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Page : 203 - 210
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- 슈퍼 오스테나이트계 스테인리스강의 시그마상 특성에 따른 부식거동 분석
- The corrosion behavior of super austenitic stainless steel was studied by examining the characteristics of
the sigma phase formed in the steel. A range of experimental and analytical methods was employed, including
potentiodynamic polarization tests, critical pitting temperature tests, transmission electron microscopy, and
energy-dispersive spectroscopy. Three steel samples with different sigma phase levels were obtained by
intentionally adjusting the manufacturing process. The results showed that the corrosion resistance of the
samples was strongly dependent upon the size and distribution of the sigma phase precipitated in the samples.
The larger the size of the sigma phase, the higher the Mo content in the sigma phase and the higher the
depletion level of Mo at the interface between the matrix/sigma phase, the more samples with a coarse-sized
sigma phase were susceptible to localized pitting corrosion at the interface. These results suggest that various
manufacturing processes, such as welding and the post-heat treatment of the steel, should be optimized so
that both the size and fraction of the sigma phase precipitated in the steel are small to improve the resistance
to localized corrosion. - KEYWORDs : Pitting corrosion, Sigma phase, Super austenitic stainless steel, Electrochemical corrosion, Molybdenum depletion
- AUTHORs : 김예은 ? 박진성 ? 조동민 ? 홍승갑 ? 김성진†
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Page : 211 - 223
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- 매설 배관 피복 결함 탐상 정확도에 미치는 인접 정류기 및 접지 구리망 간섭의 영향
- The external corrosion of buried piping can be controlled using both coating and cathodic protection. Several
factors are involved in the damage and deterioration of the coating on pipes. There are many detection
methods for coating defects on pipes and the direct current voltage gradient (DCVG) method is one of
the most powerful methods. However, the detection reliability of DCVG can be affected by interferences
such as stray current, metal objects connected to rectifiers, and copper grids. Therefore, this study focused
on the interference effects of rectifiers and a copper grid on the reliability of coating flaw detection. As
the length of the interference pipe connected to the rectifier increased, the reliability decreased. In contrast,
as the distance between the pipe and the copper grid increased, the reliability of the coating flaw detection
increased. The detection results produced by the DCVG method were discussed using current and potential
simulations for a pipe with a rectifier and copper grid interference in the soil. - KEYWORDs : Buried pipe, Coating flaw detection, Interference, Rectifier, Copper grid
- AUTHORs : 김민기 ? 임부택 ? 김기태 ? 장현영 ? 박흥배 ? 김영식†
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Page : 224 - 230
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- 해수분위기에서 스테인리스강 배관 소켓 용접부의 선택적 부식
- Stainless steel has excellent corrosion resistance. The drawback is that pitting occurs easily due to the concentration of chloride. In addition, corrosion of socket weld, which is structurally and chemically weaker than the other components of the pipe, occurs rapidly. Since these two phenomena overlap, pinhole leakage occurs
frequently in the seawater pipe socket welds made of stainless steel at the power plants. To analyze this specific corrosion, a metallurgical analysis of the stainless steel socket welds, where the actual corrosion occurred during the power plant operation, was performed. The micro-structure and chemical composition of each socket weld were analyzed. In addition, selective corrosion of the specific micro-structure in a mixed dendrite structure comprising γ-austenite (gamma-phase iron) and δ-ferrite (iron at high temperature) was investigated based on the characteristic micro-morphology and chemical composition of the corroded area. Finally, the different corrosion stages and characteristics of socket weld corrosion are summarized. - KEYWORDs : Selective corrosion, Stainless pipe, γ-austenite, δ-ferrite, Seawater
- AUTHORs : 부명환 ? 이장욱 ? 이종훈†
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Page : 231 - 231
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- Erratum to: 해수 환경에서 Al5083-H321 알루미늄 합금의 침식부식 손상에 미치는 유속의 영향과 손상 메카니즘
- Erratum to: CORROSION SCIENCE AND TECHNOLOGY, Vol. 19, No. 3(2020), pp. 115~121
DOI: 10.14773/cst.2020.19.3.115
In this study, erosion tests and erosion-corrosion tests of Al5083-H321 aluminum alloy were conducted at various flow rates in seawater. The erosion tests were conducted at a flow rate of 0 to 20 m/s, and erosion-corrosion tests were performed by potentiodynamic polarization method at the same flow rate. Characteristic evaluation after the erosion test was conducted by surface analysis. Characteristic evaluation after the erosion-corrosion test was performed by Tafel extrapolation and surface analysis. The results of the surface analysis after the erosion test showed that surface damage tended to increase as the flow rate increased. In particular, intermetallic particles were separated due to the breakdown of the oxide film at
10 m/s or more. In the erosion-corrosion test, the corrosion current density increased as the flow rate increased. Additionally, the surface analysis showed that surface damage occurred in a vortex shape and the width of the surface damage tended to increase as the flow rate increased. Moreover, damage at 0 m/s, proceeded in a depth direction due to the growth of pitting corrosion, and the damaged area tended to increase due to acceleration of the intermetallic particle loss by the fluid impact. - KEYWORDs : Aluminum alloy, Erosion corrosion, Flow rate, Potentiodynamic polarzation test, Seawater
- AUTHORs : 김영복 ? 김성종†
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Page : 231 - 238
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- Comparison of Quantitative Analysis of Radioactive Corrosion Products Using an EPMA and X-ray Image Mapping
- Radioactive corrosion product specimens were analyzed using an electron probe microanalyzer (EPMA) and X-ray image mapping. It is difficult to analyze the composition of radioactive corrosion products using an EPMA due to the size and rough shape of the surfaces. It is particularly challenging to analyze the composition of radioactive corrosion products in the form of piled up, small grains. However, useful results can be derived by applying a semi-quantitative analysis method using an EPMA with X-ray images. A standard-less, semi-quantitative method for wavelength dispersive spectrometry. EPMA analysis was developed with the objective of simplifying the analytical procedure required. In this study, we verified the reasonable theory of semi-quantitative analysis and observed the semi-quantitative results using a sample with a good surface condition. Based on the validated results, we analyzed highly rough-surface radioactive corrosion products and assessed their composition. Finally, the usefulness of the semi-quantitative analysis was reviewed by verifying the results of the analysis of radioactive corrosion products collected from spent nuclear fuel rods.
- KEYWORDs : Semi-quantitative, X-ray image mapping, Shielded EPMA, Radioactive corrosion products
- AUTHORs : Yang Hong Jung† and Yong Sun Choo
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Page : 239 - 249
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- 선박용 5052-O 알루미늄 합금의 해수 내 진폭 변수에 따른 캐비테이션-침식 손상 특성
- The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 μm, 10 μm, and 30 μm were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the
damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 μm and 30 μm was 1.48 and 2.21 times compared to 5 μm, respectively. - KEYWORDs : Al ship, 5052-O Al alloy, Cavitation-erosion, Amplitude, Seawater
- AUTHORs : 양예진 ? 김성종†
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Page : 250 - 258
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- 해수 내 다양한 알루미늄 선박용 재료의 캐비테이션 진폭에 따른 캐비테이션-침식 손상 연구
- Recently, 5000 series and 6000 series Al alloys have been used as hull materials for small and medium-sized ships because of their excellent weldability, corrosion resistance, and durability in marine environments. Al ships can navigate at high speed due to their light weight. However, cavitation-erosion problems cause reducing durability of Al ship at high speed. In this investigation, 5052-O, 5083-H321, and 6061-T6 Al alloy materials were used to evaluate the damage characteristics with amplitude (cavitation strength). As a result of the electrochemical experiments, the corrosion current density and corrosion potential of 6061-T6 in seawater were 8.52 × 10-7 A/cm2 and ?0.771 V, respectively, presenting the best corrosion resistance. The cavitation-erosion experiment showed that 5052-O had the lowest hardness value and cavitation-erosion resistance. 5052-O also had a very short incubation period. As the experiment progressed for 5052-O, pitting formed and grew in a short time, and was observed as severe cavitation-erosion damage that surface detached. Among the three specimens, 5083-H321 presented the highest hardness value and the damage rate was the smallest after the initiation of pitting.
- KEYWORDs : Hull materials, Cavitation-erosion, Amplitude, Seawater, Aluminum alloy
- AUTHORs : 양예진 ? 김성종†
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Page : 259 - 264
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- 양극산화된 5083-H321 합금의 천연해수 내 전기화학적 부식 및 응력부식균열 특성에 관한 연구
- Many studies have been conducted to improve the corrosion resistance and durability of various aluminum alloys through the anodizing technique. It is already used as a unique technique for enhancing the properties of aluminum alloys in various industries. This paper investigated the electrochemical corrosion and stress corrosion cracking characteristics of anodized aluminum 5083-H321 alloy in natural seawater. The corrosion characteristics were assessed by the electrochemical technique and potentiodynamic polarization test. The stress corrosion cracking characteristic was evaluated with a slow strain rate tensile test under 0.005 mm/min
rate, which showed that the hard anodizing film had a thickness of about 16.8 μm. Although no significant characteristics of stress corrosion cracking were observed in the slow strain rate test, the anodized specimen presented excellent corrosion resistance. The corrosion current density was measured to be approximately 4.2 times lower than that of the base material, and no surface damage was observed in the anodic polarization test. - KEYWORDs : 5083-H321, Corrosion, Stress corrosion cracking, Natural seawater, Slow strain rate test
- AUTHORs : 황현규 ? 신동호 ? 정광후 ? 김성종†
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Page : 265 - 280
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- 다전극 탐상을 통한 토중 매설배관 피복결함 탐상 정확도의 개선
- External corrosion of buried pipes can be controlled using both coating and cathodic protection. However, deterioration of the coating can occur due to several reasons. The detection reliabilty of coating flaw detection methods is affected by interference such as metal objects connected to rectifiers and copper grids. When performing parallel direct current voltage gradient (DCVG) inspection, a sine wave form without potential reversal in voltage gradient appears in the area where the interference exists. However, this area may be not identified using existing methods. The objective of this study was to determine the effect of analyzing direction on the reliability of coating flaw detection of pipes buried in soil using a multi-electrode detector. DCVG on the buried pipe was measured along the buried pipe. This measurement parallel to the pipe was repeated. Measured data were analyzed for parallel, vertical, and diagonal directions. The reliability of coating flaw detection was improved by up to 46.4% compared to the conventional method.
- KEYWORDs : Buried pipe, Coating flaw detection, Multi-electrode detector, Interference, Reliability
- AUTHORs : 김민기 ? 임부택 ? 김기태 ? 장현영 ? 박흥배 ? 김영식†
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Page : 281 - 287
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- Control of Galvanic Corrosion Between A516Gr.55 Steel and AA7075T6 Depending on NaCl Concentration and Solution Temperature
- Chloride ion is one of the most important corrosive agents in atmospheric corrosion, especially in marine environments. It has high adsorption rate and increases the conductivity of electrolytes. Since chloride ions affect the protective properties and the surface composition of the corrosion product, they increase the corrosion rate. A low level of chloride ions leads to uniform corrosion, whereas a high level of chloride ions may induce localized corrosion. However, higher solution temperatures tend to increase the corrosion rate by enhancing the migration of oxygen in the solution. This work focused on the effect of NaCl concentration and temperature on galvanic corrosion between A516Gr.55 carbon steel and AA7075T6 aluminum alloys. When AA7075T6 aluminum alloy was galvanically coupled to A516Gr.55 carbon steel, AA7075T6 was severely corroded regardless of NaCl concentration and solution temperature, unlike the corrosion properties of single specimen. The combined effect of surface treatment involving carbon steel and aluminum alloy on corrosion behavior was also discussed.
- KEYWORDs : Carbon steel, AA7075T6, Galvanic corrosion, NaCl concentration, Solution temperature
- AUTHORs : S. Y. Hur, J. M. Jeon, K. T. Kim, and Y. S. Kim†
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