Propagation phenomena of wideband guided waves in a bended pipe

Ultrasonic guided waves in pipes have been anticipated as a rapid screening technique for pipe inspection because of their long-range propagation due to low energy leakage. In this paper, the propagation phenomena of guided waves in a bended pipe were investigated using a wideband laser ultrasonic system. The laser ultrasonic system, together with wavelet transformation, is a powerful tool for observing the dispersive phenomena intrinsic to guided waves. Bended stainless steel (SUS304) pipes with 6-mm outer diameter and 1-mm wall thickness were used in the experiments. The bending angles of the pipes were set to 0 degrees ( straight pipe), 10 degrees, 30 degrees, 60 degrees and 90 degrees. The radius of the bend was 12.5 mm in all the pipes. A Q-switched Nd:YAG laser was employed to generate the guided waves. The generated guided waves were detected with a heterodyne interferometer. The obtained time-domain signals and their wavelet coefficients indicated the following two conclusions: ( 1) The amplitude of the F( 1, 1) mode converted from the L( 0, 1) mode increased with the increase of the bending angle. ( 2) Mode conversions from the L( 0, 1) to F( 1, 1) modes and vice versa were clearly observed in the low-frequency range up to around 200 kHz. (c) 2006 Elsevier B. V. All rights reserved.