Reference profile
- Designation
- API 510
- Title
- Pressure Vessel Inspection Code: In-Service Inspection, Rating, Repair, and Alteration
- Issuing body
- American Petroleum Institute (API)
- Current edition
- 11th Edition (February 2022)
- Status
- Active; globally recognized inspection code for in-service pressure vessels.
- Category
- In-Service Pressure Vessel Inspection Code
Overview
API 510 covers the in-service inspection, repair, alteration, and rerating activities for pressure vessels and pressure-relieving devices designed and constructed in accordance with ASME BPVC Section VIII or other recognized pressure vessel codes.
It outlines methodologies to evaluate corrosion rates, remaining safe operational life, minimum required wall thickness, fitness-for-service, and risk-based inspection (RBI) intervals to maintain mechanical integrity in petroleum refineries and chemical processing facilities.
Scope & Applicability
Covers
- In-Service Inspections: Internal, external, on-stream, and Corrosion Under Insulation (CUI) inspection programs for all operating pressure vessels.
- Corrosion Rate & Remaining Life Evaluations: Formulas for Short-Term (ST) and Long-Term (LT) corrosion rates, remaining life (RL), and maximum allowable working pressure (MAWP) recalculation.
- Inspection Intervals: Maximum internal inspection frequency rules (lesser of 10 years or half remaining life - RL/2 rule) or Risk-Based Inspection (RBI) per API 580/581.
- Repair & Alteration Rules: Approved welding repairs (weld metal buildup, insert plates, lap-patch temporary repairs) and major structural alterations under API 510 Inspector & PE authorization.
- Rerating Procedures: Rerating MAWP or Minimum Design Metal Temperature (MDMT) supported by current thickness measurements, NDE, and ASME code calculations.
Does NOT cover (exclusions)
- New pressure vessels prior to initial placement in service—covered by ASME BPVC Section VIII.
- Process piping systems in-service—covered by API 570.
- Aboveground atmospheric storage tanks—covered by API 653.
- Power boilers and utility boilers—refer to NBIC (National Board Inspection Code) or ASME BPVC Section I.
Key Requirements
Corrosion Rate & Remaining Life Formulas
- Corrosion Rate Calculation: Long-term rate LT = (t_initial - t_actual) / time; Short-term rate ST = (t_previous - t_actual) / time. The governing rate reflects recent process changes.
- Remaining Life Formula: RL (Years) = (t_actual - t_required) / Corrosion Rate, where t_required is minimum required thickness calculated per ASME VIII-1/Div 2.
Inspection Frequency & Interval Limits
- RL/2 Rule: The internal or on-stream inspection interval shall not exceed one-half of the estimated remaining life (RL/2) of the vessel, or 10 years, whichever is less.
- RBI Alternative: Inspection intervals may be extended beyond 10 years only if a formal Risk-Based Inspection (RBI) assessment is performed in accordance with API 580.
Repair & Alteration Authorization Rules
- Authorized API 510 Inspector: All repairs and alterations must be authorized by an API 510 Certified Inspector prior to work commencement.
- Pressure Vessel Engineer Involvement: Major repairs, alterations, and all rerating calculations must be reviewed and approved by a qualified Pressure Vessel Engineer (PE).
- Temporary vs Permanent Repairs: Fillet-welded lap patches are considered temporary repairs and must be replaced with full-penetration flush-welded insert plates at the next turnaround.
Nondestructive Examination (NDE) & Testing
- Thickness Measurement Locations (TMLs): Mandatory thickness readings at strategic TMLs (shells, heads, nozzles, high-corrosion zones) using Ultrasonic Thickness Testing (UT).
- Pressure Testing After Repair: Pressure test (Hydrostatic 1.3x MAWP) is required after major repairs or alterations, unless exempted by NDE and PE/Inspector approval.
Technical Details
RL/2 Inspection Interval Rule: Max Internal Inspection Interval = Min(RL / 2, 10 Years). If remaining life is 14 years, max interval is 7 years.
Fitness-For-Service (FFS) Reference: Flaws, local thin areas (LTA), pitting, dents, or laminations that exceed API 510 thresholds must be evaluated per API 579-1 / ASME FFS-1 Level 1, 2, or 3 FFS methods.
Minimum Required Thickness (t_required): Calculated using original design code formulas (ASME VIII-1 / Div 2) using current actual material allowable stresses and joint efficiency E.
Engineering Notes
- Prioritize Corrosion Under Insulation (CUI) inspections on carbon steel and low-alloy vessels operating between -4°C and 175°C (25°F and 350°F); use Pulsed Eddy Current (PEC) or strip insulation at high-risk nozzle and support ring locations.
- Fillet-welded lap patches are acceptable only as temporary repairs on low-pressure vessels; ensure they are engineered per API 510 Section 8.1.5 and scheduled for permanent flush insert plate repair at the next turnaround.
- When rerating a vessel for higher MAWP or temperature, verify that all components (including nozzles, flanges, bolts, and supports) are evaluated against current ASME code allowable stress limits.
Related Standards
- API 572
Companion or referenced standard; verify its exact relationship in the adopted edition.
- API 576
Companion or referenced standard; verify its exact relationship in the adopted edition.
- API 579-1 / ASME FFS-1
Fitness-For-Service assessment methodology for damaged in-service equipment.
- ASME BPVC VIII-1
Rules for Construction of Pressure Vessels Division 1 (Original design code baseline).
Source, Edition & Status
- Publisher
- API
- Edition Year
- N/A
- Industries
- Petrochemical, Refinery, Chemical, Oil & Gas
- Content Status
- reviewed
- Last Reviewed
- 2026-07-01
- Last Updated
- 2026-07-01
- Verified By
- Engineering Reviewer
- Official Link
- www.api.org
This paraphrased summary is a discovery aid. Do not reproduce or substitute it for the copyrighted official publication or jurisdictional requirements.