CASE STUDY: CP NOT WORKING!
In Texas, many municipalities require cathodic protection (CP) to be installed on metallic waterlines to typically include ductile iron, steel, and concrete pipe. And because of the considerable cost involved, many of the municipalities check or monitor the CP systems periodically to make sure they are protecting the pipe from corrosion that could result in a leak of possibly millions of gallons of processed water. In general, because water is not specifically regulated by any government agency, the need and schedule for monitoring is determined by the municipality.
During one such survey to monitor the CP system by a major Texas city, Technicians measured levels for the CP system that were not consistent with historical performance. The reason was soon discovered, but the cause was a little more elusive.
The water line in question utilized an impressed current CP system to provide protection from corrosion. One of the components used in this type of system is an external electrically powered device referred to as a rectifier. It is essentially a heavy-duty power supply for the system. In this case, the rectifier (through troubleshooting) was found to be the source of the problem. The aforementioned troubleshooting identified a damaged cable that is intended to complete the return path for the CP current. Apparently, the cable in question had been damaged during a refurbishment of the landscaping on and around the area of the waterline, specifically the installation of a bike path. While the exact details resulting in the damage have yet to be revealed, or even the exact cause, methodical troubleshooting found that the cable in question had been re-routed, presumably by a contractor, from the original connection at the waterline to an electrical utility pole ground cable.
This did not fix the problem. The contractor incorrectly identified the damaged cable as a ground cable.
For context, this cable is not related to any alternating current (AC) power source. As a result, the damaged cable does not present a shock hazard, or would anyone necessarily realize an immediate result of the cut cable such as a loss of power at a business or a residence. The result does, however, prevent the waterline from being protected from failure due to corrosion.
Although the necessary repair for the damaged cable will be at a considerable cost the typical question is always, “How could this have been avoided?” “Who is at fault?”
The short and most obvious answer is the contractor. The contractor should have contacted the appropriate agency for a dig check before excavating. But there is additional blame to go around. The municipality could have advised the contractor of the existence of the CP system, if they didn’t. Also, they should have provided an inspector to observe the excavating around the waterline. But ultimately the contractor, according to available records, did not notify the municipality of the incident, probably because of results previously cited. And while accidents happen on many projects with various trades the liability as well as the resulting consequences requires proper reporting for the damage, or full time inspection on behalf of the municipality.
Final assessment, repairable and the CP system can be returned to service to protect the municipality utilities.
The prolonged continuous solution would involve development of a periodic inspection program at a regular interval to verify the CP system(s) are operating and providing continuous protection from corrosion failures.
