Quantification of corrosion-like defect in pipelines using multi-frequency identification of non-dispersive torsional guided waves

Pipeline guided wave inspection is an efficient tool for determining the defect location. However, quantifying the defect size remains a challenging task. This paper proposes a quantification method for corrosion-like defects in pipelines based on the multifrequency identification of nondispersive torsional guided waves. First, a theoretical scattering model describing the T(0,1) wave's interaction with a simplified corrosion-like defect is introduced. Subsequently, a multifrequency identification method is proposed, enabling the inverse quantification of defect parameters by a defined spectral defect index (SDI). To implement this approach, a pseudo pulse-echo configuration is devised, which contains two rings of piezoelectric transducers attached on the pipeline's outer surface. Finite-element (FE) models are employed to test the performance of the proposed method for both axisymmetric and nonaxisymmetric defects, and an analysis of the robustness of the method is also conducted. The results show that this method has good accuracy even for signals with a very low signal-to-noise (SNR) ratio. Furthermore, an FE model is developed to validate the feasibility of this method for long-distance detection considering attenuation effect. Finally, experimental validation of the proposed method demonstrates close agreement between predicted and actual defect sizes, showing its potential for practical applications.