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Copper grounding has a detrimental effect on the cathodic protection (CP) of interconnected underground carbon steel piping. The copper can consume large amounts of protective current as well as introduce significant measurement errors when verifying the protection level of the piping. This article examines the interactions between copper grounding and pipeline systems, as well as a cost-effective solution to the problem. An actual case study is presented confirming that silicon iron can be used to replace copper electrodes, resulting in effective electrical grounding with minimal impact on CP systems.
High-pressure natural gas compressor stations routinely utilize a grounding system consisting of heavy-gauge bare copper wire that is installed during construction. In lieu of detailed calculations, grounding systems are often based on the assumption that mote is always better.
The compressor station in this case study is located on a high-resistivity shale formation. The copper grounding system was in a grid configuration with a spacing of -2 m (6.6 ft) throughout the plant. All plant piping and electrical equipment were bonded to the copper grounding system.
This system met the objectives of the local Electrical Safety Authority because it established an effective, long-lasting, and safe grounding system to guard against lightning strikes and electrical faults. The plant is located in the vicinity of two 230- and 500-kV power transmission lines, which in part run parallel to the outgoing pipelines from the plant. Calculations indicated that the largest fault currents would be transmitted to the plant via the pipelines if the power transmission system faulted where the two systems share a common right of way. The grounding system also provides protection against step-touch potentials around the many aboveground appurtenances.
Effects of Copper on Cathotlic Protection Systems
This particular arrangement of electrical grounding creates a problem for cathodic protection (CP) systems installed to protect the underground piping.1 As depicted in Figure 1, copper in aerated soils requires very large cathodic current densities to polarize to the potential required to protect carbon steel (CS).2
In addition, the couple of copper to CS precludes the use of the 100 m V depolarization criterion3 because of the different electrochemical characteristics of copper and steel. As such, in order to ensure CP of underground piping that is coupled to copper grounding...