Reason Analysis of 3PE Coating Delamination from Pipeline

The reasons for delamination of anti-corrosion coating with and without damages from pipeline in southwest China were analyzed. Firstly, field survey was carried out to preliminarily determine the main reasons for coating delamination, and then electrochemical tests were used to analyze the diffusion process of electrolyte on coating/metal interface, meanwhile differential scanning calorimetry (DSC) was applied to obtain the glass transition temperature of coating with and without delamination. The results show that the main reason for damage of coating was due to the diffusion of electrolyte on coating/metal interface. And the diffusion process could be divided into three stages: formation of corrosion crevice, oxygen concentration corrosion and hydrogen evolution process. When the glass transition temperature of epoxy coating was too low to obtain sufficient adhesion to the substrate, the coating was intact but delaminated in large area.