Failure Analysis on Fracture of a Fasten Bolt of the Stabilizer of a Nuclear Power Plant

A fasten bolt of the stabilizer of a nuclear power plant was found fractured during the onsite inspection after installation. The fracture failure analysis was performed according to the examination of the material and mechanical properties of the bolt. The microstructure, chemical compositions, mechanical properties and fracture surface were examined to investigate the root causes of the failure. Abnormal microstructure was found near the outer side at the fracture initiation position with lower micro hardness and strength which resulted in the initiation of cracks, and the bolt fractured for the cracks propagation. The abnormal microstructure was caused by the local high temperature during the heat treatment process.