Evaluation of the passivity limits in austenitic stainless steel exposed to H 2 S-containing brines using point defect model analysis

Abstract

This study evaluates the effects of temperature, H₂S, and Cl⁻ concentration on the onset of localized corrosion, in UNS S31603 stainless steel by evaluating the changes in the behavior of the passive layer. This is accomplished experimentally by using direct current electrochemical methods to study the passive layer formed by the stainless steel, in equilibrium with a gas phase at 2.8 MPa (400 psi) containing up to 60% mol of H₂S (bal. CO₂) at temperatures up to 150°C. The results indicate that the increase in the likelihood of both metastable and stable pitting on the stainless steel is consistent with the increase in the metal cation diffusivity as postulated by the point defect theory. In this context, the solution temperature was found to exert a larger effect than the H₂S activity.