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Page : 177 - 183
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- Effect of RuCl3 Concentration on the Lifespan of Insoluble Anode for Cathodic Protection on PCCP
- Prestressed Concrete steel Cylinder Pipe (PCCP) is extensively used as seawater pipes for cooling in nuclear power plants. The internal surface of PCCP is exposed to seawater, while the external surface is in direct contact with underground soil. Therefore, materials and strategies that would reduce the corrosion of its cylindrical steel body and external steel wiring need to be employed. To prevent against the failure of PCCP, operators provided a cathodic protection to the pre-stressing wires. The efficiency of cathodic protection is governed by the anodic performance of the system. A mixed metal oxide (MMO) electrode was developed to meet criteria of low over potential and high corrosion resistance. Increasing coating cycles improved
the performance of the anode, but cycling should be minimized due to high materials cost. In this work, the effects of RuCl3 concentration on the electrochemical properties and lifespan of MMO anode were evaluated. With increasing concentration of RuCl3, the oxygen evolution potential lowered and polarization resistance were also reduced but demonstrated an increase in passive current density and oxygen evolution current density. To improve the electrochemical properties of the MMO anode, RuCl3 concentration was increased. As a result, the number of required coating cycles were reduced substantially and the MMO anode achieved an excellent lifespan of over 80 years. Thus, we concluded that the relationship between RuCl3 concentration and coating cycles can be summarized as follows: No. of coating cycle = 0.48*[RuCl3 concentration, M]-0.97. - KEYWORDs : cathodic protection, insoluble anode, MMO (Mixed Metal Oxide), lifespan, ruthenium chloride, PCCP (Prestressed Concrete steel Cylinder Pipe)
- AUTHORs : H. W. Cho, H. Y. Chang, B. T. Lim2, H. B. Park, and Y. S. Kim†
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Page : 184 - 189
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- Corrosion and Repassivation Behavior of Stainless steels in Chloride and Thiosulfate Containing Environments
- In this study, the combined effect of chloride and thiosulfate ions and the effect of the ratio of the two ions on passivation in 304L, 316L, and the duplex stainless steels 2101 and 2205 are investigated using potentiostatic scratch tests. Cyclic polarization and the scratch tests were used to understand the role of anions on localized corrosion in these systems. It was found that the thiosulfate pitting began at a lower potential for 2101 than 304L in 0.6 M NaCl + 0.03 M Na2S2O3 solution. The pit morphologies for 304L, 316L, and 2101 in an 0.6 M NaCl + 0.03 M Na2S2O3 solution were very different from each other. The results indicate that the pitting switches from predominately thiosulfate pitting to chloride pitting at approximately
0.1 V. - KEYWORDs : stainless steel, chloride, thiosulfate, pitting, repassivation, pit morphology
- AUTHORs : Y. S. Wang† and P. M. Singh
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Page : 190 - 194
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- Corrosion Behaviour of DH36 Steel Used for Oil Platform in Splash Zones
- The splash zone is the most corrosive area of the marine environment, and the corrosion of steel structures exposed in this area is a serious concern. DH36 steel is one of most commonly used steels for offshore oil platforms in China, and its corrosion behaviour in splash zones was studied in this paper. Polarization curves were obtained from the corroded steel exposed in this area while the morphologies and rusts of the rust steel were characterized using scanning electron microscopy and X-ray diffraction. Double rust layers were formed in the splash zone. The inner layer contained magnetite and fine flaky lepidocrocite, and the outer layer was composed of accumulated flaky lepidocrocite and a small amount of goethite. In
the wet period, the iron dissolved and reacted with lepidocrocite, and magnetite appeared, while the magnetite was oxidized to lepidocrocite again during the dry period. Electrochemical reduction and chemical oxidization cycled in intermittent wetting and drying periods, and magnetite and lepidocrocite were involved in the
reduction reaction, leading to serious corrosion. - KEYWORDs : steel, corrosion, rust, splash zone
- AUTHORs : J. G. Liu†, Y. T. Li, and B. R. Hou
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Page : 195 - 199
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- Corrosion of Titanium Alloys in High Temperature Seawater
- Materials of choice for offshore structures and the marine industry have been increasingly favoring materials that offer high strength-to-weight ratios. One of the most promising families of light-weight materials is titanium alloys, but these do have two potential Achilles’ heels: (i) the passive film may not form or may be unstable in low oxygen environments, leading to rapid corrosion; and (ii) titanium is a strong hydride former, making it vulnerable to hydrogen embrittlement (cracking) at high temperatures in low oxygen environments. Unfortunately, such environments exist at deep sea well-heads; temperatures can exceed 120 °C, and oxygen levels can drop below 1 ppm. The present study demonstrates the results of investigations into the corrosion behavior of a range of titanium alloys, including newly developed alloys containing rare earth additions for refined microstructure and added strength, in artificial seawater over the temperature range of 25 °C to 200 °C. Tests include potentiodynamic polarization, crevice corrosion, and U-bend stress corrosion cracking.
- KEYWORDs : titanium, seawater, adhesive, high temperature, corrosion
- AUTHORs : J. J Pang and D. J. Blackwood†
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Page : 207 - 212
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- Preparation and Characterization of Coating Solution Based on Waterborne Polyurethane Dispersion containing Fluorine for Primer on Electro Galvanized Steel Sheet
- The purpose of this research was to synthesize fluorine modified waterborne polyurethane dispersion (F-WPU) by soap-free (internal emulsifier) emulsion polymerization techniques, to prepare coating solution based on fluorine modified waterborne polyurethane dispersion (F-WPU) and to compare the chemical and
thermo-mechanical properties on the electrogalvanized steel sheet. Environmentally friendly F-WPU was prepared with a fluorinated polyol containing 60 wt% of fluorine. There are various ways of combining a wide variety of fluorinated polyols and diisocyanate to exhibit novel properties of waterborne polyurethane dispersion. Components of coating solution were largely divided into 4 kinds i.e., F-WPU, acrylic emulsion, silane coupling agent, and colloidal silicate. F-WPU coating solution on the electro-galvanized steel sheet showed excellent properties of corrosion resistance, alkali resistance and heat resistance, as compared to other coating solutions using a general waterborne resin. The F-WPU coating solution’s reliable effects are possibly due to the fluorine atoms incorporated even in a small amount of F-WPU. - KEYWORDs : waterborne polyurethane, fluorine, steel, corrosion resistance
- AUTHORs : Chung Keun Jin and Sung Hyung Lim†
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Page : 213 - 217
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- Improved Corrosion and Abrasion Resistance of Organic-Inorganic Composite Coated Electro-galvanized Steels for Digital TV Panels
- Recently, household electronic industries require environmentally-friendly and highly functional steels in order to enhance the quality of human life. Customers especially require both excellent corrosion and abrasion resistant anti-fingerprint steels for digital TV panels. Thus POSCO has developed new functional electro-galvanized steels, which have double coated layers with organic-inorganic composites on the zinc surface of the steel for usage as the bottom chassis panel of TVs. The inorganic solution for the bottom layer consists of inorganic phosphate, magnesium, and zirconium compounds with a small amount of epoxy binder, and affords both improved adhesion properties by chemical conversion reactions and corrosion resistance due to a self-healing effect. The composite solution for the top layer was prepared by fine dispersion of organic-inorganic ingredients that consist of a urethane modified polyacrylate polymer, hardener, silica sol and a titanium complex inhibitor in aqueous media. Both composite solutions were coated on the steel
surface by using a roll coater and then cured through an induction furnace in the electro-galvanizing line. New anti-fingerprint steel was evaluated for quality performance through such procedures as the salt spray test for corrosion resistance, tribological test for abrasion resistance, and conductivity test for surface electric conductance regarding to both types of polymer resin and coating weight of composite solution. New composite coated anti-fingerprint steels afford both better corrosion resistance and abrasion properties compared to conventional anti-fingerprint steel that mainly consists of acrylate polymers. Detailed discussions of both composite solutions and experimental results suggest that urethane modifications of acrylate polymers of composite solutions play a key role in enhanced quality performances. - KEYWORDs : composite coating, corrosion resistance, abrasion resistance, anti-fingerprint steels, electro-galvanizing steels
- AUTHORs : Du-Hwan Jo1,†, Sang-Geol Noh, Jong-Tae Park, and Choon-Ho Kang
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Page : 218 - 225
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- Effect of Hydrodynamic Condition on the Electrochemical Behavior of Various Metals in 3.5 wt% NaCl Solution
- The electrochemical behaviors of various metals with and without diamond-like-carbon (DLC) coating in 3.5 wt% NaCl solution were investigated. The effect of hydrodynamic conditions was focused by employing a rotating disc electrode (RDE). The experimental results showed that each bare metal had a more positive corrosion potential and a higher corrosion rate due to enhanced oxygen transport at the higher rotating speed of the RDE. DLC coating caused a substantial increase in the corrosion resistance of all metals studied. However, localized corrosion was still found in the DLC-coated metal at sites where deposition defects existed. Surface morphology examination was performed after the electrochemical test to confirm the roles of hydrodynamic conditions and DLC coating.
- KEYWORDs : diamond-like-carbon (DLC), hydrodynamic, rotating disc electrode (RDE), electrochemical behavior
- AUTHORs : Szu-Jung Pan, Samuel-Sudibyo Hadinata, Ruey-Chy Kao, and Wen-Ta Tsai†
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Page : 226 - 311
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- 해양 금속재료의 부식속도와 방식전류에 미치는 유속의 영향
- In spite of highly advanced paint coating techniques, corrosion damage of marine metal and alloys increase more and more due to inherent micro-cracks and porosities in coatings formed during the coating process. Furthermore, flowing seawater conditions promote the breakdown of the protective oxide of the materials
introducing more oxygen into marine environments, leading to the acceleration of corrosion. Various corrosion protection methods are available to prevent steel from marine corrosion. Cathodic protection is one of the useful corrosion protection methods by which the potential of the corroded metal is intentionally lowered
to an immune state having the advantage of providing additional protection barriers to steel exposed to aqueous corrosion or soil corrosion, in addition to the coating. In the present investigation, the effect of flow velocity was examined for the determination of the optimum corrosion protection current density in cathodic protection as well as the corrosion rate of the steel. It is demonstrated from the result that the material corrosion under dynamic flowing conditions seems more prone to corrosion than under static conditions. - KEYWORDs : marine structure material, cathodic protection, flow velocity, corrosion rate
- AUTHORs : 이 승 준·한 민 수·장 석 기· 김 성 종†
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Page : 232 - 238
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- 해수 온도에 따른 S355ML 강재의 부식 경향 평가
- Corrosion is of greatest concern for metallic materials exposed to corrosive seawater or aggressive marine atmospheres. Marine structures and components made of metallic materials incur an initial cost and additional large costs for corrosion control and maintenance. There have been worldwide efforts to minimize marine corrosion and extend service life of the materials. It is believed that various factors are associated with corrosion of marine grade metallic materials, particularly the temperature of the solution affecting the corrosion rate by changing dissolved oxygen solubility and concentrations of chloride. In the present study, the electrochemical characteristics of S355ML steel are investigated to identify corrosion acceleration tendencies with changes in solution temperature under marine
environments. It was found that increasing seawater temperature, promoted not only activation of chloride ion transfer, but also the formation of porous Fe(OH)3 or Fe2O3, leading to the acceleration of corrosion. - KEYWORDs : marine structure, corrosion, seawater temperature, S355ML steel
- AUTHORs : 장 석 기1·이 승 준2·박 재 철3·김 성 종1,†
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Page : 239 - 246
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- 해양 환경 하에서 16.7Cr-10Ni-2Mo 스테인리스강의 표면 손상에 미치는 캐비테이션의 영향
- Stainless steel is generally known to have characteristics of excellent corrosion resistance and durability, but in a marine environment it can suffer from localized corrosion due to the breakdown of passivity film due to chloride ion in seawater. Furthermore, the damage behaviors are sped up under a cavitation environment
because of complex damage from electrochemical corrosion and cavitation-erosion. In this study the characteristics of electrochemical corrosion and cavitation erosion behavior were evaluated on 16.7Cr-10Ni-2Mo stainless steel under a cavitation environment in natural seawater. The electrochemical experiments have been conducted at both static conditions and dynamic conditions inducing cavitation with different current density parameters. The surface morphology and damage behaviors were compared after the experiment. After the cavitation test with time variables morphological examinations on damaged specimens were analyzed by using a scanning electron microscope and a 3D microscope. the galvanostatic experiment gave a cleaner surface morphology presented with less damage depth at high current density regions. It is due to the effect of water cavitation peening under the cavitation condition. In the cavitation experiment, with amplitude of 30 ㎛ and seawater temperature of 25 ℃, weight loss and cavitation-erosion damage depth were dramatically increased after 5 hours inducing cavitation. - KEYWORDs : stainless steel, cavitation, corrosion, galvanostatic experiment, seawater
- AUTHORs : 정 상 옥·한 민 수·김 성 종†
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