Category 3 Field Erected Tank

Tanks of this type are considered to have the highest level of risk of contamination in the event of a discharge and require the most stringent inspections and testing schedules.

Inspection Requirements and Schedule

Periodic AST Inspections MONTHLY unless otherwise directed by the engineer in the SPCC plan.

  • Performed by site owner/operator
  • No need to be certified, just knowledgeable
  • Checklist is included in Steel Tank Institute (STI) standard
  • Records of inspections must be maintained

Formal External Inspection by certified inspector  EVERY FIVE YEARS

These are documented external inspection conducted by a certified inspector to assess the condition of the AST and determine its suitability for continued service without entry into the AST interior.

  • Conducted by Certified Inspector
  • Inspector should review previous periodic inspection checklists and previous FEIs/FIIs
  • Includes ultrasonic thickness testing (UTT)
  • Must determine original shell thickness and establish current shell thickness
  • UTT can lead to ultrasonic testing scan (UTS)

Leak Testing by owner or owner’s designee  EVERY FIVE YEARS

Leak testing is a point in time test method to determine if an AST is liquid tight. Leak testing is not preventive in the sense that it provides an indication only if the AST integrity has already been breached. Therefore, it may be used as a tank integrity measure or as a supplement to other inspection procedures. LTMs may include the following technologies:

  • Gas pressure decay (includes vacuum decay)
  • Gas pressure soap bubble testing
  • Gas racers (e.g., helium tracer)
  • Soil tracers (chemical marker)
  • Mass measurement
  • Level measurement
  • Hydrostatic test

Formal Internal Inspection by a certified inspector EVERY TEN YEARS

A documented internal inspection is conducted by a certified inspector to assess the internal and external condition of the AST and determine its suitability for continued service. This includes the inspection requirements of a formal external inspection. A formal internal inspection satisfies the requirements of a formal external inspection and shall be considered equivalent to or better than a formal external inspection for the purposes of scheduling.

  • Performed by Qualified Tank Inspector
  • STI Trained and Certified
  • API Trained and Certified
  • Purpose is suitability for Continued Service

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