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

Abstract

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. Upon exposure to the three phases individually, at a low pressure of N2, the EN network remained unaffected and impervious. However, in the hydrocarbon-exposed zone, a combination of para-xylene, representing the hydrocarbon phase, and CO2 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 seawater-exposed zone, in the presence of CO2 at HPHT, suffered from increased seawater ion diffusion, leading to blister formation. Moreover, the most detrimental subzone for the EN network was when CO2, para-xylene, and seawater were synergistically interacting at its hydrocarbon–seawater interface. This combination resulted in an increased chain motion of the EN network, subsequently allowing CO2 and seawater ions to diffuse into the EN network to the steel substrate, imposing underfilm corrosion. In the absence of CO2, blisters were formed at the interface subzone, but no corrosion was detected. The results are of high relevance to the petroleum industry but also for the protection of transport pipelines and process equipment in the next-generation carbon capture and storage technologies.

Protective Mechanisms of Siloxane-Modified Epoxy Novolac Coatings at High-Pressure, High-Temperature Conditions

“…The hydrocarbon-exposed zone, where the softening of the neat EN networks, due to para-xylene interactions, was reported is of utmost importance in the present study. In contrast to the softening effect that lowered the T g at the hydrocarbon exposed zone of neat EN by 20 °C, the addition of the siloxane backbone into the EN network resisted the nonpolar para -xylene interaction significantly. The average T g value at the hydrocarbon-exposed zone was measured to be 156 ± 2 and 157 ± 3 °C for EN-GPTMS and EN-EPDMS, respectively.…”

“…To simulate HPHT conditions, an enclosed batch reactor (0.97 L autoclave chamber), procured from Parr instruments, was utilized. , A mixture of N 2 and CO 2 as the gas phase, para -xylene (200 mL) as the hydrocarbon phase, and 3.5% NaCl solution (400 mL) as the artificial seawater phase constituted the HPHT phases inside the reactor chamber as depicted in Figure . The completely cured EN-GPTMS and EN-EPDMS panels were placed vertically inside the chamber.…”

“…Normally, high-performance anticorrosive epoxy coatings protect the inside of wells, storage tanks, and pipelines. Due to their strong metal adhesion, high chemical resistance, and suitable processing characteristics, two-component epoxies are widely used as protective coatings in the heavy-duty industry. , However, recent studies on degradation pathways for an amine-cured epoxy novolac (EN) coating at HPHT confirmed an initial hydrocarbon interaction (softening), which significantly lowered the network T g and accelerated the diffusion of CO 2 gas and seawater ions into the EN network, subsequently triggering underfilm corrosion. , To sustain the extremity of HPHT conditions, these unfavorable attributes of EN coatings demonstrate a need for improvement. For the past two decades, silicon derivatives have been used in coatings as modification (or coupling) agents and cobinders (cross-linkers) to improve the chemical resistance, solvent resistance, thermal stability, and flexibility of the cured coating system. − Due to the polyfunctional siloxane (Si–O) bond present in the backbone chains of a silicon derivative, silanes and silicones have gained immense commercial importance.…”

Lignin Phosphate: A Biobased Substitute for Zinc Phosphate in Corrosion-Inhibiting Coatings

“…Anticorrosive coatings are widely used to protect metal substrates from the process of corrosion. − Based on the mechanisms they employ to prevent metal corrosion, anticorrosive coatings can be classified into three types, i.e., barrier, , sacrificial, , and inhibitive. , Anticorrosive coatings with an inhibitive mechanism, accounting for approximately 20–25% of the overall anticorrosive coatings market, utilize special pigments to induce passivation of the underlying metal, resulting in the formation of a protective layer (also known as a passivating film) comprising insoluble metal compounds. This layer acts as a barrier, impeding the transport of corrosive substances to the metal surface.…”

CO2 permeation through fusion-bonded epoxy coating in humid environments

“…The increasing demand for energy has driven oil and gas producers to extract fossil fuels in challenging environments, where the conditions can have a significant impact on the design of coating systems for metal infrastructure such as pipelines [1]. This is especially true in the presence of water and carbon dioxide, where CO2-rich environments can greatly increase the rate of uniform corrosion and pit formation [2]- [4].…”