-
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 : 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 : 171 - 181
DOWNLOAD
- 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 : 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
|
-
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 : 203 - 208
DOWNLOAD
- Study of Hot Salt Stress Corrosion Crack Initiation of Alloy IMI 834 by using DC Potential Drop Method
- DC potential drop technique was employed during the slow strain rate tests to study the hot salt stress corrosion crack (HSSCC) initiation at 300 and 400 °C. Threshold stresses for HSSCC initiation were found to about 88 % of the yield strength at both temperatures, but the time from crack initiation to final failure (Δtscc) decreased significantly with temperature, which reflects larger tendency for brittle fracture and secondary cracking. The brittle fracture features consisted of transgranular cracking through the primary α grain and discontinuous faceted cracking through the transformed β grains.
- KEYWORDs : titanium, stress corrosion cracking, hydrogen, fractography
- AUTHORs : Mangesh D. Pustode†, Bhupendra Dewangan, V. S. Raja, Neeta Paulose and Narendra Babu
|
-
Page : 209 - 216
DOWNLOAD
- Self-healing Anticorrosion Coatings for Gas Pipelines and Storage Tanks
- In the present study, chitosan based self-healing anticorrosion coatings were prepared by layer by layer (lbl) addition of chitosan (Ch) and polyvinyl butyral (PVB) on mild carbon steel substrate. Chitosan coatings exhibited enhanced coating stability and corrosion resistance in aggressive environments by the application
of a PVB top layer. Chitosan layer in the lbl coatings have been modified by using glutaraldehyde (Glu) and silica (SiO2). Performance of different coatings was tested using electrochemical impedance spectroscopy and immersion test. The best anticorrosion performance was observed in case of 10 % Ch_SiO2_PVB coatings,
which withstand immersion test over 25 days in 0.5 M salt solution without visible corrosion. 10 % Ch_SiO2 coatings without the PVB top layer didn’t last more than 3days. Application of PVB top layer sealed the defects in the chitosan pre-layer and improved its hydrophobic nature as well. Raman spectra and SEM of steel surfaces after corrosion study and removal of PVB_Ch/Glu_PVB coatings showed a passive layer of iron oxide, attributing to the self-healing nature of these coatings. Conducting particle like graphene reinforcement of chitosan in the lbl coatings enhanced corrosion resistance of chitosan coatings. - KEYWORDs : self-healing, chitosan, glutaraldehyde, silica, anticorrosion, layer by layer coatings
- AUTHORs : G. E. Luckachan and V. Mittal†
|
-
Page : 217 - 225
DOWNLOAD
- An Electrochemical Method to Predict Corrosion Rates in Soils
- Linear polarization resistance (LPR) testing of soils has been used extensively by a number of water utilities across Australia for many years now to determine the condition of buried ferrous water mains. The LPR test itself is a relatively simple, inexpensive test that serves as a substitute for actual exhumation and physical
inspection of buried water mains to determine corrosion losses. LPR testing results (and the corresponding pit depth estimates) in combination with proprietary pipe failure algorithms can provideauseful predictive tool in determiningthe current and future conditions of an asset1). Anumber of LPR tests have been developed
on soil by various researchers over the years1), but few have gained widespread commercial use, partly due to the difficulty in replicating the results.
This author developed an electrochemical cell that was suitable for LPR soil testing and utilized this cell to test a series of soil samples obtained through an extensive program of field exhumations. The objective of this testing was to examine the relationship between short-term electrochemical testing and long-term in-situ corrosion of buried water mains, utilizing an LPR test that could be robustly replicated. Forty-one soil samples and related corrosion data were obtained from ad hoc condition assessments of buried water mains located throughout the Hunter
region of New South Wales, Australia. Each sample was subjected to the electrochemical test developed by the author, and the resulting polarization data were compared with long-term pitting data obtained from each water main. The results of this testing program enabled the author to undertake a comprehensive review of the LPR technique as it is applied to soils and to examine whether correlations can be made between LPR testing results and long-term field
corrosion. - KEYWORDs : electrochemistry, corrosion, LPR, long-term prediction, cast iron
- AUTHORs : M. R Dafter†
|
-
Page : 226 - 236
DOWNLOAD
- Intergranular Corrosion Mechanism of Slightly-sensitized and UNSM-treated 316L Stainless Steel
- 316L stainless steels have been widely used in many engineering fields, because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering of carbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism of slightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at 650 ℃ in N2 gas atmosphere. Subsequently UNSM
treatments were carried out on the surface of the samples. The results were discussed on the basis of the sensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Even though chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel was drastically increased with aging time, and it was confirmed that the increased intergranular corrosion rate of slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation along the grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of aged
stainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinement of the outer surface, including the introduction of compressive residual stress. - KEYWORDs : 316L stainless steel, Intergranular corrosion, Sensitization, UNSM, Carbon segregation,
- AUTHORs : J. H. Lee, K. T. Kim, Y. S. Pyoun and Y. S. Kim†
|
-
Page : 237 - 244
DOWNLOAD
- 음극 인가전위 하에서 type 2205과 type 316L의 수소취성 저항성
- 2205 duplex stainless steels have been used for the construction of the marine environment, because of their excellent corrosion resistance and high strength. However, the resistance to hydrogen embrittlement (HE) may be less than that of 316L austenitic stainless steel. The reason why 316L stainless steels have
better resistance to HE is associated with crystal structure (FCC, face centered cubic) and the higher stacking faults energy than 2205 duplex stainless steels. Furthermore 2205 stainless steels with or without tungsten were also examined in terms of HE. 2205 stainless steels containing tungsten is less resistible to HE. It
is because dislocation tangle was formed in 2205 duplex stainless steels. Slow strain-rate tensile test (SSRT) was conducted to measure the resistance to HE under the cathodic applied potential. Hydrogen embrittlement index (HEI) was used to evaluate HE resistance through the quantitative calculation. - KEYWORDs : hydrogen embrittlement, 2205 duplex, 316L, SSRT, cathodic potential
- AUTHORs : 서동일·이재봉†
|
