Creep Life Prediction of Gr.91 Using Creep Parameters in Transient Region

2012 ◽  
Author(s):  
Fujio Abe
Keyword(s):  
Creep Rate ◽  
Minimum Creep Rate ◽  
Life Prediction ◽  
Test Duration ◽  
Creep Life ◽  
Average Value ◽  
Transient Region ◽  
Creep Life Prediction ◽  
Wide Range ◽  
Term Creep

The creep deformation behavior and its effect on creep life have been investigated for Gr.91 by analyzing creep strain data in the NIMS Creep Data Sheet. The creep life tr is mainly determined by the minimum creep rate ε̇min, indicating tr ∝ (ε̇min)−1. The ε̇min is mainly determined by the time to minimum creep rate tm, indicating ε̇min ∝ (tm)−1. Then the creep life is correlated with the tm as tr=3.7tm, where the constant 3.7 is as an average value for a wide range of temperature (450–725 °C), stress (40–450 MPa) and test duration (11–68,755 h). Using this equation, we can predict the creep life by carrying out a short-term creep test for up to the end of transient region, corresponding to about 30% of creep life. The (tm/tr), the ratio of duration of transient region to the creep life, slightly decreases with decreasing stress and is evaluated to be 0.22 at 100 MPa and above 550 °C, which gives us tr= 4.5 tm at 100 MPa. Taking the stress dependence of the (tm/tr) into account, the accuracy of creep life prediction is further improved.

Creep Life Prediction of HR3C Steel Using Creep Damage Models

2017 ◽  
Author(s):  
Hoomin Lee ◽  
Seok-Jun Kang ◽  
Jae-Boong Choi ◽  
Moon-Ki Kim
Keyword(s):  
Life Prediction ◽  
Power Plants ◽  
Creep Damage ◽  
Creep Rupture ◽  
Creep Life ◽  
Damage Models ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

The world’s energy market demands more efficient power plants, hence, the operating conditions become severe. For thermal plants, Ultra Super Critical (USC) conditions were employed with an operating temperature above 600°C. In such conditions, the main failure mechanism is creep rupture behavior. Thus, the accurate creep life prediction of high temperature components in operation has a great importance in structural integrity evaluation of USC power plants. Many creep damage models have been developed based on continuum damage mechanics and implemented through finite element analysis. The material constants in these damage models are derived from several accelerated uniaxial creep experiments in high stress conditions. In this study, the target material, HR3C, is an austenitic heat resistant steel which is used in reheater/superheater tubes of an USC power plant built in South Korea. Its creep life was predicted by extrapolating the creep rupture times derived from three different creep damage models. Several accelerated uniaxial creep tests have been conducted in various stress conditions in order to obtain the material constants. Kachanov-Rabotnov, Liu-Murakami and the Wen creep damage models were implemented. A comparative assessment on these three creep damage models were performed for predicting the creep life of HR3C steel. Each models require a single variable to fit the creep test curves. An optimization error function were suggested by the authors to quantify the best fit value. To predict the long term creep life of metallic materials, the Monkman-Grant model and creep rupture property diagrams were plotted and then extrapolated over an extended range. Finally, it is expected that one can assess the remaining lifetime of UCS power plants with such a valid estimation of long-term creep life.

Comparative Study of Creep Behavior in 9Cr-1Mo Steel With Different Prediction Methods

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
Lin Zhu ◽  
Xinbao Liu ◽  
Ping Fan ◽  
Jianqiu Liu ◽  
Chengfei Pan
Keyword(s):  
Creep Rate ◽  
Minimum Creep Rate ◽  
Damage Mechanics ◽  
Continuum Damage Mechanics ◽  
Model Combination ◽  
Creep Life ◽  
Physically Based ◽  
Term Creep ◽  
Short Term Creep

Abstract Over the range of variables (temperature and stress) normally encountered in service applications, creep behaviors of 9Cr-1Mo steel were investigated with various models, such as Wilshire model, combination of exponential form and omega (CEO) model, and continuum damage mechanics (CDM) model. First, a series of short-term creep data was prepared to evaluate the material parameters occurring in these models. Then, creep curve, minimum creep rate, and long-term creep life of present 9Cr-1Mo steel were extrapolated with these estimated models. Based on the analysis of obtained results in detail, it suggested that both CDM model and CEO model can give reliable minimum creep rate predictions. However, the most reliable values of long-term creep life are obtained by the CDM model, followed by the Wilshire model and then the CEO model. In particular, the physically based CDM model can provide useful insights into the underlying creep mechanisms. Therefore, the CDM model has promising potential to study the long-term creep behaviors of 9Cr-1Mo steels.

scholarly journals Long-term Creep Life Prediction Methods of Grade 91 Steel

2015 ◽  
Vol 19 (5) ◽  
pp. 45-51
Author(s):  
Jay-Young Park ◽  
Woo-Gon Kim ◽  
I.M.W. EKAPUTRA ◽  
Seon-Jin Kim ◽  
Jin-Sung Jang
Keyword(s):  
Life Prediction ◽  
Prediction Methods ◽  
Creep Life ◽  
Creep Life Prediction ◽  
Grade 91 ◽  
Term Creep ◽  
Grade 91 Steel

Taylor Series-Based Long-Term Creep-Life Prediction of Alloy 617

2010 ◽  
Vol 34 (4) ◽  
pp. 457-465
Author(s):  
Song-Nan Yin ◽  
Woo-Gon Kim ◽  
Jae-Young Park ◽  
Soen-Jin Kim ◽  
Yong-Wan Kim
Keyword(s):  
Taylor Series ◽  
Life Prediction ◽  
Creep Life ◽  
Alloy 617 ◽  
Creep Life Prediction ◽  
Term Creep

An Improved Omega-Based Method for Creep Life Prediction Using Hyperbolic Sine Stress Correlation

2019 ◽  
Vol 795 ◽  
pp. 130-136
Author(s):  
Xinyu Yang ◽  
Richard Barrett ◽  
Sean B. Leen ◽  
Jian Ming Gong
Keyword(s):  
Life Prediction ◽  
Creep Damage ◽  
Creep Life ◽  
Creep Tests ◽  
Inconel Alloys ◽  
Hyperbolic Sine ◽  
Omega Method ◽  
Creep Life Prediction ◽  
Uniaxial Creep ◽  
Term Creep

This paper is concerned with the creep life prediction of cast 20Cr32NiNb alloy, an alternative candidate material to wrought Inconel alloys for use in the gas collector pipes of CO reformers which suffer from long-term creep damage due to high temperatures and stresses. Uniaxial creep tests of 20Cr32NiNb alloy were performed at 890 °C and 950 °C for different stresses. The Omega method for creep life prediction is applied to the 20Cr32NiNb tests and shown to give reasonably accurate prediction, particularly at low stress levels. A new method, based on the use of a hyperbolic sine function for stress correlation at specific temperatures for identification of the characteristic Omega parameters is presented and validated.

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