The Study On Hydrogen Induced Vacancy Behavior Of X80 Pipeline

With the development of economy level and the improvement of living standards,coal-derived natural gas is a developing prospect.The main steel which use to transport in China New Guangdong Zhejiang pipeline is X80 pipeline steel.However,it still need take more effort to investigate the mechanism of fracture in the environment of coal-derived natural gas and different deformation conditions.Therefore,it is significant to study the effect of hydrogen on mechanical properties of metal during the deformation in the environment of coal-derived natural gas.This study use X80 pipeline steel to research the effect of plastic deformation、electrochemical hydrogen-charging and low temperature annealing on the density of traps and the species of hydrogen traps.Four conclusions are drawn from this study:（1）The diffusion coefficient of steel decreases and its traps density increases after prestrain or hydrogen-charging prestrain.The diffusion coefficient increases and its traps density decreases significantly after prestrain annealing.However,the diffusion coefficient increases and its traps density decreases slightly after hydrogen-charging prestrain annealing.（2）The hydrogen traps created by prestrain are almost unsaturated vacancies,but hydrogen-charging prestrain creates not only unsaturated vacancies but also over-saturated vacancies.The unsaturated vacancies were removed by annealing and the over-saturated vacancies will accumulate to bigger microvoids.（3）Prestrain has no effect on the plasticity of X80 pipeline steel;after hydrogen-charging strain,the elongation and section shrinkage of X80 pipeline steel decreases and the ductility losses.After hydrogen-charging strain and annealing,the elongation and plasticity of X80 pipeline steel decreases while the section shrinkage increases slightly.（4）With the temperature increasing,hydrogen diffuses so quickly that the time to penetrate and achieve steady-state current decreases obviously.（5）The density of hydrogen trap is 2.74×10^-10 and hydrogen trap binding energy is 56.471 KJ/mol in X80 pipeline steel.Hydrogen trap keeps stable and only a little of them can be reversed.