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Katsuyama, Jinya; Asano, Wataru*; Onizawa, Kunio; Mochizuki, Masahito*; Toyoda, Masao*
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 8 Pages, 2007/07
Stress corrosion cracking (SCC) of recirculation pipes of austenite stainless steel has been observed. The SCC initiates and grows near the welding zone because of high tensile residual stress by welding. Therefore, the residual stress analysis due to welds of piping is becoming important. In present work, the through-thickness residual stress distributions near multi-pass butt-welds of Type 316L pipes have been calculated by thermo-elastic-plastic analyses. Then crack growth simulations were performed using calculated residual stress distributions. The effects of geometric and welding conditions on crack growth behavior were also discussed.
Onizawa, Kunio; Osakabe, Kazuya
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 7 Pages, 2007/07
During a pressurized thermal shock (PTS) event, the overlay cladding on the inner surface of reactor pressure vessel (RPV) is subjected to high tensile stress compared to base metal because of the difference in thermal expansion coefficients between cladding and base metal. To calculate a stress intensity factor for a postulated crack considering the stress discontinuity with the plastic yielding of cladding, the scheme developed previously has been incorporated into the PASCAL code for the structural integrity analysis. Using the new scheme, conditional probabilities of crack initiation (PCI) were calculated for a typical RPV with a surface crack or under-clad crack under some PTS transients. The PCI values were quantitatively evaluated as a function of neutron fluence using the PASCAL code. It is concluded that the new scheme reduces significantly the PCI value for a surface crack as compared with the conventional methods based on elastic stress analysis.
Udagawa, Makoto; Katsuyama, Jinya; Onizawa, Kunio
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 7 Pages, 2007/07
In order to assess the structural integrity of a reactor pressure vessel (RPV), it is assumed that a surface crack resides through the cladding at the inner surface of the vessel. It is, therefore, important to precisely evaluate stress intensity factor (SIF) taking the residual stress due to weld overlay cladding and post-weld heat treatment (PWHT) into account. In this study, we performed a numerical simulation based on thermal-elastic-plastic-creep analysis using finite element method to evaluate residual stress distribution near the cladding layer produced by weld overlay cladding and PWHT. The tensile residual stress of about 400 MPa occurs in the cladding at room temperature after the PWHT. The residual stress distributions under the normal operating conditions (pressure and temperature) of RPV were also evaluated. The effect of residual stress and evaluation methods on SIF behavior for various crack size were studied under several PTS conditions such as SBLOCA, MSLB and LBLOCA.
Bubphachopt, B.*; Watanabe, Osamu*; Kawasaki, Nobuchika; Kasahara, Naoto
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 9 Pages, 2007/07
This study investigates the effects of creep behavior on fatigue strength of the perforated plate at elevated temperature, when SRL (Stress Redistribution Locus) method is applied for the perforated plate. The creep-fatigue test is carried out by using the specimens made of SUS304 stainless steel at the temperature of 550
C. The trapezoidal wave having tensile hold time at peak strain is assumed. The geometry of the perforated plate specimens are changed in the same manner of the fatigue test by number of holes and diameter size of the hole. The linear damage rule for fatigue and creep is assumed, and the comparison between the experimental results and SRL method evaluation at the Coffin diagram will be made. Both of the load and displacement are measured in all the cyclic history of the loadings to clarify the relation between crack initiation/propagation and the load decrease from the direct observation of crack at the holes side.
Watanabe, Osamu*; Bubphachopt, B.*; Kawasaki, Nobuchika; Kasahara, Naoto
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 9 Pages, 2007/07
This study reports the effects of geometry on fatigue strength of the perforated plate at elevated temperature when SRL (Stress Redistribution Locus) Method is applied for the perforated plate with stress concentration. The test specimens made of SUS304 stainless steel are carried out by keeping temperature to be 550C. The geometry of the perforated plate specimens are changed systematically by the number of holes and diameter size of the hole, where one or two holes are placed along the width direction, and the diameter is set to be from 2 mm to 8 mm. Both of the load and displacement are measured in all the cyclic history of the loadings to study the relation between crack initiation/propagation and the load decrease from the direct observation of crack at the holes side.
Sakai, Shinsuke*; Honda, Kei*; Okajima, Satoshi*; Izumi, Satoshi*; Kasahara, Naoto
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 7 Pages, 2007/07
At an incomplete mixing area of high and low temperature fluids, fluid temperature fluctuation often occurs. It induces cyclic thermal stresses in the wall, which may result in fatigue crack initiation. Kasahara et al. proposed the thermal fatigue evaluation method based on power spectrum density (PSD). This method generalizes the evaluation procedure by preparing PSD charts of fluid and frequency transfer functions of stress for various kinds of plant components. From design point of view, however, this method is too complicated due to the inverse Fourier transform and wave decomposition procedures named Rain Flow Cycle Counting (RFC). In this paper, simplified damage evaluation method for thermal fatigue is proposed by directly evaluating fatigue damage from PSD of stress.
Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 6 Pages, 2007/07
This paper describes the dynamic strength evaluation of piping installed in nuclear power plants from a viewpoint of energy balance. In this study, ultimate strength of a simple single degree of freedom model is investigated from a viewpoint of energy balance equation that is one of valid methods for structural calculation. The investigation is implemented by forced vibration experiment. In the experiment, colored random wave having predominant frequency similar to natural frequency of the experimental model is input. Stainless steel and carbon steel are selected as material of experimental model. As a result of the experiment, it is confirmed that input energy for fracture increase with an increase of time for fracture. In other words, more input energy for fracture is needed in case of small input level. Additionally it is confirmed that input energy for fracture depend on the material.
Kawasaki, Nobuchika; Hasebe, Shinichi; Kobayashi, Sumio; Kasahara, Naoto
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 8 Pages, 2007/07
Thermal fatigue strength tests subjected to sinusoidal fluid temperature waves were performed by the SPECTRA test facility, where frequencies were 0.05, 0.2, and 0.5Hz. Cracks were observed on the inner surface of cylindrical test pieces after testing. 0.05Hz's wave caused a greater number of and deeper cracks than 0.5Hz's wave under the same fluid temperature range and the same fatigue cycles. The crack initiation region of the 0.05Hz's wave was larger than for the 0.5Hz's wave. Estimated fatigue failure cycles based on the frequency transfer functions were compared with test results. Frequency-dependency in failure cycles was observed through these test results, and frequency transfer functions could estimate this dependency. The test results supported the fatigue damage evaluation method with frequency transfer functions.
Mochizuki, Masahito*; Higuchi, Ryota*; Katsuyama, Jinya; Toyoda, Masao*
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 8 Pages, 2007/07
The strength properties of structural steels or their weld zone are influenced by the microscopic heterogeneity. It is important to investigate the stress distribution for clarification of the mechanism of fracture and the material design by considering a grain boundary or its neighborhood because either can be a zone where the stress concentration is likely to occur due to a mismatch of the displacement. For this purpose, FEM-MD coupling method is one of the useful methods because it can treat the mismatch of the displacement caused by the microscopic heterogeneity. In this study, FEM-MD coupling method is proposed and the influence of the microscopic heterogeneity of steels is investigated by using FEM-MD coupling method.
Planman, T.*; Onizawa, Kunio; Server, W.*; Rosinski, S.*
Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 9 Pages, 2007/07
In the Master Curve (MC) fracture model, a universal temperature dependence is assumed for reactor pressure vessel (RPV) steels. The assumed curve shape has been observed to be generally valid for highly irradiated materials. Lower than predicted fracture toughness behavior has been occasionally observed, however, in the upper transition range. One objective of the present IAEA CRP is to clarify the MC shape issue by collecting and analyzing relevant fracture toughness data on irradiated or thermally aged RPV steels. The data reviewed in this CRP show, in general, a very consistent fracture behavior with the basic MC model that further confirms the applicability of the assumed curve shape. In cases where the basic assumptions of the MC model were not satisfied due to high proportions of intergranular fracture, correspondence with the measured and predicted behavior could be markedly improved by applying available models developed to address inhomogeneous materials.
Mitsuhara, Masatoshi*; Yoshida, Yu*; Ikeda, Kenichi*; Nakashima, Hideharu*; Wakai, Takashi
no journal, ,
The effect of V and Nb on creep strengthening was studied in 10% Cr steels. In a steel added 0.06% V where no particles were observed in the lath, creep strength was slightly increased, indicating that it was not strengthened by particle hardening effect in the lath. Lump-shaped precipitates and film-shaped precipitates including Cr and V, which were observed on lath boundaries in the steel added V, are expected to inhibit the lath boundaries from migrating. This inhibition is the mechanism of the improvement in the steel added V. In the case of steels added Nb individually, creep strength was found to be increased by dispersion hardening due to fine precipitates in the lath. These results revealed that V and Nb have each role to improve creep strength. In steels added both V and Nb, the effect on creep strength was expressed by the sum of the effects due to each element, which were the retardation of the lath boundary migrations and the pinning of the dislocations in the lath.