考虑环境对疲劳促进作用时载荷配对方法保守性研究

Conservation analysis of load pairing considering environment assisted fatigue

现有核电厂规范一级设备的疲劳评估中均需要考虑压水堆反应堆一回路水环境对疲劳的促进作用(环境促进疲劳,EAF),而高的交变应力配对往往对应更快的应变变化速率,将计算获得较低的环境修正因子(F_(en)),但现有规范在载荷配对中忽略了对F_(en)的影响。介绍了反应堆水环境影响疲劳寿命问题,包括EAF问题的发展及其评价方法。着重介绍了使用环境修正因子F_(en)评价EAF问题的方法、美国经验反馈以及法国最新版RCC-M规范针对EAF问题作出的修改和EAF评估流程。最后,基于某工程实际案例,分析不同载荷配对对疲劳分析结果的影响。案例中快速应变过程产生的Fen较小,优化后的载荷配对形成更大的疲劳损伤结果。分析案例表明,考虑EAF时,现有ASME规范载荷配对方法可能获得非保守性的结果。

The effect of reactor water environment assisted fatigue(EAF)needs to be considered in the fatigue assessment of existing nuclear ClassⅠequipment,whereas the influence trends of strain rate on environmental correction factor(F_(en))and alternating stress values are often inconsistent,and the influence of F_(en) is ignored in the load pairing in the existing specifications.The influence of reactor water environment on fatigue life was introduced,including the development of EAF and its evaluation methods.The method of using the environmental correction factor F_(en) to evaluate EAF problems,the feedback of American experience,the modification of the latest French RCC-M Code for EAF problems and the detailed process of EAF evaluation were introduced focally.Finally,based on a practical engineering case,the influence of different load pairs on the fatigue analysis results was analyzed.Rapid strain rate in the case often produces smaller F_(en),but optimized load pairs form greater fatigue damage results.The analysis case shows that when considering EAF,the existing ASME Code may obtain non-conservative results.