Cathodic disbonding is a type of coating failure that occurs on metal structures protected by a cathodic protection system. It refers to the loss of adhesion between a protective coating and the underlying metal surface. This phenomenon typically starts at defects or holidays in the coating, such as pinholes or scratches, which expose the metal to the surrounding electrolyte (e.g., soil or water). When cathodic protection is applied, an electrochemical reaction occurs at these exposed areas. This reaction generates hydroxyl ions () and sometimes hydrogen gas () at the metal-coating interface. The buildup of these byproducts, particularly the alkaline environment created by the hydroxyl ions, weakens the adhesive bond between the coating and the metal. The hydrogen gas can also create pressure, further pushing the coating away from the surface.
