Listening At Low Frequency Key To Locating Leaks In Plastic Water Pipes
Recently completed research at IRC, which was jointly funded by NRC and the American Water Works Association Research Foundation, will help water utilities worldwide to locate leaks in plastic water-distribution pipes. Water utilities typically use acoustic detection equipment to locate leaks. Although this equipment is generally satisfactory for metal pipes, its effectiveness for plastic pipes was not known.
The research showed that leaks in plastic pipes can be located using acoustic techniques, however, there are several difficulties inherent in this approach. For example, leak correlators rarely succeeded in locating simulated leaks when operated in automatic mode since the frequency range selected by the correlator was usually too high. Operators using the correlators in manual mode also tended to select a high frequency range. As a result, leaks were missed because leak signals in plastic pipes are dominated by low frequencies.
The researchers identified several improvements in field procedures and equipment that will increase effectiveness. These include:
- Revising automatic-mode algorithms to take into account the limited low-frequency content of leak signals.
- Using accelerometers with greater sensitivity.
In addition, the researchers established guidelines for the frequency guidelines for the frequency range for both hydrophones and accelerometers. Researchers used acoustic leak-detection equipment for the project — both traditional listening devices and state-of-the-art leak-noise correlators (portable computerized instruments that locate leaks by comparing leak-induced signals measured at two points — on either side of the leak).
Five professional leak-detection teams from utilities and service companies throughout North America participated in blind leak-detection tests. The tests involved locating simulated leaks without prior knowledge of their location. The researchers also investigated the effect of leak type, flowrate, pipe pressure and signal processing, as well as the acoustic characteristics of leak signals.