Monday, April 25, 2011

Cathodic Disbondment Testing

Cathodic Disbondment Testing is used to evaluate the long-term performance of barrier coatings (such as paint, epoxy etc.) used to protect metal pipe going into underground applications.

Cathodic delamination can be defined as the destruction of adhesion between a coating and the coated surface, caused by products of a corrosion reaction.

This basically means the coating delaminates or lifts and separates from the substrate, even though it exhibits good adhesion prior to exposure service conditions.

Experience in the oil and gas industry has clearly shown that coatings with better cathodic disbondment resistance (less disbondment), have better corrosion resistance and greater longevity. Cathodic disbondment is often selected as the key performance test for adhesion, as it simulates field conditions for disbonding of a coating from a pipeline. Some of the test methods can also use applied to coated rebar. Here are a few examples of standards we can test for:

ASTM G8 Involves having the pipe samples immersed in electrolyte at ambient conditions, common anode placed in electrolyte for all samples

ASTM G42 Is the same as G8, except the pipeline coating samples are subjected to elevated temperatures

ASTM G80 Is the same as G8, except that no options for variables are presented

ASTM G95 Is an attached cell method, a plastic cell is attached to the coated panel or pipe, filled with electrolyte, CP applied with individual fretted tube anode.


In Canada, the CSA standards call up these same methods, with the exception that they also provide pass/fail criteria. The electrolyte is a mixture of various salts including NaCl, KCl and sodium bicarbonate, depending on the test method.