Leak detection and location in gas pipelines by extraction of cross spectrum of single non-dispersive guided wave modes

The gas-leak-induced acoustic emission propagates along the pipe wall as a multimodal guided wave. Different modes possess variable propagation velocities and different degrees of dispersion. Thus if the cross correlation of full leak acoustic signals are used to locate a leakage, the location error is inevitably large. It will reduce the detection uncertainty and location error if using a single non-dispersive mode for leak location. The single-mode component in the cross spectrum of a leak acoustic emission can be extracted by applying the weighing window with parameters in terms of the wavenumber of a special mode. The cross spectrum of single-mode guided wave is then inversely Fourier-transformed to obtain the single-mode cross-correlation for estimating the time delay. This way, the more accurate acoustic velocity of a single mode can be used for locating a suspected gas leakage. The experimental results indicate that, for a gas pipeline, compared with the leak location by correlating the undecomposed leak acoustic emission, the average relative leak location errors are reduced by more than 7% at a distance of more than 80 m due to the enhancement of correlativity of a single mode in leak acoustic emission and the adoption of a more accurate acoustic velocity.