P-08 Application of Laser-Based Ultrasonic Technique to Evaluate Carbon Steel Pipe with FAC

Abstract

It is well known that guided waves have the multi-modes with different velocity at any given frequency. Therefore, the received signal generally contains more than one mode, and the amplitude proportion of different modes is changed when the wave meets various shape of defects. This phenomenon is called mode conversion. Although mode conversion makes the interpretation of received signal difficult, the evaluation of defect sizing could be achieved in case the interaction between multi-modes and defects could be identified. This study is based on this multi-modes method and adopted the non-contact technique which consists of laser-generation and air-coupled detection system for detecting defect. In order to induce selective mode with laser source, linear slit was used and to get single mode signal, the reception angle of air-coupled transducer was adjusted in consideration of wave velocity of carbon steel pipe and air according to Snell's law. The objective of this study is the development of non-destructive evaluation technique of defect sizing using laser-generated guided waves with non-contact reception technique. For this aim, the characteristics of guided waves with varying shape of wall-thinned defect in carbon steel pipes are investigated and consequently the trends of these characteristics are analyzed for evaluating defect sizing quantitatively.