Inhibition of Steel Corrosion under Aqueous Supercritical CO2 Conditions

A water phase in equilibrium with supercritical CO₂ (SC CO₂) proved high corrosiveness not only for carbon steels but also for CRAs, specifically at temperatures around 110°C. Rotating cage corrosion experiments were performed with 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 water saturated with CO2 und supercritical conditions to study the performance of corrosion inhibitors (oleic acid-based imidazolines, quaternary ammonium salts and alkenylsuccinic acid anhydrides) at 50, 80, 110 and 130^oC. Mass loss  and topographical measurements were used to identify average corrosion rates and local penetrations. It appeared that the corrosion inhibitors applied were effective not only at the carbon steels but also at the CRAs. Critical corrosion rates encountered at 110°C in the absence of inhibitors (13 Cr steel: 0.3-0.8 mm/y; duplex steel: >0.1 mm/y; austenitic CrNi steel >0.1 mm/y) could be reduced with inhibitors to very low corrosion intensities (< 0.04 mm/y). However, none of the inhibitors could reduce the corrosion rates at carbon steels below the 1 mm/y target line.