A novel method for defect detection of a pipe using the circumferential Lamb wave was proposed. In this method, wave-packets of multiple-turnaround Lamb waves are overlapped when the number of tone-burst cycle takes so large. The amplitudes of the overlapped signals are determined by the relative differences of phases of all the wave-packets overlapped. When a defect is existed in the propagation path of the Lamb wave, the phase of the wave is changed in general. The phase change induces the amplitude change of the overlapped portions. The principle depending on above mechanism and experimental verifications was described.
