Long-range ultrasonic non-destructive testing of fuel tanks

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Long-range ultrasonic non-destructive testing of fuel tanks

Mazeika, L. / Kazys, R. / Raisutis, R. / Demcenko, A. / Sliteris, R.

The inspection of a storage tank floor is a time consuming and expensive procedure, mainly due to necessity to empty and to clean the tank before an inspection. For this purpose a long range ultrasonic technique based on Lamb waves may be applied. Such an approach is used for inspection of pipes and can cover the distances up 100m. However the storage tanks are much more complicated structures from the point of view of ultrasonic inspection due to presence of multiple lap joint welds. In order to propose an efficient testing technique regularities of Lamb wave propagation in tank floor plates and welds loaded by sand from a bottom side and by fuel (diesel) on the top side have been investigated. It was found that each of non-uniformities in the floor, such as welds and defects act as sources of leaky waves, propagating in the liquid loading the tank floor. For a tank floor inspection two different ultrasonic techniques were proposed. The first one is based on the through transmission tomography of Lamb waves propagating in a tank floor. The second one is based on a spatial analysis of the leaky waves picked up in the liquid, loading the tank floor. Performance of the proposed techniques was tested on a scaled model of a tank and in situ experiments.