• Title/Summary/Keyword: corrosion area

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A Case Study of Ground Subsidence in a Groundwater-saturated Limestone Mine (지하수로 포화된 석회석광산의 지반침하 사례연구)

  • Choi, Woo-Seok;Kim, Eun-Sup;Kang, Byung-Chun;Shin, Dong-Choon;Kim, Soo-Lo;Baek, Seung-Han
    • The Journal of Engineering Geology
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    • v.25 no.4
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    • pp.511-524
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    • 2015
  • Groundwater causing subsidence in limestone mines is uncommon, and thus relatively poorly investigated. This case study investigated the cause and possibility of future subsidence through an evaluation of ground stability at the Samsung limestone mine, Chungcheongbuk-do. The ground near the mine area was evaluated as unstable due to rainfall permeation, and subsidence in the unmined area resulted from groundwater level drawdown. Future subsidence might occur through the diffusion of subsidence resulting from the small thickness of the mined rock roof, fracture rock joints, and poor ground conditions around the mine. In addition, the risk of additional subsidence by limestone sinkage in corrosion cavities, groundwater level drawdown due to artificial pumping, and rainfall permeation in the limestone zone necessitates reinforcements and other preventative measures.

Defects Evaluation at Lap Joint Friction Stir Welding by Lock-in Ultrasound Infrared Thermography (위상잠금 초음파 적외선열화상에 의한 겹치기 마찰교반용접부의 결함 평가)

  • Choi, Man-Yong;Park, Hee-Sang;Park, Jeong-Hak;Kang, Ki-Soo
    • Journal of the Korean Society for Nondestructive Testing
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    • v.30 no.2
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    • pp.104-109
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    • 2010
  • Lap joint friction stir welding(LFSW) is an relatively new solid state joining process. A6061-T6 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio and good corrosion resistance. Test methods used in this paper, lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. In this paper, the defects detected from the thermal image of mechanical properties for weld were evaluated and compared by the lock-in infrared thermography technique.

A Study on the Polarization Potential Distrbution of a Steel Disc in the Water by Specific Resistance of Corrosion Circumstances (환경의 비저항을 고려한 수중 원강판의 분극전위분포에 관한 연구)

  • 김귀식
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.17 no.2
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    • pp.105-108
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    • 1981
  • The oceanic effect on the climate of the southern coast of Korea was analysed based on the sea surface temperature and in order to study relationships between the fluctuation of the sea surface temperature and that of climatic elements. Meteolorogical data from 1960 to 1979 were used. In the year when difference between the air and water temperature was maximum, the air temperature in southern coast was higher than normal year. A fluctuation of the sea surface temperature plays an important influence to determine the variation of the air temperature in the coastal area. Humidity of the coastal climate depends upon the oceanic effect in summer, but not in winter. This results may be due to prevailing wind effect. The oceanic effect on the precipitation in the coastal area is not found.

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Research on Karst Landforms in Hogye, Mungyeong (문경시 호계면 일대의 카르스트 지형 연구)

  • Kim, Hwang Soon;Seo, Jongcheol
    • Journal of The Geomorphological Association of Korea
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    • v.20 no.1
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    • pp.1-9
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    • 2013
  • This study aims to provide fundamental data for further shape-factor research on karst by measuring and classifying the shape of surface topography in Hogye, Mungyeong. First, in the research area, there are 35 dolines and uvalas. Second, large uvalas are found in three places, including Gulnomjae in Bugokri, and Teotgol and Denjimigol in Urori. Third, there are 13 round dolines and 22 oval dolines. Next examining the cross section of dolines, there are 27 bowl shaped dolines, 2 plate shaped dolines, and 6 funnel shaped dolines. Fourth, most dolines lay over 200m elevation, which is ridge and top of mountain. Fifth, development direction of dolines resembles the strike direction of limestone in Hogye, suggesting that the development direction of limestone affects doline corrosion. From this situation, we can guess sinkholes of the doline would be linked with limestone caves by the underground water pipe. Three limestone caves, karren and dry valley etc. appear in the research area.

Material Degradation of Ancient Iron Pot by Repeated Heating for One Thousand Years (고대 철확(철솥)의 1천년 반복 가열 및 열화현상)

  • Go, Hyeong;Han, Min Su;Choe, Byung Hak;Min, Doo Sik;Shim, Yun Im;Jeong, Hyo Tae;Cho, Nam Chul
    • Korean Journal of Metals and Materials
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    • v.50 no.4
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    • pp.324-330
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    • 2012
  • The microstructural changes of three pieces from an ancient iron pot were studied in order to identify present the material degradation due to repeated heating for one-thousand years. The microstructures of the pieces were divided into the areas of ferrite/graphite, ferrite/pearlite, and corroded oxidation. The area of ferrite/graphite was undergone by severe Galvanic corrosion, but that of ferrite/pearlite was not even during a thousand years' using. The shape of the graphites was coexisted with types of A, B, and C of as modern graphite classification. In the ferrite/pearlite area, abnormal acicula precipitates with a high aspect ratio of $0.2{\mu}m$ thickness and several hundreds ${\mu}m$ length were presented. They might be a kind of carbide in the ferrite matrix with its special precipitate plane.

A Study on LIT Girder Performance Improvement (LIT 거더 성능 개선에 대한 연구)

  • Kim, Sung;Park, Sungjin
    • Journal of Urban Science
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    • v.11 no.2
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    • pp.19-24
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    • 2022
  • Conventional RC beams for crossing small and medium-sized rivers do not have a cross-sectional area, so the floating debris is accumulated and disasters such as damage to bridges occur. To improve this, the PSC method was invented. However, this also had problems such as transverse curvature, increase in dead weight due to cross-sectional shape, and negative moment generated during serialization, so it was necessary to develop a new type of girder. Therefore, it was intended to propose a LIT(Leton Interaction Thrust) girder bridge that is safer and has better performance than the conventional PSC girder with improved section efficiency. Unlike existing girder bridges, the LIT girder has the feature that the change in the strands of the entire girder occurs only in the vertical direction when the first tension is applied because the tendon arrangement is symmetrical by applying the raised portion. In addition, slab continuation generates a secondary moment that is advantageous to the continuous point, effectively controlling the negative moment and preventing the corrosion of the tendon. The dimensions of the cross section were determined, and the arrangement of the strands was designed to conduct structural analysis and detailed analysis. As a result of the structural analysis, the stress of the girder showed results within the allowable compressive stress, and the deflection showed the result within the allowable deflection. showed results. In addition, a detailed analysis was performed to examine the stress distribution around the girder body and the anchorage area and the stress distribution of the embossed portion, and as a result, the stress of the girder body due to the tension force showed a stable level.

A case of direct restore using 4-META/MMA-TBB resin containing organic filler in patients with severe occlusal surface wear and enamel fracture (심한 교합면 마모 및 교두 파절 환자에서 유기필러를 함유한 4-META/MMA-TBB 레진을 활용한 직접수복 증례)

  • Dae-Sik Kim;Gyeong-Je Lee
    • Journal of Dental Rehabilitation and Applied Science
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    • v.39 no.4
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    • pp.222-228
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    • 2023
  • Attrition is the loss of tooth hard tissue due to contact between teeth, and in severe cases, dentin is exposed, accompanied by selective corrosion and excessive wear of teeth, which is called cupping. If these lesions are left untreated, the size of the lesion gradually increases, breaking the unsupported enamel, resulting in a decrease in aesthetics and chewing function. In this case report, patients with cupping and enamel fracture due to severe attrition were directly restored using a resin with soft properties containing organic fillers. In the follow-up observation six years later, most of the filling of the occlusal surface was eliminated, but the filling on the buccal surfaces remained relatively intact, and it was confirmed that this type of resin was suitable for the area where the occlusal force was relatively weak rather than the area where the occlusal force was greatly applied.

Estimation of BTX Emission Using Pseudo-gasoline (유사휘발유 사용에 의한 BTX 배출량 추정)

  • Jeon, So-Young;Kim, Jeong;Jang, Young-Kee;Jung, Bong-Jin
    • Journal of Korean Society for Atmospheric Environment
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    • v.28 no.5
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    • pp.527-537
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    • 2012
  • The increasing consumption of pseudo-petroleum products (PPP) has been disturbing the national petroleum market. The use of PPP lead to tax evasion, disturbance of sound trading principles, component corrosion of cars, and explosion accident. Also, PPP have emitted hazardous air pollutants (HAP) including the carcinogenic aromatic hydrocarbons, PAHs and aldehydes more than regular-petroleum products. It thus has potentials to cause many environmental and health care problems. In this study, benzene, toluene and xylene emissions from road transport vehicles due to the use of pseudo-gasoline are estimated for the year 2008. The results of our study provide emission estimates of benzene, toluene and xylene for the year as 405, 1,711, 717 tonne/yr, respectively for regular-gasoline. BTX emissions are calculated as 452~515, 1,882~2,264 and 732~752 tonne/yr when the amount of pseudo-gasoline is estimated to account for 6~13% for regular-gasoline consumption. BTX emissions increased as much as 12~27, 10~32, 2~5% by using pseudo-gasoline. It is found that the pseudo-gasoline should be the key component to produce HAP in urban area.

A Study on the Development of Cu-based Sintered Friction Materials (동계 소결마찰재 개발에 관한 연구)

  • Lee, Jong-Hyung;Choi, Byung-Ho;Kim, Jeong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.1
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    • pp.83-92
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    • 1997
  • In a study on the development of Cu-based sintered friction materials, the specimens pressed with various compacting pressures $(3-6 ton/cm^2/)$ have been evaluated to find the optimum condition of compacting pressure. As compacting pressure increased up to $(5 ton/cm^2/)$, mechanical properties such as density, hardness, bending strength, wear and coefficient of friction, etc. improved remarkably, but up to 6 ton/cm$^{2}$, decreased slightly because of traps of gases and water vapors in specimen. Disk assembly composed of 12 pieces of Cu-based friction materials has been compared with one of asbestos-and nonasbestos-based friction materials. In dynamic and driving tests to find burst spin strength, corrosion area rate and friction properties, etc., Cu-based sintered friction materials showed better properties than the others, especially in severe conditions because oxides such as $Cu_2O; and; SnO_2$ in the friction surface of friction materials were formed.

Chloride penetration in anchorage concrete of suspension bridge during construction stage

  • Yang, In-Hwan;Yoon, Yong-Sik;Kwon, Seung-Jun
    • Advances in concrete construction
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    • v.10 no.1
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    • pp.13-20
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    • 2020
  • Steel corrosion in embedded steel causes a significant durability problems and this usually propagates to structural degradation. Large-scaled concrete structures, PSC (Pre-stressed Concrete) or RC (Reinforced Concrete) structures, are usually constructed with mass concrete and require quite a long construction period. When they are located near to sea shore, chloride ion penetrates into concrete through direct or indirect exposure to marine environment, and this leads durability problems. Even if the structures are sheltered from chloride ingress outside after construction, the chloride contents which have been penetrated into concrete during the long construction period are differently evaluated from the initially mixed chloride content. In the study, chloride profiles in cores extracted from anchorage concrete block in two large-scaled suspension bridge (K and P structure) are evaluated considering the exposure periods and conditions. Total 21 cores in tendon room and chamber room were obtained, and the acid-soluble chlorides and compressive strength were evaluated for the structures containing construction period around 3 years. The test results like diffusion coefficient and surface chloride content from the construction joint and cracked area were also discussed with the considerations for maintenance.