Improve Your CP System Performance Without Adding Another Anode Bed
If your CP potentials are lower than what you think they should be, there is a good chance that your CP system is protecting a lot more than just the piping.
Pipelines are commonly connected to electrical grounding systems to reduce the effects of unwanted AC or lightning on the pipeline. For example, AC Mitigation systems provide a path to ground to reduce AC that is induced onto the pipeline from overhead high voltage AC power lines. Also, electrical equipment connected to the pipeline must be electrically grounded to meet electrical code safety requirements. And pipe-mounted instrumentation is typically grounded through an instrument panel. Each one of these connections to ground provides a path for CP current to flow from your anode bed back to the rectifier. This means that in addition to protecting the pipeline, your CP system is protecting the grounding system and everything else to which it is electrically bonded.
Protecting a bare metal grounding system requires much more current than protecting a coated pipeline and in many such cases CP systems are not able to maintain adequate potentials for corrosion control. The solution is to install decouplers in the grounding paths between the cathodically-protected pipe and the grounding systems as shown in the figure below.
Decouplers are designed to block CP current while allowing steady state AC, AC faults and lightning to pass freely. This allows your CP system to focus on protecting just the pipe, as it was designed to do, while the pipe remains safely grounded. Since Dairyland invented the solid-state decoupler in 1994, hundreds of thousands of our decouplers have been installed in this way on pipelines around the world with virtually no failures.
Additional Application Assistance
Decoupling Electrical Equipment Grounding Systems