Compatibility of epoxy coatings in monoethylene glycol solutions: long term evaluation of coating performance

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Long term performance of phenolic epoxy coatings in monoethylene glycol (MEG) mixtures were evaluated by visual observation, degree of blistering and rusting, and pull-off adhesion and electrochemical impedance spectroscopy (EIS). The study investigated the performance of these coatings when immersed in rich and lean MEG solutions commonly encountered in gas production as a hydrate inhibitor. Further, the pH of the test solutions were also varied to simulate different service conditions. This study discussed the process and results of the coating qualification.

The test results showed that both coatings exhibited good barrier performance when immersed in neutral to alkaline MEG solutions for up to 12 months at ambient temperature. However, distinct barrier performance was noted in acidic condition (pH 3.8) which simulated the high concentration of unneutralized organic acids in the rich MEG composition. One coating was significantly more inferior and water ingress was detected as early as few days after immersion from EIS measurements (impedance dropped to below 107 ohm.cm2). Blistering became evident after 4 weeks and surface rust was apparent after 10 weeks. Good agreement between EIS and other techniques were obtained.

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