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Akita, Koichi; Shibahara, Masakazu*; Ikushima, Kazuki*; Nishikawa, Satoru*; Furukawa, Takashi*; Suzuki, Hiroshi; Harjo, S.; Kawasaki, Takuro; Vladimir, L.*
Yosetsu Gakkai Rombunshu (Internet), 35(2), p.112s - 116s, 2017/06
Ikushima, Kazuki*; Kitani, Yuji*; Shibahara, Masakazu*; Nishikawa, Satoru*; Furukawa, Takashi*; Akita, Koichi; Suzuki, Hiroshi; Morooka, Satoshi
Yosetsu Gakkai Rombunshu (Internet), 35(2), p.75s - 79s, 2017/06
Takano, Katsutoshi; Koizumi, Norikiyo; Serizawa, Hisashi*; Tsubota, Shuho*; Makino, Yoshinobu*
Yosetsu Gakkai Rombunshu (Internet), 33(2), p.126 - 132, 2015/06
A radial plates (RP), which is used in Toroidal field (TF) coil in ITER, is significantly large, such as 13 m height and 9 m wide, but thin, such as 10 cm thick, and are made of full-austenite stainless steel. Even though they are very large structures, high manufacturing tolerances are required. In addition, it is required that each RP is fabricated every three weeks. Therefore, the authors develop efficient manufacturing methods of RP. The laser welding is selected as a welding method of RP. But the development of the high power laser welding technology is necessary to avoid hot cracking of the materials used for RP, namely full austenite stainless steel with high nitrogen content. The authors carried out trial aiming at an application of the laser welding to RP. As a result, it is effective to optimize the angle of inclination of the weld head. It also seems sensitivity of hot cracking can be less by optimizing the chemical composition of materials to use for RP. It was therefore demonstrated that the application of the laser welding technology in the full austenite stainless steel.
Takano, Katsutoshi; Koizumi, Norikiyo; Masuo, Hiroshige*; Natsume, Yoshihisa*
Yosetsu Gakkai Rombunshu (Internet), 32(1), p.8 - 14, 2014/03
The authors performed trial manufacture of the RP segments using a diffusion bonding method, namely Hot Isostatic Pressing (HIP). As a result of trials, it was clarified that even when HIPping is applied, the mechanical characteristic of base metal is not deteriorated. The machining period can be reduced by half compared with the traditional manufacturing method. On the other hand, mechanical strength at 4 K is degraded due to weak bonding, that is no grain growth through joint, by HIPping. However, additional test indicates promising possibility of much better joint by higher temperature and joint surface treated HIPpings. These results justified that RP segment manufacturing is not only possible, but it is a technically valid manufacturing method that satisfies all requirements.
Suzuki, Hiroshi; Katsuyama, Jinya; Tobita, Toru; Morii, Yukio*
Yosetsu Gakkai Rombunshu (Internet), 29(4), p.294 - 304, 2011/12
The RESA-1 neutron engineering diffractometer in the JRR-3 (Japan Research Reactor No.3) at the Japan Atomic Energy Agency, which is used for stress measurements, was upgraded to realize residual stress measurements of large scaled mechanical components. A series of residual stress measurements was made to obtain through-thickness residual stress distributions in a Type 304 stainless steel butt-welded pipe of 500A-sch.80 using the upgraded RESA-1 diffractometer. We evaluated effects of crack propagation such as stress corrosion cracking (SCC) and a part-circumference repair weld on the residual stress distributions induced by girth welding. Measured residual stress distributions near original girth weld revealed good agreement with typical results shown in some previous works using finite element method, deep hole drilling as well as neutron diffraction. After introducing a mock crack with 10 mm depth in heat affected zone on the inside wall of the pipe by electro discharge method, the axial residual stresses were found to be released in the part of the mock crack. However, changes in the through-wall bending stress component and the self-equilibrated stress component were negligible and hence the axial residual stress distribution in the ligament was remained in the original residual stresses near girth weld without the mock crack. Furthermore, changes in hoop and radial residual stress were also small. The residual stress distributions after a part repair welding on outer circumference of girth weld were significantly different from residual stress distributions near the original girth weld. Membrane residual stress was increased in the axial direction since the bending moment near the heat affected zone was changed due to repair weld. Throughout above studies, we evidenced that the neutron diffraction technique is useful and powerful tool for measuring residual stress distributions in large as well as thick mechanical components.
Yamashita, Susumu; Yonemoto, Yukihiro; Yamada, Tomonori; Kunugi, Tomoaki*; Muramatsu, Toshiharu
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.48s - 52s, 2011/08
Quantitative evaluation and controlling the residual stress which is induced by laser welding is of important problem for a life extension of FBRs (Fast Breeder Reactors) and the guarantee of the reliability of the repair processes. Numerical simulation is an effective tool for deep understanding of their problems and it needs to have high accuracy, robustness and reliability. We have recently constructed the fully parallelized laser welding simulation code which satisfies above aspects using some advanced numerical models. Concretely, VSIAM3 numerical model as the spatial discretization, an efficient free surface capturing scheme, THINC scheme, and FAVOR method as the solid phase expression has been applied to the code. We have conducted laser welding simulations and obtained some reasonable results. Therefore, the numerical model will be contributed to the repairing technology of a laser welding.
Yamada, Tomonori; Yonemoto, Yukihiro; Yamashita, Susumu; Muramatsu, Toshiharu; Komizo, Yuichi*
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.86s - 89s, 2011/08
It is known that residual stress is important to keep the structural integrity. Laser welding is effective for the residual stress decrease because heat input is smaller and heats have a very small effect. Therefore, the repairing technology by laser welding has draw wide attention for a life extension of FBRs (Fast Breeder Reactors). To establish the laser repair technology, special attentions should be paid to the morphological developments. In the present work, morphological developments were directly observed using laser scanning conforcal microscopy during laser weld cooling.
Takase, Kazuyuki; Muramatsu, Toshiharu; Shobu, Takahisa
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.43s - 47s, 2011/08
At the commercial use stage in sodium-cooled fast reactors, a securing maintenance and repair more than the equal to that of present water-cooled reactors are requested. Especially, establishment of the repair technology that secures the plant integrity for long-term operation period becomes indispensable in the heat transfer tubes of the steam generator that forms the boundary of sodium and water coolants. Then, as aiming at the standardization of a fiber laser welding technology, an analytical study was begun to simulate numerically the laser welding characteristics of the micron-sized metallic particles on the stainless steel plate. The metallic particle is heated by the laser irradiation and then melts exceeding the melting temperature. From the present result, it was found that a prediction of the liquid metal thermal-hydraulics is possible and the present numerical approach is effective for the optimization of the laser welding method.
Ishikawa, Nobuyuki*; Sueyoshi, Hitoshi*; Suzuki, Hiroshi; Akita, Koichi
Yosetsu Gakkai Rombunshu (Internet), 29(3), p.218 - 224, 2011/08
Cold cracking test was conducted using Y-grooved constraint weld joint by intentionally introducing hydrogen gas, and critical hydrogen content in the weld metal to cold cracking was determined. Residual stress distribution in the weld meal was measured by neutron diffraction technique. The root portion showed highest tensile stress of over 1110 MPa in the transverse direction, which is the same as the crack opening direction.
Udagawa, Makoto; Katsuyama, Jinya; Nishikawa, Hiroyuki; Onizawa, Kunio
Yosetsu Gakkai Rombunshu (Internet), 28(3), p.261 - 271, 2010/07
Stainless steel is welded as a cladding on the inner surface of a reactor pressure vessel (RPV) made of low alloy steel. In order to assess the structural integrity of an RPV more precisely, the residual stress distribution caused by weld-overlay cladding and post-weld heat treatment (PWHT) is to be evaluated. Although cladding layer is very thin compared to vessel wall, it is not easy to evaluate steep residual stress distribution which occurs in dissimilar metal weld. In this study, cladded specimens were fabricated using different welding methods. Residual stress measurements using both sectioning and DHD methods were then performed to evaluate the residual stress distributions. It was shown that thermal-elastic-plastic-creep analysis results based on finite element method were agreed with experimental results. It was also clarified that the main cause of residual stress due to welding and PWHT was the difference of thermal expansion between weld and base metals.
Katsuyama, Jinya; Ito, Hiroto; Tobita, Toru; Onizawa, Kunio
Yosetsu Gakkai Rombunshu (Internet), 28(2), p.193 - 202, 2010/06
Weld residual stress near the welded joint of pipe is one of the most important factors to assess the structural integrity of piping because the tensile residual stress becomes a driving force of a stress corrosion cracking (SCC). In this study, a weld simulation method has been developed and verified. An effect of uncertainty of welding conditions, such as scatters of heat input and welding speed during welding, on weld residual stress at the piping butt-welds was evaluated using the simulation method by varying the welding conditions. Probabilistic fracture mechanics analysis using PASCAL-SP was also performed to evaluate the effect of uncertainty of weld residual stress on the break probability of piping. It was clarified that the break probability increased with increasing the uncertainties of residual stress.
Nishikawa, Hiroyuki; Katsuyama, Jinya; Onizawa, Kunio
Yosetsu Gakkai Rombunshu (Internet), 27(2), p.245s - 250s, 2009/08
Thermal-elastic-plastic-creep analyses based on finite element method have been performed to evaluate residual stress distribution in a RPV produced by weld-overlay cladding and PWHT. Stress intensity factors (SIFs) during PTS have also been computed based on the influence function method. The maximum value of SIF during PTS considering weld-overlay cladding is higher than that without the consideration of weld-overlay cladding. The effect of the weld-overlay cladding on the temperature margin of the structural integrity of RPVs has been evaluated. The effect of the weld-overlay cladding on the temperature margin is enough small that the effect would within the range of the margin set in the integrity assessment method.
