• Title/Summary/Keyword: Creep time to rupture

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Characteristics of Short-Term Creep Rupture in STS304 Steels (STS304강의 단시간 크리프 파단특성 평가)

  • Kim, Seon-Jin;Kong, Yu-Sik
    • Journal of Ocean Engineering and Technology
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    • v.21 no.4
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    • pp.28-33
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    • 2007
  • The objective of this paper is to investigate the relationship between the short-term creep rupture time and the creep rupture properties at three different elevated temperatures in STS304 stainless steel. Uniaxial constant stress creep rupture tests were performed on the steel to observe the creep rupture behaviors at the elevated temperatures of 600, 650 and 700, according to the testing matrix. It is very important to predict creep life in practical creep design problems. As one of the series of studies on the statistical modelling of probabilistic creep rupture time and the development of creep life prediction techniques, the relationship between applied stress and creep rupture behaviors, such as creep strain rate and rupture time, were investigated. In addition, the Monkman-Grant relationship was observed between the steady-state creep rate and the creep rupture time. The creep rupture surfaces observed by SEM showed up dimple phenomenon at all conditions.

Prediction of Creep Rupture Time and Strain of Steam Pipe Accounting for Material Damage and Grain Boundary Sliding (재료손상과 입계 미끄럼을 고려한 증기배관의 크리프 파단수명 및 변형률 예측)

  • 홍성호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.5
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    • pp.1182-1189
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    • 1995
  • Several methods have been developed to predict the creep rupture time of the steam pipes in thermal power plant. However, existing creep life prediction methods give very conservative value at operating stress of power plant and creep rupture strain cannot be well estimated. Therefore, in this study, creep rupture time and strain prediction method accounting for material damage and grain boundary sliding is newly proposed and compared with the existing experimental data. The creep damage evolves by continuous cavity nucleation and constrained cavity growth. The results showed good correlation between the theoretically predicted creep rupture time and the experimental data. And creep rupture strain may be well estimated by using the proposed method.

Weibull Statistical Analysis of Elevated Temperature Tensile Strength and Creep Rupture Time in Stainless Steels (스테인리스 강의 고온 인장강도와 크리프 파단시간의 와이블 통계 해석)

  • Jung, W.T.;Kim, Y.S.;Kim, S.J.
    • Journal of Power System Engineering
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    • v.14 no.4
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    • pp.56-62
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    • 2010
  • This paper is concerned with the stochastic nature of elevated temperature tensile strength and creep rupture time in 18Cr-8Ni stainless steels. The Weibull statistical analysis using the NRIM data sheet has been performed to investigate the effects of variability of the elevated temperature tensile strength and creep rupture time on the testing temperature. From those investigations, the distributions of temperature tensile strength and creep rupture time were well followed in 2-parameter Weibull. The shape parameter and scale parameter for the Weibull distribution of tensile strength were decreased with increasing the testing temperature. For the creep rupture time, generally, the shape parameter were decreased with increasing the testing temperature.

New Considerations on Variability of Creep Rupture Data and Life Prediction (크리프 파단 데이터의 변동성에 대한 새로운 고찰과 수명예측)

  • Jung, Won-Taek;Kong, Yu-Sik;Kim, Seon-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.33 no.10
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    • pp.1119-1124
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    • 2009
  • This paper deals with the variability analysis of short term creep rupture test data based on the previous creep rupture tests and the possibility of the creep life prediction. From creep tests performed by constant uniaxial stresses at 600, 650 and $700^{\circ}C$ elevated temperature, in order to investigate the variability of short-term creep rupture data, the creep curves were analyzed for normalized creep strain divided by initial strain. There are some variability in the creep rupture data. And, the difference between general creep curves and normalized creep curves were obtained. The effects of the creep rupture time (RT) and steady state creep rate (SSCR) on the Weibull distribution parameters were investigated. There were good relation between normal Weibull parameters and normalized Weibull parameters. Finally, the predicted creep life were compared with the Monkman-Grant model.

High Temperature Creep Rupture Characteristics of Ni-Based Alloy718 Jointed by Friction Welding (마찰용접된 니켈기 초내열합금 Alloy718의 고온 크리프 파단 특성)

  • Kwon, Sang-Woo;Kong, Yu-Sik;Kim, Seon-Jin
    • Journal of Ocean Engineering and Technology
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    • v.22 no.6
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    • pp.58-63
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    • 2008
  • The short-term high temperature creep rupture behavior of Ni-based Alloy718 steels jointed by friction welding wasinvestigated at the elevated temperatures of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture time and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 26.1, -22.4, 22.5, -18.5, 17.4, -14.3 and 6.9, -8.1, respectively. The stress exponents decreased with increasing creep temperature. The creep life prediction was derived by the Larson-Miller parameter (LMP) method and the result equation obtained is as follows: T(logtr+20)=-0.00148${\sigma}^2$-3.089${\sigma}$+23232. Finally, the results were compared with those of the base metal for Alloy718.

Improvement of long-time creep life prediction of steam turbine rotor steel (증기 터빈축 강재의 장시간 크리프 수명 예측법 개선)

  • 오세규;정순억;전태언
    • Journal of Ocean Engineering and Technology
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    • v.10 no.1
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    • pp.47-52
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    • 1996
  • This paper deals with a study on improvement of long-time creep life prediction of steam turbine rotor steels by using initial strain method as a new approach at high temperatures of 500 to 70$0^{\circ}C$ . The main result shows that the inital strain method could be reliably utilized to predict and evaluate the long-time creep life as creep rupture strength and that the predicting equation for long-time creep life under a certain creep stress at a certain high temperature could be empirically derived out from each initial instantaneous strain measured.

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High Temperature Creep Rupture Characteristics of Ni-Based Alloy718 (니켈기 초내열합금 Alloy718의 고온 크리프 파단 특성)

  • Kwon, Sang-Woo;Kong, Yu-Sik;Kim, Seon-Jin
    • Journal of Ocean Engineering and Technology
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    • v.22 no.6
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    • pp.52-57
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    • 2008
  • The short-term high temperature creep rupture behavior of Ni-based Alloy718 steel was investigated at the elevated temperatures range of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture tim and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 33.5, -24.9, 26.1, -21.2, 16.8, -12.8 and 10, -8.2, respectively. The stress exponent decreased with increasing creep temperature. The creep lift prediction was derived by the Larson-Miller parameter (LMP) method and the resultant equation was obtained as follows: T($logt_r$+20)=-0.00252 ${\sigma}^2$-1.377${\sigma}$+-22718.

Creep Life Prediction of Type 316LN Steel Using Minimum Commitment Method (최소구속법을 이용한 Type 316LN 강의 크리프 수명 예측)

  • Kim W.G.;Yoon S.N.;Ryu W.S.;Yi W.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2005.10a
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    • pp.295-298
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    • 2005
  • A minimum commitment method (MCM) was applied to predict the creep rupture life of type 316LN SS. For this purpose, a number of the creep rupture data for the type 316LN SS were collected through literature survey and experimental data of KAERl, Using the short-term creep rupture data under 2000 hr, the long-term creep rupture life above $10^5$ hour was predicted by means of the MCM. An optimum value of A, P and G function, used in the MCM equation, was determined respectively, and the creep rupture life with the A values in different temperatures was compared with the experimental data and the predicted curves.

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Prediction of Creep Deformation and Short Time Rupture Life of AZ31 Magnesium Alloy below 0.5Tm (0.5Tm 이하에서의 AZ31 마그네슘합금의 크리이프 변형과 단시간 파단수명예측)

  • Kang, D.M.;An, J.O.;Jeon, S.H.;Koo, Y.;Sim, S.B.
    • Transactions of Materials Processing
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    • v.17 no.8
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    • pp.558-563
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    • 2008
  • The initial strain, the applied stress exponent, the activation energy, and rupture time in AZ31 magnesium alloy have been measured in order to predict the deformation mechanism and rupture life of creep over the temperature range of 423-443K. Creep tests were carried out under constant applied stress and temperature, and the lever type tester and automatic temperature controller was used for it, respectively. The experimental results showed that the applied stress exponent was about 9.74, and the activation energy for creep, 113.6KJ/mol was less than that of the self diffusion of Mg alloy including aluminum. From the results, the mechanism for creep deformation seems to be controlled by cross slip at the temperature range of 423-443K. Also the higher the applied stress and temperature, the higher the initial strain. And the rupture time for creep decreased as quadratic function with increasing the initial strain in double logarithmic axis.

Numerical Analysis of Corrosion Effects on the Life of Boiler Tube (보일러관의 수명에 부식이 미치는 영향에 대한 수치해석)

  • Hong, Seong-Ho;Kim, Jong-Seong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.11
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    • pp.2812-2822
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    • 2000
  • Several methods have been developed to predict the rupture time of the boiler tubes in thermal power plant. However, existing life prediction methods give very conservative value at operating stress of power plant and rupture strain cannot be well estimated. Therefore, in this study, rupture time and strain prediction method accounting for creep, corrosion and heat transfer is newly proposed and compared with the current research results. The creep damage evolves by continuous cavity nucleation and constrained cavity growth. The corrosion damage evolves by steam side and fire side corrosion. The results showed good correlation between the theoretically predicted rupture time and the current research results. And rupture strain may be well estimated by using the proposed method.