Crack shape reconstruction from noisy signals in ECT of steam generator tube

In eddy current testing of steam generator tubes, signals are sometimes rendered noisy by the presence of other structures, such as support/tube plates outside of test materials, as well as the lift-off noise due to the expansion zone of the tube. This paper describes a new method for the crack reconstruction from these noisy signals, developed with a fast signal prediction and the steepest descent algorithm. The electromotive force signals of the mutual induction and differential outputs are obtained from a newly developed four-sensor probe. Noisy signals are processed by two kinds of signal processing method but residual noise remains. Several artificial cracks are reconstructed satisfactorily in short CPU time. Inverse results from laboratory data are shown in this paper