Pipelines and storage tanks are commonly bonded to electrical earthing systems to reduce the effects of unwanted AC voltage and lightning on the structure. These connections to earth provide a potential path for cathodic protection (CP) current to flow from the anode bed back to the rectifier. Thus, in addition to protecting the structure, the CP system protects the earthing system and everything else to which it is electrically bonded. In many such cases, CP systems are not able to maintain adequate potentials for corrosion control.

The solution is to install DC decouplers in series with the bonding connections between the cathodically-protected structure and the earthing systems. Decouplers are designed to block CP current while allowing steady state AC, AC faults and lightning to pass freely. This allows the CP system to focus on protecting just the pipe, as it was designed to do, while the pipe remains safely earthed.

This paper will review solid-state decoupler devices and how they are commonly applied in conjunction with CP systems, including induced AC mitigation, protection from exposure to AC faults and lightning and DC isolation from electrical equipment earthing systems.