During the operation of the DTC 300MW sub-critical steamturbine,there were abnormal problem of the working pressure after regulating stage increased by 17%-20%and the unit only operated at low load,which can not meet the requirements of the unit's full load operation.It was found that all the fastening bolts connecting the outer guide of the second high pressure stage partition and the partition were broken.The lost guide blocked the inlet passage of the diaphragm,and the flow area decreased,resulting in the pressure increase of the regulation stage.The reasons for bolt fracture of the diaphragm guide was studied by macroscopic morphology,chemical composition,metallographic inspection and operating conditions.The results show that the reason for bolt fracture is fatigue fracture.The bolt material can not meet the requirements of the highest temperature after regulating stage during operation under some working conditions.The operating temperature margin of bolts is low.The deformation of the partition during operation will cause shear force on the bolt.In order to avoid this type of unit to encounter the problem of diaphragm guide falling off again,the suggestions are put forward.
维普
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