The Effect of Hydrogen Sulfide on Hydrogen Permeation in High-strength Low-alloy Carbon Steel C110

Abstract

The application of high-strength low-alloy carbon steel C110 has been limited by hydrogen permeation. The effects of H2S, pH, and NaCl, on hydrogen permeation, are studied by electrochemical techniques, such as hydrogen permeation and electrochemical impedance spectroscopy (EIS). The hydrogen permeation results show that the hydrogen permeation process is accelerated by increasing H2S concentration, decreasing pH, and decreasing NaCl concentration. H2S improves the hydrogen permeation level either by accelerating the hydrogen reduction reaction or by catalyzing the hydrogen absorption. A hydrogen adsorption isotherm is developed in this study to characterize the effects of H2S on hydrogen permeation, by evaluating the inductance term detected in EIS tests. Those two roles of H2S are mathematically described, and the role of catalyzing hydrogen absorption governs the effects of H2S on hydrogen permeation when H2S concentration is lower than 90 mol%. The adsorption isotherm developed in this study is applied to sulfide stress cracking (SSC) prediction. The susceptibility to SSC is evaluated by the notched tensile slow strain rate test. The results show that H2S increases the susceptibility to SSC due to hydrogen embrittlement resulting from hydrogen permeation. Increasing NaCl concentration in solution also leads to higher susceptibility to SSC due to the increase in pit density. Pits formed at high NaCl concentration conditions facilitate crack nucleation, consequently, decreasing the fracture energy.