• Corrosion Science and Technology
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• 제19권3호
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• pp.115-121
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• 2020

In this study, erosion tests and erosion-corrosion tests of Al5083-H321 aluminum alloy were conducted at various flow rates in seawater. The erosion tests were conducted at a flow rate of 0 to 20 m/s, and erosion-corrosion tests were performed by potentiodynamic polarization method at the same flow rate. Characteristic evaluation after the erosion test was conducted by surface analysis. Characteristic evaluation after the erosion-corrosion test was performed by Tafel extrapolation and surface analysis. The results of the surface analysis after the erosion test showed that surface damage tended to increase as the flow rate increased. In particular, intermetallic particles were separated due to the breakdown of the oxide film at 10 m/s or more. In the erosion-corrosion test, the corrosion current density increased as the flow rate increased. Additionally, the surface analysis showed that surface damage occurred in a vortex shape and the width of the surface damage tended to increase as the flow rate increased. Moreover, damage at 0 m/s, proceeded in a depth direction due to the growth of pitting corrosion, and the damaged area tended to increase due to acceleration of the intermetallic particle loss by the fluid impact.

• Steel and Composite Structures
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• 제30권2호
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• pp.171-183
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• 2019

As China's infrastructure continues to grow, concrete filled steel tubular (CFST) structures are attracting increasing interest for use in engineering applications in earthquake prone regions owing to their high section modulus, high strength, and good seismic performance. However, in a corrosive environment, the seismic resistance of the CFST columns may be affected to a certain extent. This study attempts to investigate the mechanical behaviours of square CFST members under both a cyclic load and an acid rain attack. First, the tensile mechanical properties of steel plates with various corrosion rates were tested. Second, a total of 12 columns with different corrosion rates were subjected to a reversed cyclic load and tested. Third, comparisons between the test results and the predicted ultimate strength by using four existing codes were carried out. It was found that the corrosion leads to an evident decrease in yield strength, elastic modulus, and tensile strain capacity of steel plates, and also to a noticeable deterioration in the ultimate strength, ductility, and energy dissipation of the CFST members. A larger axial force ratio leads to a more significant resulting deterioration of the seismic behaviour of the columns. In addition, the losses of both thickness and yield strength of an outer steel tube caused by corrosion should be taken into account when predicting the ultimate strength of corroded CFST columns.

• Corrosion Science and Technology
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• 제18권6호
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• pp.221-227
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• 2019

During the operation, maintenance and decommissioning of nuclear power plant radioactive contaminated waste is produced. This waste is stored in an underground repository 60-100 meters below the surface. The metallic portion of this waste comprises mostly carbon and stainless steel. A long-term field exposure showed high corrosion rates, general corrosion up to 29 ㎛ a^-1 and localized corrosion even higher. High corrosion rate is possible if microbes produce corrosive products, or alter the local microenvironment to favor corrosion. The bacterial and archaeal composition of biofilm formed on the surface of carbon steel was studied using 16S rRNA gene targeting sequencing, followed by phylogenetic analyses of the microbial community. The functional potential of the microbial communities in biofilm was studied by functional gene targeting quantitative PCR. The corrosion rate was calculated from weight loss measurements and the deposits on the surfaces were analyzed with SEM/EDS and XRD. Our results demonstrate that microbial diversity on the surface of carbon steel and their functionality is vast. Our results suggest that in these nutrient poor conditions the role of methanogenic archaea in corrosive biofilm, in addition to sulphate reducing bacteria, could be greater than previously suspected.

• Corrosion Science and Technology
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• 제2권4호
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• pp.165-170
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• 2003

Atmospheric corrosion behaviors of Zn, Zn-5%Al and Zn-55%A l coated steels have been investigated under cyclic wet-dry environments containing chloride ions. The wet-dry cycle was carried out by alternate exposure to immersion in 0.5 M (or 0.05 M) NaCl solutions and drying at $25^{\circ}C$ and 60 %RH. The polarization resistance $R_p$ and solution resistance $R_s$ were monitored by AC impedance technique. From the obtained $1/R_p$ and $1/R_s$ values, the corrosion rate of the coatings and the Time of Wetness (TOW) were estimated, respectively. Effects of chloride ions and TOW on the corrosion rates of Zn, Zn-5%Al, Zn-55%Al coatings and appearance of red rust (onset of underlying steel corrosion) under wet-dry cycles are discussed on the basis of the corrosion monitoring data.

• Corrosion Science and Technology
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• 제15권4호
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• pp.189-197
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• 2016

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.

• Journal of the Korean institute of surface engineering
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• 제53권2호
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• pp.72-79
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• 2020

Two Fe-Cr steels of T22 steel and STS430 steel were corroded at 650 and 750℃ for 100hr in sewage sludge-(0.3% SO₂-6% O₂-10% H₂O-balance CO₂) mixed gas environment. T22 steel corroded faster than STS430, indicating that the Cr content significantly influence the corrosion rates. T22 formed thick and non-protective Fe₂O₃ as the major oxide and Fe₃O₄ as the minor one. With an increase in corrosion temperature, their corrosion rates increased, being accompanied with formation of pores and cracks in the thickened oxide scales that were non-adherent. STS430 steel formed Fe₂O₃, Fe₃O₄ as the outer scale and (Fe, Cr)-O as the inner layer by which its corrosion rate is greatly reduced. Both the T22 and STS430 steel samples formed multi-layered scales by outward diffusion of Fe ions and inward diffusion of oxygen and sulfur ions at high-temperature more than 650℃.

• Corrosion Science and Technology
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• 제2권4호
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• pp.183-188
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• 2003

Corrosion of carbon and weathering steels were evaluated under 3 environmental exposures in Thailand (urban, rural and marine) for a year. The seasonal study was designed to determine different corrosion mechanisms by 6 months of dry season and 6 months of rainy season in a year. The sheltered exposure racks were used to determine the washing effect of min. At each site, climatic and pollutants analyses were carried out. The present study showed that the difference in corrosion rates of carbon and weathering steels was not so distinguished in both rural (AIT) and urban (TISTR) environments. The corrosion rate of weathering steel was somewhat lower than that of carbon steel and the decreasing tendency of corrosion rate with time was slightly higher for weathering steel than for carbon steel. In marine (Rayong) environment, the corrosion rate was higher and the effect of wet and dry seasons was observed. The corrosion rate in 6 dry months was higher for direct exposure than for sheltered exposure. However, in 6 rainy months. the corrosion rate of sheltered exposure was higher than that of direct exposure. In direct exposure for I year, that is, the first 6 dry months and the next 6 rainy months, the corrosion rate decreased with time. but in sheltered exposure, the corrosion rate did not decrease with time. instead, increased in the next 6 rainy months. This indicated that the protect ive layer formed in the first 6 dry months could be destroyed by high deposition of chloride to r sheltered exposure in the next 6 rainy months; whereas the rust layer for direct exposure could be kept sound due to washing effect in rainy season, even though the deposition rate of chloride was almost the same for direct and sheltered exposures. In marine environment, the weathering steel showed higher corrosion resistance than carbon steel but its corrosion rate was higher than those in other environments.

• Journal of the Korean institute of surface engineering
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• 제39권1호
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• pp.25-34
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• 2006

Al-Mg alloy, an open rack vaporizer(ORV) material was reported to be corroded in seawater environments though the ORV material was coupled to thermally sprayed Al-Zn alloy functioning a sacrificial anode. In addition, the corrosion behavior based on the calculated corrosion potential did not match the observed corrosion behavior. Hence, the goal of this study is to get better understanding on Al or Al-Mg alloy coupled to Al-Zn alloy and to provide the calculated corrosion potential representing the corrosion behavior of the ORV material by immersion test, electrochemical tests, and calculation of corrosion and galvanic potential. The corrosion potentials of Al and Al alloys also depended on alloying element as well as surface defects. The corrosion potentials of Al and Al-Mg alloy were changed with time. In the meantime, the corrosion potentials of Al-Zn alloys were not. The corrosion rates of Al-Zn alloys were exponentially increased with zinc contents. The phenomena were explained with the stability of passive film proved by passive current density depending on pH and confirmed by the model proposed by McCafferty. Dissimilar material crevice corrosion (DMCC) test shows that higher content of zinc caused Al-Mg alloy corroded more rapidly, which was due to the fact that higher corrosion rate of Al-Zn makes [$H^+$] and [$Cl^-$] more concentrated within pit solution to corrode Al-Mg alloy. Considering electrochemical reactions within pit as well as bulk in the calculation gives better prediction on the corrosion behavior of Al and Al-Mg alloy as well as the capability of Al-Zn alloy for corrosion protection.

• Structural Monitoring and Maintenance
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• 제2권3호
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• pp.253-267
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• 2015

Corrosion has significant adverse effects on the durability of reinforced concrete (RC) structures, especially those exposed to a marine environment and subjected to mechanical stress, such as bridges, jetties, piers and wharfs. Previous studies have been carried out to investigate the corrosion behaviour of steel rebar in various concrete structures, however, few studies have focused on the corrosion monitoring of RC structures that are subjected to both mechanical stress and environmental effects. This paper presents an exploratory study on the development of corrosion monitoring and detection techniques for RC structures under the combined effects of external loadings and corrosive media. Four RC beams were tested in 3% NaCl solutions under different levels of point loads. Corrosion processes occurring on steel bars under different loads and under alternative wetting - drying cycle conditions were monitored. Electrochemical and microscopic methods were utilised to measure corrosion potentials of steel bars; to monitor galvanic currents flowing between different steel bars in each beam; and to observe corrosion patterns, respectively. The results indicated that steel corrosion in RC beams was affected by local stress. The point load caused the increase of galvanic currents, corrosion rates and corrosion areas. Pitting corrosion was found to be the main form of corrosion on the surface of the steel bars for most of the beams, probably due to the local concentration of chloride ions. In addition, visual observation of the samples confirmed that the localities of corrosion were related to the locations of steel bars in beams. It was also demonstrated that electrochemical devices are useful for the detection of RC beam corrosion.

• Journal of Ocean Engineering and Technology
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• 제10권3호
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• pp.14-23
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• 1996

The corrosion fatigue test were carried out to evaluate the fatigue characteristics of accelerated cooled (ACC) TMCP high tensile strength steels and weld joint with high heat input by one side one run submerged are welding. In this paper, the fatigue crack growth behaviors were investigated with the center crack tension specimen of base metal and heat affected zone in substitute sea water and air, respectively Main results obtained are sunnarized as follows: 1. The fatigue crack growth rates in sea water faster than those in air environment for the different heat input values, crack growth rate of base metal is very fast and effect of heat input is not remarkable. 2. In HAZ (82kJ/cm, 116kJ/cm), the crack branching phenomena were observed in both air and sea water environment, 3. In SEM observation, the corrosion effect on base metal was larger than that on HAZ in corrosion environment.