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.