• 수산해양교육연구
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• 제17권1호
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• pp.106-114
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• 2005

This paper is a study on the prevention of crevice corrosion for a stainless steel heat exchanger in various pH solutions and with Cl ion concentrations. The electrochemical polarization test and crevice corrosion test of STS 304 for a heat exchanger were carried out. The crevice corrosion aspect, a passive behavior, crevice corrosion behavior, and corrosion protection characteristics of STS 304 using Al-alloy and Mg-alloy galvanic anode were considered. The main results are as follows: 1. The crevice corrosion of STS 304 occurs in the crevice and this corrosion increases pitting according to depth direction. On the other hand, the exterior crevice becomes passive. 2. With changing from a neutral to acid environment and increasing Cl ion concentration, the pitting potential of STS 304 lowers, and thus the crevice corrosion of STS 304 is sensitive. 3. The cathodic protection potential of STS 304 in the crevice is cathodically polarized by increasing Cl ion concentration. Therefore, an Al-alloy galvanic anode is more suitable than a Mg-alloy galvanic anode to protect the crevice corrosion of STS 304.

• Nuclear Engineering and Technology
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• 제49권4호
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• pp.769-775
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• 2017

The corrosion behavior of stainless steel (304 and 316 type) and copper induced by LiCl-KCl at low temperatures in the presence of sufficient oxygen and moisture was investigated through a series of experiments (at $30^{\circ}C$, $40^{\circ}C$, $60^{\circ}C$, and $80^{\circ}C$ for 24 hours, 48 hours, 72 hours, and 96 hours). The specimens not coated on one side with an aqueous solution saturated with LiCl-KCl experienced no corrosion at any temperature, not even when the test duration exceeded 96 hours. Stainless steel exposed to LiCl-KCl experienced almost no corrosion below $40^{\circ}C$, but pitting corrosion was observed at temperatures above $60^{\circ}C$. As the duration of the experiment was increased, the rate of corrosion accelerated in proportion to the temperature. The 316 type stainless steel exhibited better corrosion resistance than did the 304 type. In the case of copper, the rate of corrosion accelerated in proportion to the duration and temperature but, unlike the case of stainless steel, the corrosion was more general. As a result, the extent of copper corrosion was about three times that of stainless steel.

• Corrosion Science and Technology
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• 제18권3호
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• pp.78-85
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• 2019

The International Maritime Organization (IMO) will administer a new 0.5% global sulfur cap on fuel content from 1 January 2020, lowering from the present 3.5% limit. Seawater $SO_x$ (sulfur oxide) scrubbing is especially spray scrubbing and a promising alternative to complying with the IMO regulation. However, the ionization of $SO_2$ (sulfur dioxide) and the $H_2SO_4$ (sulfuric acid) formed from $SO_3$ (sulfur trioxide) is proposed to accelerate corrosion of the internal seawater pipe. Apparently, the corrosion of the scrubber seawater piping system occurs in a severe and frequent manner. Hence, in this study, electrochemical measurement and weight loss of carbon steel (used as seawater pipe in most of the ships) in diluted sulfuric acid solution were investigated to determine corrosion rate, corrosion current density, corrosion potential, electrochemical behavior, and impressed-current density. Accordingly, the corrosion rate of carbon steel sheet in various diluted sulfuric acid solutions was observed to be greater than that in natural seawater, thus suggesting the fundamental data to deal with corrosion problems in scrubber seawater pipe.

• Corrosion Science and Technology
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• 제16권3호
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• pp.100-108
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• 2017

In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

• Structural Engineering and Mechanics
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• 제42권4호
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• pp.531-549
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• 2012

Numerous oil tanker losses have been reported and one of the possible causes of such casualties is caused by the structural failure of aging ship hulls in rough weather. In aging ships, corrosion and fatigue cracks are the two most important factors affecting structural safety and integrity. This research is about effect on hull girder ultimate strength behavior of double hull oil tanker according to corrosion after Part I: stiffened panel. Based on corrosion data of Part I (time-dependent corrosion wastage model and CSR corrosion model), when progressing corrosion of fourtypes of double hull oil tankers (VLCC, Suezmax, Aframax, and Panamax), the ultimate strength behavior of hull girder is compared and analyzed. In case of the ultimate strength behavior of hull girder, when occurring corrosion, the result under vertical and horizontal bending moment is analyzed. The effect of time-dependent corrosion wastage on the ultimate hull girder strength as well as the area, section modulus, and moment of inertia are also studied. The result of this research will be useful data to evaluate ultimate hull girder strength of corroded double hull oil tanker.

• 대한기계학회논문집A
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• 제36권4호
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• pp.421-428
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• 2012

본 논문에서는 알루미늄 7075-T6 재료의 부식 기간별 표면 산화막 형성이 피로거동에 미치는 영향에 대해 연구하였다. 사용된 알루미늄 재료는 부식에 대한 부동태화 현상으로 부식저항 특성이 높은 금속으로 알려져 있다. 알루미늄 합금은 다른 재료에 비해 가볍고 강한 재료 특성 때문에 항공기 부품 산업과 같은 다양한 산업분야에서 널리 사용되고 있다. 때문에 부식에 대한 재료의 피로거동 특성과 부식에 대한 부동태화 특성에 대한 연구가 요구된다. 4절점 회전 굽힘 시험기를 사용하여 부식 기간별 재료의 피로거동 특성을 확인하였고, 표면 거칠기를 측정하여 부식 기간별 알루미늄 재료의 표면 부식 정도를 평가하였다. 또한 전자주사현미경을 통해 파단면 분석 및 재료 표면에 형성된 산화막을 측정하였다. 실험결과 초기 부식 4주 동안은 부식이 활발히 진행되어 피로수명은 크게 감소하고 표면 거칠기는 증가하였다. 하지만 4주 이후부터 재료의 부동태화 현상으로 부식 반응이 둔화되는 경향을 보였다. 전자주사현미경을 통한 분석에서도 표면 산화막의 성장이 4주 이후부터 둔화되어 재료 표면의 산화막이 보호층 역할을 하여 더 이상의 부식진행을 방지한다는 결론은 얻었다.

• 대한금속재료학회지
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• 제46권9호
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• pp.577-584
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• 2008

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. So, it is essential to choose the optimum material for the process equipment handling molten salt. In this study, corrosion behavior of Inconel 713LC, Inconel MA 754, Nimonic 80A and Nimonic 90 in the molten salt $LiCl-Li_2O$ under an oxidizing atmosphere was investigated at $650^{\circ}C$ for 72~216 hrs. Inconel 713LC alloy showed the highest corrosion resistance among the examined alloys. Corrosion products of Inconel 713LC were $Cr_2O_3$, $NiCr_2O_4$ and NiO, and those of Inconel MA 754 were $Cr_2O_3$ and $Li_2Ni_8O_{10}$ while $Cr_2O_3$, $LiFeO_2$, $(Cr,Ti)_2O_3$ and $Li_2Ni_8O_{10}$ were produced from Nimonic 80A. Also, corrosion products of Nimonic 90 were found to be $Cr_2O_3$, $(Cr,Ti)_2O_3$, $LiAlO_2$ and $CoCr_2O_4$. Inconel 713LC showed local corrosion behavior and Inconel MA 754, Nimonic 80A, Nimonic 90 showed uniform corrosion behavior.

• Corrosion Science and Technology
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• 제8권1호
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• pp.27-39
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• 2009

Non metallic composite materials, for example, GECM(graphite epoxy composite material) show high specific strength because of low density. These kinds of non metallic composite materials improved the structural effectiveness and operation economics. However, if these materials contacted several metals, corrosion can be arisen since non metallic composite materials have electrical conductivity. This paper dealt with galvanic corrosion between graphite epoxy composite material and several metals. Base on the electrochemical galvanic corrosion test between GECM and metals, corrosion current of carbon steel and aluminium increased with time but corrosion current of stainless steels and titanium decreased and galvanic potential increased. This behavior shows the galvanic corrosion depends upon the presence of passive film. Also, galvanic effect of GECM coupled with ferrous alloys and non-ferrous alloys was lower than that of 100% graphite, which is attributed to lower exposed area of graphite fiber in the GECM than apparent area of the GECM specimen used for the calculation of galvanic current in this work.

• Tribology and Lubricants
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• 제20권2호
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• pp.97-101
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• 2004

This paper reports the studies on the wear-corrosion behavior of Al-Mg alloy in various pH environments. In various pH of sea water, corrosion and wear-corrosion loss of Al-Mg alloy were investigated. Also, the polarization test of Al-Mg alloy using potentiostat/galvanostat was carried out. And the rubbed surface of Al-Mg alloy using scanning electron micrographs after wear-corrosion test was examined in various pH values of sea water. The main results are as following : The polarization resistance of Al-Mg alloy in pH 4 solution is higer than that in pH 6.7 solution, and the corrosion current density in pH 4 is controlled than in pH 6.7 solution. The wear-corrosion loss of Al-Mg alloy with lowering pH becomes sensitive. As the oxide product of Al-Mg alloy appears granular structure and exholiation phenomenon, wear-corrosion loss of Al-Mg alloy increases.

• Nuclear Engineering and Technology
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• 제44권7호
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• pp.773-780
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• 2012

The article presented is concerned with an evaluation of the corrosion behavior of SA-508 low alloy steel (LAS) and Type 309L stainless steel (SS) cladding of a reactor pressure vessel under the simulated primary water chemistry of a pressurized water reactor (PWR). The uniform corrosion and galvanic corrosion rates of SA-508 LAS and Type 309L SS were measured in three different control conditions: power operation, shutdown, and power operation followed by shutdown. In all conditions, the dissimilar metal coupling of SA-508 LAS and Type 309L SS exhibited higher corrosion rates than the SA-508 base metal itself due to severe galvanic corrosion near the cladding interface, while the corrosion of Type 309L in the primary water environment was minimal. The galvanic corrosion rate of the SA-508 LAS and Type 309L SS couple measured under the simulated power operation condition was much lower than that measured in the simulated shutdown condition due to the formation of magnetite on the metal surface in a reducing environment. Based on the experimental results, the corrosion rate of SA-508 LAS clad with Type 309L SS was estimated as a function of operating cycle simulated for a typical PWR.