Influence of CO₂ at HPHT Conditions on the Properties and Failures of an Amine-Cured Epoxy Novolac Coating

Using a three-phase batch reactor with coated steel panels, this investigation studies the influence of carbon dioxide (CO₂), present in the gas phase at conditions of high pressure and high temperature (HPHT), on the degradation of an amine-cured epoxy novolac (EN) coating. The combined effect of the gas, hydrocarbon, and seawater phase compromises the coating and leads to underfilm corrosion. Consequently, an understanding of the role of each of the phases is essential for the effective design of superior epoxy-based coatings for HPHT applications in the petroleum and other industries.

The results demonstrate that para-xylene, representing the hydrocarbon phase at HPHT, initiated glass-transition temperature depression with subsequent softening of the EN network. This allowed the dissolved CO₂ gas to diffuse into the EN network, thereby generating pinholes at the coating surface. The pinholes further aided the seawater ions at its hydrocarbon−seawater interface to diffuse into the EN network to the steel substrate, imposing underfilm corrosion. The findings are of high relevance to design superior epoxy-based coatings not only for the petroleum industry but also for the protection of transport pipelines and process equipment in the next-generation carbon capture and storage technologies.