Evaluation of cross-sectional deformation in pipes using reflection of fundamental guided waves

Ultrasonic guided-wave technology has been successfully applied to detect multiple types of defects in pipes. However, cross-sectional deformation, which is a common defect, is less studied when compared with structural discontinuity defects in pipes. In this paper, the guided wave is employed to detect cross-sectional deformation. First, the effect of sectional deformation parameters on the reflection of guided waves is analyzed using a series of three-dimensional (3D) finite-element (FE) models, and the deformation parameters affecting the reflection are examined in light of the physics of the guided waves based on the FE results. The results show that the reflection occurs at the start of the cross-sectional deformation, while the subsequent gradual deformation region does not cause reflection. The reflection coefficient is dependent on the axial deformation severity, and the mode conversion ratio is dependent on the circumferential deformation extent. Second, an experimental study was conducted to evaluate guided-wave reflection characteristics due to pipe cross-sectional deformation in a realistic situation. Test pipes with local and overall deformations were manufactured, and the reflection from both types of deformation was investigated experimentally. The results show good agreement between the experimental measurement and the FE prediction. Two quantitative parameters, axial deformation rate δ and circumferential deformation rate β, are defined to represent the cross-sectional deformation, and are found to correlate well with the reflection coefficient and mode conversion ratio. The ratio of δ/βis suitable to be used to judge the deformation type.