X70管线钢焊接接头慢拉伸应力腐蚀行为

Stress corrosion behavior of X70 steel pipeline welded joints by slow strain rate testing

利用金相显微镜观察了X70管线钢焊接接头组织结构,通过慢拉伸试验分析了X70管线钢焊接接头在NACE溶液中应力腐蚀行为,测试了X70管线钢焊接接头在不同H2S浓度下电化学腐蚀电位,讨论了X70管线钢焊接接头自腐蚀电位形成机理。结果表明,X70管线钢焊接接头熔合区中M-A组元所产生的微裂纹是焊接接头应力腐蚀产生裂纹的主要来源,使得其耐腐蚀性能下降;焊接接头在腐蚀初期主要表现为典型的点腐蚀特征,点蚀坑相互连接不断扩展,点蚀坑被生成的腐蚀产物所覆盖;焊接接头自腐蚀电位随着H2S浓度的增加而发生负移,应力腐蚀敏感性增加,在含饱和H2S NACE溶液中具有明显的应力腐蚀倾向。

Microstructure of X70 pipeline steel welded joints was observed by means of metallurgical microscope,and its stress corrosion behavior in NACE solution was analyzed by slow strain rate testing（SSRT）,the self-corrosion potentials of X70 pipeline steel welded joints in NACE solution with different H2S concentrations were measured,and the forming mechanism of self-corrosion potential of X70 pipeline steel welded joints was discussed.The experimental results show that the micro-cracks produced by M-A component in the fusion zone of X70 pipeline steel welded joints are the main origins of stress corrosion cracking,that makes its corrosion properties decrease.The welded joint is characterized by pitting corrosion in the early corrosion stage,and then the corrosive pits are interconnected and covered by the corrosion products as prolonging corrosion time.The self-corroding potential of X70 pipeline steel welded joints decreases with the increase of H2S concentration and the sensibility of stress corrosion increases.The X70 pipeline steel welded joints exhibit obvious stress corrosion trend in the saturated H2S NACE solution.