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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。
The microstructure of X70 pipeline steel welded joint was observed by optical microscope. The stress corrosion behavior of X70 pipeline welded joint in NACE solution was analyzed by slow tensile test. The corrosion potential of X70 pipeline steel under different H2S concentrations , Discusses the formation mechanism of self-corrosion potential of welded joint of X70 pipeline steel. The results show that the micro-cracks generated by the MA component in the weld zone of X70 pipeline steel are the main source of stress corrosion cracking in welded joints, which leads to the decrease of corrosion resistance. The welded joints mainly exhibit typical pitting corrosion characteristics , The pits are connected with each other and the pits are covered by the corrosion products generated. The corrosion potential of the welded joints negatively shifts with the increase of H2S concentration, and the stress corrosion sensitivity increases. In the saturated H2S NACE solution, Obvious stress corrosion tendency.