Pipelines are commonly exposed to over-voltage conditions created by AC faults, lightning and induced AC voltage from high voltage power transmission lines. To protect personnel and the pipeline from the hazardous effects of these conditions, it is critical to properly ground the pipeline and provide continuity across isolation joints for AC and lightning. In addition, structures protected by cathodic protection (CP) systems must be isolated from ground for DC current in order for the CP systems to remain effective.

Solid-state decouplers are commonly used to provide over-voltage protection and simultaneous DC isolation from ground on CP-protected structures. Proper application can ensure protection of personnel from safety hazards and equipment from permanent damage.

This paper will review the common applications for over-voltage protection on pipelines, including isolation joint protection, mitigation of induced AC voltage and protection from exposure to AC faults and lightning. A brief description of solid-state DC decoupler devices, their operation, key performance characteristics and application guidelines will be presented, as well as that for selected alternative technologies. Specific examples will be presented of damaged insulators, compromised CP systems and fire resulting from lighting and AC fault occurring on unprotected isolation joints.