Guided wave mode dispersion of transient acoustic emission on copper pipes—Its visualisation and application to source location

• The successful application of source detection in copper pipe.
• A flexural wave mode based on STFT analysis of AE to detect source location.

In this paper is presented an improved method for locating a transient acoustic emission (AE) source on a pipeline with two broad-band AE sensors. Using Short Time Fourier Transform (STFT), the method identifies a flexural wave mode, F(1,1), in the two AE signals detected, notes its respective arrival times at different frequencies, and determines the location of the AE source based on the arrival times. Due to velocity dispersion, the arrival time of the wave mode varies with frequency. The method has three main advantages: that the wave speed is not required in the calculation, that it is insensitive to threshold setting for arrival time estimation, and that, at least in theory, the accuracy of the source location can be made as high as desired. The paper first demonstrates, by way of an experiment, the inadequacy of threshold-crossing as a method for identifying the first arrival time of the AE wave. The paper then presents the theory of the proposed method and of the estimated error inherent in the theory and an explanation on how the error can be reduced. The method is then verified experimentally using results obtained from a 3-m long copper pipe of 22 mm diameter.