硫黄回收装置液硫泵蒸汽回流管失效分析

摘要：硫黄回收装置液硫输送泵的蒸汽回流管多次发生开裂，开裂位置均为焊接接头部位，裂纹起源于焊缝焊趾，沿环向扩展，最终扩展至弯头母材，开裂长度达半周以上；外弯处焊缝错边量约1mm，内弯处存在整圈1．5mm高的未熔合。文章对液硫输送泵蒸汽回流管的开裂弯头进行了宏观检验、成分分析、金相检验和能谱分析，并结合工艺条件、对腐蚀机理和检测结果进行了失效分析，通过分析得出蒸汽回流管开裂主要是由于焊接质量不高、金相组织不均匀和热处理不好等原因导致焊接结构存在高残余应力，这些残余应力在连多硫酸环境下发生应力腐蚀开裂所至；提出了更换材质减少应力腐蚀开裂和控制焊接成型质量避免焊接缺陷的建议。

Analysis of Failure of Steam Return Line for Liquid Sulfur Pump in Sulfur Recovery Unit

The steam return line for liquid sulfur pump in the sulfur recovery unit fractured many times.The fractures were located in the welded joints,and the cracks originated from weld and promulgated circumferentially to the base metal of elbow.The length of cracking was as long as half circumference.The fractured elbow of steam return line was analyzed by macro testing,composition analysis,metallographic analysis and energy dispersion spectrum(EDS).The corrosion mechanisms and testing results were studied based upon process conditions.It is concluded from analysis that the main culprits of fracture of the steam return line are poor welding quality,un-uniform metallographic structure and unsatisfactory heat treatment,which resulted in high residue stress in welds and stress corrosion cracking(SCC) in polythionic acid environment.It is recommended to use new materials,reduce SSC,control welding quality and eliminate welding defects.