Numerical simulation on the interaction of longitudinal guided waves with double defects in pipes

In guided-wave based pipeline non-destructive inspection, it is inevitable that guided waves will interact with multiple defects, which makes damage identification more challenging. In this study, a numerical simulation was conducted to investigate the interaction of longitudinal guided waves with double notches in pipes. Firstly, a three-dimensional finite element model was established to simulate guided wave propagating in a pipe with a single notch. Then the established model was validated by comparing with existing experiments results. Based on the validated model, the guided wave reflection characteristics of two equal-sized notches of various relative positions were discussed systematically. The results show that, the relative circumferential positions of the two notches have little influence on the overall reflection, and the reflection coefficient rarely varies with the circumferential distance. However, the overall reflection of the two notches at the same circumferential location mainly depends on their axial positions, and the reflection coefficient varies periodically with the axial distance of the two notches. Moreover, the reflection coefficients of multiple notches within some axial range follow superposition principle approximately, which is very helpful for group corrosion detection.