汽轮机高压旁路减温水调节阀阀杆断裂原因分析

Causal Analysis on Fracture of High-pressure Bypass Desuperheating Water Control Valve Stem of Steam Turbines

通过宏观检查、化学成分分析、金相检验、硬度试验、扫描电镜断口分析等方法及综合分析,对某电厂17-4PH材质高压旁路减温水调节阀阀杆断裂失效原因进行了分析,结果表明阀杆断裂方式为疲劳断裂。断裂内在原因是阀杆组织中存在沿轴向的条状组织,条状偏析组织使阀杆沿横向的力学性能降低;外在原因是阀杆除承受正常的轴向载荷,还承受附加双向弯曲载荷。由于阀杆本身结构上存在多处变径,在内在、外在原因的共同作用下,阀杆在变径处的截面最小部位产生应力集中,在此处外表面萌生初始疲劳裂纹源,裂纹由两侧外表面向阀杆内部扩展,最终在轴心部位断裂。

By means of visual test,chemical composition analysis,metallographic inspection,hardness test,SEM fracture analysis and comprehensive analysis,the fracture cause of high-pressure bypass desuperheating water control valve stem made from the 17-4PH in a steam turbine of a power plant was analyzed.The results show that the fracture mode is fatigue fracture.The internal cause of the fracture is the existence of"band-like structure"along the axial direction in the valve stem structure,and the banded segregation structure reduces the mechanical properties of the valve rod along the transverse direction.The external cause is that the valve rod not only bears normal axial load,but also bears additional bidirectional bending load.Because there are many diameter changes in the valve stem structure,under the combined action of internal and external factors,the stress concentrates at the smallest part of the cross section,where the initial fatigue crack source is initiated on the outer surface.The crack spreads from the outer surface on both sides to the inside of the valve stem,and finally leads to fracture at the shaft center.