180MW立轴混流式水轮机顶盖螺栓断裂原因分析

Fracture Analysis of Head Cover Bolts of 180MW Vertical Francis Hydraulic Turbine

为找到某大型水电站180MW水轮机在运行过程中发生顶盖螺栓断裂的原因,利用断口分析、化学成分分析、力学性能分析、显微组织检测及强度分析等试验方法对断裂的顶盖螺栓进行分析。结果表明,顶盖螺栓冶金质量差,组织中夹杂物及带状偏析严重,且未进行调质处理,致使螺栓的强度及韧性均不合格。在运行过程中受过流产生的脉动冲击载荷作用,螺纹根部表层夹杂物处形成高应力集中并产生裂纹,以低周高应力疲劳方式扩展,最终以脆性解理的方式失稳断裂。研究成果可为预防同类事故提供借鉴。

In order to find out the cracking reason for 180 MW turbine head cover bolts of a large hydropower station,the methods of fracture analysis,chemical constituent analysis,mechanical properties test,microstructure examination and strength analysis were used to analyze the cause of bolts fracture.The results show that the head cover bolts have poor metallurgical quality,serious inclusions and zonal segregation in the microstructure,and the quenching and tempering treatment was missed,which resulting in the strength and toughness of the bolts are not qualified.Under the cyclic impact load caused by overflow,cracking occurs at the inclusions of thread root where is high stress concentration,and expands in the way of low-cycle and high-stress fatigue,and ultimately destabilizes rapidly in the way of brittle cleavage.The research findings can provide experience for the prevention of the similar type of accidents.