Influence Of Plastic Strain On Hydrogen Permeation Behavior And Hydrogen Embrittlement Susceptibility Of X80 Pipeline Steel

Coal gas and natural gas contain a certain amount of hydrogen gas,which may cause hydrogen adsorption and permeation,inducing the hydrogen embrittlement of pipeline steel.Besides,the manufacture,construction and service of pipeline steel may cause plastic strain which could affect the hydrogen penetration behavior and hydrogen embrittlement susceptibility in the pipeline steel.In this thesis,the influence of different plastic strain on hydrogen penetration behavior and hydrogen embrittlement susceptibility of X80 pipeline steel was studied by conducting high-pressure hydrogen permeation tests and high-pressure slow strain rate tension tests.Microstructure observation and dislocation density analysis were carried out to study the influence mechanism.Results of metallographic observation and electron backscatter diffraction show that plastic strain has no influence on the microstructure of X80 steel.It is the change of dislocation density that plays a leading role.For strain from 0%to 0.14%,dislocation density increases with the increase in strain.Steady-state hydrogen permeation current density and hydrogen diffusivity decrease,and hydrogen concentration increases.Moreover,the deformation,elongation and reduction of area decrease,the hydrogen embrittlement index increases.That is to say the hydrogen embrittlement susceptibility of X80 steel increases.For strain from 0.14%to 0.21%,dislocation density decreases.Steady-state hydrogen permeation current density and diffusivity increase,and hydrogen concentration decreases.Moreover,the deformation,elongation and reduction of area increase,the hydrogen embrittlement index decreases.That is to say the hydrogen embrittlement susceptibility of X80 steel decreases.For plastic strain from 1.5%to 6.0%,mechanism of dislocation multiplication plays a leading role.Change of hydrogen permeability parameters and mechanical parameters is the same as the condition when strain increases from 0%to0.14%.For post-yield macro-strain stage of X80 steel in 1.2 MPa H₂ and 40?,the empirical equations revealing the relationship between hydrogen diffusivity,absorbed hydrogen concentration or hydrogen embrittlement index and plastic strain were got by fitting.