超临界机组小汽轮机高调门调速油伺服阀螺栓断裂的原因

Fracture Reason of Servo Valve Bolt of Electrohydraulic Oil of High Regulating Valve of Small Steam Turbine in Supercritical Unit

某电厂超临界机组小汽轮机高调门调速油伺服阀螺栓工作3.5a后发生断裂,采用化学成分分析、硬度检验、金相分析和断口分析等方法对断裂原因进行了分析。结果表明:螺栓的断裂性质为疲劳断裂,断口呈现多源特征;螺栓的螺纹部位存在多处机加工缺陷,疲劳裂纹在缺陷处萌生,在复杂疲劳载荷作用下扩展,当裂纹扩展到临界尺寸后出现失稳引起瞬时断裂;当一根螺栓疲劳断裂后,其他螺栓因承受的静载荷明显增大而发生瞬间过载断裂。

Servo valve bolt of electrohydraulic oil of high regulating valve of small steam turbine in supercritical unit in a power plant fractured after working for 3.5 a.The fracture cause was analyzed by methods such as chemical composition analysis,hardness testing,metallographic analysis and fracture analysis.The results show that the fracture property of the bolt was fatigue fracture,and the fracture presented multi-source characteristics.There were many serious manufacturing machining defects in the thread of the bolt.Fatigue cracks initiated in these defects and propagated under complex fatigue load.The cracks became unstable when propagated to critical size,leading to the instantaneous fracture.The static load on the other bolts increased signi ficantly after the fatigue-fracture of one bolt,leading to the instant fracture under overload of the other bolts.