The fault analysis for low pressure last stage blade of the deep load changing gas-steam combined cycle steam turbine unit

Abstract

In this paper, the causes of the abrasion at the fir-tree type blade root of low pressure last stage which are loosely assembled and the axial movement of the blade root to the intake side of gas-steam combined cycle steam turbine unit are deeply analyzed, which are caused by the special operating conditions of long-term turning and the high-speed setting of turning gear of the deep peak load changing units. At the same time, through the analysis of the fracture of the broken blade, the damage of the top shroud and the vibration data of the accident process, it is concluded that the abrasion at the blade root results in loosening of the blade, the violent striking between the loose blades during the high-speed turning process, results in the damage of the top shroud and the blade. Under the action of centrifugal force of rated speed condition, a break first occurs, and the broken debris falls between the last rotor blade and the static blade, which causes severe impact damage to the blade body, thereby causing secondary tearing of the blade.