한국부식방식학회

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Investigation of Sweet and Sour Corrosion of Mild Steel in Oilfield Environment by Polarization, Impedance, XRD and SEM Studies
Metallic structures in the oil and gas production undergo severe degradation due to sweet and sour corrosion caused by the presence of CO2 and H2S in the fluid environment. The corrosion behavior of 304 austenitic stainless was investigated in the presence of varying concentrations of CO2 or H2S and CO2 + H2S to understand the effect of the parameters either individually or in combination. Potentiodynamic polarization study revealed that a small amount of CO2 aided in the formation of
calcareous deposit of protective layer on passive film of 304 steel, while increase in CO2 concentration ruptured the layer resulting in sweet corrosion. The presence of S2- damaged the passive and protective layer of the steel and higher levels increased the degradation rate. Electrochemical impedance studies revealed lower polarization resistance and impedance at higher concentration of CO2 or H2S, supporting the outcomes of polarization study. XRD analysis revealed different types of iron carbides and iron sulphides corresponding to sweet and sour corrosion as the corrosion products, respectively. SEM analysis revealed the presence of uniform, localized and sulphide cracking in sour corrosion and general corrosion
with protective carbide layer amid for sweet corrosion.
KEYWORDs : Oil field corrosion, mild steel, polarization, impedance spectroscopy, electron microscopy
AUTHORs : Subir Paul† and Bikramjit Kundu

Page : 242 - 248 DOWNLOAD
템퍼링 조건이 마르텐사이트계 고강도강의 수소확산거동에 미치는 영향
Martensitic high-strength steels revealed superior mechanical properties of high tensile strength exceeding 1000 Mpa, and have been applied in a variety of industries. When the steels are exposed to corrosive environments, however, they are susceptible to hydrogen embrittlement (HE), resulting in catastrophic cracking failure. To improve resistance to HE, it is crucial to obtain significant insight into the exact physical nature associated with hydrogen diffusion behavior in the steel. For martensitic steels, tempering condition should be adjusted carefully to improve toughness. The tempering process involves microstructural modifications, that provide changes in hydrogen diffusion/trapping behavior in the steels. From this perspective, this study examined the relationship between tempering condition and hydrogen diffusion behavior in the steels. Results based on glycerin measurements and hydrogen permeation evaluations indicated that hydrogen diffusion/trapping behavior was strongly affected by the characteristics of precipitates, as well as by metallurgical defects such as dislocation. Tempering condition should be adjusted properly by considering required mechanical properties and resistance to HE.
KEYWORDs : Tempering, ε-carbide, Cementite, Hydrogen diffusion, Martensitic high-strength steel
AUTHORs : 박진성·황은혜·이만재·김성진†

Page : 231 - 241 DOWNLOAD
36개월간 국내 옥외폭로시험에 따른 아연도강의 부식거동
Atmospheric corrosion is generally an electrochemical degradation process of metal. It can be caused by various corrosion factors of atmospheric component, weather, and air pollutants. Moisture, particles of sea salts, and sulfur dioxide are major factors in atmospheric corrosion. Galvanizing coating is one of the most efficient ways to protect iron from corrosion by zinc plating on the surface of the iron. Galvanized steels are being widely used in automobiles, building structures, roofing, and other industrial structures due to their high corrosion resistance compared to bare iron. Atmospheric corrosion of galvanized steel has shown complex corrosion behavior depending on coating process, coating thickness,
atmospheric environment, and air pollutants. In addition, different types and kinds of corrosion products can be produced depending on the environment. Lifespan of galvanized steels is also affected by the environment. Therefore, the objective of this study was to determine the corrosion behavior of galvanized steel under atmospheric corrosion at six locations in Korea. When the exposure time was increased, content of zinc from GA surface decreased while contents of iron and oxygen tended to increase. On the other hand, content of iron was constant even after 36 months of exposure of GI.
KEYWORDs : Galvanized steel, Outdoor exposure test, Atmospheric corrosion, Surface appearance
AUTHORs : 김기태·김영식†

Page : 225 - 230 DOWNLOAD
염화물 수용액에서 자작나무 수액을 이용한 철강의 부식 억제
The effects of birch sap, a possible natural corrosion inhibitor, on the corrosion behavior of steel in chloride solution were investigated. The corrosion rate was significantly reduced by the addition of 1~5 mL of birch sap to 500 mL of 3wt% NaCl or 3wt% CaCl2 solution. A remarkable increase in the pitting potential in NaCl solution was observed by the addition of birch sap although it was almost constant in CaCl2 solution. The corrosion rate of steel in both NaCl and CaCl2 birch sap solution without addition of water was higher compared to that of aqueous solution without birch sap as the pH of the birch sap was 4.0. The presence of organic compounds like, fructose, galactose, glucose, and palmitic acid in the birch sap are thought to be adsorbed effectively on the metal surface, which provided corrosion protection. However, the inorganic elements including Na, Ca, K, Mg, Mn, S, etc.
present in the birch sap exhibited no role in corrosion inhibition.
KEYWORDs : Steel, Chloride solution, Natural inhibitor, Birch Sap
AUTHORs : 박태준·김기애·이지이·장희진†

Page : 218 - 224 DOWNLOAD
니켈기 합금 Alloy 617의 950 ̊C 대기/헬륨 분위기에서 산화거동 고찰
Alloy 617 is a candidate Ni-based superalloy for intermediate heat exchanger (IHX) of a high-temperature gas reactor (VHTR), because of its good creep strength and corrosion resistance at high temperature. Small amount of impurities such as H2O, H2, CO and CH4 are introduced inevitably in helium, as a coolant during operation of a VHTR. Reactions of material and impurities are accelerated with increase of temperature to 950 oC of operating temperature of a VHTR, leading to material corrosion aggravation. In this circumstance, high-temperature corrosion tests were performed at 950 oC in air and impure helium environments, up to 250 hours in this study. Oxidation rate of 950 oC in an air environment was higher than that of impure
helium, explained by difference in outer oxide morphology and microstructure as a function of oxygen partial pressure. An equiaxed Cr-rich surface oxide layer was formed in an air environment, and a columnar Cr-rich oxide was formed in an impure helium environment.
KEYWORDs : Alloy 617, Impure helium, Oxidation, Corrosion, Microstructure
AUTHORs : 정수진·이경근·김동진†

Page : 211 - 217 DOWNLOAD
Corrosion Performance of Cu Bonded Grounding-Electrode by Accelerated Corrosion Test
Natural degradation of grounding-electrode in soil environment should be monitored for several decades to predict the lifetime of the grounding electrode for efficient application and management. However, long-term studies for such electrodes have many practical limitations. The conventional accelerated corrosion test is unsuitable for such studies because simulated soil corrosion process cannot represent the actual soil environment. A preliminary experiment of accelerated corrosion test was conducted using existing test standards. The accelerated corrosion test that reflects the actual soil environment has been developed to evaluate corrosion performances of grounding-electrodes in a short period. Several test conditions with different chamber temperatures and salt spray were used to imitate actual field conditions based on ASTM B162, ASTM B117, and ISO 14993 standards. Accelerated degradation specimens of copper-bonded electrodes were made by the facile method and their corrosion performances were investigated. Their corrosion rates were calculated to 0.042 μm/day, 0.316 μm/day, and 0.11 μm/day, respectively. These results indicate that accelerated deterioration of grounding materials can
be determined in a short period by using cyclic test condition with salt spray temperature of 50 °C.
KEYWORDs : Corrosion accelerated test, Soil corrosion, Grounding rods, Copper-bonded electrode, Life cycle estimation
AUTHORs : Sun Kyu Choi† and Kyung Chul Kim

Page : 203 - 210 DOWNLOAD
Study of Chloride Corrosion Organic Inhibitors in Alkaline Pore Solution
This paper compares the inhibition properties of aspartic and lactic acid salts with nitrite ions and their effect on critical chloride concentration. The tests were carried employing carbon steel specimens in saturated lime solution with varying pH in the range between13 to 13.6. The critical chloride concentration was estimated through multiple specimen potentiostatic tests at potentials in the usual range for passive rebar in the alkaline concrete of atmospheric structures. During tests, chloride salt
was added every 48 h until all the specimens showed localized attacks. The cumulative distribution curves, i.e. the number of corroded specimens as a function of the chlorides concentration was obtained. Furthermore, IR spectra were recorded for the evaluation of the presence of the organic inhibitors on the passivity film. The results confirmed the inhibitory effect of 0.1M aspartate comparable with nitrite ions, at a similar concentration. Addition of calcium lactate did not result in an increase in
the critical chloride concentration. However, the formation of a massive scale containing the substance that could reduce the corrosion propagation was observed.
KEYWORDs : Rebar, Localized corrosion, Corrosion inhibitors, Chloride, Pore solution
AUTHORs : M. Cabrini†, S. Lorenzi, T. Pastore, and S. Pellegrini

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