• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.12-17
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• 2006

A steam generator of nuclear power plant has thousands of thin tubes. These tubes play an important role in maintaining the pressure boundary between the primary and secondary side of nuclear power plant. The steam generator tube is easy to be damaged because of the severe operating conditions such as the high temperature and pressure. Therefore, tremendous efforts are made to assess the structural integrity of the steam generator tubes. The eddy current test is the most popular non-destructive test to assess the integrity of the tubes. However, the eddy current test has the limitation to size the flaw accurately because the eddy current signal behavior depends on the total volume of flaw. This paper shows the possibility that the ultrasonic test method can be applied to detect the flaws in the steam generator tubes and to measure them quantitatively. From the test results, it is expected that if the ultrasonic test is put to practical use in the steam generator tube inspection, the inspection results will be improved.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.56-56
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• 2010

최근 강구조물의 건설이 지속적으로 증가되어 왔다. 또한 강구조물의 유지관리 및 안전성에 대한 관심이 급증하고 있다. 시설물의 안전성 확보는 대형사고의 사전 예방, 공용 중 갑작스런 가동 중지에 의하여 발생되는 비용증가를 사전에 차단 할 수 있다는 점에서 그 중요성은 매우 크다고 할 수 있다. 또한 각종 구조물은 열악한 사용조건, 고온, 고압, 고속, 대형화됨에 따라 일단 사고가 발생 했을 경우 대형사고의 위험이 예상되므로, 제작시 검사의 강화뿐만이 아니라 공용 중 구조물의 안전성을 진단 할 수 있는 모니터링 체계의 확립이 필요한 시점이다. 현재 국내에서 강구조물들의 균열 모니터링 시스템에 관한 연구는 매우 미흡한 실정이며, 현재 사용되고 있는 비파괴검사 방법은 UT와 RT등이다. 이러한 방법들은 많은 시간과 경비가 소요되며 또한 거대구조물 혹은 사람의 접근이 어려운 곳에는 적용하기가 힘들다. 또한 주기적인 검사 작업으로 인한 막대한 시간과 비용의 손실이 발생되고 있으며 초기 결함을 조기에 인지하지 못함으로써 적절한 보수 보강 대책이 이루어지지 않아 보수 보강 비용의 증대를 초래한다. 더욱이, 결함이 진전된 이후에도 이것을 인지하지 못하여 적절한 대응을 하지 않는다면 대형사고로 이어질 수도 있다. 따라서 강구조물에 대한 효율적인 유지관리가 가능하고, 초기결함으로부터 균열이 진전하여 붕괴되는 사고를 미연에 방지하며 초기에 보수보강 작업을 수행함으로써 보수보강 비용도 절감 할 수 있는 모니터링 시스템의 개발이 요구되고 있다. 이러한 모니터링 시스템의 개발은 기술적 측면에서 강구조물의 효율적인 유지 관리 노하우를 얻을 수 있으며 경제 산업적 측면에서는 보수 보강 비용 및 불필요한 주기적 점검 비용을 절감 할 수 있다. 이 연구에서는 전위차법을 이용하여 강구조물의 필렛 용접부에서의 균열진전양상을 파악하고 정량화를 통해 필렛용접부의 잔여수명을 예측하였다.

• Journal of the Korean Institute of Gas
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• v.18 no.2
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• pp.16-20
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• 2014

In this paper, the performance of pressure-resistance is validated by experiment on LPG re-fillable cylinder which has increased demands for spreading of camp culture. Propane has increased suppliable requirements as fuel because of easily vaporizing effect of low boiling point. However, propane can be occurring safety problems inevitably by high vapor pressure. So, the priority is that safe cylinder should furnish in order to be circulated as safe fuel. LPG re-fillable cylinder for high pressure is tried to furnish internationally, that is restricted by safe issues. For these reasons, the pressurization and rupture are performed by using pressurizing device that is operated by hydraulic system. Also, this paper will offer rupturable characteristics comparing with vapor pressure of propane. This paper is expected as basis research for developing re-fillable cylinder and using standard for supplying them.

• Journal of the Korean Institute of Gas
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• v.17 no.2
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• pp.50-58
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• 2013

Various process piping usually carries out high flammable and explosible gas under high pressure and high temperature. Due to frequent change of design and structure it becomes more complicated and compactly located. The safety management level is relatively low since it is considered as simply designed component. In this study a safety assessment procedure is proposed for complicated piping system around a mixing drum in which natural gas and by-product gases were mixed. According to ASME code, pipe stress analysis was conducted for determining design margin at some key locations of the piping. These high stress locations can be used as major inspection points for managing the pipe integrity. Sensitivity analysis with outside temperature of the pipe and support constraint condition. Possible effect of hydroen gas to the pipe steel during the previous use of the by-product gas was also discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1359-1365
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• 2014

In this study, 1-way fluid structure interaction analysis(FSI) for the shutter, component of side jet thruster was performed to evaluate the safety. Driving torque to open nozzle, thermal and high pressure load of hot gas was applied to shutter. Thus, the shutter must be designed to endure this load during combustion. We carried out computational fluid dynamics analysis to obtain the pressure, temperature, and heat transfer coefficient of hot gas of side jet thruster. We then used the data as the load condition for a thermal structural analysis using a mapping method. The locations with the maximum stress and temperature distributions were found. We compared the maximum stress with the tensile stress of shutter material according to temperature to evaluate the safety. We also analyzed the radial deformation of the shutter to set the proper interface gap with the side jet thruster parts.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.9
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• pp.1265-1272
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• 2010

In view of the frequent start-ups and load changes in the recent past, there is a need for fossil-fuel power plants to be more efficient and reliable for long-term operation. Under high-temperature and high-pressure conditions, severe creep and fatigue damages can occur in major plant facilities, particularly, turbines and boilers. For highly stable operation and better maintenance, various techniques that facilitate a systematic assessment of the service life of critical facilities have been developed. However, to date, in Korea, to evaluate the remaining life of major facilities of fossil power plant, qualitative or semiquantitative analyses are carried out without following any standard guidelines or procedure. In this study, a standard code for assessing the remaining life of major plant facilities is proposed. This code takes into account creep and fatigue damage, which are generally accepted as dominant causes of damage to facilities. KEPIC (Korea Electric Power Industry code) is scheduled to include this guideline in 2010.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.52-52
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• 2010

본 연구에서 우리는 HPHT 처리 전 FT-IR spectrometer를 이용한 사전분석을 통해 type Ia brown 다이아몬드를 IaA, IaB, IaAB (A>B), IaAB (A=B), IaAB (A$1700-1800^{\circ}C$, 5 GPa에서 다이아몬드가 흑연화 되지 않는 범위 하에 HPHT처리를 시행하였다. 자외선-가시광선 분광분석기(UV-Vis Spectrometer, Shimadzu UV 3101PC)를 사용하여 350~800 nm에서의 가시광선 범위를 0.1nm의 분해능으로 투과(Transmittance) 모드로 측정하였고, 퓨리에 변환 적외선 분광분석기(FT-IR spectrometer, Jasco-4100)을 사용하여 $400{\sim}6000cm^{-1}$의 범위에서 $4cm^{-1}$ 의 분해능으로 흡수(Absorption) 모드로 측정한 후 HPHT 처리 전후를 비교 분석하였다. 또한 광루미네선스(Photoluminescence) 분석은 325 nm He-Cd laser를 광원으로 한(PL, Spectra-pro 2150i, Spectra-pro 2300i micro-spectrometer) 및 532 nm green laser를 광원으로 한(PL, SAS 2000)를 사용하여 각각 350~600 nm, 550~1100 nm의 범위에서 0.1nm step으로 측정하여 HPHT 처리전과 후를 비교 분석하였다. HPHT처리 후 모든 시료는 N3 center (415.4 nm), H4 center (496.4nm) 및 platelet와 연관된 ($1363\;cm^{-1}$)의 peak가 감소하였고, H3 center (503.2 nm)와 G-band가 증가하는 경향을 나타내었다. 또한 HPHT 처리 시 질소의 B집합보다 A집합이 더 감소하는 경향을 나타내었으며, A 또는 B집합의 파괴에서 발생된 질소 원자에 의해 질소의 interstitial center (594 nm)가 증가함을 알 수 있었다. HPHT 처리 후 모든 시료는 (N-V)- center가 생성됨을 확인 할 수 있었다. 결론적으로 본 연구를 통해 HPHT 처리를 통해 다이아몬드 내에 존재하는 질소결합관련 상태의 변화를 확인할 수 있었다.

• Journal of ILASS-Korea
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• v.24 no.4
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• pp.157-162
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• 2019

This numerical study was analyzed to predict the flammability limits of biodiesel and diesel fuels in the high temperature and pressure conditions. To achieve this, the biodiesel fuel was simulated with the chemical species of n-heptane (n-C₇H₁₆), methyl decanoate (C₁₁H₂₂O₂), and methyl-9-decenoate (C₁₁H₂₀O₂), and the diesel fuel was substituted the chemical species of n-heptane. The closed 0-D homogeneous reactor model which was employed the 1100 K of ambient temperature and 35 atm of ambient pressure was used for the simulation of constant volume combustion, and the equivalence ratio was changed from 0.3 to 2.5 conditions. In addition, a comparative analysis study was conducted with the results of HCCI engine simulation and flammability limits according to the changes of equivalence ratio. The results of combustion temperature, pressure, and ignition delay were increased when the equivalence ratio elevated from 0.3 to 1.3 conditions because the increase in fuel oxidation rate affects the chemical reaction of the overall combustion process. Furthermore, the CO and NO_X production under the rich combustion conditions are considered to have a trade off relationship since the OH radicals and O₂ chemical species are greatly affected the CO and NO_X production and oxidation processes.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.12
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• pp.967-972
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• 2013

A MILD (Moderate and Intense Low oxygen Dilution) combustion, which is effective in the reduction of NOx, is considerably affected by the recirculation flow rate of hot exhaust gas to the combustion furnace. The present study used the MILD combustor, which has coaxial cylindrical tube. The outside tube of the MILD combustor corresponds to the exhaust gas passage and the inner side tube is the furnace passage. A numerical analysis was accomplished to elucidate the characteristics of exhaust gas entrainment toward the inner furnace with the changes of coanda nozzle geometrical parameters, nozzle passage gap length, nozzle passage length, nozzle angle and expansion length. The optimal configuration of coanda nozzle for the best entrainment flow rate was gap length, 0.5 mm, expansion angle, 4o and expansion length, 146 mm. The nozzle passage length was irrelevant to the exhaust gas entrainement.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.87-92
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• 2003

In rocket systems, somtimes special devices or equipments are installed near the nozzle exit area where high temperature and pressure combustion gas flows. To pretect these subsystems from severe thermal environment, it is necessary to have accurate thermal data measured from the experimental liquid rocket firing test. Test variables were combustion pressure (200, 300, 400 psi) and mixture ratio (1.5, 2.0, 2.5) and quartz was used as a heat probe. Measurement technique used in this research can be also applied to measure the radiative heat flux inside the combustion chamber which is important imput data for the liquid rocket regenerative cooling system design.