镍基合金压力容器环形焊缝残余应力数值模拟与失效应力分析

Numerical simulation of residual stress in girth weld and failure stress analysis of reactor vessel

根据英国结构完整性评估标准BS7910(2013),考虑焊接残余应力影响,采用失效评估图(Failure Assessment Diagram,FAD)方法对镍基合金压力容器焊接部位内表面裂纹进行安全评估。首先采用有限元分析(Finite Element Analysis,FEA)方法,对压力容器V型、X型坡口环焊缝多层多道对接焊进行数值模拟,获取焊接残余应力分布,并将V型坡口对接焊焊接残余应力曲线与BS7910(2013)标准残余应力分布进行了对比;其次,对BS7910(2013)1级-FAC曲线进行公式化简,在焊接位置考虑残余应力、应力集中、塑性失效因子三因素的影响,对轴向内部半椭圆裂纹进行了失效应力预测。结果表明:残余应力的分布直接影响计算结果,残余拉应力越大,相应失效应力越小;残余应力值和裂纹深度a保持不变,失效应力计算结果随c/a(c为裂纹半长)增大而减小;当c/a比值不变,失效应力值随着a增大而减小。本文焊接残余应力模拟即及失效应力预测方法为以后含缺陷压力容器及管道失效应力计算(寿命预测)提供一定的参考。

[Background] Residual stress in girth weld and failure stress of reactor vessel are very important in structural integrity assessment regardless the structural material.[Purpose] This study aims to evaluate the safety of internal surface cracks in welding parts of nickel-based alloy pressure vessels.[Methods] First of all, based on the British structural integrity assessment standard BS7910(2013), the failure assessment method of failure assessment diagram (FAD) was adopted, and the finite element analysis (FEA) method was employed to carry out numerical simulation of V groove and X groove multilayer and multiple girth butt welding of pressure vessel respectively. The distribution of welding residual stresses was then obtained. In addition, the residual stress curve of V groove butt welding was compared with that of BS7910(2013) standard. Secondly, the formula of BS7910(2013) 1-FAC curve was deduced. Finally, considering the influence of residual stress, stress concentration and plastic failure factor, the failure stress of semi-elliptic crack in the axial direction was predicted.[Results] The results show that the distribution of residual stress directly affects the calculation results. When the conditions remain unchanged, the calculation result of failure stress decreases with the increase of the ratio of crack depth (c) and crack half length (a). When c/a takes the same value, failure stress decreases with the increase of a.[Conclusions] The prediction method of welding residual stress and failure stress can provide some reference for the calculation of failure stress of pressure vessels and pipeline in the future.