• 한국주조공학회지
• /
• 제43권2호
• /
• pp.55-63
• /
• 2023

Due to the importance of the surface on the final slab quality, it is essential to maintain a smooth segment roll surface that is in touch with the thin solid shell during solidification. In this paper, the surface of the used continuous casting guide roll was analyzed to realize the mechanism of its surface deterioration. Surface analysis has revealed severe corrosion at two distinct areas leading to deep roughness occurring on the guide roll. Firstly, the severe corrosion follows prior austenite grain boundary due to exposure with acidic environment. Also, in heat affected zone (HAZ) where two cladding beads overlap, more severe corrosion takes place. The overheat input results in local ferritization without full melting which increases retained δ-ferrite content almost 10 times higher than surrounding area. Corrosion was observed to happen at the δ-γ interface where Cr depletion takes place.

• Computers and Concrete
• /
• 제34권4호
• /
• pp.503-517
• /
• 2024

This study presents an analysis model to estimate the shear strength of a reinforced concrete (RC) member with corroded tensile reinforcements. The thick-walled cylinder theory was modified to fit the dual potential capacity model to reflect interdependent failure mechanisms, including the degradation effect of bonds in corroded tensile reinforcement. In the proposed model, it is considered that the shear failure of corroded RC members with no proper anchorage detail is primarily dominated by the flexural-bond mechanism, where insufficient bond strength is provided owing to corrosion damage. However, when tensile reinforcements are properly anchored in the end regions using end hooks or mechanical devices, it is assumed that the tied-arch action can be developed as a secondary shear transfer mechanism, even under severe corrosion damage. The proposed model was verified by comparison with shear test results of corroded RC members collected from the literature, and it appeared that the proposed model can estimate their shear strengths with a good level of accuracy, regardless of various anchorage details and corrosion rates in tensile reinforcements.

• Corrosion Science and Technology
• /
• 제17권4호
• /
• pp.183-192
• /
• 2018

스테인리스강은 오스테니틱 스테인리스강, 페리틱 스테인리스강과 마르텐시틱 스테인리스강으로 대별할 수 있으며, 이 고도의 안전성이 요구되는 산업계에서 스테인리스강의 입계부식, 응력부식균열과 핏팅과 같은 국부적 부식이 발생하면 대형사고로 귀결될 수 있다. 스테인리스강의 입계부식 기구와 대책 그리고 입계부식측정 방법에 대한 기술 소개를 하여 산업현장에서 흔히 접하는 스테인리스강 예민화에 대한 길잡이가 되도록 하고, 이 분야를 전문적으로 연구하려는 연구자에게 예민화 전반을 이해하는데 활용되도록 하였다.

• Corrosion Science and Technology
• /
• 제7권4호
• /
• pp.201-207
• /
• 2008

$CO_2$ corrosion product scales formed on 13 Cr tubing steel in autoclave and in the simulated corrosion environment of oil field are investigated in the paper. The surface and cross-section profiles of the scales were observed by scanning electron microscopy (SEM), the chemical compositions of the scales were analyzed using energy dispersion analyzer of X-ray (EDAX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to confirm the corrosion mechanism of the 13 Cr steel in the simulated $CO_2$ corrosion environment. The results show that the corrosion scales are formed by the way of fashion corrosion, consist mainly of four elements, i.e. Fe, Cr, C and O, and with a double-layer structure, in which the surface layer is constituted of bulky and incompact crystals of $FeCO_3$, and the inner layer is composed of compact fine $FeCO_3$ crystals and amorphous $Cr(OH)_3$. Because of the characteristics of compactness and ionic permeating selectivity of the inner layer of the corrosion product scales, 13 Cr steel is more resistant in $CO_2$ corrosion environment.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
• /
• pp.213-217
• /
• 1996

The electrochemical methods of early detection and analysis of corrosion related deterioration in concrete reinforcement structures are very useful techniques. The generally using procedure for corrosion monitoring of reinforced structures employs a method of half-cell potential measurement. Whilst the technique has provided a useful means of delineating areas of high or low corrosion risk, there are difficulties in its use and interpretation, particularly when assessing corrosion rates of reinforcement. The aim of this study is to describe the AC-impedance method being employed to monitor and assess corrosion rates, to estimate corrosion mechanism of reinfrocement in laboratory conditions. The AC-impedance monitoring technique applies a small amplitude(20mV) AC signal to embedded steel in concrete and reference electrode (Cu/$CuSo_4$). We obtained over a wide frequency range(10MHz~1mHz) to produce a complex plane plot or Nyquist plot.

• Computers and Concrete
• /
• 제19권2호
• /
• pp.161-169
• /
• 2017

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete structures. The electrochemical impedance of reinforcing steel in diatomite- and zeolite-containing concrete exposed to sodium chloride was assessed. Chemical, physical and mineralogical properties of three concrete samples (20% diatomite, 20% zeolite, and a reference containing neither) were correlated with corrosion investigations. The steel-reinforced samples were exposed to 3.5% NaCl solution for 500 days, and measured every 15 days via EIS method. Results indicated that porosity and capillary spaces increase the diffusion rate of water and electrolytes throughout the concrete, making it more susceptible to cracking. Reinforcement in the reference concrete was the most corroded compare to the zeolite and the diatomite samples.

• Corrosion Science and Technology
• /
• 제3권2호
• /
• pp.47-53
• /
• 2004

The conditions to simulate the atmospheric corrosion behavior in the laboratory were investigated to clarify atmospheric corrosion mechanism of steel material in coastal area, For airborne sea salt and artificial seawater droplet, the various behaviors were observed by optical microscope, The particle size of the dried airborne sea salt was about $20{\mu}m$, and was about 1/10 compared with the artificial seawater droplet. Though the airborne sea salt represented the same behavior as the thermodynamic water absorption, the behavior of the artificial seawater droplet deviated from the results of the thermodynamic calculation, It is concluded that the water absorption behavior is influenced by the particle size of the dried sea salt. The corrosion behaviors of carbon steels were observed under the deposited condition of airborne sea salt and artificial seawater droplet. The corrosion behaviors showed a different trend, indicating that the corrosion behavior depended on the particle size of the dried sea salt. The corrosion in the actual environrnent progressed greater than that in the chamber. Furthermore, the summer showed the greater corrosion than the spring. It is found that the corrosion behaviors are attributed to the influence of the environmental factors.

• 콘크리트학회지
• /
• 제10권6호
• /
• pp.325-333
• /
• 1998

염화물에 의한 콘크리트 중의 철근부식을 억제하기 위하여 콘크리트 배합시 방청제를 사용하는 방안이 일반적으로 많이 사용되고 있으나. 국내에서는 아직까지 방청제의 방식효과에 대한 연구는 찾아보기 어려운 실정이다. 본 연구에서는 염화물의 영향을 받는 콘크리트 중의 철근부식 억제를 위한 방안으로 방청제를 사용하여 철근의 방청효과를 알아보기 위하여 3종류의 방청제와 각각 사용량을 변화시킨 시험체를 제작하여 부식촉진 실험을 실시하였으며, 철근의 자연전위와 부시면적율을 측정하여 방식효과에 대하여 평가하였다. 그 결과 염화물의 혼입량이 지나치게 많을 경우에는 방청제의 양을 증가시켜도 방청효과가 크게 향상되지 않았으나. 염화물의 혼입량을 동일하게 사용하고 방청제의 양을 증가시켜도 방청효과가 크게 향상되지 않았으나, 염화물의 혼입량을 동일하게 방청제의 양을 증가시킬 경우에는 방청효과가 현저하게 좋아짐을 알 수 있었다.

• Advances in environmental research
• /
• 제1권1호
• /
• pp.37-55
• /
• 2012

Here we show that perchlorate reduction during pitting corrosion of zero-valent titanium (ZVT) is likely caused by dissolved titanium species, especially Ti(II). Several possible mechanisms were suggested based on the literature and were evaluated based on experimental observations. Direct reduction of perchlorate on the bare metal of the ZVT electrode was thermodynamically infeasible due to the high anodic potential that was applied. Other potential mechanisms were considered such as reduction by small ZVT metal particles released from the electrode and direct reduction on the oxide layer of the electrode where potential was sufficiently reduced by a high ohmic potential drop. However, these mechanisms were not supported by experimental results. The most likely mechanism for perchlorate reduction was that during pitting corrosion, in which ZVT is partially oxidized to form dissolved ions such as Ti(II), which diffuse from the electrode surface and react with perchlorate in solution. This mechanism is supported by measurements of the dissolution valence and the molar ratio of ZVT consumed to perchlorate reduced (${\Delta}Ti(0)/{\Delta}ClO_4{^-}$). The results shown in this study demonstrate that ZVT undergoing pitting corrosion has the capability to chemically reduce perchlorate by producing dissolved Ti(II) and therefore, it has the potential to be applied in treatment systems. On the other hand, the results of this research imply that the application of ZVT undergoing pitting corrosion in treatment systems may not be feasible now due to several factors, including material and electricity costs and possible chloride oxidation.

• Corrosion Science and Technology
• /
• 제8권3호
• /
• pp.119-125
• /
• 2009

Corrosion assessment has a number of uses but the use considered here is as a precursor to Risk-Based Inspection (RBI) planning. Systematic methods consisting of technical modules of RBI program were used to assess the effect of specific corrosion mechanism on the probability of failure in equipments of petrochemical plants. Especially in part of the damage and corrosion assessment, screening step involved evaluating the combinations of process conditions and construction materials for each equipment item in order to determine which damage mechanisms are potentially active. For general internal corrosion, either API 510 or API 570 was applied as the damage rate in the calculation to determine the remaining life and inspection frequency. In some cases, a measured rate of corrosion may not be available. The technical modules of RBI program employ default values for corrosion, typically derived from published data or from experience with similar processes, for use until inspection results are available. This paper describes the case study of corrosion and damage assessment by using RBI methodology in petrochemical plant. Specifically, this paper reports the methodology and the results of its application to the petrochemical units using the $KGS-RBI^{TM}$ program, developed by the Korea Gas Safety Corporation to suit Korean situation in conformity with API 581 Codes.