CHEVRON Pressure Vessel - Repair Rerating Alteration

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800 Repair, Alteration, and Rerating

AbstractThis section discusses repair, alteration, and rerating of pressure vessels, covepertinent code and jurisdiction requirements and the differences among the ASCode, the National Board Inspection Code, and API requirements. Topics discuinclude the following: design of repairs; planning and approval; responsible orgazation; materials; replacement parts; welding; postweld heat treatment; inspectand hydrotest procedures; and documentation and nameplates.

Contents Page

810 Introduction 800-3

820 Code and Jurisdiction Requirements 800-3

821 ASME Code

822 Jurisdiction Requirements

823 National Board Inspection Code vs. API 510

830 Repair 800-11

831 Design of the Repair

832 Planning and Approval

833 Organization Making Repair

834 Repair Materials

835 Replacement Parts

836 Repair Welding

837 Postweld Heat Treatment

838 Inspection and Hydrotest

839 Approval of Repairs, Documentation, and Nameplate

840 Alteration 800-19

841 Planning and Approval

842 Organization Making Alterations

Chevron Corporation 800-1 March 1990

800 Repair, Alteration, and Rerating Pressure Vessel Manual

843 Materials, Replacement Parts, Welding, Postweld Heat Treatment, and Inspection

844 Hydrotest after Alterations

845 Approval of Alterations, Documentation, and Nameplate

850 Rerating 800-21

851 Organization Performing Rerating

852 Calculations

853 Information Required

854 Approval of Rerating, Documentation, and Nameplate

March 1990 800-2 Chevron Corporation

Pressure Vessel Manual 800 Repair, Alteration, and Rerating

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810 IntroductionInspection of a pressure vessel frequently reveals that some form of deterioratiohas occurred during service (see Section 730). Analysis of the deterioration maindicate that the vessel must either be repaired under the original design conditor that the vessel must be rerated for less severe design conditions. Rerating fodesign conditions may also be necessary because of changes in operating requments. In addition, new process requirements may also require alterations to a vessel.

The size and location of a pressure vessel in an operating plant can make repaalteration considerably more difficult than construction of the vessel in a fabricashop. Construction in a fabrication shop permits positioning of the vessel to obtfavorable access and orientation for welding and other necessary work. Accessvessel in an operating plant can be obstructed by adjacent equipment. Weldingother work may have to be performed in unfavorable orientations with restrictedaccess for tools and welding machines. Therefore, it may not be possible to comwith all of the requirements of the ASME Code that were mandated for the origdesign and construction of the vessel.

Alternative approaches can usually be devised to accomplish a repair or alterathat will provide equivalent integrity and reliability, although they may deviate froa literal interpretation of Code criteria. Consult with a specialist to plan these repairs or alterations, if you are unsure of any step.

The inability to repair a pressure vessel at the operating plant may make it necesary to move the vessel to a fabrication shop. Repairs of this nature will normalrequire more time than if performed at the operating plant. Plans should be mawell in advance of the scheduled shutdown to make certain that the repair orgation has shop floor space and manpower available to complete the repairs on schedule.

Nondestructive examination (NDE) of repairs and alterations is very important tassure that high integrity and reliability have been obtained, because of the unfable working conditions that might prevail. More extensive NDE than was requirfor the original construction is usually advisable.

Note that repairs are closely related to the inspection of the vessel. The informain Section 700, In-Service Inspection, will be helpful in understanding the conteof the repair, and help assure a reliable correction of the problem.

820 Code and Jurisdiction Requirements

821 ASME CodeThe ASME Code applies directly only to the “design, fabrication, and inspectionduring [the original] construction of pressure vessels.” This statement is normalinterpreted to mean that the direct applicability of the ASME Code terminates w



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the authorized inspector authorizes application of the ASME Code Stamp to thenameplate on a new vessel.

The ASME Code should not be interpreted to imply that all design details and fcation procedures that are not covered by its rules are unsatisfactory for repairsalterations. The ASME Code is formulated around design details and fabricatioprocedures (welding procedures and postweld heat treatment, etc.) that are obtable with good shop practices, and that are known to provide a high level of quaHowever, this interpretation does not grant license to arbitrarily violate the rulesthe ASME Code when designing repairs and alterations.

822 Jurisdiction RequirementsMost jurisdictions have pressure vessel laws that require owner/operators to opand maintain their vessels in a safe condition. (See Appendix A.) The majority othese jurisdictions have established regulations that refer to either:

• The National Board Inspection Code or

• The API Pressure Vessel Inspection Code (API 510) for the repair, alteratioand rerating of pressure vessels.

You will need to determine which code governs your own repair, based on localjurisdictional requirements. The Company prefers to use the API Code whenevpossible, because it is specifically oriented to the needs of the hydrocarbon processing industry and provides greater flexibility for exercising engineering jument. (API 510 is included in this manual.)

It is the obligation of every operating plant to be aware of and comply with the psure vessel laws of the governing jurisdiction. Many jurisdictions make the owner/operator responsible for obtaining approvals and filing the documentationrepairs, alterations, and rerating although another organization performing the wmay actually prepare the reports and submit them to an authorized inspector foapproval. Regardless of the jurisdictional requirements, all repairs, alterations, areratings of pressure vessels must be accomplished in a manner to assure the continued integrity and reliability of the vessels by properly exercising the best engineering judgement.

823 National Board Inspection Code vs. API 510The technical requirements of the National Board Inspection Code concerning repair, alteration, and rerating are similar to those in API 510. It is very likely thathe technical details of accomplishing a repair, rerating, or alteration would be itical regardless of which code is used. However, the procedural and administraaspects of these two codes differ considerably.

The major differences are that the National Board Code:

• Requires an authorized inspector to hold a commission from the National Board.



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• Restricts the authority of an authorized inspector employed by the owner/ operator.

• Requires preparation and approval of an R-1 form, and attachment of a newnameplate for repairs and alterations that do not change the maximum alloable working pressure (MAWP) and design temperature.

The more elaborate procedural and administrative details of the National BoardCode do not necessarily result in repairs and alterations that have higher integrbut they can considerably increase the costs incurred, especially if they delay threturn of a pressure vessel to service.

Differences between the codes are discussed below, including specific differencconcerning repairs, alterations, and rerating.

Figure 800-1 is a flowchart that compares the major requirements of API 510 fomaking a repair to those of the National Board Code. In general, to expedite therepair, API 510 permits greater flexibility through the exercise of engineering judment by the owner/operator than is usually possible when following the NationaBoard Code. The owner/operator has more responsibility for the integrity of a repair completed under API 510 than for repairs made under the rules and requments of the National Board Code, which are subject to the review and approvaan authorized inspector. It is very important that the owner/operator not exceedexpertise, background, and experience when taking advantage of the flexibility permitted by API 510. More detailed discussions of the requirements for makingrepair both for API 510 and the National Board Code are given below.

References to the ASME CodeBoth the National Board Inspection Code and API 510 refer to the ASME Codemaking repairs, alterations, and reratings of pressure vessels. However, the woused by the National Board and API conveys somewhat different implications.

The National Board Inspection Code requires all repairs and alterations to confto the ASME Code whenever possible (Paragraph R-100), whereas the API Corequires following the principles of the ASME Code (Paragraph 1.2.3). Both theNational Board and API codes recognize that it may not always be possible to adhere strictly to the ASME Code when making repairs or alterations. Howeverimplication of the wording in the National Board Inspection Code is that the ASMCode must be complied with whenever possible. By comparison, API 510 permmore flexibility for deviating from the ASME Code by exercising engineering judgement. Strictly complying to the design details and fabrication requirementsthe ASME Code may not always result in a repair or alteration with the greatestintegrity and reliability because of the working conditions where the vessel is installed.

However, design details for repairs and alterations that deviate from the rules oASME Code should be justified by an appropriate stress analysis to verify that tmaximum allowable stress permitted by the Code is not exceeded (see Section400). Fabrication procedures that differ from the original construction must be perly qualified to verify that: (1) the minimum materials properties (strength and



Fig. 800-1 Flowchart for Repair: Summary of Requirements of API 510 vs National Board Inspection Code

(1) Deviations permitted within good engineering practice that is responsibility of owner/operator.



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CV-impact toughness) required by the ASME Code are obtained, and (2) any omaterials requirements specified for the service conditions (such as maximum hness of the weld metal and heat affected zones) are achieved.

Reference to the ASME Code connotes the edition used for the original designconstruction of the vessel. The current edition of the ASME Code can be used,when it is advantageous to do so, only if all details of the original design and construction comply with the current edition.

Authorizations and ApprovalsThere are significant differences between the National Board Inspection Code aAPI Code in granting authorizations for and approvals of repairs, alterations, anreratings. Both the National Board and the API Code require obtaining authoriztions and approvals from an “authorized inspector.” However, the National BoarInspection Code requires the authorized inspector to hold a commission from thNational Board (Chapter I), whereas the API Code requires only that the inspecbe qualified to perform the inspection (Paragraph 1.2.4) by virtue of his knowledand experience. Note that many Company inspectors are commissioned by theNational Board.

The National Board Inspection Code emphasizes compliance with its rules throthe scrutiny of an authorized inspector. This requirement is consistent with its dictum to conform to the ASME Code whenever possible. The API Code relies much greater extent on the expertise of pressure vessel or materials engineersassure the continued integrity and reliability of a pressure vessel, and allows thauthorized inspector to base his authorizations and approvals on consultations pressure vessel engineers. This practice follows from its underlying concept of adhering to the principles of the ASME Code while allowing flexibility to use engneering judgement.

Both codes permit the authorized inspector to be an employee of the owner/opeator, but the National Board Inspection Code prohibits an employee from approwork performed by his employer unless the governing jurisdiction (or National Board) has given its consent upon review of the owner/operator inspection procdures (Paragraph 301.2.1d). The API Code contains no such restriction.

Reports, Records, and NameplatesThe National Board Inspection Code establishes a formal administrative procedfor documenting and recording repairs, alterations, and reratings of pressure vessels. An R-1 form, shown in Figure 800-2, must be completed by the organition performing the work (with the exception of routine repairs), and submitted tthe authorized inspector for approval. Copies of the R-1 form are subsequentlyto the owner/user, governing jurisdiction (dependent upon administrative proce-dures), and National Board (alterations only) for permanent record. In contrast,API Code requires only that the owner/user maintain permanent records that doment the work performed.

Both the National Board Inspection Code and the API Code require attaching anameplate adjacent to the original nameplate when a vessel is altered or rerate



Fig. 800-2 R-1 Form Prescribed by National Board Inspection Code for Repair and Alteration of a Pressure Vessel (1 of 2)

FORM R-1, REPORT OF WELDED REPAIR OR ALTERATIONas required by the provision of the National Board Inspection Code

1. Work performed by

(name of repair or alteration organization) (P.O. no., job no., etc.)

(address)

2. Owner

(name)

(address)

3. Location of installation

(name)

(address)

4. Unit identification: Name of original manufacturer:

(boiler, pressure vessel)

5. Identifying nos.:

(mfr’s. serial no.) (original National Board no.) (jurisdiction no.) (other) (year built)

6. Description of work:

(use back, separate sheet, or sketch if necessary)

7. Replacement Parts. Attached are Manufacturers’ Partial Data Reports properly identified and signed by Authorized Inspectors for the following items of this report:

(name of part, item number, mfg’s. name and identifying stamp)

8. Remarks:

This form may be obtained from The National Board of Boiler and Pressure Vessel Inspectors, 1055 Crupper Ave., Columbus, Ohio 43229



DESIGN CERTIFICATION

The undersigned certifies that the statements made in this report are correct and that the design changes described in this report conform to the requirements of the National Board Inspection Code.

ASME Certificate of Authorization no. to use the symbol expires , 19

Date , 19 Signed (name of organization) (authorized representative)

CERTIFICATE OF REVIEW OF DESIGN CHANGE

The undersigned, holding a valid Commission issued by The National Board of Boiler and Pressure Vessel Inspectors and certificate of competency issued by the state or province of and employed by of has examined the design change as described in this report and verifies that to the best of his knowledge and belief such change complies with the applicable requirements of the National Board Inspection Code. By signing this certif-icate, neither the undersigned nor his employer makes any warranty, expressed or implied, concerning the work described in this report. Furthermore, neither the undersigned nor my employer shall be liable in any manner for any personal injury, property damage or loss of any kind arising from or connected with this inspection, except such liability as may be provided in a policy of insurance which the under-signed's insurance company may issue upon said object and then only in accordance with the terms of said policy.

Date , 19 Signed Commissions

(Authorized Inspector) (National Board (incl. endorsements), state, prov., and no.)

CONSTRUCTION CERTIFICATE

The undersigned certifies that the statements made in this report are correct and that all construction and workmanship on this conform to the National Board Inspection Code.

(repair or alteration)

Certificate of Authorization no. to use the symbol expires , 19 .

Date , 19 Signed (repair or alteration organization) (authorized representative)

CERTIFICATION OF INSPECTION

The undersigned, holding a valid Commission issued by The National Board of Boiler and Pressure Vessel Inspectors and certificate of competency issued by the state or province of and employed by of has inspected the work described in this report on , 19 and state that to the best of my knowledge and belief this work has been done in accordance with the National Board Inspection Code. By signing this certificate, neither the undersigned nor my employer makes any warranty, expressed or implied, concerning the work described in this report. Further-more, neither the undersigned nor my employer shall be liable in any manner for any personal injury, property damage or loss of any kind arising from or connected with this inspection, except such liability as may be provided in a policy of insurance which the undersigned's insurance company may issue upon said object and then only in accordance with the terms of said policy.

Date , 19 Signed Commissions (Authorized Inspector) (National Board (incl. endorsements), state, prov., and no.)

Fig. 800-2 R-1 Form Prescribed by National Board Inspection Code for Repair and Alteration of a Pressure Vessel (2 of 2)



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example of a new nameplate is shown in Figure 800-3. It must be attached to thaltered or rerated vessel by the organization performing the work after the R-1 has been approved by the authorized inspector.

The National Board Inspection Code also requires attaching a new nameplate tvessel that has been repaired (with the exception of routine repairs), as shown Figure 800-4, in a manner similar to that for an altered or rerated vessel. The ACode has no requirement for attaching a new nameplate after repairs.

Fig. 800-3 New Nameplate Prescribed by National Board Inspection Code for a Pressure Vessel That Is Altered or Rerated.

* BY

MAWP psi at °F(maximum allowable working pressure) (temperature)

(manufacturer’s alteration number, if used)

(date altered)

* Insert the word “ALTERED” or “RERATED” as applicable

Fig. 800-4 New Nameplate Prescribed by National Board Inspection Code for a Pressure Vessel That Is Repaired

(name of repair firm)

No. (National Board Repair symbol stamp no.)



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830 RepairRepair of a pressure vessel is the work necessary to restore the vessel to a suicondition for safe operation at the original design pressure and temperature, providing that there is no change in design that affects the rating of the vessel. vessel must either be repaired or replaced when deterioration renders it unsatistory for continued service.

Figure 800-5 illustrates a typical method that can be followed to decide betweerepair and replacement. The major factors that should be considered in makingdecision are shown. However, it may be necessary to deviate from these steps because of unique local circumstances.

Fig. 800-5 Logic Tree for Repair or Replacement of a Pressure Vessel



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It is generally more economical to repair a pressure vessel than to replace it, buprimary consideration is integrity and reliability for continued service. Some formof deterioration, such as creep (see Section 749) and hydrogen attack (see Sec747), may indicate that the useful remaining life of the vessel is too short to justhe expense of a repair. Furthermore, the detection of other forms of deterioratisuch as H2S stress cracking (see Section 745), may indicate that the vessel is nsatisfactory for the service environment and the deterioration will recur after rep(presenting a continuing maintenance problem).

831 Design of the RepairIt is impossible to prescribe designs for repairs that will cover all contingencies may occur. The design of a repair can be influenced by the design pressure antemperature, the form of deterioration, the extent of the deterioration, and the process environment. Some general approaches to the repair of common formsdeterioration are discussed below, with the benefits and disadvantages of each

Corrosion and cracks at weld joints are the two most common forms of deteriortion. Figure 800-6 schematically illustrates three ways in which vessels exhibitincracks or corrosion can be repaired.

Fig. 800-6 Typical Designs of Repairs to Pressure Vessels



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Weld RepairThe simplest repair of cracks consists of removing a crack by gouging or grindiand filling the groove with weld metal to restore the shell to the minimum requirthickness, plus corrosion allowance. Similarly, a corroded area can be ground smooth and free of corrosion scale, and then restored to the minimum requiredthickness plus corrosion allowance by weld build-up.

The ground area should be examined by MT or PT (see Sections 762 and 763,the discussion below) to be certain that all of the cracked or otherwise damagematerial has been removed. Welding procedures should be similar to those usethe original construction of the vessel, including preheat and postweld heat treament, and must be qualified according to ASME Code, Section IX. The entire wrepair should be examined by UT or RT (see Sections 764 and 765) for internaflaws, and by MT or PT (see Sections 762 and 763) for surface flaws to assurethe repair will have adequate integrity and reliability for continued service.

Butt-Welded PatchWhen the repair covers a relatively large area, it may be more economical to repcracks and corroded areas by removing the deteriorated area and replacing it wbutt-welded patch. In fact, if the deteriorated area is very large, it may be beneficto replace the entire component of the vessel. There is usually no difference beta weld repair and a butt-welded patch with regard to the integrity and reliability.

The butt-welded patch should be made from the same material specification angrade as the vessel component. If this is not possible because a material has bobsolete, the patch should be made from a material that has similar strength, Cimpact toughness, and welding characteristics. Procurement of the proper matewith the correct thickness can add to the “lead time” for making a repair, and should be planned as far in advance as possible.

Butt patches should be formed to the radius of the shell component that they wused to repair. Square or rectangular patches should have rounded corners witradius of at least four times the thickness. Care should be taken to obtain as gopossible fit-up of the butt patch with the actual size and shape of the opening inshell into which they will be inserted, and this fit-up should be maintained duringwelding through the use of temporary attachments (clips) welded to the patch aadjoining shell. A good fit-up is very important to obtaining high quality welds.

Hot cracking of the weld metal on cooling can be a problem with butt patches, because of the relatively high restraint imposed by the surrounding vessel shellPreheating can help alleviate this problem. Distortion (flattening) of the patch caalso occur. Shrinkage of the weld metal upon cooling tends to pull the patch flawith respect to the matching radius of the vessel shell, and this can be of concebecause it will change the stresses developed in the patch. The use of “strongbtemporarily attached to the patch can minimize the distortion. Every effort shoube made to maintain the patch and adjoining vessel shell within the ASME Codtolerances for out-of-roundness, to make certain that the stresses developed inpatch do not exceed those permitted by the Code. All clips and strongbacks shbe removed after butt welding of the patch to the shell is completed, by cutting



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above the attachment welds. After their removal, the locations where they wereattached to the patch and adjoining shell should be ground flush and smooth.

The butt weld should receive full RT or UT examination (regardless of the examtion performed during the original construction) to assure the integrity and reli-ability of the repair. Full coverage examination is especially important because the possibility of hot cracking of the weld metal. MT and PT examination shouldmade on all locations where the temporary attachments (clips and strongbackswere removed from the patch and adjoining vessel shell.

Lap-Welded PatchLap patches are sometimes thought of as an expedient way to avoid encounterlengthy out-of-service periods. Actually, a lap patch does not conform to the detion of a repair (see Section 830 above), because it constitutes a change in thedesign of a pressure-containing component. Therefore, a lap patch should be mproperly handled as an alteration (see Section 840 below). Nevertheless, API 5(Paragraph 5.2.6) recognizes the utility of this type of repair, and provides guidelines for its design.

According to API 510, a lap patch should provide equivalent integrity and reli-ability as a reinforced opening. The primary membrane stress in the lap patch should not exceed the maximum allowable design stress for the material given the ASME Code, and the elastic strain in the patch should not result in the filletwelds being stressed above their maximum allowable stress.

The major constraint in designing a lap patch to meet these criteria is the joint eciency permitted by the ASME Code for lap welds (Table UW-12). It is not possible to examine adequately by RT or UT the fillet welds for a lap patch to assure the absence of flaws; and, therefore, the efficiency of a lap-welded joint limited to 0.50.

Because of the low joint efficiency, it is almost impossible to design a lap patch will provide equivalent integrity and reliability as the original design and constrution. Lap patches are therefore not recommended for making permanent repairs.

832 Planning and ApprovalBoth the National Board Inspection Code (Paragraph R-301.1.1) and API 510 (graph 5.1.1) require obtaining authorization for making a repair from the authorinspector before the work is initiated, except for routine repairs when prior apprhas been given by the authorized inspector. Examples of routine repairs are:

1. Weld build-up of corroded areas.

2. Application of corrosion-resistant weld overlay.

3. Addition of nonpressure-containing attachments when postweld heat treatmis not required.

4. Replacement of flanges.



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Authorization for making a repair that is not routine is obtained from an authorizinspector by preparing and submitting a repair plan. The repair plan should be prepared by an engineer at the operating plant in consultation with a maintenancoordinator, and it should include the following information:

1. Areas of vessel to be repaired.

2. Repair procedures to be used for each area specifying:

a. Preparation for repair (removal of deterioration)

b. Materials

c. Welding procedures

3. NDE of repairs.

Repairs that will be made by a contractor should be discussed with the contracobtain his agreement with the plan before it is submitted to the authorized inspePlans for complex repairs (i.e., beyond the experience of an engineer at the operating plant) should be discussed with a pressure vessel or materials engine

It may not always be possible to obtain authorization from an authorized inspecbefore making emergency repairs. Under these circumstances, the repair can binitiated prior to submitting the plan to the authorized inspector, but complete domentation should be preserved and submitted to the inspector for his acceptansoon as possible. The vessel cannot be returned to service unless acceptance repair has been obtained from the authorized inspector.

833 Organization Making RepairThe National Board Inspection Code requires the organization performing a repto have either a Certificate of Authorization from the National Board for the usean “R” stamp, or a Certificate of Authorization from ASME for the use of a “U” stamp (Paragraph R-404).

API 510 also accepts an organization having an ASME “U” stamp as qualified tmake repairs (Paragraph 1.2.13), but makes no mention of a National Board “Rstamp. In addition, API 510 permits owner/operators to repair their own vesselsaccordance with its requirements, and to have repairs made by contractors whoqualifications are acceptable to them.

All repairs that are not routine should be performed by an organization that hasvalid “U” stamp, regardless of code or jurisdiction requirements that might permrepair by other organizations.

834 Repair MaterialsBoth the National Board Inspection Code (Paragraph R-305) and API 510 (Paragraph 5.2.7) require that the materials used for the repair must be an acceptabmaterial of construction in the ASME Code. In other words, the materials must conform to one of the specifications in ASME Code, Section II.



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The materials used for a repair should be the same as those used for the originconstruction whenever possible. When this is not possible, the selection of altetive materials should be discussed with pressure vessel and materials engineer

835 Replacement PartsA repair can involve replacing a deteriorated part with a new part of the same design that is manufactured in a shop. Manufacturing a replacement part generrequires welding. If the ASME Code requires inspection of the weld joints by anauthorized inspector, the National Board Inspection Code requires the replacempart to be manufactured by an organization that has an ASME Certificate for a “stamp (Paragraph R-307.1c). A “U” stamp with the word “part” is applied to the part when it is accepted by the authorized inspector. Replacement parts that dorequire inspection by an authorized inspector are not required to be manufacturby a holder of an ASME Certificate of Authorization (Paragraph R-307.1b).

API 510 requires replacement parts to be manufactured according to the principof the ASME Code, but has no requirement concerning the qualifications of themanufacturer (Paragraph 5.2.6).

A general recommendation, however, is that all replacement parts should be mfactured by an organization that has a Certificate of Authorization from ASME fothe use of a “U” stamp.

836 Repair WeldingThe National Board Inspection Code requires qualification of all welding proce-dures used for the repair of a pressure vessel, including the manufacture of repment parts, according to ASME Code, Section IX (Paragraph R-302.1). Furthermore, all welders working on the repair must pass a welder performancequalification for each welding procedure used (Paragraph R-302.2). The repair nization (see Section 833 above) must make the records of procedure and perfmance qualification available to the authorized inspector before the actual repawelding is started.

API 510 requires the repair organization (see Section 833) to qualify all weldingprocedures and welders used for a repair according to the principles of ASME Code, Section IX (Paragraph 5.2). This wording (i.e., “according to the principlediffers from that used in the National Board Inspection Code (i.e., “according toand allows more flexibility for deviating from a welding procedure acceptable tothe ASME Code when necessary to expedite a repair. The welding procedures for a repair should not deviate from what has been qualified according to ASMECode, Section IX, unless the proposed procedure has been reviewed by pressuvessel and materials engineers with regard to the design of a repair and servicerequirements of the vessel to assure adequate integrity and reliability for continservice.



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837 Postweld Heat TreatmentPostweld heat treatment (PWHT) can be a very difficult aspect of the repair andwhen improperly performed, can cause additional damage to the vessel. Repaiwelds should receive the same PWHT used for the original construction whenepossible. PWHT of a repair weld is especially important when it was specified fothe original construction of the vessel to prevent stress corrosion cracking in theprocess environment (see Section 735).

PWHT of a repair weld is most often accomplished by the local application of hto the repaired area while the remainder of the vessel is at ambient temperatureDuring PWHT high thermal stresses that can damage the vessel may develop because of severe temperature gradients and restrained thermal expansion. Nohead-to-shell weld joints, attachment welds for vessel supports, piping connectand internal components are particularly vulnerable to damage. Care should betaken to be certain that the vessel is free to expand when the local area is heatand efforts should be made to keep temperature gradients less than 100°F per along the surface and 100°F per inch through the thickness at temperatures ab400°F. When it is not possible to perform a local PWHT within these guidelinesthe risk of damage to the vessel should be carefully evaluated and alternatives repair without postweld heat treatment should be considered.

Both the National Board Inspection Code (Paragraph R-303.2.2) and API 510 (graph 5.2.4) permit substituting a temper bead (or half bead) welding procedurepostweld heat treatment for the repair of carbon steel pressure vessels. Howevneither of these documents requires a separate qualification of this welding produre to demonstrate that the weld metal and heat affected zones of the repairevessel will have the properties required to assure adequate integrity and reliabifor continued service (minimum strength, maximum hardness, and CV-impact toughness).

ASME Code, Section IX, contains superior requirements for qualifying and performing this type of repair weld. The requirements of Section IX have been adapted into recommendations for repair welding with a temper bead techniqueand are given in Appendix D of this manual. These procedures should not be ufor the repair of a vessel unless they are discussed with pressure vessel and mrials engineers, giving consideration to the design of the vessel and its service tions. The justification for the use of these procedures should also be thoroughldiscussed with the authorized inspector to obtain approval before the repair weis started.

838 Inspection and Hydrotest

Inspection of RepairsBoth the National Board Inspection Code (Paragraph R-301.2) and API 510 (Pagraph 5.1.2) require the acceptance of repairs to a pressure vessel by the authinspector before the vessel is returned to service. The authorized inspector willnormally require performing all of the nondestructive examinations for the repaithat were required by the ASME Code during original construction. Alternative



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NDE methods can be proposed (such as the substitution of UT for RT) when it not possible, or practical, to use the NDE method that was used during constru

All repair welds to vessels should be subjected to essentially full coverage NDEview of the more difficult working conditions that will usually be encountered forrepairs compared to the favorable conditions in a fabrication shop. UT is an entacceptable NDE method for verifying the quality of welds (see Section 764), andoes not involve the hazards and obstruction of other work associated with RT Section 765).

Hydrotest after RepairsNeither the National Board Inspection Code (Paragraph R-308.1) nor API 510 (5.2.9) makes it mandatory to perform a hydrostatic pressure test following the repair of a pressure vessel, but agreement from the authorized inspector is reqfor it to be waived. The purpose of the hydrotest in the ASME Code is to detectgross errors in the design, or major flaws in the construction of a new vessel. Rof a vessel restores it to a satisfactory condition without any change in design (Section 830), and, therefore, there is no need to verify the design of the repairevessel. Furthermore, full coverage NDE of all repairs will detect much smaller flaws than those that could cause failure during a hydrotest, and will, therefore,provide greater assurance of the quality of the repair than a hydrotest.

In-Service Inspection after RepairIn-service inspection of a repaired pressure vessel should be planned and scheafter it has been returned to service, to assure that the repair is providing sufficintegrity for reliable service. In-service inspection is especially important when trepair has been made by deviating from some details of the original constructiofrom ASME Code rules, through the exercise of engineering judgment. The samNDE methods should be used that were previously employed to detect the detetion of the vessel that necessitated the repair, and that were used to verify the quality of the repairs.

839 Approval of Repairs, Documentation, and NameplateThe National Board Inspection Code (Paragraph R-402) requires that the repaiorganization document the repair of a pressure vessel by completing an R-1 forthat is submitted to the authorized inspector for approval (see Figure 800-2). Suquent to obtaining approval of the R-1 form, the repair organization must attachnew nameplate to the repaired vessel (see Section 823). This name plate is stawith an “R” symbol if the repair organization has a Certificate of Authorization from the National Board. The repair organization cannot stamp this nameplate a “U” symbol, despite using its Certificate of Authorization from the ASME to qualify it for making the repair. The ASME permits using the “U” symbol only fothe design and construction of new pressure vessels or new replacement partsCompletion of an R-1 form and attachment of a new nameplate may not be reqfor routine repairs (see Section 832), dependent upon consent of the jurisdictioand approval of the authorized inspector.



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API 510 (Paragraph 4.6) requires that the documentation of repairs to a pressuvessel must be kept as permanent records, but does not prescribe using a stanform. Furthermore, it does not require attaching a new nameplate to a repairedvessel.

A new nameplate should not be attached to a vessel after a repair unless the governing jurisdiction mandates following the National Board Inspection Code. The original nameplate of the vessel has the primary purpose of permanently displaying the maximum allowable working pressure and temperature rating of vessel. A repair does not change the rating of the vessel, and, therefore, a newplate is unnecessary (unless required by the jurisdiction).

840 AlterationAlteration of a pressure vessel is a physical change to any component of the vethat affects the pressure-containing capability. An alteration can change the maximum allowable working pressure and temperature rating of a vessel from tgiven on the original nameplate with a “U” stamp applied by the manufacturer. However, alterations can usually be designed not to affect the original rating of vessel, when the operating pressure and temperature of the process are not ch

Alterations to a pressure vessel are usually made to accommodate changes in process design. The installation of new nozzles in the vessel shell is a commonalteration. Occasionally, internal components have to be changed for the new process designs. Although the internals are not pressure-containing componenthe loads that they transmit to the vessel shell can affect its pressure-containingcapability. Therefore, the effect that the design loads on the new internals (attribable to pressure drop, static weight, and liquid head, etc.) have upon the stressthe vessel shell should be calculated to determine if the maximum allowable working pressure of the vessel has to be changed.

841 Planning and ApprovalThe National Board Inspection Code (Paragraph R-501) requires all alterationspressure vessels to conform to the ASME Code, whereas API 510 (Paragraph requires adhering to the principles of the ASME Code. The wording of API 510 allows more flexibility for designing the alterations when it is not advisable or prtical to strictly conform to the ASME Code, under the circumstances prevailing making the alteration.

Both the National Board Inspection Code (Paragraph R-301.1.2) and API 510 (5.1.1) require authorization from the authorized inspector prior to initiating an alteration on the vessel. The authorized inspector will normally (1) verify that thdesign of the alterations and the calculations have followed ASME Code criteria(2) determine that acceptable materials will be used, and (3) assure that the weprocedures and welders are properly qualified. It is important to note that API 5requires the authorized inspector to consult with an experienced pressure vessengineer before giving authorization to proceed with the alteration. This require



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842 Organization Making AlterationsThe National Board Inspection Code requires that an organization performing aalteration has an ASME Certificate of Authorization covering the scope of work involved (Paragraph R-505).

API 510 does not contain specific requirements for an organization performing alteration. Presumably, the same requirements would apply as for a repair orgation (see Section 833). Alterations can be designed by qualified pressure vessematerials engineers, but it is recommended that only organizations holding an ASME Certificate of Authorization perform the work on the vessel.

843 Materials, Replacement Parts, Welding, Postweld Heat Treatment, and Inspection

The requirements for the alteration of pressure vessels concerning materials, replacement parts, welding, postweld heat treatment, and inspection are identicthose for repair (see Sections 834 through 838 above).

844 Hydrotest after AlterationsHydrotesting alterations is a mandatory requirement of the National Board Insption Code (Paragraph R-308.2). API 510 (Paragraph 5.2.9) states that hydrotesis normally required after an alteration, but permits waiving the hydrotest after consultation with a pressure vessel engineer if superior designs, materials, fabrtion procedures, and inspections are used.

A hydrotest should be performed after an alteration whenever possible. An alteation, by definition, changes the design of at least one component of the vesseshell, and the validity of the design changes cannot be verified by comprehensiinspection. In this regard, an alteration differs significantly from a repair, which does not involve design changes.

The pressure for the hydrotest should be the minimum test pressure required bASME Code for the design pressure and temperature appearing on the vessel'nameplate. This test pressure will normally be lower than the recommended hydrotest pressure required for new vessels because it is likely that some of theinal corrosion allowance will have been consumed during service before the altation is made.

Hydrotesting pressure vessels that have been altered by the installation of a nenozzle requiring reinforcement is occasionally accomplished by welding a cap tthe inside of the vessel shell covering the nozzle. This circumvents the inconvenience of preparing the entire vessel for hydrotest by providing for a “local hydrotest” of the nozzle opening. However, a local hydrotest performed in this manner will not develop the same stresses in the nozzle reinforcement and the



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845 Approval of Alterations, Documentation, and NameplateThe National Board Inspection Code (Paragraph R-502) requires that the organtion performing the alteration of a pressure vessel prepare an R-1 form (see Se823 and Figure 800-2), which must be submitted to the authorized inspector forapproval. The organization performing the repair must then attach a new namethat displays the design pressure (or MAWP) and temperature for the altered veApproval of the alteration and attachment of the new nameplate must be obtainfrom the authorized inspector before the vessel is returned to service.

API 510 (Paragraph 4.6) requires that the documentation of alterations to pressvessels must be kept as permanent records, but it does not prescribe using a sdard form (see Paragraph 813.3). Approval of an alteration by the authorized inspector is required before the vessel is returned to service, but attachment ofnew nameplate is not mandatory unless the design pressure (or MAWP) and teature are changed by the alteration.

850 ReratingRerating a pressure vessel consists of changing the design pressure (or MAWPand/or temperature from those displayed on the vessel's nameplate. Rerating usually does not involve a physical alteration of the pressure-containing capabiof the vessel, but can be required by alterations that are not designed for the ordesign pressure and/or temperature. Rerating is most commonly necessitated b

1. A change in operating conditions for the process.

2. Deterioration (i.e., the occurrence of corrosion or cracking) that affects vesintegrity and reliability for the original design pressure and temperature, anrepair cannot be economically justified.

851 Organization Performing ReratingThe National Board Inspection Code (Paragraph R-503) requires the rerating opressure vessel to be performed by the original manufacturer whenever possibThe rerating can be performed, however, by a registered professional engineerrerating cannot be obtained from the manufacturer.

API 510 (Paragraph 5.3) permits either the original manufacturer or an experienengineer employed by the owner/operator to perform the rerating. Only engineewith appropriate experience with pressure vessel design, fabrication, and inspe



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852 CalculationsRerating a pressure vessel requires making calculations for every major pressucontaining component (i.e., shell, heads, nozzles, reinforcements, and flanges,to verify that they will be adequate for the new design pressure and temperaturThe effect of all internal and external loads on the vessel shell must be considein the calculations for rerating. Therefore, rerating involves repeating all the caltions that were made for the original design of the vessel for the new design presure and temperature. However, it can be thought of as designing a pressure vein reverse. Instead of calculating the minimum required thickness for each shelcomponent for the prescribed design pressure and temperature, the calculationmade to determine if the actual thickness of each shell component is adequatethe rerated pressure and temperature.

Both the National Board Inspection Code (Paragraph R-503) and API 510 (Paragraph 5.3) require making the calculations according to the edition of the ASMECode controlling the original design and construction of the vessel. Alternativelythe latest edition of the ASME Code can be applied, if all details of design and fabrication can be verified to comply with this edition.

Decrease in PressureRerating of a pressure vessel for a lower pressure is usually required if:

1. The operating temperature is increased for new process conditions.

2. Corrosion has reduced the remaining wall thickness below the minimum required thickness for the original design conditions.

Increase in PressureRerating of a pressure vessel for a higher pressure can usually be accomplisheonly if:

1. The operating temperature is decreased.

2. Thickness measurements of all pressure-containing shell components indicthat the original corrosion allowance was greater than necessary for the accorrosion experienced, and, therefore, some of this corrosion allowance caused to gain additional shell thickness. However, the portion of the corrosioallowance that can be applied to the additional shell thickness should be evated with regard to the new process conditions.

Increase or Decrease in TemperatureAn increase in the temperature will almost always require decreasing the pressunless the new temperature remains below 450°F. A decrease in temperature walmost always permit an increase in pressure, unless the original temperature w450°F or below.



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Rerating for a lower temperature should never be allowed to violate the rules incurrent edition of the ASME Code for low temperature operation to assure adeqresistance to brittle fracture, regardless of the rules in the ASME Code when thvessel was built. It is, therefore, essential to check the vessel being rerated for compliance with the current rules for low temperature operation when the new temperature will be 120°F or below. This may be very difficult to do when the vessel is old and the materials used for construction are now obsolete. Under thcircumstances, it may be necessary to cut samples from the vessel for CV-impatesting to perform a satisfactory rerating.

853 Information RequiredA very thorough inspection should be made to assure that the vessel is in satistory condition for the new pressure and temperature. It is especially important tdetermine the minimum remaining thickness of every pressure-containing compnent of the vessel shell, and to detect any cracks that may have developed duriservice. This will usually require more NDE than normally performed during a routine in-service inspection.

854 Approval of Rerating, Documentation, and NameplateThe National Board Inspection Code treats the rerating of a pressure vessel asalteration with respect to the requirements for preparation of an R-1 form, approby an authorized inspector, and attachment of a new nameplate displaying the pressure and/or temperature. API 510 also requires approval of the rerating by authorized inspector and attachment of a new nameplate. The new nameplate should be considered mandatory, because the pressure and/or temperature forrerated vessel differ from those displayed on the original nameplate.


CHEVRON Pressure Vessel - Repair Rerating Alteration

Documents

postweld heat

heat affected

provide equivalent

low temperature

pressure vessel

pressure vessel

national board

minimum required