• 한국해양공학회지
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• 제19권6호통권67호
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• pp.72-77
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• 2005

The materials used in a ship screw propeller are commonly made with brass. The seawater corrosion and seawater cavitation of the screw propeller reduces the propulsive performance of the ship. In screw manufacturing, the corrosion rust of the screw propeller is removed through a hand grinding method. The grinding process produces dust of the heavy metals from the brass. The dust creates a poor working environment that is harmful to the health of the workers. An automatic corrosionrust removing apparatus, using a blasting method, was developed for the improvement of screw polishing conditions and its working environment. The performance of this apparatus was investigated by surface roughness, weight loss rate, hardness, electrochemical corrosion resistance, and cavitation erosion, after removing of the corrosion rust under various blasting conditions. Two medias of alumina and emery were used in this experiment. The surface roughness and hardness of the screw were improved by this apparatus. The electrochemical corrosion potential (Ecorr) and current density (Icorr) were measured by the dynamic polarization method, using a potentiostat,under the conditions of surface polishing with grinding, blasting, wire brushing, and fine sand papering. The test results prove that the new corrosion rust-removing apparatus improves the surface performance of a screw propeller.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.260-265
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• 2004

The materials of ship screw propeller are commonly the manganese bronze. The seawater corrosion and cavitation of the screw propeller reduce tire propulsive performance of ship. In screw manufactory, tire corrosion rust of tire screw propeller is removed by a hand grinding. The grinding work makes the dust of the heavy metals from the manganese bronze. The dust makes indoor working environment poor. A friendly-environmental and automatic corrosion removing apparatus was developed for the improvement of screw processing and working environment. The corrosion rust of a screw propeller was remarkably removed by using apparatus. And the screw surface roughness was improved by a blasting effect of the apparatus performance test. Anode polarization curves on jour processing conditions, that is to say, grinding, blasting, wire-brushing, fine sand papering, were confirmed by a potentiostat. Especially, two kinds of medias, alumina and emery, were used in the blasting processing. Then, investigated tire cavitation erosion of specimen. This result proved that tire blasting work has considerably improved the corrosion resistance of a screw propeller.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1105-1110
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• 2011

유동가속부식(FAC)은 가장 잘 알려진 탄소강 배관 손상 메커니즘으로 현재 국내 전 원전에서는 유동가속부식으로 인한 감육현상을 관리할 수 있는 체계적인 방안이 수립되어 있다. 그러나, 발전소 배관은 다양한 침식손상 메커니즘에 의해 여전히 손상을 받고 있다. 대표적인 침식 메커니즘은 캐비테이션, 액적충돌침식(LDIE), 플래싱, 고체입자침식(SPE)이다. 본 논문에서 기술하는 액적충돌침식 은 손상예측이 어렵고, 관리를 위한 체계적인 방안도 수립되어 있지 않다. 본 논문에서는 실제 발전소 현장에서 발생한 사례를 바탕으로 기존에 개발된 예측 모델과 실험을 통해 얻어진 상관식을 비교하여 액적충돌침식으로 인한 손상을 평가할 수 있는 방법을 제시하였다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2007년도 추계학술대회 논문집
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• pp.29-29
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• 2007

본 연구에서는 분산강화 스테인리스강을 이용하여 케비테이션 발생 시 고체입자충격에 의한 재료의 침식메커니즘 및 침식저항성을 고찰하고자 하였다. 케비테이션 시간에 따른 침식저항성 측정결과, 기존재료에 비해 분산강화된 시편의 무게손실량이 낮았으며 침식잠복기가 짧고 침식속도가 낮아 전반적으로 우수한 저항성을 보였다. 이것은 침식표면의 손상메커니즘 관찰을 통해 확인할 수 있었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 추계학술대회 초록집
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• pp.115-115
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• 2009

캐비테이션-에로젼은 침식부식과 유사한 형태의 침식에 의한 손상이다. 즉, 고속의 애체흐름에 노출된 금속 표면을 따라 압력변화에 의해서 생성된 기포들이 파괴되는 것과 관련하여 일어나는 표면손상의 한 형태이다. 본 연구에서는 캐비테이션-에로젼 손상을 억제하기 위하여 WC 서멧을 HVOF 용사하였으며, 캐비테이션-에로젼 특성에 미치는 용사조건의 영향에 중점을 비교분석하였다.

• Corrosion Science and Technology
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• 제12권5호
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• pp.227-232
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• 2013

A number of 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 components. In April 2013, one (1) inch small bore piping branched from the main steam line experienced leakage resulting from wall thinning in a 1,000 MWe Korean PWR nuclear power plant. During the normal operation, extracted steam from the main steam line goes to condenser through the small bore piping. The leak occurred in the downstream of an orifice. A control valve with vertical flow path was placed on in front of the orifice. This paper deals with UT (Ultrasonic Test) thickness data, SEM images, and numerical simulation results in order to analyze the extent of damage and the cause of leakage in the small bore piping. As a result, it is concluded that the main cause of the small bore pipe wall thinning is liquid droplet impingement erosion. Moreover, it is observed that the leak occurred at the reattachment point of the vortex flow in the downstream side of the orifice.

• 대한조선학회논문집
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• 제45권4호
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• pp.403-410
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• 2008

This paper describes the optimization of the rudder section by the genetic algorism based on VLM(Vortex Lattice Method) and panel method. The developed propeller-rudder analysis program has been validated by comparing with experimental data. The research extends to optimize the anti-erosion rudder section of the large container ship. The object function is the amount of pressure at leading edge of rudder which is closely related with erosion phenomena. The optimized rudder has been compared with conventional rudder with NACA 0021 section by analyzing with the developed program. The finally optimized section has low and mild pressure distribution in comparison with the NACA rudder. The experiments is expected to be carried out for the validation of the present optimization and more parametric study of section geometry is also expected to be conducted in the near future.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2011년도 춘계학술대회 및 Fine pattern PCB 표면 처리 기술 워크샵
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• pp.196-197
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• 2011

Rudder, one of the most important component in the marine vessel, is now being decreased life time to serve due to cavitation erosion, vortex current, high flow speed suffer from ship speed going up dramatically. In this study, 10 kinds of thermal spray coating materials(2 of Zn alloy series, 3 of Al alloy series, 3 of Cu alloy series, 2 of STS alloy series) are chosen to apply on specimens and analyze micro structure, metallic composition, properties(porosity, oxidation) by using visual observation, XRD, EDX etc.. Additionally, to refine the characteristic of corrosion endurance for thermal spray coating layer, compared with thermal spray process and 5 kinds of heavy duty painting and AC paint (Anti-Corrosion Paint). Based on above mentioned experimental results, a priority of all coated specimens on corrosion-erosion endurances finalized and summarized there by desirable composition and process of thermal sprayed material properly.

• Corrosion Science and Technology
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• 제17권6호
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• pp.317-323
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• 2018

Assumptions have always been that wall thinning on the secondary side piping in nuclear power plants is mostly caused by Flow-Accelerated Corrosion (FAC). Recent studies have showed that wall thinning on the secondary side piping is caused by Liquid Droplet Impingement Erosion (LDIE), Solid Particle Erosion (SPE), cavitation, and flashing. To manage those aging mechanisms, several software such as CHECWORKS, COMSY, and BRT-CICERO have been used in nuclear power plants. Korean nuclear power plants have been using the CHECWORKS program since 1996 to date. However, many site engineers have experienced a lot of inconveniences and problems in using the CHECWORKS program. In order to work through the inconveniences and to remedy problems, KEPCO-E&C has developed a "3D-based pipe wall thinning management program (ToSPACE)" based on the experience of over 30 years in relation to the pipe wall thinning management. This study compares the results of FAC and LDIE analysis using both the CHECWORKS and ToSPACE programs with respect to validation of the wall thinning analysis results.

• 한국결정성장학회지
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• 제16권3호
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• pp.121-126
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• 2006

HVOF thermal spray coating of Co-alloy T800 is progressively replacing the classical hard coatings such as chrome plating because of the very toxic $Cr^{6+}$ ion known as carcinogen causing lung cancer. For the study of the possibility of replacing of chrome plating, the wear properties of HVOF Co-alloy T800 coatings are investigated using the reciprocating sliding tester both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$. The possibility as durability improvement coating is studied for the application to the high speed spindles vulnerable to frictional heat and wear. Wear mechanisms at the reciprocating sliding wear test are studied for the application to the systems similar to the sliding test such as high speed spindles. Wear debris and frictional coefficients of T800 coatings both at room and at an elevated temperature of $1000^{\circ}F\;(538^{\circ}C)$ are drastically reduced compared to those of non-coated surface of parent substrate Inconel 718. This study shows that the coating is recommendable for the durability improvement coatings on the surfaces vulnerable to frictional heat. The sliding surfaces are weared by the mixed mechanisms such as oxidative wear, abrasion by the sliding ball slurry erosion by the mixture of solid particles and small drops of the melts and semi-melts of the attrited particles cavitation by the relative motions among the coating, sliding ball, the melts and semi-melts. and corrosive wear. The oxide particles and the melts and semi-melts play roles as solid and liquid lubricant reducing the wear and friction coefficient.