• Journal of Welding and Joining
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• v.20 no.6
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• pp.754-761
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• 2002

It has been reported that the creep characteristics on weldment which is composed of weld metal(W.M), fusion line(F.L), heat-affected zone(HAZ), and base meta(B.M) could be unpredictably changed in severe service conditions such as high temperature and high pressure. However, the studies done on creep damage in power plant components have been mostly conducted on B.M and not the creep properties of the localized microstructures in weldment have been thoroughly investigated yet. In this paper, it is investigated the creep characteristics for three microstructures like coarse-grain HAZ(CGHAZ), W.M, and B.M in X20CrMoV121 steel weldment by the small punch-creep-(SP-Creep) test using miniaturized specimen($10{\times}10{\times}0.5mm$). The W.M microstructure possesses the higher creep resistance and shows lower creep strain rate than the B.M and CGHAZ. In the lower creep load the highest creep strain rate is exhibited in CGHAZ, whereas in the higher creep load the B.M represents the high creep strain rate. The power law correlation for all microstructures exists between creep rate and creep load at $600^{\circ}C$. The values of creep load index (n) based on creep strain rate for B.M, CGHAZ, and W.M are 7.54, 4.23, and 5.06, respectively and CGHAZ which shows coarse grains owing to high welding heat has the lowest creep loade index. In all creep loads, the creep life for W.M shows the highest value.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1406-1411
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• 2005

The creep rupture data for type 316LN stainless steels were collected through literature survey or experimental data produced in KAERI. Using these data, polynomial equations for predicting creep life were obtained by Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D) and Manson-Haferd (M-H) etc. time-temperature parametric (TTP) methods. Standard error of estimate (SEE) values for the each parameter was obtained with different temperatures through the statistical process of the creep data. The results of L-M, O-S-D and M-H methods showed good creep-life prediction, but M-H method showed better agreement than L-M and O-S-D methods. Especially, it was found that SEE values of M-H method at $700^{\circ}C$ were lower than that of L-M and O-S-D methods.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.109-110
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• 2006

Various parametric methods, Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D), Manson-Haferd (M-H) parameters, and minimum commitment method (MCM), were used to predict longer rupture time from short-term creep data. A number of the creep data were collected through literature surveys and experimental data produced in KAERI for predicting the creep type of type 316LN SS. Polynomial equations for predicting the creep life were obtained by the time-temperature parameters (TTP) and the MCM. standard error (SE) and standard error or mean (SEM) values were compared for the each method with temperatures. The TTP methods were good in the creep-life prediction, but the MCM was much superior to the TTP ones at $700^{\circ}C\;and\;750^{\circ}C$. The MCM was found to be lower in the SE values compared to the TTP methods

• Journal of the Korean Society of Safety
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• v.4 no.1
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• pp.25-39
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• 1989

Cyclic temperature creep tests were carried out an AS 7075 alloy specimens were subjected to a constant load and stepwise temperature cycles in which temperature was fluctuated between 30$0^{\circ}C$ and 25$0^{\circ}C$ with three different cycle ratios. The highest frequency of cycling was 1 cycle per 10 hr and the lowest one was 1 cycle per 12 hr. From the creep experimental results with the above conditions the creep strain under cyclic temperature can be predicted easily by introd ucing the equivalent steady temperature because defined by Eq.(16), but the rupture life is 1.1 time than those of constant temperature because of effect of temperature history at tertiary creep range. Besides thlis result, the results of the creep test under cyclic temperature conditions are respectively compayiea with calculated rupture lives using the life fraction law and Eq.(18). The agreement between the obseried rupture times and calculated ones is fairly good. So creep rupture lives can be respectively predicted using life fraction law and Eq.(18).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.1 s.232
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• pp.74-80
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• 2005

A number of creep rupture data for type 316LN stainless steels were collected through literature survey or experimental data produced in KAERI. Using these data, polynomial equations for predicting creep life were obtained by Larson-Miller (L-M), Orr-Sherby-Dorn (O-S-D) and Manson-Haferd (M-H) parameters using time-temperature parametric (TTP) methods. Standard error of estimate (SEE) values for the each parameter was obtained with different temperatures through the statistical process of the creep data. The results of L-M, O-S-D and M-H methods showed good creep-life prediction, but M-H method showed better agreement than L-M and O-S-D methods. Especially, it was found that SEE values of M-H method at $700^{\circ}C$ were lower than that of L-M and O-S-D methods.

• Journal of Ocean Engineering and Technology
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• v.25 no.4
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• pp.12-17
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• 2011

Little design data is available for the creep life prediction of 9% Ni alloy in elevated temperatures. Therefore, in this study, a series of creep tests under 16 combined conditions with 4 kinds of stresses and 4 temperatures was performed to obtain creep design and life prediction data for 9% Ni alloy, with the following results. The stress exponents decreased as the test temperature increased. The creep activation energy gradually decreased as the stresses became larger. The Larson-Miller parameter (LMP) constant for this alloy was estimated to be about 2.

• Journal of the Korean Society of Safety
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• v.22 no.2 s.80
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• pp.22-27
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• 2007

To assess a creep life of elevated temperature plant components, inspections and analysis are usually focused on the critical locations. In this study, stress analysis of a weld region in branch part of Y-piece was conducted by using a three-dimensional finite element analysis. The stresses at the inner and outer surface in the weld part were estimated by using elastic and elastic-creep analysis. For the elastic-creep analysis two kinds of elastic-creep analysis was conducted. The one was assumed that base and weld material properties were same and the other was that material properties were different between base and weld metal. The material properties of base and weld metal were used from reference data. The results showed the stress relaxation level and its location. The result stresses are also compared with elastic stresses.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.45-51
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• 2015

Grade 91 steel is used for the major structural components of Generation-IV reactor systems such as a very high temperature reactor (VHTR) and sodium-cooled fast reactor (SFR). Since these structures are designed for up to 60 years at elevated temperatures, the prediction of long-term creep life is very important to determine an allowable design stress of elevated temperature structural component. In this study, a large body of creep rupture data was collected through world-wide literature surveys, and using these data, the long-term creep life was predicted in terms of three methods: Larson-Miller (L-M), Manson-Haferd (M-H) and Wilshire methods. The results for each method was compared using the standard deviation of error. The L-M method was overestimated in the longer time of a low stress. The Wilshire method was superior agreement in the long-term life prediction to the L-M and M-H methods.

• Journal of Power System Engineering
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• v.6 no.2
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• pp.40-47
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• 2002

In this paper, friction welding optimization for 1Cr0.5Mo-STS304 (${\phi}14\;mm$), AE applications for the weld quality evaluation and the applications of various life prediction methods such as LMP (Larson-Miller Parameter) and ISM (initial strain method) were investigated : The creep behaviors of those steels and the friction welded joints under static load were examined by ISM combined with LMP at 400, 500, 550 and $600^{\circ}C$, and the relationship between these two kinds of phenomena was studied. The real-time predicting equations of elevated-temperature creep life (rupture time) under any creep stress at any elevated-temperature could be developed by LMP and LMP-ISM. It was confirmed that the life prediction equations by LMP and LMP-ISM are effective only up to 102 h and can not be used for long times of 103-106 h, but by ISM it can be used for long times creep prediction of more than 104 h with most reliability.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.307-313
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• 2001

In this Paper, friction welding optimization for 1Cr0.5Mo-STS304($\Phi$14mm), AE applications for the weld quality evaluation and the applications of various life prediction methods such as LMP(Larson-Miller Parameter) and ISM(initial strain method) were investigated : the creep behaviors of those steels and the friction welded joints under static load were examined by ISM combined with LMP at 400, 500, 550 and $600^{\circ}C$, and the relationship between these two kinds of phenomena was studied. The real-time predicting equations of elevated-temperature creep life(fracture time) under any creep stress at any elevated- temperature could be developed by LMP and LMP-ISM, It was confirmed that the life prediction equations by LMP and LMP-ISM are effective only up to 10$^2$hrs and can not be used for long times of 10$^3$-10$^{6}$ hrs, but by ISM it can be used for long times creep prediction of more than 10$^4$hrs with most reliability.