Sizing of axial defects in pipes with FEM simulation of wave propagation and wavelet transformation

Finite element analysis of the circumferential wave propagation of pipes has been performed for evaluation of defect size. When an angle-beam technique is used, waves reflected many times at the pipe walls. Therefore, the received wave has complicated RF forms even for a defect-free pipe, which make difficult to estimate the defect size from the received waveforms. In this paper, an oblique incident shear wave is given on the outer surface of pipe and the propagated waves are received at three points, and the received signal in time domain is converted to that in time frequency domain. Then, the difference between defect-free pipe and pipe with defect is discussed in detail. The results show the received signal from the defect is longer and smaller amplitude than those of the defect-free pipe and the number of peaks increases with the depth of defect increasing. Finally, the relation between the depth of defects and wavelet transformation is derived