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AC8A 알루미늄합금 주조재의 열처리에 의한 특성 평가
Aluminum is on active metal, but it is well known that its oxide film plays a role as protective barrier which is comparatively stable in air and neutral aqueous solution. Thus, aluminum alloys have been widely applied in architectural trim, cold & hot-water storage vessels and piping etc., furthermore, the aluminum alloy of AC8A
have been widely used in mold casting material of engine piston because of its properties of temperature and wear resistance. In recent years, the oil price is getting higher and higher, thus the using of low quality oil has been significantly increased in engines of ship and vehicle. Therefore it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and prolong its lifetime. In this study, the effect of solution and tempering heat treatment to corrosion and wear resistance is investigated with electrochemical method and measurement of hardness. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment and exhibited the highest value of hardness with tempering heat treatment temperature at 190 ℃ for
24hrs. Furthermore, corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. As a result, it is suggested that the optimum heat treatment to improve both corrosion and wear resistance is tempering heat treatment temperature at 190 ℃ for 16hrs.
KEYWORDs : aluminum alloy, mold casting, corrosion resistance, wear resistance, solution heat treatment,
AUTHORs : 이성열․ 박동현․ 원종필․ 김윤해․ 이명훈․ 문경만․ 정재현†

Page : 275 - 279 DOWNLOAD
나노결정질 Ni-W 합금전착의 내부응력에 미치는 공정조건 변수의 영향
Ni-W alloy deposits have lately attracted the interest as an alternative surface treatment method for hard chromium electrodeposits because of higher wear resistance, hardness at high temperature, and corrosion resistance. This
study deals with influences of process variables, such as electodeposition current density, plating temperature and pH, on the internal stress of Ni-W nanocrystalline deposits. The internal stress was increased with increasing the applied current density. With increasing applied current density, the grain size of the deposit decreases and concentration of hydrogen in the deposit increases. The subsequent release of the hydrogen results in shrinkage of the deposit and the introduction of tensile stress in the deposit. Consequently, for layers deposited at high current density, cracking occurs readily owing to high tensile stress value. By increasing the temperature of the electrodeposition from 60 ℃ to 80 ℃, the internal stress was decreased. It seems that an increase in the number of active ions overcoming the activation energy at elevated temperature caused a decline in the concentration
polarization and surface diffusion. It decreased the level of hydrogen absorption due to the lessened hydrogen evolution reaction. Therefore, the lower level of hydrogen absorption degenerated the hydride on the surface of the electrode, resulting in the reduction of the internal stress of the deposits. By increasing the pH of the
electrodeposition from 5.6 to 6.8, the internal stress in the deposits were slightly decreased. It is considered that the decrease in internal stess of deposits was due to supply of W complex compound in cathode surface, and hydrogen ion resulted from decrease of activity.
KEYWORDs : Ni-W, electroplating, internal stress, current density, nanocrystalline
AUTHORs : 김경태†․ 이정자․ 황운석

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철근 콘크리트 구조물용 다기능 멀티센서의 부식 모니터링에 관한 연구: Part 1
This study represents the result of corrosion monitoring on reinforced concrete specimens by means of multi-functional corrosion monitoring sensors. To confirm the effectiveness of the sensors, eight different kinds of condition were adopted. Test factors were corrosion potential, current, corrosion rate, resistivity, and temperature, which were monitored with the sensors. Through this study, judging corrosion of steel in concrete with single corrosion factor such as corrosion potential was difficult, because many other factors can have an influence on the reaction of corrosion. By using three different kinds of sensors, it could enhance the accuracy of corrosion monitoring.
KEYWORDs : corrosion sensor, monitoring, reinforced concrete, corrosion potential
AUTHORs : 진충국․ 정진아†․ 경은진

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구리합금에 대한 WC-27NiCr 초고속화염용사 코팅층의 해수내 캐비테이션 특성 평가
Copper alloys are commonly applied to ship\\\'s propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates
surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test
was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of 30 μm with seawater temperature. The cavitation at 15 ℃ caused exfoliation of the coating layer in 17.5 hours while that of 25 ℃ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to 25 ℃ from 15 ℃, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.
KEYWORDs : copper alloy, high velocity oxygen fuel(HVOF), cavitation, WC-27NiCr coating, exfoliation
AUTHORs : 한민수․ 김민성․ 장석기․ 김성종†

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Rotating cylinder를 이용한 탄소강의 유동가속부식 평가
Flow accelerated corrosion (FAC) of the carbon steel piping in nuclear power plants (NPPs) has been major issue in nuclear industry. Rotating cylinder FAC test facility was designed and fabricated and then performance of the facility was evaluated. The facility is very simple in design and economic in fabrication and can be used
in material and chemistry screening test. The facility is equipped with on line monitoring of pH, conductivity, dissolved oxygen(DO), and temperature. Fluid velocity is controlled with rotating speed of the cylinder with a test specimen. FAC test of SA106 Gr. B carbon steel under 4 m/s flow velocity was performed with the rotating
cylinder at DO concentration of less than 1 ppb and of 1.3 ppm. Also a corrosion test of the carbon steel at static condition, that is at zero fluid velocity, of test specimen and solution was performed at pH from 8 to 10 for comparison with the FAC data. For corrosion test in static condition, the amount of non adherent corrosion product was almost constant at pH ranging from 8 to 10. But adherent corrosion product decreased with increasing pH. This trend is consistent with decrease of Fe solubility with an increase in pH. For FAC test with rotating cylinder FAC test facility, the amount of non adherent corrosion product was also almost same for both DO
concentrations. The rotating cylinder FAC test facility will be further improved by redesigning rotating cylinder and FAC specimen geometry for future work.
KEYWORDs : flow accelerated corrosion, rotating cylinder, carbon steel, nuclear power plant, dissolved oxygen
AUTHORs : 박태준․ 이은희․ 김경모․ 김홍표†

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조화 전류 측정에 의한 분극 저항 평가
Harmonic current was measured for a dummy cell with various values of resistance, and the procedure developed through the measurements was applied to the investigation of effects of the amplitude of applied frequency and applied potential on the harmonic current of a stainless steel and a carbon steel in chloride containing solutions. From the measurements of harmonic current in the dummy cell, the optimum values of applied frequency and applied potential in harmonic current measurements were found to be 1 mHz and 20 mV (or lower), respectively.
Increase in harmonic current with applied frequency was observed in the case where the level of harmonic current is low as in a stainless steel. Decrease in polarization resistance was also noted in this corrosion system with either increasing applied frequency or decreasing applied potential. However, no obvious effects of applied frequency was observed on harmonic current and polarization resistance in a carbon steel in which the level of harmonic current is high.
KEYWORDs : harmonic current, applied frequency, applied potential, polarization resistance
AUTHORs : 김종집†․ 유미영

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희생양극식 음극방식이 적용된 해안 교량 구조물의 방식거동
This measurement represents the effectiveness of sacrificial anode cathodic protection (SACP) system in a coastal bridge structure. To verify the cathodic protection (CP) effect, the monitoring sensor (DMS-100) that could measure
potential, corrosion rate, current, concrete resistivity, and temperature was embedded. The measurement conducted for three years after CP system was installed. Specifically, due to the fact that fresh water and sea water was
repeated in the bridge structure, this bridge structure presented special CP behavior. Measurement factors were CP potential, CP current, concrete resistivity, and depolarization potential. In addition, visual inspection was also carried out. As a result of current and depolarization measurement, CP system was well activated in most piers.
KEYWORDs : cahtodic protection, potential, concrete resistivity, SACP, depolarization
AUTHORs : 하지명․ 진충국․ 정진아†

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탄소강 볼트 체결된 GECM(Graphite Epoxy Composite Material)/Al 판재의 구성 부재의 부식 거동
This work focused on corrosion of carbon steel bolted GECM/Al parts in tap water and NaCl solutions. In tap water and NaCl solutions, open circuit potential of GECM and its potentials in a series of carbon steel bolt>Ti>Al became active. Regardless of test materials, open circuit potentials in tap water were noble, and increasing NaCl
concentration, its potentials became active. Immersion test of single specimen showed that no corrosion occur in Ti and GECM. In tap water, carbon steel bolt didn\\\'t show red corrosion product and in chloride solutions, corrosion rate in 1% NaCl solution was greater than its rate in 3.5% NaCl solution and red corrosion product in 1% NaCl solution was earlier observed than that in 3.5% NaCl solution. It seems that this behavior would be related to zinc-coatings on the surface of carbon stee l bolt. On the other hand, aluminium was corroded in tap water and chloride solutions. Corrosion of aluminium in tap water was due to the presence of chloride
ion in tap water by sterilizing process.
KEYWORDs : galvanic corrosion, carbon steel bolted GECM, Al, tap water, NaCl
AUTHORs : 김영식†․ 박수진․ 유영란

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ASME Code Case N-806을 활용한 매설배관 사용적합성 평가 고찰
Fitness-for-Service is a useful technology to determine replacement timing, next inspection timing or in-service when nuclear power plant\\\'s buried pipes are damaged. If is possible for buried pipes to be aged by material loss, cracks and occlusion as operating time goes by. Therefore Fitness-for-Service technology for buried pipe is useful for plant industry to perform replacement and repair. Fitness-for-Service for buried pipe is studied in terms of existing code and standard for Fitness-for-Service and a current developing code case. Fitness-for-Service for buried pipe was performed according to Code Case N-806 developed by ASME (American Society of Mechanical Engineers).
KEYWORDs : buried pipe, fitness for service, soil load, ASME code case N-806, inspection
AUTHORs : 박상규†․ 이요섭․ 소일수․ 임부택

Page : 218 - 224 DOWNLOAD
원전 탄소강 배관의 액적충돌침식 손상에 대한 B-Scan 검사 및 수치해석적 분석
Liquid droplet impingement erosion (LDIE) known to be generated in aircraft and turbine blades is recently appeared in nuclear piping. UT thickness measurements with both A-scan and B-scan UT inspection equipments were performed for a component estimated as susceptible to LDIE in feedwater heater vent system. The thickness data measured with B-Scan equipment were compared with those of A-Scan. Thermal hydraulic analysis based on ANSYS FLUENT code was performed to analyze the behavior of liquid droplets inside piping. The wall thinning rate and residual lifetime based on both existing Sanchez-Caldera equation and measuring data were also calculated to identify the applicability of the existing equation to the LDIE management of nuclear piping. Because Sanchez-Caldera equation do not consider the feature of magnetite formed inside piping, droplet size, colliding frequency, the development of new evaluation method urgently needs to manage the pipe wall thinning caused by LDIE.
KEYWORDs : liquid droplet impingement erosion, flow accelerated corrosion, UT inspection, thermal hydraulic
AUTHORs : 황경모†․ 이대영

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