ベローズを伝搬する弾性波の特性評価

抄録

Bellows pipes are piping joints with bellows structure, and they are excellent in elasticity, airtightness, and spring characteristics. It has been used to connect equipment piping in power plants and industrial plants, and exhaust pipes for transportation equipment. On the other hand, the thickness of the bellows is extremely thin compared to that of conventional pipes, and fatigue cracks and corrosion thinning lead to rapid damage propagation. Therefore, it is expected that the Guided wave inspection method and acoustic emission (AE) method will be used for screening and condition monitoring as the nondestructive inspection. However, the characteristics of elastic waves propagating through bellows have not been shown in the previous studies. In this study, the characteristics of elastic waves propagating in the bellows are evaluated. Artificial AE signals were excited to the bellows by a pulsed YAG laser, and time-frequency analysis of the detected AE signals were performed using the wavelet transform. As a result, it was classified into L (0, 1) mode and F (1, 1) mode as cylindrical wave mode of the approximate pipe. In addition, the relationship between the cylindrical modes and the circumferential waveform distribution of the bellows was investigated, and it was found that the intensity of the F (1,1) mode changed depending on the detection position in the circumferential direction, and that the characteristics of the mode were close to the characteristics of the elastic wave propagating through the pipe.