• Korean Journal of Materials Research
• /
• v.17 no.5
• /
• pp.268-272
• /
• 2007

Inconel 617 is a candidate tube material for high temperature gas-cooled reactors(HTGR). The microstructure and mechanical properties of Inconel 617 were studied after exposure at high temperature($1050^{\circ}C$). The dominant oxide layer was Cr-oxide. The internal oxide and Cr-depleted region were observed below the Cr-oxide layer. The depth of Cr-depleted zone and internal oxide increased with exposure time. The major phases of carbides are $M_{23}C_6\;and\;M_6C$. The composition of $M_{23}C_6\;and\;M_6C$ were determined to be Cr-rich and Mo-rich, respectively. $M_6C$ carbide is more stable than $M_{23}C_6$ at high temperature. From the results of high temperature compression test, there were no significant changes in hardness and yield strength upon increasing exposure time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05c
• /
• pp.132-137
• /
• 2002

The mold transformers have been widely used in underground substations in large building and have some advantages in comparison to oil-transformer, that is low fire risk, excellent environmental compatibility, compact size and high reliability. In addition, the application of mold transformer for outdoor is possible due to development of epoxy resin. The mold transformer generally has cooling duct between low voltage coil and high voltage coil. A mold transformer made by one body molding method has been developed for small size and low loss. The life of transformer is significantly dependent on the thermal behavior in windings. To analyse winding temperature rise, many transformer designer have calculated temperature distribution and hot spot point by finite element method(FEM). Recently, numerical analyses of transformer are studied for optimum design, that is electric field analysis, magnetic field, potential vibration, thermal distribution and thermal stress. In this paper, the temperature distribution of 50 kVA pole mold transformer for power distribution are investigated by FEM program and the temperature rise test of designed mold transformer carried out and test result is analyzed compare to simulation data. In this result, the designed mold transformer is satisfied to limit value of temperature and the other property is good such as voltage ratio, winding resistance, no-load loss, load loss, impedance voltage and percent regulation.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.23 no.1
• /
• pp.14-20
• /
• 2003

Piezoelectric ultrasonic transducers for high temperature contact measurement were developed. These high temperature ultrasonic transducers (HTUT) consisted of bismuth titanate piezoceramic element whose Curie temperature is higher than $600^{\circ}C$, a backing material of the mixture of tungsten powder and inorganic binder, an inner alumina tube, a wear Plate and a housing. The operational frequencies or the HTUT were 1.04 and 2.08 MHz, respectively. Various commercially available couplants for high temperature were evaluated and compared. As a couplant for high temperature ultrasonic testing between HTUT and test specimen, gold epoxy was selected. The peak amplitude of pulse-echo signals from steel test specimen decreased with increasing temperature. The operational temperature of the HTUT reached up to $500^{\circ}C$ at which the continuous contact measurement was possible.

• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.99-104
• /
• 2000

This paper describes the high temperature creep characteristics for virgin material of 9Cr1MoVNb steel using small punch creep(SP-Creep) test technique which is developing recently. In addition, the several results of SP-Creep test are compared with that of 2.25Cr- 1Mo steel which is widely used as boiler materials and that of conventional uniaxial creep test. The obtained SP-Creep curves show the creep behaviors of three regimes like that obtained from conventional uniaxial creep test, and SP-Creep properties are definitely depended on applied load and test temperature. The correlation of SP-Creep rate and creep rupture life with applied load has been determined like the correlation between creep rate/rupture life and stress in uniaxial creep test, and also is satisfied with Power law. The creep rupture times of newly 9Cr1MoVNb steel are higher than those of 2.25Cr1Mo steel at the same creep temperature and applied loading condition, and the decrease extent of creep rupture life with loads is very lower compared with 2.25Cr1Mo steel.

• Journal of Welding and Joining
• /
• v.22 no.4
• /
• pp.50-58
• /
• 2004

In this study, high temperature tensile properties of high strength steels(POSTEN60, POSTEN80) were investigated. The three-dimensional thermal elastic-plastic analyses were conducted to investigate the characteristics of welding residual stresses in welds of high strength steels on the basis of thermal and mechanical properites at high temperature obtained from the experiment. According to the results, high temperature tensile strength of POSTEN60 steel deteriorated slowly to 10$0^{\circ}C$. As the temperature went up, the tensile strength became better because of blue shortness, and it deteriorated radically after reaching to the maximum value around 30$0^{\circ}C$. For the POSTEN80 steel, high temperature tensile strength deteriorated slowly to 20$0^{\circ}C$. As the temperature went up the tensile strength became better and it deteriorated slowly to $600^{\circ}C$ after reached to the maximum value around 30$0^{\circ}C$. Strain of high strength steels at the elevated temperature increased radically after the mercury rose to $600^{\circ}C$. The strain hardening ratio of POSTEN60 steel was larger then that of POSTEN80 steel at the elevated temperature as in the case at the room temperature and it became smaller radically after the mercury rose to 40$0^{\circ}C$. And, in the welding of high strength steels, increasing tensile strength of the steel (POSTEN60

• Proceedings of the KIEE Conference
• /
• 2000.11a
• /
• pp.265-268
• /
• 2000

In this study, a small punch creep (SP-Creep) test using miniaturized specimen has been described for the development of the new creep test method for high temperature structural components such as headers and tubes of boiler, turbine casing and rotor, and reactor vessel. The SP-Creep testing technique has been applied to 1Cr-0.5Mo steel used widely as boiler header material and the creep test temperature are varied at $550^{\circ}C{\sim}600^{\circ}C$. From the experimental results, e.g. SP-Creep curve behaviors, the creep rate in steady state and creep rupture life with test temperature and load, the load exponential value(n, m), the activation energy($Q_{spc}$), the Monkman-Grant relation and the creep life assessment equation etc., it can be summarized that the SP-Creep test may be a useful test method to evaluate the creep properties of the heat resisting material such as boiler header.

• Tribology and Lubricants
• /
• v.12 no.3
• /
• pp.33-38
• /
• 1996

High temperature wear behaviors of plasma-sprayed ZrO$_{2}$-$Y_{2}O_{3}$ composite coatings were investigated for high temperature wear resistance applications. The composite powders containing 20, 50, 80 vol% of alumina for plasma spray were made by spray drying method. Wear tests with composite coated specimens were performed at temperature ranges from room temperature to 800$^{\circ}$C. Wear tests were also carried out with heat treated specimens at room temperature. The microstructural change of coatings and the worn surface were examined by SEM and XRD. Sharp increase of wear loss at high temperature wear test was observed in specimens containing 50 and 80 vol% alumina. Similar trend was observed in the heat treated coatings. The measured residual stress was increased with increased alumina contents and heat treating temperatures. Residual stress induced during heat treatment appeared to be responsible to the observed harmful effect of alumina additions on the high temperature wear.

• Proceedings of the KSR Conference
• /
• 2009.05a
• /
• pp.1536-1541
• /
• 2009

When water inside the concrete member evaporates by high temperature, the evaporation heat which absorbs surrounding temperature occurs. The rate of increment of the internal temperature in concrete is reduced due to the evaporation heat in spite of continuously increasing external temperature. In this paper, the prediction method of internal temperature of high strength concrete members considering the evaporation heat under the high temperature is presented. Finite element method is employed to facilitate thermal analysis for any position of member. And the thermal characteristics models of high strength concrete affected by high temperature are proposed. To demonstrate the validity of this numerical procedure, the prediction by the proposed algorithm is compared with the test results of other researchers. The proposed algorithm shows a good agreement with the experimental results including the phenomenon that temperature is lost by the evaporation heat.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2003.10a
• /
• pp.163-166
• /
• 2003

This paper presents the results of a series of performance tests for the Stilting cryocooler. Infrared sensor systems incorporating cryocoolers are required to be qualified to the appropriate environmental specification. Linear drive Stilting cryocooler have matured to the stage of undergoing formal qualification test program The thermal environmental test of the Stilting cryocooler is presented in this paper. We performed that low and high temperature keeping test from －4$0^{\circ}C$ to ＋6$0^{\circ}C$ and operating test at high and low temperature cyclic range with acceptance tests performed at scheduled intervals. Cooling capacity was determined as a function of cooler components temperatures at the compressor, hot end and cold tip. Tests performed on this cooler have been successful with a measured cooling performance of more than 0.8W＠80K for 23$^{\circ}C$ ambient temperature with 40 $W_{ac}$ input power.

• Journal of Ocean Engineering and Technology
• /
• v.13 no.2 s.32
• /
• pp.90-98
• /
• 1999

Boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants are degraded by creep damage due to severe operationg conditions like high temperature and high pressure for an extended period time. Such material degradation lead to various component faliures causing serious accidents at the plant. Conventional measurement techniques such as replica method, electric resistance method, and hardness test method have such disadvantages as complex preparation and measurement procedures, too many control parameters, and therefore, low practicality and they were applied only to component surfaces with good accessibility. In this study, both artificial creep degradation test using life prediction formula and frequency analysis by ultrasonic tests for their preparing creep degraded specimens have been carried out for the purpose of nondestructive evaluation for creep damage which can occur in high-temperature pipelline of fossil power plant. As a result of ultrasonic tests for crept specimens, we confirmed that the high frequency side spectra decrease and central frequency components shift to low frequency bans, and bandwiths decrease as increasing creep damage in backwall echoes.