API 510 is the industry standard for in-service inspection of pressure vessels, the standard that tells inspection professionals what to look for, how often to look, and how to make run/repair/retire decisions. If you operate pressure vessels in oil and gas, petrochemical, refining, or power generation, API 510 is the code your inspection program runs on.
This guide explains what API 510 inspection actually involves, written from the perspective of a certified API 510 inspector who has performed this work across Alberta and the Gulf Coast.
What Is API 510?
API 510 is a standard published by the American Petroleum Institute titled 'Pressure Vessel Inspection Code: In-Service Inspection, Rating, Repair, and Alteration.' It covers the inspection and maintenance of pressure vessels that were originally constructed to recognized pressure vessel codes, primarily ASME Section VIII Division 1 or Division 2.
The standard establishes requirements for:
- ▸Inspection intervals: How often internal and external inspections are required, and what factors can extend those intervals
- ▸Inspection techniques: Visual examination, NDE methods (UT, RT, MT, PT), and when each applies
- ▸Corrosion allowance and remaining life: How to calculate remaining life based on measured thickness and corrosion rate
- ▸Fitness-for-service assessment: Reference to API 579-1/ASME FFS-1 for evaluating equipment with identified damage
- ▸Repair and alteration: Requirements for authorizing and documenting repairs, and when re-inspection is required after
- ▸Inspector qualifications: Who is authorized to perform and certify API 510 inspections
What Pressure Vessels Does API 510 Cover?
API 510 covers pressure vessels in petroleum refining and chemical process service that were originally built to a recognized construction code. This includes:
| Vessel Type | Typical Examples |
|---|---|
| Unfired pressure vessels | Separators, scrubbers, filters, accumulators, receivers |
| Heat exchangers | Shell-and-tube exchangers, reboilers, condensers |
| Reactors | Fixed-bed reactors, hydrotreaters, reformers |
| Columns and towers | Distillation columns, absorbers, strippers |
| Drums | Knockout drums, surge drums, flash drums |
API 510 does not apply to pressure vessels covered by API 653 (atmospheric storage tanks), pipeline pressure equipment covered by ASME B31.4 or B31.8 exclusively, or certain low-pressure utility equipment. A certified API 510 inspector can confirm applicability for specific equipment.
Who Can Perform API 510 Inspections?
API 510 requires that inspections be performed or directly supervised by an Authorized Pressure Vessel Inspector (API ICP). This is the individual who holds an active API 510 certification, a credential issued by the American Petroleum Institute after passing a comprehensive written examination.
The API 510 certification exam covers: ASME Section VIII (Div. 1 and Div. 2), API 510 itself, API 571 (damage mechanisms), API 579-1/ASME FFS-1 (fitness for service), ASME Section V (NDE), and related codes. The exam is open book but technically demanding. Certification must be renewed every 3 years through continuing education and professional development hours.
In Alberta, the ABSA (Alberta Boilers Safety Association) adds a layer of regulatory oversight. ABSA is the provincial pressure equipment safety authority, and API 510 inspection programs in Alberta must comply with ABSA's regulatory framework and Pressure Equipment Safety Regulation (PESR).
ABSA requires that alterations to registered pressure vessels be authorized by an ABSA-accepted QC program. Inspection reports for ABSA-regulated equipment must meet both API 510 and ABSA regulatory requirements.
What Happens During an API 510 Inspection?
An API 510 inspection typically involves both external inspection (vessel in service) and internal inspection (vessel out of service during a turnaround). Here is what each involves:
External Inspection (On-Stream)
- ▸Visual examination of vessel shell, heads, nozzles, and attachments for external corrosion, CUI (corrosion under insulation), bulging, settlement, or distortion
- ▸Inspection of supports, skirts, lugs, and baseplates for corrosion and structural integrity
- ▸Review of pressure relief valve records and test certification
- ▸Verification of vessel nameplate data and operating conditions against design limits
- ▸Review of previous inspection records for trend analysis
Internal Inspection (Turnaround)
- ▸Visual examination of internal surfaces: shell, heads, internals (trays, packing, demisters), nozzle bores
- ▸Ultrasonic thickness (UT) measurements at defined corrosion monitoring locations (CMLs)
- ▸Assessment of damage mechanisms: general corrosion, localized pitting, SCC, HIC, HTHA, erosion, fouling
- ▸NDE follow-up (MT, PT, RT, TOFD, phased array UT) on identified anomalies
- ▸Weld examination at high-stress or high-risk locations
- ▸Documentation of all findings with photographic evidence
Common Damage Mechanisms API 510 Inspectors Look For
API 571 (Damage Mechanisms Affecting Fixed Equipment in the Refining Industry) is one of the companion codes to API 510. A competent API 510 inspector understands how damage mechanisms behave and where to look. The most common mechanisms in Alberta oil and gas service include:
| Damage Mechanism | Description | Where Found |
|---|---|---|
| General corrosion | Uniform wall loss from corrosive process streams or external environments | Carbon steel vessels in wet service; underside of vessel heads near waterdraws |
| Pitting corrosion | Localized penetrations deeper than surrounding metal loss; high remaining life concern even with acceptable average thickness | Bottom of separators, drawoff sumps, carbon steel in H2S-water service |
| Stress corrosion cracking (SCC) | Cracking driven by combination of tensile stress, susceptible material, and corrosive environment | Austenitic stainless steel in chloride environments; amine service on carbon steel |
| Hydrogen-induced cracking (HIC) | Blistering and stepwise cracking from hydrogen absorption in wet H2S service | Carbon steel separators and drums in sour service |
| High-temperature hydrogen attack (HTHA) | Decarburization and fissuring from hydrogen at elevated temperature and pressure | Hydroprocessing reactors and hot-wall vessels |
| Creep | Time-dependent deformation at elevated temperature | High-temperature process vessels operating above material creep threshold |
| Corrosion under insulation (CUI) | Accelerated external corrosion beneath insulation in temperature cycling zones | Insulated vessels at nozzles, supports, and damaged insulation sections |
Inspection Intervals Under API 510
API 510 establishes maximum inspection intervals based on service conditions and corrosion rate history. The interval types are:
- ▸Internal inspection interval: Maximum 10 years in most services, or one-half of remaining life (whichever is less). Risk-based inspection (RBI) can justify extended intervals with supporting analysis.
- ▸External inspection interval: Maximum 5 years, or whenever the vessel is shut down for maintenance.
- ▸Pressure relief valve (PRV) inspection interval: Defined by API 510 based on service history: typically 10 years maximum; shorter in corrosive or fouling service.
Risk-Based Inspection (RBI), referenced in API 510 and detailed in API 580/581, allows operators to rationalize inspection resources by prioritizing equipment based on probability and consequence of failure. An RBI program properly implemented can extend some inspection intervals and focus resources on the highest-risk equipment.
What the API 510 Inspection Report Contains
An API 510 inspection report is a signed, professional document that records all findings and supports future integrity decisions. A complete report includes:
- ▸Equipment identification (tag number, ASME nameplate data, ABSA registration number where applicable)
- ▸Inspection scope and limitations
- ▸All UT thickness measurements at corrosion monitoring locations, compared to previous results
- ▸Calculated corrosion rates and remaining life
- ▸Next recommended inspection date
- ▸Findings: description, location, photograph, severity assessment
- ▸NDE reports (UT, MT, PT results) attached as appendices
- ▸Fitness-for-service assessment where applicable
- ▸Repair recommendations and follow-up requirements
- ▸Inspector's signature and API 510 certification number
Reports are formatted for regulatory submission (ABSA in Alberta), client records, and future inspection reference. All Norman QC reports are issued as signed PDF documents.
When Do You Need an API 510 Inspector?
You need an API 510 certified inspector in these situations. For typical inspection costs in Canada, see our 2026 API inspection pricing guide.
- ▸Scheduled turnaround inspections: Code-required internal inspections during planned shutdowns
- ▸Fitness-for-service determination: When UT measurements reveal wall thinning or damage that needs a run/repair/retire decision
- ▸Repair authorization: Repairs to pressure vessels under ASME Section VIII require an Authorized Inspector's sign-off
- ▸ABSA compliance: Alberta-registered pressure vessels require inspection under the PESR by qualified personnel
- ▸Pre-purchase inspection: Buying or acquiring used pressure vessels; establishing a baseline integrity assessment
- ▸Owner-engineer program establishment: Setting up or auditing a plant inspection program
FAQs
Is API 510 inspection required by law in Alberta?
Indirectly, yes. Alberta's Pressure Equipment Safety Regulation (PESR) requires that pressure vessels be inspected according to applicable codes. The ABSA-regulated inspection program for pressure vessels references API 510 as an accepted inspection code. Operators cannot simply choose not to inspect registered pressure vessels.
What is the difference between an API 510 inspection and a regular maintenance inspection?
An API 510 inspection is performed by or under the supervision of a certified Authorized Pressure Vessel Inspector, follows the specific requirements of the API 510 standard, and results in a signed report that legally certifies the vessel's fitness for continued service. A routine maintenance inspection (by plant operations or maintenance personnel) is not an API 510 inspection and cannot substitute for one under most operating permits and regulatory requirements.
How long does an API 510 inspection take?
It depends heavily on vessel size, accessibility, scope of NDE, and documentation requirements. A simple inspection of a small vessel during a shutdown can be completed in a few hours. A large separator or column during a turnaround, with extensive UT mapping, NDE follow-up, and full report documentation, may take 2 to 5 days including report preparation.
Can API 510 inspection be done while the vessel is in service?
External inspection can be done on-stream. Internal inspection requires the vessel to be taken out of service, depressurized, purged, and entered safely. Some advanced NDE techniques (PAUT, TOFD) can be applied externally on in-service vessels to assess internal conditions, but cannot fully substitute for an internal inspection.
What is the difference between API 510 and API 570?
API 510 covers pressure vessels (separators, drums, heat exchangers, reactors, columns). API 570 covers piping systems (process piping, utility piping, injection points, injection risers). Many inspection assignments involve both. A turnaround will typically include vessel inspection under API 510 and piping inspection under API 570. Norman QC holds both certifications.