Contribution of CO2 on hydrogen evolution and hydrogen permeation in low alloy steels exposed to H2S environment

Hydrogen charging in low alloy steels is a major problem in oil and gas environments containing hydrogen sulfide (H2S). The risk of sulfide stress cracking (SSC) is usually determined from the values of water pH and H2S partial pressure (PH2S). The goal of the present study is to check if hydrogen charging is influenced by other parameters than the sole pH and PH2S, and especially by carbon dioxide (CO2). Experiments engaged the measurement of hydrogen permeation through thin mild steel membranes under potentiometric control. Charging solutions with different H2S concentrations with or without CO2 were used, in order to examine their individual contributions to the charging flux. ► Hydrogen charging occurring during steel corrosion by CO2 and H2S is examined. ► H2S and CO2 enhance the cathodic reactions in water. ► H2S and CO2 enhance hydrogen charging through the steel. ► At low PH2S, the permeation efficiency is strongly enhanced in the presence of CO2.