Disbondment Mechanisms for a Heat Shrink Polyethylene Coating on a Cathodically Protected Hot Pipeline

Interfacial adhesive failure of a pipeline coating was found to be related to the operating temperature of the pipeline, the presence of moisture at the coating/steel interface and cathodic polarisation of the steel. The application of cathodic protection was found to be more detrimental to a pipeline coating than was the immersion of the coating specimens in alkaline environments without polarisation. It is suggested that in the system examined cathodic disbondment is initiated at a coating holiday by the electrochemical reduction of Fe3O4 in the interfacial oxide film and that propagation of the disbondment is associated with electrocapillary action which reduces the surface tension between the steel and the crevice solution. This process increases the thermodynamic disbonding force between the adhesive and the steel in the aqueous environment.