Causes of Fracture of High Temperature Bolt of High-Medium Pressure Cylinder in a Power Plant

After a power plant operated for 1. 5×10⁵ hours, high temperature bolt of high-medium pressure cylinder was fractured. Through chemical composition analysis, mechanical performance test, fracture analysis, microstructure observation and energy spectrum analysis, the reasons for bolt fracture were analyzed. The results showed that under the action of long-term high temperature and complex stress, creep occurred at local grain boundaries and the material properties declined. During the operation of the unit, cracks initiated at creep location and propagated along grain boundaries, eventually leading to bolt fracture.