Characteristics of Spiral Lamb Wave Triggered by CL-MPT and Its Application to the Detection of Limited Circumferential Extent Defects and Axial Extent Evaluation Within Pipes

The traditionally used cylindroid guided wave modes are not suitable for the detection of limited circumferential extent defects and the evaluation of the axial extent of defects within a pipe. The reason is that it is difficult to generate reflections from limited circumferential extent defects using traditional modes. It is also difficult to evaluate the axial extent of defects by using them. This article proposes using the spirally propagating circumferential Lamb (CL) wave triggered by a specially designed circumferential Lamb wave-based magnetostrictive patch transducer (CL-MPT). It can rapidly detect the position of a defect regardless of its limited circumferential extent, rather than the axial scanning of pipes using traditional circumferential modes. The axial extent of a defect can also be evaluated by summating the number of the signals that contain defect reflections. It was experimentally proven that the CL wave could be applied to supplement the traditional modes.