核电厂齿轮箱蜗轮固定螺栓断裂失效分析

Fracture Failure Analysis of Fixing Bolt of Worm Gear in Gearbox of a Nuclear Power Plant

电厂在设备检修过程中发现桥架滚珠螺母齿轮箱蜗轮固定螺栓断裂,为分析固定螺栓的断裂原因,对其进行了宏观观察、化学成分分析、硬度测试、显微组织测试和微观观察等分析手段。排除材料不合格或者材料老化因素,得出螺栓断裂的根本原因为氯离子引起的应力腐蚀开裂,而腐蚀过程的析氢反应促进了裂纹扩展,最终在外力作用下导致螺栓断裂。

During the equipment maintenance of the power plant,it was found that the ball nut of the bridge and the fixing bolt of the worm gear of the gearbox were broken.In order to analyze the fracture cause of the fixed bolt,the macro observation,chemical composition analysis,hardness test,microstructure test and micro observation were carried out.Excluding the factors of unqualified materials or material aging,it was concluded that the root cause of bolt fracture is stress corrosion caused by chloride ion.The hydrogen evolution reaction in the corrosion process promoted the crack propagation,and finally lead to the bolt fracture under the action of external force.