关键词: 管道；扭转模态；衰减；小波包分析；缺陷

Abstract:

Propagation characteristics of torsional modes in pipes with viscoelastic coating were investigated theoretically.T(0,1), the lowest torsional mode which attenuates and disperses low, is suitable for defect detection in pipes with viscoelastic coating according to theoretical analysis.T(0,1) modes at 50kHz and 75kHz were excited to detect two completely different kinds of defects, artificial longitudinal and circumferential notches,in 4m long epoxy coated pipe using developed transducers in the experiment.In order to make the defects easilier identified, the received signals were denoised using wavelet packet analysis. Experimental results show that it is feasible for defect detection in pipes with viscoelastic coating using T(0,1) mode at low frequency of ultrasonic guided waves. Furthermore,signal processing which is wavelet packet analysis denoises the received signals and can improve their signal/noise (S/N) ratio of defect echoes efficiently,implementation convenience of locating defects is dramatically improved.

Key words: pipe;torsional mode；attenuation；wavelet packet analysis；defect