Defect induced non-axisymmetric transmitted wave model based on the periodic energy distribution changing analysis for high attenuation circular tube defect detection

The pulse-echo signal receiving model can effectively determine a defect's axial position through the time flight of the defect echo. However, some materials or buried structures may significantly attenuate the ultrasonic- guided wave, making the defect echo challenging to observe. Compared with the pulse-echo mode, the guided wave in the pitch-catch signal-receiving model only needs to propagate a one-way distance. Its transmitted wave is more straightforward to observe. However, the pitch-catch model is difficult to judge if a defect exists in the pitch-catch model and identify the position of a defect through the transmitted wave. The paper presents a defect-induced non-axisymmetric transmitted wave model. It can balance the advantages and disadvantages of the two signal-receiving models. First, the periodic energy distribution altering rule of the non-axisymmetric torsional guided wave within a circular tube was theoretically analyzed. Second, the numerical and experimental results verified the theoretical analysis. Third, the defect-induced non-axisymmetric transmitted wave model was proposed based on its periodic energy distribution changing rule analysis to evaluate whether a defect exists, while the traditional pitch-catch models cannot achieve it. The axial and circumferential positions of a circumferential crack within a circular tube encased in concrete can be estimated using the proposed model, which is challenging to realize by the traditional pulse-echo models.