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Erratum to: 해수 환경에서 Al5083-H321 알루미늄 합금의 침식부식 손상에 미치는 유속의 영향과 손상 메카니즘
Erratum to: CORROSION SCIENCE AND TECHNOLOGY, Vol. 19, No. 3(2020), pp. 115~121
DOI: 10.14773/cst.2020.19.3.115

In this study, erosion tests and erosion-corrosion tests of Al5083-H321 aluminum alloy were conducted at various flow rates in seawater. The erosion tests were conducted at a flow rate of 0 to 20 m/s, and erosion-corrosion tests were performed by potentiodynamic polarization method at the same flow rate. Characteristic evaluation after the erosion test was conducted by surface analysis. Characteristic evaluation after the erosion-corrosion test was performed by Tafel extrapolation and surface analysis. The results of the surface analysis after the erosion test showed that surface damage tended to increase as the flow rate increased. In particular, intermetallic particles were separated due to the breakdown of the oxide film at
10 m/s or more. In the erosion-corrosion test, the corrosion current density increased as the flow rate increased. Additionally, the surface analysis showed that surface damage occurred in a vortex shape and the width of the surface damage tended to increase as the flow rate increased. Moreover, damage at 0 m/s, proceeded in a depth direction due to the growth of pitting corrosion, and the damaged area tended to increase due to acceleration of the intermetallic particle loss by the fluid impact.
KEYWORDs : Aluminum alloy, Erosion corrosion, Flow rate, Potentiodynamic polarzation test, Seawater
AUTHORs : 김영복 ･ 김성종†

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해수분위기에서 스테인리스강 배관 소켓 용접부의 선택적 부식
Stainless steel has excellent corrosion resistance. The drawback is that pitting occurs easily due to the concentration of chloride. In addition, corrosion of socket weld, which is structurally and chemically weaker than the other components of the pipe, occurs rapidly. Since these two phenomena overlap, pinhole leakage occurs
frequently in the seawater pipe socket welds made of stainless steel at the power plants. To analyze this specific corrosion, a metallurgical analysis of the stainless steel socket welds, where the actual corrosion occurred during the power plant operation, was performed. The micro-structure and chemical composition of each socket weld were analyzed. In addition, selective corrosion of the specific micro-structure in a mixed dendrite structure comprising γ-austenite (gamma-phase iron) and δ-ferrite (iron at high temperature) was investigated based on the characteristic micro-morphology and chemical composition of the corroded area. Finally, the different corrosion stages and characteristics of socket weld corrosion are summarized.
KEYWORDs : Selective corrosion, Stainless pipe, γ-austenite, δ-ferrite, Seawater
AUTHORs : 부명환 ･ 이장욱 ･ 이종훈†

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매설 배관 피복 결함 탐상 정확도에 미치는 인접 정류기 및 접지 구리망 간섭의 영향
The external corrosion of buried piping can be controlled using both coating and cathodic protection. Several
factors are involved in the damage and deterioration of the coating on pipes. There are many detection
methods for coating defects on pipes and the direct current voltage gradient (DCVG) method is one of
the most powerful methods. However, the detection reliability of DCVG can be affected by interferences
such as stray current, metal objects connected to rectifiers, and copper grids. Therefore, this study focused
on the interference effects of rectifiers and a copper grid on the reliability of coating flaw detection. As
the length of the interference pipe connected to the rectifier increased, the reliability decreased. In contrast,
as the distance between the pipe and the copper grid increased, the reliability of the coating flaw detection
increased. The detection results produced by the DCVG method were discussed using current and potential
simulations for a pipe with a rectifier and copper grid interference in the soil.
KEYWORDs : Buried pipe, Coating flaw detection, Interference, Rectifier, Copper grid
AUTHORs : 김민기 ･ 임부택 ･ 김기태 ･ 장현영 ･ 박흥배 ･ 김영식†

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슈퍼 오스테나이트계 스테인리스강의 시그마상 특성에 따른 부식거동 분석
The corrosion behavior of super austenitic stainless steel was studied by examining the characteristics of
the sigma phase formed in the steel. A range of experimental and analytical methods was employed, including
potentiodynamic polarization tests, critical pitting temperature tests, transmission electron microscopy, and
energy-dispersive spectroscopy. Three steel samples with different sigma phase levels were obtained by
intentionally adjusting the manufacturing process. The results showed that the corrosion resistance of the
samples was strongly dependent upon the size and distribution of the sigma phase precipitated in the samples.
The larger the size of the sigma phase, the higher the Mo content in the sigma phase and the higher the
depletion level of Mo at the interface between the matrix/sigma phase, the more samples with a coarse-sized
sigma phase were susceptible to localized pitting corrosion at the interface. These results suggest that various
manufacturing processes, such as welding and the post-heat treatment of the steel, should be optimized so
that both the size and fraction of the sigma phase precipitated in the steel are small to improve the resistance
to localized corrosion.
KEYWORDs : Pitting corrosion, Sigma phase, Super austenitic stainless steel, Electrochemical corrosion, Molybdenum depletion
AUTHORs : 김예은 ･ 박진성 ･ 조동민 ･ 홍승갑 ･ 김성진†

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맨홀에 설치된 지역난방 열공급관 에어벤트의 전단부 파손 원인 규명
The air vent connected to a heat supply pipeline in the district heating system has been used to eliminate the existing air in the pipe, which has a detrimental effect on corrosion durability and heat efficiency. Recently, the air vent installed under a manhole for 22 years was corroded and several pinholes were detected in the front-end of the air vent. To identify the cause of the failure, thickness reduction, corrosion products, and water quality were examined. The corrosion damage was significant at the outside of the front-end of the air vent where the insulator was covered. While a thin oxide layer was formed in the interior of the tube, the coarse and porous corrosion products consisting of magnetite and hematite were found externally. Water flowing into the thermal insulator was absorbed by the insulator following hydrolysis. The hydrolyzed insulator ejected the corrosion factors such as Cl-, SO4 2-, and NH4+. The findings suggest that the corrosion under insulation due to rain water is the main cause of the underlying failure in the air vent.
KEYWORDs : District heating, Air vent, Corrosion, Manhole, Rain water
AUTHORs : 조정민 ･ 채호병 ･ 김희산 ･ 김정구 ･ 김우철 ･ 정준철 ･ 이수열†

Page : 189 - 195 DOWNLOAD
지역난방수 공급관 에어벤트 부식 파손 분석
Two air vents situated on a heat transport pipe in district heating system were exposed to the same environment
for 10 years. However, one air vent was more corroded than the other. It also had a hole on the top of
the front-end pipe. Comparative analysis was performed for these air vents to identify the cause of corrosion
and establish countermeasures. Through experimental observation of the damaged part and analyses of powders
sampled from air vents, it was found that corrosion was initiated at the top of the front-end pipe. It then
spread to the bottom. Energy dispersive X-ray spectroscopy results showed that potassium and chlorine were
measured from the corroded product in the damaged air vent derived from rainwater and insulation, respectively.
The temperature of the damaged air vent was maintained at 75 ~ 120 °C by heating water. Rainwater-soaked
insulation around the front-end pipe had been hydrolyzed. Therefore, the damaged air vent was exposed
to an environment in which corrosion under insulation could be facilitated. In addition, ion chromatography
and inductively coupled plasma measurements indicated that the matrix of the damaged front-end pipe contained
a higher manganese content which might have promoted corrosion under insulation.
KEYWORDs : District heating system, Heat transport pipe, Air vent, Rainwater, Corrosion under insulation
AUTHORs : 이형준 ･ 채호병 ･ 조정민 ･ 김우철 ･ 정준철 ･ 김희산 ･ 김정구 ･ 이수열†

Page : 174 - 188 DOWNLOAD
Comprehensive Empirical Equation for Assessing Atmospheric Corrosion Progression of Steel Considering Environmental Parameters
Atmospheric corrosion is a natural surface degradation process of metal due to changes in environmental
parameters in the surrounding atmosphere. It is very sensitive to environmental parameters such as temperature,
relative humidity, sulphur dioxide, and chloride, making it a major global economic challenge. Existing
forecasting empirical corrosion models including the ISO standard are based on statistical analysis of experimental
studies without considering the behavior of atmospheric parameters. The present study proposes a reliable
global empirical model for estimating short and long-term atmospheric corrosion rates based on environmental
parameters and corrosion mechanisms obtained from a parametric study. Repercussion of atmospheric corrosion
rate due to individual and combined influences of environmental parameters specifies their importance in
the estimation. New global empirical coefficients obtained for environmental parameters are statistically
established (R2 =0.998) with 95% confidence limit. They are validated using experimental datasets of existing
studies observed at 88 different continental locations. The current proposed model can predict atmospheric
corrosion by means of corrosion formation mechanisms influenced by combined effects of environmental
parameters, further abating applicability limitations of location and time.
KEYWORDs : Atmospheric corrosion, Empirical model, Corrosion rate, Prediction, Environmental parameters
AUTHORs : Arjun Sil† and Vanapalli Naveen Kumar

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Effects of Ultrasonic Amplitude on Electrochemical Properties During Cavitation of Carbon Steel in 3.5% NaCl Solution
Cavitation corrosion in many industrial plants has recently become a serious issue. Cavitation corrosion has generally been investigated using a vibratory method based on ASTM G32 standard, and the test can be divided into direct cavitation and indirect cavitation. Cavitation corrosion test uses the vibration frequency of the horn of 20 kHz with constant peak-to-peak displacement amplitude. In this work, the peak-to-peak amplitude was controlled from 15 μm to 85 μm, and electrochemical measurements were obtained during indirect cavitation. The relationship between cavitation corrosion rate and electrochemical properties was discussed. Corrosion steps of carbon steel at the initial stage under cavitation condition in 3.5 % NaCl
can be proposed. When the cavitation strength is relatively low, corrosion of the steel is more affected by the electrochemical process than by the mechanical process; but when the cavitation strength is relatively high, corrosion of the steel is affected more by the mechanical process than by the electrochemical process.
This work confirmed that the critical ultrasonic amplitude of 0.42 %C carbon steel is 53.8 μm, and when the amplitude is less than 53.8 μm, the corrosion effect during the cavitation corrosion process is higher than the mechanical effect.
KEYWORDs : Carbon steel, Cavitation corrosion test, Cavitation corrosion rate, Electrochemical properties, Critical ultrasonic amplitude
AUTHORs : I. J. Jang, K. T. Kim, Y. R. Yoo, and Y. S. Kim†

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