The macroscopic inspection,spectral analysis,hardness testing,mechanical property testing,metallographic inspection,scanning electron microscope observation and energy spectrum analysis were carried out on the failed bolts of the power plant.Combined with the fracture location and fracture mode of the bolts,the failure causes of the bolts were comprehensively analyzed.The results showed that the im-proper heat treatment control during the manufacturing process of the end cover bolts,excessive the tighte-ning torque during installation,and long-term exposure to alternating load ultimately led to fatigue fracture of the end cover bolts.
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