Epoxy coatings for anticorrosion challenges :a link between chemistry and performance ?

摘要

Epoxy coatings have been used extensively for pipeline protection in the oil and gas industriesrnover the past decades [1]. Thank to their outstanding adhesive properties, epoxy resins arernclassically used for external coating of offshore pipelines although cathodic protection isrnapplied. They provide corrosion protection while being used as neat coating or as primer layerrnin a three-layer coating. Protection of internal pipelines devoted to gas transport is anotherrnapplication of epoxy coatings. Whatever the case, the choice of the right epoxy formulationrnshould be adapted to the service conditions, namely exposition medium and temperature, inrnorder to provide efficient and sustainable corrosion protection.rnEpoxy resins constitute a wide family and classical formulations may not fulfil thernrequirements of today's challenges: as pipelines are required to operate in more and morerndifficult conditions, coatings are expected to function in higher temperature conditions ;rnadditionally, practical conditions such as temporary injection of methanol make thernenvironmental exposure of the epoxy coating harsher. Therefore, there is a need of a betterrnknowledge of technical performance and limitations of high temperature epoxy resins.rnThis paper examined the influence of the epoxy network architecture on their protectionrnproperties and durability while exposed to distilled / sea water at 110 ℃ and to methanol atrnroom temperature. The objective was to investigate the link between resin chemistry and finalrnperformance with respect to anticorrosion applications. Five epoxy resin formulations mixedrnin stoichiometric proportions were cured & post-cured to infinite extent in order to achieverndensely cross-linked networks exhibiting controlled and reproducible architectures.rnGravimetric and pressurised differential scanning calorimetry (DSC) measurements werernperformed to evaluate the plasticization effect of both water and methanol on formulationsrnunder study. The related depressions of glass transition temperature were somewhat surprisingrnwhile evaluated by in situ technique in comparison to classical dynamic mechanical analysisrndata. Besides, the coating performance under severe exposure conditions during 3000 hoursrnwere investigated by EIS. Laboratory results were presented and analysed: the benefits andrnlimitations of the use of plasticised Tg values (not initial Tg) as key parameters for thernprediction of coating performance were discussed.