API Standard 653 provides minimum requirements for maintaining the integrity of welded or riveted, non-refrigerated, atmospheric pressure, above-ground storage tanks after they have been placed in service. This comprehensive guide covers inspection, repair, alteration, relocation, and reconstruction of existing storage tanks.

1. Inspection Intervals

External Inspections: Conducted at intervals not exceeding 5 years to assess the tank's external condition, including shell, bottom, roof, and appurtenances.

Internal Inspections: Required at intervals based on corrosion rate calculations, typically ranging from 10 to 20 years for tanks in good condition.

Ultrasonic Thickness Testing: Performed to determine remaining shell thickness and assess corrosion rates.

2. Suitability for Service Assessment

Tanks must be evaluated for continued service based on:

• Minimum shell thickness requirements
• Bottom plate condition and settlement
• Roof structural integrity
• Foundation stability
• Appurtenance condition

3. Repair & Alteration Standards

All repairs and alterations must meet specific welding, material, and design requirements outlined in API 653. Critical considerations include:

• Qualified welders and welding procedures
• Material compatibility and traceability
• Non-destructive examination requirements
• Hydrostatic testing when required

Visual Inspection

Comprehensive visual examination of all accessible tank surfaces, including shell plates, welds, nozzles, and appurtenances. Inspectors look for corrosion, deformation, leaks, and structural damage.

Ultrasonic Thickness Measurement

Systematic thickness measurements using ultrasonic testing equipment to determine remaining shell thickness and calculate corrosion rates. Critical for assessing tank fitness for service.

Bottom Inspection

Internal bottom inspection using visual examination, vacuum box testing, or magnetic flux leakage (MFL) scanning to detect corrosion, pitting, and through-wall defects.

  Maintain comprehensive inspection records and documentation

  Implement risk-based inspection (RBI) programs to optimize intervals

  Use qualified API 653 certified inspectors

  Establish corrosion monitoring programs

  Conduct regular training for inspection personnel