UV degradation of fusion bonded epoxy coating in stockpiled pipes

Abstract

Sunlight exposure is known to cause degradation in polymer coatings. However, quantitative data relating exposure to mechanical and corrosion properties is missing. Thus, it is very difficult for pipeline operators to make fair assessment of the impact of stockpiling coated pipe on project economics and pipeline integrity. As a result, a study was undertaken to quantify the effects of sunlight exposure on Fusion Bonded Epoxy (FBE) coating on stockpiled pipe. Sections of production pipe stockpiled in the southern Alberta area for the Alliance Pipeline project was selected, and a plan to evaluate the coating properties at periodic exposure intervals, to a total duration of approximately 2 years was implemented. The coating was tested at both full sunlight exposure condition (12 o'clock position) and with minimal exposure condition (6 o'clock position). The properties evaluated include residual coating thickness, cathodic disbondment, adhesion, flexibility, and impact. These tests were carried out following procedures in CSA Z245.20-98 standard. Results after 15-21 months of aging indicate that the coating with full sunlight exposure, had a reduction in thickness, flexibility and loss of gloss with chalking due to degradation of the FBE coating by the UV radiation. However, there were no significant differences for cathodic disbondment, adhesion, and impact properties compared to the 6 o'clock position.