Effects of the pipe-joints on acoustic emission wave propagation velocity

Abstract

In jointed-pipes, a variety of different acoustic emission (AE) waves can be generated by way of mode conversion, wave reflection and wave transmission from a joint. This can lead to interference waves as resulting complicated signals propagate along the pipe structure. To find out how the joint affects AE wave propagation in the jointedpipes, experiments were conducted on a thin-walled copper pipes connected with two types of joint, compression and soldered. By using wavelet packet decomposition (WPD) analysis and the time-of-flight method, the apparent velocity of AE waves near the joints could be estimated as a narrow frequency band individually. Results confirmed that the wave velocities determined near a joint were influenced by not only the wave reflection but also the wave transmission. The measured wave velocity was least affected by those for the wave in the low frequency band (<125 kHz). It was also observed that a compression or soldered joint behaved like a low-pass filter to the transmitted AE signal.