S-Zorb烟气管线弯头焊缝失效分析

Failure Analysis of Weld Cracks of Flue Gas Elbow of S-Zorb Unit

介绍了S-Zorb烟气管线弯头焊缝腐蚀开裂情况,对开裂部位进行了外观检查发现弯头断裂失效部位在焊缝附近区域,内壁裂纹清晰,有多处二次裂纹产生。对弯头开裂部位取样,利用电镜扫描、电子能谱等技术对失效焊缝样品进行化学组成和金相热力学分析。在装置停工期间,生成连多硫酸,导致管线焊接处内壁出现晶间腐蚀,并在应力作用下发生应力腐蚀开裂,形成自内壁向外壁的扩展裂纹,最终导致弯头的腐蚀开裂失效。从这些现象可以得出管线失效的主要原因是典型的奥氏体不锈钢在连多硫酸中发生沿晶应力腐蚀开裂。文章对材质的选择以及停工过程中如何防止应力腐蚀开裂提出了建议。

The corrosion cracking of the flue gas elbow of the S- Zorb unit is described. The macroscopic morphology showed that the cracking failure occurred near the area of ring weld. The inner cracking was clear and many secondary cracks were found. The chemical compositions and metallographic structure of failed elbow sample were analyzed by various techniques including EDX and SEM examinations. The results showed that the weld cracks failure was the result of cracking propagated from the internal to external under the impacts of stress corrosion attributed to intergranular corrosion by polythionic acid which was generated during the overhaul of sulfur unit. As the intergranular stress corrosion cracking of austenitic stainless steel occurred in polythionic acid,the effective SCC control measures to be considered in material selection and unit shutdown are recommended.