Nondestructive evaluation of wall thinning inside a pipe using the reflection of microwaves with the aid of signal processing

This study demonstrates that the reflection of microwave propagating inside a pipe enables one to nondestructively detect and locate wall thinnings appearing inside the pipe. A signal processing method is proposed to compensate for the dispersion of microwave and to make the reflection due to a wall thinning clearer. After fundamental characteristics of the microwave signals were evaluated using 3D finite element simulations, verifications were made by both experiments and numerical simulations using straight brass pipes whose outer diameter and wall thickness were 25 and 3 mm, respectively. The verifications revealed that imposing the signal processing method provided a clear indication of the location of wall thinning, and no significant deterioration was observed even when the pipe was as long as 2000 mm. The verifications also showed that the amplitude of reflection signal was almost proportional to the volume of wall thinning, which agreed with another report, and the reflections were sufficiently clear even when the edge of a flaw was not stepwise but curved like actual wall thinnings.