• Journal of the Korean Society for Precision Engineering
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• v.29 no.12
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• pp.1267-1271
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• 2012

Demand for optical glass device used for lighting could increase rapidly because of LED lighting market growth. The optical glass devices that have been formed by hot press molding process the desired optical performance without being subjected to mechanical processing such as curve generation or grinding. EL-Max material has been used for many engineering applications because of their high wear resistance, high compressive strength, corrosion resistant and very good dimensional stability. EL-Max is very useful for a glass lens mold especially at high temperature and pressure. The performance and reliability of optical components are strongly influenced by the surface damage of EL-Max during grinding process. Therefore, the severe process condition optimization shall be necessary for the highly qualified EL-Max glass lens mold. To get the required qualified surface of EL-Max, the selection of type of the diamond wheel is also important. In this paper, we report best grinding conditions of ultra-precision grinding machining. The grinding machining results of the form accuracy and surface roughness have been analyzed by using Form Talysurf and NanoScan.

• Journal of the Korean Institute of Gas
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• v.20 no.5
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• pp.89-95
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• 2016

Keeping the gas pipelines in the common utility tunnel is useful because it has a lower risk of corrosion than conventional burial, and can prevent from excavating construction. But, explosions in common utility tunnels can cause greater damage from the blast overpressure compared to outdoor explosions, due to nature of the confined environment. Despite this fact, however, research on common utility tunnels has been limited to fire hazard and little has been studied on the dangers of explosions. This study developed scenarios of methane gas explosion caused by gas leak from gas piping within the common utility tunnel followed by unknown ignition; the study then calculated the extent of the impact of the explosion on the facilities above, and suggested the needs for designing additional safety measures. Two scenarios were selected per operating condition of safety devices and the consequence analysis was carried out with FLACS, one of the CFD tools for explosion simulation. The overpressures for all scenarios are substantial enough to completely destroy most of the buildings. In addition, we have provided additional measures to secure safety especially reducing incident frequency.

• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.

• Journal of the Korea Institute of Building Construction
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• v.2 no.2
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• pp.165-172
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• 2002

A reinforced concrete building neighboring in Pusan or Ulsan where is directly exposed to salt water contrasting with other in land areas contains much salt content percolated from the outside that the high salt content percolates and diffuses through the inside of reinforced concrete; therefore, an immovable tunic surrounding it begins to be destroyed and eroded with high speed. At the time, the cross-sectional area and volume expansion of re-bar reinforcing result in being cracks make a rapid progress gradually until they appear in the surface of the one, the phenomenon such as being a thin layer or falling off the part of it causes a lowering of its durability and might collapse the concrete construction. So far, we've investigated into salt content of reinforced concrete constructions neighboring in a seaside district and damage by carbonation, and we came to a conclusion as follows: $\circled1$ Under the oceanic circumstance a concrete construction is influenced by sea water directly that contains much amount of salt content contrasting with other constructions on inland areas. $\circled2$ Because of chloride penetration the carbonation of reinforced concrete made a rapid progress until more than the covering thickness of re-bar. $\circled3$ An old reinforced concrete building which has been piled up salt injury and proceeding the carbonation of its cross-sectional area. $\circled4$ According to rapidly cracking from the inside to surface of reiforced concrete, the phenomenon of being a thin layer or falling off the part of reinforced concrete results in a lowering of durability and shortening the life-time of concrete construction itself.

• Journal of Energy Engineering
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• v.15 no.3 s.47
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• pp.146-153
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• 2006

A performance test of the stainless steel based sintered metal filter was conducted on the low and intermediate level radioactive waste (LILW) vitrification process. The applicability of the metal filter was based on the test results as well. The baseline pressure drop of the metal filter was evaluated similar to the ceramic filter. During the test, when the flow rate of off-gas was $110Nm^{3}/h$, the total baseline pressure drop was shown as $92mmH_{2}O$. The total pressure drop was attributed to the filter media and the residual dust layer and the value of each was $25mmH_{2}O\;and\;67mmH_{2}O$ respectively. The SEM-EDS spectrum and micrograph of the metal filter specimen showed, no corrosion and no physical damage both at the skin membrane and at the support layer. And most of the baseline pressure drop was caused by the deposition of dust on the surface of the membrane. In conclusion, even though the filter exposure time was short at the test, the performance of the stainless steel based metal filter was acceptable for the treatment of LILW vitrification process.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.149-154
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• 2012

The size and distribution of welding residual stress and welding deformation in welding structures have an effect on various sorts of damage like brittle failure, fatigue failure and stress corrosion cracking. So, research for this problem is necessary continuously. In this study, non-destructive technique using laser electronic speckle pattern interferometry, plate of welding specimen according to the external load on the entire behavior of residual stress are presented measurement techniques. Once, welding specimen force tensile loading, using electronic speckle pattern interferometry is measured. welding specimen of base metal and weld zone measure strain from measured result, this using measure elastic modulus. In this study, electronic speckle pattern interferometry use weld zone and base metal parts of the strain differences using were presented in residual stress calculated value, This residual stress value were calculated by numerical calculation. Consequently, weld zone of modulus high approximately 3.7 fold beside base metal and this measured approximately 8.46 MPa.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.11-17
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• 2011

A major source of durability problems in concrete structures is the corrosion of steel by the damage of passivity layer around steel bars. As chloride ion penetration is major cause of the destruction of passivity layer, evaluation of depth and concentration profile of chloride ion is the essential factor for the service-life estimation of concrete structure. To estimate chloride ion penetration characteristics, this paper on the basis of in-situ experimental data investigated the depth and concentration profile of chloride ion penetration. The core specimens are obtained at air-zone, splash zone, and tidal zone in Wando, Masan, Incheon, Gwangyang, and donghae harbors. Colorimentric method measured the chloride ion penetration depth and ASTM C 114 evaluated the concentration profile of chloride ion. Based on experimental data, the influence of harbor location and exposure condition on chloride ion penetration is evaluated.

• Journal of the Korean Institute of Gas
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• v.5 no.4 s.16
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• pp.40-48
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• 2001

For a Liquified Petroleum Gas(LPG) station, the reliability analysis, such as Fussell-Vesely importance, risk decrease factor and risk increase factor, was carried out and the risk ranks of events were determined. In order to confirm the degree of the risks identified in the reliability analysis, the quantitative risk analysis was done for the equipments which had the large values of risk ranks. As a result of the importance analysis for the LPG station, the external event was identified as the most riskful event. The defect of construction structure and the pipe corrosion were riskful as well. The result of quantitative risk analysis showed that the length of 46.3 meters were estimated to damage the process equipments by the thermal flux from the catastrophic rupture of storage tank in Boiling Liquid Expanding Vapor Explosion.

• Journal of Power System Engineering
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• v.19 no.5
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• pp.60-66
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• 2015

Embrittlement of material by hydrogen charging should be cleared for safety of storage vessel of hydrogen and components deal with hydrogen. A stainless steel is generally used as materials for hydrogen transportation and storage, and it has a big advantage of corrosion resistance due to nickel component in material. In this study, microscopic damage behavior of stainless steel according to the hydrogen charging time using nondestructive evaluation was studied. The surface of stainless steel became more brittle as the hydrogen charging time increased. The parameters of nondestructive evaluation were also changed with the embrittlement of stainless steel surface by hydrogen charging. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties of stainless steel by hydrogen charging. The attenuation coefficient of ultrasonic wave was increased with hydrogen charging time because of surface embrittlement of stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced hydrogen charging. AE event at the hydrogen charged specimen was obviously decreased at the plastic zone of stress-strain curves, while the number of event for the specimen of hydrogen free was dramatically generated when compared with the specimens underwent hydrogen charging.

• Journal of Korean Ophthalmic Optics Society
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• v.4 no.2
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• pp.147-154
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• 1999

This study was performed to survey the exchange of frames on 83 persons. We investigated frame size, frame type, binocular prism effect etc. 80.4% among motives of frame-exchanges was a damage or corrosion. The type of frames was round-like 62.4% and 37.6% square-like. The size of frames was $49{\Box}18$ and vertical length 33mm on old-frames, $47{\Box}17$ and 31mm on new-frames. The scope of axis variation was average +3.20~3.80. According to estimation by the rule of RAL-RG 915, the inappropriate horizontal prism effect of new spectacles was 42.2%, more than 38.5% on old spectacles. The inappropriate vertical prism effect was 24.1% on old, 33.7% on new spectacles.