Large vertical storage tank bottom evaluation via Acoustic Emission signal analysis

Security of above ground storage tanks is extremely important that tanks are scheduled to be inspected periodically according to its service year. Traditional practice is to empty and clean the tank, then enter the tank using ultrasonic B-scan or magnetic flux leakage methods to detect the corrosion condition of the tanks, which is both time and money consuming. Acoustic Emission (AE) is a valuable non-destructive tool for detecting the corrosion condition or leak of above ground storage tanks floor and there is little disruption to plant operation, as tanks only have to be taken off line for a short period of time. There are even environmental benefits by not emptying and cleaning tanks that do not require inspection or work to be carried out on them. In this paper, AE parameters which are used to evaluate the corrosion condition of tank plate are investigated. Factors that may affect the evaluation results are discussed and compensating factors are proposed to modify evaluation results. Gradation rules for storage tank floor are introduced. In the end, 4 aboveground storage tanks containing different media were inspected using AE method. With the help of AE inspection and evaluation results, tanks which are in serious corrosion condition and require urgent attention can be identified and scheduled for maintenance first, while good tanks can be left in service. It is demonstrated that AE is a very useful tool in detecting and monitoring corrosion of above ground storage floor.