Because PVC is a non-magnetic and non-conductive material, direct location by magnetic and electronic means is not possible. Several techniques are appropriate.
Metal Detectable Tapes
The use of metal detectable tapes is now common. These offer the dual facility of a colour-coded early warning visual marker during excavation and traceability of the pipe when the precise location is not known.
The tape is placed on top of the pipe surround material and can later be located by using simple metal detectors operating in the 4 – 20 MHz range at depths ranging to 450 – 600 mm depending on equipment.
Trace Wires
Trace wires are useful where pipes are buried significantly deeper. The trace wire is usually laid under the pipe, to avoid damage, and when a suppressed current is applied it can be detected at depths up to 3 metres using commercially available inductive detectors.
Suitable trace wires are the vinyl-coated single copper wire conductors for conveyance of an electric current. Disadvantages of the system are that both ends of the wire have to be accessed to apply the current, and if the wire is broken the system cannot be used.
Audio Detection
Several excellent audio leak detectors are now available. One type requires an acoustic signal to be introduced to the pipe at some convenient location, e.g. a hydrant. A tuned detector is then used to locate the pipeline. These units are still effective with high background noise levels.
A second type picks up the sound of turbulence from flowing water in the pipe. This must be done in the absence of extraneous background noise, particularly traffic sounds. Skilled operators can also pinpoint the location of fittings. The equipment can also be used for detecting underground leaks.
