What Does Disbonding Mean?
Disbonding is the failure of a coating to adhere to the substrate to which it was applied. It is a loss of adhesion between a cathodic coating and its metal substrate due to a cathodic reduction reaction (corrosion reaction) taking place.
The purpose of cathodic protection (CP) systems is to prevent corrosion in metals. The primary reason for any coating disbonding is a chemical or physical interaction of the coating material in a cathodic protection system, which ultimately causes corrosion beneath the coating.
Disbonding is also known as cathodic disbondment.
Corrosionpedia Explains Disbonding
In cathodic protection (CP) systems, the coating disbonding from a metal surface may occur because an electric current passes through the metal surface that needs to be protected, which frees up the hydrogen atoms that cause the coating disbondment. Here the current passes through any faults, cracks or defects in the metal coating. The amount of current flow through a defect or fault depends on the size of the coating fault. As the size of the fault or defect increases, the current forces more coating away from the metal. This results in a voltage drop at the interface and causes cathodic disbondment. If there are no defects in the coating, then cathodic disbondment does not occur.
Cathodic disbondment protection shows a much more consistent performance when the coating thickness is over 200 microns; therefore, coating thicknesses less than 200 microns should be avoided to achieve good cathodic disbondment protection.
Factors affecting disbondment:
- Coating thickness
- Formulation of the product
- Cure percentage