한국부식방식학회

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아황산나트륨을 이용한 스프링클러 동배관 공식 부식 방지
Inhibition of pitting corrosion of the copper sprinkler tubes by removing dissolved oxygen in water with sodium sulfite was studied on the wet sprinkler systems operated in 258 household sites. First, air in the sprinkler tubing was removed by vacuum pumping. The tube was then filled with sodium sulfite dissolved in water. Sodium sulfite was very effective in maintaining a very low dissolved oxygen concentration in water in the sprinkler tube for the observation period of six months. Water leakage from the copper sprinkler tube was reduced significantly by using sodium sulfite. Both pitting corrosion process and pitting corrosion inhibition mechanism were investigated by examining microscopical and structural aspects of corrosion pits formed in failed copper sprinkler tube. Pitting corrosion was caused by pressurized air as well as sediments such as sand particles in copper tubes through oxygen concentration cells. It was confirmed microscopically that growth of corrosion pits was stopped by reducing dissolved oxygen concentration to a very level by using sodium sulfite.
KEYWORDs : pitting corrosion, copper sprinkler tube, sodium sulfite, corrosion inhibition, SEM
AUTHORs : 서상희†·서영준·권혁상

Page : 257 - 264 DOWNLOAD
Oxide Nanolayers Grown on New Ternary Ti Based Alloy Surface by Galvanic Anodizing–Characteristics and Anticorrosive Properties
Film of new Ti-15Zr-5Nb alloy formed during galvanic anodizing in orthophosphoric acid solution was characterized by optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman micro-spectroscopy. Its anticorrosive properties were determined by electrochemical
techniques. The film had a layer with nanotube-like porosity with diameters in 500-1000 nm range. The nano layer contained significant amounts of P and O as well as alloying element. Additionally, Raman micro-spectroscopy identified oxygen as oxygen ion in TiO2 anatase and phosphorous as P2O7 4- ion in phosphotitanate compound. All potentiodynamic polarization curves in artificial Carter-Brugirard saliva with pH values (pH= 3.96, 7.84, and 9.11) depending on the addition of 0.05M NaF revealed nobler behavior of anodized alloy and higher polarization resistance indicating the film is thicker and more compact nanolayer. Lower corrosion rates of the anodized alloy reduced toxicity due to less released ions into saliva. Bigger
curvature radii in Nyquist plot and higher phase angle in Bode plot for the anodized alloy ascertain a thicker, more protective, insulating nanolayer existing on the anodized alloy. Additionally, ESI results indicate anodized film consists of an inner, compact, barrier, layer and an outer, less protective, porous layer.
KEYWORDs : Ti-15Zr-5Nb alloy, carter-brugirard saliva, galvanic anodisation, nanotubes, corrosion behaviour, surface analyses
AUTHORs : J. M. Calderon Moreno†, P. Drob, C. Vasilescu, S. I. Drob, M. Popa, and E. Vasilescu

Page : 247 - 256 DOWNLOAD
Use of Hydrazine for Pitting Corrosion Inhibition of Copper Sprinkler Tubes:Reaction of Hydrazine with Corrosion By-Products
The feasibility of using hydrazine for inhibiting pitting corrosion in copper sprinkler tubes was investigated by examining microscopical and structural evolution of corrosion by-products with SEM, EDS, and XRD. Hydrazine removed dissolved oxygen and reduced CuO and Cu2O as well. The stable phase was changed from CuO to Cu2O or Cu depending on hydrazine concentration. Hydrazine concentration
of 500 ppm could convert all CuO corrosion by-products to Cu2O. In a tightly sealed acryl tube filled with aqueous solution of 500 ppm hydrazine, octahedral Cu2O particles were formed while plate-like structures with high concentration of Cu, O, N and C were formed near a corrosion pit. The inside structure of a corrosion pit was not altered by hydrazine aqueous solution. Uniform corrosion of copper was almost completely stopped in aqueous solution of 500 ppm hydrazine. Corrosion potential of a copper plate was linearly dependent on log (hydrazine concentration). The concept of stopping pitting corrosion reaction by suppressing oxygen reduction reaction could be verified by applying this method to a reasonable number of real sprinkler systems before full-scale application.
KEYWORDs : pitting corrosion inhibition, hydrazine, SEM, EDS, XRD
AUTHORs : Sang Hee Suh†, Sohee Kim, and Youngjoon Suh

Page : 241 - 246 DOWNLOAD
Atmospheric Corrosion of Hot Dip Zinc Coated Steel in Coastal and Rural Areas of Vietnam
The comparative results of corrosion testing in humid tropical atmosphere in rural and coastal areas for hot dipped zinc coatings are presented below. The test was conducted in outdoor conditions over a period of five years. The mass loss and other performance characteristics of two types of zinc coatings were evaluated,
analysed and discussed in relation to the climatic and environmental parameters. The corrosion rates of the coatings exposed to coastal conditions were about three times higher than the corrosion rates appreciated in rural conditions. The data demonstrates that the corrosion process obeys an equation of the form M=Atn,
where M is the loss of metal and t is the time of exposure. A and n are constants which values depend on the environmental characteristics and the physicochemical behavior of the corrosion products respectively. Corrosion is strongly influenced by atmospheric time of wetness (TOW) and airborne salinity. The nature and composition of corrosion products are also considered. Simonkolleite, a major crystalline phase, was found in the zinc corrosion products exposed to coastal conditions, while zinc hydroxide and zinc hydrosulfate are easily found in rural settings.
KEYWORDs : zinc coating, corrosion rate, corrosion product, airborne salinity
AUTHORs : Nguyen Nhi Tru†, Le Khac Duyen, and Tran Mai Han

Page : 235 - 240 DOWNLOAD
Regional Cathodic Protection Design of a Natural Gas Distribution Station
Regional cathodic protection has significant impact on pipeline integrity management. After risk analyses of a newly built gas distribution station constructed in an area with large dwelling density, risk score was high because of potential threat caused by galvanic corrosion. Except reinforced steel in concrete, there
are four kinds of metal buried under earth: carbon steel, galvanized flat steel, zinc rod and graphite module. To protect buried pipeline from external corrosion, design and construction of regional cathodic protection was proposed. Current density was measured with potential using potential dynamic test and boundary element
method (BEM) was used to calculate current requirement and optimize best anode placement during design. From our calculation on the potential, optimized conditions for this area were that an applied current was 3A and anode was placed at 40 meters deep from the soil surface. It results in potential range between -1.128 VCSE and -0.863 VCSE, meeting the -0.85 VCSE criterion and the -1.2 VCSE criterion that no potential was more negative than -1.2 VCSE to cause hydrogen evolution at defects in coating of the pipeline.
KEYWORDs : regional cathodic protection, galvanic corrosion, BEM method, anodic interference
AUTHORs : Hu Yabo†, Zhang Feng, and Zhao Jun

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Reference Electrode for Monitoring Cathodic Protection Potential
Reference electrodes are generally implemented for the purpose of monitoring the cathodic protection potentials of buried or immersed metallic structures. In the market, many types of reference electrodes are available for this purpose, such as saturated calomel, silver/silver chloride and copper/copper sulfate. These electrodes contain a porous ceramic junction plate situated in the cylindrical body bottom to permit ionic flux between the internal electrolyte (of the reference electrode) and the external electrolyte. In this work, the copper/copper sulfate reference electrode was modified by replacing the porous ceramic junction plate for a metallic platinum wire. The main purpose of this modification was to avoid the ion copper transport from coming from the inner reference electrode solution into the surrounding electrolyte, and to mitigate the copper plating on the coupon surfaces. Lab tests were performed in order to compare the performance of the two mentioned
reference electrodes. We verified that the experimental errors associated with the measurements conducted with developed reference electrode would be negligible, as the platinum surface area exposed to the surrounding electrolyte and/or to the reference electrolyte are maintained as small as possible.
KEYWORDs : reference electrode, cathodic protection, corrosion
AUTHORs : Z. Panossian† and S. E. Abud

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