Precise Measurement of Pipe Wall Thickness in Noncontact Manner Using a Circumferential Lamb Wave Generated and Detected by a Pair of Air-Coupled Transducers

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In this paper, we present a novel method of accurately estimating pipe wall thickness by detecting the minute difference in the angular wave number of a circumferential (C-) Lamb wave. A C-Lamb wave circling along a circumference of a pipe is transmitted and received by a pair of noncontact air-coupled ultrasonic transducers. For the accurate detection of the angular wave number, a large number of tone-burst cycles are used so as to superpose the C-Lamb wave on itself along its circumferential orbit. In this setting, the amplitude of the superposed region changes considerably with the angular wave number, from which the wall thickness can be estimated. This method is very useful to monitor the integrity of piping in high-temperature environments because of its noncontact nature. The principle of the method and experimental verification are shown.
2011-07-25