Effect Of Sulfide Films Formed On MS X65 Steel Surface On Hydrogen Permeation In H₂S Environments

In this work,sulfide films were formed quickly on a MS X65 pipeline steel in solutions with various pH values and H₂S concentrations by cyclic voltammetry,the morphology and structure of surface sulfide films were characterized by field emissionscanning electron microscopy?FE-SEM?and X-ray diffraction?XRD?,and ionselectivity of surface sulfide films was characterized by the traditional method of measuring membrane potential.Electrochemical hydrogen permeation curves were measured using a modified Devanathan-Stachurski cell and the hydrogen permeation behavior on the filmed steel was investigated.And the effect of the film on hydrogen permeation was investigated.The main results are as follows:?1?Crystalline iron sulfide?FeS?and/or mackinawite forms on the steel surface during H₂S corrosion,depending on the H₂S concentration and the solution pH.?2?The presence of sulfide films blocks the hydrogen permeation through the steel,and the blocking effectincreases with the increasing H₂S concentration and reducing pH value.Compared to the film containing crystalline FeS only,the mixed compositions of mackinawite and FeS in the film cause an increased effect to block hydrogen permeation.?3?The sulfide films are an n-type semiconductor with the anion selectivity,which contributes to the blocking effect on hydrogen permeation into the filmed steel.?4?The tensile stress does not change the semiconductor property and anion selectivity of sulfide films,the sulfide films also have the blocking effect on hydrogen permeation into the filmed steel under tensile stress.The results can be used to reveal the intrinsic relationship between sulfide films and hydrogen induced cracking?HIC?and contribute to development of a science base for improving safety and integrity of pipelines and other facilities used in H₂S environments.