The application of a reflected non-axisymmetric torsional guided wave model for imaging crack-like defects in small-diameter pipes

Crack imaging of a pipe can provide detailed information about defects within the pipe such as the circumferential and axial position of the defect and its circumferential coverage. Due to the complicated propagation characteristics of a non-axisymmetric guided wave within a small pipe and the limited surface area available to install the transducer, crack imaging within a small-diameter pipe is difficult. This paper reports a reflected non-axisymmetric torsional guided wave model for imaging a crack in a small pipe. First, the reflected non-axisymmetric torsional guided wave model was proposed based on the theory of the normal mode expansion method. Then, the crack imaging algorithm was determined based on the theoretical reflected non-axisymmetric torsional guided wave model. Subsequently, the relationships between the angular profiles of the reflected T(M,1) and the axial distance of the cracks, the relationships between the angular profiles of the reflected T(M,1) and the circumferential length of the cracks predicted by the theoretical model were supported by the simulation results and the experimental data. Next, the crack imaging based on the proposed reflected non-axisymmetric torsional guided wave model was carried out for four pipes to verify its practicability. The axial position and circumferential range of the cracks within the four pipes were different. The experimental and numerical results demonstrated that the reflected non-axisymmetric torsional guided wave model has the potential to image cracks within a small pipe.