Session: CS-12-01 High Temperature Codes and Standards

Paper Number: 105707

105707 - Development of the Buckling Evaluation Method for Large Scale Vessels in Fast Reactors by the Testing of Grade 91 Steel and Austenitic Stainless Steel Vessels Subjected to Horizontal and Cyclic Vertical Loading 

Larger-diameter cylindrical vessels, because of their capacity enlargement, are pursued in response to the demand for economic competitiveness of commercial fast reactors (FRs). To accommodate the thinner vessel accompanied with larger diameter and the increasing seismic design load in Japan, the seismic base isolation is being devised for next-generation FR power plants. When a horizontal seismic base isolation design is adopted, cylindrical vessels are subject to cyclic vertical seismic load with long-period horizontal seismic load. Since the deformation generated by cyclic vertical load reduces the buckling strength, the effect should be taken into account. Although superposition of elasto-plastic axial compression, bending and shear buckling are expected in the larger-diameter cylindrical vessels, the current rules of buckling limit in the Japan Society of Mechanical Engineers (JSME) standard “Design and Construction for Nuclear Power Plants, Division 2 Fast Reactors” cannot estimate these complex elasto-plastic buckling modes adequately.
Therefore, we proposed the modified buckling strength evaluation method focusing superposition of elasto-plastic axial compression, bending and shear buckling under cyclic axial load, and evaluated their applicability through the buckling tests and analyses under monotonic or cyclic axial compressive load accompanied with constant horizontal load in the previous studies. In the most of tests, the modified 9Cr-1Mo steel (ASME Grade 91 steel) and austenitic stainless steel with a circumferential initial imperfection corresponding to elephant’s foot buckling mode under monotonic compressive load accompanied with constant horizontal load, were applied to confirm the applicability of the proposed modified buckling strength evaluation method to the vessels which has various yield stresses corresponding to the materials applied in FRs under the severe imperfection. Meanwhile, the applicability of the proposed method considering the effect of cyclic axial load was confirmed for only a Grade 91 steel vessel with longitudinal wrinkles imperfection resembling the shear buckling mode, where the test result showed larger buckling strength compared to the vessels with the circumferential initial imperfection, and slight reduction of buckling strength due to elastic buckling by applying high yield stress material.
In this paper, we confirmed the applicability of the proposed modified evaluation method considering the reduction of buckling strength due to cyclic axial load with constant horizontal load corresponding to seismic isolation design calculated by the analyses, through a series of buckling test of vessels with the circumferential initial imperfection made of Grade 91 steel (high yield stress) and austenitic stainless steel (low yield stress) subject to the cyclic axial loading. The initial imperfection was designed as the most severe shape decreasing buckling strength, and the austenitic stainless steel vessels with low yield stress resulting elasto-plastic buckling was considered to have a larger reduction in buckling strength accompanied by the plastic deformation prior to buckling than Grade 91 steel vessels. The experimental results confirmed the conservativeness of the proposed modified evaluation method to the elasto-plastic buckling of both Grade 91 steel and austenitic stainless steel vessels considering cyclic axial load and a severe imperfection shape. The buckling behavior and the buckling load estimated by the elasto-plastic buckling analysis considering the actual material stress–strain relationship and imperfections in these test vessels suitably agreed with corresponding test results.

Presenting Author: Takashi Okafuji Mitsubishi Heavy Industries, LTD.

Presenting Author Biography: Working for Mitsubishi Heavy Industries in Strength Laboratory, Research & Innovation Center
as Manager.
Obtained Ph.D degree from Kyushu university.
Adressing buckling and impact strength for 10 years.

Authors:

Takashi Okafuji Mitsubishi Heavy Industries, LTD.
Kazuhiro Miura Mitsubishi Heavy Industries, LTD.
Hiromi Sago Mitsubishi Heavy Industries, LTD.
Hisatomo Murakami Mitsubishi FBR Systems, Inc.
Masanori Ando Japan Atomic Energy Agency
Satoshi Okajima Japan Atomic Energy Agency