• 한국표면공학회지
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• 제51권6호
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• pp.405-414
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• 2018

The present study investigated the adhesion and corrosion resistance of subsequent electrophoretic paint (E-paint) on "electroless" paint coated AZ31 Mg alloy, which was formed by immersion of AZ31 Mg alloy in E-painting solution. It was found that with increasing immersion time of AZ31 in E-painting solution, the amount of paint deposited by electroless process increased but it decreased the electrochemical equivalent of E-painting process and the adhesion of the subsequent E-paint layer. The E-paint on electroless paint coated AZ31 contained pores with the highest pore density and the largest pore size was obtained on the samples with electroless times of 2 and 5 minutes, respectively. Results of the salt-spray test showed an accelerated growth of blisters over the entire surface of the sample immersed for less than 5 minutes whereas blisters were observed only in the vicinity of the scratch in case of samples treated for 15 and 30 minutes. The E-paint on AZ31 with shorter electroless immersion time in E-painting solution was found to have good adhesion and better corrosion resistance.

• Nuclear Engineering and Technology
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• 제37권4호
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• pp.375-384
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• 2005

To investigate the flow-accelerated corrosion (FAC) dependency of carbon steel (A106 Gr. B) and low-alloy steels (1Cr-1/2Mo, 21/4Cr-1Mo) on pH, orifice distance, and material, experiments were carried out. These experiments were performed using a flow velocity of 4 m/sec (partly 9 m/sec) at pH $8.0\~10.0$ in an oxygen-free aqueous solution re-circulated in an Erosion-Corrosion Test Loop at $130^{\circ}\;{\ldots}$ for 500 hours. The weight loss of the carbon steel specimens appeared to be positively dependent on the flow velocity. That of the carbon and low-alloy steel specimens also showed to be distinguishably dependent on the pH. At pH levels of $8.0\~9.5$ it decreased, but increased from 9.5 to 10.0. Utility water chemistry personnel should carefully consider this kind of pH dependency to control the water system pH to mitigate FAC of the piping system material. The weight loss of the specimens located further from the orifice in the distance range of $6.8\~27.2$ mm was shown to be greater, except for 21/4Cr-1Mo, which showed no orifice distance dependency. Low alloy steel specimens exhibited a factor of two times better resistance to FAC than that of the carbon steel. Based on this kind of FAC dependency of the carbon and low-alloy steels on the orifice distance and material, we conclude that it is necessary to alternate the composition of the secondary piping system material of NPPs, using low-alloy steels, such as 21/4Cr-1Mo, particularly when the system piping has to be replaced.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
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• pp.203-206
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• 2005

The purpose of this study is to develop the evaluation method of repair performance for the repair method of reinforced concrete structures deteriorated due to combined deterioration, its results are summarized as the follows. After investigating and analyzing the experimental data of this study and existing research, it is proposed the evaluation method on the repair performance for the repair method of reinforced concrete structures using evaluation method of reinforcing corrosion by combined deterioration accelerated test.

• Corrosion Science and Technology
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• 제5권3호
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• pp.99-105
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• 2006

This paper is to investigate feasibility on quantitative aging state of epoxy coating on concrete wall in containment structure under operation of nuclear power plants. For evaluating the physical characteristics of the epoxy coating, adhesion strengths of two kinds of degraded epoxy coating systems on both steel surfaces and concrete surfaces were measured via accelerated aging. Comparatively impedance data taken by ultrasonic test were also taken to relate with adhesion data. After aging, in case of concrete, from half of specimens, aging of epoxy coating was developed. As for steel, on $4^{th}$ inspection day, adhesion force was failed. To improve reliability on quality degradation of epoxy, relationship between adhesion and impedance was analyzed. By tracing to co-respond to these data, it was possible to Fig. out physical state of as-built epoxy coating. The possibility to develop new methodology of time - dependent aging state on epoxy coating was found and discussed.

• 한국구조물진단유지관리공학회 논문집
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• 제26권6호
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• pp.1-13
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• 2022

이 연구에서는 콘크리트 표면에서 측정된 반전지전위(half-cell potential, HCP)값을 활용하여 철근 부식 상태 및 부식속도의 정량적 평가 가능성을 논의하였다. 이 연구에서는 염수에 침지된 콘크리트 속 철근에 전류를 인가하여 다양한 부식상태의 철근 콘크리트 실험체(한 변의 길이가 200mm 인 정육면체)를 준비하였다. 부식촉진시험을 마치고, 염수 포화상태의 콘크리트 실험체 표면에서 HCP값을 측정하였고, 바로 이어서 동일한 조건의 실험체에서 전기화학적 임피던스 분광법을 활용하여 콘크리트 속 철근의 분극저항값을 측정하였다. 측정된 분극저항값을 Stern-Geary식에 대입하여 부식전류밀도(corrosion current density, i_corr)를 계산하였다. 실험결과를 바탕으로 염해에 따라 다양한 부식상태의 철근이 매입된 철근 콘크리트 실험체의 염수 포화상태에서 HCP와 i_corr의 상관관계를 도출하였다. 대체적으로 HCP와 i_corr은 로그선형관계를 보였으며, R2값이 0.87이상의 높은 적합도를 확인하여 통계적인 유의함을 확인하였다. 이러한 결과는 일정한 환경에 노출된 철근 콘크리트일 경우 자연전위값을 측정함으로서 철근의 부식상태 및 속도를 평가할 수 있음을 실험적으로 확인하였다.

• 수산해양기술연구
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• 제38권4호
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• pp.265-270
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• 2002

증류수 및 수도수 중에서 방열기로 사용되는 알루미늄합금재의 온도 변화, 탈기에 의한 개로전위, 부식전류밀도에 관하여 연구한 결과 다음과 같은 결론을 얻었다. 1. 청수 중에서 개로전위는 온도가 높아짐에 따라 비전위화 되고, 또한 탈기 후의 개로전위는 탈기 전의 개로전위보다 비전위화 된다. 2. 증류수 중에서의 부식전류밀도는 수도수 중에서의 부식전류밀도보다 더 억제된다. 3. 탈기 후의 부식전류밀도는 탈기 전의 부식전류밀도보다 크게 억제된다

• 한국압력기기공학회 논문집
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• 제20권1호
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• pp.49-55
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• 2024

Stainless 630 (or 17-4PH) is a precipitation-hardening martensitic stainless steel that has excellent mechanical properties and corrosion resistance. These characteristics make the STS630 to be used as a consisting material for various components such as spider, pin, spring, and spring retainer, of the control rod drive mechanism (CRDM) in pressurized water reactors (PWRs). In general, it is well known that the oxide layer of stainless steel consists of a duplex layer, a compact inner layer of FeCr₂O₄ spinel, and a coarse-grained outer layer of Fe₃O₄ spinel in PWR primary coolant condition. However, the characteristics of the oxide layer can be sensitively influenced by various water chemistry conditions such as temperature, dissolved oxygen, dissolved hydrogen, pH, pH adjuster type, and exposure time. In this work, we investigate the corrosion properties of the STS630 as a function of coolant temperature in an NH3 alkaline solution for its boron-free application in a small modular reactor, to confirm the feasibility for usage as a boron-free SMR structural material. As a result, oxide layer of corroded STS630 is consist of double-layer oxides consisting of a Cr-rich dense inner oxide and a Fe-rich polyhedral outer particles like as that in commercial PWR primary coolant. The corrosion rate of STS630 increases with increase in test time and temperature and the corrosion rate-time model equation was developed based on experimental data. Overall, it is expected that the results in this study provides useful data for the corrosion behavior of STS630 in alkaline environments, contributing to the development of selecting suitable materials for SMRs.

• 한국산학기술학회논문지
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• 제15권5호
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• pp.3251-3259
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• 2014

본 논문에서는 철근의 부식을 고려한 철근콘크리트(RC)보의 휨파괴거동을 규명하기 위하여 수행한 일련의 3점휨 파괴시험 및 해석적 연구 결과를 제시하였다. 실험적 연구를 위하여 총12개의 시편보를 제작하였으며, 염수분무시험 챔버를 이용하여 10개월간 촉진부식토록 하였다. 철근부식에 미치는 균열의 영향을 분석하기 위하여 일부 시험체를 공칭휨강도의 30% 와 60%에 해당하는 최대하중으로 미리 하중을 가한 후 염소분무 시험챔버에 보관하였다. 재령 5개월 및 10월에 각각 휨파괴시험을 실시하였으며 최대하중과 하중-처짐곡선을 측정하였다. 실험결과 철근의 부식정도에 따라 철근과 콘크리트간의 부착력 손실이 발생하고 그에 기인하여 휨강도는 최대 5.4%, 연성도는 최대 43%의 저하가 발생하여 철근의 부식이 최대 하중 보다 연성도에 미치는 영향이 큰 것으로 나타났다. 한편, Maaddawy의 해석적 모델을 이용한 수치해석결과 철근의 부식을 고려한 RC보의 휨파괴거동을 상당부분 잘 묘사할 수 있는 것으로 나타났다.

• 한국산학기술학회논문지
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• 제20권5호
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• pp.559-568
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• 2019

최근 해양환경의 대형 SOC구조물 증가에 따른 구조물 내구성 증진에 관심이 증가되고 있다. 내구성 증진을 위해 개발된 FRP Hybrid Bar의 구조적 성능은 검증 되었으나 부식에 대한 저항성을 평가한 연구는 미흡하여 본 연구를 수행 하였다. 본 연구에서는 콘크리트 중의 철근 종류에 따른 철근부식 저항성을 평가하였다. 평가를 위하여 철근은 일반철근과 FRP hybrid Bar을 사용하였다. 시험방법은 갈바닉전류(Galvanic)와 반전지법(Half-Cell)을 사용하였으며, 철근부식 촉진을 위하여 콘크리트 내부에 염분을 0%, 1.5%, 3%, 6% 첨가하였다. 그 결과 갈바닉전류측정에서 FRP Hybrid Bar는 부식전류가 측정되지 않았다. 반면 일반철근에서는 시험 직후 부식이 발생하는 결과를 나타내었다. Half-Cell측정 결과에서도 4단계의 염분 함유량의 차이와 광물질혼화재료를 사용한 콘크리트와 일반콘크리트에 관계없이 FRP Hybrid Bar의 부식 저항성이 우수하게 나타났다. 따라서 FRP Hybrid Bar는 해양환경 및 철근부식이 예측되는 구조물용 대체 철근으로 사용이 가능하나 부착성능, 탄성계수, 절곡부의 강선 노출에 대한 처리 방법 등이 개선되면 염해로부터 철근부식 저항성 확보를 요구하는 구조물에 사용 할 수 있는 우수한 소재로 판단된다.

• Corrosion Science and Technology
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• 제13권2호
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• pp.62-69
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• 2014

A huge number of carbon steel piping components installed in the secondary system of nuclear power plants are exposed to aging mechanisms such as FAC (Flow-Accelerated Corrosion), Cavitation, Flashing, and LDIE (Liquid Droplet Impingement Erosion). Those aging mechanisms can lead to thinning of the piping components. To manage the wall thinning degradation, most of utilities in the world predict the wall thinning rate based on the computational program such as CHECWORKS, COMSY, and BRT-CICERO, evaluate the UT (Ultrasonic Test) data, and determine next inspection timing, repair or replacement, if needed. There are several evaluation methods, such as band, blanket, and strip methods, commonly used for determining the wear of piping components from single UT inspection data. It has been identified that those single UT evaluation methods not only do not consider the manufacturing features of pipes, but also may exclude the data of the most thinned point when determining the representative wear rate of piping components. This paper describes a newly developed single UT evaluation method, E-Cross method, for solving above problems and introduces application examples for several pipes and elbows. It was identified that the E-Cross method using the length and width of UT data excluded the most thinned points appropriate as the single UT evaluation method for thinned piping components.