Dispersion characteristics and leakage localization experimental study of ultrasonic guided waves in steel pipes

Abstract

Leak detection and location in a gas distribution network are significant issues. The acoustic emission (AE) technique can be used to locate a pipeline leak. Firstly, this paper introduces the basic concepts of guided waves and proposes the derivation of the three-dimensional displacement vector and the group velocity dispersion curve of the guided wave in a pipe. Then the influence of the wall thickness and diameter on the dispersion curve of guided wave in a pipe is proposed. The location error of the leak detection method depends on three parameters. They are the distance between two sensors, estimation of the time delay between two measured signals and the propagation velocity of leak-induced signals in the pipe. To decrease the error of leak location, some methods to determine the time delay and the wave velocity are proposed. To reduce the effects of noise on the time delay estimation, two kinds of filters are introduced, which are wavelet decomposition and empirical mode decomposition. Then a new leakage location method using the modified generalized cross-correlation (GCC) location method in combination with the attenuation-based location method using multilayer perceptron neural networks (MLPNN) is proposed. The GCC location method can compensate for the weakening effect of the different propagation paths on the leakage-induced signals, it also can increase the degree of the correlation between two measured signals and improve the accuracy of the time delay estimation. Besides, the wave speed was determined more accurately by using the peak frequency in combination with the group speed dispersive curve of the fundamental flexural mode. The MLPNN locator was experimentally verified by using a pressurized piping system and a signal acquisition system. The average of the relative location errors obtained by the MLPNN locator was reduced by 14% compared to that using the cross-correlation (CCF) location method. Hence, the MLPNN locator is more suitable for locating a leak in a gas pipe than the CCF location method is.