Hashimoto Tadafumi, Osawa Yusuke, Itoh Shinsuke, Mochizuki Masahito, Nishimoto Kazutoshi
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J Press Vessel Technol. 2013 Jun;135(3):0316011-316018. doi: 10.1115/1.4023417. Epub 2013 May 21.
To prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). Before WJP, the welds are machined and buffed in order to conduct a penetrant test (PT) to verify the weld qualities to access, and microstructure evolution takes place in the target area due to the severe plastic deformation. The compressive residual stresses induced by WJP might be unstable under elevated temperatures because of the high dislocation density in the compressive stress layer. Therefore, the stability of the compressive residual stresses caused by WJP was investigated during long-term operation by considering the microstructure evolution due to the working processes. The following conclusions were made: The compressive residual stresses were slightly relaxed in the surface layers of the thermally aged specimens. There were no differences in the magnitude of the relaxation based on temperature or time. The compressive residual stresses induced by WJP were confirmed to remain stable under elevated temperatures. The stress relaxation at the surface followed the Johnson-Mehl equation, which states that stress relaxation can occur due to the recovery of severe plastic strain, since the estimated activation energy agrees very well with the self-diffusion energy for Ni. By utilizing the additivity rule, it was indicated that stress relaxation due to recovery is completed during the startup process. It was proposed that the long-term stability of WJP under elevated temperatures must be assessed based on compressive stresses with respect to the yield stress. Thermal elastic-plastic creep analysis was performed to predict the effect of creep strain. After 100 yr of simulated continuous operation at 80% capacity, there was little change in the WJP compressive stresses under an actual operating temperature of 623 K. Therefore, the long-term stability of WJP during actual operation was analytically predicted.
为防止一次水应力腐蚀开裂（PWSCC），水喷射喷丸处理（WJP）已应用于压水反应堆（PWR）中镍基合金的焊缝。在进行WJP之前，需对焊缝进行加工和抛光，以便进行渗透检测（PT）以验证焊缝质量，并且由于严重的塑性变形，目标区域会发生微观结构演变。由于压缩应力层中的位错密度较高，WJP引起的压缩残余应力在高温下可能不稳定。因此，通过考虑工作过程中微观结构的演变，研究了WJP引起的压缩残余应力在长期运行期间的稳定性。得出以下结论：在热时效试样的表层中，压缩残余应力略有松弛。基于温度或时间的松弛幅度没有差异。证实WJP引起的压缩残余应力在高温下保持稳定。表面的应力松弛遵循约翰逊 - 梅尔方程，该方程指出应力松弛可能由于严重塑性应变的恢复而发生，因为估计的激活能与镍的自扩散能非常吻合。通过利用叠加规则表明，由于恢复引起的应力松弛在启动过程中完成。建议必须基于相对于屈服应力的压缩应力来评估WJP在高温下的长期稳定性。进行了热弹塑性蠕变分析以预测蠕变应变的影响。在实际运行温度为623 K的情况下，以80％的容量模拟连续运行100年后，WJP压缩应力几乎没有变化。因此，通过分析预测了WJP在实际运行期间的长期稳定性。
