Ultrasonic guided wave tomography for the inspection of the fuel tanks floor

A novel ultrasonic non-destructive technique (NDT) based on application of a transmission tomography of guided ultrasonic waves is proposed for floor inspection of large storage tanks and detection of non-uniformities, such as corrosion. The technique needs access only to the outer edge of the tank floor and does not require emptying the tank. Theoretical estimations have been verified by laboratory experiments using a scaled physical model of the tank. Estimation of the attenuation of different wave modes propagating in steel plates and determination of the losses in the lap welds showed that most suitable is S0 Lamb wave mode which possesses smallest losses and consequently enables investigation of tank floors up to average diameter 20–30 m. The in situ experiments carried out in a real 8 m diameter tank demonstrated that the developed technique could be used for reconstruction of the spatial distribution of the non-uniformities in a tank floor.