Storage Tank Inspection — API 653
Inspection intervals, minimum thickness criteria, and the repair framework for above-ground storage tanks under API 653.
API 653 Overview
API 653 is the governing standard for in-service inspection, assessment, repair, and alteration of atmospheric above-ground storage tanks (ASTs) built to API 650. It is the most widely applied tank integrity standard in oil and gas, refining, and chemical industries.
Inspection Types and Intervals
External Inspection: Every 5 years (or per RBI). Covers foundation, shell, roof, floating roof seals, and external corrosion.
Internal Inspection: Every 10 years (extendable to 20 with RBI). Tank out of service, emptied, cleaned, gas-freed, and entered. Floor scanning (AUT robotic scanners) maps floor corrosion.
Floor corrosion (external from soil contact, internal from water bottoms) is the most common cause of tank failure. Floor scanning at every internal inspection is essential.
Key Takeaways
API 653 governs in-service inspection of above-ground storage tanks built to API 650
External inspections every 5 years; internal inspections every 10 years (extendable with RBI)
Floor corrosion is the most common cause of tank failure — floor scanning at every internal inspection is essential
RBI assessment can extend internal inspection intervals from 10 to 20 years — significant cost savings
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