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

In the context of high-pressure, high-temperature (HPHT) conditions resembling those in the oil and gas industry, the performance of epoxy-siloxane hybrid coatings is investigated. Neat amine-cured epoxy novolac (EN) coatings exhibit drawbacks under these conditions, including softening upon exposure to hydrocarbons, leading to underfilm corrosion triggered by CO₂ gas and seawater ion diffusion. To address these issues, two hybrid coatings, long-chain epoxy-terminated polydimethylsiloxane-modified EN (EN-EPDMS) and short-chain 3-glycidyloxypropyltrimethoxysilane-modified EN (EN-GPTMS), are assessed in HPHT environments. Both hybrids mitigate drawbacks observed in neat EN, with EN-GPTMS completely eliminating them due to the chemical inertness of inorganic siloxane networks. While EN-EPDMS exhibits a higher glass transition temperature than EN-GPTMS, it is susceptible to rapid gas decompression due to its lengthy and flexible siloxane backbone, resulting in unburst blisters. Conversely, EN-GPTMS demonstrates superior performance in HPHT environments, highlighting its potential for effective corrosion protection in harsh conditions encountered by the oil and gas industry.