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  • Page : 70 - 80 DOWNLOAD
  • 질소 보호 가스 첨가가 하이퍼 듀플렉스 스테인리스 밀봉용접재의 마모부식 저항성에 미치는 영향
  • Duplex stainless steels with nearly equal fraction of the ferrite(α) phase and austenite(γ) phase have been increasingly used for various applications such as power plants, desalination facilities due to their high resistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel
    (HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE=wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungsten arc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fraction of α-phase and γ-phase is changed and harmful secondary phases can be formed in the welded zone. In other words, the balance of corrosion resistance between two phases and reduction of Cr2N are the key points of this study. The primary results of this study are as follows. The addition of N2 to the Ar shielding gas provides phase balance under weld-cooling conditions and increases the transformation temperature of
    the α-phase to γ-phase, increasing the fraction of γ-phase as well as decreasing the precipitation of Cr2N. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values of the electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSS welded with shielding gas containing N2 decreased the weight loss, compared to HDSS welded with the Ar pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing the fraction of γ-phase and the stability of passive film according to the addition N2 gas to the Ar shielding gas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.
  • KEYWORDs : hyper duplex stainless steel, TIG Welding, Cr2N, potentiodynamic, erosion-corrosion
  • AUTHORs : 김 혜 진·전 순 혁·김 순 태·이 인 성·박 용 수†
  • Page : 62 - 69 DOWNLOAD
  • 원전 배관감육 평가를 위한 새로운 기법의 도입 및 타당성
  • 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.
  • KEYWORDs : wall thinning, UT inspection, UT data single evaluation method, E-Cross evaluation method, manufacturing tolerance
  • AUTHORs : 황 경 모†·윤 훈·박 현 철
  • Page : 56 - 61 DOWNLOAD
  • 핵연료 피복관 부식생성물 부착에 대한 용존수소의 영향
  • The purpose of this work is to investigate the effect of dissolved hydrogen concentration on crud deposition onto the fuel cladding surface in the simulated primary environments of a pressurized water reactor. Crud deposition tests were conducted in the dissolved hydrogen concentration range of 5~70 cc/kg at 325℃ for 14 days. Needle-shaped NiO deposits were formed in the hydrogen range of 5~25 cc/kg, while polygonal nickel ferrite deposits were observed at a hydrogen concentration above 35 cc/kg. However, the dissolved hydrogen content seems to have little effect on the amount of crud deposits.
  • KEYWORDs : dissolved hydrogen, axial offset anomaly, crud, deposit, primary water chemistry
  • AUTHORs : 백 승 헌·김 우 철·심 희 상·임 경 수·원 창 환·허 도 행†
  • Page : 48 - 55 DOWNLOAD
  • Influence of Annealing Temperature on Microstructure and Pitting Corrosion Behavior of the 27Cr-7Ni Hyper Duplex Stainless Steel
  • Influence of annealing temperature on the microstructure and resistance to pitting corrosion of the hyper duplex stainless steel was investigated in acid and neutral chloride environments. The pitting corrosion resistance is strongly dependent on the microstructure, especially the presence of chromium nitrides (Cr2N), elemental
    partitioning behavior and volume fraction of ferrite phase and austenite phase. Precipitation of deleterious chromium nitrides reduces the resistance to pitting corrosion due to the formation of Cr-depleted zone. The difference of PREN (Pitting Resistance Equivalent Number) values between the ferrite and austenite phases was the smallest when solution heat-treated at 1060 oC. Based on the results of electrochemical tests and critical crevice temperature tests, the optimal annealing temperature is determined as 1060℃.
  • KEYWORDs : duplex stainless steel, pitting corrosion, solution heat treatment, chromium nitride
  • AUTHORs : 전순혁, 김혜진, 공경호, 박용수†
  • Page : 41 - 47 DOWNLOAD
  • Corrosion Behaviors of Structural Materialsin High Temperature S-CO₂Environments
  • The isothermal corrosion tests of several types of stainless steels, Ni-based alloys, and ferritic-martensitic steels (FMS) were carried out at the temperature of 550 and 650℃ in SFR S-CO₂environment (200 bar) for 1000 h. The weight gain was greater in the order of FMSs, stainless steels, and Ni-based alloys. For the FMSs (Fe-based with low Cr content), a thick outer Fe oxide, a middle (Fe,Cr)-rich oxide, and an inner (Cr,Fe)-rich oxide were formed. They showed significant weight gains at both 550 and 650 oC. In the case of austenitic stainless steels (Fe-based) such as SS 316H and 316LN (18 wt.% Cr), the corrosion resistance was dependent on test temperatures except SS 310S (25 wt.% Cr). After corrosion test at 650℃, a large increase in weight gain was observed with the formation of outer thick Fe oxide and inner (Cr,Fe)-rich oxide. However, at 550℃, a thin Cr-rich oxide was mainly developed along with partially distributed small and nodular shaped Fe oxides. Meanwhile, for the Ni-based alloys (16-28 wt.% Cr), a very thin Cr-rich oxide was developed at both test temperatures. The superior corrosion resistance of high
    Cr or Ni-based alloys in the high temperature S-CO₂environment was attributed to the formation of thin Cr-rich oxide on the surface of the materials.
  • KEYWORDs : super-critical CO2, stainless steel, weight gain, corrosion resistance
  • AUTHORs : 이호중, 김현명, 장창희†