Gas Leakage in Buried Gas Pipe Based on Wavelet Analysis for Vibro-Coustic Signal in a Long Duct

Gas leakage is often caused by the mechanical impact forces of construction equipment. In a long duct with large diameter, acoustic waves caused by the impact force are transferred to a far distance through the medium inside the duct. This wave is very complex since it includes an acoustic wave and solid wave. In general, the solid wave is attenuated faster than the acoustic wave in a buried duct because it is damped out by the soil covering the duct. The acoustic wave is propagated to the far distance with direct and reflective waves on the wall. The directive wave is non-dispersive and the reflected waves are dispersive due to the cavity modes of the duct. The typical correlation method has used both dispersive and non-dispersive waves to estimate the arrival time delay. Thus this method induces a degree of error for leak detection. In this article, time-frequency method is developed to classify the wave speed of direct waves (non-dispersive waves) and the reflective waves (dispersive waves), respectively. It can determine the leak location with more accuracy than the correlation method.