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Selective Catalytic Reduction (SCR) 환경에서 18% 크롬 스테인리스강의 부식 거동
김희산 ( Heesan Kim ) 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.3
Effects of high-temperature environment and low-temperature environment on corrosion behaviours of 18Cr stainless steels (type 304L, type 441) in simulated selective catalytic reduction (SCR) environments were studied using weight loss test in each environment and rust analysis. With time to exposure to the hightemperature environment, type 441 was more resistant to corrosion than type 304L due to both higher diffusivity of Cr and lower thermal expansion coefficient in α-iron. The former provides a stable protective Cr<sub>2</sub>O<sub>3</sub> layer. The latter leaded to low residual stress between scale and steel, reducing the spallation of the scale. With time to exposure to the low-temperature environment, on the other hand, type 304L was more resistant to corrosion than type 441. The lower resistance of type 441 was caused by Cr-depleted zone with less than 11% formed during the pre-exposure to a high-temperature environment, unlike type 304L. It was confirmed by results from the crevice corrosion test of sensitised 11Cr steel. Hence, to achieve higher corrosion resistance in simulated SCR environments, ferritic stainless steels having lower thermal expansion coefficient and higher diffusivity of Cr but containing more than 18% Cr are recommended.
채호병 ( Hobyung Chae ),김우철 ( Woo Cheol Kim ),김희산 ( Heesan Kim ),김정구 ( Jung-gu Kim ),김경민 ( Kyung Min Kim ),이수열 ( Soo Yeol Lee ) 한국부식방식학회 2021 Corrosion Science and Technology Vol.20 No.2
In this work, we have performed a corrosion failure analysis of a leaking tube connected to an upper header of a condensate pre-heater in a heat recovery steam generator. It was revealed that the leakage position in the tube was the location where the materials were easily vulnerable due to tensile residual stresses induced by the material manufacturing process and welding process. In addition to an imbalance in the module induced by temperature difference during operation of the pre-heater, the weight of the modules and thermal fatigue provoked a type of stress of tensile-tensile fatigue on the tube. Thus, the leakage position of the pre-heater was exposed to the tensile stress on the inner surface of the tube facing the gas, which rendered the unstable oxide layer susceptible to corrosion and the formation of pits on the water side. The cracks propagated along with the degraded microstructure in a transgranular cracking mode under fatigue loading and finally resulted in water leakage.
정준철 ( Joon-cheol Jeong ),김우철 ( Woo-cheol Kim ),김경민 ( Kyung Min Kim ),손홍균 ( Hong-kyun Sohn ),김정구 ( Jung-gu Kim ),이수열 ( Soo-yeol Lee ),김희산 ( Heesan Kim ) 한국부식방식학회 2020 Corrosion Science and Technology Vol.19 No.6
Failure analysis on the welded type 304 pipe used for cooling water piping in the district heating primary side was conducted. Inorganic elements and bacteria in the cooling water and in corrosion products were analyzed, and the weldment was inspected by microscopy and a sensitization test. Corrosion damages were observed in the heat-affected zone, on weld defects such as incomplete fusion or excessive penetration caused by improper welding, or/and at the 6 o'clock position along the pipe axial direction. However, the level of concentration of chloride in the cooling water as low as 80 ppm has been reported to be not enough for even a sensitized type 304 steel, meaning that the additional corrosive factor was required for these corrosion damages. The factor leading to these corrosion damages was drawn to be the metabolisms of the types of bacteria, which is proved by the detection of proton, sulfur containing species, biofilms, and both bacteria and corrosion product analyses.
김종수(Jongsoo Kim),김희산(Heesan Kim) 한국표면공학회 2006 한국표면공학회지 Vol.39 No.1
Al-Mg alloy, an open rack vaporizer(ORV) material was reported to be corroded in seawater environments though the ORV material was coupled to thermally sprayed Al-Zn alloy functioning a sacrificial anode. In addition, the corrosion behavior based on the calculated corrosion potential did not match the observed corrosion behavior. Hence, the goal of this study is to get better understanding on Al or Al-Mg alloy coupled to Al-Zn alloy and to provide the calculated corrosion potential representing the corrosion behavior of the ORV material by immersion test, electrochemical tests, and calculation of corrosion and galvanic potential. The corrosion potentials of Al and Al alloys also depended on alloying element as well as surface defects. The corrosion potentials of Al and Al-Mg alloy were changed with time. In the meantime, the corrosion potentials of Al-Zn alloys were not. The corrosion rates of Al-Zn alloys were exponentially increased with zinc contents. The phenomena were explained with the stability of passive film proved by passive current density depending on pH and confirmed by the model proposed by McCafferty. Dissimilar material crevice corrosion (DMCC) test shows that higher content of zinc caused Al-Mg alloy corroded more rapidly, which was due to the fact that higher corrosion rate of Al-Zn makes [H?] and [Cl?] more concentrated within pit solution to corrode Al-Mg alloy. Considering electrochemical reactions within pit as well as bulk in the calculation gives better prediction on the corrosion behavior of Al and Al-Mg alloy as well as the capability of Al-Zn alloy for corrosion protection.
인공 해수 중에서 탄소강의 부식특성에 미치는 합금원소 (Cr, Mn)의 영향
현영민 ( Youngmin Hyun ),김희산 ( Heesan Kim ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.2
Effects of alloying elements, manganese and chromium, on corrosion resistance of carbon steel were examined using weight loss test and electrochemical tests (polarization test and electrochemical impedance spectroscopy (EIS)) in synthetic seawater at 60 ℃. The results from the weight loss test showed that chromium effectively improved corrosion resistance of carbon steel during the entire immersion time, but manganese improved corrosion resistance after the lowered corrosion resistance at the beginnings of immersion. Unlike the weight loss test, the electrochemical tests showed that the corrosion resistance did not increase with immersion time, in all the specimens. This disagreement is explained by the presence of rust involved in electrochemical reaction during electrochemical tests. The analysis of rust with transmission electron microscopy (TEM)-energy dispersive spectroscopy (EDS) showed that the amorphous-like rust layer located at the metal/rust interface with enriched alloying element (Cr, Mn) prevents diffusion of corrosive species into a metal/rust interface effectively, which leads to increased corrosion resistance. The initial corrosion behaviour is also affected by the rust types. In other words, manganese accelerated the formation of spinel oxides, negatively affecting corrosion resistance. Meanwhile, chromium accelerated the formation of goethite but impeded the formation of spinel oxides, positively affecting the corrosion resistance. From the above results, the corrosion resistance of steel is closely related with a rust type.(Received May 12, 2015)
사워(Sour) 환경에서 고강도강의 내식성에 미치는 합금원소의 영향
현영민 ( Youngmin Hyun ),김희산 ( Heesan Kim ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.12
The effects of alloying elements (Mn, Cr, and C) on the corrosion resistance of steel were examined using weight loss test, polarization test in a sour environment, analysis of rust, and the prediction of stable corrosion product. Carbon was found to improve corrosion resistance after 7-day immersion, while manganese and chromium negatively affected the corrosion resistance of steels during the entire immersion time. The negative effect of manganese and chromium on the corrosion resistance in the sour environment was explained, in that both manganese and chromium were stable as ionic species were dissolved in the sour solution, which was proved by the prediction of stable phases based on phase equilibria. The positive effect of carbon, on the other hand, was due to the formation of amorphous carbon distributed near the metal/rust interface, which may improve the adhesion of the corrosion product to the matrix. This is consistent with not only the formation of adhesive rust on the high carbon-containing steels but also the change in the corrosion behaviour of the high carbon-containing steels, from linear to parabolic behaviour, with time. †(Received May 23, 2016; Accepted June 11, 2016)
우드칩을 연료로 하는 열병합발전소의 회분 퇴적 및 설비 고장 원인 분석
송민지 ( Min Ji Song ),김우철 ( Woo Cheol Kim ),김희산 ( Heesan Kim ),김정구 ( Jung-gu Kim ),이수열 ( Soo Yeol Lee ) 한국부식방식학회 2023 Corrosion Science and Technology Vol.22 No.3
The use of biomass is increasing as a response to the convention on climate change. In Korea, a method applied to replace fossil fuels is using wood chips in a cogeneration plant. To remove air pollutants generated by burning wood chips, a selective denitrification facility (Selective catalytic reduction, SCR) is installed downstream. However, problems such as ash deposition and descaling of the equipment surface have been reported. The cause is thought to be unreacted ammonia slip caused by ammonia ions injected into the reducing agent and metal corrosion caused by an acidic environment. Element analysis confirmed that ash contained alkali metals and sulfur that could cause catalyst poisoning, leading to an increase in the size of ash particle and deposition. Measurement of the size of ash deposited inside the facility confirmed that the size of ash deposited on the catalyst was approximately three times larger than the size of generally formed ash. Therefore, it was concluded that a reduction in pore area of the catalyst by ash deposition on the surface of the catalyst could lead to a problem of increasing differential pressure in a denitrification facility.
TiO<sub>2</sub> 나노튜브 형상에 미치는 NH<sub>4</sub>F와 H<sub>2</sub>O의 영향
김건두 ( Geon-du Gim ),장상순 ( Sang-soon Jang ),김희산 ( Heesan Kim ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.3
The aim of this work is the attainment of the TiO<sub>2</sub>-nanotube photocatalytic-growth condition using anodization, whereby the NH<sub>4</sub>F-H<sub>2</sub>O weight ratio is appropriately controlled. We fabricated the TiO<sub>2</sub> nanotubes using a two-step anodization (first step is 1 hr; second step is 30 hr) under the ambient pressure and the room temperature at 60 V in ethylene-glycol solutions to investigate the effects of the NH<sub>4</sub>F(0.1,0.3,0.5wt%) and H<sub>2</sub>O(1-3wt%) on the Ti<sub>O</sub>2-nanotube geometry and the photocatalytic efficiency. Further, the decomposition efficiency of the methylene blue on the Ti<sub>O</sub>2 nanotubes by the UN radiation depended on the geometrical change of the nanotube geometry, indicating the proportionality of the decomposition efficiency to the surface area that was affected by the NH4F and H<sub>2</sub>O concentrations. As the NH4F weight was increased, the surface area initially decreased but slightly increased later, and the length consistently increased. As the H<sub>2</sub>O weight was increased, the surface area and length initially increased, but later decreased with the 3 wt% H<sub>2</sub>O.