Nace CP 1, Course Manual

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Troubleshooting 9:3
CP 1 – Cathodic Protection Tester Course Manual
©
NACE International, 2000
07/01/04
Figure 9.2 Locating a Short Through Current Flow
Tone Generator
Audio tone pipe locators are very useful for finding shorted isolating
fittings or underground contacts. The transmitter creates a low frequency
signal that is carried to the pipe through test wires. The signal creates an
electromagnetic field around the pipe. The receiver picks up this field. The
signal will travel only along electrically continuous paths.
Use caution when connecting and disconnecting this type of locators as
high voltages may be involved. Also, do not use this type locator in an
explosive atmosphere as a spark might cause ignition.
The transmitter is connected between the pipeline and a suitable ground
such as a steel post, probe bar, etc. If a service line is shorted, the signal
will travel up the line and across the isolating fitting. If an underground
contact exists, the signal will generally be lost on the pipeline under test at
this point and will be found on some other structure, often running at an
angle from the pipeline. Figure 9.3 shows a typical situation.
Short
Clamp-On
Ammeter on
Service Line
CP Current