The Investigation of Ultrasonic Guided Waves Reflection to Assess Corrosion Defect Sizes in the Pipelines

In this article, reflection coefficient of ultrasonic guided waves from surface of a circumferential corrosion is evaluated to find the relation between this coefficient and the size of defect. In the present work, firstly, by solving the governing equations of the wave propagation with general matrix method and according to the boundary conditions in the pipe, dispersion curves of the phase velocity and group velocity were obtained, then simulation of wave propagation was performed using Abaqus finite element software. In this method, a longitudinal L(0,2) mode, which has good frequency characteristics, was used to generate the wave in the pipe. After determining the convergence, the wave propagation was carried out in the pipe with different dimension of defect. It was observed that part of the generated wave after collision to defect was reflected and various modes were generated that the first reflected mode was L(0,2) and the second reflected mode according to the group velocity dispersion curves of different modes was F(1,2). Different reflection coefficients were obtained due to different dimension of defects, and it was observed that with increasing defect depth, the reflection coefficient of the reflected wave also increased. In this article, the effect of circumferential corrosion width on the reflection coefficient of longitudinal wave has been investigated and it has been observed that the reflection coefficient of waves depends only on the depth of the defect and does not change much with the change of circumferential corrosion width.