Estimating corrosion induced thickness loss in Q690E high-strength steel using multimodal ultrasonic guided waves

The estimation of corrosion induced thickness loss is critical for evaluating the remaining strength of high-strength steel (HSS) structures, particularly due to their emerging applications in ocean platforms and coastal bridges. In this study, an ultrasonic approach based on multimodal guide waves is proposed to identify thickness loss induced by electrical accelerated corrosion (EAC) in Q690E HSS samples. Both pitting corrosion and uniform corrosion were observed in the samples during the EAC testing. The average thickness loss due to corrosion in a plate-like structure can be correlated with the velocity of certain guided wave modes according to their dispersion characteristics. However, in practice, when the frequency-thickness product exceeds 1.5MHzmm, it becomes difficult to separate a single mode of guided wave. Hence, this paper addresses the use of multimodal guided waves and proposes a stretching factor that could describe the averaged velocity from different guided wave modes. This stretching factor is found to be linearly correlated to the averaged thickness loss from an analytical approach and validated by experiments. The influence of surface roughness due to pitting is found to be negligible due to the large wavelengths of guided waves. This method provides a simple and effective alternative to estimate the average thickness loss due to corrosion damage in HSS structures.