Pipeline corrosion detection via group delay accumulation effect of multi-path circumferential guided wave packets

Circumferential Guided Waves (CGW) inspection offers a prospective approach for detecting corrosion damage in metallic pipeline structures. It could be used to identify the circumferential location of defects and provide quantitative assessments of defects. Typically, the group delay of the first wave packet passing through the corroded region is utilized to evaluate the variation in group velocity due to corrosion. However, the initial corrosion may induce group delay variations that fall below the sampling interval, thereby existing below the detection limit of conventional Time-Of-Flight (TOF) approaches. In this circumstance, a pipeline corrosion detection method based on the group delay accumulation effect of CGW multi-path wave packets is presented in this paper. In particular, it estimates the group delay of multi-path wave packets of normal and corroded CGW responses using the discrete analytic cross-correlation method. The experimental results indicate that due to the accumulation effect of multi-path wave packets, the group delay of the wave packets passing through the corroded region exceeds the sampling frequency limitation and becomes detectable. The multi-path wave packets pass through the corroded region multiple times, and with each pass, the group delay is accumulated. Thus, the accumulated group delay of the wave packets could increase detection sensitivity. Additionally, the stability of variations in group delay and phase shift is also considered. The experimental results show that with the corrosion area increasing, the group delay could consistently maintain the accumulation effect, while the variation in phase shift is irregular.