FRI - Internal Design vol 5

FRI VOLUME 5: FRACTIONATION DESIGN HANDBOOK

GENERAL INSPECTION GUIDE FOR PRESSURE VESSELS

Issued:

02/15/1993

5.01.01

Revised:

GENERAL INSPECTION GUIDE FOR PRESSURE VESSELS

GENERAL INSPECTION GUIDE FOR PRESSURE VESSELS ........................................... 1 1.

Scope ....................................................... ............................................................................................................... ........................................................................... ................... 2

2.

Responsibilities ................................................. ....................................................... .................................................................. ........... 2

3.

Inspection Points ...................................................... ................................................................................................................ .......................................................... .2

4.

General Inspections ................................................... ........................................................ ..........................................................2

Page 1 of 8

Issued: 02/15/1993

GENERAL INSPECTION GUIDE FOR PRESSURE

Revised:

1

VESSELS

5.01.01

Scope

This guide covers responsibilities, definitions, routines, and methods applicable to when BuyerInspection is specified. Section VIII of the ASME Boiler and Pressure Vessel Code is the principle source of information for inspection of pressure vessels. vessels. Other documents, such as company imposed standard standard specifications serve as additional sources of information. information. This guide includes portions portions of the principle principle sources in lesser details and therefore is not necessarily all-inclusive all-inclusive of the equipment inspection requirements. requirements. This guide does not address, but is supplemented with guides for, post-weld heat treatment, low temperature, clad components, or lethal service conditions and/or environments.

2

Responsibilities

The Specifying Engineer is responsible for deciding the need for Buyer-Inspection and for communicating this need for inclusion in the the purchase contract. For critical items, requiring inspection in excess of normal methods, the engineer shall, along with inspection/expediting personnel, prepare a special inspection brief covering the excess requirements. The Inspector/Expeditor is responsible for performing and/or witnessing examinations or testing of materials and major equipment for conformance with purchase specifications. specifications. The Vendor is responsible for the quality of his product and for demonstrating to the customer that it conforms to the specifications.

3

Inspection Points

Points at which inspections inspections are to be conducted conducted are determined determined largely by the inspector. inspector. Inspection check-lists covering pressure vessels and other types of equipment are utilized in making these inspections. A general checklist for pressure vessel vessel inspection accompanies this guide. Witness points designate inspections or checks normally made by the inspector throughout the manufacturing cycle. Where the inspector is unable unable to be present at these specified times times the vendor may proceed with manufacture without without formal waiver of the inspection. inspection. Hold points designate inspections which shall be made by the inspector and beyond which the vendor is not to proceed without formal formal waiver of inspection. Hold points are to be agreed upon upon by the inspector and vendor prior to start of fabrication.

4

General Inspections

The following inspections/checks inspections/checks are common to most types of equipment and are to be applied accordingly. Witness and Hold points points are identified by "W" and "H" "H" in this guide. Welding Qualifications -

Page 2 of 8

Issued: 02/15/1993


Revised:

VESSELS

5.01.01

1.0 (W) Prior to the start of fabrication, fabrication, assure that welding procedures procedures and operators have have been qualified in accordance accordance with Section IX, ASME Boiler and Pressure Pressure Vessel Code. 1.1 (W) Examine filler metal to assu assure re it is in accordance with the qualifi qualified ed procedure and applicable specifications and the minimum tensile strength is equal to or greater than the base metal. Visual Inspection -

2.0 (W) Examine mill test reports of materials used used for pressure parts and non-pressure parts welded to pressure pressure parts to assure assure compliance with material specifications. specifications. Obtain copies of mill test reports and mark to indicate vessel parts provided from material listed thereon. 2.1 (W)

Check that all materials for pressure parts and non-pressure parts welded to pressure parts are marked for proper identification identification and recorded on check drawings. drawings.

2.2 (W)

Check for compliance with UCS-79 (d) and(e) for carbon steel shells and heads.

2.3 (W)

Check standard flanges for identification, type and rating; check dimensions of all special flanges and those flanges fabricated from plate.

2.4 (W)

Examine gaskets and bolting material to assure proper type and size.

2.5 (W)

Check that formed heads conform to specified configuration.

2.6 (W)

Check pipe and fittings for proper type and schedule.

2.7 (W)

Examine all welds for weld contour, height of reinforcement, reinforcement, size of fillets, undercuts, pin-holes, and other defects.

2.8 (W)

Check that drain and safety safety valve connections are ground ground flush flush with with the inside contour of the vessel.

2.9 (W)

Check that the proper radius is ground on the inside corners of all openings. Check for internal fillet weld on all nozzles with internal projection.

3.0 (W)

Check that bolt holes in flanges and anchor bolt holes, unless otherwise specified, straddle the centerline.

3.1 (W)

Check for weep holes in reinforcing rings.

3.2 (W)

Check for grounding lug, nameplates, insulation supports, and other attachments.

3.3 (W)

Check that bolt holes in double base rings are properly aligned.

3.4 (W)

Check that all skirts are vented and have access openings.

3.5 (W)

Check trays, trays, packing, packing, internals, internals, etc. for proper material and conformance to to drawings.

Page 3 of 8

Issued: 02/15/1993


Revised:

VESSELS

5.01.01

In-Process Inspection -

4.0 (W)

Check materials, especially pressure parts, for finish, damage, laminations, cracks, scars, excessive pitting and proper identification markings.

4.1 (W)

Check beveling of heads and plates for welding. Assure that slag and other detrimental substances are removed.

4.2 (W)

Check that joint design being employed is in accordance with the qualified procedure and specifications.

4.3 (H)

Check fit-up for conformance to the weld procedure. Check alignment of longitudinal and circumferential joints for compliance with Code tolerances. Tack welds used for alignment are not to become part of the joint unless specifically described in the Weld Procedure Specifications.

4.4 (W)

Perform random check of back-gouging on all pressure resisting welds to assure sound weld joints.

4.5 (W)

Check out-of-roundness for the cylindrical shells and cones. Particular attention should be given to vessels for vacuum service.

4.6 (H)

Witness all in-process non-destructive testing specified, such as radiography, magnetic particle, liquid penetrant and ultrasonic. Refer to Supplemental Inspection Guide for Non-Destructive Testing.

4.7 (W)

Check the location, spacing and particularly the levelness of tray support rings. Refer to Supplemental Inspection Guide for Tray Installation.

4.8 (H)

Check installation of each individual tray assuring installation of proper configuration in proper location, levelness, bolting, sealing, etc. Refer to Supplemental Inspection Guide for Tray Installation.

4.9 (H)

Check seal pans, downcomers, weirs, for proper orientation, spacing and settings. Refer to Supplemental Inspection Guide for Tray Installation.

Measurements -

5.0 (W)

Measure to assure all dimensions are within tolerances on drawings and standards. This normally includes sizes, locations, thicknesses, projections, tower bow, levelness of tray supports, weir heights, and downcomer length.

5.1 (H)

Mark actual measurements on one drawing print for submittal with the Final Inspection Report. Refer out-of-tolerance dimensions to Inspection/Expediting for acceptance or rejection.

Final Tests and Inspection -

6.0 (H)

Examine radiographs, where applicable, for adequate definition, identification, and material or weld defects.

6.1 (H)

Witness all other non-destructive tests and review certified examination reports, as Page 4 of 8

Issued: 02/15/1993


Revised:

VESSELS

5.01.01

specified. Cleaning and Painting -

7.0 (W)

Check to assure that vessel has been completely drained of water and is dry.

7.1 (W)

Check to assure that all foreign material has been removed from interior of vessel before shipment.

7.2 (W)

When specified, interior of carbon steel vessels may require coating with a rust preventive or may require sealing against moisture.

7.3 (H)

Assure that any special cleaning procedures have been performed if required by the specifications (e.g. oxygen service).

7.4 (W)

Vessels are not to be painted unless otherwise stated in specifications.

Page 5 of 8

Issued: 02/15/1993


Revised:

5.01.01

VESSELS

GENERAL CHECKLIST PRESSURE VESSEL SHEET 1 OF 3

Inspection Performed

Req'd

Reference

1. Material a. Examine Mill Reports UG-93 b. Thickness (head knuckle and plate edges)

UG-96

c. Conformance to specs Specifications d. UT at mill

2. Welding a. Procedure specification UW-28 b. Qualification and Performance qualification

UW-29

3. Non-Destructive Tests a. Hydrostatic (NOTE: Water temperature and quality required)

UG-99

b. Air UG-100 c. Halide d. Proof UG-101 e. Radiography - type UW-51 f. Liquid penetrant - type ASME, Apdx 8 g. Magnetic Particle - type ASME, Apdx 6 h. Test Reinforcing pads UW-15 (c) i. Physically verify hardness of nuts 1" and larger

ASME Sec. II spec. SA-194

4. Fabrication a. Examine plate surface UG-95 b. Examine cut edges UG-93 (d) and (e) c. Check weld groove preparation

UW-28

d. Welding procedures verified

UW-28

Page 6 of 8

Date

Remarks

Issued: 02/15/1993


Revised:

5.01.01

VESSELS



e. Cutting, fitting, alignment

Req'd

Reference

UW-31,-33

f. Back chip

UW-37

g. Record actual material thickness ((cut-outs)

UG-96

h. Corrosion test result releases i. Welders symbols

Specifications

UW-37

j. Record mill stamping and transfers

UG-94,-77

k. Finish of flanges and machined parts

Drawings

l. Stiffening ring attachment

UG-30

m. Verify nozzle thickness and flange rating

UG-45

n. Atmospheric conditions for welding

UW-30

5. Final Inspection a. Weld appearance and reinforcement

UW-35

b. Check fillet weld sizes

Fig. UW-13,-16

c. Workmanship (comment under "Remarks") d. Out-of-roundness

UG-80

Vacuum Internal Pressure e. Drain and safety valve nozzles flush f. Nozzles radiused inside g. Moly Test h. Dimensional tolerances

UG-76 Specifications Standards

i. Grounding connections

Page 7 of 8

Date

Remarks

Issued: 02/15/1993


Revised:

5.01.01

VESSELS



Req'd

Reference

6. Post-Weld Heat Treatment a. Type b. Thermocouples attached to vessel

UW-40 UW-40, (a), (4)

c. Charts reviewed d. Witnessed e. Verify up, hold and down periods

UCS-56 and UHA-32

7. Preparation for Shipment a. Drain and clean b. Painting

Specifications

c. Flange Protection d. Loading and Tie-Down e. Code Nameplates

UG-116

Page 8 of 8

Date

Remarks

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS SPECIAL CONDITIONS

FRI VOLUME 5: FRACTIONATION DESIGN HANDBOOK Issued:

02/15/1993

5.01.02

Revised:

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – SPECIAL CONDITIONS

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – SPECIAL CONDITIONS .............................................................................................. ............................. 1 1.

Scope .................................................................................................................................. 2

2.

Preface ................................................................................................................................ 2

3.

Inspection Points................................................................................................................ .2

4. Clad Vessel Components ............................................ .........................................................4

Page 1 of 5

Issued: 02/15/1993 Revised:

1

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – SPECIAL CONDITIONS

5.01.02

Scope

This guide supplements the General Inspection Guide For Pressure Vessels and covers special conditions including: • • • •

2

Post-weld Heat Treatment (Stress Relief) Low Temperature Clad Vessel Components Lethal Service

Preface

Certain operating conditions and/or environments require special inspections and tests of the material and equipment. These requirements are presented in general terms for the conditions covered by this supplement.

3

Inspection Points

Points at which inspections are to be conducted are determined largely by the inspector. Inspection check-lists covering pressure vessels and other types of equipment are utilized in making these inspections. Witness Points designate inspections or checks normally made by the inspector throughout the manufacturing cycle. Where the inspector is unable to be present at these specified times the vendor may proceed with manufacture without formal waiver of the inspection. Hold Points designate inspections which shall be made by the inspector and beyond which the vendor is not to proceed without formal waiver of inspection. Hold points are to be agreed upon by the inspector and vendor prior to start of fabrication.

Witness and Hold points are designated by "W" and "H" in this guide. Post-Weld Heat Treatment - Section VIII of the ASME Boiler and Pressure Vessel Code is the principal source of information for post-weld heat treatment of pressure vessels and shall be the reference for detailed requirements.

It is normally not required that the inspector be present for heat treating operations. It is recommended, however, that for large or complex vessels, the inspector observe the set-up for the heat treatment. 1.0 (W)

Post-weld heat treatment, when required, shall be prior to hydrostatic test and after repairs to welding.

1.1 (W)

Examine material and equipment specifications for post-weld heat treatment requirements. Check the Code for proper temperature and holding time per material thickness and assure that vendor has access to adequate heat treating facilities. Assure that Code procedures are followed for vessels heat treated in sections; also that local heat treatments follow Code procedures.

1.2 (W)

Page 2 of 5

Issued: 02/15/1993

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE

Revised:

VESSELS – SPECIAL CONDITIONS

5.01.02

1.3 (W)

Assure that vessels are adequately supported in the furnace to avert deformation or damage during the treatment.

1.4 (W)

Check that thermocouples are attached directly to the vessel and that a sufficient number are used to obtain proof of uniform temperature.

1.5 (W)

Check that there is no direct flame impingement upon the item being heat treated.

1.6 (W)

Check that temperatures are maintained within specified allowable ranges.

1.7 (W)

Obtain and review copies of the heat charts for each furnace charge.

1.8 (W)

Check flatness of large machined surfaces after post-weld heat treatment. Assure remachining, if required, is completed.

Low Temperature - Process vessels to be used in low temperature services are to be inspected for strict observance to governing rules. Section VIII of the ASME Code is the principal source of information for inspection of low temperature process vessels and are to be referenced for detailed requirements. A supplemental checklist for low temperature inspection accompanies this guide.

This guide covers: a.

the inspection requirements for carbon steel, low-alloy steel, and austenitic stainless steel process vessels with design temperatures between minus 20° Fahrenheit and minus 325° Fahrenheit; and,

b. inspection requirements for impact-tested carbon steel and low-alloy process vessels with design temperatures between 32° Fahrenheit and minus 20° Fahrenheit. Vendor Qualifications -

2.0 (W)

Check welding procedures, welders, and welding operators qualifications. Assure tests include impact tests. Specimens for weld metal and heat-affected zone are required for ferritic steel. Weld specimens only are required for austenitic stainless steel.

2.1 (W)

Assure that operators of welding machines are qualified by the same tests as manual welders.

Material Qualifications -

2.2 (W)

Check the results of impact tests on ferritic steel plate conducted at the mill. Longitudinal and transverse tests are required and plate is not to be used until certified results are received and accepted.

2.3 (W)

Check that impact test specimens are heat treated by the same procedure to be used for the completed vessel.

2.4 (W)

Check that low hydrogen type electrodes are used for metal arc welding.

2.5 (W)

Assure that bolting and nut materials meet the low temperature requirements.

Page 3 of 5

Issued: 02/15/1993


Revised:


5.01.02

In-Process Inspection -

4

2.6 (W)

Assure each heat of ferritic steel plate is represented by an impact test on the heat affected zone adjacent to the weld in a sample plate and check the results of the tests.

2.7 (W)

Check results of impact tests on run-off plates including weld metal and heat affected zone tests for ferritic steel and weld metal tests for austenitic stainless steel.

2.8 (W)

Assure no peening is performed on final weld pass.

2.9 (W)

Assure no stress risers are introduced in material. No stamping permitted.

3.0 (W)

Assure all ferritic steel vessels are post-weld heat treated.

3.1 (W)

Assure no welding is performed on vessel after post-weld heat treatment.

Clad Vessel Components

The severity of corrosion expected during service is a prime factor in determination of the amount of corrosion resistance provided. Most common methods of compensating for corrosion are: increased material thickness, integrally clad materials and applied linings to material. 4.0 (W)

Check that tell-tale holes have been properly provided in accordance with the drawing.

4.1 (W)

Check mill shear test reports on clad steel plates when any part of the cladding has been included in the design calculations or required in the specification.

4.2 (W)

Because of the difficulty in welding materials of greatly different composition and properties, examine closely the welder qualification and procedures for depositing corrosion resistant welds and overlayments.

4.3 (W)

Assure weld metal has essentially the same or better mechanical properties and resistance to corrosion as the metal being joined.

Page 4 of 5



5.01.02


SUPPLEMENTAL CHECKLIST LOW TEMPERATURE SHEET 1 OF 1


Req'd

Reference

Impact Values

UG-84

UG-84

Longitudinal

UG-84

UG-84

1. Material a. Examine Mill Reports

Transverge Specimen Size

UG-84

Test Temperature

UG-84

Heat Treatment

UG-84

b. Bolt and Nut Material

2. Welding

NOTE: Assure that qualification tests were impact tested if necessary

a. Welding Procedure and Operator Qualifications b. Use of Low Hydrogen Electrode

3. Fabrication a. Examine Plate and Welds for Stress Risers. (Welder Stamps Not Permitted) b. Positively No Welding After Post-Weld Heat Treatment

UCS-56 (a)

Page 5 of 5

Date

Remarks

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – CRITICAL INSPECTION REGIONS FOR EXISTING VESSELS


2/15/1993

Revised:

5.01.03


SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESS ELS – CRITICAL INSPECTION REGIONS FOR EXISTING VESSELS............................................................ 1 1.

Scope.............................................. ..................................................................................... 2

2.

Preface ........................................... ..................................................................................... 2

3.

Inspection Points .................................................................................................................2

4.

General Inspections ................................................... .........................................................3

5.

Thickness Measurements .................................................................................................... 3

6.

Critical Regions Near Nozzles and Other Discontinuities ................................................ .4

Page 1 of 22


1


5.01.03

Scope This guide supplements the General Inspection Guide For Pressure Vessels and covers critical inspection regions for existing vessels.

2

Preface Other than certain of those related solely to erosion/corrosion, most of the critical regions (those most probable regions where problems will be discovered) included herein, are associated with welds - and more specifically with toes of welds. This is easily explained by the fact that the highest localized (peak) stress in the weldment is typically at the toe of the weld. This is particularly true if the reentrant angle (see Figure 1) is small and even more so if weld undercut is also present. Thus, it becomes the initiation point of fatigue crack if exposed to a cyclic stress environment. As illustrated in Figure 1, the degree of weld contour can have a significant influence on fatigue life. Operating stresses from most services, however, are basically static (the combination of number of cycles and amplitude of peak stress variation is relatively small). As a result, most as-welded Code construction, even with heavily "reinforced" butt welds and fillet welds with a convex contour,etc., (see Figure 1) performs reliably from a fatigue standpoint except when an improperly designed vessel is willfully placed in what is easily recognized as fatigue service. One exception to this is when corrosion and fatigue combine, causing the material to act as if it is being subjected to an intensified form of fatigue even though the cyclic peak stress amplitude/number of cycles combination is small. Other environmentally assisted cracking phenomena result in fatigue failures in certain fluid environments that would otherwise be considered impossible or unlikely when viewed only from a stress history standpoint. Regardless of the exact mechanism, experience shows that the fluid environment (both internal and external) to which a vessel is exposed often plays a major role in determining the reliability performance of the pressure-resisting components. Therefore, any "critical" region inspection list must be considered a generic "laundry list" rather than an inspection guideline for a particular vessel in a particular service.

3

Inspection Points Points at which inspections are to be conducted are determined largely by the inspector. Inspection check-lists covering pressure vessels and other types of equipment are utilized in making these inspections. A general checklist for pressure vessel inspection accompanies this guide. Witness points designate inspections or checks normally made by the inspector throughout the manufacturing cycle. Where the inspector is unable to be present at these specified times the vendor may proceed with manufacture without formal waiver of the inspection. Hold points designate inspections which shall be made by the inspector and beyond which the vendor is not to proceed without formal waiver of inspection. Hold points are to be agreed upon by the inspector and vendor prior to start of fabrication.

Page 2 of 22


4


5.01.03

General Inspecti ons To assure that a meaningful inspection will take place, it is essential that several inputs be involved. 1.0 (W)

Obtain/Examine previous inspection information. The thickness loss pattern of a vessel can often be predicted from records of previous inspections and/or from experience with previous vessels in the same service.

1.1 (W)

Gather/Review information regarding the service conditions since the last inspection; e.g., have they remained the same or have they changed? If so, what are the changes?

1.2 (W)

Gather/Review information.on how the service conditions since the last inspection might have affected the vessel in question. What are the critical regions that need inspection? Are isolated corroded, eroded, or pitted areas expected?

1.3 (W)

Seek advice regarding the type and extent of non-destructive examination needed to verify the vessel integrity. Will an internal inspection be required, or can the desired results be achieved via external non-destructive examination?

Armed with this essential information, a well-reasoned inspection plan can be developed. Additionally, needed repairs/alterations, if any, and what the next inspection interval should be can now be defined.

5

Thickn ess Measur ements It is essential that thickness measurements be taken and recorded in such a way that corrosion rates can be calculated. These measurements provide a basis to set the next inspection interval, possibly identify areas requiring either immediate or potential repairs, downrating of the MAWP, and/or a change in the coincident temperature rating. In some cases, the inspection may be associated with evaluating the vessel for uprating of the MAWP. In order to obtain accurate corrosion rates, it is imperative that the locations of the measurements be accurately recorded so that subsequent measurements will be obtained at the same locations. This can be accomplished by making a sketch of the item and recording measurement location from carefully documented reference points, e.g., nozzles, welds, etc. Attachment of a measurement point identification label may also be a feasible means of precisely locating future measurement points. The guidelines in Par. U-107 of the National Board Inspection Code may be useful in determining the effective thickness of nonuniformly corroded regions. Those guidelines in Par. U-106(b) are generally used for establishing the interval between inspections once the engineering judgements associated with selecting the design-basis corrosion rate have been agreed upon. Guidelines for repair and alteration of vessels are generally covered by company specifications.

Page 3 of 22


6


5.01.03

Criti cal Regio ns Near Nozzles and Other Discon tin uiti es A thinning pattern at the fluid inlet nozzles has been noted in services generally considered to be noncorrosive, whereby apparently combined corrosion-erosion effects have caused thinning due to the fluid running down the side of the vessel. As shown in Figure 2, the thinning is greatest (widest and deepest) at the inside corner of the nozzle opening and decreases rapidly as the distance from the nozzle increases. This thinning in a vertical vessel reduces the shell thickness that supports the primary stress in the "basic" critical region of openings in cylinders (plane of greatest loading due to pressure) as shown in Figure 3. Refer to Par. UG-37(b) of the ASME Pressure Vessel Code. Such thinning can have an adverse effect on the pressure rating of the vessel. Accordingly, when inspecting a vessel that has been in service, this critical region of all shell nozzles should be given close scrutiny, especially if the tendency for the development of cracks has been noted. Of course, if the nozzle is in the center of a flat head, or is a radial nozzle in a sphere or spherical portion of a flat head, the stress due top pressure in all planes containing the nozzle axis is the same and hence all points along the circumference of the corner region are of equal importance. Compliance with the ASME Pressure Vessel Code rules for nozzle reinforcement is intended to prevent failures due to pressure loading in the "basic" critical region for pressure loading that is illustrated in Figure 3. Service experience indicates that the Code reinforcing rules do indeed properly reinforce this plane of greater loading due to pressure, and failures at this location are accordingly rare. In fact, service experience clearly indicates that the most likely location for failure of a Code reinforced nozzle to occur is at a location 90 degrees away from the basic critical region (at the toe of the nozzle or reinforcing pad attachment weld) as shown on Figure 4. High discontinuity stresses at this location for nozzle types customarily used for Division 1 vessels are the r esult of the relatively rigid nozzle attachment that restrains the natural change in radius of curvature (dilation) of the vessel due to internal pressure. Oftentimes, superposed of this stress is a high stress due to moment loading (this location is particularly sensitive to out-of-plane moment loading), and both stresses are intensified by the stress riser caused by the abrupt change in contour at the toe of the fillet weld. Additionally, welding may be difficult because of the constraint against weld metal contraction, possibly leading to cracking at the toe of the fillet weld during fabrication or during the initial hydrostatic test. Because of the high local stresses, plus the possibility of macroscopic cracks, this area is especially sensitive to "brittle fracture" problems if the material is low in notch toughness at the metal temperature during the stressing condition. Obviously, thinning of the shell in this region will intensify the stresses and can also have an adverse effect on the total ductile strength of the vessel. Therefore, it is recommended that this weld toe region be given careful inspection following nozzle installation (after hydrotesting if possible) and routinely during periodic inspections. It is further recommended that this general region be avoided for the location of seam welds, clip attachments, nozzle and coupling attachments, etc. The problem discussed above and shown on Figure 4 is probably not a nozzle reinforcement problem per se; that is, any relatively rigid attachment fillet welded to the surface of the vessel may create the same conditions. A well-known example of a rigid non-nozzle attachment is that of a saddle for a horizontal vessel as shown in Figure 5. The shell stress condition at the horn of the saddle compares with that due to a nozzle and accordingly should be treated in a similar manner from a fabrication and inspection standpoint.

Page 4 of 22



5.01.03

SUPPLEMENTAL CHECKLIST CRITICAL INSPECTION REGIONS PRESSURE VESSEL(EXISTING) INTERNAL SHEET 1 OF 3


Req'd

Reference

Date

Remarks

1. Any (all previously repaired region(s): 2. Longitudinal Seams

a. Peaked seam regions

Along seam welds, including weld toe regions and 1/2" wide bank on each side of weld. Fig.6

Note that crack initiation is most likely to occur at inside of vessel, prob ably along the weld itself rather than along weld toe.

b. Intersections with circumferential seams 3. Circumferential Seams

See Remarks, Item 2

a. Offset between shell courses

Look carefully at regions where offset is greatest

b. Dished head-to-shell joints c. Cone-to-cylinder joints d. Joints between shell courses of different thicknesses e. Joints connecting com ponents with different coefficients of expansion 4. Inside corner of nozzle openings in cylindrical shell 5. Inside corner of nozzle openings in head, around entire circumference

Write-up, Fig. 3

Particularly in longitudinal seams

Write-up

6. Horizontal Nozzle a. (6 o'clock region)

Fig. 2

Page 5 of 22

"Tear-drop" corrosion/erosion pattern often observed at inlet nozzles



5.01.03

SUPPLEMENTAL CHECKLIST CRITICAL INSPECTION REGIONS PRESSURE VESSEL (EXISTING) INTERNAL SHEET 2 OF 3


Req'd

Reference

Date

Remarks

b. "Dead" (blind flanged) nozzles

Grooving is sometimes observed

c. Longitudinal weld in nozzles rolled from plate

Preferentially attached, especially if oriented in 6 o'clock position

7. Bottom Nozzles a. "Dead" (blind flanged) nozzles

Sometimes corrosive layers will "decant out" in bottom nozzles that are blind flanged;check for thinning

b. Erosive/corrosive attack

Sometimes experienced around bottom outlet nozzle;check for thinning

8. Inlet Nozzles erosion/ corrosion a. Erosion/Corrosion

Look for possible erosion/corrosion in nozzle bore

b. Shell region where flow from tangential nozzle impinges

Sometimes impingement across a radial inlet nozzle is sufficient to cause erosion; e.g., in base of column across calandria discharge nozzle

c. Inlet nozzles where ID of inlet piping is larger than ID of nozzle

9. Nozzle on shell flange attachment welds

Fig. 7

This can be particularly critical if nozzle flange is lap jo int style since thinning can reduce throat thickness of lap attachment to dangerous proportions

Fig. 8(a),-8(b)

The weld attaching shop-fabri cated lap rings to cylinder. If weld is as in Fig.8(a), it will not be visible during internal inspection except when joint has been disassembled and face of lap has been cleaned. If weld is as shown in Fig.8(b), it will be visible from inside without disturbing the lap joint (either lap attachment arrangement is Code acceptable).

a. Lap-Joint type flanges

Page 6 of 22



5.01.03

SUPPLEMENTAL CHECKLIST CRITICAL INSPECTION REGIONS PRESSURE VESSEL(EXISTING) INTERNAL SHEET 3 OF 3


Req'd

Reference

b. Weld-Nut type flanges

Remarks

Thinning of tapered hub region at or near attachment weld is particularly significant

c. Slip-on type flanges

10. Toe of fillet welds attaching rigid attachments

Date

Check for erosion/corrosion of internal fillet weld

Write-up

11. Knuckle region of dished leads

Locations along the axis of the vessel are the most highly stressed due to pressure loadings Sometimes the location of stress-induced preferential corrosion

12. Internal non-pressure parts, e.g., coil supports, impingement plates, anti-swirl baffles

Fillet weld toe areas, crevice areas and threaded components are particularly suspect

a. Toe areas of longitudinal fillet weld attachments

The stress concentration from pressure stress is greatest at fillet weld toe areas running parallel to the longitudinal axis of the shell, therefore, all else equal-these areas are more suspect than those running circumferentially

13. I.D. surfaces opposite welds on outside surface for attachment of clips, stiffening rings, reinforcing pads, etc.

These areas on I.D. can be subject to stress corrosion cracking (SCC) in environments that cause SCC.

14. Any visibly deformed or thinned regions

Page 7 of 22



5.01.03

SUPPLEMENTAL CHECKLIST CRITICAL INSPECTION REGIONS PRESSURE VESSEL (EXISTING) EXTERNAL SHEET 1 OF 4


Req'd

Reference

Date

Remarks

1. Underneath insulation Likely regions for breaks are: a. Breaks in insulation vapor barrier

Fig. 9 and 10

*Any penetrations through shell/head insulations, e.g., at nozzles, lugs etc. Such locations are particularly suspect if in top head insulation of vertical vessel *At interface regions such as where insulation abuts vacuum insulation or base rings. These have proven to be regions where chlorides form the atmosphere can concentrate. Moisture can be “wicked up” the insulation and corrod e/stress crack shell of vertical vessels.

b. Sweating Zone

Suspect regions are those where the operating temperature is in the range of 0° Fahrenheit, including cycling to 430° Fahrenheit

c. Nozzle gasket leakage or chemical spillage d. Sweating zone or melt line of icecovered areas e. Wet insulation

Cut inspection windows through insulation as required to determine extent of wet zone Repair windows promptly to avoid further water damage, e.g., rain Complete removal of insulationprior to vessel inspection may be necessary if the insulation is found to be in “bad shape”

f. Steam Tracing

Lack of painting underneath steam tracing can result in external chloride-induced stress corrosion cracking in austenitic stainless steel piping or vessels

Page 8 of 22



5.01.03



Req'd

Reference

Date

Remarks

2. Any (all previously repaired region(s)

Along seam welds, including weld toe regions and 1/2” wide bank on each side of weld. These are zones of possible preferential attack and stress corrosion cracking

3. Longitudinal Seams

a. Packed seam regions

Fig. 6

4. Circumferential Seems

See Remarks, Item 3 Look carefully at regions where offset is greatest

a. Offset between shell courses

b. Dished head-to-shell joints c. Cone-to-cylinder joints d. Joints between shell courses of different thicknesses e. Joints connecting components with different coefficients of expansion

5. Toe of nozzle-to-shell attachment weld or, if reinforcing pad is p rovided, at toe of reinforcing pad-to-shell attachment weld

Write-up Fig. 4

In either case, the toe region tangent to a longitudinal plane is the most likely region of cracking

6. Toe of nozzle-to-head attachment weld or, if reinforcing pad is p rovided, at toe of reinforcing pad-to-head attachment weld

Write-up

Applies to nozzle installations in flat heads (blind flanges) as well as those in dished heads

Page 9 of 22



5.01.03



Req'd

Reference

7. Toe of saddle bank attaching fillet weld in saddle horn region

Write-up

8. Toe of fillet welds attaching support lugs or other rigid attachments

Write-up

Fig. 5

Date

Remarks

Particularly at corners of saddle bank (more recent designs will have radiused “corners”)

Locations parallel with the axis of the vessel are the most highly stressed due to pressure loadings

9. Toe of fillet weld attaching tubesheet to shell

Check peripheral edge of tubesheet for delaminations

10. Toe of skirt attachment weld 11. Offset between shell courses a. Half-pipe jackets

Half pipe-to-shell welds, particularly near hot end of jacket Butt welds between half-pipe sections, particularly near hot end of jacket

12. Nozzle or shell flange attachment welds a. Lap-joint type flanges

Fig. 8(a),-8(b)

b. Welding neck type flanges

The weld attaching shop fabricated lap rings to cylinder. This weld is arranged as shown in the figures, and hence will not be visible during external inspection except where bolted joint has been disassembled (either lap arrangement shown is Code acceptable) Thinning of tapered hub region at or near attachment weld is particularly significant

c. Slip-on type flanges

Check for corrosion of external fillet weld

13. Knuckle region of dished heads 14. Support legs

Check behind bolted-on support legs

Page 10 of 22



5.01.03



15. Nozzle and main shell lap flanges 16. Thickness of bolted flanges

Req'd

Reference

Fig. 11

Remarks

Check behind these flange

Write-up

a. Integral (e.g., welding neck t ype) flanges

The small end of hub region near attachment weld is particularly sensitive to thickness loss

b. Nut bearing surfaces 17. Zones adjacent to stiffening ring or insulation support rings

Date

Check for evidence of scoring and corrosion Fig. 1 and Fig. 9

Moisture can be retained here. These are especially suspect areas for vertical vessels that are insulated

18. Gasket contact surfaces or bolted flanges a. Pitting and/or crevice corrosion

Check for evidence

b. Radial scratches across contact surface

Check for presence

c. Distortion d. Backside of lap (applies only to lap joint flages)

Check for evidence. Lap joints are most suspect

Fig. 11

e. Gasket surface machining

Check for evidence of corrosion If gasket surface must be machined to eliminate unacceptable surface imperfections, the most desireable surface finish for the gasket to be employed should be determined

19. Flange bolts/nuts; anchor bolts/nuts; leg attachment bolts/nuts 20. Any visibly deformed or thinned regions 21. Paint

Paint scraped from the vessel to facilitate thickness measurements should be repaired to avoid continued corrosion

22. Grounding clip

Does it exist? Is it connected?

Page 11 of 22



Figure 1. ILLUSTRATIONS SHOWING WELD GEOMETRY

AND ASSOCIATED REENTRANT ANGLE 0/ is termed the REENTRANT or REINFORCEMENT ANGLE. It determines the notch sharpness and hence the fatigue strength.

Page 12 of 22

5.01.03



Figure 2. INLET NOZZLES "TEAR DROP" EROSION/CORROSION PATTERN

Page 13 of 22

5.01.03



Figure 3. PLANE OF GREATEST PRESSURE LOADING AT NOZZLE

Page 14 of 22

5.01.03



Figure 4. ILLUSTRATION OF TOE OF NOZZLE-TO-SHELL ATTACHMENT WELD

Page 15 of 22

5.01.03



Figure 5. ILLUSTRATION OF TOE OF SADDLE BANK

Page 16 of 22

5.01.03



Figure 6. ILLUSTRATION OF PEAKED LONGITUDINAL SEAM See UG-79 (B) and UG-80 of SECTION VIII, Div. I for rules relating to peaked seams and out-of-roundness

Page 17 of 22

5.01.03



Figure 7. INLET NOZZLES ILLUSTRATION OF EROSION/CORROSION DAMAGE

Page 18 of 22

5.01.03



Figure 8. TYPES OF LAP ATTACHMENTS See FIGURE 2-41(A) of Section VIII, DIV. I for weld requirements

Page 19 of 22

5.01.03



Figure 9. CORROSION AT VACUUM OR INSULATION SUPPORT RINGS

Page 20 of 22

5.01.03



Figure10. CORROSION AT BOTTOM PLATES OF FLAT BOTTOM TANKS

Page 21 of 22

5.01.03



Figure 11. CORROSION BEHIND MAIN SHELL OR NOZZLE LAP FLANGES

Page 22 of 22

5.01.03

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS NON-DESTRUCTIVE TESTING


02/15/1993

5.01.04

Revised:

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – NON-DESTRUCTIVE TESTING

SUPPLEMENTAL INSPECTION GUIDE FOR PRESSURE VESSELS – NONDESTRUCTIVE TESTING ......................................................... ............................................. 1 1.

Scope .................................................................................................................................. 2

2.

Preface ................................................................................................................................ 2

3.

Radiography ........................................................................................................................ 2

4.

Ultrasonic................................................ ............................................................................ 2

5.

Magnetic Particle ................................................ ................................................................ 3

6.

Liquid Penetrant................................................. ................................................................. 3

7.

Other Methods .................................................................................................................... 3

Page 1 of 4

Issued: 02/15/1993


Revised:

1

VESSELS – NON-DESTRUCTIVE TESTING

5.01.04

Scope

This guide supplements the General Inspection Guide For Pressure Vessels and covers Non- Destructive Tests including: • • • •

Radiographic Ultrasonic Magnetic Particle Liquid Penetrant

In addition, mention is made of certain other tests/techniques available for examining the integrity of a pressure vessel.

2

Preface

The primary purpose for inspecting a vessel is to ensure that the vessel, as completed, complies with the specifications for the vessel. Tests are used to confirm the strength of the vessel and/or to ensure that no leaks will occur. The greater the extent of the inspection or test, the greater the assurance the vessel meets the specifications but at an increasing cost. Non-Destructive testing of both plate and the finished vessel is important to safety. In the analysis of fracture hazards, it is important to know the size of the flaws that may be present in the completed vessel. The four most widely used methods of examination are radiographic, magnetic particle, liquid-penetrant, and ultrasonic (27). The Specifying Engineer should use the "penalty of failure" concept to determine the extent to which a vessel is to be tested beyond the minimum requirements. Consultation with Safety and Fire Protection personnel and/or Process Vessel Design personnel is recommended.

3

Radiography

Radiographing is the process of passing radiation through an object to obtain a record of its soundness upon sensitized film. Radiographic examination is either by x-rays or by gamma radiation. The former has greater penetrating power, but the latter is more portable. Few x-ray machines can penetrate beyond 12 inches (305 mm) thickness. Three degrees of radiographic examination are generally employed. These include Spot, Partial, and Full Radiography. SPOT Radiography is a random sampling of welding used to aid quality control. One spot is examined for about each 50 feet (15.24 meters) of weld. PARTIAL Radiography is an examination at least six inches long of any section of the weld picked at random, plus a similar examination of certain intersections of the weld as required by the ASME Code. Acceptance standards for the partial radiography are more stringent than for spot radiography. FULL Radiography is frequently used to indicate that the main seams of a vessel are to be radiographed. The use of the term in this manner should be avoided; it is much more precise to specify the extent of the radiographic examination required by specifying radiographing for each of the various categories of joints established in the ASME Code. It is proper to say that a particular weld is to be fully radiographed, meaning that the entire weld is to be so examined (27).

4

Ultrasonic

Ultrasonic techniques use vibrations with a frequency between 0.5 and 20 Mhz transmitted to the metal by a transducer. The instrument sends out a series of pulses. These show on a cathode-ray screen as they Page 2 of 4



5.01.04

are sent out and again when they return after being reflected from the opposite side of the member. If there is a crack or an inclusion along the way, it will reflect part of the beam. The initial pulse and its reflection from the back of the member are separated on the screen by a distance which represents the thickness. The reflection from a flaw will fall between these signals and indicate its magnitude and position. Ultrasonic examination can be used for almost any thickness of material from a fraction of an inch to several feet. Its use is dependent upon the shape of the body because irregular surfaces may give confusing reflections. Ultrasonic transducers can transmit pulses normal to the surface or at an angle (27).

5

Magnetic Particle

Magnetic particle examination is used only on magnetic materials. Magnetic flux is passed through the part in a path parallel to the surface. Fine magnetic particles, when dusted over the surface, will concentrate near the edges of a crack. The sensitivity of magnetic-particle examination is proportional to the sine if the angle between the direction of the magnetic flux and the direction of the crack. To be sure of picking up all cracks, it is necessary to probe the area in two directions (27).

6

Liquid Penetrant

Liquid penetrant examination involves wetting the surface with a fluid which penetrates open cracks. After the excess liquid has been wiped off, the surface is coated with a material which will reveal any liquid that has penetrated the cracks. In some systems a colored dye will seep out of cracks and stain whitewash. Another system uses a penetrant that becomes fluorescent under ultraviolet light. Each of these popular methods has its advantages. Frequently, best results are obtained using more than one method. Magnetic particles or liquid penetrants are effective on surface cracks. Radiography and Ultrasonics are necessary for subsurface flaws. No known method of nondestructive testing can guarantee the absence of flaws (27).

7

Other Methods

There are other less widely used methods of examination. Among these are eddy-current, and electrical resistance testing. The eddy-current technique involves an alternating current coil along and close to the surface being examined. The electrical impedance of the coil is affected by flaws in the structure or changes in composition. Commercially, the principal use of eddy-current testing is for the examination of tubing. It could, however, be used for testing other things. The electrical resistance method involves passing an electrical current through the structure and exploring the surface with voltage probes. Flaws, cracks, or inclusions will cause a disturbance in the voltage gradient on the surface. Finally, the hydrostatic test is, in one sense, a method of examination of a vessel. It can reveal gross flaws, inadequate design, and flange leaks. Many believe that a hydrostatic test guarantees the safety of a vessel. This is not necessarily so. A vessel that has passed a hydrostatic test is probably safer than one that has not been tested. It can, however, still fail in service, even on the next application of pressure. Care in material selection, examination, and fabrication do more to guarantee vessel integrity than the hydrostatic test (27).

Page 3 of 4



5.01.04

References and Further Readings

27.

Perry, R.H., and Green, D.W., "Perry's Chemical Engineers' Handbook", 6th Edition, McGrawHill, 1984, pp. 6-118.

Page 4 of 4


DEFINITION OF COMMON TERMS

Issued:

02/15/1993

5.01.05

Revised:


DEFINITION OF COMMON TERMS ........................................................... .......................... 1 1.

Definition of Common Terms ............................................................................................ 2

Page 1 of 4


1


5.01.05

Definition of Common Terms ABRASION -The process of rubbing away; scraping, grinding, or wearing away by friction (see also Erosion). AGE HARDENING - A process of increasing the strength and hardness of a metal or alloy by a relatively low temperature heat treatment that causes precipitation from solid solution of a second structural component or phase, usually sub-microscopic. AIR (PNEUMATIC) TEST - A leak test. ANNEALING - A process of controlled heating and cooling which is designed to soften, relieve stresses and to refine the grain structure of a metal. The rate of cooling required varies with the alloy involved. AUSTENITIC (or AUSTENITE) - The non-magnetic, face centered, cubic lattice consisting of iron atoms at temperatures above 1500 degrees Fahrenheit. This structure will dissolve carbon and forms the basis of the hardenability of steel. This is also the normal room temperature structure of the 18-8 chrome-nickel stainless steels, 35 percent nickel cast iron, and Hadfield manganese steel. BACK GOUGING (BACK CHIPPING) - Gouge and sound metal from the opposite side of a weld. CAST STEEL - Molten steel cast into molds and used without any special heat treatment or cold working. Have properties close to steel in that it is ductile and stronger than cast iron. CONTACT OR CREVICE CORROSION - Corrosion of a metal at a recessed area where mechanical contact is made with the same or a different material. Corrosion is created by concentration cell or galvanic effects. CORROSION - Destruction of a metal by chemical or electrochemical reaction with its environment. CORROSION FATIGUE - Reduction of fatigue durability by a corrosive environment. DESIGN PRESSURE and TEMPERATURE - The Design Pressure is the pressure used to determine the minimum permissible thickness of physical characteristics of the different parts of the vessel. When applicable, the static head of fluid in the vessel is added to the design pressure to determine the thickness of any specific part of the vessel. The Design Temperature is the metal temperature coincident with the design pressure. EMBRITTLEMENT - Severe loss of ductility of a metal or alloy, as of steel by hydrogen. EROSION - Destruction of a metal or other material by the abrasive action of liquids, solids, or gas. Most times accelerated by corrosion. FATIGUE - The tendency of a metal to rupture under conditions of repetitive cyclis stress, where the magnitude of the stress is usually considered to be below the tensile strength. FERRITE - This is the magnetic, body-centered, cubic lattice form of iron at room temperature. Carbon is insoluble in this structure and thus is present in steel as the compound iron-carbide.

Page 2 of 4



5.01.05

FILLER METAL - Weld metal. FILLET - Typical weld, usually triangular in cross-section. A very common weld. FULL RADIOGRAPHY - "FULL" Radiography is frequently used to indicate that the main seams of a vessel are to be radiographed. The use of the term in this manner should be avoided; it is much more precise to specify the extent of radiographic examination required by specifying radiographing for each of the various categories of joints established in the ASME Code. It is proper to say that a particular weld is to be fully radiographed, meaning that the entire weld is to be so examined. HALIDE TEST - A sensitiver leak test. IMPACT TEST - A qualification of material test for low temperature service. IMPINGEMENT ATTACK - Corrosion associated with turbulent flow of a liquid. For some metals, the action is considerably accelerated by entrained bubbles in the liquid. JOINT EFFICIENCY - The efficiency of a welded joint is expressed as a numeral (decimal) quantity and is used in the design of a joint as a multiplier of the appropriate allowable stress value for the material. The joint efficiency depends upon the type of joint and the extent of examination of the joint. LAMINATIONS - Separation of metal into layers. LIQUID - PENETRANT EXAMINATION - Liquid-penetrant examination is a method of testing for surface defects or sub-surface defects with surface openings by relying upon a penetrant seeping into the defect. It is normally used for non-magnetic materials. MAGNETIC PARTICLE EXAMINATION - Magnetic Particle Examination is a method of detecting cracks and similar discontinuities at or near the surface in iron and magnetic alloys of steel. It consists of properly magnetizing the material and applying finely divided magnetic particles which form patterns indicating discontinuities. MAXIMUM ALLOWABLE WORKING PRESSURE - The Maximum Allowable Working Pressure (MAWP) is the maximum gage pressure permissible at the top of a completed vessel in its operating position for a designated temperature. This pressure is the basis for the pressure setting of the pressure relieving devices protecting the vessel. MOLY TEST - Test performed to differentiate 316 and 316l materials from other Molybednum alloys. NON-PRESSURE PARTS - Those parts not containing pressure (i.e. lugs, clips, etc.) OPERATING PRESSURE and TEMPERATURE - The Operating Pressure is the pressure at the top of a pressure vessel at which it normally operates. The Operating Temperature is the temperature that will be maintained in the metal of the vessel for the specified operation of the vessel. For insulation purposes, warm service mean metal temperatures above 10° Centigrade while cold service is for metal temperatures 10° Centigrade or below. PARTIAL RADIOGRAPHY - "PARTIAL" Radiography is an examination at least six inches long of any section of the weld picked at random, plus a similar examination of certain intersections of the welds as required by the ASME Code. Acceptance standards for partial radiography are more

Page 3 of 4



5.01.05

stringent than for spot radiography. PRESSURE/PRESSURE RESISTING WELDS OR PARTS - Those parts/welds exposed to (containing) pressure. PEENING - A method of stress relieving metal. RADIOGRAPHING - Radiographing is the process of passing electronic radiations through an object to obtain a record of its soundness upon sensitized film. REENTRANT ANGLE - Notch effect, or abrupt change in metal thickness. RUN-OFF PLATE - A tab used to catch weld metal. SENSITIZATION - The process in stainless steels in which the alloy becomes susceptible to intergranular corrosion because of prolonged exposure to temperatures in the range of 800 to 1500° Fahrenheit. SHEAR TEST - A characteristic metal strength test. SPOT RADIOGRAPHY - "SPOT" Radiography is a random sampling of welding used to aid quality control. One spot is examined for about each 50 feet of weld. STRESS CORROSION CRACKING - Cracking resulting from the combined effect of corrosion and stress. STRESS RELIEF - Stress Relief (Postweld Heat Treatment) is the uniform heating of a structure or portion thereof to a sufficient temperature below the critical range to relieve the major portion of the residual stresses, followed by uniform cooling. STRESS RELIEVING - A heat treatment for reducing the internal residual stresses in metal parts by heating to a suitable temperature and cooling uniformly. STRESS RISER - Same as REENTRANT angle. TEMPERING - The heat treatment process whereby hardened steel is brought up to some temperature below the hardening temperature and then slowly cooled. This partially softens the metal and makes it more ductile while still retaining some of the increase in hardness and strength produced by the hardening process. ULTRASONIC EXAMINATION - Ultrasonic Examination is made by introducing a beam of ultrasonic energy into a specimen and measuring the reflected energy. Defects in the specimen affect wave reflection. UNDERCUT/WELD UNDERCUT - Area burned out but not filled with weld metal. WELD DECAY - Corrosion, notably of austenitic steels, at specific zones near a weld where sensitization has occurred.

Page 4 of 4

SUPPLEMENTAL GUIDE TO VISUAL EXAMINAION OF DISTILLATION TOWER INTERNALS


06/15/2003

5.02.01

Revised:

SUPPLEMENTAL GUIDE TO VISUAL EXAMINATION OF DISTILLATION TOWER INTERNALS

SUPPLEMENTAL GUIDE TO VISUAL EXAMINATION OF DISTILLATION TOWER INTERNALS .................................................................... .........................................................1 1.

Overview........................................................ ..................................................................... 2

2. Requirements ....................................................................................................................... 2

Page 1 of 2


1

SUPPLEMENTAL INSPECTION GUIDE TO VISUAL EXAMINTION OF DISTILLATION TOWER INTERNALS

5.02.01

Overview Scope - This document provides requirements for visual examination of distillation tower internals (both trayed towers and packed towers) and their installation. Applicability - The requirements of this document apply to field inspection (i.e., at the plant site) of new or repaired distillation tower internals including their installation. This document also covers inspection of tray installation at vessel shops or in the field, inspection of packed tower internals in the field, and inspection of tray and packed tower internals at tower internals vendor shops.

2

Requirements Drawing Review - Review the most recent installation drawings provided by the vendor for the tower internals. The inspector must understand how the various tray or packed tower components fit together and what the bolting assemblies should look like when properly installed. Useful Equipment - Besides any required safety gear, the following equipment may be useful:

• • • • • • •

High intensity flashlight Inspection mirror 6 inch (150 mm) steel ruler 10-25 foot (3-8 m) tape measure Templates (for measuring repetitious internals) Paint pen (or other device for marking deficiencies) Digital camera (for recording proper installation as well as deficiencies or errors)

Trial Assembly - When practical, conduct a trial assembly of a tray (or packed tower distributor, for example) outside the tower where there is good light and ample room to see all parts of the tray. Note: This trial assembly will be a valuable training tool for installers, inspectors, and plant operating personnel. Checklist Selection - Select and use the proper checklist(s) as follows: Item

Checklist

Tray Installation (Vessel Shop or Field)

5.02.2

Packed Tower Internals Installation (Field)

5.02.3

Trays at Vendor Shop

5.02.4

Packed Tower Internals at Vendor Shop

5.02.5

Note: These inspections are very important since this is the last opportunity to identify design, fabrication, or installation errors prior to startup. While these checklists are intended to be comprehensive, they are not all-inclusive. Inspectors must proactively look for other inspection points based on their on-site perspective.

Page 2 of 2

CHECKLIST FOR VISUAL EXAMINATION OF TRAY INSTALLATION (VESSEL SHOP OR FIELD)

FRI VOLUME 5: FRACTIONATION DESIGN HANDBOOK Issued: Revised:

6/15/2003

5.02.02

CHECKLIST FOR VISUAL EXAMINATION OF TRAY INSTALLATION (VESSEL SHOP OR FIELD)

CHECKLIST FOR VISUAL EXAMINATION OF TRAY INSTALLATION (VESSEL SHOP OR FIELD) ................................................... .................................................................................................... 1 1.

Checklist For Visual Examination of Tray Installation (Vessel Shop or Field) .................................. 2

2.

In structions for Checkist for Visual Examination of Tray Installation (Vessel Shop or Field) .......... 3 2.1

General Instructions ............................................................................................ ........................... 3

2.2

Instructions and Acceptance Criteria For Checklist Items............................................................. 4

Page 1 of 7


1

CHECKLIST FOR VISUAL EXAMINATION OF TRAY INSTALL ATION (VESSEL SHOP OR FIELD)

5.02.02

Checklist for Visual Examination of Tray Installation (Vessel Shop or Field)

Vessel #

Location

Lighting

Dwg # Remote Visual Aids

Item

Other

Responsible Engineer Inspected By

Date Cert. Level

Comments

Tray Number

1. Trays Installed Flat and Level [D] 2. Absence of Tray Damage [D] 3. Correct Downcomer Part Numbers 4. Correct Tray Floor Part Numbers [D] 5. Correct Outlet Weir Type and Height 6. Correct Downcomer Clearance 7. Spacer/Brackets Under Downcomer 8. Horizontal Clearance Downcomer-to-Inlet Weir 9. Seal Plates in Place [D] 10. Bolting Assemblies Tight [D] 11.Valve Caps Securely in Place 12. Valve Caps Move Up and Down Freely 13. Orientation of Slots on Slotted Sieve Trays 14. Special Items, e.g. Feed P ipes, Draw-Offs, etc. [D] 15. Dimensions Around Seal Pans 16. Tray Manways Fit and Have Proper Clamps [D] 17. Trays and Downcomers Clean [D] 18. Orientation [Crt] 19. Bottom Bundle Rests on Support Lugs [Crt] 20. Seal Rings [Crt] 21. Top Securement Assembly [Crt] 22. Chimney and Hat Dimensions [Chm] 23. Downpipe Cleanliness and Dimensions [Chm] 24. Seal Welds [Chm] 25. Gaskets and Bolting Assemblies [Chm] 26. 27. 28. NOTES:

N = Not Applicable E = Condition Accepted by Engineering [D] = Item also Applicable to Dualflow Trays [Crt] = Cartridge Trays Only

Page 2 of 7

[Chm] = Chimney Trays Only

N

E


2


5.02.02

Instructions for Checklist for Visual Examination of Tray Installation (Vessel Shop or Field)

2.1

General Instructions Application - This checklist covers inspection of new or replacement tray installations. This checklist is applicable to the following situations: •

•

•

The trays are installed at the vessel shop and the inspector is present during tray installation. The trays have been installed at the vessel shop prior to the arrival of the inspector. Tray manways have been removed (or never installed) for access by the inspector. The trays are installed at the plant site (often occurs with large towers and with tray replacements). The inspector is present during or at the completion of tray installation.

Tray sets may have been inspected at the tray vendor shop (5.02.4) to verify conformance to the vendor's drawings. The guidelines 5.02.4 may also be used for tray inspection after the trays arrive at the plant site. This is particularly advisable if the trays were not inspected at the vendor shop. Responsibilities of Inspector - The Inspector is responsible for visually examining each item covered by the checklist. (Check the boxes under column "N" to indicate any items that are not applicable.) Write the tray number for the tray being inspected in the box at the top of each column of check boxes. Then, check the appropriate boxes under these columns to indicate acceptance of the items that have been inspected. The Inspector records comments as required to describe any unacceptable items and records the following information (at the top of the checklist), when applicable: Item

What to Record

Vessel #

Property number or other vessel identification.

Location

Location of the vessel (unit, building, or other description).

Dwg. #

Tray drawing number.

Other

Other pertinent information, such as service.

Lighting

Type of artificial lighting used.

Remote Visual Aids

Borescope, video scope, etc., if used.

Inspected by

Name of Inspector who performs the visual examination.

Cert. Level

Certification level of Inspector.

Date

Date the visual examination was performed.

Responsible Engineer

Name of Responsible Engineer (see Responsibilities of Engineer)

Note: Performing a rigorous check of all items on all trays can be a long, tedious process for towers with many trays. Therefore, a detailed quantitative check on 10 to 20 trays selected from the various tray zones may be performed subject to approval by the Responsible Engineer. All of the other trays should be visually examined for consistency with the trays which were checked in detail. Templates made from wood, for example, can be used to check repetitious items such as downcomer clearance or weir height.

Page 3 of 7



5.02.02

Responsibilities of Engineer - The responsible engineer is responsible for the evaluation and reconciliation of all unacceptable items described by the Inspector, and for checking the appropriate box under column " E" (condition accepted by engineering) when, in the judgment of the responsible engineer, evaluation shows the condition to be acceptable. The name of the engineer performing the evaluation/reconciliation is recorded in the "Responsible Engineer" box (at the top of the checklist).

2.2

Instructions and Acceptance Criteria for Checklist Items

The numbered paragraphs in this section are keyed to line numbers on the checklist. Dualflow Trays - For dualflow trays, only the conventional tray items marked with a " [D]" are inspected (i.e. Items 1, 2, 4, 9, 10, 14, 16, and 17). Dualflow trays are similar to sieve trays (perforated decks) except that there are no downcomers. Vapor and liquid pass through the same holes in a pulsating sort of action. Among other reasons, dualflow trays are a popular choice for dirty systems since there are no downcomers to collect solids. The detrimental impact of out of levelness or non-flatness is more severe for dualflow trays. For this reason, extra precautions should be directed at measuring tray levelness and making necessary corrections to achieve the requirements of the design specifications. Similar to packed towers, dualflow trays require uniform initial distribution to achieve maximum efficiency. Items 1 though 17 Apply to Conventional Trays. 1 [D]

Trays installed flat and level - The main concern is to identify visually detectable bowing of tray decks or bent tray parts. Possible causes of tray bowing are trays that were not fabricated to be flat or the tray installers put too much torque on the bolting assemblies. Quantitative levelness checks may be made if the tower is vertical during inspection. The tolerance for tray levelness may be noted on the vendor's installation drawings. If not, review the functional specifications for the trays. The tolerance for tray levelness ranges between 1/8 inch (3.2 mm) and 3/8 inch (9.5 mm) high to low and depends on tower diameter.

2 [D]

Absence of tray damage - While tray damage is rare on new trays, check for damage that may have occurred during tray shipment, tray installation, or tower shipment.

3

4 [D]

Correct downcomer part numbers - Verify correct downcomer part numbers for each tray. These part numbers may be different for different zones of the tower. The downcomer part numbers should either be stamped into the sheet metal or stenciled. For field inspections after tray installation, part numbers may be hard to find due to access limitations; in this case, correct downcomer part numbers may be inferred if the outlet weir height and downcomer clearance are correct and if the downcomer fits the tray supports in the proper way. (Downcomer part numbers can be visually verified when inspection is performed simultaneously with tray installation.) Correct tray floor part numbers - Verification of correct tray floors (bubbling areas) is especially important since the open area (sieve holes or valve caps) is likely to vary from one zone to the next. Each tray floor will be identified by its part number - either stamped into the metal or stenciled. Many, if not all of the tray floor part numbers should be visible from the tray manway(s).

Page 4 of 7



5.02.02

5

Correct outlet weir type and height - Most trayed towers use standard outlet weirs. However, some applications call for notched (saw-tooth) weirs or picket fence weirs. If so, verify that the pickets (tall sections which block a portion of the overflow weir) are properly installed and are dimensionally correct. Verify that weir height is within tolerance. The tolerance for weir height, measured at the high point of the weir is ± 1/16 inch (± 1.6 mm) from the nominal weir height. Tolerance for weir height levelness is 1/8 inch (3.2 mm) high to low. When checking weir height, it is important to know whether the weir height on the vendor drawings is dimensioned relative to the tray surface or relative to the top of the tray supports.

6

Correct downcomer clearance - This is the vertical gap between the bottom of the downcomer and the tray below. Tolerance on downcomer clearance is ± 1/16 inch (± 1.6 mm) relative to the nominal downcomer clearance. It is important to verify that downcomers are not "pinched off" which would cause excessive resistance to liquid flow and downcomer backup.

7

Spacer/brackets under downcomer - Some types of trays use spacers, brackets, or clips to ensure proper downcomer clearance and prevent downcomer pinching if the downcomer plate should vibrate loose during operation. If spacers are used, verify that they are properly installed.

8

Horizontal clearance downcomer-to-inlet weir - All slotted sieve trays have an inlet weir (bubbling promoter). Inlet weirs may also be used on other types of trays. If so, check the horizontal clearance between the downcomer and inlet weir. Tolerance is ± 1/16 inch (± 1.6 mm) relative to the nominal value. This is another place where liquid flow can be "pinched off."

9 [D]

Seal plates in place - Some tray designs use "seal plates" to block large cracks or gaps where tray sections meet. Another type of sliding seal plate may be used to extend the outlet weir to the tower wall. Verify that seal plates (if used) are properly installed.

10 [D] Bolting assemblies tight - Check bolting assemblies for tightness since it is not uncommon for tray installers to fail to tighten a few nuts. Usually, loose nuts are very loose and can be turned by hand. If lock washers have been used, also check tightness by seeing if the lock washers are compressed. Although an exact check of torque is not essential, it should be approximately 12 - 14 ft-lb (16 - 19 N-m). The tray installers will probably use impact wrenches on the tray bolting. If so, be on the lookout for cases where they may over-tighten the bolting which can cause distortions to the tray decks. 11

Valve caps securely in place - In the case of valve trays, the legs on the valve caps should be spread sufficiently so that the valve caps cannot come out of their hole.

12

Valve caps move up and down freely - The valve cap legs should not be spread to the point that valve cap movement is hindered. Hitting the bottom of the tray deck is a good way to see that valve caps move freely.

13

Orientation of slots on slotted sieve trays - When slotted sieve trays are used, the slots are supposed to be on the top side of the tray. Generally, the slots at the tray inlet point straight ahead or toward the column wall (to help establish liquid flow along the "streamlines"). The slots in the outlet region point toward the outlet weir. Slot orientation will be correct IF the correct tray floors have been used in the correct location on each tray.

Page 5 of 7



5.02.02

14 [D] Special items, e.g. feed pipes, draw-offs, etc. - Special items should be identified from the drawings on a case-by-case basis. When internal feed pipes are used, their orientation should be checked to ensure sparger holes point in the correct direction. The top of draw-off sumps should be open for liquid flow. Other special items may include entrainment separators, feed baffles, false downcomers or inlet weirs at the top tray, transfer pipes from seal pans, etc. Installation of these items should be checked against the tray vendor's drawings. 15

Dimensions around seal pans - Seal pans are typically used below the bottom tray. They may also be used at intermediate trays where there is a transition from one type of tray to another. Dimensions to be checked include the vertical clearance between the downcomer plate and the floor of the seal pan, seal pan weir height, and the horizontal clearance between the downcomer and weir of the seal pan.

16 [D] Tray Manways fit and have proper clamps - Verify that manways fit in their space and that the proper manway bolting assemblies will be used. Most tray manways are removable by working from the top or bottom side of the tray. This is possible when the correct manway clamps are used. 17 [D] Trays and downcomers clean - No foreign material should be left behind. Things to look for include drinking cups, gloves, tools, loose hardware, rags, boards, etc. While the trays should be free from heavy grease, a thin coating of residual cutting oil is normal, and its removal is usually unnecessary. Reasonable measures should be taken to protect carbon steel trays from rusting. Even so, some surface rust may appear on carbon steel trays. However, scale or rust formation that could block the perforations of sieve trays or cause the valve caps on valve trays to stick or malfunction MUST be avoided. Items 18 through 21 Apply to Cartridge Trays Only.

Cartridge or package trays are used in trayed towers smaller than about 3 ft (0.9 m) ID. They are assembled at the tray vendor shop in bundles up to 12 ft (3.6 m) long. Bundles will typically have 4 to 8 trays each. Other items such as mesh pads or chimney trays may be included in the bundle. A system of rods and spacers is used to fix the tray spacing and support the trays. Cartridge trays have a seal ring around the periphery of each tray which will seal against the tower wall. One common type of cartridge tray has a metal seal ring with a gap which allows it to be compressed much like a piston ring. Other types of cartridge trays use a flexible rope packing or Teflon tape gasket around the outside of the tray. Cartridge trays may either be installed at the vessel shop or in the field. Field installation in a vertical tower is generally considered to be easier since gravity helps (rather than hinders) tray installation. 18

Orientation - Verify correct tray orientation with respect to key nozzles such as feed or reflux nozzles. If this is a field installation, verify that individual bundles have the correct orientation, i.e. downcomers are rotated 180 where the top of a lower bundle mates with the bottom of the next bundle.

̊

19

Bottom bundle rests on support lugs - Verify that the bottom bundle has been inserted far enough into the tower so that the bottom support assembly rests on the support lugs welded to the tower wall. It may be possible to see the bottom lugs if there is a fairly large nozzle conveniently located below the bottom tray. Use of mirrors may be helpful. If the bottom assembly cannot be seen, take measurements

Page 6 of 7



5.02.02

from the top tray to a convenient reference point such as reflux nozzle or top body flange. 20

Seal rings - Verify that the seal ring contacts the tower wall for most of its circumference. Small gaps [up to 5/64 inch (2.0 mm) wide] caused by tower imperfections are acceptable.

21

Top securement assembly - Verify proper installation of the top securement assembly. There should be some type of securement assembly above the top tray to prevent tray bundle uplift. This is typically a horizontal bar welded to the shell after the top tray is installed or a vertical bar welded to the top head. Items 22 through 25 Apply to Chimney Trays Only.

Chimney trays may be used in trayed towers or packed towers. They are typically used as collector trays and may have provision for total or partial liquid draw-off. Chimney trays may have downcomers or down pipes which transfer liquid to a tray below or to the liquid distributor of a packed tower. The gas risers on chimney trays are normally equipped with "hats" to prevent liquid, which may be r aining down from above, from entering the gas risers. Chimney trays are frequently used in situations where leakage of liquid from one zone to the next must be eliminated or minimized. In such cases, chimney trays are likely to be seal welded in position. In other cases, the chimney tray may be seal welded with the exception of a removable manway. This manway is likely to have gasket material at the tray joints to minimize leakage. In situations where significant leakage from chimney trays cannot be tolerated, it is advisable to perform a leak test. Any weep holes would be plugged, and the chimney tray would be filled with water to a depth of about 6 inches (150 mm) or to the height of the overflow weirs or pipe. Typical leakage specifications call for the level to drop no more than 1 inch (25 mm) in 20 minutes. Check the vendor drawings and/or equipment specifications to see if more or less stringent criteria have been specified. Another benefit of the leak test is to identify leakage points where repairs need to be made. 22

Chimney and hat dimensions - Verify that hats are present (if called for on the vendor drawings). The vertical height between the top of the risers and the bottom of the hats should be verified. This is the area for vapor flow which should not be restricted.

23

Downpipe cleanliness and dimensions - Chimney tray down pipes (if used) are frequently quite small. They should be free of obstructions. Also, the vertical clearance between the bottom of the down pipe and the tray below should be checked against the required dimension. Liquid flow may be restricted if this clearance is too small.

24

Seal welds - If the chimney tray is seal welded, the welds should be visually inspected for possible leakage sites.

25

Gaskets and bolting assemblies - Some chimney trays use bolted construction either for the whole tray or perhaps just for the manway. Gaskets are typically used to seal these joints. Verify that the gasket material is properly positioned along the entire length of all tray joints. All bolting assemblies must be checked for tightness. Experience suggests that leakage can never be totally eliminated with bolted construction even if gaskets are used.

Page 7 of 7

CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS INSTALLATION (FIELD)


06/15/2003

Revised:

5.02.03


CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS INSTALLATION (FIELD)................................................ ......................................................................... 1 1.

Checklist For Visual Examination of Packed Tower Internals Installation (Field) ............................. 2

2.

Instructions for Checklist for Visual Examination of Packed Tower Internals Installation (Field) .... 3 2.1

General Instructions ................................................ ....................................................................... 3

2.2 Instructions and Acceptance Criteria For Checklist Items..................................... ......................... 4

Page 1 of 8


1


5.02.03

Checklist For Visual Examination of Packed Tower Internals Installation (Field)

Vessel #

Location

Lighting Item

Dwg #

Other

Remote Visual Aids


Cert. Level Comments

Packed Bed Number

1. Packing Support Plate Properly Installed [R, S] 2. Packing Installed from Outside Toward Center [S] 3. Packing Tight Against Wall (wall wiper bands) [S] 4. Packing not Gouged or Distorted [S] 5. Gaps Between Bricks Eliminated [S] 6. Excessive Compression Eliminated [S] 7. Alternating Layers with Correct Rotation [S] 8. Correct Number of Layers and Packed Height [S] 9. Thermowells Properly Installed [R,S] 10. All Foreign Objects Removed from Bed [R,S] 11. Correct Packing Type and Size [R] 12. Packing not Crushed or Broken [R] 13. Proper Packing Installation (wet or dry packed) [R] 14. Packing Evenly Spread (avoid hill formation) [R] 15. Packing not Compressed [R] 16. Correct Bed Depth [R] 17. Bed Limiters (hold downs) Properly Installed [R,S] 18. Proper Assembly of Distributor Parts [R,S] 19. Alignment of Parting Box Holes [R,S] 20. Distributors Level within Tolerance [R,S] 21. Distributor Leveling Screws are Tight [R,S] 22. Gaskets Properly Installed [R,S] 23. Distributor Bolting Assemblies Tight [R,S] 24. Distributor Components Clean [R,S] 25. Successful In Situ Water Test [S] 26. Other Internals Properly Installed [R,S] 27. 28. NOTES:

N = Not Applicable E = Condition Accepted by Engineering [S] = Item also Applicable to Structured Packing [R] = Item Applicable to Random Packing

Page 2 of 8

Date

N

E


2


5.02.03

Instructions for Checklist for Visual Examination of Packed Tower Internals Installation (Field)

2.1

General Instructions Application - This checklist covers field inspection of packed tower internals installation for towers containing either random (dumped) packing or structured packing.

Tower packing and related internals such as packing supports and distributors are always installed in the field instead of vendor shops. Therefore, the ideal time to inspect packed towers is during installation rather than waiting until it has been completed. Items such as liquid distributors are typically more mechanically complex and "unusual" than distillation trays. Proper installation of these items is crucial to the performance of packed towers. For this reason, purchaser specifications often require that packed tower internals be installed by the packing vendor's field service organization. As a minimum requirement, the packed tower internals vendor should send a field service supervisor to oversee the installation of tower packing and related internals. Several types of liquid distributors are used. Towers with very low liquid flow (such as vacuum towers) are likely to use spray nozzles or trough type distributors. Trough-type distributors typically have one or more parting boxes or predistributors which feed a multiplicity of narrow troughs. The troughs typically have very small holes [possibly as small as 1/16 inch (1.6 mm)] located in the sides of the troughs approximately 1 to 2 inch (25 to 50 mm) above the trough floor. Towers with high liquid rates may use orifice plate distributors with risers for vapor flow. The holes in the floor of these distributors are usually fairly large. As with trays, it is frequently beneficial to do trial assemblies (at ground level) of packing supports, bed limiters, liquid distributors, and flashing feed devices. These assemblies will clearly show how the pieces fit together which will serve as a valuable training aid to the installers and inspectors. This step is strongly recommended unless the installers and inspectors are very familiar with the particular device being installed. Responsibilities of Inspector - The Inspector is responsible for visually examining each item covered by the checklist. (Check the boxes under column " N" to indicate any items that are not applicable.) Write the bed number for the packed bed being inspected in the box at the top of each column of check boxes. Then, check the appropriate boxes under these columns to indicate acceptance of the items that have been inspected The Inspector records comments as required to describe any unacceptable items and records the following information (at the top of the checklist), when applicable: Item

What to Record

Vessel #

Property number or other vessel identification.

Location

Location of the vessel (unit, building, or other description).

Dwg. #

Tower internals drawing number.

Other

Other pertinent information, such as service.

Lighting

Type of artificial lighting used.

Remote Visual Aids


Inspected by

Name of Inspector who performs the visual examination.

Cert. Level

Certification level of Inspector.

Page 3 of 8



5.02.03

Date

Date the visual examination was performed.


Name of Responsible Engineer (see Responsibilities of Engineer )

Responsibilities of Engineer - The responsible engineer is responsible for the evaluation and reconciliation of all unacceptable items described by the Inspector, and for checking the appropriate box under column " E" (condition accepted by engineering) when, in the judgment of the responsible engineer, evaluation shows the condition to be acceptable. The name of the engineer performing the evaluation/reconciliation is recorded in the "Responsible Engineer" box (at the top of the checklist).

2.2

Instructions and Acceptance Criteria For Checklist Items

The numbered paragraphs in this section are keyed to line numbers on the checklist. Items pertaining to structured packing are designated by [S] and items for towers with random packing are designated by [R]. 1

Packing support plate properly installed [R,S] - Towers with random packing normally use "gas injection" support plates which have peaks for vapor flow and valleys for liquid flow. Towers with structured packing use a flat grid to support the packing. Installation of both types is straightforward. Mid-span beams may be required for larger towers. Verify that all bolting assemblies are tight. Also, with random packing, verify that the openings in the support plate are small enough so that individual packing pieces cannot slip through.

2

Packing installed from outside toward center [S] - Structured packing is installed in sections or "bricks." Each brick is narrow enough to pass through the tower manhole and may be several feet long. To obtain the best overall fit, bricks should be installed starting at the wall and working toward the tower center. The final center element is best installed with help of slide plates or "shoe horns."

3

Packing tight against wall (wall wiper bands) [S] - Verify that gaps at the tower wall have been minimized. Some brands of structured packing are equipped with flexible bands (wall wipers) which are intended to seal against the tower wall. If so equipped, these wall wipers should be bent outward to touch the tower wall.

4

Packing not gouged or distorted [S] - Structured packing is fairly delicate and fragile. Walking directly on the packing surface is not permitted. Boards or other protection may be placed on the top surface of structured packing to distribute the weight of the workers. If used, boards should be selected which are NOT prone to splinters (safety) and shavings which might cause plugging of tiny distributor holes (see Item 24). After each layer is installed, check for gouging caused by boot heels and other distortion such as gaps where one brick meets the next.

5

Gaps between bricks eliminated [S] - The packing vendor should supply a few extra individual sheets of the corrugated sheet metal used in the packing bricks. These extra sheets may be used to fill in gaps that may result from factors such as tower out of roundness.

6

Excessive compression eliminated [S] - It is fairly common that the space available for the "final brick" is too small. Excessive compression of the packed bed may result

Page 4 of 8



5.02.03

if the bricks are forced into position. This can cause increased pressure drop during operation. To prevent excessive compression, individual sheets of corrugated sheet metal may be removed from the final brick. 7

Alternating layers with correct rotation [S]. Verify correct orientation of alternating packing layers. Successive layers of structured packing are rotated – typically 90 from the layer below. However, rotation angles other than 90 are used by some vendors, so drawings should be consulted to determine the correct angle of rotation.

̊

̊

8

Correct number of layers and correct packed height [S] - Each bed has a required number of layers with each layer having a fixed height in the range of 7 to 12 inches (178 to 305 mm). The depth of the bed may be checked by measuring from the top of the bed to a reference point above the packing such as a nozzle. If the correct number of layers has been used and if the packed bed is too deep, this may be an indication that the packing is bulging due to an overly tight fit.

9

Thermowells properly installed [R,S] - Typically, packed beds require thermowells projecting into the bed. •

•

In preparation for the thermowells in structured packing, holes should be pierced into the packing by the use of sharp pointed rods. Two or three rods of increasing diameter are sometimes used. The OD of the final rod should be slightly larger than the OD of the thermowell and smaller than the nozzle in which it is inserted. If there is a sharp point on the end of the rod, it should be fairly easy to bore a hole by tapping the other end of the rod. Failure to follow these procedures can result in damaged packing, higher pressure drop, maldistribution of liquid and vapor and inaccurate temperature measurements. For towers with random packing, it is preferable to install thermowells before the packing is dumped into the tower.

10

All foreign objects removed from bed [R,S] - No foreign material should be left behind in the packed bed (or distributors). In particular, check for drinking cups, gloves, tools, loose hardware, rags, plastic film, etc. If boards are used inside the tower, extra precautions should be exerted to ensure that wood chips and shavings do not get into the packed beds. Wood chips can easily find their way into distributors and may block the small liquid distribution holes.

11

Correct packing type and size [R] - Verify that the packing type and size agree with the design specifications. If a multi-bed tower uses more than one type or size of packing, there is additional risk that the packings will be interchanged or mixed.

12

Packing not crushed or broken [R] - Ceramic packing is prone toward breakage and should be inspected before installation. To avoid breakage, ceramic packings should be dropped from heights less than 2 ft (0.6 m). To avoid distortion, crushing, and bed compression, metal and plastic packing should be dropped from heights no more than 10 ft (3 m) above the bed surface.

13

Proper packing installation (wet or dry packed) [R] - Wet packing installation refers to the procedure of filling the tower with water to a level at least four feet above the top surface of packing. The water cushions the fall of the packing and helps to achieve a random distribution of packing. Wet packing is definitely preferred with ceramic

Page 5 of 8



5.02.03

packing and may be preferred for other towers. The packing vendor's recommendations on this issue should be solicited and followed. 14

Packing evenly spread (avoid hill formation) [R] - In larger towers greater than 3 ft (0.9 m) in diameter, the packing should be dumped at random spots across the tower area to avoid the formation of upright or inverted cones (hills). The packing should be spread as evenly as possible. Failure to follow this suggestion can lead to maldistribution and reduced tower capacity and efficiency. The packing vendor's installation instructions may include specific suggestions on how to avoid hill formation. Further information on this topic can also be found on pages 266-271 in H. Z. Kister's book Distillation Operation.

15

Packing not compressed [R] - Installers should avoid tamping the packing, walking directly on the packing, or other activities which would compress the bed. A packed bed that is more dense than its "natural" density will lead to increased pressure drop and reduced capacity. Correct bed depth [R] - The elevation for the top of the packed bed should be identified relative to some point, such as a nozzle, located a few feet above the packed bed. As an additional rule of thumb, the top surface of packed beds are typically about 6 inches (152 mm) below the bottom of the liquid distributor. Consult vendor drawings for exact bed height and clearance to the distributor. (Vendors often supply 5 % - 10 % extra packing to allow for losses, breakage, or variations in packing procedures, so using all of the supplied packing may over-fill the available space leading to flow restrictions that can reduce capacity.)

16

17

Bed limiters (or hold downs) properly installed [R,S] - Verify that the bed limiter pieces are in proper position and that all bolting assemblies are tight. Most packed towers will have some type of bed limiter to prevent packing from being displaced or migrating up the tower which could happen during upsets. Bed limiters may be attached to the bottom of the liquid distributor, or they may be separate items supported by rings or clips welded to the tower wall. In some cases, bed limiters rest on top of the packing. These may also have an expandable feature to force them against the tower wall. In some cases, orientation of the bed limiter is important to prevent it from interfering with liquid distribution. A review of vendor drawings will show the required orientation and the mechanical details of the bed limiter.

18

Proper assembly of distributor parts [R,S] - There are many different styles of distributors. Even for a specific type of distributor (such as narrow trough) the mechanical details depend on tower diameter and vary from one vendor to the next. A careful review of vendor drawings and study of the trial assembly are required to see how the distributor parts fit together. For a given tower, there is likely to be more than one distributor, each with different design details (e.g. hole sizes). A superficial observation may lead to the mistaken belief that parts from one distributor are interchangeable with another distributor; such an error could cause a tower failure. The inspection must verify that the correct part numbers have been used at the proper elevation within the tower and that distributor parts are properly assembled.

19

Alignment of parting box holes [R,S] - Many distributor designs use a parting box (pre-distributor) which is mounted directly above a group of narrow troughs. The widths of the gaps between the troughs are normally about the same as the widths of the troughs. Typically, there are holes in the floor of the parting box to transfer liquid to the troughs. Verify that all of these holes are in fact above the troughs to ensure that liquid will not bypass the troughs by flowing through the gaps.

Page 6 of 8



5.02.03

20

Distributors level within tolerance [R,S] - Most modern liquid distributors have leveling screws or rods of some type so that precise levelness can be achieved. A typical levelness criterion is 1/8 inch (3.2 mm) high-to-low. However, the vendor drawings or design specifications should be consulted to determine the requirements for each specific distributor. A water level (or perhaps an optical level) is required for the necessary accuracy in measuring distributor levelness. In towers where the liquid rate is reasonably high, the liquid distributor may rest on a tray support ring. In this case, leveling screws may not be included, and distributor levelness is determined by the levelness of the support ring.

21

Distributor leveling screws are tight [R,S] - After the required levelness has been achieved, verify that the leveling screws are tight so that the levelness will not be lost due to vibrations during operation. Consult the vendor drawings regarding the bolting assemblies. Some additional security, such as double nuts, may be recommended.

22

Gaskets properly installed [R,S] - Some liquid distributors require gaskets at all joints. Other vendors may use gaskets for distributor assembly in special situations. For example, in large diameter towers, the long distributor troughs may have been fabricated in two pieces with a gasket joint at their connection. Extra attention must be given to gasketed distributors to make sure that the gaskets are properly installed to eliminate leakage. For applications with low liquid rates, what appears to be a small leak may actually be a significant proportion of the total liquid flow.

23

Distributor bolting assemblies tight [R,S] - Verify that all bolting assemblies have the proper nuts and washers and that they are tight.

24

Distributor components clean [R,S] - Distributor components (parting boxes, troughs, feed piping, etc.) must be clean. In particular, check for drinking cups, gloves, tools, loose hardware, rags, plastic film, dirt, metal shavings from the packing, wood shavings from boards, etc. Dirt and sand which have been tracked into the tower by the installers must be thoroughly removed from parting boxes and troughs. Vacuum cleaners will be helpful in removing dirt from the narrow (sometimes deep) troughs. If possible, reach into the troughs and feel the small distributor holes to ensure they are open. This is most easily done during a water test, when the flow from the individual holes can be readily seen. Simple finger rubbing may be enough to clear a hole during the water test. If badly clogged, they can be reamed out with a small gage wire.

25

Successful in situ water test [S] - Even when the distributor appears to have been properly installed and leveled, there can be oversights and problems. For situations where the liquid rate is low (these are situations where near perfect liquid distribution is required), it may be practical to do an in situ water flow test. A hose can be used to bring fresh water to the distributor. Adjust the water flow rate to approximate the design volumetric liquid rate for the packed bed below the distributor being tested. Try to introduce the water in such a way that splashing and wave formation in the predistributor (parting box) are minimized. Measure the liquid depth in various troughs. The depth should be essentially the same in each trough. Also, these liquid depths can be compared to expected liquid depths which may be shown on the vendor drawings. Look for locations in the distributor which are passing too much or too little water (compared with other locations). This inspection may reveal areas where there are leaks or where individual distributor points are plugged. It also may be informative to move to the next lower manhole in order to observe the rain pattern leaving the packed bed being tested. Unusual flow patterns, including uneven wall flow below the bed,

Page 7 of 8



5.02.03

should be noted. An in situ water test may also be useful for spray nozzles to verify that all nozzles are working properly and have symmetrical spray patterns. 26

Other packed tower internals properly installed [R,S] - Other packed tower internals may include feed pipes, flashing feed galleries, vane type collector trays, chimney type collector trays, or vapor distribution devices at the bottom of the tower. For chimney trays, refer to 5.02.2. For the other miscellaneous packed tower internals, refer to the vendor drawings and trial assemblies for proper installation. As always, verify tight bolting assemblies, proper installation of gaskets, etc.

Note: Flashing feed galleries are an issue of special concern and are another location where a water test may show excessive leakage at the panel joints. Severe damage has been discovered during some maintenance shutdowns in several towers which handle flashing feeds. While this is primarily a design issue, the field inspector has one last chance to "raise a red flag." If the flashing feed device appears to be a "flimsy" installation, document with photos, dimensions, etc. and contact the Responsible Engineer for further analysis.

Page 8 of 8

CHECKLIST FOR VISUAL EXAMINATION OF TRAYS (TRAY VENDOR SHOP)


06/15/2003

5.02.04


CHECKLIST FOR VISUAL EXAMINATION OF TRAYS (TRAY VENDOR SHOP) ......................... 1 1.

Checklist For Visual Examination of Trays (Tray Vendor Shop) ........................................... ............ 2

2.

General Instructions .................................................. ......................................................... .................. 3

3.

Instructions and Acceptance Criteria For Checklist Items............................................ ....................... 4

Page 1 of 7


1


5.02.04

Checklist For Visual Examination of Trays (Tray Vendor Shop)

Vessel #

Location

Lighting

Dwg #

Other

Remote Visual Aids

Item


1.

Tray Diameter

2.

Tray Material and Gage (thickness)

3.

Valve Material and Gage (thickness)

4.

Valve Count

5.

Valve Lift

6.

Sieve Tray Perforation Diameter

7.

Sieve Tray Perforated Area

8.

Sieve Tray Direction of Punch

9.

Sieve Tray Perforations Free of Burrs

10.

Outlet Weir Type and Height

11.

Downcomer Height

12.

Truss Depth

13.

Seal Pan Width and Height

14. Feed Baffle (false downcomer) and Feed Pipes 15.

Bolting Material

16.

Bolt Hole Sizes and Alignment of Assemblies

17.

Welded Nits Alignment and Clean Threads

18.

Flatness of Tray Parts

19.

Tray Parts Properly Identified by Part

20.

General Workmanship and Clean-Up

21.

Correct Number of Tray Parts

22.

Correct Amount of Tray Hardware

23.

Proper Crating and Preparation for Shipping

24. 25. 26. 27. 28. NOTES:

N = Not Applicable


Tray Number

E = Condition Accepted by Engineering

Page 2 of 7

Date

N

E


2


5.02.04

General Instructions Application - This check list covers inspection of trays at the tray vendor shop. This checklist is applicable to either valve or sieve trays which are by far the most common types. It is also applicable for trays using “fixed open valves” (e.g. V-grid tray s from Sulzer Chemtech). While these tray s perform more like sieve trays, they have retained some of the valve tray nomenclature. The checklist can also be used for dualflow tray s or baffle tray s by ignoring the items that don’t apply. While this checklist i s generally applicable for high capacity trays (e.g. MD , Superfrac, Triton, etc.) these tray s usually some special features NOT covered by the generic checklist. Whe n proprietary high capaci ty trays are involved, consult with the responsible engineer regarding additional inspection points.

Inspection visits to a tray vendor shop may occur at any time during tray fabrication. However, the most common time for inspecti on is after th e tray fabrication has been co mpleted but prior to shipment. In preparation for this inspection visit, the tray vendor should be requested to set up trial assem blies of the trays. There should be one trial assembly for each tray design (i.e. each set of tray part numbers) used in the tower. Also, unique t ower internals (e.g. false d owncomers, feed baffles, seal pans, draw off tray s, feed pipes, etc.) should be made available for in spection. T he tray vendo r’s drawings should be thoroughly reviewed prior to the inspection visit. Responsibilities of Inspector - The Inspector is responsible for visually examining each item covered by the checklist. (Check the boxes under column " N" to indicate any items that are not applicable.) Write the tray number for the tray being inspected in the box at the top of each column of check boxes. Then, check the appropriate boxes under these colu mns to i ndicate acceptance of the items that have been inspected. The Inspector records comments as required to describe any unacceptable items and records the following information (at the top of the checklist), when applicable: Item

What to Record

Vessel #

Pro ert number or other vessel identification.

Location

Location of the vessel unit buildin

Dw . #

Tower internals drawin number.

Other

Other ertinent information, such as service.

Li htin

T

Remote Visual Aids

Boresco e, video sco e, etc., if used.

Ins ected b

Name of Ins ector who erforms the visual examination.

Cert. Level

Certification level of Ins ector.

Date

Date the visual examination was erformed.



or other descri tion .

e of artificial li htin used.

Responsibilities of Engineer - The responsible engineer is responsible for the evaluation and reconciliation of all unacceptable items described by the Inspector, and for checking the appropriate box under column "E" (condition accepted by engineering) when, in the judgment of the responsible engineer, evaluation shows the condition to be acceptable. The name of the engineer performing the evaluation/reconciliation is recorded in the "Responsible Engineer" box (at the top of the checklist).

Page 3 of 7


3


5.02.04


The numbered paragraphs in this section are keyed to line numbers on the checklist. 1

Tray diameter - The tray diameter wi ll be approximatel y equal to the t ower ID m inus the tray support ring width. Therefore, when installed, the tray will overlap the tray support ring by about half of the ring width. The exact tray diameter will be clearly shown on the tray vendor drawings.

2

Tray material and gage (thickness) - The tray co mponents should be checked to verif y that the proper material of constru ction has been used. Als o verify that the tra y material has the proper thickness.

3

Valve material and gauge (thickness) - When valve trays are used, the valve caps normally use the same material of construction as the re st of the tra y except when the tra y base material is carbon steel. In that case, stainless steel valve caps are normally specified to minimize the chance of valves "freezing up" due to rust. Also, the valve caps may be thinner than the base tr ay material. Valve trays are frequently designed with two gages of valves on the same tray. For example, there may be alternating rows of light and heavy valve caps. Verify correct valve cap thickness using a micrometer or calipers.

4

Valve count - The number of valve caps (or fixed open units) should be counted to verify that the correct pitch and row spacing has been used.

5

Valve lift - The valve cap lift should be checked by measuring the valve cap leg length and subtracting the deck thickness. In the c ase of fixed open valve units or in the case where the valve caps are retained by a cage (and therefore do not ha ve legs) the valve lift (clea rance between top of the tray deck and bottom of valve unit) can be m easured directly with the valve in the fully open position. Co nsult with the vendor reg arding his t olerance on valve lift. The valve lift sho uld be within about 3% of the specified lift.

6

Sieve tray perforation diameter - When sieve tray s are used , the b ubbling area perforation diameter should be checked and com pared to the specified hole diameter. Many towers use s mall [typically 3/16 inch (4.8 mm)] diameter perforations in the sieve tray bubbling area. The tray vendor shop should have pin gages or tape r gages which can be used to check the diameters of these smal l holes. In the case of larger hole sieve trays [i.e. 1/2 inch (13 mm)], calipers can be used.

7

Sieve tray perforated area - Sieve trays are specified to have a specific "net free unobstructed hole area." To achieve this area, the tray vendor will determ ine the required num ber of unobstructed holes. This, of course, depends on the perforation diameter. The tray vendor will also calculate the mechanical area available for these pe rforations. In general, the mechanical area available for perforations will be the tray active area minus all areas obstruct ed by tray beams, suppor t rings, bolting assemblies, etc. This leads to a fractional mechanical open area which is the net free hole area divided by the mechanical area available for perforations. The fractional mechanical open area (or required perforation pattern) may be shown on t he vendor drawings. If not, ask the ve ndor for this information. The a ctual fractional mechanical open ar ea (F pm) can be compared to the theoretical fraction open area using the method shown in Figure 1 assuming the tray decks have been perforated with a triangular pitch. For the deck in question, measure 10 hole spaces in each direction. These ar e dimensions X and Y. To determine the value of F pm, multiply the area of one individual hole (using the perforation diameter determined in Item 6) by 200 and divide by X times Y: F pm = 200 A h/XY. This actual value should be within plus or minus 2% of the theoretical F pm.

8

Sieve tray direction of p unch..- The functional tray specifications (and vendor drawings) will probably indicate whether the direction of punch for the sieve tray perforations should be from the

Page 4 of 7



5.02.04

bottom side (burrs up) or from the top side (burrs down). The burr or rough side of the tra y should be evident by feeling both sides of the tray deck. In some cases, direction of punch is not part of the tray specifications. In this case "burrs up" and "burrs down" are equally acceptable. 9

Sieve tray perforations free of burr s - Even though the burr side of the tray should be evident by touch, the burrs should be very small (almost non-existent). They should not be sharp (safety hazard), and they should not block the sieve tray perforations.

10

Outlet weir type and he ight - Most trayed towers use standa rd outlet weir s. However, some applications call for notched (saw-tooth) weirs or pi cket fence weirs. If so, verify that the pickets (tall sections which block a portion of the overflow weir) are present and are dimensionally correct. Verify that weir heights are within tolerance. The tolerance for w eir height, m easured at the high point of the weir is plus or minus 1/16 inch (1.6 mm) from the nominal weir height. T olerance for weir height levelness is 1/ 8 inch (3.2 mm) high-to -low. When checking weir height, it is important to know whether the weir height on the vendor drawings is dimensioned relative to the tray surface or relative to the top of the tray supports.

11

Downcomer height - Verify the downcomer height. Downco mer height is im portant since this dimension fixes the downcomer clearance on the tray below.

12

Truss depth - Verify depths of loose beams and in tegral trusses by comparing with the dr awing dimensions.

13

Seal pan width and height - Seal pans are typically used below the bottom tray. They may also be used at intermediate trays where there is a transition from one type of tray to another. Dimensions to be checked include the width of the seal pan and the s eal pan weir height. Verify that drain holes, if specified, are present in seal pans.

14

Feed baffle (false downcomer) and feed pipes - A feed baffle (also known as false downco mer) is typically used above the t op tray to assist with reflux distribution. Feed baff les could be used at other locations as well. Verify dimensions of the f eed baffle. I f internal feed pipes are part of the tray vendor's scope of supply, verify their presence and dimensions.

15

Bolting material - Verif y that the correct material of construction has been used for hardware including bolts, nuts, washers, tray clips, and manway fasteners.

16

Bolt hole sizes and alignment of ass emblies - Verify that the bolt hole sizes are correct and that there is good alignment between the holes in mating pieces. When two tray parts are through-bolted to each other , the hole (or slot) on one piece shoul d be oversized relative to the bolt used in the bolting assembly. This is required to pr ovide adjustment to co mpensate for tower out of roundness and other tower and tray fabrication tolerance issues.

17

Welded nuts alignment and "clean" threads - If welded nuts are used in the tray fabrication, ensure the nuts have good alignment with the holes in the tray so th at the bolt can easily be threaded into the nut. Also verify that there is no weld splatter interfering with the nut threads.

18

Flatness of tray parts - For this inspection point, the main concern is to identify visually obvious bowing of tray decks or bent tray parts. A possible cause of tray b owing would be if the tra ys were not fabricated to be flat. It is generally not practical to make quantitative levelness measurements at the tray vendor shop since the framework supporting the trial assemblies may not be level and since the bolting assemblies are not fully tightened.

19

Tray parts properly identified by part numbers - The preferred way to identify major tray parts is

Page 5 of 7

the tray



5.02.04

to have part num bers stamped into the sheet metal. Verify that the part num bers are present and legible. A much less satisfactory way to identify tray parts is by stenciling numbers on the parts. If this technique has been us ed, ensure that the stencil ed part numbers do not dissolve in the residual cutting oil that will be present on the trays. 20

General workmanship and clean-up - Observe the trial asse mblies for general workmans hip and clean-up. Weld slag should have been rem oved, and there should be no sharp b urrs at the edges of the tray pieces. Unless otherwise specifi ed, the presence of a light coating of residual cutting oil on tray parts is acceptable. I n fact, this ai ds in rust prevention for carbon steel tr ay parts. A heavy coating of oil or grease is not acceptable.

21

Correct number of tray p arts - It may be impractical to do a co mplete inventory of all tra y parts. However, an audit may be performed of the tray vendor's Quality Control, bill of materials, packing lists, etc. to gain confidence that the correct number of parts have been fabricated and will be shipped.

22

Correct amount of tray hardware - In general, it is not practical to do a complete inventory of tray hardware. Tray hardware is usually packaged in small boxes or bags with piece count determined by weight. Ho wever, an audit m ay be p erformed of the tray vend ors techniques for packagi ng the correct amount of hardware and verification that the hardware is available for shipping.

23

Proper crating and prep for shipping - In t hose cases where carbon steel has been used, the specifications may include instructions for rust pr evention. Th is may include application of rust preventative coating on the tray parts. If so, verify that the tray parts have been (or will be) coated prior to ship ment. Also, special export packaging and crating may be specified to minimize the exposure of t ray parts to water during transport an d storage. E xport crating typically consists of fully enclosed wooden boxes rather than boxes with open sides.

Page 6 of 7



5.02.04

Figure 1. PROCEDURE FOR DETERMINING FRACTIONAL MECHANICAL OPEN AREA

Page 7 of 7

CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS (VENDOR SHOP)


6/15/2003

5.02.05

CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS (VENDOR SHOP)

CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS (VENDOR SHOP) ......................................................................................................................................................... 1 1.

Checklist for Visual Examination of Packed Tower Internals (Vendor Shop) .................................... 2

2.

In structions for Checkist for Visual Examination of Packed Tower Internals (Vendor Shop) .......... 3 2.1

General Instructions ............................................................................................ ........................... 3

2.2

Instructions and Acceptance Criteria For Checklist Items............................................................. 4

Page 1 of 6


1

CHECKLIST FOR VISUAL EXAMINATION OF PACKED TOWER INTERNALS ( VENDOR SHOP)

5.02.05

Checklist for Visual Examination of Packed Tower Internals (Vendor Shop)

Vessel # Lighting Item

Location

Dwg #

Other

Remote Visual Aids



Packed Bed Number

1. Correct MOC for All Tower Internals [R,S] 2. Structured Packin Dimensions [S] 3. Packing not Gouged or Broken [S] 4. Correct Number of Layers [S] 5. Packing not Crushed or Broken [R] 6. Correct Packing Type and Size [R] 7. Correct Volume of Packing Being Shipped [R] 8. Assembly of Packing Support Plate [R,S] 9. Assembly of Bed Limiters [R,S] 10. Assembly of Other Packed Tower Internals [R,S] 11. Proper Assembly of Distributor Parts [R,S] 12. Dimensions of Distributor Components [R,S] 13. Number and Size of Distributor Holes [R,S] 14. Distributor Holes: Burr-free, Punch Direction [R,S] 15. Alignment of Parting Box Holes [R,S] 16. Distributors Level within Tolerance [R,S] 17. Operation of Leveling Screws Demonstrated [R,S] 18. Gaskets Properly Installed [R,S] 19. Distributor Bolting Assemblies [R,S] 20. Tower Internals Identified with Part Numbers [R,S] 21. General Workmanship and Clean-Up [R,S] 22. Correct Number of Parts [R,S] 23. Correct Amount and Type of Hardware [R,S] 24. Proper Crating and Preparation for Shipping [R,S] 25. 26. 27. 28. NOTES:

N = Not Applicable E = Condition Accepted by Engineering S] = Item Applicable to Structured Packing [R] = Item Applicable to Random Packing

Page 2 of 6

Date

N

E


2


5.02.05

Instructions for Checklist for Visual Examination of Packed Tower Internals (Vendor Shop)

2.1

General Instructions Application - This checklist covers inspection of packed tower internals at the tower internals vendor shop for towers containing either random (dumped) packing or structured packing.

Inspection visits to the shop fabricating tower packing and related internals may occur at any time during the fabrication. However, a good time for inspection is after the packed tower internals fabrication has been completed but prior to shipment. Prior to this inspection visit, the tower internals vendor should be requested to set up trial assemblies of all internals such as packing support plates, bed limiters, distributors, redistributors, collector trays, etc. The vendor's drawings should be thoroughly reviewed prior to the inspection visit. This is especially important for packed tower internals since some items (such as distributors) can be quite complex. Photographs of the trial assemblies should be taken to document the proper assembly of the packed tower internals. It is very likely that this visit can be combined with a distributor flow test which is recommended for most packed towers. For that reason, the checklist points for distributors have been selected with the assumption that the distributor will be fully assembled and leveled for the water flow test. Responsibilities of Inspector - The Inspector is responsible for visually examining each item covered by the checklist. (Check the boxes under column "N" to indicate any items that are not applicable.) Write the bed number for the packed bed being inspected in the box at the top of each column of check boxes. Then, check the appropriate boxes under these columns to indicate acceptance of the items that have been inspected. The Inspector records comments as required to describe any unacceptable items and records the following information (at the top of the checklist), when applicable: Item

What to Record

Vessel #

Pro ert number or other vessel identification.

Location

Location of the vessel unit buildin

Dw . #

Tower internals drawin number.

Other

Other ertinent information such as service.

Li htin

T

Remote Visual Aids


Ins ected b

Name of Ins ector who erforms the visual examination.

Cert. Level

Certification level of Ins ector.

Date

Date the visual examination was erformed.



or other descri tion .

e of artificial li htin used.

Responsibilities of Engineer - The responsible engineer is responsible for the evaluation and reconciliation of all unacceptable items described by the Inspector, and for checking the appropriate box under column "E" (condition accepted by engineering) when, in the judgment of the responsible engineer, evaluation shows the condition to be acceptable. The name of the engineer performing the evaluation/reconciliation is recorded in the "Responsible Engineer" box (at the top of the checklist).

Page 3 of 6


2.2


5.02.05


The numbered paragraphs in this section are keyed to line numbers on the checklist. Items pertaining to structured packing are designated by [S] and items for towers with random packing are designated by [R]. 1

Correct material of construction for all tower internals [R,S] - Verify that the correct material of construction has been used for the tower packing and all packed tower internals.

2

Structured packing dimensions [S] - The characteristic dimension of structured packing is the crimp height. To determine the actual crimp height, measure across several sheets of the packing and divide by the number of sheets. This can be compared against the theoretical crimp height provided by the packing vendor. The corrugated sheets should have been sheared and assembled so that the corrugations have the proper slope with respect to horizontal. This "angle of inclination" is typically 45 for sheet metal packing and 60 for wire gauze packing. The vendor should be consulted to verify that these are the correct angles. The height of the packing "bricks" should be checked against the vendor drawings.

̊

̊

3

Packing not gouged or distorted [S] - Structured packing is fairly delicate and fragile. Check bricks for gouging and distortion.

4

Correct number of layers [S] - The vendor's bill of material should be checked to verify that the correct number of bricks are being supplied so that the final installation will have the correct number of layers of packing and the correct total bed depth.

5

Packing not crushed or broken [R] - If ceramic packing is being supplied, verify that it is not broken prior to shipment. For all types of random packing, verify that the pieces have uniform size and shape.

6

Correct packing type and size [R] - Verify that the packing type and size agree with the design specifications. A multi-bed tower may use more than one type or size of packing.

7

Correct volume of packing being shipped [R] - The vendor's bill of material should be checked to verify that the correct volume of random packing is being supplied.

8

Assembly of packing support plate [R,S] - Towers with random packing normally use gas injection support plates which have peaks for vapor flow and valleys for liquid flow. Towers with structured packing use a flat grid to support the packing. Mid-span beams may be required for larger towers. Verify proper fit-up of all support plate components and bolting assemblies. For random packing, verify that the openings in the support plate are small enough so that individual packing pieces cannot slip through.

9

Assembly of bed limiters [R,S] - Verify that the bed limiter pieces fit together properly and that the holes for the bolting assemblies have proper alignment. Most packed towers will have some type of bed limiter to prevent packing from being displaced or migrating up the tower which could happen during upsets. Bed limiters may be attached to the bottom of the liquid distributor, or they may be separate items supported by rings or clips welded to the tower wall. In some cases, bed limiters rest on top of the packing. These may also have an expandable feature to force them against the tower wall. A review of vendor drawings will show the required mechanical details of the bed limiter.

Page 4 of 6



5.02.05

10

Assembly of other packed tower internals [R,S] - Other packed tower internals may include feed pipes, flashing feed galleries, vane type collector trays, chimney type collector trays, or vapor distribution devices at the bottom of the tower. For these miscellaneous packed tower internals, refer to the vendor drawings for correct dimensions. Check the trial set-ups for proper assembly. Verify that bolting assemblies have proper hole alignment for mating parts.

11

Proper assembly of distributor parts [R,S] - Verify that the distributor parts fit together properly and that the holes for the bolting assemblies have proper alignment. There are many different styles of distributors. Even for a specific type of distributor (such as narrow trough) the mechanical details depend on tower diameter and vary from one vendor to the next. A careful review of vendor drawings and study of the trial assembly will show how the distributor parts fit together.

12

Dimensions of distributor components [R,S] - Check critical dimensions for the distributor. This includes the height and width of distributor parting boxes and troughs.

13

Number and size of distributor holes [R,S] - A variety of hole sizes may be used on a given liquid distributor. The size of small holes can be checked with pin gages or taper gages. Larger holes, like those typically found in parting boxes, can be checked with calipers. In addition to hole diameter, the number of distribution holes must be compared to the drawings.

14

Distributor holes: free of burrs, punch direction [R,S] - The holes in the distributor should be free of burrs which might restrict liquid flow or cause maldistribution. In some cases, the functional specifications or vendor drawings may indicate "direction of punch" for the distributor holes. For example the specifications for a parting box or orifice plate distributor may require "punch entry from the top side." This can be verified by feeling the top and bottom side of the sheet metal. The punch entry side of the sheet metal will feel smoother compared to the punch exit side even when there are no objectionable burrs. In the case of trough style distributors, verify that the distribution holes for all troughs have the SAME punch direction (even if punch direction is not indicated on the drawings).

15

Alignment of parting box holes [R,S] - Many distributor designs use a parting box (predistributor) which is mounted directly above a group of narrow troughs. The widths of the gaps between the troughs are normally about the same as the widths of the troughs. Typically, there are holes in the floor of the parting box to transfer liquid to the troughs. Verify that all of these holes are in fact above the troughs to insure that liquid will not bypass the troughs by flowing through the gaps.

16

Distributor level within tolerance [R,S] - Most modern liquid distributors have leveling screws or rods of some type so that precise levelness can be achieved. A typical levelness criterion is 1/8 in. (3.2 mm) high-to-low. However, the vendor drawings or design specifications should be consulted to determine the requirements for each specific distributor. A water level (or perhaps an optical level) is required for the necessary accuracy in measuring distributor levelness. In towers where the liquid rate is reasonably high, the liquid distributor may rest on a tray support ring. In this case, leveling screws may not be included, and distributor levelness is determined by the levelness of the support ring.

17

Operation of leveling screws demonstrated [R,S] - While at the vendor shop, it may not be possible to exactly duplicate the mechanical installation details used to support the

Page 5 of 6



5.02.05

distributor in the tower. tower. However, during the inspection, inspection, the vendor vendor should demonstrate demonstrate how the leveling screws (or other leveling device) are supposed to work. They should describe how the distributor is expected to maintain its levelness during (years of) operation and vibration. Some additional security, such as double nuts, may be recommended. 18

Gaskets properly installed [R,S] - Some liquid distributors require gaskets at all joints. Other vendors may use gaskets for distributor assembly in special situations. For example, in large diameter towers, the long distributor troughs may have been fabricated in two pieces with a gasket joint at their connection. connection. Extra attention must be given to gasketed distributors to understand and achieve proper gasket installation and thereby eliminate leakage. For applications with with low liquid rates, what appears to be a small leak may actually be a significant proportion of the total liquid flow .

19

Distributor bolting bolting assemblies assemblies [R,S] [R,S] - The trial assembly should demonstrate the alignment of holes for all bolting assemblies and the correct components (nuts, bolts, washers) for each type of assembly.

20

Tower internals identified with part numbers [R,S] - For a given tower, there is likely to be more than one distributor, each with different design details (e.g. holes sizes). A superficial observation may lead to the mistaken belief that the parts from one distributor are interchangeable with another distributor; such an error could cause a tower performance failure. The shop inspection must verify that the distributor components are identified numbers are also also required required for the with clearly legible and correct part numbers. Part numbers other tower internals such as support plates, bed limiters, and flashing feed galleries. The preferred way to identify major parts is to have part numbers stamped into the sheet metal. metal. A less satisfactory satisfactory way to identify major parts is by stencil stencil painting part numbers. numbers. If this technique has been used, make sure that the painted part numbers do not dissolve in the residual cutting oil that will be present on the parts.

21

General workmanship and clean-up [R,S] - Observe the trial assemblies for general workmanship and clean-up. Weld slag should have been removed, and there should be no sharp burrs at the edges of pieces. Unless otherwise specified, the presence of a light coating of residual cutting cutting oil on parts is acceptable. In fact, this aids in rust prevention for carbon steel tray parts. A heavy coating of oil or grease is not acceptable.

22

Correct number of parts [R,S] - For packed tower internals, it should be practical to do a complete inventory of all major parts. However, an audit may be performed of the packed tower internals vendor's bill of materials, packing lists, etc. to gain confidence that the correct number of parts have been fabricated and will be shipped.

23

Correct amount amount and type of hardware hardware [R,S] - It may not be practical to do a complete inventory inventor y of hardware. However, an audit may be performed of the vendor's techniques for packaging the correct amount of hardware and verification verification that the correct types of hardware are available for shipping.

24

Proper crating and preparation preparation for shipping shipping [R,S] [R,S] - Special export packaging and crating may be specified to minimize the exposure of tray parts to salt and water during transport and storage. Export crating typically consists of fully enclosed wooden boxes rather than boxes with open sides.

Page 6 of 6


LEVELING TRAYS AND DISTRIBUTORS

Issued:

01/15/1996

5.05

Revised:

LEVELING TRAYS AND DISTRIBUTORS

LEVELING TRAYS AND DISTRIBUTORS .................................................................. ........ 1 Introduction ................................................................................ ......................... ....................................................... ............................................... 2 Level Specifications............................................................... .................................................... 2 Measurement Technique ............................................ ............................................................................................... ................................................................ ............. 3 Vertical Dimension Checks ..................................................................................... .................. 4 Installation Issues ....................................................................... ................ ....................................................... ............................................... 4 Other Practical Considerations ....................................................................................... ........... 5

Page 1 of 5


1

LEVEL ING TRAYS AND DISTRIBUTORS

5.05

Introduction

Distillation tower internals (trays, packings, or distributors) that are significantly out of level may fall well short of desired performance. performance. Out of level problems usually usually result in poor poor mass transfer efficiency or lack of operating flexibility flexibility (turndown). (turndown). In some cases, internals which which are particularly sensitive sensitive to level such as packed column liquid distributors, distributors, may not function function at all when installed improperly. There is a long history of cases in which re-leveled equipment has corrected problems of poor efficiency, unstable turndown performance performance and troubled separations. Unfortunately, there is a tendency tendency to overlook this important factor.

2

Level Specifications

Level specifications include gross side-to-side tilting of equipment as well as localized sags or humps in tray decks. Internals may be out of level in two planes, parallel to and/or normal to the direction of liquid flow. Tilted trays or distributors creates a non-random out of levelness that is considerably more serious than random out of level level problems. Tilted equipment creates a gross gross maldistribution of the the fluids in the tower resulting in efficiency or capacity losses. losses. For example, when all trays are titled to one side, the vapor preferentially rises up one side of the tower through the high side because of the smaller hydraulic head of froth on this side. To avoid confusion, the levelness levelness specifications must be clear to everyone involved. involved. Does "plus or minus one quarter inch" mean that the high high point can be vertically vertically one half inch from the low point? point? The expression "levelness to be (within) one quarter inch" also causes considerable debate among installation personnel. The recommended method is to specify the maximum allowable vertical distance from the highest point to the lowest point on the device. Economics dictate that that the out of levelness allowance allowance be related to the diameter of the the vessel. A brief analysis of data submitted by eight member companies on the subject indicates that the high point to low point allowance of installed installed trays falls essentially essentially in a band limited by by the following graph:

Page 2 of 5

Issued: 01/15/1996


Revised:

5.05

Range of Level Allowances Conventional Trays

Tower Diameter, mm 0

2

4

6

8

10

12

0.5 12

0.4

10

s e h c n 0.3 i , e c n a w o l l A l 0.2 e v e L

8

6

4

m m , e c n a w o l l A l e v e L

Max Min

0.1 2

0

0 0

10

20

30

40

Tower Diameter, ft.

Some systems require a higher degree of tray levelness than others. Some companies recognize this in their specifications by having two classes of out of level allowances. As several parties are usually involved in a tower project: vessel fabricators, internals suppliers, and installation crews, each should be constrained so the finished installed assembly is within specification. Consideration should be given to limiting the levelness of the tray support rings and the trueness of internals parts. The recommended practice is to allow the support rings to be out of level one half of the maximum installed levelness allowance. The design of the leveling system to be installed should also be considered (for example: the levelness of a distributor support ring is not as critical if the distributor will be hung from threaded support rods).

3

Measurement Technique

The level measurement technique is critical to leveling an internal. There are at least four major techniques in general use: the carpenter's level, the manometer tube, the water level, and various optical devices. Of these, only the water level and the optical devices can be recommended for all types of tower internals in all diameter ranges. A carpenter's level may be satisfactory for small diameter (48 inches (1200 mm) or less) equipment or for quick spot checks in larger towers. However, due to the short span of a carpenter’s level, it is not suitable for installation or final inspection in larger towers. The manometer tube is a common measuring device constructed from a flexible plastic tube filled with water and held against two vertical rulers placed on the surfaces to be compared. The measurement requires two people, each reading the liquid level at each end. Unless fastidious effort is applied, this technique is subject to serious error. Among the many factors that affect accuracy are air bubbles in the liquid, dirt and oil in the tube affecting the meniscus, density differences in the liquid, oscillations, Page 3 of 5



5.05

parallax, each person reading a different elevation on the meniscus, and background noise affecting communication. A hand-held mirror can be used to facilitate accurate readings in tight spaces. An improvement to the manometer method is to connect one end of the tube to the bottom of a large diameter reservoir which is temporarily fixed in the vessel. A coffee can or other container of approximately 1 gallon (5 litres) capacity is a convenient reservoir size. Since the liquid level in the reservoir remains essentially constant, the readings can be taken by a single person at the other end of the tube. The differences in the readings reflect the level at each point. The water level is still subject to some of the air and dirt problems cited above, but has been successfully used in all diameter columns. Perhaps the best method of measuring levels in larger columns (> 8 feet (2.4 m) in diameter) is with the use of a temporarily fixed optical level and a stiff ruler held vertically on the surface to be measured. The differences between such readings taken across the tray will accurately determine levelness. Modern optical level devices ("laser levels") have replaced the ruler with optical sensors that indicate the out of level directly. These devices are available for under $2,000 (1994 prices). It is a good idea to state specifically where the measurements are to be made on the tray deck. Some tray seams overlap adjoining panels which adds an additional deck thickness (usually 3 mm or 1/8 inch) to level measurements made on top of those seams. Likewise, minor tray deck components such as seal plates, fasteners, washers, etc. should be avoided during leveling measurements. Without clear measurement guidelines, minor imperfections which may not be functionally objectionable, may make meeting tight level tolerances very costly or impossible.

Finally, care must be taken that the weight of the inspecting personnel does not create erroneous readings by temporarily causing the equipment to sag.

4

Vertical Dimension Checks

Another inspection item closely related to levelness are the various vertical dimension checks such as tray weir heights and downcomer clearances. Errors in setting these dimensions can cause maldistribution of liquid or vapor flow leading to poor mass transfer efficiency or turndown limitations. These dimensions are often inspected at the same time as the levelness is checked. Common vertical dimensions which should be carefully set and inspected include: • • • •

tray weir heights downcomer clearances feed pipe clearances chimney riser hat clearances

To minimize installation and inspection effort, templates should be used to check items such as weir heights which are repeated many times in the column. The templates can be fashioned from wood blocks, rigid plastic or metal plates.

5

Installation Issues

Installation of the internals in the proper sequence is often the key to achieving the levelness specification. The equipment manufacturer’s recommended installation sequence should be followed. In the absence of specific information, the following general guidelines may be used. Trays - If recessed seal pans are used, the panels comprising the pan should be installed and tightened (or Page 4 of 5

FRI - Internal Design vol 5

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