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Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 6 Pages, 2008/08
Ito, Hiroto; Katsuyama, Jinya; Onizawa, Kunio
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 6 Pages, 2008/07
In JAEA, we have been developing probabilistic fracture mechanics (PFM) analysis methods for aged piping based on latest aging knowledge and an analytical code, PASCAL-SP. PASCAL-SP evaluates the failure probability of piping at aged welded joints under SCC and In-Service Inspection by a Monte Carlo method. We proposes a probabilistic model which can be applied to the failure probability analysis based on PFM for welded joint of piping considering the uncertainty of welding residual stress. And the probabilistic evaluation model is introduced to PASCAL-SP. A parametric PFM analysis concerning uncertainties of residual stress distribution using PASCAL-SP was performed. The PFM analysis showed that the uncertainties of residual stress distribution about heat input and welding speed largely influenced break probability. The break probability increased with increasing the uncertainties.
Katsuyama, Jinya; Tobita, Toru; Ito, Hiroto; Onizawa, Kunio
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 9 Pages, 2008/07
Stress corrosion cracking (SCC) in recirculation pipes has been observed near butt-welding joints due to high tensile residual stress by welding. In present work, scatters of welding conditions such as heat input and welding speed were measured experimentally by producing a series of butt-welding pipe specimens. Distribution and its scattering of residual stress were also measured by non-destructive and destructive methods. The effects of welding conditions on residual stress have been evaluated by parametric FEM analyses considering the variation of some parameters based on the welding experiments. The effects of welding conditions on crack growth behavior have been also evaluated by SCC growth simulations using calculated residual stress distributions and a procedure in the fitness-for-service code. Welding conditions such as heat input and welding speed have a strong influence on crack growth rate since residual stress is also affected by scatter of these welding conditions.
Asano, Wataru*; Katsuyama, Jinya; Onizawa, Kunio; Mochizuki, Masahito*; Toyoda, Masao*
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 8 Pages, 2008/07
Stress corrosion cracking near welding zone of core internals and/or recirculation pipes of Type 316L stainless steel are initiated and grown at inner surface due to tensile residual stress and hardening. Surface-machining is conducted before and after piping butt-welding to match the ID of pipes and to provide a smooth surface finish, respectively. In present work, simulation evaluated residual stress by surface-machining before welding by using full scale FEM analysis was compared with experimental measurements. Piping-butt welding simulation was conducted after the surface-machining to evaluate redistribution behavior of residual stress by welding. Estimation of Vickers hardness distribution by surface-machining was carried out based on strained region map observed by FE-SEM equipped with EBSD and compared with experimental measurements. The effect of surface-machining before/after welding on distribution of residual stress and hardening are presented.
Kawasaki, Nobuchika; Takasho, Hideki*; Kobayashi, Sumio; Hasebe, Shinichi; Kasahara, Naoto
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 9 Pages, 2008/07
To clarify frequency-dependent attenuation effects of fluid temperature fluctuation on fatigue strength, thermal fatigue strength tests subjected to superposed sinusoidal temperature fluctuations were performed by the SPECTRA test facility. After these fatigue tests, cylindrical test pieces were cut away from the test loop, and cracks were observed on the inner surface of the test pieces. Fatigue lives at crack initiation positions were evaluated based on the test conditions. Adopting power spectrum density functions and frequency transfer functions, fatigue lives were predicted within a factor 3.
Ando, Masanori; Takasho, Hideki*; Kawasaki, Nobuchika; Kasahara, Naoto
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 10 Pages, 2008/07
Adoption of double-wall-straight tube steam generators made of Mod.9Cr-1Mo steel is planned for next generation fast breeder reactors in Japan. One of the major concerns relevant to the SG is structural integrity of tubesheets. In the reactor transient operation, thermal stress is induced by the temperature distribution in tubesheet and the magnitude of it depends on configurations of tubesheet. Stress generation mechanism of tubesheets was revealed through Finite Element analysis. Semi-spherical tubesheet models were investigated for the first survey of the thermal stress mechanism. As calculated results, semi-spherical tubesheet model gave the extensive peak stress around the outermost hole. Based on the those stress generation mechanism, authors proposed a stress mitigated tubesheet. It is center flatted spherical tubesheet as improved configuration.
Asayama, Tai; Jetter, R.*
Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 9 Pages, 2008/07
Renewed interest in elevated temperature nuclear reactors has occasioned a reassessment of creep-fatigue damage evaluation methods. Points to be improved in the current methods employed in Subsection NH of the ASME Boiler and Pressure Vessel Code and other design codes are discussed. Most current creep-fatigue damage evaluation methods separately evaluate cyclic fatigue damage and creep damage and assess the combined damage through interaction diagrams. In this paper, an alternate approach to determination of cyclic life has been proposed which avoids parsing the damage into creep and fatigue components. This approach, called the Simplified Model Test (SMT) has two major advantages. First, it is not necessary to calculate the inelastic stress-strain history for a design evaluation. Second, it is not necessary to rely on theoretical modeling of these effects in an artificial separate accounting of creep and fatigue damage.
Wakai, Takashi; Isobe, Nobuhiro*; Date, Shingo*; Asayama, Tai; Kubo, Shigenobu*
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