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Inspection & Process Safety

Tank Inspection — API 653

In-service inspection, repair, alteration and reconstruction of API 650 / 12C tanks.

Category
Inspection & Process Safety
Subcategory
In-Service Inspection
Applicable standards
4
Issuing bodies
1

Description

In-service inspection, repair, alteration and reconstruction of API 650 / 12C tanks.

Applicable Standards (4)

API — 4 standards

API 653 Tank Inspection, Repair, Alteration, and Reconstruction
Edition: 5th Edition (2014, A3 2020) Region: USA, Global
In-service inspection and repair of API 650 and 12C tanks.
Key requirements (7)
  • Applies to API 650 / API 12C atmospheric storage tanks in service.
  • External inspection ≤ 5 years; internal ≤ 10 years (extendable via RBI to 15–20 yr).
  • Bottom MFL/UT scanning during internal inspection — quantifies underside corrosion.
  • Settlement survey at intervals (cosine-curve fit, edge settlement criteria).
  • Reconstruction: hydrotest required after major shell replacement.
  • Authorized Tank Inspector (API 653 ICP) required.
  • Repairs categorized as 'Major Alteration', 'Repair' or 'Routine Maintenance' with different documentation.
API 575 Inspection Practices for Atmospheric and Low-Pressure Storage Tanks
Edition: 4th Edition (2020) Region: USA, Global
Inspection practice companion to API 653.
API 650 Welded Tanks for Oil Storage
Edition: 13th Edition (2020, A1 2021, A2 2023) Region: USA, Global
Atmospheric, vertical, cylindrical above-ground welded steel tanks for liquid storage.
Key requirements (11)
  • Atmospheric tanks — design pressure –0.25 in WC to 2.5 psig (≈17 mbar) max.
  • Design temperature: ambient up to 93 °C (200 °F); higher → API 620 Annex M.
  • Bottom plate min thickness: 6 mm (1/4") nominal.
  • Shell design: 1-foot method (Section 5.6.3) or variable design point (5.6.4).
  • Joint efficiency: 0.85 (lap-welded) or 1.0 (butt-welded with full RT).
  • Hydrotest: filled with water to design liquid level; 24-hour holding test.
  • Wind girders / top angle stiffeners: Section 5.9.6.
  • Annex E: seismic; Annex C: external floating roof; Annex H: internal floating roof.
  • Annex F: internal pressure up to 18 in WC; Annex M: elevated temperature; Annex S: stainless.
  • Default allowable stress: 2/3 yield or 2/5 UTS (whichever lower) at design temp.
  • Foundation: Annex B guidance (ringwall, slab, piled).
Note: Default global standard for atmospheric oil/petroleum storage tanks.
API 579-1 / ASME FFS-1 Fitness-for-Service
Edition: 2021 Edition Region: USA, Global
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.