Techniques for testing and monitoring the cathodic disbondment of organic coatings: An overview of major obstacles and innovations

Coatings in conjunction with cathodic protection (CP) have been widely used for protecting buried metallic structures such as steel pipelines against corrosion. A drawback of the combined use of these two techniques is cathodic disbondment of coatings, i.e. the loss of adhesion between a coating and its metal substrate due to the products of cathodic reactions that take place at the coating and metal interface. Disbonded coatings provide easy lateral paths for corrosive species to reach the metal surface while simultaneously shielding cathodic protection currents from reaching the metal substrate. Currently, corrosion under disbonded coatings remains as a major issue affecting the integrity of civil and industrial infrastructures such as buried pipelines; therefore the ability of testing and monitoring coating disbondment is important for ensuring the durability of these infrastructures. This paper provides an overview of major innovative efforts made over the past several decades to overcome technical obstacles in testing and monitoring the cathodic disbondment of coatings. The limitations of various techniques including the standard cathodic disbondment test (CD test), electrochemical impedance spectroscopy (EIS), localized electrochemical spectroscopy (LEIS), scanning Kelvin probe (SKP) and scanning acoustic microscopy (SAM), have been critically reviewed. The recent application of multi-electrode array method has been discussed to illustrate an innovative approach aimed at addressing major difficulties in the in situ measurement and monitoring of cathodic disbondment of coatings.