Abstract
The non-destructive measurement system for adhesion layer thickness of the inner wall of piping using the ultrasonic Lamb wave was examined. The correlation between the frequency characteristics of the phase velocity of the ultrasonic Lamb wave and the substance and thickness of the adhesion was investigated. Steel pipes with adhesions, including plaster, acrylic resin, and aluminum hydroxide, were applied to an experiment. Changes in the frequency characteristics of the Lamb wave were observed at the early stages of the 0.5mm thin adhesion layer of a pipe with 3.5mm wall thickness (where adhesion is 15% of the wall thickness). Furthermore, when the thickness of the adhesion was 1mm or more (30% of the wall thickness), a new phenomenon was observed that was a derivation of higher mode waves. The occurrence of this new phenomenon was explained theoretically by an analysis of a frequency equation.
