Water Effect on Steel Corrosion under Supercritical CO2 Conditions

Rotating cage corrosion experiments were performed in autoclaves with flat coupons of 2 carbon steels (38Mn6/C75 and X65), with the martensitic steel X20Cr13 (AISI 420), the austenitic-ferritic (duplex) steel X2CrNiMoN22-5-3 (1.4462; S 31803) and the austenitic CrNi steel X1NiCrMoCu 25-20-5 (1.4539, Alloy 904L) in the presence of supercritical carbon dioxide (SC CO₂) and different concentrations of water at 50, 80, 110 and 130^oC. Mass loss  and topographical measurements were used to identify average corrosion rates and local penetrations. While water-free SC CO₂ is not corrosive for all steels tested, water mist saturated with SC CO₂ caused localized corrosion at C-steels, however, not at the CRAs even up to 130°C. A water phase saturated with SC CO₂ yields corrosion rates at C-steels in the order of 5-15 mm/y and mesa-type localized attack in the whole temperature range of 50 to 130°C. Under such conditions also the resistance of 13Cr steel is not acceptable (corrosion rates 0.3 to 0.8 mm/y) and even the duplex steel  and the austenitic CrNi steel surpass the target line of  0.1 mm/y at 110°C.