316L不锈钢短接过早腐蚀开裂的机制与预防

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(1. 淮安信息技术学院 机电工程系，淮安 223003； 2. 中国科学院 金属研究所，沈阳 110016)

316L不锈钢短接过早腐蚀开裂的机制与预防

孙少东1,陈玮1,何时剑1,舒韵2,王翔2,吴欣强2

(1.淮安信息技术学院机电工程系，淮安223003； 2.中国科学院金属研究所，沈阳110016)

分析了盐化工环境中316L不锈钢短接腐蚀裂纹的宏观特征、微观形貌及显微组织，研究了卤水介质参数及短接制造工艺对316L不锈钢腐蚀的影响。结果表明：短接过早失效的机制是点蚀和应力腐蚀开裂；短接点蚀主要由卤水高温以及高Cl-含量引起，焊接残余应力及卷曲加工应力的共同作用促进了短接的应力腐蚀开裂；用铸造成形代替焊接成形，并适当增加316L不锈钢的钼含量，有利于延长短接的使用寿命。

316L不锈钢；点蚀；应力腐蚀开裂；焊接残余应力；卤水

Abstract： Macro characteristics, micro morphology and microstructure of the corrosion cracks of a 316L stainless steel short connection in the environment of salt chemical industry were analyzed. The influences of brine parameters and manufacturing processes on the corrosion of 316L stainless steel short connection were investigated. The results show that the premature failure of the short connection was due to pitting and stress corrosion cracking (SCC). The pitting of short connection was mainly caused by high temperature and high Cl-concentration of brine, and the combined action of welding residual stress and crimping stress promoted SCC of the short connection. Adopting casting instead of welding and appropriately increasing the content of molybdenum were helpful to extend the service life of the short connection.

Keywords： 316L stainless steel; pitting; stress corrosion cracking (SCC); welding residual stress; brine

某盐化企业将开采的井矿卤水通过蒸馏、离子交换等工艺实现制盐、制碱。原料卤水为NaCl和Na2SO4的饱和水溶液，其中NaCl含量一般在17%(质量分数，下同)左右，pH为7.1～7.5。短接是用于连接输卤泵和蒸发罐的一个两端带有法兰的锥形圆筒件。其上口内径为900 mm，下口内径为800 mm，锥形圆筒部分由壁厚7 mm的316L不锈钢板材卷曲后焊接而成，两端法兰由Q235板材切削加工而成。现场安装时，先将两个法兰分别与输卤泵、蒸发罐螺栓联接固定，圆筒部分调整到位后与法兰焊接。服役时，短接中原料卤水的温度为90～100 ℃，压力为0.48～0.55 MPa。在盐化工生产过程中，上述316L不锈钢短接常因腐蚀开裂而过早失效，一般1 a左右即出现渗漏现象，现场多次焊补也仅能使用2 a左右，不仅影响正常生产，造成经济损失，而且可能引发严重的安全事故。……