X90管线钢母材和焊缝在近中性模拟溶液中不同加载电位下的应力腐蚀行为

Stress corrosion cracking behavior of X90 pipeline steel and its weld joint at different applied potentials in near-neutral solutions

X90是继X80和X100管线钢后开发的新一代管线钢,已成为国内外研究的新热点。为了深入了解加载电位对X90管线钢土壤应力腐蚀行为的影响,采用电化学测试和慢应变速率拉伸试验(SSRT)的方法研究了X90管线钢直缝焊管母材和焊缝在近中性模拟溶液(NS4)中不同加载电位下的应力腐蚀行为,应用扫描电子显微镜(SEM)对其断口形貌进行了观察,分析应力腐蚀行为的机理。研究结果表明:(1)NS4溶液中的X90管线钢直缝焊管母材、焊缝的极化曲线均表现为阳极溶解特征,无活化—钝化现象;(2)X90管线钢直缝焊管母材和焊缝在NS4溶液中具有一定的应力腐蚀敏感性,随着加载电位的负移,用延伸率的损失率和断面收缩率的损失率表示的应力腐蚀敏感性指标先减小后增大,焊缝的应力腐蚀敏感性大于母材的应力腐蚀敏感性;(3)X90管线钢直缝焊管母材和焊缝在NS4溶液中的应力腐蚀开裂行为存在以下3种机制——外加电位为EOCP的阳极溶解机制、外加电位为-850 mV的阳极溶解+氢脆机制、外加电位为-1 000 mV和-1 200 mV的氢脆机制。结论认为,该研究成果可以为X90管线钢的大规模使用提供技术支撑和理论依据。

X90 pipeline steel is a new generation of pipeline steel developed after X80 and X100 pipeline steels,and it is now a new research hotspot at home.In order to thoroughly study the effect of applied potential on the soil stress corrosion cracking（SCC） behavior of X90 pipeline steel,we investigated the SCC behaviors of base metal and weld joint samples in the straight-weld pipe of X90 pipeline steel at different applied potentials in near-neutral solution using electrochemical measurements methods and slow strain rate testing（SSRT）.Besides,the fracture surfaces were observed through scanning electron microscopy（SEM） and the mechanisms of the corrosion cracking behaviors were analyzed.And the following research results were obtained.First,the polarization curves of the base metal and weld joint samples in NS4 solution present the typical characteristics of anodic dissolution but no activation–passivation phenomenon happens.Second,In NS4 solution,the base metal and weld joint samples present SCC sensitivity.The SCC sensitivity indicator which is expressed by yield loss percentage elongation and yield loss percentage elongation area decreases firstly and then increases with the negative increase of the applied potential,and the SCC sensitivity of weld joint is higher than that of base metal.Third,there are three mechanisms on the SCC behaviors of base metal and weld joint samples,i.e.,anodic dissolution mechanism when the applied potential is open circuit potential（EOCP）,anodic dissolution and hydrogen embrittlement mechanism when the applied potential is -850 mV,and hydrogen embrittlement mechanism when the applied potential is -1000 mV and -1200 mV.It is concluded that the research results can provide a technical support and theoretical basis for the large-scale application of X90 pipeline steel.