从断口形貌、组织、化学成分、硬度、碳当量及扭矩等方面对丙烯腈生产中浮头式换热器内紧固螺栓断裂原因进行了分析。结果表明：在含0.5%~0.6%（质量分数）HCN的丙烯腈富水中，施加过量扭矩的内浮头35CrMoA钢螺栓，极易发生晶间应力腐蚀开裂。根据分析结果，建议在施加标准推荐力矩情况下，更换螺栓材料。

The reasons for fracture of internal fixing bolts for a floating heat-exchanger in acrylonitrile production were analyzed by means of fracture morphology, microstructure, chemical composition, hardness, carbon equivalent and torque. The results show that in acrylonitrile rich water containing 0.5%－0.6% (mass fraction) HCN, the bolts of 35CrMoA steel with excessive torque applied was prone to intergranular stress corrosion cracking. According to the analysis results, it was suggested to change the material of bolt under the condition of applying standard recommended torque.