Abstract: In January 1991, American Petroleum Institute published its first edition of API Std? 653, entitled Tank Inspection 9 Repair, Alteration, and Reconstruction? In this standard, three types of periodical inspections, namely, route in - service inspection, formal in - service inspection an(J formal out - of - service inspection, are introduced, with their specific requirements specified. The scope of API 653 is limited to the tank foundation, shell, bottom, structure, roof, attached appurtenances and nozzles, as well as tank leakage inspection and qualification requirements for personnel performing these inspections.