Circumferential Guided Wave Inspection for a Defect at Inner Surface of a Pipe

Circumferential guided wave, that is ultrasonic wave propagating in the circumferential direction in a pipe, has attracted considerable attention due to its prominent characteristics. However, its complex wave mechanics such as multi-mode generation and mode conversion often prevent us from quantitative evaluation such as defect sizing. In this study, modal analysis and guided wave simulation are done by a semi-analytical finite element technique to clarify that a defect at an inner surface of a pipe cannot be quantitatively measured by the amplitude of guided wave signals. Energy distributions in the thickness direction that shows the sensitivity to the defect depth are calculated for various guided wave modes. These calculation results and experimental group velocity dispersion curves show that the conventional angle beam transducers do not excite the mode with inner concentrated energy and so inner defects cannot be measured well by the amplitude of received signals, which was improved with the special angle beam transducers.