重沸器换热管应力腐蚀开裂分析

Stress Corrosion Cracking Analysis of Heat Exchange Tube of Reboiler

针对某重沸器换热管发生点腐蚀并且开裂的问题,对其进行宏观检验、化学成分以及金相组织分析的同时,采用扫描电镜分析换热管断口微观形貌,用能谱对腐蚀产物进行成分分析。结果表明,裂纹起源于换热管外壁的腐蚀坑,且从换热管外壁向内壁穿晶扩展,存在分叉,裂纹中充满灰色腐蚀产物,断口微观形貌为河流状解理花样,存在二次裂纹,均为应力腐蚀开裂特征。分析认为,重沸器壳程介质中存在的氯离子是引起换热管应力腐蚀开裂的主要原因。

Aiming at the orrosion and cracking on a heat exchange tube of the reboiler,macro examination,chemical composition,and microstructure were examined respectively.And the fracture morphology and corrosion products were analyzed by SEM and EDS.The results show that the path of crack initiation and growth is transgranular from outer surface of tube to its inside,etching pits on the outside surface act as crack initiation sites,branching and gray corrosion products exists,the fracture morphology is river pattern,secondary crack exists,all of these are characteristics of stress corrosion cracking.Analysis suggests that chloride ions in the medium are the cause of stress corrosion cracking.