Maximum distances between the transmitting and receiving stations are approximately 1.61 km (1 mile), although the length of pipeline monitored can be twice this using a single transmitter and one receiver on each side (since the signal travels in both directions). The instrumentation is relatively simple, consisting of (1) a transmitting station with a frequency-stable more » oscillator and amplifier and (2) a receiving station with a filter, lock-in amplifier, frequency-stable oscillator, and remote reporting device (e.g. Electrical connections to the pipeline can be made through existing cathodic protection (CP) test points without the need to dig up the pipe. The IACC method was shown to be a viable method that can be used to continuously monitor pipelines for third-party contact. Third-party contact to the pipe that breaks through the coating (thus resulting in a signal path to ground) changes the signal received at the receiving stations. The signal voltage between the pipe and ground is monitored continuously at receiving stations located some distance away. The impressed alternating cycle current (IACC) pipeline monitoring method developed by Southwest Research Institute (SwRI) consists of impressing electrical signals on the pipe by generating a time-varying voltage between the pipe and the soil.
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Because this type of damage often goes unreported and can lead to eventual catastrophic failure of the pipe, a reliable, cost-effective method is needed for monitoring the pipeline and reporting third-party contact events.
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Third-party contact with pipelines (typically caused by contact with a digging or drilling device) can result in mechanical damage to the pipe, in addition to coating damage that can initiate corrosion.