Corrosion of low alloy steel and stainless steel in supercritical CO2/H2O/H2S systems

• Corrosion of low alloy steel in supercritical CO2/H2O/H2S system was studied.
• A scale consisted of FeCO3, Cr(OH)3 and mackinawite formed on low alloy steel.
• Mackinawite only formed via the solid state reaction.
• Low alloy steel suffered severe general and localized corrosion in aqueous phase.
• 316 L stainless steel suffered pitting corrosion in aqueous phase.

The corrosion of low alloy steel and stainless steel in the dynamic supercritical CO2/H2O/H2S system was studied. A Cr-containing scale, mainly consisted of FeCO3, Cr(OH)3 and iron sulfide (mackinawite), formed on low alloy steel. FeCO3 formed via the solid state reaction and precipitation reaction, while mackinawite could only form via the solid state reaction. In the aqueous phase, low alloy steel suffered severe general and localized corrosion, but 316 L stainless steel suffered pitting corrosion. In the supercritical CO2 phase, localized corrosion was dominant for low alloy steel, and 316 L stainless steel was highly resistant to corrosion.