• Title/Summary/Keyword: Fatigue Usage Factor

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FATIGUE ANALYSIS OF A REACTOR PRESSURE VESSEL FOR SMART

  • Jhung, Myung-Jo
    • Nuclear Engineering and Technology
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    • v.44 no.6
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    • pp.683-688
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    • 2012
  • The structural integrity of mechanical components during several transients should be assured in the design stage. This requires a fatigue analysis including thermal and stress analyses. As an example, this study performs a fatigue analysis of the reactor pressure vessel of SMART during arbitrary transients. Using heat transfer coefficients determined based on the operating environments, a transient thermal analysis is performed and the results are applied to a finite element model along with the pressure to calculate the stresses. The total stress intensity range and cumulative fatigue usage factor are investigated to determine the adequacy of the design.

Fatigue Evaluation on the Inside Surface of Reactor Coolant Pump Casing Weld

  • Kim, Seung-Tae;Park, Ki-Sung
    • Proceedings of the Korean Nuclear Society Conference
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    • 1998.05b
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    • pp.795-801
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    • 1998
  • Metallic fatigue of Pressurized Water Reactor(PWR) materials is a generic safety issue for commercial nuclear power plants. It is very important to obtain the fatigue usage factor for component integrity and life extension. In this paper, fatigue usage was obtained at the inside surface of Kori unit 2, 3 and 4 RCP casing weld, based on the design transient. And it was intended to establish the procedure and the detailed method of fatigue evaluation in accordance with ASME Section III Code. According to this code rule, two methods to determine the stress cycle and the number of cycles could be applied. One method is the superposition of cycles of various design transients and the other is based on the assumption that a stress cycle correspond to only one design transient. Both method showed almost same fatigue usage in the RCP casing weld.

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Stress Classification Using Artificial Neural Networks and Fatigue Life Assessment (인공신경망을 이용한 계측응력 분류 및 피로수명 평가)

  • Jung Sung-Wook;Chang Yoon-Suk;Choi Jae-Boons;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.5 s.248
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    • pp.520-527
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    • 2006
  • The design of major industrial facilities for the prevention of fatigue failure is customarily done by defining a set of transients and performing a calculation of cumulative usage factor. However, sometimes, the inherent conservatism or lack of details as well as unanticipated transients in old plant may cause maintenance problems. Even though several famous on-line monitoring and diagnosis systems have been developed world-widely, in this paper, a new system fur fatigue monitoring and life evaluation of crane is proposed to reduce customizing effort and purchasing cost. With regard to the system, at first, comprehensive operating transient data has been acquired at critical locations of crane. The real-time data were classified, by using adaptive resonance theory that is one of typical artificial neural network, into representative stress groups. Then the each classified stress pattern was mapped to calculated cumulative usage factor in accordance with ASME procedure. Thereby, promising results were obtained fur the crane and it is believed that the developed system can be applicable to other major facilities extensively.

Effect of Weld Residual Stress on Fatigue Analysis of Nozzle (노즐의 피로해석에 미치는 용접잔류응력의 영향)

  • Kim, Sang-Chul;Kim, Man-Won
    • Journal of Welding and Joining
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    • v.32 no.1
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    • pp.71-78
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    • 2014
  • Although the fatigue design curve of ASME Code has enough margin with respect to alternating stress and cycles, the welding residual stress(WRS) should be included in fatigue analysis. In this paper, WRS distribution in a nozzle with dissimilar metal weldment was obtained by finite element analysis and was added in fatigue analysis. The fatigue analysis was performed by following the ASME Code including thermal and stress analysis applying with postulated 30 transient conditions. The calculated results of a cumulative fatigue usage factors(CUF) were compared for the case of the models with or without WRS effects. The results showed that the CUF at weldment and heat affected zone was affected by the WRS.

A Study on Application of Fatigue Correction Factor for Environmental Fatigue Evaluation of Pressurizer Surge Line (가압기 밀림관 환경피로평가를 위한 피로보정계수 적용에 관한 연구)

  • Yang, Jun-Seog;Park, Chi-Yong;Kang, Seon-Ye
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.10
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    • pp.1151-1157
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    • 2009
  • Nuclear power plants applying for the continued operation over design life are required to address the effects of reactor water environment in fatigue design requirement of the ASME Code. Reactor water environmental effects are generally evaluated by calculating fatigue correction factors on fatigue usage. This paper describes the application for pressurizer surge line of environmental fatigue correction factors and the strain rate impact in the application. From this paper, the environmental fatigue correction factors resulted from the assumption of a step change in temperature are especially compared with those calculated from the data measured during plant startup. As a conclusion of this paper, the design transient conditions applied to the fatigue design may be conservative in case of the environmental fatigue evaluation.

Environmental Fatigue Evaluation for Thermal Stratification Piping of Nuclear Power Plants (열성층을 포함하는 원자력발전소 배관의 환경피로평가)

  • Kim, Taesoon;Kim, Kyuhyung
    • Journal of the Korean Society of Safety
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    • v.33 no.5
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    • pp.164-169
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    • 2018
  • A detailed fatigue evaluation procedure was developed to mitigate the excessive conservativeness of the conventional environmental fatigue evaluation method for the pressurizer spray line elbow of domestic new nuclear power plants. The pressurizer spray line is made of austenitic stainless steel, which is relatively sensitive to the environmentally assisted fatigue, and has a low degree of design margin in terms of environmentally assisted fatigue due to the thermal stratification phenomenon on the pipe cross section as a whole or locally. In this study, to meet the environmental fatigue design requirements of the pressurizer spray line elbow, the new environmental fatigue evaluation has been performed, which used the ASME Code NB-3200-based detailed fatigue analysis and the environmental fatigue correction factor instead of the existing NB-3600 evaluation method. As a result, the design requirements for environmentally assisted fatigue were met in all parts of the pressurizer spray line elbow including the fatigue weakened zones by thermal stratification.

Proposal of the Penalty Factor Equations Considering Weld Strength Over-Match

  • Kim, Jong-Sung;Jeong, Jae-Wook;Lee, Kang-Yong
    • Nuclear Engineering and Technology
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    • v.49 no.4
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    • pp.838-849
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    • 2017
  • This paper proposes penalty factor equations that take into consideration the weld strength over-match given in the classified form similar to the revised equations presented in the Code Case N-779 via cyclic elastic-plastic finite element analysis. It was found that the $K_e$ analysis data reflecting elastic follow-up can be consolidated by normalizing the primary-plus-secondary stress intensity ranges excluding the nonlinear thermal stress intensity component, $S_n$ to over-match degree of yield strength, $M_F$. For the effect of over-match on $K_n{\times}K_{\nu}$, dispersion of the $K_n{\times}K_{\nu}$ analysis data can be sharply reduced by dividing total stress intensity range, excluding local thermal stresses, $S_{p-lt}$ by $M_F$. Finally, the proposed equations were applied to the weld between the safe end and the piping of a pressurizer surge nozzle in pressurized water reactors in order to calculate a cumulative usage factor. The cumulative usage factor was then compared with those derived by the previous $K_e$ factor equations. The result shows that application of the proposed equations can significantly reduce conservatism of fatigue assessment using the previous $K_e$ factor equations.

Effect of Stress Concentration Factors on the Fatigue Evaluation of the Direct Vessel Injection Nozzle (원자로 직접주입노즐의 피로평가에 미치는 응력집중계수의 영향)

  • Kim, Tae-Soon;Lee, Jae-Gon
    • Journal of the Korean Society of Safety
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    • v.25 no.6
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    • pp.53-59
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    • 2010
  • A fatigue damage caused by cyclic load is considered as one of the important failure mechanisms that threaten the integrity of structures and components in a nuclear power plant. In ASME code section III NB, the fatigue analysis procedure and standard S-N curves for the class 1 components are described and these criteria should be met at the design step of components. As the current ASME S-N curves are based on the very conservative assumptions such as a local stress concentration effect, immoderate transient frequencies and a constant Young's modulus, however, they can not precisely address the fatigue behavior of components. In order to find out the technical solution for these problems, a number of researches and discussion have been carried out continuously at home and abroad over the decades. In this study, detailed fatigue analyses for DVI nozzle with various mesh density of finite elements were performed to evaluate effect of stress concentration factors on the fatigue analysis procedure and the excessive conservatism of stress concentration factors are confirmed through the analysis results.

Development and Application of Detailed Procedure to Evaluate Fatigue Integrity for Major Components Considering Operating Conditions in the Nuclear Power Plant (원전 운전환경을 고려한 주기기 피로 건전성 상세평가 절차개발 및 적용)

  • Kim, Byong-Sup;Kim, Tae-Soon
    • Journal of the Korean Society of Safety
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    • v.21 no.6 s.78
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    • pp.20-25
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    • 2006
  • In the design of class 1 components to apply ASME code section III NB, a fatigue is considered as one of the important failure mechanisms. Fatigue analysis procedure and standard fatigue design curve(S-N curve) is suggested in ASME code, which had to be performed to meet the integrity of components at the design step. As the plant life extension for operating power plants and the long-lived plant design, however, are being progressed, the fact which the existing ASME fatigue design curve can not consider fatigue effects sufficiently comes to the fore. To find the technical solution for these problems, a number of researches and discussion are continued up to now. In this study, the detailed fatigue analyses using the 3 dimensional modeling for the fatigue-weakened components were performed to develop the optimized fatigue analysis procedure and their results are compared with other reference solutions.

Optimization of District Heating Pipes Considering Thermal Fatigue Life (열피로 수명을 고려한 지역난방 배관의 최적화)

  • Ahn Min-Yong;Chang Yoon-Suk;Choi Jae-Boong;Kim Sang-Ho;Kim Youn-Hong;Kim Young-Jin
    • Journal of the Korean Society for Precision Engineering
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    • v.23 no.6 s.183
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    • pp.143-150
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    • 2006
  • Recently, in proportion to increased demand on environmentally-friendly heat source, efficient management of district heating(DH) system becomes one of important issue. The objectives of this paper are to systematize data processing of transition temperature, investigate the effect of temperature variations on thermal fatigue and find out a way to improve design fractures of Korean DH pipes. For this purpose, reliable fatigue lift evaluation procedures are examined and applied to quantify thermal fatigue lives. Also, as a prototypal optimization analysis results, mean value of original cross sectional area of selected pipes was reduced 18.6% sustaining their sufficient margins against fatigue failure. So, it is anticipated that the output of this research can be used as useful information of optimal design and operation in the future.