S31608不锈钢弯头在四氯化硅冷氢化工艺中的失效分析

Failure analysis of S31608 stainless steel elbow in silicon tetrachloride cold hydrogenation process

本文主要对S31608不锈钢弯头在四氯化硅冷氢化工艺中失效形式及原因进行研究,采用金相分析、ESD和SEM等方法对弯头失效部位的化学组成、显微结构和腐蚀产物成分等进行分析。结果表明:弯头的失效形式主要为应力腐蚀开裂,内壁向外壁扩展。开裂的外因是弯头内壁接触的含Cl^(-)腐蚀性介质和加工产生的残余应力以及内压作用下的应力叠加;内因是弯头晶界上有析出和形变组织。S31608不锈钢失效的主要原因是介质中存在Cl^(-)、P^(-)等引起腐蚀的成分和应力。弯头晶界上有析出和形变组织导致其耐腐蚀性能下降,弯头断口上存在含Cl^(-)腐蚀性介质,氯离子对奥氏体不锈钢表面膜有极强的穿透、侵蚀作用,能够溶解覆盖在表面的保护膜,在加工产生的残余应力以及工作应力等作用下,从而产生应力腐蚀而失效。

In this paper,the form and reason of S31608 stainless steel elbow’s failure in silicon tetrachloride cold hydrogenation process are studied.The chemical composition,microstructure and corrosion product composition of the elbow failure location are analyzed by metallographic analysis,ESD and SEM method.The results show that the main failure mode of elbow is stress corrosion cracking with the inner wall extends to the outer wall.The external cause of cracking is the combination of Cl-containing corrosive medium in contact with the inner wall of the elbow,residual stress produced by fabrication and stress superposition under the action of internal pressure.The internal reason is the precipitation and deformation structure on grain boundary of elbow.The main reason for S31608 stainless steel failure is the presence of Cl^(-),P^(-) and other corrosion components in the medium and stress.With a decline in corrosion resistance caused by the precipitation and deformation structure on the grain boundary of the elbow,the Cl^(-) contained in the corrosive medium on the elbow fracture,which poses a extremely strong penetration and erosion effect on the Austenitic stainless steel surface film,is able to dissolve the protective film and causes the failure of the elbow due to stress corrosion under the action of residual stress and working stress.