超临界350MW机组给水泵汽轮机第5级动叶片断裂原因调查分析

Fracture Analysis on the Fifth Stage Moving Blade of Feed Water Pump Turbines of a Supercritical 350MW Unit

对某电厂超临界350MW机组给水泵汽轮机第5级动叶片进行了故障现场调查、断裂叶片的材质检验和断口分析、叶片离心应力和叶轮叶片系统振动特性的有限元计算分析及断裂原因分析。结果表明,叶片的断口性质为高周疲劳断裂,裂纹起源于叶片出汽侧的腐蚀坑,叶片材料与断裂无关;叶片断裂的原因为机组给水泵汽轮机存在超负荷运行的情况,致使给水泵小汽轮机叶片所承受了比设计工况更大的蒸汽弯应力及交变应力;汽水中超标的腐蚀性元素将腐蚀叶片表面并形成腐蚀坑,降低了该区域叶片的疲劳强度,在综合交变应力作用下叶片出汽侧腐蚀坑处容易形成应力集中并出现微裂纹,逐渐扩展,最终断裂。

On the fifth stage moving blade of a supercritical 350MW unit in a power plant,fault field investigation,material inspection and fracture analysis of the broken blade,finite element calculation analysis of the centrifugal stress of the blade and the vibration characteristics of the impeller blade system and analysis of the cause of the fracture were carried out.The results show that the fracture nature of the blade is high-cycle fatigue fracture,the crack originates from the corrosion pit on the steam outlet side of the blade,and the blade material has nothing to do with the fracture;the cause of the blade fracture is the overload operation of the unit feed pump steam turbine,which makes the feed pump steam turbine blades bear greater steam bending stress and alternating stress than the design conditions,the corrosive elements in the steam water will corrode the surface of the blade and form corrosion pits,reduce the fatigue strength of the blade in this area,and in the comprehensive alternating stress under the action,the corrosion pits on the steam outlet side of the blade are prone to stress concentration and micro-cracks.