Study on the effect of initial imperfection shape on buckling strength of cylindrical vessel under the horizontal and vertical loads

The current buckling criteria given by the design standard of Class 1 vessels for fast reactors (FRs) power plant in Japan, “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” by JSME, focuses primarily on plastic buckling of austenitic stainless steel vessel. For next-generation FRs, the higher-yield material such as modified 9Cr-1Mo steel, larger and thinner vessel due to capacity increase and seismic isolation system plan to be applied. In previous study, a series of buckling tests and analyses of modified 9Cr-1Mo steel vessels was conducted and the results showed that the previously proposed modified buckling strength equations are applicable to evaluate buckling strength under these conditions. In this study, the effects of initial imperfection and residual stress of large vessels manufactured by welding multiple plates on the buckling load were evaluated via a series of analyses. By these analyses, the global initial imperfection, from the superimposition of imperfection over the entire vessel due to accumulation of misalignment in buckling mode imperfection, had weak effect on the buckling strength. And the local initial imperfection and residual stress by welding also exerted weak effects on the buckling strength.