한국부식방식학회

Page : 189 - 197 DOWNLOAD
알루미늄 합금 대기부식 예방을 위한 대한민국 공군 항공기 세척주기 최적화 연구
It is a common practice to conduct periodic washes at designated intervals in order to prevent the atmospheric corrosion of aircraft. The wash interval depends on the atmospheric conditions, but the wash intervals set by the U.S. Air Force were widely adopted in Korea without detailed knowledge of the background data. Therefore,
it is necessary to determine our own wash intervals representing the atmospheric and geographical conditions in Korea. This study analyzed previous wash interval algorithms and atmospheric data in Korea. New wash intervals are then proposed based on the corrosion rate equation in ISO-9223:2012. Atmospheric corrosion testing was conducted using 7075 and 1050 aluminum alloy specimens to verify the accuracy of the corrosion rate equation in ISO-9223:2012. Test results showed a reasonable agreement with the corrosion rates predicted by the equation.
KEYWORDs : atmospheric corrosion, aircrafts wash interval, aluminum alloy, ISO-9223, pitting
AUTHORs : 박원동 · 국필준 · 조윤호 · 반치범†

Page : 182 - 188 DOWNLOAD
Cause Analysis of Flow Accelerated Corrosion and Erosion-Corrosion Cases in Korea Nuclear Power Plants
Significant piping wall thinning caused by Flow-Accelerated Corrosion (FAC) and Erosion-Corrosion (EC) continues to occur, even after the Mihama Power Station unit 3 secondary pipe rupture in 2004, in which workers were seriously injured or died. Nuclear power plants in many countries have experienced FAC and EC-related cases in steam cycle piping systems. Korea has also experienced piping wall thinning cases including thinning in the downstream straight pipe of a check valve in a feedwater pump line, the downstream elbow of a control valve in a feedwater flow control line, and failure of the straight pipe downstream of an orifice in an auxiliary steam return line. Cause analyses were performed by reviewing thickness data using Ultrasonic Techniques (UT) and, Scanning Electron Microscope (SEM) images for the failed pipe, and numerical simulation results for FAC and EC cases in Korea Nuclear Power Plants. It was concluded that the main cause of wall thinning for the downstream pipe of a check valve is FAC caused by water vortex flow due to the internal flow shape of a check valve, the main cause of wall thinning for the downstream elbow of a control valve is FAC caused by a thickness difference with the upstream pipe, and the main cause of wall thinning for the downstream pipe of an orifice is FAC and EC caused by liquid droplets and vortex flow. In order to investigate more cases, additional analyses were performed with the review of a lot of thickness data for inspected pipes. The results showed that pipe wall thinning was also affected by the operating condition of upstream equipment. Management of FAC and EC based on these cases will focus on the downstream piping of abnormal or unusual operated equipment.
KEYWORDs : FAC, erosion-corrosion, pipe wall thinning, numerical simulation
AUTHORs : Y. S. Lee†, S. H. Lee, and K. M. Hwang

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Effect of Ethanolamines on Corrosion Inhibition of Ductile Cast Iron in Nitrite Containing Solutions
In this work, synergistic corrosion inhibition effect of nitrite and 3 kinds of ethanolamines on ductile cast iron using chemical and electrochemical methods was evaluated. This work attempts to clarify the synergistic effect of nitrite and ethanolamines. The effects of single addition of TEA, DEA, and MEA, and mixed
addition of nitrite plus TEA, DEA or MEA on the corrosion inhibition of ductile cast iron in a tap water were evaluated. A huge amount of single addition of ethanolamine was needed. However, the synergistic effect by mixed addition was observed regardless of the combination of nitrite and triethanolamines, but their effects increased in a series of MEA + nitrite > DEA + nitrite > TEA + nitrite. This tendency of
synergistic effect was attributed to the film properties and polar effect; TEA addition couldn’t form the film showing high film resistance and semiconductive properties, but DEA or MEA could build the film having relatively high film resistance and n-type semiconductive properties. Moreover, it can be explained that this behaviour was closely related to electron attractive group within the ethanolamines, and thus corrosion inhibition power depends upon the number of the electron attractive group of MEA, DEA, and TEA.
KEYWORDs : corrosion inhibitor, ductile cast iron, nitrite, ethanolamine, synergistic effect
AUTHORs : K. T. Kim, H. Y. Chang, B. T. Lim, H. B. Park, and Y. S. Kim†

Page : 166 - 170 DOWNLOAD
Improvement of Corrosion Resistance of Aluminum Alloy with Wettability Controlled Porous Oxide films
The combined process of porous type anodizing and desiccation treatment was applied to improve wettability of A1050 aluminum alloy. The water contact angles of anodized samples were increaseds considerably with desiccation treatment. However, there was no considerable effect of polishing and anodizing time on water contact angle. The corrosion behavior with the treatments was investigated electrochemically. The corrosion resistance of the samples in 3.5 mass% NaCl solutions increased with higher contact angle. Anodized and desiccated samples showed better corrosion resistance than un-desiccated samples around rest potential region.
KEYWORDs : aluminium, anodizing, wettability, desiccation
AUTHORs : M. Sakairi†, and V. Goyal

Page : 159 - 165 DOWNLOAD
Influence of Retrogression and Re-aging on the Exfoliation Corrosion Behavior of AA 7085 Sheets
An attempt has been made to understand the influence of retrogression and re-aging (RRA) on the exfoliation corrosion behaviour of AA 7085 alloy in comparison with the peak aged condition (PA). Immersion tests using ASTM G34 and studies involving electrochemical impedance spectroscopy showed that the RRA treated alloy provided higher resistance to exfoliation corrosion than the PA treated alloy. The improved resistance was attributed to the enhanced Cu content and the discontinuous nature of the grain boundary precipitate, which was revealed through transmission electron microscopy.
KEYWORDs : aluminium alloy, exfoliation corrosion, impedance spectroscopy
AUTHORs : Ajay Krishnan, V. S. Raja†, and A. K. Mukhopadhyay

Page : 153 - 158 DOWNLOAD
Precursor Events in Environmentally Assisted Cracking Behaviour of Light Metals
Light metal alloys of Mg, Ti, and Al undergo environmentally assisted cracking (EAC). Passive film breakdown and pitting are not only precursor events for stress corrosion, but can accelerate hydrogen evolution that is responsible for hydrogen embrittlement. This is clearly demonstrated in the case of Mg and Ti alloys. The so-called innocuous precipitates, which do not directly participate in either alloy strengthening or EAC
can be effective precursors for initiating EAC. This aspect is highlighted using high strength aluminium alloys. Such behaviours lead to a paradigm shift in the design of alloys with resistance to EAC.
KEYWORDs : environmentally assisted cracking, aluminium alloys, titanium alloys and magnesium alloys
AUTHORs : V. S. Raja†

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