Passive acoustic detection of gas leaks in buried pipes

The feasibility of using microphones to detect sounds generated by small (1.1 to 3.5 mm dia) buried jet-like gas leaks is examined. The main aspects of the problem, namely, the determination of leak-radiated sound power, the attenuation of air waves in sands and soils, and the measurement of ambient sound pressure levels below ground are explored experimentally under laboratory and simulated field conditions. It is found that there are fairly severe range limitations to detection due to low source strengths and high attenuation rates in soils and sands, even though ambient noise below ground tends to be of a low level. Nevertheless, detection to ranges of 3 m or more is feasible at line pressure above approximately 60 kPa. This capability could be useful in the precise location of leaks once an approximate leak position has been established by other means. Errors in previously published values of attenuation constants in sands are identified.