Detection of Crack in Thin Cylindrical Pipes Using Piezo-actuated Lamb Waves

摘要

Lamb waves have been known for their suitability in non-destructive evaluation (NDE) of thin plate structures due to their efficiency in interrogating extensive distance along the plate. It has been shown that for a thin-walled pipe, the assumption of Lamb wave propagation is valid. Such waves can be efficiently excited using piezoceramic transducers (PZT) with good control on the pulse characteristics to assess the health of structural components, such as the presence of cracks. In this paper, a systematic methodology to detect and locate cracks in homogenous cylinder/pipe based on the time-of-flight and amplitude analysis of propagating Lamb wave is proposed. By observing the attenuation in the strength of the direct wave incidence, the presence of a crack along the propagation path towards the sensor can be determined. At least four actuation positions with two on each end of the pipe segment of interest are needed to exhaustively interrogate for the presence of cracks. The detailed procedure for locating and tracing the geometry of the crack(s) is described. It is shown experimentally that the detection using circular PZT actuator and sensor, with dimensions: 5mm diameter and 0.5mm thick, is possible for an aluminum pipe segment of up to at least 4m in length. The proposed methodology is also explored for the aluminum pipe under more practical situations, such as burying it in sand with only the actuator and sensor positions exposed. Experimental results obtained showed the feasibility of detecting the 'concealed' crack on pipes buried in sand.