• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.3
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• pp.13-22
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• 2012

According to recent research on leak-rate estimates to assess rupture probabilities of nuclear piping which contains a circumferential surface/through-wall cracks due to PWSCC, i.e., xLPR (Extremely Low Probability of Rupture) program, it has been revealed that the use of crack shape with an idealized circumferential through-wall crack during actual crack growth can lead to overestimate of the leak-rate. Thus, for accurate estimation of the leak-rate during crack growth, the more realistic crack shape that can simulate the crack shape transition from surface crack to through-wall crack should be used. In this context, in the present study, the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder was proposed based on 3-dimensional elastic finite element fracture mechanics analyses. To propose the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder, the geometric variables affecting crack opening displacement, i.e., thickness of cylinder, reference inner crack length and slant crack ratio were systematically varied. In terms of loading conditions, axial tension, global bending moment and internal pressure were considered. The present results can be applied to calculate the leak-rate considering more realistic crack shape transition from surface crack to idealized through-wall crack, and can be expected to enhance current leak-rate estimation scheme, for instance, in xLPR program etc.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.4
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• pp.160-166
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• 2001

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.417-420
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• 2000

The theoretical analyses for stresses induced in axial direction in the buried pipelines are reviewed. The influences of the axially directed stresses on the surface elliptical crack are studied in detail and thus some engineering technical informations are provided to use reliability assessment of buried pipelines. The change in temperature, the effect of inner pressure and soil friction in the buried pipeline constrained in axial direction are included to determine the axial stresses in the buried pipeline. Furthermore, the stress induced by the pipeline bending are also considered. The stress intensity factors calculated by two models such as a simple plane crack and an elliptical surface crack for a circumferential surface elliptical crack are compared.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1798-1809
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• 1996

The purpose of this paper is to develop new Z-Factors to evaluate the behavior of circumferential surface crack in ferritic steel piping including base metal and Submerged Arc Weld(SAW) metal in nuclear power plant. The Z-factor is a load multiplier to convert plastic load to elasto-plastic load. However the current Z-Factor is a load multiplier to convert plastic load to elasto-plastic load. However the current Z-Factor gives too conservative results. In this study, a J-estimation method, SC.TNP method, which is based on GE/EPRI expression, is used to develop new Z-Factors. The desirabilities of both the SC.TNP mehtod and the new Z-Factors are examined using the previous experimental results for the circumferential surface crack in ferritic steel pippings. The results are as follows ; (1) The SC.TNP mehtod is good for describing the circumferential surface crack behavior in farritic steel pipings, while the well-known R6 mehtod and DPFAD method give too conservative results. (2) The ASME-Z-Factor method using nwe Z-Factors well predicts the behavior of circumferential surface crack in ferritic steel pipings including base emtal and SAW metal.

• Nuclear Engineering and Technology
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• v.28 no.2
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• pp.185-196
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• 1996

The purpose of this paper is to modify the ASME Code Z-Factor, which is used in the evaluation of circumferential surface crack in nuclear ferritic pipings. The ASME Code Z-Factor is a load multiplier to compensate plastic load with elasto-plastic load. The current ASME Code Z-Factor underestimates pipe maximum load. In this study, the original SC. TNP method is modified first because the original SC. TNP method has a problem that the maximum allowable load predicted from the original SC. TNP method is slightly higher than that measured from the experiment. Then the new Z-Factor is developed using the modified SC. TNP method. The desirability of both the modified SC. TNP method and the new Z-Factor is examined using the experimental results for the circumferential surface crack in pipings. The results show that (1) the modified SC. TNP method is good for predicting the circumferential surface crack behavior in pipings, and (2) the Z-Factor obtained from the modified SC. TNP method well predicts the behavior of circumferential surface crack in ferritic pipings.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.139-146
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• 2002

This paper provides validations of the reference stress based J and $C^{*}$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^{*}$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^{*}$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.front.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.310-315
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• 2001

This paper provides validations of the reference stress based J and $C^*$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^*$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^*$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1182-1195
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• 1999

The purpose of this study is to investigate experimentally the effects of both seismic loading and crack length on the fracture behavior of piping system with a circumferential crack in nuclear power plants. The experiments were performed using both large scale piping system facility and 4 points bending test machine under PWR operating conditions. The difference in the load carrying capacities between cracked piping and non-cracked piping was also investigated using the results from experiments and numerical calculations. The results obtained from the experiments and estimation are as follows : (1) The safety margin under seismic loading is larger than those under quasi static loading or simple cyclic loading. (2) There was no significant effect of crack length on tincture behavior of piping system with both a surface crack and a through-wall crack. (3) The load carrying capacity in cracked piping was reduced by factors of 7 to 46 compared to non-cracked piping.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.26-33
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• 2003

Based on detailed FE limit analyses, the present paper provides tractable approximations fer plastic limit pressure solutions fur axially through-wall-cracked pipe; axially (inner) surface-cracked pipe; circumferentially through-wall-cracked pipe; and circumferentially (inner) surface-cracked pipe. In particular, for surface crack problems, the effect of the crack shape, the semi-elliptical shape or the rectangular shape, on the limit pressure is quantified. Comparisons with existing analytical and empirical solutions show a large discrepancy in circumferential short through-wall cracks and in surface cracks (both axial and circumferential). Being based on detailed 3-D FE limit analysis, the present solutions are believed to be the most accurate, and thus to be valuable information not only for plastic collapse analysis of pressurised piping but also for estimating non-linear fracture mechanics parameters based on the reference stress approach.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1766-1771
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• 2007

This paper presents plastic limit loads and approximate J-integral estimates for circumferential part-through surface crack at the interface between elbows and pipes. Based on finite element limit analyses using elastic-perfectly plastic materials, plastic limit moments under in-plane bending are obtained and it is found that they are similar those for circumferential part-through surface cracks in the center of elbow. Based on present FE results, closed-form limit load solutions are proposed. Welds are not explicitly considered and all materials are assumed to be homogeneous. And the method to estimate the elastic-plastic J-integral for circumferential part-through surface cracks at the interface between elbows and straight pipes is proposed based on the reference stress approach, which was compared with corresponding solutions for straight pipes.