Circumferential SH Wave Piezoelectric Transducer System for Monitoring Corrosion-Like Defect in Large-Diameter Pipes

The fundamental circumferential shear horizontal (CSH₀) wave is of practical importance in monitoring corrosion defects in large-diameter pipes due to its virtually non-dispersive characteristics. However, so far, there have been limited CSH₀ wave transducers which can be used to constitute a structural health monitoring (SHM) system for pipes. Moreover, the CSH₀ wave's capability of sizing the corrosion-like defect has not yet been confirmed by experiments. In this work, firstly, the mechanism of exciting CSH waves was analyzed. A method based on our previously developed bidirectional SH wave piezoelectric transducers was then proposed to excite the pure CSH₀ mode and first order circumferential shear horizontal (CSH₁) mode. Both finite element simulations and experiments show that the bidirectional transducer is capable of exciting pure CSH₀ mode traveling in both circumferential directions of a 1 - mm thick steel pipe from 100 to 300 kHz. Moreover, this transducer can also serve a sensor to detect CSH₀ mode only by filtering circumferential Lamb waves over a wide frequency range from 100 to 450 kHz. After that, a method of sizing a rectangular notch defect by using CSH₀ wave was proposed. Experiments on an 11 - mm thick steel pipe show that the depth and circumferential extent of a notch can be accurately determined by using the proposed method. Finally, experiments were performed to investigate the reflection and transmission characteristics of CSH₀ and CSH₁ waves from notches with different depths. It was found that transmission coefficients of CSH₀ mode decrease with the increasing of notch depth, which indicates that it is possible to monitor the depth change of corrosion defects by using CSH₀ wave.