Xmic
24/01/05
MAN-095-0001 Revision B
© Palmer Environmental Ltd 2005
Page 17
Guidance to Effective Acoustic Leak Detection
All acoustic leak detection methods are based on the premise that normal water
passage through pipelines takes place noiselessly. When the water passage is
disturbed a noise is created. Causes can include partial pipe blockages, sudden
changes in pipe diameter, abrupt changes in pipe direction, pumps or meters
installed in the pipeline, consumer usage or pipeline damage. Pipeline damage can
include holes, cracks or splits, complete pipeline rupture, leaking joints or leaking
valves.
Careful application of leak detection techniques will enable the operator to eliminate
detected noises generated by poor pipeline design or consumer usage and to identify
leakage due to pipe system damage.
The strength and clarity of noise generated by leaks will be affected by the water
pressure, the size and shape of the orifice allowing leakage, the type of ground
material around the pipeline, the type of ground cover over the pipe, the diameter,
wall thickness and material of the pipeline and the quantity of water leaking.
A small orifice or hole and high water pressure generally produces a higher
frequency noise. Often the noise level increases around valves, pipe elbows, T-
connections and pipe ends, etc… since the partial obstruction increases pressure and
creates some further disturbance in the water path.
Leak noise is transmitted along the pipeline both through the water and the pipe wall
as well as into the ground around the pipe. The noise travels much better through
"hard" materials: further along metallic pipes than asbestos cement pipes which
themselves are better than plastic pipes. Ground material generally provides a
poorer travel path than the pipeline itself. Soft sandy ground provides a worse travel
path than well compacted ground with a hard paved surface covering.
The leak noise can change in strength and pitch as it travels along the pipe or
through the ground. The deeper the pipe is buried and the softer the ground the
more the noise will be dampened.
When a leak is produced in a metallic pipe the leak noise will transmit well through
the pipe. It does not travel so well through a plastic pipe. This means that a leak