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Page : 288 - 295
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- 선박용 AA5083-H321의 유속에 의한 침식손상 방지를 위한 최적 음극방식전위 규명
- This study investigated the erosion-corrosion characteristics of 5038-H321 aluminum alloy in a natural seawater solution through various electrochemical experiments and flow rate parameters. Cathodic polarization experiments were conducted at flow rates ranging from 4 to 12 knots. Considering the concentration polarization section representing a relatively low current density, the range of the potentiostatic experiment was determined to be -1.6 to -1.0 V. The potentiostatic experiment was conducted at various potentials for 180 minutes in seawater. After the experiment, the corrosion characteristics were evaluated by observing surface morphology and measuring surface roughness. As a result, as the applied potential was lower, the amount of calcareous deposits increased and the roughness tended to increase. On the other hand, it was confirmed that the roughness was larger in the static condition than the flow rate condition due to the influence of the flow velocity. Variations in the chemical composition with flow rate variations were analyzed by energy-dispersive spectroscopy (EDS). In conclusion, the cathodic potential of AA5083-H321 in seawater was determined to be -1.0 V.
- KEYWORDs : Erosion-corrosion, Aluminium alloy, Seawater, Flow rate
- AUTHORs : 정상옥 ? 박일초 ? 김성종†
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Page : 296 - 301
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- 지역난방 냉각수 배관의 용접부 파손 분석
- Failure analysis on the welded type 304 pipe used for cooling water piping in the district heating primary side was conducted. Inorganic elements and bacteria in the cooling water and in corrosion products were analyzed, and the weldment was inspected by microscopy and a sensitization test. Corrosion damages were observed in the heat-affected zone, on weld defects such as incomplete fusion or excessive penetration caused by improper welding, or/and at the 6 o\\\'clock position along the pipe axial direction. However, the level of concentration of chloride in the cooling water as low as 80 ppm has been reported to be not enough for even a sensitized type 304 steel, meaning that the additional corrosive factor was required for these corrosion damages. The factor leading to these corrosion damages was drawn to be the metabolisms of the types of bacteria, which is proved by the detection of proton, sulfur containing species, biofilms, and both bacteria and corrosion product analyses.
- KEYWORDs : HAZ, Sensitization, District heating, Bacteria, Cooling water pipeline
- AUTHORs : 정준철 ? 김우철 ? 김경민 ? 손홍균 ? 김정구 ? 이수열 ? 김희산†
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Page : 302 - 309
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- 다중선형회귀법을 활용한 예민화와 환경변수에 따른 AL-6XN강의 공식특성 예측
- This study aimed to predict the pitting corrosion characteristics of AL-6XN super-austenitic steel using multiple linear regression. The variables used in the model are degree of sensitization, temperature, and pH. Experiments were designed and cyclic polarization curve tests were conducted accordingly. The data obtained from the cyclic polarization curve tests were used as training data for the multiple linear regression model. The significance of each factor in the response (critical pitting potential, repassivation potential) was analyzed. The multiple linear regression model was validated using experimental conditions that were not included in the training data. As a result, the degree of sensitization showed a greater effect than the other variables. Multiple linear regression showed poor performance for prediction of repassivation potential. On the other hand, the model showed a considerable degree of predictive performance for critical pitting potential. The coefficient of determination (R2) was 0.7745. The possibility for pitting potential prediction was confirmed using multiple linear regression.
- KEYWORDs : AL-6XN, Corrosion characteristics, Sensitization, Environmental variable, Multiple linear regression
- AUTHORs : 정광후 ? 김성종†
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Page : 310 - 317
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- 경질양극산화된 5083-H321 알루미늄 합금의 해수 내 액적충격침식부식 손상 연구
- This study investigated the damage to the specimen due to liquid droplet impingement erosion corrosion, which improved the corrosion resistance and durability via hard anodization of 5083-H321 aluminum alloy, which is widely used for small ships and marine structures. The experiment combined liquid droplet impingement erosion and electrochemical equipment with the flow rates in natural seawater solution. Subsequently, Tafel extrapolation of polarization curves was performed to evaluate damage due to the liquid droplet impingement erosion corrosion. The damaged surface was observed using a 3D microscope and a scanning electron microscope. The degree of pitting damage was measured using the Image J program, and the surface hardness was measured using the micro-Vickers hardness tester. The corrosion current density, area, depth, and ratio of the damaged areas increased with the increase in flow rate. The grain size of the damaged area at a flow rate of 20 m s-1 showed fewer and minor differences in height, and a smooth curved shape. The hardness of the damaged surface tended to decrease with increase in flow rate.
- KEYWORDs : Sea water, 5083-H321 Al alloy, Marine structures, Flow rate, Liquid droplet impingement erosion corrosion
- AUTHORs : 신동호 ? 김성종†
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Page : 318 - 325
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- Al 6061-T6 합금의 해수 내 캐비테이션 진폭에 따른 캐비테이션-침식 조건하에서 전기화학적 특성
- Generally, Al alloys of 5000 and 6000 series show excellent weldability, workability, and specific strength, and are widely used in ship building. A combined experiment via cavitation erosion and corrosion damage involving 6061-T6 Al alloy was performed using potentiodynamic polarization under cavitation erosion (hybrid experiments) with amplitude (cavitation strength). The corrosion current density was approximately 52-fold higher at 30 μm than under static conditions, suggesting that the amplitude greatly affected the damage. The degree of damage increased with increasing cavitation amplitude. After the hybrid experiment, the corrosion rate was compared according to the weight loss and damage depth, and the relationship between the two values was expressed as alpha value. The alpha (α) values at amplitudes of 5 μm, 10 μm and 30 μm were 5.11, 12.81 and 8.74, respectively, suggesting that the α value at 10 μm was greater than at 5 μm, and indicating local corrosion damage. However, the α value at 30 μm was smaller than that of 10 μm, which is attributed to higher damage via uniform corrosion than damage induced by local corrosion.
- KEYWORDs : 6061-T6, Cavitation-erosion, Electrochemical damage, Amplitude, Hybrid experiment
- AUTHORs : 황현규 ? 김성종†
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Page : 326 - 336
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- 36개월간 국내 옥외폭로시험에 따른 갈바륨 강판의 대기부식거동 및 표면외관 변화
- Galvalume steel (GL) is widely used in marine and industrial environments. It is characterized by better corrosion resistance than carbon steel. However, corrosion and economic losses may occur as the usage time is increased. Therefore, in this study, an outdoor exposure test of GL for 36 months was conducted across six regions of Korea. Parameters such as corrosion rate, chrominance (color, chroma, and brightness), glossiness, and surface appearance were analyzed. The results showed no significant change in appearance, and the initial corrosion rate was large, but a tendency to decrease with time was observed. Increased outdoor exposure time led to increase in the level of corrosion products. In the case of coastal areas where S, Cl, and other elements were detected, a relatively high decrease in Zn content was observed. Al forms a protective oxide film and exists in the coating layer, but Zn dissolves due to its chemical activity and low potential.
- KEYWORDs : Galvanized steel, Outdoor exposure test, Galvalume steel, Atmospheric corrosion
- AUTHORs : 김기태 ? 유영란 ? 김영식†
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Page : 1 - 6
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- Cause Analysis for a Lining Damage in Sea Water System Piping Installed in a Korean Industrial Plant
- Many Korean industrial plants including nuclear and fossil power plants use seawater as the ultimate heat sink to cool the heat generated by various facilities. Owing to the high corrosivity of seawater, facilities and piping made of metal material in contact with seawater are coated or lined with polymeric materials to avoid direct contact with seawater. However, polymeric materials used as coating and lining have some level of permeability to water and are degraded over time. Korean industrial plants have also experienced a gradual increase in the frequency of damage to pipes in seawater systems due to prolonged operating periods. In the event of a cavitation-like phenomenon, coating or lining inside the piping is likely to be damaged faster than expected. In this paper, the cause of water leakage due to base metal damage caused by the failure of the polyester lining in seawater system piping was assessed and the experience with establishing countermeasures to prevent such damage was described.
- KEYWORDs : Lining, Coating, Seawater piping, Cavitation, Computational fluid dynamics
- AUTHORs : K. M. Hwang† and S. K. Park
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Page : 7 - 14
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- Anti-Corrosion Performance and Applications of PosMAC? Steel
- PosMAC? is a brand of Zn-Mg-Al hot-dip coated steel sheet developed by POSCO. PosMAC? can form dense surface oxides in corrosive environments, providing advanced corrosion resistance compared to traditional Zn coatings such as GI and GA. PosMAC? 3.0 is available for construction and solar energy systems in severe outdoor environments. PosMAC?1.5 has better surface quality. It is suitable for automotive and home appliances. Compared to GI and GA, PosMAC? shows significantly less weight reduction due to corrosion, even with a lower coating thickness. Thin coating of PosMAC? provides advanced quality and productivity in arc welding applications due to its less generation of Zn fume and spatters. In repeated friction tests, PosMAC? showed lower surface friction coefficient than conventional coatings such as GA, GI, and lubricant film coated GA. Industrial demand for PosMAC? steel is expected to increase in the near future due to benefits of anti-corrosion and robust application performance of PosMAC? steel.
- KEYWORDs : Anti-corrosion, Zn-Mg-Al alloy coating, PosMAC?1.5, PosMAC?3.0
- AUTHORs : Il-Ryoung Sohn†, Tae-Chul Kim, Gwang-Il Ju, Myung-Soo Kim, and Jong-Sang Kim
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Page : 15 - 21
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- Using Coffee-Derived Hard Carbon as a Cost-Effective and Eco-Friendly Anode Material for Li-Ion Batteries
- Through a simple filtration process, followed by carbonization within a reductive environment, coffee waste grounds can be transformed into a non-porous hard carbon for use in multiple contexts. This resulting coffee-waste carbon has been evaluated as an eco-friendly and cost-effective replacement for conventional graphite. When compared with different types of carbon, our study found that the coffee-waste carbon fell into the category of hard carbon, as verified from the galvanostatic charge/discharge profiles. The coffee-waste carbon showed a superior rate capability when compared to that of graphite, while compromising smaller capacity at low C rates. During electrochemical reactions, it was also found that the coffee-waste carbon is well exposed to electrolytes, and its disordered characteristic is advantageous for ionic transport which leads to the low tortuosity of Li ions. Finally, the high irreversible capacity (low initial Coulombic efficiency) of the coffee-waste carbon, which if also often observed in amorphous carbon, can be adequately resolved through a solution-based prelithiation process, thereby proving that the coffee-waste carbon material is quite suitable for commercial use as an anode material for quickly-chargeable electrodes.
- KEYWORDs : Coffee waste, Hard carbon, High-rate anodes, Li-ion batteries
- AUTHORs : Sung Joo Hong, Seong Su Kim, and Seunghoon Nam†
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Page : 22 - 25
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- Factors Affecting Stress Corrosion Cracking Susceptibility of Alloy 600 MA Steam Generator Tubes
- In the past, Alloy 600 nickel-based alloys have been widely used in steam generators. However, most of them have been replaced by thermally treated alloy 690 tubes in recent years because mill annealed alloy 600 materials are known to be susceptible to stress corrosion cracking. Unlike this general perception, some
steam generators using mill annealed alloy 600 tubes show excellent performance even though they are designed, manufactured, and operated in the same way. Therefore, various analyses were carried out to determine causes for the degradation of steam generators. Based on the general stress corrosion cracking
mechanism, tube material susceptibility, residual stress, and sludge deposits of steam generators were compared to identify factors affecting stress corrosion cracking. It was found that mill annealed alloy 600 steam generator tubes showed higher resistance to stress corrosion cracking when the amount of sludge deposits on tube surface was smaller and residual stress generated during the fabrication was lower. - KEYWORDs : Stress corrosion cracking, Alloy 600 mill annealed tubes, Residual stress, Sludge deposits,Steam generator
- AUTHORs : Kang Yong Seok†, Lee Kuk Hee, and Shin Dong Man
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