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Page : 218 - 224
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- 니켈기 합금 Alloy 617의 950 ?C 대기/헬륨 분위기에서 산화거동 고찰
- Alloy 617 is a candidate Ni-based superalloy for intermediate heat exchanger (IHX) of a high-temperature gas reactor (VHTR), because of its good creep strength and corrosion resistance at high temperature. Small amount of impurities such as H2O, H2, CO and CH4 are introduced inevitably in helium, as a coolant during operation of a VHTR. Reactions of material and impurities are accelerated with increase of temperature to 950 oC of operating temperature of a VHTR, leading to material corrosion aggravation. In this circumstance, high-temperature corrosion tests were performed at 950 oC in air and impure helium environments, up to 250 hours in this study. Oxidation rate of 950 oC in an air environment was higher than that of impure
helium, explained by difference in outer oxide morphology and microstructure as a function of oxygen partial pressure. An equiaxed Cr-rich surface oxide layer was formed in an air environment, and a columnar Cr-rich oxide was formed in an impure helium environment. - KEYWORDs : Alloy 617, Impure helium, Oxidation, Corrosion, Microstructure
- AUTHORs : 정수진·이경근·김동진†
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Page : 225 - 230
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- 염화물 수용액에서 자작나무 수액을 이용한 철강의 부식 억제
- The effects of birch sap, a possible natural corrosion inhibitor, on the corrosion behavior of steel in chloride solution were investigated. The corrosion rate was significantly reduced by the addition of 1~5 mL of birch sap to 500 mL of 3wt% NaCl or 3wt% CaCl2 solution. A remarkable increase in the pitting potential in NaCl solution was observed by the addition of birch sap although it was almost constant in CaCl2 solution. The corrosion rate of steel in both NaCl and CaCl2 birch sap solution without addition of water was higher compared to that of aqueous solution without birch sap as the pH of the birch sap was 4.0. The presence of organic compounds like, fructose, galactose, glucose, and palmitic acid in the birch sap are thought to be adsorbed effectively on the metal surface, which provided corrosion protection. However, the inorganic elements including Na, Ca, K, Mg, Mn, S, etc.
present in the birch sap exhibited no role in corrosion inhibition. - KEYWORDs : Steel, Chloride solution, Natural inhibitor, Birch Sap
- AUTHORs : 박태준·김기애·이지이·장희진†
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Page : 231 - 241
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- 36개월간 국내 옥외폭로시험에 따른 아연도강의 부식거동
- Atmospheric corrosion is generally an electrochemical degradation process of metal. It can be caused by various corrosion factors of atmospheric component, weather, and air pollutants. Moisture, particles of sea salts, and sulfur dioxide are major factors in atmospheric corrosion. Galvanizing coating is one of the most efficient ways to protect iron from corrosion by zinc plating on the surface of the iron. Galvanized steels are being widely used in automobiles, building structures, roofing, and other industrial structures due to their high corrosion resistance compared to bare iron. Atmospheric corrosion of galvanized steel has shown complex corrosion behavior depending on coating process, coating thickness,
atmospheric environment, and air pollutants. In addition, different types and kinds of corrosion products can be produced depending on the environment. Lifespan of galvanized steels is also affected by the environment. Therefore, the objective of this study was to determine the corrosion behavior of galvanized steel under atmospheric corrosion at six locations in Korea. When the exposure time was increased, content of zinc from GA surface decreased while contents of iron and oxygen tended to increase. On the other hand, content of iron was constant even after 36 months of exposure of GI. - KEYWORDs : Galvanized steel, Outdoor exposure test, Atmospheric corrosion, Surface appearance
- AUTHORs : 김기태·김영식†
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Page : 242 - 248
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- 템퍼링 조건이 마르텐사이트계 고강도강의 수소확산거동에 미치는 영향
- Martensitic high-strength steels revealed superior mechanical properties of high tensile strength exceeding 1000 Mpa, and have been applied in a variety of industries. When the steels are exposed to corrosive environments, however, they are susceptible to hydrogen embrittlement (HE), resulting in catastrophic cracking failure. To improve resistance to HE, it is crucial to obtain significant insight into the exact physical nature associated with hydrogen diffusion behavior in the steel. For martensitic steels, tempering condition should be adjusted carefully to improve toughness. The tempering process involves microstructural modifications, that provide changes in hydrogen diffusion/trapping behavior in the steels. From this perspective, this study examined the relationship between tempering condition and hydrogen diffusion behavior in the steels. Results based on glycerin measurements and hydrogen permeation evaluations indicated that hydrogen diffusion/trapping behavior was strongly affected by the characteristics of precipitates, as well as by metallurgical defects such as dislocation. Tempering condition should be adjusted properly by considering required mechanical properties and resistance to HE.
- KEYWORDs : Tempering, ε-carbide, Cementite, Hydrogen diffusion, Martensitic high-strength steel
- AUTHORs : 박진성·황은혜·이만재·김성진†
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Page : 249 - 256
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- Investigation of Sweet and Sour Corrosion of Mild Steel in Oilfield Environment by Polarization, Impedance, XRD and SEM Studies
- Metallic structures in the oil and gas production undergo severe degradation due to sweet and sour corrosion caused by the presence of CO2 and H2S in the fluid environment. The corrosion behavior of 304 austenitic stainless was investigated in the presence of varying concentrations of CO2 or H2S and CO2 + H2S to understand the effect of the parameters either individually or in combination. Potentiodynamic polarization study revealed that a small amount of CO2 aided in the formation of
calcareous deposit of protective layer on passive film of 304 steel, while increase in CO2 concentration ruptured the layer resulting in sweet corrosion. The presence of S2- damaged the passive and protective layer of the steel and higher levels increased the degradation rate. Electrochemical impedance studies revealed lower polarization resistance and impedance at higher concentration of CO2 or H2S, supporting the outcomes of polarization study. XRD analysis revealed different types of iron carbides and iron sulphides corresponding to sweet and sour corrosion as the corrosion products, respectively. SEM analysis revealed the presence of uniform, localized and sulphide cracking in sour corrosion and general corrosion
with protective carbide layer amid for sweet corrosion. - KEYWORDs : Oil field corrosion, mild steel, polarization, impedance spectroscopy, electron microscopy
- AUTHORs : Subir Paul† and Bikramjit Kundu
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Page : 257 - 264
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- The Corrosion Behavior of Anti-Graffiti Polyurethane Powder Coatings
- Anti-graffiti coatings have become more important. These layers must guarantee excellent corrosion protection properties, and graffiti must be easily removable, without reducing protection and aesthetic properties. In this study, anti-graffiti and corrosion behavior of two anti-graffiti polyurethane powder coatings were studied.
These layers were deposited on aluminum substrate, with two different surface finishes, smooth, and wrinkled. The action of four different removers are investigated. Graffiti were drawn on coatings by means of red acrylic spray paint. Methyl-ethyl-ketone (MEK) and a “commercial” remover were the most effective solvents, in terms of graffiti removal capability, producing limited change in aesthetical surface aspect for smooth finishing. The wrinkled surface was less resistant. Corrosion protection properties, after removal action and contact with the remover, were evaluate by electrochemical impedance spectroscopy. After approximately 5 hours, coatings were no longer protective due to formation of defects. To simulate the weathering effect, UV-B cyclic test (4 hours of UV exposure followed by 4 hours of saturated humidity at 50 °C) were performed for 2000 hours. Gloss and color changes were measured, and electrochemical impedance spectroscopy measurements were performed after aging and graffiti removal. - KEYWORDs : Organic coatings, Anti-graffiti layer, Powder coatings, Electrochemical impedance spectroscopy
- AUTHORs : S. Rossi†, M. Fedel, F. Deflorian, and A. Feriotti
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Page : 265 - 271
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- Analysis of CRUD Flake Applied to Abnormal High Beam Current by Shielded-EPMA
- CRUD specimens, scraped from twice-burned fuel cladding in the Korean Nuclear Power Plant, were analyzed using Shielded-EPMA. The principal elements of the CRUD were identified as Ni and Fe, at an approximate ratio of 1.3 Ni/Fe. To investigate the morphology and composition of the pure metallic materials in the CRUD, coolant impurities must be removed. This can be accomplished by
increasing the EPMA current to an abnormally high intensity until the impurities are melted. Normally, EPMA applications are performed at conditions of 20 kV voltage and 20 nA current. But in our study, the applied current was increased up to 1200 nA, over time increments ranging from 5 to 30 seconds. This technique was performed by opening an adjustable aperture for the gun alignment. Results showed
impurities contained in the CRUD material disappeared and pure metal materials, e.g., Ni and Fe, remained. This method presents an innovative way to analyze CRUD. - KEYWORDs : CRUD, Shielded-EPMA, Abnormal beam current, Boling chimney hole, NiFe2O4
- AUTHORs : Y. H. Jung†, S. J. Baik, and S. B. Ahn
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Page : 272 - 278
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- A Study on the Effect of the ICCP System in Reinforced Concrete Specimens of Slab Type
- Reinforced concrete (RC) has been used as a construction material in various environments, such as airports, bridges, and ocean concrete structures, etc. Over time, however, rebar in the concrete is prone to corrosion from environmental forces and structural defects of the concrete. Cathodic protection (CP) was invented
to prevent problems with corrosion and is widely used for different applications. Cathodic protection is divided into two types: sacrificial anode cathodic protection (SACP) and impressed current cathodic protection (ICCP). There are several limitations to the use of sacrificial anode cathodic protection in complex reinforced
concrete structures, including concrete resistivity, throwing power of the CP, and environmental conditions. These limitations can affect the protection performance of SACP. Therefore, we used impressed current cathodic protection in our study. We tested Ti-Mesh, Ti-Rod, and Ti-Ribbon anodes in slab type reinforced concrete specimens. Electrochemical tests were conducted to confirm the impressed current cathodic protection performance under different environmental conditions. - KEYWORDs : Reinforced concrete, Cathodic protection, Concrete resistivity, Throwing power
- AUTHORs : Jin-A Jeong, Kwon-Heum Ko†, Mun-Su Kim, and Du-Hyeong Lee
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Page : 279 - 286
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- 8인치 직경의 304L 스테인리스강관의 부식특성에 미치는 제작공정의 영향
- Austenitic stainless steels used in nuclear power plants mainly use pipes made of seamless pipes, which depend on imports. The manufacturing process and high cost are some of the problems associated with seamless pipes. Therefore, in this study, the corrosion characteristics of the seamless pipe and the SAW pipe were assessed to determine the safety and reliability of the SAW pipe in a bid to
replace the seamless pipe. Microstructure was analyzed using an optical microscope and the degree of hardness was measured using a Rockwell B scale. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. Anodic polarization test was performed in deaerated 1% NaCl solution at 30 oC and
the U-bend method was used to evaluate the SCC resistance in 0.01 M Na2S4O6 at 340 oC and 40% NaOH solution at 290 oC. Weld metal of the SAW pipe specimen showed relatively high degree of sensitization and intergranular corrosion rate. However, annealing to SAW pipes improved the corrosion properties in comparison to that of the seamless pipe. - KEYWORDs : 304L stainless steel, Seamless pipe, Welded pipe, Annealing, Nuclear power plant
- AUTHORs : 김기태·허승영·장현영·김영식†
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Page : 287 - 291
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- 지역난방 시스템의 순환수에 따른 보일러 튜브의 부식 특성
- In this study, corrosion behavior of a SA178-A alloy used in the boiler tube of a district heating system
was investigated in different environments where it was exposed to pure water, district heating (DH) water,
and filtered district heating (FDH) water. After the corrosion test, the surface morphology was examined
for observation of the number of pitting sites and pitting area fraction, using a scanning electron microscope.
The DH water and FDH water conditions resulted in a lower corrosion potential and pitting potential, and
revealed a significantly higher corrosion rate than the pure water condition. The pitting sites in the DH
water (pH 9.6) were approximately eighteen times larger than those in the pure water (pH 9.6). Compared
to the DH water, the corrosion potential became more noble in the FDH water condition, where iron ions
were reduced through filtration. However, the corrosion rate increased in the FDH water due to an increased
concentration of chloride ions, which deteriorated the stability of passive film. - KEYWORDs : District heating system, Boiler water, Corrosion, Potentiodynamic polarization
- AUTHORs : 홍민기·조정민·송민지·김우철·하태백·이수열†
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