API 510 Repairs, Alterations and Rerating: Who Authorizes What

Short answer: under API 510, the inspector must authorize all repair and alteration work before a qualified repair organization starts it. For alterations, and for repairs to ASME Section VIII Division 2 vessels, the pressure vessel engineer must authorize the work as well. The inspector sets the hold points and accepts the finished work. A rerating needs justifying calculations, current inspection data, a pressure test or approved alternative, and the engineer's acceptance. It is complete once the records are updated and an additional nameplate or stamping is attached.

Most confusion about repairs comes from not knowing who decides. In an API 510 programme, five parties are involved: the owner-operator, the authorized inspector, the pressure vessel engineer, the repair organization and the NDE examiner. Each has defined authority, and the code puts limits on all of them. This guide sets out that division of authority as the eleventh edition (October 2022, with Errata 1 in 2023 and Errata 2 in 2025, per API's announcement) describes it. It covers the repair, alteration and rerating categories, the authorization sequence, the rerating checklist, and how the National Board and provincial rules sit on top. The code text is copyrighted, so everything here is paraphrased. Check details against your licensed copy and your jurisdiction.

The five parties and what API 510 makes each responsible for

API 510 can only be used by owner-operators who employ or have access to an authorized inspection agency, a repair organization, an engineer, an inspector and examiners. Each role is defined.

• Owner-operator. Controls the operation, engineering, inspection, repair, alteration, maintenance, pressure testing and rerating of its vessels, and runs the quality assurance system that the other roles work within. The owner-operator also has to respond to inspection findings that require corrective action.
• Inspector (authorized pressure vessel inspector). An employee of an authorized inspection agency, qualified and certified under the code's Annex B. The inspector may work for the owner-operator or be a contractor acceptable to the owner-operator. The inspector answers to the owner-operator for making sure that inspection, NDE, repairs, alterations and pressure testing meet API 510. All NDE results are evaluated and accepted under API 510 by the inspector, who then recommends repair, replacement or continued service.
• Pressure vessel engineer. A person acceptable to the owner-operator with the engineering knowledge to assess mechanical and material issues that affect vessel integrity. The engineer is treated as a composite of whatever specialists the question needs. Design, engineering review, analysis and evaluation belong to this role.
• Repair organization. Supplies the materials, equipment, quality control and workmanship for the repair, and answers to the owner-operator. The code lists who qualifies (see below).
• Examiner. Performs specific NDE and evaluates results against the applicable acceptance criteria. The examiner does not evaluate results under API 510 unless the owner-operator has specifically trained and authorized them to. Examiners do not need API 510 certification and do not need to be owner employees. They must be trained and competent in the procedures they use, and the owner may require certification. The code gives ASNT SNT-TC-1A, ASNT CP-189, CGSB and AWS QC1 as examples. The examiner's employer keeps the certification records, and the inspector confirms the examiners are qualified.

The code also expects operations, maintenance and engineering staff to tell the inspector or engineer about anything that could affect integrity. That includes changes needing management of change (MOC), operation outside integrity operating windows, feedstock changes, failures and repairs, and engineering evaluations such as FFS assessments.

Who can be the repair organization

API 510's list of acceptable repair organizations is broader than many people assume. Any of the following can qualify:

• a holder of a valid ASME Certificate of Authorization for the appropriate ASME Code symbol stamp;
• a holder of another recognized construction-code certificate authorizing the appropriate symbol stamp;
• a holder of a valid National Board R stamp for pressure vessel repair;
• a holder of a valid National Board VR stamp, for repair and servicing of relief valves;
• an owner-operator repairing its own vessels or relief valves under the code;
• a repair contractor whose qualifications the owner-operator accepts;
• an individual or organization authorized by the legal jurisdiction.

The code allows all of these, but the jurisdiction may not. Where a state, province or city requires work by an R-stamp holder, or registration of repair reports, that requirement applies whatever API 510 permits. API 510 states that it does not allow use in conflict with prevailing regulations, and that where it is stricter than a regulation, the code governs.

Repair, major repair, alteration, rerating: drawing the lines

Authorization depends on classifying the work correctly, so the definitions come first. In summary of API 510's definitions:

• A repair restores the vessel to a condition suitable for safe operation at its design conditions. Any welding, cutting or grinding on a pressure-containing component that is not specifically an alteration is a repair.
• A major repair is non-alteration work that removes and replaces a major part of the pressure boundary other than a nozzle, such as part of the shell or a head.
• An alteration is a physical change with design implications that affect pressure-containing capability beyond what the existing data reports describe. These are not alterations: a comparable or duplicate replacement, adding a reinforced nozzle no larger than existing reinforced nozzles, and adding a nozzle that needs no reinforcement.
• A rerating changes the design temperature, the MDMT or the MAWP, upward or downward. Derating, rerating below the original design conditions, is an accepted way to gain more corrosion allowance.

The rule that ties these together: if repair work changes the design temperature, MDMT or MAWP, it is treated as an alteration and the rerating requirements apply too. A repair cannot quietly change the vessel's rating.

Roles matrix: who authorizes, approves and performs each step

The table summarises how API 510's eleventh edition splits authority. "Inspector or engineer" means either may approve under the owner-operator's QA system. "Both" means both must approve.

What the matrix shows: the repair organization and the examiner do the physical work, the inspector controls when work starts, pauses and is accepted, and the engineer controls anything with design consequences.

The authorization sequence on a real job

Under the eleventh edition, repair and alteration work proceeds in this order.

1. Finding and evaluation. Inspection finds damage, which is characterised and evaluated under the code's Section 7. The inspector recommends repair, replacement or continued service. If continued service depends on an FFS assessment, that is an engineering evaluation the owner commissions under API 579-1/ASME FFS-1.
2. Repair plan. The inspector or engineer prepares an equipment-specific repair plan. All work follows the applicable principles of the ASME Code or other construction or repair code, plus this plan.
3. Classification and authorization. The work is classed as repair, major repair, alteration or temporary repair. The inspector authorizes it before the repair organization starts. For alterations and Division 2 repairs, the engineer authorizes it too.
4. Approval of methods. Before work starts, the design, execution method, materials, welding procedures, NDE and testing are approved by the inspector or engineer, or by both for alterations, major repairs and temporary repairs.
5. Hold points. The inspector designates hold points. Typical ones are surface NDE after defect excavation, fit-up, root pass, completed weld NDE, PWHT records and the pressure test or its alternative.
6. Execution and NDE. The repair organization works to the plan. Examiners carry out the specified NDE, usually MT or PT of the prepared area and appropriate NDE of the completed weld against the repair specification or construction code acceptance standards.
7. Acceptance. The inspector approves the work at each hold point and after completion. Records go into the vessel file, along with any jurisdictional reports.

The code also lets the inspector give prior general authorization for limited or routine repairs on a specific vessel. The conditions are that the inspector is satisfied with the repair organization's competency and the repairs will not need a pressure test. API 510 gives weld overlay of corrosion on a vessel that does not need PWHT as an example. This keeps small, repetitive work moving without lowering control over anything significant.

Materials, welding and temporary repairs: limits that apply to everyone

Some API 510 requirements bind whoever does the work.

• Materials must conform to the applicable construction code, be of known weldable quality and be compatible with the original. Carbon or alloy steel with carbon content above 0.35% must not be welded. Carbon steel above 0.30% may need special attention and preheat. If material documents are in doubt, the inspector should specify positive material identification. The code also requires the inspector to verify that new materials, carbon steel included, meet specification, by full checking, full PMI or sampling according to criticality.
• Design of new parts. New nozzles, connections and replacement parts must meet construction-code design requirements and use the same allowable stress basis as the vessel. Parts damaged beyond restoration are replaced.
• Temporary repairs, such as fillet-welded patches, lap bands and non-penetrating nozzles, are allowed when the inspector and engineer are satisfied the repair keeps the vessel fit until permanent repair. They should be replaced at the next available maintenance opportunity, and can stay longer only if the engineer and inspector evaluate, approve and document it. Non-metallic composite wraps can be installed on-stream as temporary repairs if the engineer approves them, designed to ASME PCC-2 Part 4, and reviewed before the next turnaround.
• PWHT alternatives. The code allows preheat or controlled-deposition welding in place of PWHT in defined cases, with limits on material and qualification. The engineer and inspector decide whether a given repair qualifies.
• NDE of repair welds. New welds the construction code originally required to be radiographed must be radiographed. Where that is impractical, UT in lieu of RT and other techniques are allowed within the code's conditions. Alternative NDE needs the engineer's and inspector's approval.

Rerating: the checklist API 510 sets

A rerating changes what the nameplate says the vessel can do, so API 510 makes it the most controlled activity of all. In summary, the eleventh edition allows a rerating only when all of these are met:

1. Calculations justify it. They are prepared by the manufacturer or by an owner-operator engineer (or designated representative) experienced in pressure vessel design, fabrication or inspection.
2. The right code basis is used. The rerating follows the vessel's construction code. Alternatively, the latest edition's formulas can be used if all of the vessel's essential details comply with the ASME Code. Vessels designed before the 1999 addendum, and not to Code Case 2290 or 2278, can be rerated to the latest edition only where the code's eligibility figure allows. For vessels built to a code earlier than 1968, the original design allowable stress must be kept.
3. Current inspection records support it. The vessel must be shown suitable for the new conditions with an appropriate corrosion allowance. Any increase in pressure or temperature must be based on thickness data from a recent internal or on-stream inspection.
4. A pressure test, unless an exemption applies. The test uses the formula of the code used for the rerating calculations. The two exemptions are a previous test at or above the required pressure, or integrity confirmed by special NDE techniques in lieu of testing. See our guide to API 510 pressure testing after repairs and alterations.
5. The engineer accepts the rerating.

The rerating is complete only when the engineering records are updated and an additional nameplate or stamping with the new rating is attached. The original nameplate stays. A rerating that exists only in a calculation file is not finished.

Derating is the most common rerating in practice. A thinning vessel that cannot reach its next turnaround at the current MAWP can sometimes be derated to a lower pressure or temperature that its measured thickness still supports. That trades capacity for remaining life. It still needs the full checklist: calculations, recent thickness data, engineer acceptance, the test question and the new nameplate.

A worked example, described qualitatively

Take a carbon steel knockout drum built to Section VIII, Division 1, inspected under API 510 at a Gulf Coast plant. An on-stream UT survey shows localized thinning in the lower shell near the inlet. The process engineer also wants to raise operating pressure, which needs a higher MAWP.

The two requests are classified separately. Restoring the thinned area with an insert plate is a repair, and possibly a major repair depending on how much of the shell is replaced. Raising MAWP is a rerating, which is an alteration. The inspector and engineer jointly prepare the repair plan. The inspector authorizes the work. Because it includes a rerating, the engineer authorizes and approves the methods, materials, welding procedure, NDE and test approach.

The engineer runs the rerating calculations using thickness data from the recent on-stream survey. The examination company performs the survey, including corrosion mapping of the thinned area. The inspector confirms the records support the new conditions. The plan's hold points cover excavation MT, fit-up, root, final RT or UT of the insert-plate welds, and the pressure test. In this example a hydrotest to the rerating basis is practical, so it is performed. Once records are updated, the repair organization attaches a supplementary nameplate. The original nameplate remains. Because the plant's jurisdiction requires it, the R-stamp holder's alteration report is filed.

Jurisdiction overlay: NBIC, OSHA PSM and Canada

• National Board Inspection Code. Where a US jurisdiction has adopted the NBIC, Part 3 governs repairs and alterations. Welded work is typically done by an R Certificate holder, accepted by a commissioned inspector, and documented on National Board report forms, R-1 for repairs and R-2 for alterations. Jurisdictions differ on whether owner-user programmes run to API 510 are accepted for process vessels. See our pages on NBIC NB-23 and the ASME Authorized Inspector versus the API inspector, and confirm with your jurisdiction.
• OSHA PSM (29 CFR 1910.119). In covered processes, an alteration or rerating usually also triggers management of change and updated process safety information. API 510's MOC definition expects inspection personnel to be involved so the inspection plan is updated. Mechanical integrity records should show the API 510 authorization chain.
• Canada. In Alberta, ABSA's AB-513 sets requirements for repairs and alterations to pressure equipment, separate from its AB-506 owner-user inspection requirements. Other provinces have their own regulators and adopt CSA B51. Registration, inspector involvement and documentation differ by province, so confirm before the work starts.

Common mistakes

• Starting work before the inspector authorizes it, or using a blanket authorization outside the vessel or repair type it was given for.
• Treating a nozzle addition as a repair. A larger reinforced nozzle is an alteration and needs the engineer, and every nozzle installation needs the engineer's approval.
• Repair work that changes the rating without the rerating steps. For example, restoring a section at a thickness that assumes a different MAWP or MDMT.
• Treating the examiner's report as acceptance. The examiner reports against criteria. The inspector evaluates and accepts under API 510.
• Using an unqualified repair organization where the jurisdiction requires an R-stamp, even though API 510 alone would allow it.
• A rerating left half done. Calculations exist but the nameplate, drawings, PSI or relief device set pressures were not updated.
• Temporary repairs left in service for years without the engineer and inspector evaluating and documenting the extension.

How Atlantis supports this

In an API 510 repair, Atlantis NDT is the examiner. Our ASNT-certified technicians, working under ASNT NDT Level III oversight, perform the NDE at the inspector's hold points. That includes MT or PT of excavations and weld preparations, RT through radiography crews licensed where the work is, encoded phased array UT and TOFD of completed welds, and the thickness and corrosion mapping data that rerating calculations rely on. Results go to your API-certified Authorized Inspector, who stays inspector of record. Atlantis does not authorize repairs, design alterations, approve reratings, act as a repair organization, or perform FFS or RBI. See pressure vessel inspection services and API 510 inspector support services. Quotes within 24 hours: ask us to cover your repair hold points.

Frequently asked questions

Who authorizes repairs under API 510, the inspector or the engineer?

The inspector authorizes all repair and alteration work before it starts. The engineer must also authorize alterations and repairs to Division 2 vessels. Methods and materials for alterations, major repairs and temporary repairs need approval from both.

What is the difference between a repair, an alteration and a rerating in API 510?

A repair restores a vessel to safe operation at its design conditions. An alteration is a physical change with design implications beyond the existing data reports. A rerating changes MAWP, design temperature or MDMT. A repair that changes any rating becomes an alteration.

Is adding a nozzle an alteration under API 510?

Not if it is a reinforced nozzle no larger than existing reinforced nozzles, or a nozzle that needs no reinforcement. A larger reinforced nozzle is an alteration. In every case an engineer approves the nozzle installation.

Does API 510 require an R-stamp holder for repairs?

No. API 510 accepts R-stamp holders and also ASME certificate holders, owner-operators repairing their own vessels, contractors acceptable to the owner and jurisdiction-authorized organizations. Your jurisdiction may require an R-stamp.

Can the inspector give blanket approval for routine repairs?

Yes. Prior general authorization is allowed for limited or routine repairs on a specific vessel, if the inspector is satisfied with the repair organization and the repairs will not need a pressure test.

What are the API 510 rerating requirements?

Justifying calculations, the correct construction-code basis, current inspection records (with recent internal or on-stream thickness data for any increase), a pressure test or permitted exemption, and the engineer's acceptance. It is complete when records are updated and an additional nameplate or stamping is attached.

Can a vessel be derated to extend its life?

Yes. API 510 recognises derating below the original design conditions as a permissible way to gain corrosion allowance, but it still follows the full rerating requirements.

Does the NDE examiner need API 510 certification?

No. Examiners must be trained and competent in their NDE procedures. Owners often require certifications such as ASNT SNT-TC-1A or CP-189. The inspector evaluates results under API 510.

How long can a temporary repair stay in service?

It should be replaced at the next available maintenance opportunity. It can stay longer only if the engineer and inspector evaluate, approve and document it.

Repair or rerating coming up? Request thickness and corrosion mapping data for a rerating or get a quote for repair weld NDE.