Effect Of Stress On Corrosion And Hydrogen Permeation Behavior Of MS X65 Pipeline Steel In H₂S Environment

Hydrogen-induced cracking（HIC）is one of the main failure forms of pipeline steel in H₂S-containing solution,which is related to the penetration,diffusion and capture of hydrogen in steel.Stress is considered to be one of the important factors that affect the hydrogen evolution and hydrogen penetration of pipeline steel in acidic H₂S solution,especially when the surface of the steel was covered with sulfide film.The effects of different tensile stresses on the surface morphology,thickness,composition and ion selectivity of the sulfide corrosion product film were explored,and the effecting law and mechanism on hydrogen permeation behavior of the MS X65 pipeline steel under the sulfide film was studied by combining the hydrogen permeation kinetic parameters.In addition,the effect of alternating load frequency on cathodic hydrogen evolution and hydrogen permeation behavior was also preliminarily explored to provide theoretical guidance and data support for the failure mechanism and anti-corrosion measures of pipeline steel under complex conditions.The main research results and progress are as follows:（1）The cathodic hydrogen evolution reaction of MS X65 pipeline steel in acidic H₂S solution can be promoted by the applied elastic or plastic constant stress.The hydrogen permeation flux J_∞L and the effective diffusion coefficient D_apppp both increase with the increase of elastic constant stress and decrease with the application of plastic stress.The hydrogen concentration on the cathode side c₀ increases with the increase of stress in the elastic zone and plastic zone.（2）When there is a prefabricated sulfide film on the surface of MS X65 pipeline steel,the hydrogen evolution reaction is promoted by elastic constant stress and suppressed by plastic constant stress.The change law of J_∞L and D_apppp with constant stress with film is the same as that without film.The hydrogen concentration on the cathode side c₀ increases with the increase of elastic constant stress,but decreases with the application of plastic constant stress.（3）The blocking effect of the sulfide film on the surface of MS X65 pipeline steel on hydrogen penetration hardly changes with the constant tensile stress,that is,the hydrogen penetration retard factor HPRF（film）of the single sulfide film is almost unchanged;the total hydrogen penetration retard factor HPRF（stress-film）is not a simple addition of HPRF（stress）and HPRF（film）,and the interaction of stress and film causes HPRF（stress-film）to decrease first and then increase with stress;The effect of hydrogen penetration is mainly reflected in the effect of tensile stress on the integrity of the sulfide film.（4）The open circuit potential of MS X65 pipeline steel in acidic H₂S solution increases first and then stabilizes with the increase of cyclic load frequency,and the self-corrosion current density i_corrorr increases first and then stabilizes with increasing frequency.And the critical cyclic stress frequency when the the stress ratio R=0.4 and stress ratio R=0.85 is 0.25Hz and 1Hz respectively.When the load frequency is increased from 0.5Hz to 1.5Hz,both J_∞L and c₀ rise first and then fall,and the effective diffusion coefficient D_apppp continues to rise.This is the joint effect of the cathodic hydrogen evolution reaction and the alternating load on the interior,surface and surface reaction of the sample result.