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

Abstract

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 H 2 S-containing media. In this second paper, as part of a series of articles that evaluates how traces of oxygen modify the corrosion of pure iron and hydrogen permeation across iron membranes in H 2 Scontaining solutions, the impact of changing the H 2 S partial pressure from 100 kPa to 0.1 kPa was investigated. It was found that bulk solution chemistry for all H 2 S partial pressures changes with time, due to the formation of H 2 SO 2 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 H 2 S-containing solutions decrease with decreasing H 2 S partial pressure, although these are observed to be much higher under continuous oxygen contamination. With decreasing H 2 S partial pressure, hydrogen uptake in Fe also decreases, due to lower and lower concentrations of dissolved H 2 S and the associated increase in pH. However, even at 1 kPa and 0.1 kPa H 2 S, permeation effciencies remain close to 100% when no O 2 contamination is present. The hydrogen uptake is always relatively lower in Fe exposed to oxygen-polluted H 2 S solutions. Permeation efficiencies decrease continuously. From electrochemical data and surface characterization, these observations at lower H 2 S partial pressures are attributed to the disruptive effect of oxygen on the nature of sulfide corrosion products, and hydrogen entry promotion, along with the contribution of an additional cathodic reaction that does not result in hydrogen entry into the metal.

Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, Part 3: The Impact of Acetate-Buffered Test Solution Chemistry

“…Furthermore, Liu et al have observed the formation of troilite, atop mackinawite, with long aging times. 29 By comparison, the exposure of X52 to identical H 2 S-saturated NACE A solution (1 bar), 30 or the exposure of pure Fe to unbuffered H 2 S-saturated brine for a similar period of time only led to the development of mackinawite, 8 in line with another literature reports in similar nonbuffered conditions.…”