Failure Analysis on the Bolt Connecting the Head-Cover and Stay Ring in Pumped Storage Unit: Part Ⅰ-Experimental Study

This paper analyzed a typical failure case of the bolt which connect the head-cover and stay ring of the pumped storage unit by means of experimental study and numerical method. The nondestructive testing, chemical composition tests, metallographic inspection and mechanical properties test are performed for three different bolts, and the finite element analysis of the bolt used in the prototype pump-turbine is carried out to discuss the stress characteristics. Combined the experimental study with finite element analysis, the failure reason of the bolt is concluded as the tensile strength Rm, the plastic elongation strength and the Brinell hardness of the tested bolts do not meet the requirements of standard, and the value of the stress concentration 694 MPa exceeds the yield limit 650 MPa of the bolt. The research in this paper is helpful for analyzing the fracture mechanism of the bolt, and then ensure the safe and stable operation of the unit.