Influence of H2S on the Cyclic Polarization Behavior of 316L Stainless Steel in Oilfield Brines

Cyclic polarization measurements were conducted for 316L stainless steel (SS) in a simulated oilfield brine under conditions close to the pass/fail boundary for pitting and stress corrosion cracking of the material but at different partial pressures of H2S, balanced with CO2 to a consistent total pressure. The potential was scanned until a defined anodic current density was achieved, and then reversed to yield insight with respect to the repassivation behavior. The forward scans in many cases showed unexpected additional waves that could not be explained based on complementary studies of H2S oxidation. The electrochemical measurements at varying H2S partial pressure were inconsistent with corrosion coupon testing. These results demonstrate that the use of electrochemical measurements to rank the aggressivity of different sour environments for the purposes of materials selection should be treated with caution.