Corrosion Detection in Pipelines Using Group Delay Accumulation Effect of Multi-Path Circumferential Guided Waves

A circumferential guided-wave strategy is developed for early corrosion detection in metallic pipelines by using the cumulative group-delay response generated during repeated wave propagation. For shallow wall loss, the delay caused by a single interaction with the corroded region can be smaller than the sampling interval, which makes conventional time-of-flight analysis insensitive to early defects. To address this problem, later-arriving circumferential guided-wave packets are used because they pass through the affected region several times and therefore carry an enlarged delay response. The delay difference between healthy and corroded signals is quantified by a discrete-time analytic cross-correlation estimator. Numerical and experimental results show that the group delay increases as the wave packet repeatedly traverses the corrosion zone. Once the accumulated delay exceeds the temporal resolution of the acquisition system, the corrosion-induced change becomes detectable. Compared with phase shift, which shows less stable variation during corrosion growth, the group-delay feature provides a more consistent indicator. These results demonstrate that cumulative group delay is a practical and robust metric for identifying early-stage pipeline corrosion.