Non-contact imaging of pipe thinning using elastic guided waves generated and detected by lasers

Defect images in a plate can be obtained by the generation and detection of flexural elastic waves using a pulsed laser and a laser Doppler vibrometer. The author has developed an experimental system-called an E-camera-that establishes extremely fast imaging. This paper describes the application of the E-camera to imaging of pipe thinning. The first experiments using a straight pipe revealed that resonance patterns appear significantly at certain frequencies due to guided waves propagating both in the longitudinal and circumferential directions, which is a unique characteristic of pipe structures. A pipe thinning located at various circumferential positions could also be visualized appropriately. Moreover, pipe thinning was successfully detected in both straight and branch pipes located at a distance of 6.0 m from the E-camera system.