The effect of complex defect profiles on the reflection of the fundamental torsional mode in pipes

The capacity of guided ultrasonic waves to size real corrosion defects remains challenging due to the complexity of the profiles encountered in practice. In the past many studies on the reflection from defects with relatively simple shapes have been done. The purpose of this work is to analyze the effect of complex defect profiles on the reflection coefficient. A study of the reflection of the fundamental torsional mode T(0, 1) from three dimensional (3D) defects in pipes with different shapes has been carried out. Firstly, flat-bottomed defects with different surface profiles have been analyzed, and then the reflection from 3D defects with varying depth profile has been studied. It is revealed that at a given maximum depth of a finite discontinuity, the peak of the reflection coefficient from a defect is linearly dependent on the circumferential extent of the defect, and is independent of its shape. The influence of the depth profile of a real corrosion defect in the axial and circumferential directions on the reflection coefficient has also been studied. The results from these analyses have been used to propose a practical approach to determine the maximum depth of a complex discontinuity from the reflection coefficient behaviour. This method has been applied to real corrosion patches and validated with experiments.

► Guided wave reflection from complex defects in pipes predicted and measured.
► Linear behaviour between max reflection and max depth of axi-symmetric defects.
► Linear dependence between max reflection and circumferential extent of 3D defects.
► Max value of the reflection from a finite defect is independent of its shape.
► Max defect depth is estimated if circumferential extent and max reflection are known.