• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.63-64
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• 2008

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.85-86
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• 2007

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.143.2-143.2
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• 2005

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.12
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• pp.1995-2001
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• 2001

In this study, a small punch creep(SP-Creep) test using miniaturized specimen(10${\times}$10${\times}$0.5mm) is described to develop the new creep test method for high temperature structural materials. The SP-Creep test is applied to 2.25Cr-lMo(STBA24) steel which is widely used as boiler tube material. The test temperatures applied for the creep deformation of miniaturized specimens are between 550∼600$^{\circ}C$. The SP-Creep curves depend definitely on applied load and creep temperature, and show the three stages of creep behavior like in conventional uniaxial tensile creep curves. The load exponent of miniaturized specimen decreases with increasing test temperature, and its behavior is similar to stress exponent behavior of uniaxial creep test. The creep activation energy obtained from the relationship between SP-Creep rate and test temperature decreases as the applied load increases. A predicting equation or SP-Creep rate for 2.25Cr-lMo steel is suggested. and a good agreement between experimental and calculated data has been found.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2565-2573
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• 2002

A basic research was performed to ensure the usefulness of Small Punch-creep(SP-creep) test for residual life evaluation of heat resistant components effectively. This paper presents analytical results of initial stress and strain distributions in SP specimen caused by constant loading for SP-creep test and its experimental correlations with uniaxial creep(Ten-creep) test on 9Cr1MoVNb steel. It was shown that the initial maximum equivalent stress, ${\sigma}_{eq{\cdot}max}$ from FE analysis was correlated with steady-state equivalent creep strain rate, ${\epsilon}_{qf-ss'}$ rupture time, $t_r$, activation energy, Q and Larson-Miller Parameter, LMP during SP-creep deformation. The simple correlation laws, ${\sigma}_{sp}-{\sigma}_{TEN}$, $P_{sp}-{\sigma}_{TEN}\; and\; Q_{sp}-Q_{TEN}$ adopted to established a quantitative correlation between SP-creep and Ten-creep test data. Especially, the activation energy obtained from SP-creep test is linearly related to that from Ten-creep test at $650^{\circ}C$ as follows : $Q_{SP-P}\;{\risingdotseq}\;1.37 \;Q_{TEN},\; Q_{SP-{\sigma}}{\risingdotseq}1.53\; Q_{TEN}$.

• Journal of the Korean Institute of Gas
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• v.16 no.5
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• pp.28-34
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• 2012

Material degradation of Cr steels in using for boiler tubes was studied in the relation of microstructural changes like carbide behavior and mechanical properties of hardness and creep-rupture life. The carbide dissolution was occurred in 2Cr steel of T22 during high temperature operation. And the grain refinement within martensite lath of 12Cr steel of X20 was derived by the high temperature-long time exposure. But the specific phenomena of material degradation which might be represented by hardness or creep-rupture time of the used tubes were not shown in all the tubes of T22 and X20 even in the fire-side using.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.55-60
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• 2002

For the development of a new creep test technique, the availability of SP-Creep test is discussed for 1Cr-0.5Mo boiler header material. And some results are also compared with those of 2.25Cr- 1Mo steel which widely uses as boiler superheater tube. The results can be summarized as follows. The load exponents(n) obtained by SP-Creep test for 1Cr-0.5Mo steel are decreased with increasing creep temperature and the values are 15.67, 13.89, and 17.13 at 550$^{circ}C$ ,575$^{circ}C$ and 600$^{circ}C$, respectively. The temperature dependence of the load exponent is given by n = 107.19 - 0.1108T. This reason that load exponents show the extensive range of 10∼16 is attributed to the fine carbide such as M$_{23}$C$_{6}$ in lath tempered martensitic structures. At the same creep condition, the secondary creep rate of 1Cr-0.5Mo steel is lower than the 2.25Cr-1Mo steel1 due to the strengthening microstructure composed by normalizing and tempering treatments. Through a SEM observation, it can be summarized that the primary, secondary, and tertiary creep regions of SP-Creep specimen are corresponding to plastic bending, plastic membrane stretching, and plastic instability regions among the deformation behavior of four steps in SP test, respectively.y.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.180-185
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• 2001

In the life assessment for plant structural component, the research on deterioration of toughness and material properties occurred in weldments has been considered as very important problems. In general, the microstructures composed in weldments are hugely classified with weld metal(W.M), fusion line(F.L), heat affected zone(HAZ), and base metal(B.M). It has been reported that the creep characteristics on weldments having variable microstructures could be unpredictably changed. Furthermore, it is also known that HAZ adjacent to F.L exhibits the decreased creep strength compared to those in base or weld metals, and promotes the occurrence of Type III and Type IV cracking due to the growth of grains and the coarsening carbides precipitated in ferritic matrix by welding and PWHT processes. However, the lots of works reported up to date on creep damage in power plant components have been mostly conducted on B.M and the creep properties on a localized microstructures in weldments have not as yet been throughly investigated. In this paper, for various microstructures such as coarse grain HAZ(CGHAZ), W.M and B.M in X20CrMoV121 steel weldment, the small punch-creep(SP-Creep) test using miniaturized specimen(t=0.5mm, 0.25mm) is performed to investigate a possibility for creep characteristics evaluation.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3571-3580
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• 2023

The application of the induction bending process to pipe systems in various industrial fields is increasing. Recently, efforts have also been made to apply this bending process to nuclear power plants because it can innovatively reduce welded parts of the curved pipes, such as elbows. However, there have been no cases of the application of induction bending to the piping of nuclear power plants. In this study, the applicability of the P91 induction bending piping for the sodium-cooled fast reactor PGSFR was validated through high temperature low cycle fatigue tests and creep tests using P91 induction bending pipe specimens. The tests confirmed that the materials sufficiently satisfied the fatigue life and the creep rupture life requirements for P91 steel at 550 ℃ in the ASME B&PV Code, Sec. III, Div. 5. The results show that the effects of heating and bending by the induction bending process on the material properties were not significant and the induction bending process could be applicable to piping system of PGSFR well.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.3
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• pp.595-602
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• 1998

Specimens of 304 stainless steel were tested to failure at elevated temperatures under multiaxial stress states, uniaxial tension using smooth bar specimens, biaxial shearing using double shear bar specimens, and triaxial tension using notched bar specimens. Rupture times are compared for uniaxial, biaxial, and triaxial stress states with respect to the maximum principal stress, the von Mises effective stress, and the principal facet stress. The results indicate that the principal facet stress gives the best correlation for the material investigated, and this parameter can predict creep life data under multiaxial stress states with rupture data obtained with specimens under uniaxial stresses. The results also suggest that grain boundary cavitation, coupled with localized deformation processes such as grain boudary sliding, controls the lifetimes of the specimens.