掺氢天然气环境CH_(4)对管线钢氢脆的抑制行为

Inhibition of hydrogen embrittlement induced by CH_(4) in pipeline transportation of hydrogen-natural gas mixtures

H2在管线钢表面吸附并解离是H原子在钢基体中渗透扩散的前提条件,掺氢天然气管道内H2的存在增加了管道氢脆风险。基于分子动力学模拟与第一性原理计算方法,开展了管线钢表面H2吸附行为研究,得到不同掺氢比例下CH_(4)与H2混合气的竞争吸附规律,明确了管线钢近壁面CH_(4)的存在对H2解离行为的影响机制。研究发现:对于纯气体组分,CH_(4)与H2均具有近壁吸附特性;对于CH_(4)/H2混合组分,CH_(4)具有优先吸附性,显著降低了管线钢表面H2的吸附浓度;通过第一性原理计算方法,发现CH_(4)与H2在管线钢表面的吸附类型不同,CH_(4)的存在不能阻止H2在管线钢表面的化学分解吸附行为,但可以有效降低H2分子出现在管线钢近壁面的概率。研究结果表明:掺氢天然气管道内氢分压无法准确定量反映管线钢表面H2浓度分布,开展相关研究时需考虑气体组分之间的竞争吸附行为。同时,CH_(4)的存在将降低H2出现在管线钢近壁面的概率,在一定程度上可减小氢脆出现的可能。研究成果有助于深入理解掺氢天然气管道的氢脆发生机制。(图9,表3,参33)

The adsorption and dissociation of H2on the surface of pipe steel is the prerequisite for the permeation and diffusion of hydrogen atoms in steel matrix.The existence of H2in natural gas pipeline increases the risk of hydrogen embrittlement.Based on the molecular dynamics simulation and first-principles calculation method,the H2adsorption on the surface of pipeline steel is studied.Also the competitive adsorption law of CH_(4)and H2at different hydrogen ratios is analyzed.The influence of CH_(4)on H2dissociation behavior near the pipeline steel surface is probed comprehensively.Major results are listed below:(1) for pure gas components,both CH_(4)and H2exhibit near surface adsorption characteristics;(2) for CH_(4)/H2mixtures,CH_(4)has preferential adsorption characteristics,which significantly reduces the adsorption concentration of H2on pipeline steel surface;(3) The adsorption behavior of CH_(4)and H2on the surface of pipeline steel are distinguished.The existence of CH_(4)cannot completely prevent the adsorption of H2on the surface,but can effectively reduce the H2adsorption possibility.Hydrogen partial pressure cannot accurately and quantitatively reflect the distribution of hydrogen concentration on the surface.In addition,the competitive adsorption of gas components should be considered when conducting relevant research.Simultaneously,the existence of CH_(4)could reduce the possibility of Hydrogen Embrittlement (HE) to some extent.The research is beneficial for understanding the mechanism of HE in hydrogen-doped natural gas pipelines.(9 Figures,3 Tables,33 References)