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Udagawa, Makoto; Katsuyama, Jinya; Yamaguchi, Yoshihito; Li, Y.; Onizawa, Kunio
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 9 Pages, 2015/07
The J-integral solution for cracked pipes is a high important parameter in crack growth calculation and failure evaluation based on the elastic-plastic fracture mechanics. One of the most important crack types in structural integrity assessment for nuclear piping systems is circumferential semi-elliptical surface crack. Although several J-integral solutions have been provided, no solution was developed at both the deepest and the surface points of circumferential semi-elliptical surface cracks. In this study, the J-integral solutions of circumferential semi-elliptical surface cracks were developed by numerical finite element analyses. Moreover, in order to benefit users in practical applications, a pair of convenient J-integral estimation equations were developed. The accuracy and applicability of the convenient equations were confirmed by comparing with the provided stress intensity factor solutions in elastic region and with finite element analysis results in elastic-plastic region.
Takamizawa, Hisashi; Tobita, Toru; Otsu, Takuyo; Katsuyama, Jinya; Nishiyama, Yutaka; Onizawa, Kunio
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
Fracture toughness evaluation by the Master Curve method using miniature compact tension (Mini-C(T)) specimens taken from the broken halves of surveillance Charpy specimens has been proposed. We performed finite element analysis (FEA) to examine the difference in constraint effect of the crack tip for the different size C(T) and precracked Charpy v-notch specimens. The constraint effect for Mini-C(T) specimens in terms of the T-stress and Q-parameter was similar to the larger C(T) specimens. To optimize the fatigue precracking conditions for the Mini-C(T) specimen fabrication, plastic zone distribution analysis was performed. We confirmed the fatigue precrack length and the availability of the mitigated crack shape for Mini-C(T). We also obtained the fracture toughness data for different sizes specimen. It was shown that To obtained from the Mini-C(T) specimens is in reasonably good agreement with that from others. We compared the fracture toughness data with T41J based fracture toughness curves proposed in recent study. All of the data were well enveloped by the proposed lower bound curve.
Yamaguchi, Yoshihito; Katsuyama, Jinya; Li, Y.; Onizawa, Kunio
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 8 Pages, 2015/07
Japanese nuclear power plants have recently experienced several large earthquakes beyond the previous design basis ground motion. In addition, cracks resulting from long-term operation have been detected in piping lines. Therefore, it is very important to establish a crack growth evaluation method for cracked pipes that are subjected to large seismic cyclic response loading. In our previous study, we proposed an evaluation method for crack growth during large earthquakes through experimental study using small specimens. In the present study, crack growth tests were conducted on pipes with a circumferential through-wall crack, considering large seismic cyclic response loading with complex wave forms. The predicted crack growth values are in good agreement with the experimental results for both stainless and carbon steel pipe specimens and the applicability of the proposed method was confirmed.
Li, Y.; Hasegawa, Kunio; Miura, Naoki*; Hoshino, Katsuaki*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 10 Pages, 2015/07
The failure estimation method in ASME Code Section XI accounts for the bending moment and axial force due to pressure into account. The torsion moment is not considered. Recently, analytical investigations have been carried out by several authors on the limit load of cracked pipes considering multi-axial loads including torsion and two failure estimation methods for multi-axial loads including torsion moment with different ranges of values have been proposed. In this study, to investigate the failure behavior of cracked pipes subjected to multi-axial loads including the torsion moment and to provide experimental support for the failure estimation methods, failure experiments were performed on 20 mm diameter pipes with a circumferential surface crack or a through-wall crack under combined axial force and bending and torsion moments. Based on the experimental results, the proposed failure estimation methods were confirmed to be applicable to cracked pipes subjected to multi-axial loads.
Li, Y.; Hasegawa, Kunio; Miura, Naoki*; Hoshino, Katsuaki*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 8 Pages, 2015/07
Piping lines in nuclear power plants may experience multi-axial loads including tensile force, bending and torsion moments during operation. There is a lack of guidance for failure evaluation under the multi-axial loads including torsion moment. ASME B&PV Code Section XI Working Group is currently developing fully plastic failure evaluation procedures for pressurized piping items containing local wall thinning subjected to multi-axial loads. A failure estimation method for locally wall thinned pipes subjected to multi-axial loads including torsion moment has been proposed through numerical analyses. In this study, in order to investigate the failure behavior of the pipes with local wall thinning subjected to multi-axial loads including the torsion, failure experiments were performed on 20 mm diameter carbon steel pipes with a local wall thinning. Based on the experimental results, the proposed failure estimation method is confirmed to be applicable to pipes with local wall thinning.
Hasegawa, Kunio; Li, Y.
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 9 Pages, 2015/07
Stress intensity factors (SIFs) for pipes with semi-elliptical cracks containing large aspect ratios were calculated by finite element analysis. The cracks were circumferential and axial surface cracks inside the pipes. The parameters of the SIFs are crack aspect ratio, crack depth and the ratio of pipe radius to wall thickness. In comparing SIFs for plates and pipes, it can be clarified that SIFs for both plates and thin pipes are almost the same, and the SIFs for plates are used as a substitute for pipes. This means that it is not necessary to provide SIF solutions for thin wall pipes, and it is suggested that tables for influence coefficients G values for pipes might reduce to one third.
Hasegawa, Kunio*; Li, Y.; Lacroix, V.*; Strnadel, B.*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
A subsurface flaw located near a component surface is transformed to a surface flaw in accordance with a flaw- to-surface proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the criteria of the re-characterizations are different among the FFS codes. In addition, the proximity factors in the rules are defined by constant values, irrespective of flaw aspect ratios. This paper describes the stress intensity factor interaction between the subsurface flaw and component free surface, and proposes a proximity factor from the view point of fatigue crack growth rates.
Katsuyama, Jinya; Huang, L.; Li, Y.; Onizawa, Kunio
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 8 Pages, 2015/07
When the structural integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) events is assessed, an underclad crack is postulated at the inner surface of RPV and the stress intensity factor (SIF) is evaluated for this crack. On the inner surface of RPV, cladding of stainless steel is overlay-welded as a means for corrosion protection. Because the cladding is a ductile material, it is important to evaluate the SIF considering the plasticity of cladding. A SIF evaluation method considering the effect of plasticity has been established in France. In this study, we examined the SIF evaluation method for underclad cracks during PTS transients. The elastic and elastic-plastic analyses based on the finite element method considering PTS events and inner pressure were performed using three-dimensional models including an underclad semi-elliptical crack with different geometry. We showed the conservativeness of plastic correction method based on the analysis results.
and K
for Japanese RPV steelsKatsuyama, Jinya; Katsumata, Genshichiro; Onizawa, Kunio; Osakabe, Kazuya*; Yoshimoto, Kentaro*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 9 Pages, 2015/07
Probabilistic fracture mechanics (PFM) analysis code PASCAL3 has been developed to apply the PFM analysis to the structural integrity assessment of domestic RPVs. In this paper, probabilistic evaluation models of fracture toughness KIc and KIa which have the largest scatter among the associated factors based on the database of Japanese RPV steels are presented. We developed probabilistic evaluation models for KIc and KIa based on the Weibull and lognormal distributions, respectively. The models are compared with the existing lower bound of fracture toughness in the Japanese code and probabilistic model in USA. As the results, the models established in present work satisfy lower bounds of fracture toughness in the Japanese code. The comparison in the models between present work and US showed significant differences that may have an influence on fracture probability of RPV.
Osakabe, Kazuya*; Masaki, Koichi*; Katsuyama, Jinya; Katsumata, Genshichiro; Onizawa, Kunio; Yoshimura, Shinobu*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 8 Pages, 2015/07
A probabilistic fracture mechanics (PFM) analysis method for pressure boundary components is useful to evaluate the structural integrity in a quantitative way. This is because the uncertainties related to influence parameters can be rationally incorporated in PFM analysis. From this viewpoint, the probabilistic approach evaluating through-wall cracking frequencies (TWCFs) of reactor pressure vessels (RPVs) has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. As a study of applying PFM analysis to the integrity assessment of domestic RPVs, JAEA has been preparing input data and analysis models to calculate TWCFs using PFM analysis code PASCAL3. In this paper, activities have been introduced such as preparing input data and models for domestic RPVs, verification of PASCAL3, and formulating guideline on general procedures of PFM analysis for the purpose of utilizing PASCAL3. In addition, TWCFs for a model RPV evaluated by PASCAL3 are presented.
Katsumata, Genshichiro; Li, Y.; Hasegawa, Kunio; Lacroix, V.*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 6 Pages, 2015/07
If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the specific criteria of the re-characterizations are different among the FFS codes. Recently, the authors have proposed a new subsurface-to-surface flaw proximity rule based on experimental data and equivalent fatigue crack growth rates. In this study, fatigue crack growth calculations were carried out for pipes with subsurface flaws, using the proposed subsurface-to-surface flaw proximity rule and the current proximity rule provided in the current JSME and ASME Section XI. Different pipe sizes, flaw aspect ratios and ligament distances from subsurface flaws to inner surface of pipes were taken into account. As the results, the current proximity rule gives less conservative fatigue lives, when the aspect ratios of the subsurface flaws are small.
Azuma, Kisaburo*; Li, Y.; Hasegawa, Kunio
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 5 Pages, 2015/07
Multiple flaws detected during in-service inspections are evaluated in accordance with the flaw combination rule provided in the ASME B&PV Code Section XI. The rule treats adjacent two flaws as a single combined flaw if the distance between the two flaws is equal to or less than half of the flaw depth. That is, the combination rule is consisted of flaw depth basis. However, its applicability has not been clarified systematically to the flaws with large aspect ratio, the depth of which are greater than half its length. Interactions of stress intensity factors for multiple flaws under membrane stress were investigated using finite element analyses. The numerical results suggest that the flaw combination rule might be better to use flaw length basis, instead of flaw depth.
Nagae, Yuji; Yamamoto, Kenji*; Otani, Tomomi*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
Lacroix, V.*; Hasegawa, Kunio; Li, Y.
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The authors have proposed a new subsurface-to-surface flaw proximity rule based on the experiments data and the interaction of stress intensity factors. In this study, eXtended Finite Element fatigue crack growth calculations were carried out for thick wall component like vessels with subsurface flaws, using the proposed subsurface-to-surface flaw proximity rule and the proximity rule provided in the current ASME Code Section XI. Different flaw aspect ratios and ligament distances from subsurface flaws to inner surface of vessel were taken into account. As the results, the current proximity rule and proposed one provide relatively similar fatigue lives, whatever the aspect ratios of the initial subsurface flaws. However, when the thickness of the component decreases this similarity between both proximity rules appears not to be valid anymore.
Kawasaki, Nobuchika; Yamamoto, Tomohiko; Fukasawa, Tsuyoshi*; Okamura, Shigeki*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 9 Pages, 2015/07
Japanese seismic conditions are getting severer and natural frequencies of components are getting lower due to the enlargements of components' size, therefore response accelerations and buckling margins of reactor vessels were parametrically surveyed with attention to thicknesses, diameters, and isolation frequencies for reviewing necessary isolation specification. RV installed floor responses and buckling margins were calculated based on this seismic condition. Expansion characteristic of isolation system was evaluated by parametric acceleration response analyses. Japanese seismic design condition may become severer than present one, and a natural frequency of main component may decrease. However based on the buckling margin with present plant specifications and the expansion characteristic of isolation system, the advanced isolation system with 8Hz vertical natural frequency was selected as the isolation system of JSFR at still present occasion.
Takaya, Shigeru; Tanaka, Masaaki; Fujisaki, Tatsuya*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
Flow-induced vibration of hot-leg pipings is one of concerns for the design of Japan Sodium-cooled Fast Reactor (JSFR) which is now being developed. The flow field in the hot-leg pipings is supposed to be affected by flow disturbances at the entrance, so it is important to evaluate flow fields including the upper plenum. In this study, a simulation model of the upper plenum and the hot-leg piping system of JSFR was developed. Unsteady fluid flow analyses were then conducted by unsteady Reynolds averaged Navier-Stokes simulation (URANS) with Reynolds stress model. The appropriateness of the calculated results was discussed by comparing available scale model test results. Furthermore, a prototype model for vibration analysis of the hot-leg piping was developed. In the model, the transient pressure data predicted by the URANS were used as input data for the vibration analysis.
Nishida, Akemi; Iigaki, Kazuhiko; Sawa, Kazuhiro; Li, Y.
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
The objective of this research was to investigate the influence of differences between methods for evaluating the seismic safety of the equipment and piping of a nuclear facility. For the input ground motion, one wave was chosen from among 200 waves of input ground motions of maximum acceleration of 700-1100 cm/s
created for the Oarai District of the Ibaraki Prefecture. Seismic safety evaluations were performed using the conventional method, which relies on floor response spectrum data, and using the multi-input method. The differences between the two methods were summarized. The target equipment and piping system were cooling systems in a model plant. It was found that the response predicted by the multi-input method was approximately half of the response predicted by the conventional method. The third trial evaluation method using the floor response of a three-dimensional building model as input was also reported.
Yamamoto, Tomohiko; Kawasaki, Nobuchika; Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Somaki, Takahiro*; Samejima, Yusuke*; Masaki, Nobuo*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 7 Pages, 2015/07
Since a SFR (Sodium-cooled Fast Reactor) has thin-walled component structures, a seismic isolation system is employed to mitigate the seismic force. Seismic isolation system for applying the SFR consists of the laminated rubber bearing considering characteristics of SFR structures. This paper describes a basic mechanical characteristic examination with a 1/8 scale model and a characterization examination plan of half-scale laminated rubber.
Fukasawa, Tsuyoshi*; Okamura, Shigeki*; Yamamoto, Tomohiko; Kawasaki, Nobuchika; Somaki, Takahiro*; Sakurai, Yu*; Masaki, Nobuo*
Proceedings of 2015 ASME Pressure Vessels and Piping Conference (PVP 2015) (Internet), 10 Pages, 2015/07
This paper described the results of static loading tests using a half-scale rubber bearing model to investigate the fundamental characteristics such as restoring force of a rubber bearing applied to a Sodium-Cooled-Fast-Reactor (SFR). Since the SFR has thin-walled structures, a seismic isolation system is employed to mitigate the seismic force. The static loading tests were performed using the half-scale rubber bearing with a diameter of 800 mm in the range which exceeds a linear limit of horizontal direction and a yield stress of vertical direction to investigate the horizontal and vertical of each stiffness and damping ratio. The fundamental characteristic of rubber bearing employed to the SFR and the validity of a design formula became clear through the static tests.
