Abstract
A novel method for measuring wall thinning of pipes using the circumferential (C-) Lamb waves was proposed. The C-Lamb waves were generated and detected by noncontact air-coupled ultrasonic transducers (NAUT) that were extremely useful for ISI because of the non-contacting nature. In the method, wave-packets of multiple-turnaround C-Lamb wave are overlapped and interfere themselves when the number of tone-burst cycle takes large enough. Amplitudes of the overlapped signals are determined by the relative differences of phases of all the wave-packets overlapped. When the group velocity of the C-Lamb wave is changed due to pipe wall thinning (the dispersion relation change), amplitude of the overlapped signal is also changed in principle. In the proposed method, the wall thinning can be detected by measuring the frequency of the C-Lamb wave in the case of taking the maximum overlapped amplitude because the amplitude is also changed as a function of frequency of the C-lamb wave. The principle and verifications of the method were shown.
