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Page : 99 - 105
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- 모르타르(W/C:0.5)내의 철근의 부식 특성에 미치는 재령 년수와 피복두께의 영향
- The structures of reinforced concrete have been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as seawater, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, specimens having six different coating thickness (W/C:0.5) were prepared and immersed in flowing seawater for five years to evaluate the effect of coating thickness and immersion time on corrosion property. The polarization characteristics of these embedded steel bars were investigated using electrochemical methods such as corrosion potential, anodic polarization curve, and impedance. At the 20-day immersion, the corrosion potentials exhibited increasingly nobler values with coating thickness. However, after 5-yr. immersion their values were shifted in the negative direction, and the relationship between corrosion potential and coating thickness was not shown. Although 5-yr. immersion lowered corrosion potential, 5-yr. immersion did not increase corrosion rate. In addition, after 5-yr. immersion, the thinner cover thickness, corrosion current density was decreased with thinning coating thickness. It is due to the fact that ease incorporation of water, dissolved oxygen and chloride ion into a steel surface caused corrosion and hence, leaded to the formation of corrosion product. The corrosion product plays the role as a corrosion barrier and increases polarization resistance. The corrosion probability evaluated depending on corrosion potential may not be a good method for predicting corrosion probability. Hence, the parameters including cover thickness and passed aged years as well as corrosion potential is suggested to be considered for better assessment of corrosion probability of reinforced steel exposed to partially or fully in marine environment for long years.
- KEYWORDs : reinforced concrete, corrosion potential, anodic polarization, impedance, cover thickness, W/C
- AUTHORs : 문 경 만·이 성 열†·정 진 아·이 명 훈·백 태 실
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Page : 113 - 119
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- Effects of Hydrogen on the PWSCC Initiation Behaviours of Alloy 182 Weld in PWR Environments
- Alloy 82/182 weld metals had been extensively used in joining the components of the PWR primary system. Unfortunately, there have been a number of incidents of cracking caused by PWSCC in Alloy 82/182 welds during the operation of PWR worldwide. To mitigate PWSCC, optimization of water-chemistry conditions,
especially dissolved hydrogen (DH) and Zn contents, is considered as the most promising and effective remedial method. In this study, the PWSCC behaviours of Alloy 182 weld were investigated in simulated PWR environments with various DH content. Both in-situ and ex-situ oxide characterizations as well as PWSCC initiation tests were performed. The results showed that PWSCC crack initiation time was shortest in PWR water (DH: 30 cc/kg). Also, high stress reduced crack initiation time. Oxide layer showed multi-layered structures consisted of the outer needle-like Ni-rich oxide layer, Fe-rich crystalline oxide, and inner Cr-rich
inner oxide layers, which was not altered by the level of applied stress. To analyse the multi-layer structure of oxides, EIS measurement were fitted into an equivalent circuit model. Further analyses including TEM and EDS are underway to verify appropriateness of the equivalent circuit model. - KEYWORDs : PWSCC, oxide, in-situ EIS, initiation, alloy 182
- AUTHORs : H.-S. Kim, J.-D. Hong, J. Lee, O. S. Gokul, and C. Jang†
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Page : 120 - 126
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- Effects of Induction Heat Bending Process on Microstructure and Corrosion Properties of ASME SA312 Gr.TP304 Stainless Steel Pipes
- The usage of bending products recently have increased since many industries such as automobile, aerospace, shipbuilding, and chemical plants need the application of pipings. Bending process is one of the inevitable steps to fabricate the facilities. Induction heat bending is composed of compressive bending process by local heating and cooling. This work focused on the effect of induction heat bending process on the properties of ASME SA312 Gr. TP304 stainless steel pipes. Tests were performed for base metal and bended area including extrados, intrados, crown up, and down parts. Microstructure was analyzed using an optical microscope
and SEM. In order to determine intergranular corrosion resistance, Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) test and ASTM A262 practice A and C tests were done. Every specimen revealed non-metallic inclusion free under the criteria of 1.5i of the standard and the induction heat bending process
did not affect the non-metallic inclusion in the alloys. Also, all the bended specimens had finer grain size than ASTM grain size number 5 corresponding to the grain sizes of the base metal and thus the grain size of the pipe bended by induction heat bending process is acceptable. Hardness of transition start, bend,
and transition end areas of ASME SA312 TP304 stainless steel was a little higher than that of base metal. Intergranular corrosion behavior was determined by ASTM A262 practice A and C and DL-EPR test, and respectively step structure, corrosion rate under 0.3 mm/y, and Degree of Sensitization (DOS) of 0.001 ~ 0.075 %
were obtained. That is, the induction heat bending process didn’t affect the intergranular corrosion behavior of ASME SA312 TP304 stainless steel. - KEYWORDs : induction heat bending, 304 stainless steel, microstructure, intergranular corrosion
- AUTHORs : Nam In Kim, Young Sik Kim†, Kyung Soo Kim, Hyun Young Chang,Heung Bae Park, and Gi Ho Sung
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Page : 127 - 131
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- Effect of Si on Corrosion of Fe-Cr and Fe-Cr-Ni Alloys in wet CO₂Gas
- Model alloys Fe-9Cr, Fe-20Cr and Fe-20Cr-20Ni (wt. %) with 0.1 and 0.2 % Si were exposed to Ar-20CO₂-20H₂O gas at 818 oC. The undoped alloys formed a thick iron-rich oxide scale. The additions of Si reduced scaling rates of Fe-9Cr to some extent but significantly suppressed the formation of iron oxide scales on Fe-20Cr
and Fe-20Cr-20Ni. Carburisation also occurred in all undoped alloys, but not in Si-containing Fe-20Cr and Fe-20Cr-20Ni. Protection against carburisation was a result of the formation of an inner scale layer of silica. - KEYWORDs : steel, silicon, high temperature corrosion
- AUTHORs : T. D. Nguyen, J. Zhang, and D. J. Young†
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Page : 132 - 139
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- 분말야금법과 주조법으로 제조한 자동차 터보차져강의 고온산화
- Turbocharger steels were manufactured by the powder metallurgical and casting method. They consisted primarily of a large amount of γ-Fe, a small amount of α-Fe, and fine Nb6C5 precipitates. The casting method was better than the powder metallurgical method, because a sound matrix with little oxides were obtained. When turbocharger steels were oxidized at 900 ℃ for 50 h, Mn₂VO₂and (Mn,Si)-oxides were formed along grain boundaries, while Mn2O3 and CrMn₂O₂ were formed intragranularly. Fe, Nb, and Ni were depleted in the oxide scale.
- KEYWORDs : turbocharger, oxidation, powder metallurgy, casting
- AUTHORs : 박순용·이동복†
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Page : 140 - 147
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- 캐비테이션 특성에 미치는 알루미늄 합금의 양극 산화 용액 온도의 영향
- The commercialization of aluminum had been delayed than other metals because of its high oxygen affinity. Anodizing is a process in which oxide film is formed on the surface of a valve metal in an electrolyte solution by anodic oxidation reaction. Aluminum has thin oxide film on surface but the oxide film is inhomogeneous having a thickness only in the range of several nanometers. Anodizing process increases
the thickness of the oxide film significantly. In this study, porous type oxide film was produced on the surface of aluminum in sulfuric acid as a function of electrolyte temperature, and the optimum condition were determined for anodizing film to exhibit excellent cavitation resistance in seawater environment. The result revealed that the oxide film formed at 10 ℃ represented the highest cavitation resistance, while
the oxide film formed at 15 ℃ showed the lowest resistance to cavitation in spite of its high hardness. - KEYWORDs : aluminum, anodizing, oxide film, cavitation, seawater
- AUTHORs : 이승준·이정형, 김성종†
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Page : 147 - 152
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- 부식전위 기준에 의한 철근콘크리트 구조물의 부식진단의 위험성에 관한 고찰
- Corrosion of steel reinforcement is a major factor in the deterioration of harbour and bridge structure. Steel corrosion in concrete must be checked for assessing the condition of a reinforced concrete structure. There are several ways how to measure the corrosion condition of reinforced concrete, but the corrosion potential
measurement is a very simple, rapid, cost-effective and non-destructive technique to evaluate the severity of corrosion in reinforced concrete structure, therefore commonly used by engineers. However some particular situations may not relate to the reinforcement corrosion probability and a simple comparison of the corrosion
potential data with the ASTM C876 Standard on steel reinforcement corrosion probability could be meaningless and not give reliable informations because of environment factors as oxygen concentration, chloride content, concrete resistance. Therefore this paper explains the risk of corrosion assessment in reinforced concrete
structure and how many factors can affect the reliability of the corrosion potential data. - KEYWORDs : steel reinforcement, corrosion potential, oxygen, chloride, concrete resistance
- AUTHORs : 정진아†
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Page : 161 - 165
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- Stress Analysis in Polymeric Coating Layer Deposited on Rigid Substrate
- This paper presents an analysis of thermal stress induced along the interface between a polymeric coating layer and a steel substrate as a result of uniform temperature change. The epoxy layer is assumed to be a linear viscoelastic material and to be theromorheologically simple. The viscoelastic boundary element method is employed to investigate the behavior of interface stresses. The numerical results exhibit relaxation of interface stresses and large stress gradients, which are observed in the vicinity of the free surface. Since the exceedingly large stresses cannot be borne by the polymeric coating layer, local cracking or delamination
can occur at the interface corner. - KEYWORDs : thermal stress, coating layer, polymeric layer, interface stress
- AUTHORs : Sang Soon Lee†
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Page : 166 - 171
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- Influence of Citric Acid on the Metal Release of Stainless Steels
- Knowledge of how metal releases from the stainless steels used in food processing applications and cooking utensils is essential within the framework of human health risk assessment. A new European standard test protocol for testing metal release in food contact materials made from metals and alloys has recently been published by the Council of Europe. The major difference from earlier test protocols is the use of citric acid as the worst-case food simulant. The objectives of this study were to assess the effect of citric acid at acidic, neutral, and alkaline solution pH on the extent of metal release for stainless steel grades AISI 304 and 316, commonly used as food contact materials. Both grades released lower amounts of metals than the specific release limits when they were tested according to test guidelines. The released amounts of metals were assessed by means of graphite furnace atomic absorption spectroscopy, and changes in the outermost surface composition were determined using X-ray photoelectron spectroscopy. The results demonstrate that both the pH and the complexation capacity of the solutions affected the extent of metal release from stainless steel and are discussed from a mechanistic perspective. The outermost surface oxide was significantly enriched in chromium upon exposure to citric acid, indicating rapid passivation by the acid. This study
elucidates the effect of several possible mechanisms, including complex ion- and ligand-induced metal release, that govern the process of metal release from stainless steel under passive conditions in solutions that contain citric acid. - KEYWORDs : metal release, stainless steel, citric acid, food, surface oxide
- AUTHORs : N. Mazinanian†, I. Odnevall Wallinder, and Y. S. Hedberg
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Page : 172 - 176
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- Corrosion Fatigue of Austenitic Stainless Steel in Different Hot Chloride Solutions
- Austenitic stainless steel was investigated under cyclic loading in electrolytes with different chloride contents and pH and at different temperatures. The testing solutions were 13.2 % NaCl (80,000 ppm Cl-) at 80 °C and 43 % CaCl2 (275,000 ppm Cl-) at 120 °C. In addition to S?N curves in inert and corrosive media, the fracture surfaces were investigated with a scanning electron microscope (SEM) to analyse the type of attack. The experimental results showed that a sharp decrease in corrosion fatigue properties can be correlated with the occurrence of stress corrosion cracking. The correlation of occurring types of damage in different
corrosion systems is described. - KEYWORDs : corrosion fatigue cracking, stress corrosion cracking, austenitic stainless steel, pitting, chloride
- AUTHORs : A. Visser†, G. Mori, M. Panzenb?ck, and R. Pippan
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