Effect of Different H2S and CO2 Concentrations on Corrosion of Mild Steel at Elevated Temperatures (120-160 °C)

Abstract Both H2S and CO2, ubiquitous in hydrocarbon production, can severely compromise asset integrity. While both are corrosive, H2S-containing environments tend to be more aggressive, causing faster and more severe corrosion than CO2—especially in high-temperature oil and gas systems. Research on H2S corrosion at elevated temperatures has been limited, leading to an incomplete understanding of the mechanisms behind observed phenomena. As a result, corrosion in the presence of H2S remains a key concern for the oil and gas industry. This experimental work aimed to examine the effects of varying CO2 and H2S concentrations at high temperatures. Data for autoclave experiments conducted at pHinitial 5.0, 0.00385-0.0385 M [H2S]aq (0.13-1.65 bar pH2S), 0.009-0.093 M [CO2]aq (1-13 bar pCO2) contrasting corrosion product layers at 120 and 160 °C are reported. The corrosion specimens were machined from X65 steel. Experimental results demonstrate that corrosion rates at 120 and 160 °C for different concentrations of CO2 and H2S were essentially the same, within error, with a combination of various iron sulfides (pyrrhotite, mackinawite, pyrite, troilite) and magnetite found as corrosion products. Also, localized corrosion appeared on the X65 steel specimens in select cases, with no clear pattern identified yet.