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

The fundamental circumferential shear horizontal (CSH) 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 CSH wave transducers which can be used to constitute a structural health monitoring (SHM) system for pipes. Moreover, the CSH 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 CSH mode and first order circumferential shear horizontal (CSH) mode. Both finite element simulations and experiments show that the bidirectional transducer is capable of exciting pure CSH 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 CSH 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 CSH 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 CSH and CSH waves from notches with different depths. It was found that transmission coefficients of CSH mode decrease with the increasing of notch depth, which indicates that it is possible to monitor the depth change of corrosion defects by using CSH wave.