Method and apparatus for determining the time between internal inspections of a tank

The method and apparatus of the present invention will provide a means for a tank owner to determine the time until the next out-of-service API 653 internal inspection of an aboveground storage tank (AST) or an underground storage tank (UST) should be considered or performed based on in-service measurements of the tank filled with fuel or another liquid. The inspection interval is determined from a leak detection test with a pass and a probability distribution of the survival rate of the tank bottom that is representative of the tank being inspected. More accurate estimates are obtained by using measurements of the thickness and corrosion rate of the tank bottom at one or a few locations in the tank and the results of an acoustic emission (AE) corrosion activity test and/or previous out-of-service inspection measurements of the tank floor bottom thickness of the floor at many locations. The method is based on the concept of equivalent risk.