脱甲烷塔重沸器釜液出口管线开裂原因分析

Cracking Analysis of Outlet Pipeline of Demethanizer Reboiler

某厂脱甲烷塔重沸器釜液出口管线发生开裂,通过宏观检查、金相组织分析、化学成分分析、断口形貌分析、EDAX分析等方法对其开裂原因进行了研究。结果表明,失效管符合晶间腐蚀开裂特征,化学成分不合格且存在晶粒粗大、晶界敏化等原始缺陷是导致管开裂的根本原因,水相的存在是导致管开裂的直接原因,焊接引起的热影响区应力偏大是导致管开裂的间接原因。建议加强制造重沸器所需金属材料的入厂检验;同时避免壳体内水相的聚集,包括气相水;改进焊接工艺,减小焊接接头应力,也可减缓开裂的发生。

Cracking occurred in the outlet pipeline of the reboiler of a demethane tower in a factory.The cracking reason was analyzed by means of macroscopic inspection,metallographic structure analysis,chemical composition analysis,fracture morphology analysis and EDX analysis.The results show that the failure pipe conforms to the characteristics of intergranular corrosion cracking,the chemical composition is unqualified,the grain size is coarse,the grain boundary sensitization and so on,the original defect is the root cause of pipe cracking,the existence of water phase is the direct cause of pipe cracking,the heat affected zone stress caused by welding is the indirect cause of pipe cracking.It is suggested to strengthen incoming inspection of raw materials.At the same time,avoid the accumulation of water phase in the shell,including gas phase water;Improve welding process,reduce welding joint stress,it can slow down the occurrence of cracking.