Page 305 - Water Loss Control

274 Cha pte r S i x tee n

Digital Correlating Leak Noise Logger
The next step in noise logger technology was the devolvement of digitally correlating
leak noise loggers, which combine acoustic noise logging and leak noise correlation.
This technology has the advantage of reducing the time span between identification of
a leak noise and localization of a leak. Nevertheless, it is still highly recommended that
the exact location of the leak be verified by a trained leak detection specialist using a
ground microphone before excavating for the leak repair.

16.4.2 Nonacoustic Leak Detection Equipment

Tracer Gas
Water insoluble gas such as helium or hydrogen is inserted into an isolated segment of
a water pipe. The gas escapes at the leak and permeates to the surface where it can be
detected by using a highly sensitive gas detector. Solid surfaces such as concrete slow
the process of gas permeating to the surface. Tracer gas is an option used for transmis-
sion mains, on low pressure mains where the acoustic sounding is difficult and for leaks
on small plastic pipes on house connections. This technique is also used to validate
watertight construction of new water mains before they are commissioned into service.
A disadvantage of this technique is that water pipelines must be removed from active
service in order to apply this method.

Ground Penetrating Radar
Ground penetrating radar identifies water leaks by detecting cavities around the pipe
created by the leak, detecting the presence of water around the pipe stemming from the
leak, or through the observation of disturbed ground caused by the leak. This technol-
ogy is not in wide use because of its relatively high logistical requirements and related
cost. However, it can be a highly effective tool in situations such as low pressure or
plastic pipe leaks where very little sound is generated and sonic leak detection is not
possible.

16.4.3 Leak Detection Equipment for Transmission Mains
The general difficulty one faces when trying carry out a leak detection survey on a
transmission main is the long distance between fittings that can be used as sounding
contact points and the fact that the leak sound decreases with increasing pipe diameter
and increasing distance from the leak.

Sensors Inserted into the Transmission Main
One type of leak detection equipment developed for transmission mains uses the princi-
ple of a sensor (different manufacturers use different types of sensors) being inserted in
the transmission main, which then travels along with the flow in the pipe picking up any
noise generated by a leak. The use of inline transmission main leak detection service is
proving to be very accurate. It is still a new technology in North America but has a well-
established history in the United Kingdom. This technology is expected to be more widely
embraced in the North American water utility industry in the near future.
Fiber Optics
Another type of technology utilizes acoustic fiber optics for managing and monitoring
large diameter mains. A continuous fiber optic cable is installed in the pipeline and the