This checklist reflects what a certified API 510 inspection actually covers, drawn from field practice, not from a generic safety poster. It is written for operations personnel, integrity engineers, and plant coordinators who are preparing for a scheduled inspection or commissioning one for the first time. Use it as a readiness guide, not as a substitute for the inspector's own judgment.
Pressure vessel inspection under API 510 has two distinct phases with different requirements: external inspection performed on-stream, and internal inspection performed during a shutdown. Both have their own checklist. NDE follow-up, documentation, and report output are covered separately below.
External Inspection Checklist (On-Stream)
External inspection is performed while the vessel is in service. It does not require a shutdown and is typically conducted on a 5-year interval (or more frequently if corrosion rates warrant it). Here is what the inspector is checking:
- ▸Shell and head condition: Visual examination for bulging, distortion, dents, and external corrosion. Any visible deformation or pitting through coating is flagged for follow-up UT.
- ▸Insulation condition: Damaged, missing, or wet insulation sections are flagged as CUI risk locations. Holiday cracks, open joints, and failed jacketing allow water ingress, the primary driver of corrosion under insulation on Alberta vessels.
- ▸Nozzles and manway covers: External condition of nozzle necks and flanges; flange face condition where visible; manway cover studs and gasket ring area for external corrosion.
- ▸Foundation, supports, and skirt: Base plate and anchor bolt condition; skirt-to-shell junction for crevice corrosion; foundation cracking or differential settlement; grout condition under base plates.
- ▸Pressure relief valve accessibility and records: PRV is accessible and not blocked by ice, debris, or temporary scaffolding; last test date is within the required interval per API 510; discharge piping is unobstructed.
- ▸Nameplate legibility: ASME nameplate and ABSA registration plate are present, legible, and consistent with current service data. Missing or painted-over nameplates are a deficiency.
- ▸Safety systems: Level gauges, sight glasses, and pressure gauges accessible and readable; isolation block valves are exercisable; instrumentation connections for external corrosion.
- ▸Piping connections at first flanged joint: Condition of piping connections to the vessel at the first flanged joint (the boundary of API 510 scope). This is where external corrosion often concentrates at dissimilar materials or crevice locations.
Internal Inspection Checklist (Shutdown)
Internal inspection requires the vessel to be taken out of service, depressurized, de-inventoried, purged, and properly prepared for confined space entry. The inspector cannot begin internal work until vessel preparation is confirmed. Here is what the internal inspection covers:
Pre-Entry Confirmation
- ▸Vessel has been purged and a gas-free certificate has been issued by a competent person
- ▸All process connections are blinded (not just valved off)
- ▸Confined space entry permit is completed, posted, and attendant is at the manway
- ▸Adequate lighting is arranged (explosion-proof if required by area classification)
- ▸Internal surfaces have been cleaned, with scale, sludge, and residue removed (an inspector cannot perform meaningful visual on a dirty vessel)
Internal Visual Examination
- ▸Shell internal surface: General surface condition, including uniform corrosion, pitting, blistering, delamination, and grooving. Active pitting is distinguished from old inactive pitting.
- ▸Head internals: Bottom head particularly, this is where corrosive water or sludge pools. Pitting at the knuckle radius and any low-point sumps.
- ▸Nozzle bore condition: Internal face of each nozzle, corrosion, erosion, or cracking at the attachment weld.
- ▸Weld seams: Longitudinal seams, circumferential seams, and nozzle attachment welds are visually examined. Any cracking, undercutting, or unusual surface condition triggers NDE follow-up.
- ▸Internal attachments: Tray supports, downcomer bolting, baffle clips, demister pads and their supports, condition and integrity of welds at attachment points.
- ▸Crevice areas: Behind stiffener rings, under support brackets, and in any low-point geometry that can trap moisture or process fluid. These are the locations where localized corrosion is most active.
UT Thickness Measurements
- ▸Ultrasonic thickness (UT) measurements taken at all defined corrosion monitoring locations (CMLs)
- ▸Measurements recorded and compared to previous inspection values to calculate corrosion rate
- ▸Additional UT grid readings taken at any areas of visible pitting or surface anomaly
- ▸Remaining life calculated from measured thickness, corrosion rate, and minimum required thickness
NDE Follow-Up Checklist
Visual inspection identifies where NDE is needed. The type of NDE follows from the suspected damage mechanism and geometry. Here is how the inspector decides:
| Indication or Concern | Appropriate NDE | Notes |
|---|---|---|
| Widespread pitting or general wall loss | UT mapping (grid scan) | Single-point CML readings are not sufficient. Area scan establishes minimum thickness in affected zone |
| Isolated pitting visible on surface | Single-point UT at pits | Depth of deepest pit governs remaining life calculation |
| Visible surface cracking or crack-like indication | PT (liquid penetrant) or MT (magnetic particle) | PT for all materials; MT for ferromagnetics. MT is more sensitive for surface and near-surface cracks |
| SCC-susceptible environment (amine, caustic, wet H2S) | MT or WFMT (wet fluorescent MT) | Standard visual is insufficient in SCC-prone service; WFMT is preferred for highest sensitivity |
| Weld anomaly or suspected subsurface flaw | RT (radiography) or PAUT (phased array UT) | RT for weld quality; PAUT for volumetric examination without radiography access requirements |
| Suspected HTHA or HIC (hydrogen damage) | PAUT or TOFD (time-of-flight diffraction) | Volumetric technique required. Conventional UT is inadequate for hydrogen-induced blistering |
| CUI suspected at insulated nozzle or support | Profile RT or pulsed eddy current (PEC) | Non-intrusive methods through insulation; PEC does not require insulation removal |
NDE is subcontracted to a qualified NDE contractor. The API 510 inspector directs the NDE scope and reviews and interprets results. The inspector does not perform the NDE unless separately certified.
Documentation Checklist
Having the right documents on hand before the inspection starts materially affects how efficiently the inspection proceeds and how complete the report can be. Here is what to have ready:
If a hold point was missed during a previous inspection, for example, an NDE scope that was called for but never executed, or a repair that was made without inspector sign-off, it must be flagged in the current inspection report with a corrective action note. Missed hold points are not erased by subsequent inspections; they are documented and closed out through a defined corrective action process. Attempting to ignore a previously missed hold point creates regulatory and liability exposure.
- ▸Previous inspection report: The most recent signed API 510 inspection report. Ideally the last two to three inspection cycles so corrosion rate trends can be confirmed, not just calculated from a single data point.
- ▸Corrosion rate history: CML thickness data from all previous inspections in tabular form, if maintained separately from the inspection report. This is the basis for remaining life calculations.
- ▸P&ID showing vessel connections: Current as-built P&ID showing all nozzle connections, process streams, and service conditions. The inspector uses this to assess damage mechanism exposure at each connection.
- ▸Design data sheet: MAWP, design temperature, shell and head material specification, corrosion allowance, and ASME code edition of construction. If the original data sheet is lost, the ASME nameplate data provides the minimum required information.
- ▸Repair history: Any weld repairs, liner installation, or alterations made since original construction. Repaired areas need to be disclosed and examined specifically.
- ▸ABSA registration documentation: For Alberta vessels, ABSA registration certificate and registration number. Required for regulatory reporting. If the vessel is unregistered when it should be, that is a compliance issue that needs to be resolved before continued operation.
- ▸PRV test records: Documentation of last bench test for all pressure relief devices. Out-of-interval PRVs are flagged in the inspection report.
Report Output: What the Inspector Delivers
After the inspection is complete, the inspector prepares a signed report. This is the deliverable that supports continued operation, ABSA compliance, and future inspection planning. A complete API 510 inspection report includes:
- ▸Equipment identification: tag number, ASME nameplate data, ABSA registration number, service description
- ▸Inspection scope, date, and any scope limitations (areas not accessible, internal not entered, etc.)
- ▸All UT thickness measurements at CML locations, tabulated with previous values and calculated corrosion rates
- ▸Remaining life calculation and basis
- ▸Next recommended inspection date for both internal and external inspection
- ▸Findings: description, location, photograph, and severity assessment for each finding
- ▸NDE reports attached as appendices (UT grid maps, PT/MT reports)
- ▸Recommendations: repair items, monitoring requirements, follow-up NDE, PRV action items
- ▸Inspector's signature, API 510 certification number, and date
Reports are issued as signed PDF documents. For a sense of what this inspection costs, see our API inspection cost guide for 2026.
FAQs
How far in advance should I schedule a pressure vessel inspection?
For a turnaround internal inspection, 6 to 10 weeks is the recommended lead time. This allows time to confirm the inspection scope, gather documentation in advance, and coordinate NDE subcontractors if needed. For an on-stream external inspection with less logistical complexity, 2 to 4 weeks is typically sufficient. During peak turnaround seasons (spring and fall in Alberta), availability compresses, so book earlier.
Who performs the confined space entry, the inspector or the operator?
Confined space entry is the operator's responsibility. The operator provides the gas-free certificate, the entry permit, and the entry attendant. The inspector enters the vessel as an entrant under the permit that the operator has prepared and authorized. The inspector does not issue the permit or certify the vessel as gas-free. Those are operator obligations under Alberta Occupational Health and Safety legislation.
What if the vessel cannot be entered, is inspection still possible?
Yes, inspection can still proceed under limitations. External UT can assess wall thickness from outside the vessel. Advanced NDE techniques such as PAUT, TOFD, and phased array can provide volumetric data without internal access. The inspection report will note the scope limitation and may call for internal inspection at the next available opportunity. Remaining life calculations with external-only data carry additional conservatism.
Does the inspector need P&IDs before arriving on site?
Providing the P&ID in advance is strongly recommended, not just at the time of inspection. It allows the inspector to review the service conditions, identify damage mechanism exposure at each nozzle, and plan the inspection scope before mobilizing. Showing up with documentation on the day of inspection works, but it adds time and means less preparation. Send the P&ID along with the previous inspection report when booking.
What if previous inspection records are missing entirely?
If no previous records exist, the current inspection becomes a baseline inspection. CML locations are established from scratch, no corrosion rate calculation is possible (only remaining life from nominal or nameplate thickness can be estimated), and the next inspection interval defaults to the conservative end of the API 510 range. Missing records also mean there is no historical context for evaluating whether observed pitting or corrosion is new or long-standing. The report will document the absence of prior records and establish the baseline for future inspections.