Cathodic protection (CP) and pipeline coatings are the two pillars of corrosion control for buried and submerged pipelines. Neither system is sufficient on its own — coatings reduce the current demand on CP systems by orders of magnitude, while CP protects coating holidays that inevitably develop over time. Understanding how these systems interact is fundamental to effective pipeline integrity management.
How Cathodic Protection Works
CP works by making the pipeline the cathode of an electrochemical cell, suppressing the oxidation reactions that cause metal to dissolve into solution. Impressed current CP (ICCP) systems use an external power source to drive current from ground anodes through the soil to the pipeline. Sacrificial anode systems use more reactive metals (zinc, magnesium, aluminum) that corrode preferentially, protecting the pipeline steel.
Coating Condition and CP Current Demand
A well-maintained, high-quality pipeline coating may require as little as 0.1–1.0 mA/m² of CP current to maintain protection. As the coating ages and holidays develop, current demand increases — a phenomenon tracked by impressed current rectifier output trends over time. Polyurea coatings demonstrate significantly lower coating conductance (higher electrical resistance) than aged epoxy or bituminous systems, reducing CP energy costs throughout the pipeline’s life.
Shielding and AC Interference
Certain coating systems — particularly disbonded polyethylene — can shield the metal surface from CP current, creating protected pockets where corrosion continues undetected. This “shielding” phenomenon is a key driver of stress corrosion cracking incidents on older HDPE-coated pipelines and underscores the importance of choosing coatings with appropriate electrical properties and CP compatibility.
For in-depth technical resources on CP system design and coating compatibility, visit our resources library. Our Corrosion Engineering Working Group hosts quarterly webinars on CP system optimization that are available to all members.