| As a safe,economic and efficient transportation mode,pipeline transportation is the main mode of oil and gas transportation,and also one of the main transportation modes of hydrogen energy in the future.With the development of China’s "West to East Gas Transmission","West to East Power Transmission",urban subway,high-speed rail,etc.,the oil and gas pipelines suffer from more and more electric interference by different infrastructures.This interference not only causes the increasingly serious corrosion,but also causes the risk of hydrogen embrittlement of the pipeline.In particular,the strength grade of the pipeline has developed to X90,resulting in more prominent hydrogen embrittlement problems.The corrosion and hydrogen embrittlement of pipeline steel under complex service environment with interference has become a key technical challenge to ensure the safe service of oil and gas pipelines and avoid pipeline fracture accidents.The conclusion is as follows:(1)In this thesis,the field data of different interferences are monitored and statistically analyzed.The interference parameters of steady-state DC continuous interference,dynamic DC intermittent interference and high-voltage DC impulse interference are obtained.(2)The surface ablation of pipeline steel caused by high voltage DC interference and its influence on subsequent corrosion were studied,including the influence of different interference parameters on the surface ablation of pipeline steel,and the influence of ablation damage on the resistance of pipeline steel in near neutral and high pH environment.The boundary conditions of interference voltage and interference duration leading to the surface ablation of pipeline steel are put forward.It is found that the ablation occurs preferentially at the inclusion position on the surface of pipeline steel,and the mechanism of ablation damage promoting the development of local corrosion on the surface in the subsequent corrosion process of pipeline steel is clarified.(3)The influence of different DC interference characteristics on the susceptibility of pipeline steel to hydrogen embrittlement was studied.Through insitu slow strain rate tensile testing and morphology observation under steady-state DC interference,dynamic DC intermittent interference and high-voltage DC impact interference,the effects of interference duration and interference current density on hydrogen embrittlement of pipeline steel were analyzed.The influence mechanism of different DC interference characteristics on hydrogen embrittlement susceptibility of pipeline steel is clarified,the quantitative relationship between interference current density and hydrogen embrittlement susceptibility coefficient is established,and the critical current density of hydrogen embrittlement of pipeline steel under different interference is proposed.(4)The influence of DC interference on the hydrogen embrittlement susceptibility of high-grade pipeline steel X90 was studied.The characteristics of hydrogen diffusion,accumulation and escape in X90 steel were studied through hydrogen permeation and hydrogen content tests.The influence of negative potential on the hydrogen embrittlement of X90 steel and the reasons for the difference of hydrogen embrittlement susceptibility of different X90 steels were obtained.(5)The hydrogen embrittlement susceptibility of pipeline with mechanical scratches on the surface coupled with DC interference was studied,and the effects of mechanical scratches on the hydrogen embrittlement susceptibility under cathodic protection conditions and dynamic DC interference were established.For the pipeline steel with surface mechanical scratch,the susceptibility mechanism of pipeline hydrogen embrittlement under the coupling effect of mechanical scratch and stray current interference is proposed,and the boundary conditions of pipeline hydrogen embrittlement induced by the combined effect of mechanical scratch depth and dynamic DC interference current density are established.Based on the results and mechanisms of corrosion and hydrogen embrittlement of pipeline steel under different interferences,important theoretical and engineering application value can be drawn and effectively support the safety guarantee of longdistance transmission pipeline. |
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