Measurement and simulation of the propagation of impulsive acoustic emission sources in cylinders, with potential application to pipeline monitoring

Abstract

Acoustic Emission (AE) monitoring of processes, machines and structures consists of using one or more surface-mounted sensor to listen for sources, which could come from structural degradation, process conditions or machine operation. Since real AE sources have a temporal structure, often over the millisecond range or longer, it is of general interest to examine what can be recovered of this temporal structure using an array of sensors of known positions relative to each other. Experiments and simulations were carried out with impulsive sources (pencil-lead breaks) and the propagating AE resulting from these sources was recorded over a period of around 2 seconds for both experiments and simulations. Two test objects were used; a solid steel cylinder to provide a relatively simple and well-studied platform to examine a number of essential principles, and a 2m length of pipe to provide some conclusions relevant to impact monitoring of pipelines. Comparison of the simulated and experimental results indicates that the frequency content of the resulting wave is not very sensitive to unloading rate at the source, although the amplitude of the simulated signal is. Comparison of the first few tens of microseconds of the simulated and experimental waveforms suggests that the first arrival is consistent with a wave speed of around 5000ms− 1. In addition, both simulations and experiments indicate that, in the sizes of the objects examined, reflections at interfaces quickly introduce interference, so the nature of the impulsive part of the source can only reasonably be preserved in the fastest-moving components of the propagating wave and before arrival of any reflections from interfaces.