Ultrasonic method for detection and location of defects in three-layer plastic pipe based on the wavelet transform

Abstract

Ultrasonic NDT of composite materials or multi-layer plastic pipes meets serious problems. An important issue in ultrasonic non-destructive testing of composite fiber-reinforced materials is detection of flaw echoes in the presence of a structural noise due to scattering of ultrasonic waves and high attenuation of the ultrasonic signal. In this paper a new ultrasonic method for detection and location of defects an in internal inhomogeneous layer of three-layer plastic pipe based on the wavelet transform is presented. This method consists of the improved algorithm eliminating the signals reflected by interfaces and the optimized wavelet analysis. It was shown that in an inhomogeneous layer after choosing the wavelet Coiflet-5, reconstruction of the signal according to the 5-th level coefficients and rejection of the unwanted reflected signals, detection of the artificial defect with the diameter 0,7 mm was obtained. The absolute error of the defects location is not bigger than ± 1.0 mm.