Failure Analysis of Coupling Bolt of Tubular Turbine

A coupling bolt of turbine in a hydroelectric power plant is fractured during operation.The failure is analyzed by stress calculation and the experiments of metallurgical microscopy,scanning electron microscope and mechanical properties.The results show that the state of bolt is a non-normal network ferrite which will create obvious decrease in bolt impact energy,and there are inclusions of Mn and S in bolt body which will create local stress concentration.These defects are main causes of bolt fracture.