含缺陷的蒸汽发生器管口热冲击失效风险评定

Thermal shock failure risk assessment of a steam generator nozzle with flaws

承压部件中裂纹在热冲击交变载荷下扩展造成的结构可靠度问题是近几十年来反应堆结构力学领域中被广泛讨论的问题。概率断裂力学作为一种有效的计算工具,被用于反应堆压力容器和管道等重要承压结构的概率失效评定中。在现有的算法基础上,本文以一个含椭圆表面裂纹的管口结构为例,提出了一种适用于复杂结构的概率失效评定方法。考虑到驱动裂纹扩展的复合型(Ⅰ+Ⅱ)载荷,算法使用应力强度因子的等效变化幅ΔKeq计算裂纹扩展速率;在失效评定算法中,采用有效应力强度因子Keff和失效评定图(FAD)。由于管口结构的几何形状和载荷条件相对复杂,有限元方法被用于裂纹的应力强度因子计算,计算结果通过多元非线性回归法插入概率断裂力学算法过程中。验证算例对含裂纹缺陷的复杂管口承压部件进行结构可靠度评估,估算出五十年运行过程中裂纹导致的结构破口失效概率。

Crack propagation in pressure bearing components under pressurized thermal shock loading conditions as well as the caused structural reliability problem was widely discussed within the field of reactor structural mechanics during past decades. Probabilistic fracture mechanics as an effective engineering tool was used to perform structural failure assessment for reactor pressure vessel and pipes. Based on the existing research work, a probabilistic failure assessment method applying to complex structures is presented in this paper focused on a nozzle structure containing an elliptical surface crack. Taking into account the mixed-mode crack loading conditions, crack growth rate is estimated using the magnitude of equivalent stress intensity factor ΔKeq and the effective stress intensity factor Keff is applied in failure assessment diagram(FAD). Finite element method is used to calculate stress intensity factors due to complex geometry as well as loading conditions and the calculation results is integrated into probabilistic process through multiple nonlinear regression algorithm. This method is verified by calculating the leak probability of the above mentioned example nozzle structure within next fifty years equipment run time.