PSI - Issue 13

Rui Guo et al. / Procedia Structural Integrity 13 (2018) 2202–2209 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

2203

2

long-term operation of nuclear equipment in nuclear advanced countries in the world shows that SCC has became one of the main reasons for the failure of PWR components. Since the discovery of the SCC of dissimilar welds in the primary circuit of PWR, Li et al. (2011) and Dong (2010) used experiments, while Xue (2009) used numerical simulations to concentrate on the study of SCC in dissimilar welded structures. Zinkle and Was (2013) studied the influential factors of microstructure of the material, while Zhao and Zhu (2006) and Hayashi et al (2009) studied the influence of residual stress, and Hanninen et al. (1990) and Wells et al. (1992) studied the effect of water chemistry on the behaviour of SCC. Luo and Fu (2008) found that the welding residual stress caused by the welding process is the main cause of stress cracking. Meanwhile, Lundin (1982) and Gong et al. (2013) consider these dissimilar metal welded components have a series of material and mechanical problems in welding and post-weld treatment due to the significant differences in welding parent materials. Shoji et al. (1995) claim the SCC cracking in the safety end is affected by many factors such as residual stress, material and geometric heterogeneity, which makes the mechanical environment at the crack tip complex.

Alloy182 Alloy182

316L A533B 304

316L

2

(a)

Alloy182 Alloy182

1

Crack

A533B

304

(b)

(c)

Figure 1 Schematic diagram of the welded joint in nuclear safety end and its FEM model (a) Schematic diagram of the safety end in the primary circuit of nuclear reactor (b) Geometric dimensions of the welded joints (mm) (c) Sketch of FEM model (mm) Hearn (1997) believes the welding residual stress is mainly formed by the residual strain caused by the phase change and thermal expansion and contraction of the welding structure. Ren et al. (2017) proved that sometimes the welding residual stress can reach or even exceeds the yield stress of the material, and the working load of the safety end of the nuclear power plant is relatively small, welding residual stress becomes the main driving load for SCC crack propagation. The influence of residual stress in key structures of nuclear power around the SCC crack tips has been studied in foreign countries. Hayashi et al. (2009) used numerical simulation to study and compare the influence of the residual stress of the safety end welded joints in PWR and boiling water reactors (BWR) on the SCC crack growth rate. Zhao et al. (2011) analyzed the stress and strain around the SCC crack tips in the welded joints with non-uniform mechanical properties in PWR safety ends. It is believed that the material mismatch can cause changes in the local stress and plastic strain around the crack tips. Hou et al. (2010) found the welding interface in dissimilar metal welded joints may lead to changes in the rate and direction of crack propagation according to experiments, which can tell that the heterogeneity of welded joints has a great influence on cracks in weldments. Finite Element Method (FEM) software has been widely accepted by the academia as a numerical simulation experiment tool (Liu et al., 2002). In this paper, FEM software ABAQUS was used to simulate the mechanics field around crack tips in the welded joints of the pressure vessel safety end of the nuclear power reactor, and the influence of welding residual stress, material and geometric heterogeneity on the welded end in the dissimilar metal welded structures in the pressure vessel were studied.