows as positive (this is the Hardy-Cross convention) . If the estimated flow rates are correct, this sum will be zero for all the loops. If this sum is rrot zero, an adjustment must be made to the estirnated flows. The adjustment is made ac-
About the qulhors B. Wsst i,s a pt'ocess engineer usith Polymer Corp. Ltd,., Sa't'nia, Ont., Canad,a. His utork inaolaes responsibility for p,t'ocess design, quality con-
cording to the Hardy-Cross5 formula which is a special application of the Newton-Ralphson technique.
atton
Algebraic Sum
:
Or,
:
-t_,
t-rt r
r,,
:
r=J1
la,,f*-,
rlt!r+f") (9)
L
to the
- lon,)^,
f
li, Le"
H.,rt
Q,r'/Dur'1
l
L=t1
i-in ,,dtyji I
L,,
t _ )l
'
dO
L,i
,1u,,
Le;
i Q;i 'o
( 10)
,,"f
The new estimated flows are used to recalculate the until the loops
pressure drops and the procedure continues
are balanced i.e. until jil
X
j=r
Tolerqnces on
AS1
Mr. West
a B.Sc. (Tech) 'in chemical en-
gineet'ing i rom M anchester (Inht ersitE, England. He joi,ned Polgmer after graduo,tion ds d, process engineer i,n the Uti,li,ties Depan'tment, was transfet'red, to the Butadiene Depo,,rtment, o,nd now to the Stgrene Depo,rtment. He is o, g,t'aduate of th,e Institution of Chemical Engineet's, London, and, is a registered en-
gineerin Ontari,o.
7- ln
l)
uvvit under constt'uct'ion.
hold,s
rvhere
LO.:
Litol
o,t
If z4S is not equal to zero a correction is inade estimated flows in the loop, j.
lr,,f*:
trol, plant efficiencg control and. eao'luin the Styrene Depat'tment ttsith particular responsibilitg towards the
A. J. Nnwrox is a process engineer uitlt, Polgmer Corp. Ltd., San'nia, Ont., Canada. Hi,s utork 'inaohses process design, qualitg contt'ol and. other technical assista,nce in the Styrene Department. Mr. Neutton holds a B.Sc. degree in chemical engineeri,ng fl'om the Uniuersitg of Saska,tcheutan. Pq'ior to his pt esent assignment, he usas a, process eng,ineet, in the comitang'e Util:ities Department. He is a member of the Association of Professional Engine,ers of the Proaince of Onta,r"i,o, the Eng,ineering Institute of Co,nad,a, the Chemical Institute of Canada, and the Association of tlrc Clrcytui,cal Profession of Ontwrio.
:o
the herqtive Procedures.
Iterativo
techniques are used to determine the friction factors and the correct flows in the network. The criterion for finding the correct value is that a test variable (FY and E ,4St) should become zero. An optimum tolerance is required on the conve,rgence test of these variables. A balance must be struck between the accuracy of the results and the computing time.
Friction Factor Calculation. Two different tolerances are used on the test variable FY. Initially a tolerance of -+. 0.1 is used and if the flow rates are changed by less than 5 percent from the flows in the previous iteration, a new friction factor is not calculated. When the flows are almost balanced the friction factor criterion is tightened. The tolerance becomes -F 0.001 and a new friction factor is calculated for each change of flow rate.
Flow Balancing Criterion. Ideally, when the loops are in balarrce the values of ,4S in each loop equals zero. To attain this value would require considerable computing time. The criterion used to decide whether the flow rates need further modification is to sum the absolute values of the deviations from zero of each loop, and if this exceeds a desired value, a further change is made to the flow rates. This desired value is best determined anew for each system, taking into account the computing time available and the desired accuracy of the results.
Absolute Pressure Colculotions. The pressure drops in each main in the network are now known. For completeness, it is necessary to calculate the absolute pressure at the end of each pipe.
The following systematic approach is used. The loops are treated in turn. Loop one contains the input (or the highest pressure input if there are several inputs) to the system,
at which point the
pressure
is known. All
the
pressures are calculated around loop one.
The next loop in numerical order is then considered. A pipe is found which is common to a previous loop or enters an intersection common to a previous loop. This search provides a point of known pressure from which the other pressures around the loop may be determined. All the loops are examined to give all the pressures throughout the system. It is important to number the loops in such a way that they have mains or intersections in common with lower numbered loops. This is necessary to ensure that each loop has a starting point where the pressure has already been found.
Fig. 1 shows a simplified flow diagram of the computer program.
Experience Wifh the Progrom. The program described here has been used extensively by the Utilities Department of Polymer Corp. for evaluating proposed changes to the
steam and water distribution systems. The program has been checked by comparing the results obtained with the actual system. A good agreement has been obtained.
The great reduction in calculating time has enabled more varied modifications to be studied for each expansion. A sample problem follows which shows the preparation and computing times for the problem and for typical utility problems. For the example shown, the computer gives the result in about 15 minutes; whereas the hand
t23
SIMPLIFIED UTITITY LOOP BALANCING
..
The service water distribution system consists of l0 loops.
.
41
mains and 2,000
U.S. gpm
1,000 u.s.
3,000
U.
S. gpm
A typical computing time is 15 minutes. No specific times of calculation by hand are available, but several days of continuous work were required to produce results of comparable accuracy. A recent papers gives an excellent description of a much
more rigorous method of solution to complex pipe system problems. The method has obvious attractions for use in systems where the fluid conditions and properties are subject to considerable change. The simple procedure presented here, appears su'fficiently accurate for fluids at Fig. 2-Sample problem. TABTE |
Dqtn for the Somple Problem
-lnpuf
MainNumber Dian.
(in.)
2
t0
3
10
+
10
5 6
10 10
7
10
TABTE
F4.Lgth.
r2
1
steady conditions.
(ft.)
Est.FlowUSgpm
1000 600 500 1 200 1 500 200 I 000
-5000 4000 -5000 -3000 4000 1000
2-Computer Cqlculqted Vqtues of
Number
Balanced Flow, USgpm
I
5934
2
---4065
J
4934
4 6
-4065 -2235 4764
7
1764
5
Flow qnd
Outlet Pressure, psia 68.2 80.7 34.6 3+.6 16.4 24.1
t6.4
calculation would take at least one hour. The advantages of the computer are greatly increased as the size of the
is increased. One hour's computing time replaces two weeks or more required for hand calculations on the system
big utility systems.
and the outlet pressure. The time taken to complete the problem was
Prepare data Punch data Computer solution
AS CF
D
t lr
FY
G
H k*
as
follows:
Time 10 minutes 2 minutes 3 minutes
Algebraic sum of pressure drops in a loop Compressibility factor of fluid Diameter of pipe, inches Weisbach-Darcy friction factor Fanning friction factor
Friction factor test variable Newtons-law conversion factor, ft.-lbs. ma;s/lb. force-sec.2 Mass velocity, lbs. mass/ft.' sec. Pressure drop in pipe, lbs. force/in,2 (lbs.-force:,/ in.a) (units for compressible fluids) Constant for noncompressible fluids, lbs. force in.s min.2/ft.S USG2
kc
Constant for compressible fluids. lb. force: hr.2/ft.8 "R lb. mass
K Ka
Constant for system and fluid Absolute roughness magnitude
Le
Equivalent length of pipe. ft.
M Total number of
Total number of pipes
p1
Inlet
p2
Outlet pressurc, lbs. force/ft.:
pressure, lbs. force/ft.2
a Volume or mass/hr. Re ,s.G.
T
p
in.-'
loops
N
VO
Somple Problem. Determine the flow rates and pressures in the network shown on Fig. 2. Table 1 gives the main numbers in the loop and tabulates the diameter of the main, the equivalent length, and the estimated flow in USgpm. Table 2 is the computer calculated flow in each main
Function
NOMENCLATURE
5000
Pressure in Eoch Loop Moin
Main
ACKNOWLEDGMENT The Polymer Corp, Management is duly acknowledged for the pemissioa to publish this aticle.
mass
flow rate, USgpm or ilbs.
)
Reynolds no. Specific gravity of fluid at florv temperature
Absolute temperature, ('R) Specific volume of gas at standard temp. and press.
(ft.3/lb. mass) Fluid density at flow temperature, ibs. mass/ft.:r Flow correction factor, USgpm or (Jbs. mas:/'hr.)
^QE Friction factor correction factor SUBSCRIPTS
i j m I jn
Pipe number Loop number Over-all iteration number Friction factor iteration number Number of pipes in loop j. LITERATURE CITED ngineur
ad
Phpicits.
ork Progru. 15 minutes
Hqnd vs Computer Colculotion Time. A steam distribution system consists of 29 mains and 7 loops. A typical computing time for this system based on a reasonably accurate initial estimate is 30 minutes. 124
for Friction Factor,,, AICilE l-,
Piping Design Stops Pulsating Flow Reciprocating compressor piping requires special design considerations. Analog computers can be used to size the pipe and predict performance. Rolph Jqmes Humble Oil & Refining Company Baytown, Texas
THE DESIGN of
reciprocating
compressor piping can be resolved into two catergories: (1) measures to pre-
vent
excessive mechanical vibration of the piping and (2) selection of the pipi"S system which will provide the maximum compressor efficiency. These
two categories are interrelated. For examplg it may be necessary to add flow resistance at certain points to reduce pressure pulsations so that piping vibration can be minimized. The efficiency may be reduced by this step but vibration that could lead to fatigue failure is prevented.
Disturbing Forces. Both periodic
machine forces and gas pulsations
may provide the alternating
forces
sure
or flow superimposed on steady or flow) behave in the same
pressure
fashion as sound waves, even though the pressure variations in sound waves are very minute. In other words, dre wave theory which is used to predict acoustic phenomena such as resonance and wave addition and reflec-
tion may be applied to pressor may contain
all the harmonics
of the fundamental pulse frequency. flowever, the intensity of the components decreases rapidly as the fre-
quency increases. If the acoustic character of the piping components
are such that wave reinforcement from reflections (acoustic resonance) of a certain frequency component is
which can excite mechanical vibration of piping. Machine exciting frequen-
t-rle'
cies that usually must be guarded against include one half the rpm, the rpm, and multiples of the rpm up to five times the rpm. The base or fundamental pressure and flow pulsation frequency from one double-acting
cylinder is twice the rpm. If more than one cylinder is discharging into the system, the pulse frequency is a function of the crank angles. Twice the fundamental pulse frequency is called the second harmonic, three times the fundamental frequency is the third harmonic, etc. The pulsations from a compressor are propagated through the piping by wave action at the speed of sound in the gas (neglecting the fluid velocity which may add or subtract velocity) . The wave length of the gas pulsations is equal to the velocity of sound divided by the frequency of pulsation. Gas pulsations (which may be considered as periodic variations in pres-
compressor
piping design. Pulsations from a com-
obtained, the resonant frequency will
be amplified to produce combined pulsations of much greater intensity.
Allowoble Vibrolion. There is always some mechanical vibration in any piping attached to a reciprocating compressor. If the vibration is perceptible and of pronounced amplitude, the piping stress and fatigue life should be calculated to determine if corrective measures should be taken. Usually, if the vibration frequency can be counted by eye there is not much likelihood of piping failure. High frequency vibrations are of greater significance-especially
if
the
amplitude at the antinode (loop) of vibration can be visually observed. fn
ota. BAcx sPorFAcE
OETAIL
.'A.'
r'd HoLEsEAUALLY SPAOEO HOLES PER ROW. zRows
IO
I.3/4..
BETWEEN
ROVIS
t"d
DRA|N HoLE
FIGURE l-Surge bottles should be supported on springs.
125
oqe case, a t/a-inch schedule 80 instrument connection pipe attached to a 600 rpm hydrogen compressor failed in approximately three weeks. The pipe that failed was in three planes anchored only at the ends. A similar connection on an identical spare compressor was found to be vi-
brating with all frequency components that were multiples of 600 cycles per minute up to 18,000 cycles per minute. Calculated stresses in this pipe based on measured amplitudes indicated a fatigue life almost exactly
as occurred (considering stress intensification factors) . This problem was solved by replacing part of. the pipe with flexible hose. Observed fatigr-re life in large piping, (3 inches and over) has been much longer, usually a number of years. Since failure occurled, indications are that stress concentrations or vibraticn magnitude rnay have been underestirnated.
In
many cases, the alternating stresses in a vibrating pipe are not
considered to be serious, but additional restraints are provided because the vibration looks bad and is a source of concern to the operators.
Foundqtions. A well designed foundationl is essential if the major portion of mechanical vibration so often present in large compressor plants is to be avoided. It is not the intent here to go into foundation design; however, a few observations may be of interest. First, a wide foundation mat of proper design provides a better installation (vibration wise) than a narrow and deep foundation block. If more than one compressor is to be installed, it is recommended that a single continuous mat be poured. A natural frequency of the foundationsoil mass combination that coincides with the compressor rpm or multiples thereof should be avoided.
A
serious problem from both the maintenance and piping vibration aspects is the tendency of many types of compressors to break loose from the grout and shake relative to the
foundation. One preventive measure is to slope and seal the surface of the grout adjacent to the compressor so as to reduce grout deterioration from
oil seepage. Another measure is to mechanically key the machine base to the foundation. Occasionalln it may be desirable to isolate a compressor from the piping to minimize mechanical vibration of the piping. The size and critical serv126
ice of most process compressors prevent the use of most of the conventional flexible joints. One way to provide flexible piping connections to medium size process machines handling fluids of suitable composition and temperature would be to use ball joints that employ thick contained synthetic rubber gaskets. No
relative motion between the gasket and joint surfaces would be required for the moderate movements encountered. fnstead, movement would occur by shear in the rubber gasket. An al-
most unlimited cyclic life of the joints
could be obtained in this manner. This method was proposed to isolate
a
gas-conservation compressor which
was rocking
its
entire foundation
block.
Supporls. Supports for piping attached to compressors should be so spaced that the natura.l frequency of the piping between supports does not
coincide with significant disturbing
frequencies discussed previously. Natural frequencies of straight lengths of piping' with various end conditions can be easily computed.2,3 Even
though such a pipe has an infinite number of degrees of frbedom, all frequencies involved are identical. On the other hand, it is difficult to calculate the spring factor for bends in one plane and three-plane secticns between anchors. A number of resonant frequencies, depending on direction of vibration, can occur in these
cases. For this reason, it is recommended that where possible supports be placed near all changes in direction so that piping between supports is essentially straight. Another important factor is that pulsating flow sets up a cyclic force at bends because
of the change in time.
Supports
for
mass
flow rate with
duced before a restraint becomes effective.
To avoid cylinder alignment problems, the piping forces on the c,vlinder nozzles should be quite low. The flexibilitv of a seemingly massive cast iron structure is quite surprising. It is recommended that there be no rigid piping betrveen the cylinder and foundation, i.e., the lower bottle should be supported on sprir-re.. (multi-sprinq t1 pe with damper ar, the lavout of piping should pror-icsome inherent flexibility in other. d:rections. The use of cast iron base ei.. and cast iron transition pieces bri
t'"r,een c)'linders and bottles shotrld he
avoided. (See Figure 1 for sussi.,t: connectins nozzle details). In a number of vibraticn stLrc.it. has been deterrnined that tl.ie ,:,:,::--
rvill vibrate r e ;. to the crankshaft center.line T:-..
pressor cylinder
movement occurs because of ll-= r=riodic elongalion ancl eo11113g':n-. - : the distance piece and other- c.,:r--pressor parts. Ordinarih' this .r:--a movement is of nc concern. bur r::a., need to be considered if extreme.'.
rigid piping is involr.ed.
Design of Surge Bottles When Required? AIl larse colpressors require surge bottle, inrmediately adjacent the ,suction and discharge flanges of cach cvlinder. Sufficient capacity for smr]l cornpressors may be obtained bv incr.easins the size of the suction and dischar.ee lines to one or more pipe sj76s 1"11o"' than the compressor inlet or. orrl"r. Surge bottles serve two purposes. A surge capacity r,vilI help reduce the transmission of compressor pul,satrons into the piping svstem and /2 r efficiency of the compressor rrill be 1
improved by adequare sulse capaLir\. surge bottle on the suction side rrill
A compressor piping
should restrain movement in all directions. Because of this, and to allow for thermal expansion, a spring loaded clamp may be necessary. Piping just above grade is easier to support and
usually provides a much better installation, vibration wise, than, overhead suction and discharge piping. If overhead piping that is vibrating excessively is anchored to a structure, the usual result in that both the structure and pipe continue to vibrate.
High frequency vibrations caused
by g^ pulsations are particularly difficult to control by restraints. In many cases, the gas pulsations must be re-
decrease pressure drop
on the suction stroke,
at the
r ah'es
tl'rerebr- pr e-
venting cylinder "stan'ation." It has been reported that cylinder capacitv has been reduced by as much as 25 percent by operating lvithout a suction surge chamber.a A discharse surge chamber will tend to pr.r..i,
greater than average momentar\in the discharge valve cham-
pressure
ber. Momentary pressures can result severe overloads and may also re-
in
duce capacity. Acoustic pulsations a part in determining the effect of surge capacity-as will be also play
discussed later.
Techniques used to size surge bot-
tles vary widely. A survey of a number of compressor installations placed in service over the last 15-20 years (excluding certain recent installa-
tions) revealed no correlation
be-
tween surge capacity and compressor or fluid characteristics. Bottle capaci-
ties ranged from
0 to 15 or more
times the piston displacernent volume. Some installations have proven satis-
factory. Other installations have a history of piping failure and maintenance problems. While attempting to coffect some of the more troublesome vibration problems, it became obvious that piping design, including acoustic phenomena, was an important factor. The need for a logical and consistent design technique was evident. Sample surge bottle calculations in the ap-
pendix illustrate the different methods used by various designers as recorded in the literature or learned
first hand. Semi-Empirical Methods. Semiempirical methods are usually based on experience andf or fluid flow analysis. IJsually, however, the derivation is not supplied. These methods are easy to apply and may be satisfactory for cost estimating and certain actual installations. The disadvantage of this rule-of-thumb approach is that acoustic resonance factors are ignored. On occasion, this has resulted in unsatisfactory installations. fn one case involving three identical compressors, piping vibration was re-
duced
by replacing the acoustically
resonant interstage bottle and piping
with a new design. It is believed that fluid pulsations occurring in the original installation contributed to the excessive maintenance costs experienced.
Surge Tank Approach. On pages 333 to 335 of Reference 5 is an idealized derivation of the amount of pulse smoothing to be expected from a volume capacity (energy storage) acting
together with
a
moderate pressure
drop (resistance) of the piping system. The effectiveness of the surge tank is expressed as the attenuation factor
:A.F. :
Piping Design Stops iPulsafing Flow
problem of selecting a satisfactory attenuation'factor and pressure drop is difficult. The' usual procedure is to make the bottle as large as practical so that the highest possible A.F. is obtained. Method 5C. will glve an erroneous answer if the size arrived at is resonant to the compressor exciting frequency. This brings up the next topic-acoustic resonance. Acoustic Resonance. Consider a capacity volume with a neck such as would correspond to a surge bottle and the nozzle connecting the bottle to the compressor cylinder. This acoustic element is known as a Helm-
holtz resonator. ft is supposed that the air in the neck vibrates as a solid mass while the air in the char[ber acts as a spring as it is alternately compressed and rarified. The acoustic resonate frequency of this device can
be calculated by methods detailed in the appendix. The acoustic frequency of sections of piping can be determined by the familiar "organ pip"" formulas. Acoustic frequencies of various combined systems are discussed in Reference 5. The polar-diagram methods of determining natural frequencies discussed by Warming6 may be easier to apply in many cases. fn general, the acoustic frequency of a surge bottle and piping should not be the same as the pulse frequency of the compressor. In fact, it is good practice to design so that the acoustic frequency of the surge bottle is 3 to 4 times the compressor pulse frequency (computed frequency should not be a multiple of the pulse frequency. Reasons for this rule are: (1) Pressure surges in the bottle at resonance can build up to appreciable values. These surges can, especially when in phase with the compressor
Inflow Variation Relative to Mean Flow Rate Outflow Variation Relative to Mean Flow Rate
Thus, an attenuation factor of 20 indicates the amplitude of pulsations has been reduced to 5 percent of the original value. The advantage of this method is that it is based on a logical analysis which gives some insight into the ex-
pected pulsation attenuation. The
pulses, "starve" or overload the cylinder as previously discussed. Such a reaction between the pressure pulqes
of the comprssor and the fundamental or a harmonic of the acoustic pressure wave may cause, severe vibration from varying power requirements
(as
waves change phase), overloading of the driver, poor compressor capacity,
or valve breakage.ra (2) The bottle will no longer to attenuate the ^ctbut may increase compressor pulses the transmission of pulses into the piping system. (Of interest is that Rayleigh (Sound, 2,p 42) has proved mathematically that the mean pressure inside a resonator is greater than
that in the surrounding medium.) Plane Wave Theory Filters. This method of attack in designing pulsation attenuation filters is well described in References 8 and 9. A brief explanation is as follows. When longitudinal waves (such as a sound wave or pressure wave) traveling through a pipe arrive at a discontinuity (surge chamber, etc.) where the acoustical impedance (Ratio of pressurb to the product of linear velocity and the cross sectiorral area) is either much higher or much lower than the characteristic impedance of the pipe, only a Small fraction of the acoustical energy can flow through the discontinuity. The rest of the energ'y goes into a reflected whve that originates at the discontinuity and travels back toward the source. Thus,
transmission of energy can be reduced by inserting suitable discontinuities in the pipe, even though these discontinuities may not absorb any of the energy directly. One type of filter designed by this principle is called a low-pass pulsa-
the
tion damper or filter. This
device
of a combination of two bottles and an interconnecting pipe. It is characteristic of this arrangement that all wave frequencies up to a consists
point known as the cut-off frequency are transmitted with negligible at-
tenuation through the filter. Above this frequency, up to the, next transmission band (1st pass band), all frequencies are eflectively attenuated, The higher band passes need to be determined but usually these bands are quite narrow. By increasing the length or de-
creasing the size of the connecting pipe, the volume needed for the surge bottles can be reduced. Ifowever, the length of pipe is a factor in determining the high-pass bands.ro The de-
t27
I
RECOROING POINTS:
^
PRESSURE PATTERN
l-z,ols t9r rol !el Or tr 9l @l jl Or.l
lN.3
I
Or At >t
a o-
rdl
>4
AP
o:
+
2., dl ol
r.26 AP
a'. =l ldl
ol
-l I
I I I
o
so%
75%
loo%
t25%
% DESIGN VOL. OF LOW STAGE SUCTION FIGURE 2-Analog computer used to simulate this system.
sign should be such that the first and second band-pass frequencies do not correspond to harmonics of the compressor frequency. The resonant frequency of the piping components adjacent to the compressor should not coincide with the compressor base
frequency
or the first and
second
harmonics. Space requirements may
application
limit the of this type filter. Also,
the cost of two separate bottles may be greater than the cost of a suitable single bottle even though internal pulse attenuating devices are required
in the single bottle. As can be seen by comparing the surge bottle requirements determined by methods detailed in the appendix, the designer is faced with a selection of met[rod, allowable pressure drop, and surge amplitude. Based on three methods from different sources the proper size of the capacity bottle for the case stated is approximately five times the swept volume of the cylin-
der. The same result could be obtained by the use of another method if an allowable pressure fluctuation of 7.65 percent is selected. Also involved, is the economic problem of reducing first cost while considering future maintenance and operating efficiency.
Boftles. A baffle is a plate or tube containing multiple holes. The baffle is arranged in the capacity chamber so that the large flow stream is divided into individual streams which flow through the baffle holes and are recombined again into a single stream.
One or more ba.ffles have been found to be quite effective in reducing
pulses without significdnt pressure
128
l5oz
BOTTLE
FIGURE 3-A minimum pulsation occurs in the low,stage suction bottle who the compressor is operated at 3@ rpm.
loss. For the size dampeners used on compressors, the diameter of holes in
the tubular type baffle is usually z/ inch to 1 inch. Enough holes are provided so that the combined flow arpa of the ba-ffle is greater than the flow area of the single stream of the inlet or'outlet nozzle. The author knows of no mathematical study of the action of a baffle. Possibly the action might be as follows. First, the baffle orifices act preferentially on the high velocity pulsating flow component, i.e., the resistance to flow through an orifice is proportional to the square of the ve-
locity. Therefore, the resistance to steady flow is nil while the resistance to the high velocity components of
pulsating flow is appreciable. Another
important factor rnay be the reflection of the waves from the orifices. Also, the multiple transmitted waves may recombine to produce a much smoother wave pattern because of phase differences. A typical baffle installation is detailed in Figure 1. Orifices. In a number of cases, the installation of an orifice upstrearn of a vibrating piping system has greatly reduced the amplitude of vibration. Only a nominal pressure drop across the orifice is usually sufficient. Several successful orifice installations were designed to produce a pressure drop across flange taps of 1 percent of the average line pressure. Steady flow conditions were assumed. Pulsqtion Contro!. (a) Arrive at a tentative capacity volume for each side of each cylinder by one of the semi-empirical methods discussed
viously. (b) Check the
pre-
of the various piping s-vstem components singly and in cornbination to determine if acousiic resonant frequencies coincide rvith tire pulse frequencies of the compressor-. If necessary make changes to the piping components. In general, pipe size. should be somewhat larger than a size established by pressure drop calculations which assume steady florv. (c) Design a cylindrical baffle for frequency
each surge bottle. (d) Size an orifice for the last sur.se bottle outlet flange for a pless'.rre drop across flange taps of 1 percent of the average discharge line pressure. Figure 1 is a dra,rvins of a trpical surge bottle of a t1'pe nou' being tested in se\/eral installations. Adequate Teinforcing of nozzles and bracing of small piping connections is ertremely important. Supports and
bracing for small piping should be carefully detailed. Often this problem is neglected, resultins in vibration and possible breakase. Admittedly, some of these recommendations are based on erperience and rule-of-thumb techniques. For this reason, efforts are being made to increase the knowledge of acoustic phenomena. The only knorvn practical way to completely analyze a compressor installation is by means of an analog computer, which is recommended for all critical compressor installations.
Anolog Compufer Tests. It became evident during the investigation of pulsating flow that the available mathematical methods left much to be desired since the complete system
acoustic resonant should be considered as a whole. The
great many factors involved made mathematical analysis prohibitive. Even if one case could be worked mathematicalln a change in one component would require that the entire problem be reworked. The use of an electrical analog is based on the fact that mechanical, electrical, and acoustical phenomena are analogous and can be expressed in the same mathematical languags.?'12'rs'ra For example, the circuit of an acoustic analog would behave electrically precisely as the compressor and associated piping behave acousti-
cally. Electrical voltage
corresponds
to gas pressure, electrical current corresponds to gas flow, and electrical frequency corresponds to acoustic frequency. Measurement of the voltage and current patterns at certain points of the analog circuit indicate compressor performance
with various
systems, compressor loads, compressor ratios, and speeds. On investigation, was soon
piping
it
learned that only a very large analog computer could handle a comPressor problem, and only a few such installations are available. The problem was discussed
with Walter Brunner,
an
Applications Engineer for the Princeton Computation Center, which is an
analog and digital computer center maintained by Electronic Associates,
Incorporated. After analyzing the problem, Brunner and his associates arrived at an anaTog circuit which was different from some reported in the literature in that the elements of the circuit were actiae. An actiue component analog consists primarily of high gain amplifters which can by various externa^l electrical hookups be made to differentiate, integrate, add, multiply, divide, provide various voltage patterns with time. etc. A passiae
element analog consists primarily of resistances, condensers, and induct. ances. The advantage of the 'actiae' element computer is that system non-
linearities are easily handled.
Nonlinear characteristics must be included in a system analysis in order to optimize volumetric efficiency. For example, compressor phenomena and compressor valve characteristics are nonlinear. The analog developed produces a very accurate simulation of the pressure-volume relationship within the cylinder. This relationship was derived from a consideration of the energ'y balance including gas flow. The actual piston displacement with time was used in the simulation. Ileat
Piping Design Stops Pulsating Flow
of heat
loss effects including transfer
through the piston rings, piston ring friction, etc. can be simulated if desired. The valve analogy used in the test case assumed the flow across the valve to be proportional to the square root of the pressure drop, but ignored valve ind.uctance. Since then the inductance term has been included.l6 To evaluate the analog circuit, it was decided to simulate an actual
pulsation in the low-stage suction surge bottle when the comPressor rpm is 300. Either increasing or decreasing the volume would result in greater pressure surges. However, the
tem tested. Pressure and flow Patterns were recorded on strip charts' with
pressure pulsation level is not the only factor to be considered in piping design. A maximum comPressor efficiency is the real goal. Pulsation Frequency. A Fourier analysis can be made of the pressure or flow pattern strip charts by means of a mechanical analyzer. This analysis will show the intensity and phase angle of the various frequency components making up the complex wave pattern. A number of the wave Patterns recorded during this test have been analyzed which show that the
grams of both the head end and crank end of each cylinder. At first the entire system was being simulated. However, there was a tend-
compressor under test,
comprressor system
by
which had
been
conventional methods. The computer results would then be designed
checked against the actual performance,
Figure 2 is a schematic of the
sys-
intensity of some of the harmonics of the compressor pulse frequency are quite high. Varying Suction Pressure. Since three 600 rpm compressors are connected to the same headers as the
200 mm of the chart coresponding to one second of real time. X-Y plotters were connected to draw P-V dia-
it was decided to make two simulated runs on the analog with simulated varying suc-
ency for the interstage pressure to drift upward. Because of time limitations, it was then decided to run each stage separately. Changes to any part of the simulated system was easily done by adjusting potentirometers or other computer components. IIowever, the optimization of the system by varying all components until best results were obtained from the compressor could not be completed in the time available. Items that can be determined from the test data include:
tion pressures. Runs were made with pressure, in the suction header varying sinusoidally -f 10 percent at 600 and 1200 cycles per minute. During the 600 cycle-per-minute disturbance the pressure variations in the line to the compressor increased 250 percent as compared to the pressure variations with constant header pressure. A beat frequency was also discernable. The pressure pulses in the suction surge bottle increased 100 percent; however, the volumetric efficiency of the cornpressor did not seem to be much affected. Varying the suction pressure at 1200 cycles per minute did not have nearly so great affect as the 600 cycle per minute variation. Valve Chamber Volume. It was
the
Size of Surge Bottles. If the peakto-peak pressure variations in the low-stage suction bottle are plotted against the simulated volume, the curve in Figure 3 is obtained. From this curve it appears that a volume of approximately 20,750 cubic inches will result in a minimum pressure
TABIE I-Comporison of Three Pressure-Volume Diogroms
Work Per Cycle, In. Lbs.
DIAGRAM . Ideal. .. -c.*i,it.i*iiri . ;iDGs . Computer with piping connected,
ilt t.;;i;a+; ..,. ,
* Compresor diagrams are for 300 rpm.
**
r07,000 17,000 131,400 1
Consiant Dressuie supplied at valves. The valve
the idml diagmm.
IEdlcated
Horsepower
At
3OO
RPM*
47.2 88.5 99.5
Dellvered Flow Per Cycle In. 3 at
Suctlon Conditlons 4L40 4220 4740
In.-Lbs. of Indlcated Work Per Cublc In. of Gas Dellvered 25.4 27.a 27.8
los can be estimated by comparing this diagram with
129
found that the
compressor-valvea pronounced eflect on the pressure and flow patterns. This factor is not considered in other techniques of compressor piping
interactions that occur
chamber volume had
design.
Compressor Efficiency. Table 1 is comparison of three pressure-volume diagrams of the low-stage head
a
The author is convinced that
ciency. Note that though the indicated horsepower increases when the piping is connected, a compensating increase in flow js achieved. Ffowever, at 320
rpm,
it
requires 30.2 inch-pounds of indicated work per cubic inch of fluid delivered at suction conditions. By comparisons such as this, it is believed that the computer can indicate
the conditions that will provide the maimum compressor efficiency. In this connection, it would help to have an electronic circuit to measure the average flow. This can easily
by adding some integrators to the circuit. The strip/chart flow pulses are too small for accurate be done
planimeter readings. Data from the analog test are now being checked by comparison with actual compressor installations. A beat-frequency pressure pattern was made recording from one suc-
Aboul the Speoker
tem can be analyzed to determine optimum piping design and operating conditions. Originally presented before the API Division of Refining, Los AneeIes, May 13, 1958.
tion line of a multiple compressor installation similar to, but not the same as, the one simulated on the analog. An alternate reinforcing and cancelling action between pressure pulses from adjacent compressors was observed and was predicted by the
t30
Ralph James, Jr., is a supervising engineer in the Engineering division of the Design department at Humble
Oil and Refining Co.'s Baytown
re-
in mechanical engineering from
the
finery. He has a B.S. degree in mechanical engineering from the University of Texas and an M.S. degree University of Houston. james is a member of ASME, the American Welding Society, the American So-
ciety for Metals, and the
Texas
Society for Professional Engineers.
analog analysis. Such a phenomena has long been suspected to be the cause of the periodic variations in the intensity of mechanical vibration at certain compressor installations. At
some of these installations, pulsation snubbers have greatly reduced the pressure variations. A quartz crystai transducer together with an amplifier
that operates by
-calibrator electrostatic principle
an
analog computer is the most practical way to study flow and pressure variations in a complex piping system. In addition, the analog computer provides a means whereby the total s1's-
end.
The last column is a measure of the compressor efficiency-the lower the number-the greater the effi-
in a compres-
sor piping system.
an
was used to
obtain the actual pressure patterns. The amplifier----calibrator output was connected to an oscilloscope and a polaroid carnera was used to photograph the pressure versus time patterns displayed on the oscilloscope. It is ofuvious from this study that the analog, computer circuit.can very closely simulate the complex acoustic
Find Line Pressure Drop by Nomograph Using this nomograph, you can perform five important steps in line sizing and even correct for changes in friction factor
John D. Lewis, Hydrocarbga Research, New York City
lnc.
3.
(for gases only): A. Find a working point as in 1. B. Move horizontally from the working point until a vertical line extended up from the prepsure scale is
HERE'S A NEW TYPE of nomograph for sizing lines and estimating pressure drop. It is easy to use and gives rapid results of sufficient accuracy for ordinary line
intersected.
C. Read the line size on the diagonal
sizing problems.
Using this nomograph you can find the following: o The pressure drop in a given Iine o The line size giving a desired pressure drop o The line size giving "economic" pressure drop (for gases only)
.
Correct for a different friction factor o The pressure drop in a new line size o The allowable. flow in a given line.
This nomograph solves the Fanning equation exin the form:
pressed
Ap,/100 where
ft
:
fw, 74,000 pds
Ap: pressure drop, psi per 100 ft of pipe W: flow, pounds per hour p: fluid density, lbs/t3 d
- inside diameter, inches
f : friction factor, assumed equal to 0.004. The chart can be corrected for other friction factors as described below.
To find the line size giving "economic" pressure drop
scale.
Note 1: The "economic" pressure drop is based on a correlation given in the Prtnor,r,ulr RrrrNrn, Vol. 3, No. 7, Page 151 (1951). Note 2: The pressure scale does not necessarily show the actual pressure except at the economic size. 4.
To correct for a different friction factor: A. Find a working point as in l. B. Move diagonally to 100 times the new friction factor as shown on the pressure drop scale.
(Note: This is the only time a diagonal move should be made.)
C. Move horizontally back to the reference line to find the corrected workirg point.
D. Continue with Steps B and C as in paragraph 1, 2 and 3. For example, suppose we had 1,000 lbs/hr of material with a density of 0.12 lbs/ft,s and our pre-
liminary w-ork had shown that a 2.7 inc}r, dia line was required to give the desired pressure drop of 0.3 psi/100 ft. We decided to use a 3 inch line. A more careful check later on shows that the actual friction factor is 0.006 instead of 0.004. We make the correction as follows:
A. Start where the 2.7 rr;rch line intersects the 0.3 psi line. B. Move horizontally back to the reference line to find the old working point, then move diagonally to the 0.6 psi vertical line.
and can be used as follows:
1. To find the pressure drop in a given line:
A. Locate a working point on the
reference line, by laying a straight edge from the density scale to the flow scale. B. Move horizontally from the working point until the diagonal line showing the correct line size is intersected. C. Read the pressufe drop.
2. To find the line size giving a desired pressure drop: A. Find a working point as in 1. B. Move horizontally from the working point until the vertical line showing the desired pressure drop is intersected.
C. Read the line size on the diagonal
Aboul lhe Author John D. Lewis is a project engineer
for Hydrocarbon Research, Inc., and supervises the design of petrochemical
plants in this country and abroad. Mr. Lewis started with HRI in 1952 and before that was in the research department of Standard Oil Company of Indiana. Mr. Lewis received a B.S. in chemical engineering from Cornell University in 1948 and has studied at MIT and Manchester University.
scale.
l3r
Find Line Pressure Drop by Nomograph...
5. To find the pressure drop in a new line size: A. Find the point on the chart where the old line size
C. Move horizontally back to the reference line to find
B. Move horizontally to the new linc size and read the
intersects the existing pressure drop.
the corrected woiking point.
new pressure drop.
D. Move horizontally back to the 0.3 psi vertical line. The new required line size is seen io be 2.9 inches instead of 2.7 inches as estimated originally. E. Instead of stopping at the 0.3 psi vertical line, we could continue moving horizontally past the 0.3 psi
6. To find the allowable flow in a given line: A. Use^ the given line size and the allowable pressure to find a point on the chart.
B. Move horizontally to the reference line to find a work-
line to the 3 inch diagonal line. Here we can read tf,at the actual pressure drop will be 0.27 psi/100 ft. in
C.
a 3 inch line.
ing point. Lay_ a straight edge from the density scale through the working point to find the allowable flow.
0.01
t,000,000
60q000
0.02
400p00
0.03 0.04
300,000
,{ffi
0.06 0.
200,000
r00000
I
60p00
0.2
4q00o 30p00
0.3 0.4
20,000
0.6 ro
I
t0,0@
#
uU'
! J
>\
'6 L
oc)
6p00
2
4,00o
3
4 6
r0 ?o 30
40
60
drop
g
ar,
#
3p00 -o
o o
2p00
U' o-
1,00o
J
tJ-
o o
o
= o L-
600 lr)
o d
400
o,
300
= U'
200
aD
o)
!
or00
o lr,o oo ooooo oo o o oo o o oo o - -(\r ro\f @ooo'oR 33 3 O loO e - -A'
200
Pressure Using"Economic" Instructions-l. Locate a working point on the reference line by luyi"S I straight edge from ihe density scale to the flow scale. 2. Move horizontally to the desired pressure drop
t32
or the desired line
ro
t00 70 50
Size, pSlA
size, or to the operatinq pressure to find the "economic" size. Note: Chart is f,ased o"n i friction factor
of
0.004.
New Approach to Pipe Reactions Computer calculation of pipe expansion forces and moments carurot be justified on many two-anchor pipe Ioops. This estimating method is quick and economical G. R. Kent Stone
&
Webster Engineering Corp., boston
Corrpurr,ns rrAvE TAKEN the hand calculation work out of piping stress analysis. Ifowever, because of time and cost, the computer is not available for many simple two anchor pipe loops. Fast estimating procedures were developed for less complicated configurations based on the cantilever principle. The procedure predicts excessive loop requirements which, in turn, increase piping cost estimates. An alternative to the cantilever prinoiple is to rely on generalized charts for estimates; but very often they do not cover the range for the problem at hand.
Fig. 2-Beam cantilever moment at end.
Then: k* FLz
_
kM
ML
Hence:
M-kF/kMFL-koFL need of less pipe for a required flexibility.
The improved accuracy of the proposed method results from the use of "generalized parameters" obtained from several calculated pipe loops. No claim is made that the outlined procedure will equal the accuracy of a detailed pipe loop calculation. It is expected that the results will deviate by a reasonable amount from the most probable values.
Bosis
for Pqromelers. Referring to
Figs.
I
and 2 and
applying the principles of the moment area method described in texts on mechanics of materials,l the expression for the net deflection is: EIl -
1,,
FLl
-
kM
-
kM
ML2
The net angular change is: EIO
If
:
ko FL2
ML
the free end is held against rotation:
O:0
(1)
From the expression for deflection: EI6/Lz
:
kt'
FL
Substituting from Equation EI6/1'z or
EI6/az
:
-
k* M
1:
-
kF
FL
-
(ko
-
kM
kd FL
kM ke
FL
- k5FL
(2)
. Solving for the constants Ke and Ko in Equations 1 and 2 and using the minimum distance between anchors (L-) results in: Ks: M/FL,* K6: EI6/FL*'
(3) (4)
The values for Ke and Ko were determined for a number of. analyzed pipe loops of varying line sizes and configuration. Several of the sample pipe arrangements used in this study are listed in Table 1. The results of the calculations were plotted against the coordinate (2LlL*), refer to Fig. 3. From the curve which sum-
t33
TABLE
C. S.
l-Tabulation of Calculated Pipe Loop Data Evaluated in This
Pipe
I
Size ln. Schd. No.
Arrangement
ln.
j
Temp. "F
Lb.
Lb.
F
M
Ft.
Study
>L/1.
L/K6
L
/Ko
95' 8
40
72.5
700
533
28,330
1.3
109.8
2.24
10
40
160.8
500
2,295
7,000
1.57
91.5
19.5
28.74
425
2,055
1.
15
1055
2,O30 1,787 1,660
1.195 1.135
1050
1.155
r.4
225
925 864
6
40
5
t20
49.96
625
1,930
10
60
2t2
750
3,040
22,380
t,7
45.2
7.2
10
40
160.8
750
L,572
17,850
2.33
7.35
2.24
lo
40
160.8
750
1,300
L4,700
2.12
6.O7
2.28
were
With the values of Ke and Ko deternined flom equations 5 and 6, respectively, the value of the resultant force and moment at an anchor, for a given pipe arrangement, may be determined. For convenience, Equations 3 and 4 are rearranged to solve for the desired resultant forces and moment.
rS.
marizes the calculations, determined:
the following equations
150 K^ " - Fr \r'8,
(5)
(;)
(6)
F: EI3/K6LiL3 M
About fhe quthor GEoRcE R. KoNr is a proiect eng'i,neer with Stone & Webster Engineec"ing Co,t"p., Boston. He is responsible for the mechanical design and operation
of petrochemi,cal plants. Mr. Kerut holds a B.S. degree in ciail engineering from Cooper Union School of Engineet"ing.
engi,nee,r prio,t' to 1948. Since then, he branched 'into eng i,n e e r in g a,s s o c ia t e d u; it lt p e t r o c h e m-i c al plants including uessel, heat e*change, yrping, and maclainerg desi,gn as toell as project respon-
He worked as a ciuil
sibilits.
r34
Refer to Fig.
- KoFLm
4 for a diagrammatic
(7) (B)
representation of
key variables. It should be noted that
2L represents the actual length of pipe including e length of bends.
Limiting Recrclions. It is always necessary to limit the force and momen on a piece of machinery such as a pump, compressor or turbine. When the manufacturer of equipment is asked for their limitations, some sort of "bargain counter" approach is used, starting with zero allowable. Obviousln no piping can be made sufficiently fledble to result in zero thrust or torque. The following formulas yield values of force and moment
t00
(D
-lY
E, o 6
-l-
t0
/tL\ \Lr/ Fig. 3-Reaction parameters.
It
which have been found acceptable to several equipment
Exomple.
manufacturers:
and moment for the arrangement shown in Fig. 5. Given: l0-inch schedule, 40 C.S. pipe, L.R. bends, I : 160.7 in.a, T : 7500 F, E : 25 X 106 lb./in.2, t:7.35 X 10-6 length/oF. (Note: 1.6 feet corrects the length for pipe bends.)
The Limiting Force
Fo:140 I'he Limiting Moment ML- t.72
(e)
eN/6
FL
: L*-
10)
>L
From Equations 9 and 10, a reasonable value for the limiting force and moment may be obtained. It is cautioned that the equipment mar-rufacturer's approval be obtained before proceeding with final piping design.
AT
(
is desired to determine the resultant force
+ 14 + 18 + B - 1.6 - 5B.4ft. ll42 + 18, + (20-8121 o.s - 25.8 ft.
20
:750-70 - 680' F 6 : (7.35/106) 680 (25.8)
12
-
1.55 in,
135
NEW APPROACH TO PIPE REACTIONS
From Eq.
.
8,
M:
1/0.98 (900) 25.8
-
23,700 lb.
ft.
Pipe Stress. After the thrust and moment at an anchor has been determined, it is necessary to determine if the selected pipe size and configuration have sufficient strength to withstand the combined stresses to which the pipe would be subjected. The contributing factors to pipe stress may be caused by any combination or following: a
all of
the
fnternal or external pressure,
a Bending in the straight pipe or at an elbow, o Torsion which subjects the pipe section to shear, a
Direct
stress
by axial forces, and
a Pipe support spacing affecting local bending.
Before calculating the individually contributed stre,ss, the resultant thrust and moment at an anchor to their equivalent componer.i-i: axial and perpendicular to each plane of projection. It is generally a simple matter, after the p\re geonrei:y is studied, to select the point of maximum bendin,q in the pipe loop. After taking moments about the selected
it is often convenient to resolve
It- =Lzr*Lx+LY+Lz2 [tr-r, + trrl\ *^
r rlr)"'
(INCLUDE LENGTH CORRECTIONS FOR
PIPE BENDS)
Fig. ,4-Typical pipe
arrangement.
pipe section for investigation, the resultant unit
sire.'se-<
may be calculated. By combining stresses rrith the aictre of Mohr's Circle and employing the marimum silear theory, the resultant stress should be compared r.r.ith the limiting value for the pipe material. Should the calculated results exceed the allowable stressr it r,r.ill be necessa.ry either to select a heavier u,a1l pipe or increase its flexibility by changing its geometrr,. The procedure ior calculating the unit stresses for piping is thoror-rglily covered in many texts on this subject; hence, t-he reader rvill not be subjected to its repetition in this article.
NOMENCLATURE E e
: Resultant displacement, in. : Natural Iogarithm base,2.7l82B
- Modulus of elasticity, Lb./tn.' : Resultant force or axial thrust, K : Constant or parameter E
F
Fig. S-Piping configuration for example given.
L)L M: 0: IN:
lb.
Lcngth, ft. Total Iength of pipe, ft. Resultant mo,ment, lb-ft.
Angular displacement Moment of inertia, in.a Nominal nozzle size, in.
Subscripts: 3
F: O
From Eq.
5,
Related to displacenent and force Related to angular change and moment Related to force Rclated to moment or bending
ML - i,imiting value
m: Minimum
From Eq. 6,
value LITERATURE CITED
From Eq.
7,
F_ r36
and M,acCullough, G. FI. "Elements oI Strength ol _1 -S.,Netrand -Materials", D. Van Co., Inc. Timoshenko,
25
X
rOu (160.7) 1.ss_(4.3)
(25.a1s 172,
-
900 lb.
Indexing Terms: Analyzing-8, Bending-6, Computinq-8. Deflections-9. Eouations-10, Flexure-7, Force,/Energy/-9, Layout-6,-Loops-9, Mom.nts-9.'Parimetcrs-10, Piping-9, Pressue-6. Strc"ses-7, Supports-6, Thrusts-6, Toision-6,
NOTES
137
EAM TRACING
'.flv"
L
ni:*
New Guide to Steam Tracing Design Test results recomrnend using Ys-inc}r. floating disc thermodynamic steam
trap as standard and prescribe maximum tracer size and length of run
fABLE I-Sleom
The following tests were conducted indoors on 100 psig steam. The traps were instailed so that no condensate could reach them. This test, in effect, gives the minimum condensate load required to operate the trap without steam loss.
AtlanticRichfieldCo., Philadelphia,
Pa.
Trap A
coMpoNENT DESTGN and selection variprocess and instrument piping, can and does Iead to steam wastage. We decided that a standard application method for steam tracing components would not only minimize steam losses but eliminate design time on run-of-the-mill steam tracing systems. The following facts are based on tracing systems using 150 psig saturated steam. (The basic findings and recommendations will also hold true for all lower-pressure tracing systems.) Capacities and the length of tracer runs u,iJl, of course, vary. There is a steam pressure belolv which
for
will govern the length of a tracer run rather than the condensate load. This is true for 15 psig exhaust steam systems which are quite prevalent. A great deal of basic information was gathered by observing the operation of various traps in the field. Checking cycle times, discharge times, and taking upstream and dor,r,nstream pyrometer readings on many traps gave an excellent indication of quality and repeatability of each pressure drop
vendor's product. The effect of design and quality control on field operation may be demonstrated by the results of a series of no-load laboratory tests which showed that each of the
Pounds per
Inches
1A
D,
r/"
TABLE
llour
2,8 1.9 1.6 2.3
"/a "/8
C
Srr,,c.N( TRACTNG
ations
Condensate Recovered
Size
B
Kenneth G. Elqnd
Trop fests No-Lood Operotion
2-Steom frop
fests
Field tests conducted at AtlanticRichfieldCo., f 90.1 Paraffin Wax Hydrogenation Unit, Point Breeze refinery, Philadelphia,
Pa. The trap was allowed to discharge into a calorimeter and the results were obtained by heat balance calculations.
Trap/Test No.
A-1 2 3
I
B-1 2 C1 D,2 E-1 ,2 1
,2
Inches
Steam Load Lbs.
% % % % % % % % % % % %
Steam Loss
/Hr.
Lbs.,/Hr.
B.7B
0.3,t
tt.52
None None
4.80 26.35 2.78 2.62 20.78 20.88
t5.7 I
None None 0.62 0.40
3.Bo
2.tB
2.68 2.+6
0.+2
3.r1
t.t2
t.32
ject to freezing, the thermodynamic trap is generally used in outdoor locations. Because of handling ease and reduced inventory, the thermod),namic trap is also used to a great extent in indoor locations. Other advantages
traps tested was capable of operating on less than 5 pounds per hour of condensatel These results are shown
of the thermodynamic trap are its small size and insensitivity to pressure variations (up to 600 psig)
in Table 1. Tests were conducted in Atlantic's Refinery to obtain operating data under the rigors of field conditions. These results are shown in Table 2.
Trap Sizing. The sizing of thermodynamic traps is more critical than for other types. Size a trap too small and it rvill back up condensate; too large, and it will
Typicol Trocing Syslem. A typical steam tracing system is shown in Fig. 1. The keystone of this system is the steam trap. Correct selection and application of other components is to no avail if the steam trap is inproperly chosen. Selection must be based on tr,r,,o choices: type and size of the trap.
Trap Types. The two types of traps normally used in steam tracing service are the bucket trap and the floating disc thermodynamic trap. Since the bucket trap is sub-
.
r.vaste steam. Excessive oversizing
will
destroy itself. This occurs u,hen the
cause the
trap to
trap cannot
get
enough condensate to fulfill its energy requirements and, therefore, begins to cycle more rapidly partly on live steam. This causes an accelerated wear rate, which causes an even more rapid cycling, which causes an even more rapid r'r,ear rate, and so on until the trap becomes useless. Sizing to include potential startup loads leads to oversizing in thermodynamic traps. A thermodynamic trap r.vill handle a great deal more cold condensate than hot condensate; and if a still greater rate is desired, the line
t39
FLASH FOT
TO SEUER OR RECOVERY
Fig.
l-Typical
steam tracing system.
can be manually blown down. For applications other than steam tracing, careful consideration should be given before introducing any startup allowance, especially if the addition requires an increase in trap size. For steam tracing applications, a flow rate of 100 pounds per hour gives the best balance between trap sizing and traced length of pipe. The allowable lengths at various temperatures stays within the realm of possibility while the unavoidable short runs do not cause the flow rate to fall into the trap's inefficient range. On this basis, the selection of a group of steam traps to handle all steam tracing situations is possible. Actually this consists of a zft-\ndn nominal size trap; but lately the steam trap manufacturers have begun to rate their traps by orifice size rather than by connection size. Suitable traps should have 150 psig steam condensate capacities from 350 to 600 pounds per hour at saturation tem-
perature and from 550 to 850 pounds per hour at,30o below saturation temperature. Some representative traps are shown in Table 3. Field and laboratory tests conducted by the author show that the nominal zft-inch size trap will operate efficiently below 20 pounds per hour and has enough capacity to give safety factors of two or more, depending on the trap, based on a 100 pounds per hour normal load.
Low Loads and Cycling. The trap should be able to handle loads down to a very small percent of its rating which should be in the realm of 2-3 percent at operating temperature. Cycling, or condensate blowing, should occur at a three-to-four-cycle-per-minute rate, with a blowing time of five to ten seconds duration. With proper operation, the trap will not allow condensate buildup in
the tracer and will blow down completely each time. This, of course, is based on a bare trap; insulation should not be applied to a thermodynamic steam trap.
Trop Operoting Problems. Determining the causes of erratic and improper operation leads to a comparison of operating theories and manufacturing techniques. The operation of a floating or tilting disc trap is based,
in part, on the Bernoulli effect. When air and/or condensate enter the trap, the disc is raised from its seat
t40
which allows flow at full trap capacity. As steam enters the trap, the high velocity between the disc and seat creates a low pressure area beneath the disc, and at the same time, steam is recompressing above the disc raising the pressure at that point. This combination causes the disc to snap down on its seat, sealing the trap. As the steam above the disc condenses, the pressure decreases to a point where the cycle is repeated. (See Fig. 2) In studying manufacturing techniques, it was noted that some manufacturers use a small scribe mark in the disc to prevent air binding, while others rough grind the disc to a 7 to 12 microinch finish. This rough grinding apparently controls steam losses much better than the scribe mark. Recompression volume and radiation surface directly affect trap operation. If they are small or there is a poor balance between them, the result will be poor cycling and discharge characteristics which will cause a condensate buildup upstream
of the trap. The
required
balanco is achieved when the radiation of heat is such that the steam trapped above the disc condenses at a rate which gives the desired cycling rate. If the volume is large compared to the surface, the cycling rate will be too slorr': if the volume is small compared to the surface, the cycling rate will be too fast. Replaceable-seat Traps. A more nebulous area but y'et directly involved is the gasketing between the body and
seat
of
replaceable-seat traps.
A poor fit in this area
evidently causes live steam loss and consequent erratic cycling. Atlantic does not normally use replaceable-seat traps, but of the few tested, the losses were high. The type tested used a flat metal gasket to seal the body-seat joint. This sealing problem has been recognized by the manufacturers and they have done extensive testing rvhich has resulted in no t'uvo using the same method; one does not even offer a replaceable-seat. The problem, of course, can be avoided by using integral seat traps. The decision to use or not to use replaceable-seat traps must be based on economics of the individual user.
Trqcer Lengihs. As mentioned earlier,
recommended
maximum traced lengths have been computed to give steam flow
a
of
100 pounds per hour and are shor,vn in Table 4. For the majority of steam-tracing applications. the length of the tracer run is uncontrollably short. Onl1, for long transfer line runs can the length be controlled for effective trap utilization. The usual length of a tracer run produces a condensate flow much below the capacitr' of the trap. Grouping of small systems is useful but limited, since combined s'ystems rapidly become unra.ieldy. By basing traced lengths on a flow of 100 pounds per hour. fABIE 3-Sreom Trop Copocities Contlnuous Dischorge Capacity, Pounds per Hour 15 psig
Size
Trap Inches
A% B% cYB Dr% D, /,
Sat.
Temp.
230 195 135
250
250
Steam
150 psig Stearr. 30o Below 30" Below Sat. Temp. Sat. Temp. Sat. Temp. 330 850 (300) 490 (725) 350 570 850 380 850
575
225 380
575 575
Numbers in parentheses are approximate; normal trap operation consists of three to four discharges per minute of six-to-ten seconds duration.
NEW GUIDE TO STEAM TRACING DESIGN
..
.
Gtt
a trap can be
selected which
is
srr-rall enough
to
avoid
orSc
oversizing, while the allowable runs are reasonably long.
(sflovfl tfl oPEil PtOStflolt
)
In
cases where looping or pocketing of the tracer exists, the tracer should incorporate no more total pocket height than determined by the following API forrnula: Sum of pocket heights : 2.31 \ 10 percent of inlet steam pressure, psig. This condition will occur in the majority of tracing applications within a refinery unit.
Strqiners. To insure trouble-free operation, once the steam trap has been selected, it is necessary to keep dirt
away from the orifices and the disc seating area. This is best accomplished through the use of a strainer, although an alternate method is manual blowdown of all tracing headers and lines before startup. However, using the blowdown nethod, it is difficult to assure that the system is properly blor,l'n down. After startup, the majority of tracers are a clean service; but it is during initial startup
and any subsequent startup following a shutdown that problems arise. Either a tr^p may seal itself because of an accumulation of sludge, or it may trap dirt under the disc, allowing the steam to blow freely. With a closed condensate system, such malfunctioning is not readily apparent; and during the duress of a startup, it will probably go unnoticed. In the course of conducting field tests, 2 out of 14 traps in norrnal tracing serwice were malfunctioning because of dirt under the disc. To provide strainers for each and every tracer, to prevent possible trouble during startup, is undoubtedly false economy, especially when the frequency of such problems appears to be no more than five percent. A better solution is to install a strainer in each small header feeding a number of tracers, thereby cover-
ing all
outr.Cr
Fig. 2-Cross-s_ection of typical floating-disc steam trap. Sreanr flow is shown by the arrows. TABLE
Based on the
formula:
L:
o/s-inch
frop
ry- \L-y,)
Q (^sr)
Where: I - Length of tracer per foot W : Stearn flow, pounds per hour LH:Latent heat of vaporization, Btu per pound Q- Heat loss, Btu per hour-foot SF - Safety factor And: W :100 pounds per hour SF: 2 (basic) 1.5-3.5 (actual) 150 psig Steam
Line
Tracer Length
Insulation Thickness Inches
2
Feet 400
.1
5t3
Size
Inches
4
3tJ
6
275 250
B
NOTES: (1) Chart
is valid
1
to 325' , l/z above to 27 5" , 7/t above to 225' , l/z above
1to 225",1% to 325". 2 above from 150" F to 350" F fluid temper-
ature.
systems.
Integral-Strainer Traps. The author believes that integral-strainer traps are not suitable for large refinery units for the following reasons: their straining capacity is too small, especially for startup conditions; they cost considerably more than separate units; and for complete coverage. each traccr rvould have to be equipped with an integral-
strainer trap.
(2)
The tracer should incorporate no more total pocket height than computed by the following API formula: Sum
of pocket heights - 2.31 x 10 percent of
inlet steam pressure, psig
(3) Insulation thicknesses are based studies for the Philadelphia area.
pot. Insuflicient sizing of these,
Condensole Collection Sysfem. The remaining facet of tracing systems is the condensate collection system. For undersround systerrs) Atlantic uses a small flash pot rvhich will handle a given number of traps. The tracing systems are broken down into groups, each having its or,r,n flash
About fhe oulhor KnNrvnrn G. Er,lwn
is an autumotiue
equipment engineer uith AtlanticRichfi.eldCo. in Pluiladelphia, specifging and selecting automotiue equipment for
the Atlantic Diaision as utell as conlponent testing. He receiued lyis B.S. degree in mechanical engineerirug from Drerel Institute of TechnologA, Phi.ladelphia. IIe utas formedy a design en-
.WhiLe
4-r$oximum frocer Lengths for
gineer u;ith Atlantic Refining Co., assisting in the engineering of refinerE the military seruice, he seraed as test engi-
uni,ts. in neer on the Nike-Hercules launcher research project.
as
on
economic
well as any other open
condensate collection system, will cause a steady rain of condensate in the area of the vent pipe, and the sew-ers in the area will emit flash steam. An underground system can cause maintenance problems when the coolers must be installed beneath concrete.
The alternative is to install an above-ground condensate collection system. From a maintenance viewpoint, a single centralized unit would be even better. Undersround flash pots, being generally horizontal, do not eive as good a separation as an above ground vertical unit. The difficulty in drawing any specific conclusions on condensate collection systems is the nature of the application and the existence of local codes. Originally presented to the ASME Petroleum Mechanical Engineering Conference, New Orleans, September 18-21,1966. ACKNOWLEDGMENT The author wishes to ackoowledge the cooperation of various steam trap manufacturers aod their representatives in obtaining data lor this report.
t4t