Study On Inhibition Mechanism Of CO On Hydrogen Embrittlement Of High-Pressure Hydrogen Transport Pipeline

For now,the government actively promotes the use of clean energy.Hydrogen,hydrogen-containing coal gas and hydrogen-injected natural gas are greatly developing.However,the transport of hydrogen-containing gas will put the pipeline in high pressure hydrogen environment,resulting in the hydrogen embrittlement?HE?of the pipeline.It is difficult to prevent the HE of pipeline effectively by general methods.In this paper,carbon monoxide?CO?was added to hydrogen,the possibility and inhibition mechanism of CO on HE of hydrogen transport pipeline were studied through the slow strain rate tension test?SSRT?,hydrogen permeation experiment and theoretical calculation.The SSRT and hydrogen permeation experiment results of smooth specimen showed that hydrogen almost had no effect on the uniform deformation stage of X80 steel before the necking,but the influence of hydrogen greatly increased after the local plastic deformation occurred.When the hydrogen pressure is fixed at 10MPa,the elongation after fracture and the reduction of area of X80 steel increased,the hydrogen embrittlement coefficient?F_H?,steady-state hydrogen permeation current density and the adsorbed hydrogen concentration?C₀?decreased with the increasing of partial pressure of CO.The change law of C₀ and F_H of X80steel is basically same with the increasing of partial pressure of CO.CO reduced the HE susceptibility of X80 steel by reducing the C₀ of the specimen.Using the standard notch specimen simulated the state of smooth specimen's local plastic deformation after necking,and studied the mechanism inhibition of CO on HE of X80 steel under local plastic deformation by SSRT.The result showed that the tensile strength did not change much under different conditions.The F_H was largest when adsorbed hydrogen and dissolved hydrogen worked simultaneously.When only the adsorbed hydrogen worked,the F_H was slightly smaller than the F_H of adsorbed hydrogen and dissolved hydrogen worked simultaneously,but was obviously larger than the F_H when only dissolved hydrogen worked.The influence of adsorbed hydrogen was greater than that of dissolved hydrogen.What's more,the influence of adsorbed hydrogen was obviously weakened after CO was added to hydrogen.Hydrogen adsorption is the main factor which affect the HE susceptibility under local plastic deformation.CO can effectively inhibit the HE of X80 steel by inhibiting hydrogen adsorption on the surface of the specimen.In order to study the influence mechanism of CO on hydrogen adsorption,the CASTEP module of Materials Studio software based on the first principle was used for theoretical calculation.The surface energy of the three low-index surface of Fe were calculated,selecting the Fe?110?which had the smallest surface energy and was most stable surface,and calculated the CO and H adsorption on the four high symmetric adsorption sites of Fe?110?.The results showed that the most stable adsorption site of CO was T site,the most stable adsorption site of H was TF site,and the adsorption energy of CO on four adsorption sites were obviously larger than that of the most stable adsorption site of H.CO will adsorb on Fe surface prior to H,occupying adsorption sites and hinder the adsorption of H.What's more,when CO was pre-adsorbed on Fe?110?surface,the absolute value of H adsorption energy of TF site decreased with the number of CO increased.The CO which has been adsorbed on the Fe surface will ulteriorly hinder the adsorption of H.CO reduce the adsorbed hydrogen concentration of pipeline by occupying adsorption sites,hindering adsorption of H on surface,can inhibit HE of pipeline steel effectively.