Cathodic shielding occurs in cathodic protection systems where a protective coating or material prevents cathodic current from reaching the surface of a buried or submerged metal structure, such as a pipeline or storage tanks. In a cathodic protection system, current is applied to prevent corrosion by making the protected structure a cathode. However, if a coating, such as polyethylene tape or certain epoxy layers becomes disbonded or damaged, but remains intact over the metal surface, it can trap water and corrosive elements underneath while also acting as an electrical insulator. This creates a shielded area where the cathodic current cannot penetrate to stop corrosion. Because the current cannot access the metal beneath the coating, the protective mechanism of the cathodic system fails in that region, allowing localized corrosion to occur unchecked. This can lead to serious integrity issues, especially in buried pipelines or marine structures, where such damage may go unnoticed until failure occurs. Cathodic shielding is a major concern in pipeline integrity management, and mitigating it often requires using coatings that are either compatible with cathodic protection or selecting materials that do not shield current if disbondment occurs.
