A Model to Predict Stress Corrosion Cracking of Welded Stainless Steel Canister
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A Model to Predict Stress Corrosion Cracking of Welded Stainless Steel Canister Gen Nakayama 1, Yohei Sakakibara 1, Tomomi Kouketsu 1, Kouji Arakawa 1, Yutaka Mizo 2, Iku Miyasaka 3, Yumiko Iwata 3, Susumu Kawakami 3, Hirotomo Setaka 4, Naoki Hieda 5 1
Research Laboratory, IHI Corporation, 1, Shin-nakahara-cho, Isogo-ku, Yokohama 235-8501, Japan 2 Production Engineering Center, IHI Corporation 3 Nuclear Power Operations, IHI Corporation 4 Plant Project Department, IHI Corporation 5 Kitakyushu Liquefied Natural Gas CO., Inc., Kitakyuushu, 804-0002, Japan ABSTRACT Fabricated stainless steel structures are susceptible to stress corrosion cracking (SCC), despite being placed in chloride-containing natural water or humid atmospheres. The present paper describes a model that can define the conditions under which SCC is initiated and propagated, based on analyses of actual SCC incidents induced at welded flanges of cylindrical stainless steel structures. Whenever the vitrified radioactive waste canister storage conditions deviate from normal and appropriate conditions due to earthquakes or tsunamis, the exposed canisters are expected to suffer SCC within 400 hours to 7 years, according to the analytical results obtained such as degree of sensitization, residual stress distribution, chloride ion concentration, and temperature. INTRODUCTION The vitrified radioactive waste materials into stainless steel canisters are to be stored at the environmentally controlled indoor sites for about 30 to 50 years before being treated in formation geological disposal. The heat generation rate after 50 years is expected to be 350 W and the dose is expected to be 160 Sv h-1. A temperature history is assumed in which canisters are exposed to disaster such as tsunami at a temperature of 70°C and under semi-immersed sea water conditions. Stainless steel is widely known to be susceptible to SCC in a neutral environment containing chloride ions. However, welded parts of SUS304 (18Cr-8Ni) stainless steel are severely sensitized when the heat affected zone (HAZ) is reheated by repair welding. Furthermore, the cold-worked materials for manufacturing such as bending and forging are easy to sensitize. The SUH309 (22Cr-12Ni-high C) steel used for the canister specification deals with heat-resistant stainless steel and contains more chromium and carbon, which means it becomes susceptible to sensitization. Furthermore, when the HAZ is subjected to residual fields of tensile stress due to repair welding, the sensitized repair welded parts in a semi-immersed sea water condition are prone to SCC. SCC FACTORS and EVALUATION Chemical compositions belong to series of SUS304, SUS309 and SUS321 are shown in Table 1. The intergranular SCC to be induced by the sensitization of the alloy is initiated at the
4179 Downloaded from https:/www.cambridge.org/core. Monash University, on 22 Apr 2017 at 08:54:02, subject to the Cambridge Core terms of use, available at https:/www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2017.206
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