Cracking Failure Analysis of Bolts for Floating Heat-Exchanger in Acrylonitrile Production

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.