Category
Inspection & Process Safety
Subcategory
In-Service Inspection
Applicable standards
5
Issuing bodies
2
Description
In-service inspection, repair, alteration and rerating of pressure vessels.
Applicable Standards (5)
API — 4 standards
API 510
Pressure Vessel Inspection Code: In-service Inspection, Rating, Repair, and Alteration
In-service inspection, repair, alteration and re-rating of pressure vessels.
Key requirements (8)
- Applies to in-service pressure vessels covered originally by ASME VIII or other recognized code.
- Inspection intervals: external ≤ 5 years, internal ≤ 10 years OR ½ remaining life — whichever is less.
- On-stream UT inspection can replace internal at user's choice if conditions permit.
- Authorized Inspector (AI) certification required for inspection signoff (API ICP).
- Repair/alteration must follow original construction code; reratings allowed via re-calculation + hydrotest waiver if conditions met.
- RBI per API 580/581 may justify extended intervals beyond default limits.
- Damage mechanisms reference: API 571.
- Fitness-For-Service per API 579 when defects exceed acceptance limits.
API 572
Inspection Practices for Pressure Vessels
Companion to API 510 — practical inspection methods.
Key requirements (8)
- Inspection practices for pressure vessels (companion to API 510).
- External inspection minimum: every 5 years.
- Internal inspection minimum: every 10 years (or one-half remaining corrosion allowance life).
- On-stream UT inspection acceptable in lieu of internal in many cases.
- Damage mechanisms reference: API 571 (HIC, SOHIC, polythionic SCC, CUI, HTHA).
- TML (Thickness Measurement Location) selection on injection points, dead legs, mixing zones.
- RBI (API 580/581) may extend interval based on risk assessment.
- WFMT, PAUT, AUBT for high-priority weld inspection.
API 579-1 / ASME FFS-1
Fitness-for-Service
Quantitative engineering assessment of equipment with flaws (corrosion, cracks, dents, blisters, fire damage, creep, etc.) for continued service.
Key requirements (7)
- Fitness-For-Service standard, jointly with ASME (FFS-1).
- Three assessment levels: 1 (screening), 2 (detailed analytical), 3 (advanced FEA / fracture mechanics).
- Part 4: General metal loss; Part 5: Local metal loss; Part 6: Pitting.
- Part 7: HIC and SOHIC; Part 8: Weld misalignment; Part 9: Crack-like flaws.
- Part 10: Creep; Part 11: Fire damage; Part 12: Dents and gouges; Part 13: Laminations.
- RSF (Remaining Strength Factor) method for general metal loss; RSF ≥ 0.90 typical screening.
- Companion to API 510, 570, 653 for repair-vs-replace decisions.
API 571
Damage Mechanisms Affecting Fixed Equipment in the Refining Industry
Catalog of ~70 damage mechanisms (corrosion, cracking, metallurgical, mechanical, environmental).
Key requirements (5)
- Catalog of >70 damage mechanisms in refining and petrochemical service.
- For each mechanism: description, materials affected, factors, appearance, prevention/mitigation.
- Examples: high-temp H2S corrosion, naphthenic acid corrosion, polythionic acid SCC, CUI, MIC.
- Hydrogen damage: HTHA per Nelson curves (now revised post-Tesoro 2010 incident).
- Used as input to RBI (API 580/581) and inspection planning.
ASME — 1 standard
ASME BPVC Sec VIII Div 1
Rules for Construction of Pressure Vessels
Mandatory rules for design, fabrication, inspection, testing and certification of pressure vessels operating above 15 psig (~1 barg).
Key requirements (12)
- Applies to vessels with internal pressure > 15 psig (1.03 barg) up to ~3000 psi (Div 1 sweet spot).
- Joint efficiency E: 1.0 (full radiography), 0.85 (spot RT), 0.70 (no RT) for Type 1 butt joints.
- Shell thickness: t = P·R/(S·E – 0.6·P) for circumferential stress (UG-27).
- Head thickness: t = P·D/(2·S·E – 0.2·P) for 2:1 ellipsoidal heads (UG-32).
- Hydrostatic test pressure: 1.3 × MAWP × (S_test/S_design) — UG-99.
- Pneumatic test (when hydro impractical): 1.1 × MAWP — UG-100.
- Corrosion allowance is added to calculated thickness (not included in S formula).
- MDMT and impact testing per UCS-66 / Figure UCS-66; below the curve, Charpy V-notch impacts are required.
- PWHT thresholds per UCS-56 — generally required above 19 mm thickness for P-No. 1 carbon steels.
- Nozzle reinforcement: area replacement method (UG-37) within reinforcement zone.
- Maximum allowable stress S: from ASME II Part D, Table 1A/1B/3 — temperature dependent.
- Flanges per ASME VIII-1 Appendix 2 (or B16.5 for standard sizes).
Note: Most widely used pressure vessel code worldwide.