某核电厂汽轮发电机组末级叶片拉筋凸台的断裂原因

Fracture Cause of Tie Piece Boss in Last Stage Blade of Steam Turbine Generator Unit in Nuclear Power Plant

某核电厂汽轮发电机组低压缸末级叶片在累积运行约72个月后,在拉筋凸台处发生了断裂,通过宏观形貌观察、化学成分分析、显微组织观察以及硬度测试等方法分析了拉筋凸台的断裂原因。结果表明:末级叶片拉筋凸台断裂性质为疲劳断裂,发生断裂的原因是相邻叶片拉筋凸台的实际配合状态不佳,造成拉筋凸台表面受力不均匀,局部承受的挤压力过大,使得拉筋凸台在汽轮发电机轴转动时承受不均匀的接触摩擦,在交变载荷的作用下,疲劳裂纹在接触面受力最大的粗糙表面处萌生并逐渐扩展,最终导致拉筋凸台的局部断裂。

The tie piece boss of the last stage blade of the low-pressure cylinder of a nuclear power plant steam turbine generator unit was fractured after cumulative operation for about 72 months.The reason for the fracture of the tie piece boss of the last stage blade was analyzed by macroscopic morphology observation,chemical composition analysis,microstructure observation and hardness test.The results show that the fracture mechanism of the tie piece boss of the last stage blade was fatigue fracture,and the reason for the fracture was that the poor actual matching state of the tie piece bosses of the adjacent blades,resulting in uneven stress on the surface of the tie piece bosses and excessive local extrusion pressure.This caused the tie piece boss to bear uneven contact friction during the rotation of the steam turbine generator shaft,and under alternating loads,the fatigue cracks were initiated on the rough surface of the contact surface with the maximum stress and propagated gradually,ultimately leading to local fracture of the tie piece boss.