Experimental investigation into acoustic characteristics of leakage signals from underwater plastic water-filled pipes

Acoustic techniques based on cross-correlation are in common use for leak detection in water distribution pipes. However, little work has been done in underwater pipeline leak detection. This paper is concerned with experimental investigation into water leakage from a underwater plastic pipe, with particular emphasis on the acoustic characteristics of the propagating leak noise measured under controlled conditions, including the leak hole size, water pressure and submerged depth of the pipe. It is found that the leak noise from a submerged PE water pipe concentrates at low frequencies, with a flat spectrum that has been observed in the frequency range below 650 Hz. Experimental results demonstrate that the attenuation of a leak signal in the submerged water pipe is larger than the in-air case, whereas the propagation wavespeed is mainly affected by the pressure within the pipe. Specifically it is shown that for a lower pressure, the wavespeed is almost identical to that for the in-air water pipe; for a higher pressure, an increase in the wavespeed may occur. In this paper preliminary measurements are made, and test results show the detectability of the leakage from a submerged water pipe. Further work will be carried out to investigate the feasibility of the transient leak signals for online leak detection.