Long-Term Corrosion Behavior of Cr Alloyed Steels in Aqueous CO2/H2S Environments Containing Chlorides

The present study was designed to evaluate the long-term corrosion behavior of 3Cr and 13Cr steels in a single-phase flow environment containing aqueous carbon dioxide (CO2), hydrogen sulfide (H2S), and dissolved chlorides (Cl-). Long-duration tests, each lasting 40 or 100 days, were conducted using a flow loop equipped with a Thin Channel Flow Cell. The experimental setup aimed to replicate field conditions with varying H2S concentrations over time and included surface conditioning in NaCl brine before exposure to the corrosive solution. The results indicated that 3Cr and 13Cr steels exhibited different uniform and localized corrosion behaviors. The 3Cr steel exhibited average corrosion rates ranging from 0.03 to 0.12 mm/y, depending on specific test conditions and H2S concentrations. A beneficial effect of preconditioning was noted, potentially related to the formation of corrosion product layers with higher amounts of chromium rich oxides. However, localized corrosion was found in 3Cr steel when exposed to an increased H2S concentration of 100 mbar, even if its surface was preconditioned and the H2S concentration was increased gradually throughout the test duration. The 13Cr steel demonstrated a more stable corrosion rate, maintaining an average rate of approximately 0.01 mm/y, even with increased H2S content. However, minor localized corrosion was still detected at low H2S concentrations.