• Journal of the Korean Solar Energy Society
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• v.37 no.5
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• pp.65-75
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• 2017

In this study, the change of heat loss due to the degree of deterioration of the XPS insulation in KEPCO's office buildings is analyzed. The acceleration aging test of the XPS insulation was carried out according to the test method A of KS M ISO 11561: 2009. The performance of the insulation was analyzed by applying it to the three - dimensional steady state heat transfer analysis program. The acceleration aging test of the XPS insulation, show that the thermal resistance performance decreased by 1.44% at the A regional headquarters, 0.85% at the B regional headquarters, 6.41% at the C branch office, 7.76% at the D regional headquarters, 8.51% at the E branch office, and by 8.54% at the F branch office respectively. Using simulation, we determined that the thermal resistance value of E branch office decreased by 8.04%, while its heat loss increased by 8.52%. At A regional headquarters, the thermal resistance decreased by 1.38%, and the heat loss increased by 1.51%. At D regional headquarters, these value are 6.82% and 7.17%, respectively.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.1-8
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• 2024

In this study, the influence of thermal aging on structural integrity is investigated for Gr. 91 steel. A commercial grade Gr. 91 steel is used for the virgin material, and service-exposed Gr. 91 steel is sampled from a steam pipe of a super critical plant. Time versus creep strain curves are obtained through creep tests with various stress levels at 600 ℃ for the virgin and service-exposed Gr. 91 steels, respectively. Based on the creep test results, the improved Omega model is characterized for describing the total creep strain curve for both Gr. 91 steels. The proposed parameters for creep deformation model are used for predicting the steady-state creep strain rate, creep rupture curve, and stress relaxation. Creep-fatigue damage is evaluated for the intermediate heat exchanger (IHX) in a large-scale sodium test facility of STELLA-2 by using creep deformation model with proposed creep parameters and creep rupture curve for both Gr. 91 steels. Based on the comparison results of creep fatigue damage for the virgin and service-exposed Gr. 91 steels, the thermal aging effect has been shown to be significant.

• Elastomers and Composites
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• v.46 no.2
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• pp.132-137
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• 2011

In the present investigation, thermal aging behavior of H-NBR/NBR blend with various H-NBR content was investigated. Mixture of dicumyl peroxide and sulfur were used as a curing agent. The influence of the thermal aging of the H-NBR/NBR blends on the solid state properties such as tensile strength, elongation at break, hardness and abrasion resistance was investigated. Tensile strength was increased with increasing H-NBR content, while abrasion resistance was decreased. Both elongation at break and hardness were not affected by the addition of H-NBR. The properties such as hardness, tensile strength and elongation at break of the aged samples were lower than unaged samples. However, the rate of deterioration of those properties was decreased by increasing the H-NBR content, which indicated that improved thermal aging behavior was obtained by the addition of H-NBR. Abrasion loss was increased with increasing aging time, but it became less by the addition of H-NBR addition.

• Transactions on Electrical and Electronic Materials
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• v.8 no.3
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• pp.143-146
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• 2007

Polymer insulators are used widely in variable fields for high voltage insulation and separating people from high voltage charging parts for safety and also supporting overhead power line in electric railway. But it may be broken down by tracking path resulting from continuous surface discharge. This paper has investigated synthetically both the characteristics of electrical aging using precision CT(current transformer) and the thermal aging using thermography method. Electrical aging was analyzed for time-frequency region and thermal aging was illustrated by image processing method. This synthetic method may be an appropriate one to evaluate the surface degradation of polymer insulator.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.26-34
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• 2001

Most research to date concerning the cryogenic toughness of austenitic stainless steels has concentrated on the base metal and weld metal in weldments. The most severe problem faced on the conventional austenitic stainless steel is the thermal aging degradation such as sensitization and carbide induced embrittlement. In this paper, we investigate the cryogenic toughness degradation which can be occurred for austenitic stainless in welding. The test materials are austenitic stainless JN1, JJ1 and JK2 steels, which are materials recently developed for use in nuclear fusion apparatus at cryogenic temperature. The small punch(SP) test was conducted to detect similar isothermally aging condition with material degradation occurred in service welding. The single-specimen unloading compliance method was used to determine toughness degradation caused by thermal aging for austenitic stainless steels. In addition, we have investigated size effect on fracture toughness by using 20% side-grooved 0.5TCT specimens.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.10
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• pp.473-478
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• 2002

Accelerated thermal aging conditions of polymeric materials were studied by Kissinger equation with TGA analysis. The activation energy was obtained from the slope of straight line of each specimen at the different TGA heating rate. Estimating activation energy from Kissinger equation was acquired, and the resulting calculation showed that 3.59, 3.0, 3.86, 3.73 for the PEEK, polyimide, polysulfone and Viton, respectively. The studied polymeric specimens are used for electrical penetration assembly in nuclear power plant. Accelerated aging time and temperature were also determined corresponding to actual service temperature and 41 years.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.492-497
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• 2017

In this study, we investigated the effect of thermal aging on mechanical characteristics of Inconel 600 nickel-based alloy. The thermal aging was conducted up to 1000 hours at an atmosphere of $650^{\circ}C$. The microstructure of thermally aged specimens was investigated by an optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). In addition, tensile test (strain rate: 2 mm/min) and micro Vickers hardness test were conducted to evaluate mechanical properties with time. As a result of the experiment, Cr-rich carbide continuously precipitated during thermal aging, leading to the change of the mechanical characteristics and fracture mode. With the increase of aging time, tensile strength, yield strength, and hardness gradually decreased. The fracture mode changed from ductile to brittle with the increase of grain boundary carbide.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.303-312
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• 1999

An investigation of the CrMoV rotor steel weldment which experienced by cyclic thermal aging heat treatment and as-received condition was performed. This evaluation was carried out to confirm whether this type of weldment is appropriate for the service environment in terms of microstructural examinations, microhardness measurements and tensile tests. The cyclic thermal aging heat treatment, containing continuous heating and cooling thermal cycle was programmed to simulate the real rotor service condition. The heat treatment was performed for 40 cycles(5920hrs). The results indicated that the weldment was composed of 4 different regions such as heat affected zone of the base metal, butter weld(initial weld), full thickness weld(final weld) and the base metal. The double welding process was applied to eliminate the susceptibility of reheat cracking at heat affected zone of base metal. The grain refinement at the HAZ due to the welding process could reduce the possibility of cracking susceptibility, but its tensile properties was appeared to be low due to the weld metal in as-received condition. The benefit effect, grain refinement was extended with carbides coarsening during the cyclic thermal aging heat treatment. However the poor mechanical properties of the weldment was more degraded as undergoing the heat treatment.

• Fire Science and Engineering
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• v.18 no.3
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• pp.45-50
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• 2004

Thermal degradation of PVC which used for insulator of 600V vinyl insulated wire has been studied by thermo gravimetry analysis and accelerated thermal aging test. The activation energy using thermo gravimetry analysis was determined by the kinetic methods, such as Kissinger and Flynn-Wall-Ozawa. The activation energy was determined to from 89.29 kJ/mol to 111.39 kJ/mol in 600V PVC insulated wire and from 97.80 kJ/mol to 119.25 kJ/mol in 600v heat-resistant PVC insulated wire. And also, the activation energy through a long-term thermal aging test was calculated by using Arrhenius equation In the low temperature of 8$0^{\circ}C$, 9$0^{\circ}C$, 10$0^{\circ}C$. The results showed that 600V PVC insulated wire was 92.16 kJ/mol, and 600v heat-resistant PVC insulated wire was 97.52 kJ/mol. Consequently, the activation energy of 600V heat-resistant PVC insulated wire is larger than 600V PVC insulated wire. Therefore, it can be predicted that 600V heat-resistant PVC insulated wire has a long-term stability relatively.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.12
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• pp.1155-1159
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• 2014

Thermal barrier coating (TBC) which is used to protect the substrate of gas turbine is exposed to high temperature environment. Because of high temperature environment, thermally grown oxide (TGO) is grown at the interface of thermal barrier coating in operation of gas turbine. The growth of TGO critically affects to durability of TBC, so the evaluation about durability of TBC with TGOs of various thickness is needed. In this research, TGO was inserted by aging of TBC specimen to evaluate the effect of the TGO growth. Then thickness of TGO was defined by microstructure analysis, and thermal fatigue test was performed with these aging specimens. Finally, the relation between thermal fatigue life and the TGO growth according to aging time was obtained.