Fracture Reason Analysis on a Hollow Bolt of 1 000 MW Nuclear Power Turbine

The fracture causes of a hollow bolt used on the radial tilting bearing of a 1 000 MW nuclear power turbine were analyzed by macro examination, chemical composition analysis, mechanical property test, metallographic examination and macroscopic and microscopic fracture analysis. The results show that the failure type of the bolt was overload fracture. The unqualified bolt quality was the main reason for its fracture. On the one hand, the size of the cutter groove of inner thread of the bolt didn't meet the standard requirements, which significantly reduced the bearing area of the bolt. On the other hand, the strength and hardness of the bolt were rather low, which also reduced the bearing capacity of the bolt.