• Title/Summary/Keyword: cumulative 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.

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.

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.

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.

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.

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.

Sensitivity Analysis for Allowable Operating Period Based on the Flaw Tolerance Evaluation of ASME BPVC Section XI Appendix L (ASME BPVC Section XI Appendix L의 결함허용평가에 따른 허용운전주기 민감도 분석)

  • Changsik Oh;Dooho Cho;Myung Jo Jhung
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.2
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    • pp.126-136
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    • 2021
  • During operation of nuclear power plants, the fatigue assessment should be conducted repeatedly, considering changes of operating environments. For the case that cumulative usage factors (CUFs) may exceed the acceptance limit, flaw tolerance evaluation can be an alternative method to meet the regulatory requirements. In this respect, this paper analyzes the effects of the input variables for flaw tolerance evaluation based on ASME BPVC Section XI Appendix L. The reference analysis is performed for the example problem in NUREG/CR-6934. Then effects of the crack orientation, stress intensity factor solutions, thermal stress profiles, fatigue stress decomposition and fatigue crack growth curves are considered for the sensitivity analysis. The results show that the stress analysis considering the actual environment plays a crucial role in flaw tolerance evaluation.

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.

Fatigue Evaluation of Steam Separators of Heat Recovery Steam Generators According to the ASME Boiler and Pressure Vessel Code (ASME Boiler & Pressure Vessel Code에 따른 배열회수보일러 기수분리기의 피로 평가)

  • Lee, Boo-Youn
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.17 no.4
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    • pp.150-159
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    • 2018
  • The present research deals with a finite element analysis and fatigue evaluation of a steam separator of a high-pressure evaporator for the Heat Recovery Steam Generator (HRSG). The fatigue during the expected life of the HRSG was evaluated according to the ASME Boiler and Pressure Vessel Code Section VIII Division 2 (ASME Code). First, based on the eight transient operating conditions prescribed for the HRSG, temperature distribution of the steam separator was analyzed by a transient thermal analysis. Results of the thermal analysis were used as a thermal load for the structural analysis and used to determine the mean cycle temperature. Next, a structural analysis for the transient conditions was carried out with the thermal load, steam pressure, and nozzle load. The maximum stress location was found to be the riser nozzle bore, and hence fatigue was evaluated at that location, as per ASME Code. As a result, the cumulative usage factor was calculated as 0.00072 (much less than 1). In conclusion, the steam separator was found to be safe from fatigue failure during the expected life.