丙烯腈装置中反应气体冷却器用热电偶套管的泄漏原因

Leakage Reason of Thermocouple Bushing in Reactive Gas Cooler in Acrylonitrile Plant

某丙烯腈装置反应气体冷却器热电偶套管在使用过程中发生泄漏。采用宏观观察、化学成分分析、显微组织观察、显微硬度测试、扫描电镜和能谱分析等方法,分析了该热电偶套管泄漏的原因。结果表明:该热电偶套管的开裂形式为应力腐蚀开裂,其泄漏的主要原因是套管热影响区和母材区的表面状态和显微组织差异产生应力,在硫化氢和氯化物共存的环境中,在热影响区优先形成应力腐蚀裂纹,裂纹沿着晶界向母材扩展,从而在套管与法兰凸台的焊缝连接处发生开裂,最终导致热电偶套管在使用过程中发生泄漏。

The thermocouple bushing of reaction gas cooler in an acrylonitrile plant leaked during use.The causes of the leakage were analyzed by means of macroscopic observation,chemical composition analysis,microstructure observation,microhardness test,scanning electron microscopy and energy dispersive spectroscopy.The results showed that the cracking mode of the thermocouple bushing was stress corrosion cracking.The main reason of its leakage was the difference of surface state and microstructure between heat affected zone and base metal zone of thermocouple bushing produced stress,which led to the formation of stress corrosion cracks in the heat affected zone preferent ially.In the environment where hydrogen sulfide and chloride coexisted.The cracks propagated along the grain boundary to the base metal,which led to cracking at the weld joint between the thermocouple bushing and the flange boss,and finally led to the leakage of thethermocouple bushing during use.