The pipeline industry is very collaborative in terms of cathodic protection, as everyone’s protection systems can affect each other’s assets detrimentally and end up inadvertently causing corrosion. Therefore, when a water authority wanted to increase the current output of their protection system, and hence increase risk of interfering with other asset owners in the area, they contacted the gas authority for that area. It was previously identified through prior testing that the lower output that the system was running at was causing unacceptable levels of corrosion and hence a bond was installed making the water and the gas mains continuous.
Collaborative investigation into what the consequences of increasing the water systems current output to 10 Amps would be, found that the gas pipeline drained almost all of the additional protection current. The protection levels on the gas pipeline, however, remained fairly unchanged and unprotected to the -850mV criterion in AS2832.1:2015. The 10 Amps of current drained to the gas main would be expected to improved potentials quite substantially, especially close to where the current was being picked up from the water pipeline. This was however not the case. Why? The suspicion was formed that there was an electrical fault along the gas pipeline that was earthing any current being supplied to the gas main from the water main to earth and was hence not protecting either the gas or water main as intended.
To determine where, what and even if this electrical fault existed a coiling survey was undertaken. A coiling survey consists of a signal being applied to the pipeline in question and an experienced technician tracing this signal along the path of the pipeline. As the technician is following the signal, if it attenuates suddenly or goes off in an unexpected direction, this can indicate a fault. In this case the signal diverted from the expected path of the gas pipeline, and was found to follow a copper fire service to a motel. This indicated that the suspected fault had been found, and that the problem was the gas main and fire service touching underground and hence earthing all of the protective current from the gas pipeline and, by the same token, the bonded water pipeline.
To confirm and rectify this issue the fault location was excavated, and, indeed the fire service and the gas main were found to be touching and the electrical fault was confirmed. Refer to picture below. The gas main was uncovered and shown to have a very good coating, which the only exception being around the copper pipe, where the coating appeared to have been damaged during its construction. At this point the pipes were prized apart with wooden wedges to separate them from each other. It was found that the copper service had a small hole in it which was weeping water at the area of contact between the gas and the copper pipeline. Since this pipe was a fire service the damage had to be repaired within 2 days to ensure the integrity of the emergency system in case of a fire. The decision was made that the best way to simultaneously fix the fire service, separate the pipes and also give enough clearance to repair the coating on the gas main would be to reroute the copper fire service with 45 degree bends around the gas main. The gas main was wrapped in Denso and then a PVC plastic tape.