Cathodic Disbondment Coating

Definition - What does Cathodic Disbondment Coating mean?

A cathodic disbondment coating is a type of protective coating that acts to prevent corrosion on a metal substrate.

Cathodic disbonding is the loss of adhesion between a cathodic coating and its metal substrate due to the products of a cathodic reduction reaction (corrosion reaction) that occurs in the coating's interface.

To prevent cathodic disbonding, cathodic protection (CP) systems are installed that ensure the coating adheres to the metal's surface. Coating disbondment occurs when coatings in a CP system interact either chemically or physically, ultimately causing corrosion beneath the coating.

Corrosionpedia explains Cathodic Disbondment Coating

Cathodic disbondment coatings are useful when cathodic protection systems are not in place or the systems failed to perform. These coatings act as a secondary solution to prevent corrosion due to cathodic disbondment.

In CP systems, a current passing through the metal can free hydrogen atoms, causing coating disbondment. This current passes only through a defect (holiday) in the metal coating, and amount of the current flow depends on the size of the coating defect. If the size of the defect increases, the current forces the coating away from the metal, resulting in a voltage drop at the interface, causing cathodic disbondment. If there is no coating fault, then cathodic disbondment does not occur.

Cathodic disbondment coating performance is much more consistent at thicknesses over 200 µm; therefore, thicknesses less than 200 µm should be avoided to achieve good cathodic disbondment protection.

Factors affecting disbondment include:

  • Thickness of the coating.
  • Formulation of the coating product.
  • Cure percentage.
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