Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, Part 2: Impact of H2S Partial Pressure

Materials selection in the oil and gas industry relies on engineering standards, such as NACE TM0177 and NACE TM0284, which stipulate that oxygen contamination should be avoided during materials testing in H2S-containing media. In this second paper, as part of a series of articles that evaluate how traces of oxygen modify the corrosion of pure iron and hydrogen permeation across iron membranes in H2S-containing solutions, we investigate the impact of changing the H2S partial pressure from 100 kPa to 0.1 kPa. It is found that bulk solution chemistry for all H2S partial pressures changes with time, due to the formation of H2S-O2 reaction products (sulfates, sulfites and thiosulfates) which results in bulk solution acidification. Electrochemical and weight-loss measurements confirm that Fe corrosion rates in baseline well-deaerated H2S-containing solutions decrease with decreasing H2S partial pressure, although these are observed to be much higher under continuous oxygen contamination. With decreasing H2S pa...