한국부식방식학회

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밀폐 박스거더형 무도장 내후성강 교량의 부식취약부에 대한 방식대책 연구(I)
In corrosion-sensitive areas of exsisting unpainted weathering steel bridges with closed box girder structures. there are some serious local corrosion problems because of rain water or dew water which can not be solved by exsisting maintenance methods. These problems must be controled technically because of bad. influence on the safety of bridge. This study is the first stage of developing the economic corrosion control manual for these local corrosion problems. Through the injection of tar sealant into the crevice of mock-up equipment, it was prooved that the corrosive sealant can be useful to corrosion control at crevice of corrosion sensitive area.
KEYWORDs : unpainted weathering steel, splice connection part, corrosion, corrosion sensitive area, multiunction sealant
AUTHORs : 송창영†·이의호·이제현·박현출·최재석·노영태

Page : 142 - 148 DOWNLOAD
원전 배관의 반복 측정 데이터에 대한 신뢰도 분석 방법
Safety is a major concern in Nuclear Power Plants (NPPs). Piping systems in NPPs are very complex and composed of many components such as tees, elbows, expanders and straight pipes. The high pressure and high temperature water flows inside piping components. As high speed water flows inside piping, the pipe wall thinning occurs in various reasons such as FAC (Flow Accelerated Corrosion), LDIE (Liquid Droplet Impingement Erosion) and Flashing. To inspect the wall thinning phenomenon and protect the piping from damages, piping components are checked by UT measurement in every overhaul. During every overhaul, approximately 200~300 components (40,000~60,000 UT data) are examined in NPPs. There are some methods from EPRI for evaluating wear rate of components. However, only few studies have been conducted to find out the raw data reliability for the wear rate evaluation. Securing the reliable raw data is the key factor for a reasonable evaluation. This paper suggests the reliability analysis method for the repeatedly
measured data for wear rate evaluation.
KEYWORDs : UT measurement, repeated measurement, wall thinning, error, reliability, wear rate
AUTHORs : 윤훈†·황경모

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실험 계획법 및 열역학 계산법을 이용한 초고온가스로용 니켈계 초합금 설계 방법론
This work is concerning a methodology of Ni-base superalloy development for a very high temperature gas-cooled reactor(VHTR) using design of experiments(DOE) and thermodynamic calculations. Total 32 sets of the Ni-base superalloys with various chemical compositions were formulated based on a fractional factorial design of DOE, and the thermodynamic stability of topologically close-packed(TCP) phases of those alloys was calculated by using the THERMO-CALC software. From the statistical evaluation of the effect of the chemical composition on the formation of TCP phase up to a temperature of 950 oC, which should be suppressed for prolonged service life when it used as the structural components of VHTR, 16 sets were selected for further calculation of the mechanical properties. Considering the yield and ultimate tensile strengths of the selected alloys estimated by using the JMATPRO software, the optimized chemical composition of the alloys for VHTR application, especially intermediate heat exchanger, was proposed for a succeeding experimental study.
KEYWORDs : design of experiments, intermediate heat exchanger, Ni-base superalloy, thermodynamic calculation, very high temperature gas-cooled reactor
AUTHORs : 김성우†·김동진

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액적충돌침식으로 인한 배관감육 예측체계 구축에 관한 연구
The most common pipe wall thinning degradation mechanisms that can occur in the steam and feedwater systems are FAC (Flow Acceleration Corrosion), cavitation, flashing, and LDIE (Liquid Droplet Impingement Erosion). Among those degradation mechanisms, FAC has been investigated by many laboratories and industries. Cavitation and flashing are also protected on the piping design phase. LDIE has mainly investigated in aviation industry and turbine blade manufactures. On the other hand, LDIE has been little studied in NPP (Nuclear Power Plant) industry. This paper presents the development of prediction system for pipe wall thinning caused by LDIE in terms of erosion rate based on air-water ratio and material. Experiment is conducted in 3 cases of air-water ratio 0.79, 1.00, and 1.72 using the three types of the materials of A106B, SS400, and A6061. The main control parameter is the air-water ratio which is defined as the volumetric ratio of water to air (0.79, 1.00, 1.72). The experiments were performed for 15 days, and the surface morphology
and hardness of the materials were examined for every 5 days. Since the spraying velocity (v) of liquid droplets and their contact area (Ac) on specimens are changed according to the air-water ratio, we analyzed the behavior of LDIE for the materials. Finally, the prediction equations(i.e. erosion rate) for LDIE of the materials were determined in the range of the air-water ratio from 0 to 2%.
KEYWORDs : liquid droplet impingement erosion, two phase nozzle, air-water ratio, erosion rate
AUTHORs : 김경훈†·조연수·황경모

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High-temperature Oxidation of Nano-multilayered AlTiSiN Thin Films deposited on WC-based carbides
Nano-multilayered, crystalline AlTiSiN thin films were deposited on WC-TiC-Co substrates by the
cathodic arc plasma deposition. The deposited film consisted of wurtzite-type AlN, NaCl-type TiN,
and tetragonal Ti2N phases. Their oxidation characteristics were studied at 800 and 900°C for up to
20 h in air. The WC-TiC-Co oxidized fast with large weight gains. By contrast, the AlTiSiN film
displayed superior oxidation resistance, due mainly to formation of the α-Al2O3-rich surface oxide
layer, below which an (Al2O3, TiO2, SiO2)-intermixed scale existed. Their oxidation progressed primarily by the outward diffusion of nitrogen, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.
KEYWORDs : AlTiSiN thin films, WC carbides, oxidation, Al2O3 oxide
AUTHORs : Yeon Sang Hwang and Dong Bok Lee†

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