核电汽轮机60Si2MnA弹簧钢垫片的老化行为

核电厂汽轮机叶片叶根底部的60Si2MnA弹簧垫片在服役过程中受到潜在的腐蚀、疲劳、应力松弛等多种老化效应的影响。针对某核电厂汽轮机低压转子末级、次末级叶片根部弹簧垫片,综合分析其服役过程中潜在的腐蚀、磨损及疲劳等方面影响,对垫片老化行为和服役寿命进行研究。结果表明,已服役10年旧弹簧垫片表面存在微动磨痕,微观上未见明显的腐蚀产物及腐蚀形貌,在长期服役过程中,腐蚀效应对垫片寿命的影响有限,不是限制其服役寿命的主要因素。由于材料在初始循环阶段表现出明显的强化和硬化特性,拆卸后的弹簧垫片与原始状态之间存在一定差异,电厂应明确初始安装指导文件不能用于已安装过的弹簧垫片。基于当前的运行状态和试验保守分析预测,已服役10年旧弹簧垫片至少可以继续服役5年,可延长现有检修和更换周期,节约大修工期及成本。

Aging behavior of 60Si2MnA spring steel shims for steam turbine in nuclear power plant

The 60Si2MnA spring shims locating at the bottom of the roots of steam turbine blades subject to various aging effects such as potential corrosion, fatigue, and stress relaxation during service.Thus the aging effects caused by corrosion, wear and fatigue during service were comprehensively analyzed for the spring shims at roots of the last blade and the secondary blade in the low-pressure rotors in a nuclear power plant, and the aging behavior and service life of the shims were studied.The results show that the surface of the spring shims after service for 10 years has wearing traces formed by fretting wear, however, no obvious corrosion products or morphology have been found,which implies that the corrosion effect has a limited impact on the service life of the spring shims in the course of long service. Besides,certain differences exist between the disassembled spring shim and the original state because the material shows obvious strengthening and hardening characteristics during the initial cycles.Therefore,it should be explicited by the power plant that the installation instructions for new shims are not applicable for the installed ones.Moreover, the used spring shim after service for 10 years is estimated conservatively to serve for at least another 5 years based on the practical operating state, in consequence, the existing maintenance and replacement cycle can be extended to save the overhaul period and economic cost.