Effect of contaminants on FBE performance

Fusion bonded epoxy (FBE) external coatings have been used since early to middle 1960s. Since that time, improvements have been made and the acceptance of this type of coating has grown to the point to become the most used coating for new construction. Close attention must be paid during the application. That is the reason, in many cases, FBE is the only coating for which pipeline company representatives will always be present to inspect the application. Although improvements have been made, the effect of all possible contaminants on the performance of FBE has not been studied. The presence of contaminants on pipe surface will reduce the life time of the coating due to reduction of adhesion and increase of cathodic disbonding. This paper describes a study on the effect of contaminant on the FBE performance. Several variables were considered in this investigation: presence of varnish or previous coating on the pipe, phosphoric acid treatment, water and grit or shot quality. The presence of contaminants on the pipe surface was identified using EDAX (X-ray energy dispersion analysis), optical and electron microscopy analysis, grit and water conductivity and acid wash location. The results indicate that all varnished pipes presented high cathodic disbondingmore » (above 17 mm). This high cathodic disbonding was attributed to varnish particles located on the anchor pattern of pipe surface. It was also found that the phosphoric acid application after the blasting section gives better adhesion and lower cathodic disbonding. This has been attributed to the surface active pattern provided by the acid that gives better interaction between the pipe surface and FBE.« less