API 510 is the American Petroleum Institute's in-service inspection code for pressure vessels. It tells owner-operators how to inspect, rate, repair and alter vessels once they are in service, and it is also the basis of API's individual API 510 Pressure Vessel Inspector certification. This guide covers what the code actually requires (with clause references to the current 11th edition), how inspection intervals are set, which NDE methods are typically used, and how the separate inspector certification works.
\nEditions: the current edition is the 11th edition, October 2022. It replaced the 10th edition (May 2014, with Addenda in 2017 and 2018). Clause numbers below follow the 11th edition; always confirm against your licensed copy and the API ICP Publications Effectivity Sheet if you are preparing for the exam.
\n\nAPI 510, Pressure Vessel Inspection Code: In-service Inspection, Rating, Repair, and Alteration, covers the in-service inspection, repair, alteration and rerating of pressure vessels and the pressure-relieving devices protecting them. It applies to vessels in the refining and chemical process industries that have been placed in service, unless specifically excluded, and owners may apply it to process vessels in other industries. It is an in-service code: new construction is governed by the construction code (typically ASME Section VIII), not by API 510.
\n\nAPI 510 covers:
\nExclusions and optional exemptions: Annex A lists equipment outside the code (for example mobile/transport vessels and certain fired equipment) and optional exemptions an owner may choose to apply, including vessels whose internal or external pressure does not exceed 15 psig (100 kPa) and small vessels below specified volume/pressure limits. Piping is covered by API 570 and atmospheric storage tanks by API 653. Boilers and other jurisdictionally regulated equipment may fall under the National Board Inspection Code (NBIC) and local rules.
\n\nAPI 510 has been revised many times since its first edition. Rather than reproduce an unverified timeline, here are the recent editions that matter in practice:
\nAPI reviews its standards at least every five years, so check api.org for addenda or errata before relying on any clause number.
\n\nAPI 510 (11th ed., 7.8) requires owner-operators to maintain permanent and progressive records of their pressure vessels and pressure-relieving devices. There is no "10-year retention" limit in the code: the records are kept for the life of the vessel and added to after each inspection.
\n| Record | What it typically contains |
|---|---|
| Construction and design information | Manufacturer's data report / U-1A, drawings, design pressure and temperature, materials, corrosion allowance |
| Inspection history | External, internal and on-stream inspection reports, thickness data by CML, corrosion rates, remaining life, next due dates |
| Inspection plan | Inspection activities, methods, extent and intervals for each vessel, whether set by the code's fixed limits or by an RBI assessment |
| Repairs, alterations and rerating | Authorization, procedures, NDE and pressure-test records, calculations, nameplate/stamping changes |
| Pressure-relieving devices | Test and inspection history and set-pressure records |
The code's fixed-interval limits (which an RBI assessment per API RP 580 may replace) are:
\n| Inspection type | Maximum interval (API 510, 11th ed.) | Notes |
|---|---|---|
| External (visual) | Lesser of 5 years or the required internal/on-stream interval | Performed while in service; looks at insulation, supports, coatings, leaks, CUI-prone areas. There is no annual external requirement in the code, although owners may choose shorter intervals. |
| Internal or on-stream | Lesser of one-half the remaining life or 10 years | When remaining life is under four years, the interval may be the full remaining life up to a maximum of two years. On-stream inspection may substitute for internal inspection only when the code's conditions are met (e.g., low corrosion rate, remaining life over 10 years, no environmental cracking). |
| RBI-based intervals | Set by the RBI assessment | Where RBI sets intervals beyond 10 years, the assessment must be reviewed and approved by the engineer and inspector at intervals not exceeding 10 years. |
| Pressure test | No routine interval | Pressure tests are not normally conducted as part of routine inspection (5.8). They are normally required after an alteration, and after repairs when the inspector judges it necessary. |
Pressure-relieving devices are tested and inspected at intervals set by the owner's program; API 510 gives default maximums (typically five years for typical process services and ten years for clean, non-fouling, non-corrosive services) unless experience or RBI supports otherwise.
\n\nAPI 510 does not mandate a particular NDE method for every vessel; it requires the inspection plan to use methods capable of finding the damage mechanisms that are credible for that vessel (API RP 571 is the reference for damage mechanisms and API RP 572 for inspection practice). NDE examiners must be qualified to the owner-operator's requirements; in North America this is usually an employer program under ASNT SNT-TC-1A.
\n\nPurpose: Measure remaining wall at condition monitoring locations (CMLs) to establish corrosion rates and remaining life.
\nPurpose: Surface and slightly subsurface cracks in ferromagnetic materials (carbon and low-alloy steel). Not applicable to austenitic stainless steel. Wet fluorescent MT is common for internal crack inspections, e.g., wet H2S service.
\n\nPurpose: Surface-breaking discontinuities on non-porous materials, including austenitic stainless steels and non-ferrous alloys.
\n\nPurpose: Volumetric examination of welds (e.g., repair welds) and profile radiography for wall loss. Requires radiation-safety controls; in the USA, industrial radiographers must also meet NRC or Agreement State radiographer requirements.
\n\nPurpose: Weld examination, crack detection and sizing, and corrosion mapping. Often used in lieu of RT for repair welds where the construction code and owner permit, and for HIC/SOHIC assessment in wet H2S service.
\n\n| Vessel type/material | Common methods | When a pressure test is considered |
|---|---|---|
| Carbon steel vessels | UT thickness/corrosion mapping + MT on welds where cracking is credible | After alterations, or after repairs where the inspector requires it |
| Stainless steel vessels | UT thickness + PT (e.g., chloride SCC) | As above |
| Clad or overlay vessels | UT (thickness and bond), PT on cladding, ET where suitable | As above |
| Nickel alloys | UT with material-specific velocity, PT, ET | As above |
The code and the certification are separate things. API's Individual Certification Programs (ICP) run the API 510 Pressure Vessel Inspector certification; Atlantis NDT does not offer API exam training. The details below are from api.org (October 2026) - always confirm on the API 510 program page before applying.
\n\n| Education | Experience required (pressure-vessel related) |
|---|---|
| BS or higher in engineering or technology (or 3+ years technical military) | 1 year in supervision or performance of inspection activities |
| 2-year degree or certificate in engineering/technology (or 2 years technical military) | 2 years in design, fabrication, repair, operation or inspection, including 1 year in supervision or performance of inspection |
| High school diploma or equivalent | 3 years, including 1 year in supervision or performance of inspection |
| No formal education | 5+ years, including 1 year in supervision or performance of inspection |
No ASNT Level III (or any NDT certification) is required to sit the API 510 exam. Experience must be relevant to pressure vessels and recent (API checks the last 10 years).
\n\nThe exam covers the documents in API's Body of Knowledge: API 510, API RP 571, RP 572, RP 576, RP 577 and RP 578, plus ASME Section V, Section VIII Division 1, Section IX and ASME PCC-2. API does not publish percentage weightings by topic; use the current BOK and effectivity sheet on api.org. See our API 510 Body of Knowledge explainer.
\n\nApplication and exam fees are set by API and change periodically; check the current fee schedule on api.org. Certification is valid for 3 years.
\n\nEvery 3 years: at least 20% of working time on inspection activities, 24 hours of continuing professional development (CPD), and an online web quiz every 6 years. API does not count ASNT SNT-TC-1A activity as API CPD by default; check API's CPD rules.
\n\n| Role | Typical background | Key responsibilities |
|---|---|---|
| NDE technician | ASNT SNT-TC-1A Level I/II in UT, MT, PT, RT | Thickness surveys, weld NDE, reporting to the inspector |
| Authorized pressure vessel inspector | API 510 certified | Inspection planning, interval setting, evaluating findings, authorizing and accepting repairs |
| Senior inspector / integrity lead | API 510/570/653, often API 571/580 as well | Inspection strategy, damage-mechanism reviews, RBI team participation |
| NDT Level III | ASNT NDT Level III | NDE procedures, written practice, technique qualification and audits |
Pay varies widely by region, employer and rotation; for US figures see the Bureau of Labor Statistics (inspectors, testers, sorters, samplers and weighers) or the ASNT salary survey rather than unsourced bands. Our NDT inspector salary guide lists attributed sources.
\n\nRisk-based inspection is defined in API RP 580 (with the quantitative method in API RP 581). API 510 permits an RBI assessment to set inspection intervals and scope instead of the fixed limits above. Risk combines probability of failure (PoF) and consequence of failure (CoF).
\nAPI 510 distinguishes repairs (restoring a vessel to a condition suitable for safe operation at the existing design conditions) from alterations (physical changes with design implications affecting pressure-containing capability beyond the existing data report). All repair and alteration work must be authorized by the inspector before it starts (an engineer is also involved for alterations and certain repairs), and accepted by the inspector on completion.
\n| Work | Typical NDE | Pressure test |
|---|---|---|
| Localized weld repair | MT or PT; volumetric NDE where required by the construction code or inspector | At the inspector's discretion |
| Nozzle replacement or new opening | Per construction code, often RT or UT of butt welds | Normally required for alterations; NDE may be substituted only where the code's conditions are met and the engineer and inspector approve |
| Rerating | As specified in the rerating calculation | Pressure test or NDE alternatives per the code |
General corrosion: Uniform wall loss, found by UT thickness surveys and trended by corrosion rate. Acceptability depends on required thickness, not on a universal mpy limit.
\nPitting: API 510 includes specific rules for evaluating widely scattered pits and local thin areas; anything outside those rules goes to an engineering evaluation (e.g., API 579-1/ASME FFS-1, performed by qualified engineers).
\nEnvironmental cracking: Chloride SCC in austenitic stainless steels, wet H2S damage (HIC, SOHIC, SSC) and caustic cracking in carbon steel. Response depends on extent and engineering evaluation; detection uses WFMT, PT, ET and angle-beam/PAUT methods as appropriate.
\nCorrosion under insulation (CUI): Wet insulation on vessels operating in the CUI temperature range. Detection includes targeted insulation removal, profile RT, pulsed eddy current screening and thermography of wet insulation; see our CUI guide.
\nCracks, lack of fusion, slag and porosity in repair welds are evaluated against the acceptance criteria of the construction code (e.g., ASME Section VIII), not against generic dimensions.
\n\nA: API 510 itself requires inspections to be performed by an authorized pressure vessel inspector, and API 510 certification is the usual way to demonstrate that. Whether it is legally required depends on the jurisdiction and on the owner's program (for example, OSHA PSM requires inspection following recognised and generally accepted good engineering practice, which many owners meet using API 510). NDE technicians working under the inspector do not need API 510 certification.
\nA: Under the fixed-limit approach, external visual at the lesser of 5 years or the internal interval, and internal/on-stream at the lesser of one-half remaining life or 10 years. An RBI assessment may set different intervals. Thickness monitoring between internals is set by the inspection plan.
\nA: API 510 covers in-service pressure vessels and their relief devices, API 570 covers in-service piping, and API 653 covers aboveground atmospheric storage tanks. Each has its own API inspector certification. See which API certification to take first.
\nA: Yes, by using an RBI assessment per API RP 580 that meets API 510's requirements, with engineer and inspector review at least every 10 years when intervals exceed 10 years. Without RBI, the fixed limits apply.
\nA: The owner can repair, rerate, replace, or have a qualified engineer perform a fitness-for-service evaluation (API 579-1/ASME FFS-1). Atlantis NDT does not perform FFS assessments; that is an engineering service.
\nA: Use material-specific UT velocities and calibration blocks, PT for surface cracking, and ET where suitable. Intervals still follow API 510 (or RBI); material choice changes the damage mechanisms, not the code's interval logic.
\nA: Education plus pressure-vessel experience per API's table (1 year with an engineering degree up to 5+ years with no formal education). No ASNT Level III is required.
\nA: It depends on vessel size, access, insulation, cleaning, scaffolding and NDE scope. Contractors quote per scope; get a written scope against your inspection plan.
\nA: New construction is inspected to the construction code (ASME Section VIII) by the manufacturer and an Authorized Inspector. In-service inspection follows API 510 (or the NBIC, depending on jurisdiction and owner choice).
\nA: API 510 requires permanent and progressive records for the life of the vessel. Digital records (with backup) make trending easier.
\n\nAPI 510 is the in-service code most refineries and chemical plants use for pressure vessels: intervals are capped at 5 years external and one-half remaining life or 10 years internal unless RBI justifies otherwise, records are permanent, and repairs need inspector authorization. The API 510 inspector credential is a separate API certification with its own eligibility, exam and 3-year recertification.
\nNext steps: Read the API 570 piping inspection guide, compare API 510 vs API 570, or see how inspection teams manage CMLs, due dates and reports in the Atlantis ERP.
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