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Page : 26 - 36
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- Ultrasonic Cavitation Behavior and its Degradation Mechanism of Epoxy Coatings in 3.5 % NaCl at 15 oC
- Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component,as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 oC using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile
strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings. - KEYWORDs : Ultrasonic Cavitation test, Amplitude, Epoxy coating, 3.5% NaCl
- AUTHORs : I. J. Jang, J. M. Jeon, K. T. Kim, Y. R. Yoo, and Y. S. Kim†
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Page : 37 - 43
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- 적층가공 (3D 프린팅) Ti-6Al-4V합금의 국부부식 저항성 평가를 위한 임계국부부식온도와 임계국부부식전위 측정방법의 비교
- Additively manufactured (AM) Ti-6Al-4V alloys exhibit a dominant acicular martensite phase (α\\\'), which is characterized by an unstable energy state and highly localized corrosion susceptibility. Electrochemical critical localized corrosion temperature (E-CLCT, ISO 22910: 2020) and electrochemical critical localized corrosion potential (E-CLCP, ISO AWI 4631: 2021) were measured to analyze the localized corrosion resistance of the AM Ti-6Al-4V alloy. Although E-CLCP was measured under mild corrosive conditions such as human body, the validity of evaluating localized corrosion resistance of AM titanium alloys was demonstrated by comparison with E-CLCT. However, the mechanisms of resistance to localized corrosion on the as-received and heat-treated AM Ti-6Al-4V alloys under E-CLCT and E-CLCP differ at various temperatures because of differences in properties under localized corrosion and repassivation. The E-CLCT is mainly measured for initiation of localized corrosion on the AM titanium alloys based on temperature, whereas the E-CLCP yields repassivation potential of re-generated passive films of AM titanium alloys after breaking down.
- KEYWORDs : Ti-6Al-4V, Additive manufacturing, E-CLCT, E-CLCP, Repassivation
- AUTHORs : 서동일 ? 이재봉†
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Page : 45 - 51
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- An Investigation of Pulse Anodization Duty Ratio and Sealing Treatment on the Corrosion Behavior of the Anodic Coating Layer in Magnesium AZ31B
- In this work, we describe the effect of pulse anodizing duty ratio on the corrosion resistance of anodic films in magnesium AZ31B. The process involves the application of square pulse potential for a constant period with a duty ratio varying from 40, 60 and 80%. In several samples, a sealing treatment for 30 min utes was conducted after anodization in order to seal the pores available in the anodic layer. After anod izing, the surface morphology of the anodic layer was examined using a scanning electron microscope (SEM Hitachi SU3500). The corrosion characteristics of the sample were evaluated through an open cir cuit potential (OCP) and potentiodynamic polarization test using potentiogalvanostat. SEM observation
shows that the increase of anodization duty ratio (α) results in a more uniform anodic layer, with fewer pores and cracks. The increase of duty ratio (α) decreases the OCP value from approximately -1.475 to about -1.6 Volt, and significantly improves the corrosion resistance of the anodic coating by 68%. The combination of anodization and sealing treatment produces an anodic coating with a very low corrosion rate of 4.4 mpy. - KEYWORDs : Anodization, Corrosion, Magnesium AZ31B, Sealing, Coating
- AUTHORs : Asep Ridwan Setiawan† and Muhammad Dani Rachman
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Page : 52 - 61
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- An Investigation on Application of Experimental Design and Linear Regression Technique to Predict Pitting Potential of Stainless Steel
- This study using experimental design and linear regression technique was implemented in order to predict the pitting potential of stainless steel in marine environments, with the target materials being AL-6XN and STS 316L. The various variables (inputs) which affect stainless steel’s pitting potential included the pit ting resistance equivalent number (PRNE), temperature, pH, Cl- concentration, sulfate levels, and nitrate levels. Among them, significant factors affecting pitting potential were chosen through an experimental design method (screening design, full factor design, analysis of variance). The potentiodynamic polariza tion test was performed based on the experimental design, including significant factor levels. From these
testing methods, a total 32 polarization curves were obtained, which were used as training data for the lin ear regression model. As a result of the model’s validation, it showed an acceptable prediction perfor mance, which was statistically significant within the 95% confidence level. The linear regression model based on the full factorial design and ANOVA also showed a high confidence level in the prediction of pit ting potential. This study confirmed the possibility to predict the pitting potential of stainless steel accord ing to various variables used with experimental linear regression design. - KEYWORDs : Experimental design, Linear regression, Stainless steel, Pitting potential
- AUTHORs : Kwang-Hu Jung and Seong-Jong Kim†
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Page : 62 - 68
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- An Experimental Investigation of the Application of Artificial Neural Network Techniques to Predict the Cyclic Polarization Curves of AL-6XN Alloy
- Artificial neural network techniques show an excellent ability to predict the data (output) for various com plex characteristics (input). It is primarily specialized to solve nonlinear relationship problems. This study is an experimental investigation that applies artificial neural network techniques and an experimental design to predict the cyclic polarization curves of the super-austenitic stainless steel AL-6XN alloy with sensitization. A cyclic polarization test was conducted in a 3.5% NaCl solution based on an experimental design matrix with various factors (degree of sensitization, temperature, pH) and their levels, and a total of 36 cyclic polarization data were acquired. The 36 cyclic polarization patterns were used as training data for the artificial neural network model. As a result, the supervised learning algorithms with back-propagation showed high learning and prediction performances. The model showed an excellent training performance (R2=0.998) and a considerable prediction performance (R2=0.812) for the conditions that were not included in the training data.
- KEYWORDs : Artificial neural network, AL-6XN, Cyclic polarization curve, Sensitization, Environmental variable
- AUTHORs : Kwang-Hu Jung and Seong-Jong Kim
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Page : 69 - 76
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- 배열회수보일러 복수예열기 부식 파손 분석
- In this work, we have performed a corrosion failure analysis of a leaking tube connected to an upper
header of a condensate pre-heater in a heat recovery steam generator. It was revealed that the leakage posi tion in the tube was the location where the materials were easily vulnerable due to tensile residual stresses
induced by the material manufacturing process and welding process. In addition to an imbalance in the
module induced by temperature difference during operation of the pre-heater, the weight of the modules
and thermal fatigue provoked a type of stress of tensile-tensile fatigue on the tube. Thus, the leakage posi tion of the pre-heater was exposed to the tensile stress on the inner surface of the tube facing the gas,
which rendered the unstable oxide layer susceptible to corrosion and the formation of pits on the water
side. The cracks propagated along with the degraded microstructure in a transgranular cracking mode
under fatigue loading and finally resulted in water leakage. - KEYWORDs : Heat Recovery Steam Generator, Condensate Pre-Heater, Corrosion, Fatigue
- AUTHORs : 채호병 · 김우철 · 김희산 · 김정구 · 김경민 · 이수열†
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Page : 77 - 84
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- 다구찌 설계를 이용한 듀플렉스 스테인리스강 S31083용 DL-EPR 시험용액의 최적화
- This study aims to optimize the DL-EPR test solution for duplex stainless steel S31083 using the Taguchi design. The test solution parameters applied to the Taguchi design are H2SO4, NaCl, KSCN concentration, and temperature. In the experimental design, an orthogonal array of 4 levels 4 factor L16(44) was used. Output values for the orthog onal array were used for resolution (degree of sensitization) and selective etch (Ia) values. The optimal test solution conditions were selected by comparing the normalized S/N ratio for the two reaction properties. As a result, the H2SO4 and NaCl were identified as the main factors influencing the sensitivity measurement, but the delta statistics showed that the KSCN concentration and temperature had relatively low influence. The optimal condition was iden tified as 1.5 M H2SO4+0.03 M KSCN+1.5M NaCl at 30 oC. The degree of sensitization presented a tendency to depend on the heat treatment temperature and time in the optimal test solution. This investigation confirmed the pos sibility of optimizing the experiment solution for the DL-EPR test of stainless steel using the Taguchi technique.
- KEYWORDs : Taguchi design, Duplex stainless steel, DL-EPR test, Test solution optimization
- AUTHORs : 정광후 · 김성종†
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Page : 85 - 93
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- 스테인리스강과 양극산화된 알루미늄 합금의 전기화학적 부식특성에 미치는 해수온도의 영향
- The corrosion damage of materials in marine environment mainly occurs by Cl-
ions due to the breakdown of passive films. Additionally, various characteristics in seawater such as salinity, temperature, immersion time, flow rate, and biological activity also affect corrosion characteristics. In this study, the corrosion characteristics of stainless steels (STS 304 and STS 316L) and anodized aluminum alloys (AA 3003 and AA 6063) were evaluated with seawater temperature parameters. A potentiodynamic polarization experi ment was conducted in a potential range of -0.25 V to 2.0 V at open circuit potential (OCP). Corrosion cur rent density and corrosion potential were obtained through the Tafel extrapolation method to analyze changes in corrosion rate due to temperature. Corrosion behavior was evaluated by measuring weight loss before/after the experiment and also observing surface morphology through a scanning electronic microscope (SEM) and 3D microscopy. Weight loss, maximum damage depth and pitting damage increased as seawater temperature increased, and furthermore, the tendency of higher corrosion current density with an increase of temperature attributed to an increase in corrosion rate. There was lower pitting damage and lower corrosion current density for anodized alu minum alloys than for stainless steels as the temperature increased. - KEYWORDs : Corrosion, Seawater, Stainless steel, Aluminum alloy, Temperature
- AUTHORs : 정상옥 · 김성종†
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Page : 94 - 104
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- 항공기 주기환경이 대기부식위험도에 미치는 영향
- Atmospheric corrosion severity associated with aircraft parking environment was studied using metallic
specimens, and temperature and humidity sensors installed at each aircraft operating base. Data were ana lyzed after a year of exposure. Silver was used to measure chloride deposition by integrating X-ray pho toelectron spectroscopy depth profiles. Carbon steel was utilized to determine the corrosion rate by measuring
the weight loss. The time of wetness was determined using temperature and humidity sensor data. Analysis of
variance followed by Tukey’s “honestly significant difference” test indicated that atmospheric environment
inside the shelter varied significantly from that of unsheltered parking environment. The corrosion rate of
unsheltered area also varies with the roof. Hierarchical clustering analysis of the measured data was used to clas sify air bases into groups with similar atmospheric corrosion. Bases where aircraft park at a shelter can be
grouped together regardless of geographical location. Unsheltered bases located inland can also be grouped
together with sheltered bases as long as the aircraft are parked under the roof. Environmental severity index was
estimated using collected data and validated using the measured corrosion rate. - KEYWORDs : Environmental severity index, Atmospheric corrosion, Outdoor exposure test
- AUTHORs : 윤주희 · 이두열† · 박승렬 · 김민생 · 최동수
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Page : 105 - 111
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- Three-dimensional Computational Modeling and Simulation of Intergranular Corrosion Propagation of Stainless Steel
- In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.
- KEYWORDs : Intergranular corrosion, Stainless steel, Corrosion shape, Computer simulation, Cellular automata method
- AUTHORs : T. Igarashi†, A. Komatsu, T. Motooka, F. Ueno, and M. Yamamoto
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