한국부식방식학회

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원전 2차계통수 모사 환경에서 용접배관 감육 특성에 미치는 재료 및 유속의 영향
The pipelines and equipments are degraded by flow-accelerated corrosion (FAC), and a large-scale test facility was constructed for simulating the FAC phenomena in secondary coolant environment for PWR type nuclear power plants. Using this facility, the FAC test was performed on a weld pipe (carbon steel and low alloy steel) under the high velocity flow conditions (> 10 m/s). Wall thickness was measured by high temperature ultrasonic monitoring systems (four-channel buffer rod type and waveguide type) during the test period and the room temperature manual ultrasonic method before and after the test period. This work deals with the complex effects of flow velocity on wall thinning of a weld pipe, and the test results
showed that higher flow velocity induced different increments in the wall thinning rate for the carbon steel and low alloy steel pipe.
KEYWORDs : FAC, wall thinning, ultrasonic measurement, carbon steel, low alloy steel
AUTHORs : 김경모†·정용무·이은희·이종연·오세범·김동진

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음극 인가전위 하에서 type 2205과 type 316L의 수소취성 저항성
2205 duplex stainless steels have been used for the construction of the marine environment, because of their excellent corrosion resistance and high strength. However, the resistance to hydrogen embrittlement (HE) may be less than that of 316L austenitic stainless steel. The reason why 316L stainless steels have
better resistance to HE is associated with crystal structure (FCC, face centered cubic) and the higher stacking faults energy than 2205 duplex stainless steels. Furthermore 2205 stainless steels with or without tungsten were also examined in terms of HE. 2205 stainless steels containing tungsten is less resistible to HE. It
is because dislocation tangle was formed in 2205 duplex stainless steels. Slow strain-rate tensile test (SSRT) was conducted to measure the resistance to HE under the cathodic applied potential. Hydrogen embrittlement index (HEI) was used to evaluate HE resistance through the quantitative calculation.
KEYWORDs : hydrogen embrittlement, 2205 duplex, 316L, SSRT, cathodic potential
AUTHORs : 서동일·이재봉†

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Intergranular Corrosion Mechanism of Slightly-sensitized and UNSM-treated 316L Stainless Steel
316L stainless steels have been widely used in many engineering fields, because of their high corrosion resistance and good mechanical properties. However, welding or aging treatment may induce intergranular corrosion and stress corrosion cracking etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled by methods such as the lowering of carbon content, solution heat treatment. This work focused on the intergranular corrosion mechanism of slightly-sensitized and Ultrasonic Nano-crystal Surface Modification (UNSM)-treated 316L stainless steel. Samples were sensitized for 1, 5, and 48 hours at 650 ℃ in N2 gas atmosphere. Subsequently UNSM
treatments were carried out on the surface of the samples. The results were discussed on the basis of the sensitization by chromium carbide and carbon segregation, the residual stress and grain refinement. Even though chromium carbide was not precipitated, the intergranular corrosion rate of 316L stainless steel was drastically increased with aging time, and it was confirmed that the increased intergranular corrosion rate of slightly-sensitized (not carbide formed) 316L stainless steel was due to the carbon segregation along the grain boundaries. However, UNSM treatment improved the intergranular corrosion resistance of aged
stainless steels, and its improvement was due to the reduction of carbon segregation and the grain refinement of the outer surface, including the introduction of compressive residual stress.
KEYWORDs : 316L stainless steel, Intergranular corrosion, Sensitization, UNSM, Carbon segregation,
AUTHORs : J. H. Lee, K. T. Kim, Y. S. Pyoun and Y. S. Kim†

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An Electrochemical Method to Predict Corrosion Rates in Soils
Linear polarization resistance (LPR) testing of soils has been used extensively by a number of water utilities across Australia for many years now to determine the condition of buried ferrous water mains. The LPR test itself is a relatively simple, inexpensive test that serves as a substitute for actual exhumation and physical
inspection of buried water mains to determine corrosion losses. LPR testing results (and the corresponding pit depth estimates) in combination with proprietary pipe failure algorithms can provideauseful predictive tool in determiningthe current and future conditions of an asset1). Anumber of LPR tests have been developed
on soil by various researchers over the years1), but few have gained widespread commercial use, partly due to the difficulty in replicating the results.
This author developed an electrochemical cell that was suitable for LPR soil testing and utilized this cell to test a series of soil samples obtained through an extensive program of field exhumations. The objective of this testing was to examine the relationship between short-term electrochemical testing and long-term in-situ corrosion of buried water mains, utilizing an LPR test that could be robustly replicated. Forty-one soil samples and related corrosion data were obtained from ad hoc condition assessments of buried water mains located throughout the Hunter
region of New South Wales, Australia. Each sample was subjected to the electrochemical test developed by the author, and the resulting polarization data were compared with long-term pitting data obtained from each water main. The results of this testing program enabled the author to undertake a comprehensive review of the LPR technique as it is applied to soils and to examine whether correlations can be made between LPR testing results and long-term field
corrosion.
KEYWORDs : electrochemistry, corrosion, LPR, long-term prediction, cast iron
AUTHORs : M. R Dafter†

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Self-healing Anticorrosion Coatings for Gas Pipelines and Storage Tanks
In the present study, chitosan based self-healing anticorrosion coatings were prepared by layer by layer (lbl) addition of chitosan (Ch) and polyvinyl butyral (PVB) on mild carbon steel substrate. Chitosan coatings exhibited enhanced coating stability and corrosion resistance in aggressive environments by the application
of a PVB top layer. Chitosan layer in the lbl coatings have been modified by using glutaraldehyde (Glu) and silica (SiO2). Performance of different coatings was tested using electrochemical impedance spectroscopy and immersion test. The best anticorrosion performance was observed in case of 10 % Ch_SiO2_PVB coatings,
which withstand immersion test over 25 days in 0.5 M salt solution without visible corrosion. 10 % Ch_SiO2 coatings without the PVB top layer didn’t last more than 3days. Application of PVB top layer sealed the defects in the chitosan pre-layer and improved its hydrophobic nature as well. Raman spectra and SEM of steel surfaces after corrosion study and removal of PVB_Ch/Glu_PVB coatings showed a passive layer of iron oxide, attributing to the self-healing nature of these coatings. Conducting particle like graphene reinforcement of chitosan in the lbl coatings enhanced corrosion resistance of chitosan coatings.
KEYWORDs : self-healing, chitosan, glutaraldehyde, silica, anticorrosion, layer by layer coatings
AUTHORs : G. E. Luckachan and V. Mittal†

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Study of Hot Salt Stress Corrosion Crack Initiation of Alloy IMI 834 by using DC Potential Drop Method
DC potential drop technique was employed during the slow strain rate tests to study the hot salt stress corrosion crack (HSSCC) initiation at 300 and 400 °C. Threshold stresses for HSSCC initiation were found to about 88 % of the yield strength at both temperatures, but the time from crack initiation to final failure (Δtscc) decreased significantly with temperature, which reflects larger tendency for brittle fracture and secondary cracking. The brittle fracture features consisted of transgranular cracking through the primary α grain and discontinuous faceted cracking through the transformed β grains.
KEYWORDs : titanium, stress corrosion cracking, hydrogen, fractography
AUTHORs : Mangesh D. Pustode†, Bhupendra Dewangan, V. S. Raja, Neeta Paulose and Narendra Babu

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