API 510 cheat sheet

API 510 governs in-service pressure vessels: inspection, examination, testing, rating, repair, alteration, and rerating, plus the pressure-relieving devices that protect those vessels.

Excluded from scope: vessels under the jurisdiction of another code (such as ASME Section III nuclear vessels), fired boilers, and vessels whose design pressure is below 15 psig.

The owner/user owns the inspection program: it designates the authorized inspector, sets intervals, approves repairs and alterations, and retains records for the vessel's life.

The authorized inspector must hold a current API 510 certification, obtained by examination after satisfying the required industry experience, and must maintain it per API's recertification cycle.

Repairs, alterations, and rerating are performed by an organization holding a valid ASME Certificate of Authorization (R-stamp), unless the owner/user formally qualifies a different organization.

Core references: ASME BPVC Sections VIII (construction) and IX (welding), API 571, 572, 576, 577, 579-1/ASME FFS-1, 580, 581, 520/521, and ASME PCC-2.

Inspector duties include reviewing construction records, selecting inspection methods and locations, establishing inspection intervals, and concurring with repairs, alterations, and pressure-relief device test results.

Records the owner/user must keep include the manufacturer's data report, drawings, material and heat-treatment records, inspection history, thickness surveys, repairs, and rerating data.

Inspection categories are internal, external, and on-stream; on-stream inspection may substitute for internal inspection when the damage mechanisms are known and thickness or other monitoring confirms the corrosion behavior.

External inspection covers insulation condition, supports, foundations, nozzles, and visible shell surfaces, and the interval shall not exceed 5 years.

Thickness surveys are the primary quantitative tool: ultrasonic readings at established CMLs are compared with prior surveys to compute corrosion rate and remaining life.

tmin is calculated with the construction code's design formulas at the original design conditions, taking the corrosion allowance as zero; measured thickness below tmin requires repair, rerating, or retirement.

Hydrostatic test pressure for a vessel is normally 1.3 times the MAWP, corrected for metal temperature at test time; vents, temporary supports, and the test medium must be addressed in the procedure.

Pneumatic testing is used only where hydrostatic testing is impractical; per the construction code it is typically 1.1 times MAWP and requires enhanced exclusion and safety precautions because of stored energy.

Examination methods on repairs: PT or MT for surface-breaking flaws, RT or UT for volumetric examination of welds, and UT for thickness and lamination checks, applied per the code and the inspector's instructions.

If inspection or examination reveals a condition unsafe for continued service, the inspector notifies the owner/user and the vessel is shut down, depressurized, or its operating limits restricted until corrected.

Corrosion rate = metal loss divided by time in service, in the same units per year; long-term rate uses initial-to-current thickness, short-term rate uses the last two surveys.

Remaining life = (t actual − t min) ÷ corrosion rate. It is computed with both the long-term and short-term rates, and the shorter (governing) result controls.

Maximum internal or on-stream inspection interval = the lesser of one-half the remaining life or 10 years, unless a risk-based inspection program per API 580/581 establishes the interval.

External inspection interval shall not exceed 5 years, regardless of calculated remaining life.

When long-term and short-term corrosion rates diverge, the difference indicates a change in operating conditions; the interval is based on the more conservative prediction until the cause is resolved.

A short remaining life (on the order of a few years) signals that repair, rerating, or replacement must be planned, and intervals are shortened accordingly.

Risk-based inspection assigns intervals from probability and consequence of failure using API 580/581, and the documented assessment must be reviewed and updated by the inspector.

All thickness readings, calculated corrosion rates, remaining lives, and resulting intervals are documented and signed by the authorized inspector in the vessel record.

The pressure relief device protects the vessel from overpressure; its set pressure may not exceed the vessel MAWP and its capacity is sized per API 520/521 for the governing relief scenario.

Pressure-relieving devices are inspected, tested, and maintained at intervals set by the owner/user, and API 510 limits the interval to a maximum of 5 years absent a documented basis for extension.

Bench set-pressure verification acceptance is ±3% of set pressure for set pressures above 70 psig, and ±2 psi for set pressures at or below 70 psig.

Seat tightness after set-pressure adjustment is verified per API 527, with leakage limits based on bubble or flow criteria for the device type.

Where inlet or outlet block valves are used, they must be locked or car-sealed open, full port, and their pressure drop must be included in the relief sizing calculation.

Rupture discs and pilot-operated devices are examined for damage and correct rating; non-reclosing devices are replaced at intervals established by the owner/user based on service experience.

The inspector reviews each test report for correct set pressure, condition of the seat and internals, and confirmation that the device is the one specified for that vessel and service.

A vessel may not be operated without adequate pressure relief; test records, set pressures, and any repairs to the device are retained with the vessel records.

Repair: work needed to restore a vessel to a condition suitable for safe operation at the existing design conditions, with no change to design parameters.

Alteration: a physical change with design implications, such as a change in MAWP, design temperature, material, pressure-retaining capability, or a nozzle addition beyond code limits.

All repairs and alterations require prior authorization by the authorized inspector; alterations also require design review by an engineer experienced in pressure vessel design.

Repair welds use a WPS qualified by PQR testing under ASME Section IX, and welders and operators hold current performance qualifications for the process and position used.

Postweld heat treatment follows the original construction code; where it is impractical, the engineer may approve alternatives such as controlled-deposition welding with hardness and NDE verification.

Major repairs and alterations normally require a hydrostatic test at 1.3 times MAWP after completion, unless the inspector and engineer waive it based on the nature of the work.

Rerating requires recalculation of MAWP or design temperature, inspector concurrence, revision of records and markings, and a new nameplate showing the revised rating.

A vessel found with thickness below tmin must be repaired, rerated to a lower rating, or retired from service; it may not remain in operation at the original rating.