Effects of CO 2 and H 2 S on Corrosion of Martensitic Steels in Brines at Low Temperature

• Published in: Corrosion
• Main Authors: Feng, Ruishu, Beck, Justin R., Hall, Derek M., Buyuksagis, Aysel, Ziomek-Moroz, Margaret, Lvov, Serguei N.
• Language: unknown
• Published: 2023
• Subjects: 37 INORGANIC; ORGANIC; PHYSICAL; AND ANALYTICAL CHEMISTRY; Arctic; Psi
• Online Access: http://www.osti.gov/servlets/purl/1461642; https://www.osti.gov/biblio/1461642; https://doi.org/10.5006/2406

Corrosion studies were conducted for martensitic carbon steels in 5 wt% NaCl brine solutions at 4°C and 10 MPa (1,450 psi). These studies simulated different subsurface environments relevant to Arctic drilling. Here, two high-strength martensitic carbon steels, S-135 and UD-165, were studied in three different environments: (1) a CO 2 -NaCl-H 2 O solution with a CO 2 :H 2 O molar ratio of 0.312 in the whole system, (2) an H 2 S-NaCl-H 2 O solution with an H 2 S:H 2 O molar ratio of 3.12 × 10 –4 , and (3) a CO 2 -H 2 S-NaCl-H 2 O solution with the same acid gas to water ratios as environments 1 and 2. Results from the CO 2 +H 2 S mixed environment indicated that sour corrosion mechanism was dominant when the CO 2 :H 2 S molar ratio was 1,000. This impact of a small amount of H 2 S on the corrosion mechanism could be attributed to the specific adsorption of H 2 S on the steel surface. Electrochemical and mass loss measurements showed a distinct drop in the corrosion rate (CR) by more than one order of magnitude when transitioning from sweet to sour corrosion. This inhibiting effect on CR was attributed to the formation of a protective sulfide thin film. Tafel analyses of the anodic reaction showed that the Bockris mechanism was unlikely in the conditions tested. As a result, when comparisons were made between modeled and experimental CRs, good agreement was found in the CO 2 -only and H 2 S-only environments, but not in the CO 2 +H 2 S environment.