Characterization of axial and oblique defects in pipes using fundamental torsional guided modes

A quantitative study of the interaction of the T(0,1) torsional mode with axial and oblique defects in a pipe is presented in this paper. A mode decomposition technique employing the chirplet transform is used to separate the multimodal signals reflected from the defects. Reflection signals are obtained from experiments on a carbon steel pipe. The influence of the crack length and inclination angle on the reflection is investigated. Reflection from an axial defect is found to consist of a series of the wave pulses with gradually decaying amplitude. Results show that the reflection coefficient of the axial crack initially increases with the crack length, but finally reaches an oscillating regime. Furthermore, it is revealed that for an oblique crack, the reflection coefficient is linearly dependent on the equivalent circumferential extent of the defect and is independent of the axial length. In addition, it is shown that the coefficients for a steep defect are greater than those for a gentle defect.