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Page : 292 - 300
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- 3D 유한요소법을 이용한 원전 매설배관 부식결함 탐상기술 개발
- The modeling of 3D finite elements based on CAD data has been used to detect sites of corrosion defects in buried pipes. The results generated sophisticated profiles of electrolytic potential and vectors of current distributions on the earth surface. To identify the location of defects in buried pipes, the current distribution on the earth surface was projected to a plane of incidence that was identical to the pipe locations. The locations of minimum electrolytic potential value were found. The results show adequate match between the locations of real and expected defects based on modeling. In addition, the defect size can be calculated by integrating the current density curve. The results show that the defect sizes were 0.74 m2 and 0.69 m2, respectively. This technology may represent a breakthrough in the detection of indirect damage in various cases involving multiple defects in size and shape,
complex/cross pipe systems, multiple anodes and stray current. - KEYWORDs : Nuclear Power Plant, Buried Pipe, Indirect Inspection, FEM, Corrosion
- AUTHORs : 김재원·임부택·박흥배·장현영†
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Page : 301 - 309
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- 36개월간 국내 옥외폭로시험에 따른 아연도강의 표면외관 변화
- If galvanized steel is exposed to an outdoor environment, atmospheric corrosion will occur with time and red rust will form when the sacrificial protection capacity of zinc reaches its limit. With corrosion, the surface appearance of steel changes, and the properties of the exterior materials degrade. In this study, two kinds of galvanized steel, (GA and GI specimens) were subjected to an outdoor exposure test for 36
months in six regions of Korea. Chrominance (color, chroma, and brightness) and glossiness surface analyses were performed. The color change was not significant, regardless of the exposed area or the specimens tested. With increasing exposure times, the GA specimen became blackened by the formation of zinc oxide, and red coloration was increased by the formation of red rust. As the exposure time of GI specimen increased, the surface proceeded to blacken, but no red rust was formed and the color did not change significantly. Regardless of the outdoor exposure area or the specimen, longer exposure times led to lower glossiness, and this behavior appears to be influenced by the formation of zinc oxide. - KEYWORDs : Galvanized steel, Outdoor exposure test, Atmospheric corrosion, Chrominance, Glossiness
- AUTHORs : 김기태·김영식†
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Page : 310 - 316
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- 적층가공 방식으로 제조된 CP-Ti의 캐비테이션 중 부식에 대한 전기화학적 접근
- The effect of passive film on corrosion of metals and alloys in a static corrosive environment has been studied by many researchers and is well known, however few studies have been conducted on the electrochemical measurement of metals and alloys during cavitation corrosion conditions, and there are no test standards for electrochemical measurements ‘During cavitation’ conditions. This study used
commercially additive manufactured(AM) pure titanium in tests of anodic polarization, corrosion potential measurements, AC impedance measurements, and repassivation. Tests were performed in 3.5% NaCl solution under three conditions, ‘No cavitation’, ‘After cavitation’, and ‘During cavitation’ condition. When cavitation corrosion occurred, the passive current density was greatly in creased, the corrosion potential largely lowered, and the passive film revealed a small polarization resistance. The current fluctuation by the passivation and repassivation phenomena was measured first, and this behavior was repeatedly generated at a very high speed. The electrochemical corrosion mechanism that occurred
during cavitation corrosion was based on result of the electrochemical properties ‘No cavitation’, ‘After cavitation’, and ‘During cavitation’ conditions. - KEYWORDs : Additive manufactured CP-Ti, Cavitation corrosion, Electrochemical mechanism
- AUTHORs : 김기태·장현영·김영식†
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Page : 317 - 323
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- CHECWORKS와 ToSPACE 프로그램의 배관감육 해석결과 비교
- Assumptions have always been that wall thinning on the secondary side piping in nuclear power plants
is mostly caused by Flow-Accelerated Corrosion (FAC). Recent studies have showed that wall thinning
on the secondary side piping is caused by Liquid Droplet Impingement Erosion (LDIE), Solid Particle
Erosion (SPE), cavitation, and flashing. To manage those aging mechanisms, several software such
as CHECWORKS, COMSY, and BRT-CICERO have been used in nuclear power plants. Korean nuclear
power plants have been using the CHECWORKS program since 1996 to date. However, many site
engineers have experienced a lot of inconveniences and problems in using the CHECWORKS program.
In order to work through the inconveniences and to remedy problems, KEPCO-E&C has developed
a “3D-based pipe wall thinning management program (ToSPACE)” based on the experience of over
30 years in relation to the pipe wall thinning management. This study compares the results of FAC
and LDIE analysis using both the CHECWORKS and ToSPACE programs with respect to validation
of the wall thinning analysis results. - KEYWORDs : Pipe wall thinning, Flow-accelerated Corrosion, Liquid droplet impingement erosion, CHECWORKS, ToSPACE
- AUTHORs : 황경모†·윤훈·서혁기
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Page : 1 - 7
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- Effects of Surface Machining by a Lathe on Microstructure of Near Surface Layer and Corrosion Behavior of SA182 Grade 304 Stainless Steel in Simulated Primary Water
- To find proper lathe machining parameters for SA182 Grade 304 stainless steel (SS), six kinds of samples with different machining surface states were prepared using a lathe. Surface morphologies and microstructures of near surface deformed layers on different samples were analysed. Surface morphologies and chemical composition of oxide films formed on different samples in simulated primary water with 100 μg/L O2 at
310 °C were characterized. Results showed that surface roughness was mainly affected by lathe feed. Surface machining caused grain refinement at the top layer. A severely deformed layer with different thicknesses formed on all samples. In addition to high defect density caused by surface deformation, phase transformation, residual stress, and strain also affected the oxidation behaviour of SA182 Grade 304 SS in the test solution. Machining parameters used for # 4 (feed, 0.15 mm/r; back ngagement, 2 mm; cutting speed, 114.86 m/min) and # 6 (feed,0.20 mm/r; back engagement, 1 mm; cutting speed, 73.01 m/min) samples were found to be proper for lathe machining of SA182 Grade 304 SS. - KEYWORDs : Surface machining, Cold-working, Microstructure, SS, Oxidation
- AUTHORs : Zhiming Zhang, Jianqiu Wang†, En-hou Han, and Wei Ke
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Page : 8 - 15
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- High Temperature Oxidation Behavior of Nickel and Iron Based Superallo in Helium Containing Trace Impurities
- A high-temperature gas-cooled reactor (HTGR) is recognized as the best candidate reactor for next generation nuclear reactors. Helium is used to be the coolant in the core of the HTGR with temperature expected to exceed 900 °C at the core outlet. Several iron- and nickel-based superalloys, including Alloy 800H, Hastelloy X, and Alloy 617, are potential structural materials for intermediate heat exchanger (IHX) in
an HTGR. Oxidation behaviors of three selected alloys (Hastelloy X, Alloy 800H, and Alloy 617) were investigated at four different temperatures from 650°C to 950 °C under helium environments with various concentrations of O2 and H2O. Preliminary results showed that chromium oxide as the primary protective layer was observed on surfaces of the three tested alloys. Based on results of mass gain and SEM analyses, Hastelloy X alloy exhibited the best corrosion resistance in all corrosion tests. Further details on the oxidation mechanism of these alloys are presented in this study. - KEYWORDs : HTGR, Superalloys, Oxidation, Corrosion, Helium gas
- AUTHORs : C. J. Tsai, T. K. Yeh, and M. Y. Wang†
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Page : 16 - 23
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- Excellent Seam Weldable Nano-Composite Coated Zn-Ni Plating Steels for Automotive Fuel Tank
- Steels for automotive fuel tank require unique properties such as corrosion resistance for fuel, welding for joining, forming for press, and painting for exterior. Recently, automakers have been requiring excellent seam weldable steels to enhance manufacturing productivity of fuel tank. Thus, POSCO developed a new
type of functional steels coated with nano-composite thin layer on Zn-Ni plating steels. The nano-composite coating solution was prepared by mechanical fine dispersion of solutions consisting of polymeric resin and nano-composite materials in aqueous media. The composite solution was coated on the plating steel surface
by using roll coater and cured through induction furnace. These new developed plating steels were evaluated for quality performances such as seam and spot weldability, press formability, and corrosion resistance. These new functional steels coated with nano-composite layer exhibited excellent seam weldability and press formability. Detailed discussion of coating solution and experimental results suggest that nano-sized composite dispersion as coating layer plays a key role in enhancing the quality performance. - KEYWORDs : Automotive fuel tank, Zn-Ni Plating steels, Corrosion resistance, Seam weld, Press forming
- AUTHORs : Du-Hwan Jo†, Sang-Man Yun, Kee-Cheol Park, Myung-Soo Kim, and Jong-Sang Kim
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Page : 24 - 32
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- 아연 코팅과 열처리에 따른 알루미늄 열교환기 소재의 부식
- The effects of zinc coating and heat treatment on the corrosion resistance of aluminum alloys including A1100 and the modified A3003, used as heat exchanger tube were investigated in this study. The grain size of the heat-treated specimen is larger than that of the specimen without heat treatment, but the grain size did not significantly affect the corrosion behavior. The concentration of zinc was noted at 11.3 ~ 31.4 at.% for the as-received Zn-coated samples and reduced to 1.2 ~ 2.4 at.% after the heat treatment, as measured by the scanning electron microscopy (SEM) with an energy dispersive spectrometer (EDS) on the surface. The concentration of oxygen is 22 ~ 46 at.% for the zinc coated specimens while noted at 7.4 ~ 12.8 at.% for the specimens after the removal of the coating. The corrosion behavior depended largely on the concentrations of zinc, aluminum, and oxygen on the specimen surface, but not on the Mo content. The corrosion potential was high and the corrosion rate was low for a specimen with a low zinc content, a high aluminum content, and a high oxygen content.
- KEYWORDs : Corrosion, Heat exchanger, Heat treatment, Zinc coating, Aluminum
- AUTHORs : 조수연·김재중·장희진†
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Page : 33 - 38
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- 니켈 합금 모재 및 용접재의 일차수응력부식균열 균열성장속도 시험
- Alloy 600/182 with excellent mechanical/chemical properties have been utilized for nuclear power plants. Although both alloys are known to have superior corrosion resistance, stress corrosion cracking failure has been an issue in primary water environment of nuclear power plants. Therefore, primary water stress corrosion
crack (PWSCC) growth rate tests were conducted to investigate crack growth properties of Alloy 600/182. To investigate PWSCC growth rate, test facilities including water chemistry loop, autoclave, and loading system were constructed. In PWSCC crack growth rate tests, half compact-tension specimens were manufactured. These specimens were then placed inside of the autoclave connected to the loop to provide primary water environment. Tested conditions were set at temperature of 360℃ and pressure of 20MPa. Real time crack growth rates of specimens inside the autoclave were measured by Direct Current potential drop (DCPD) method. To confirm inter-granular (IG) crack as a characteristic of PWSCC, fracture surfaces of tested specimens were observed by SEM. Finally, crack growth rate was derived in a specific stress intensity factor (K) range and similarity with overseas database was identified. - KEYWORDs : Primary water stress corrosion cracking, Crack growth rate, Inter-granular crack, Ni-base alloy, Nuclear power plants
- AUTHORs : 이종훈†
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Page : 39 - 48
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- Pitting Corrosion Inhibition of Sprinkler Copper Tubes via Forming of Cu-BTA Film on the Inner Surface of Corrosion pits
- The feasibility of using benzotriazole (BTAH) to inhibit pitting corrosion in the sprinkler copper tubes was investigated by filling the tubes with BTAH-water solution in 829 households at an eight-year-old apartment complex. The water leakage rate was reduced by approximately 90% following BTAH treatment during 161 days from the previous year. The leakage of one of the two sprinkler copper tubes was investigated with optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis to determine the formation of Cu-BTA film inside the corrosion pits. All the inner components of the corrosion pits were coated with Cu-BTA films suggesting that BTAH molecules penetrated the corrosion products. The Cu-BTA film was about 2 nm in thickness at the bottom of a corrosion pit. A layer of CuCl and Cu2O phases lies under the Cu-BTA film. This complex structure effectively prevented the propagation of corrosion pits in the sprinkler copper tubes and reduced the water
leakage. - KEYWORDs : Copper, Pitting corrosion inhibition, Benzotriazole, EDS, XPS
- AUTHORs : Sang Hee Suh†, Youngjoon Suh, Sohee Kim, Jun-Mo Yang, and Gyungtae Kim
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