X70管线钢埋弧自动焊接接头的盐雾腐蚀行为

Salt spray corrosion behavior of X70 pipeline steel welded joints by submerged arc automatic welding

利用扫描电镜对X70管线钢焊接接头微观结构进行了观察,采用中性5%连续盐雾试验考察了其焊接接头表面的腐蚀性能,分析了X70管线钢焊接接头在盐雾介质中腐蚀行为,对点蚀坑内腐蚀产物进行EDS分析,探讨了X70管线钢焊接接头表面点蚀机理。结果表明,X70管线钢焊接接头在盐雾环境中耐蚀性低,容易诱发局部点蚀,Cl-对X70管线钢焊接接头的腐蚀起主导作用;其腐蚀过程主要由表面点蚀、形成腐蚀产物层、裸露的焊接接头表面腐蚀等3个部分组成,其中点蚀是裂纹萌生和扩展的主要来源;腐蚀产物主要是由Fe的氧化物和少量Fe的氯化物构成,其形成的氧化膜提高了其防盐雾腐蚀能力。

Microstructure of X70 pipeline steel welded joints was observed with SEM,and the corrosion performances in 5% neutrally continuous salt spray solution were researched.The behavior of electrochemiscal corrosion of X70 pipeline steel welded joints in salt spray environment was analyzed,and chemical composition of the corrosion product in corrosive pits was examined.The micro-mechanism of pitting corrosion of the weld joint in salt spray was discussed.The results show that corrosion resistance of X70 pipeline steel welded joints is poor in salt spray,and local pitting corrosion easily occurs.Cl-ions are responsible for the corrosion of X70 pipeline steel welded joints.Its corrosion process is composed of pitting corrosion,the forming corrosion products layer and the corrosion of X70 pipeline steel welded joints.The pitting corrosion is the main factor of crack initiation and propagation.The corrosion products are composed of a multitude of Fe oxide and a small quantity of Fe chloride,and the forming of the oxide film improves the resistance to salt fog corrosion.