-
Page : 122 - 130
DOWNLOAD
- 지역난방 열수송관 국부 부식 파손 분석
- In this study, a corrosion failure analysis of a heat transport pipe was conducted, as the result of a pinhole leak. Interestingly, the corrosion damage occurred externally in the pipeline, resulting in severe thickness reduction near the seam line. Also, while a stable magnetite protective film formed on the inner surface, the manganese oxide formation occurred only on the outer surface. The interior and exterior of the pipe were composed of ferrite and pearlite. The large manganese sulfide and alumina inclusions were found near the seam line. In addition, the manganese sulfide inclusions resulted in grooving corrosion, which progressed in the seam line leading to the reduction in the thickness, followed by the exposure of the alumina in
the matrix to the outer surface. To note, the corrosion was accelerated by pits generated from the boundaries separating the inclusions from the matrix, which resulted in pinhole leaks and water loss. - KEYWORDs : District heating, Heat transport pipe, Localized corrosion, Inclusion
- AUTHORs : 김유섭 ? 채호병 ? 김우철 ? 정준철 ? 김희산 ? 김정구 ? 이수열†
|
-
Page : 131 - 137
DOWNLOAD
- ToSPACE 프로그램을 이용한 FAC 해석결과와 실험결과 비교
- A number of piping components in the secondary system of nuclear power plants (NPPs) are exposed to aging mechanisms, such as flow-accelerated corrosion (FAC), cavitation, flashing, solid particle erosion, and liquid droplet impingement erosion. Those mechanisms may lead to thinning, leaking, or rupture of the components. Due to the pipe ruptures caused by wall thinning in Surry unit 2 in the USA in 1986 and Mihama unit 3 in Japan in 1994, pipe wall thinning management has emerged as one of the most important issues in the nuclear industry. To manage pipe wall thinning, a foreign program has been utilized for NPPs in Korea since 1996. As our experience and knowledge of pipe wall thinning management have accumulated, our program needs to reflect our experience, requests from users, and the result of recent experiments using Flow Accelerated Corrosion Testing System (FACTS). FACTS is the empirical experimental facility developed by Korea Atomic Energy Research Institute (KAERI) for tests. Accordingly, KEPCO-E&C developed a 3D-based pipe wall thinning management program called ToSPACE in 2016. This paper describes a comparison between the FAC analysis results using ToSPACE and the experimental results using FACTS to verify their applicability to pipe wall thinning management in NPPs.
- KEYWORDs : ToSPACE, FACTS, Pipe Wall Thinning, Flow-Accelerated Corrosion (FAC), FAC Experiment
- AUTHORs : 황경모† ? 윤훈 ? 서혁기 ? 정의제 ? 김경모 ? 김동진
|
-
Page : 138 - 145
DOWNLOAD
- Alloy 600의 결정립계 산화에 대한 표면 변형의 영향
- Immersion tests of Alloy 600 were conducted in simulated primary water environments of a pressurized water reactor at 325 °C for 10, 100, and 1000 h to obtain insight into effects of surface deformation on internal and intergranular (IG) oxidation behavior through precise characterization using various microscopic
equipment. Oxidized samples after immersion tests were covered with polyhedral and filamentous oxides. It was found that oxides were abundant in mechanically ground (MG) samples the most. The number density of surface oxides increased with time irrespective of the method of surface finish. IG oxidation occurred in mechanically polished (MP) and chemically polished (CP) samples with thin internal oxidation layers. However, IG oxidation was suppressed with relatively thick internal oxidation layers in MG samples compared to MP and CP samples, suggesting that MG treatment could increase resistance to primary water stress corrosion cracking (PWSCC) from the standpoint of IG oxidation. As a result, appropriate surface treatment for Alloy 600 could prevent oxygen diffusion into grain boundaries, inhibit IG oxidation, and finally induce its high PWSCC resistance. - KEYWORDs : Alloy 600, PWSCC, Surface deformation, Immersion test, Intergranular oxidation
- AUTHORs : 하동욱 ? 임연수† ? 김동진
|
-
Page : 146 - 155
DOWNLOAD
- F316 오스테나이트 스테인리스강의 상변태 및 입계부식저항성에 미치는 입열의 영향
- To elucidate the effect of heat inputs on phase transformation and resistance to intergranular corrosion of F316 austenitic stainless steel (ASS), thermodynamic calculations of each phase and time-temperature-transformation diagram were conducted using JMaPro simulation software, oxalic acid etch test, double-loop electrochemical potentiokinetic reactivation test (DL-EPR), field emission scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy analyses of Cr carbide (Cr23C6), austenite phase and ferrite phase. F316 ASS containing a relatively low C content of 0.043 wt% showed a slightly sensitized microstructure (acceptably dual structure) due to a small amount of Cr carbide precipitated at heat affected zone irrespective of heat inputs. Based on results of DL-EPR test, although heat input was increased, the ratio of Ir to Ia was only increased very slightly due to a slight sensitization. Therefore, heat inputs have
little influences on resistance to intergranular corrosion of F316 austenitic stainless steel containing 0.043 wt% C. - KEYWORDs : Stainless steel, DL-EPR, Heat input, δ-ferrite, Cr-carbide
- AUTHORs : 정규석† ? 이인성 ? 김순태
|
-
Page : 156 - 162
DOWNLOAD
- 타이타늄 합금에서 산소발생전위 지연이 부동태 피막 특성과 국부부식 저항성에 미치는 영향
- The objective of this study was to investigate delayed oxygen evolution and localized corrosion resistance of titanium alloys by performing potentiodynamic polarization, potentiostatic polarization, and Mott-Schottky measurements. Delayed oxygen evolution was compared among titanium alloys, 316 stainless steel, and platinum. Difference in delayed oxygen evolution between titanium alloys and other metals was attributed to specific surface characteristic of each metal. Delayed oxygen evolution of titanium alloys resulted from the predominant process of ionic conduction over electronic conduction. The effect of oxygen evolution on localized corrosion of titanium alloys was investigated using electrochemical critical localized corrosion temperature (E-CLCT) technique. Mott-Schottky measurement was performed to clarify the difference in film properties between titanium alloys and stainless steels. Titanium alloys were found to have much lower donor density than
stainless steels by 1/28. These results indicate that delayed oxygen evolution has little influence on the concreteness of passive film and the resistance to localized corrosion of titanium alloys. - KEYWORDs : Corrosion, Oxygen evolution, Titanium, Polarization, Mott-Schottky
- AUTHORs : 오유수 ? 서동일 ? 이재봉†
|
-
Page : 163 - 163
DOWNLOAD
- Erratum to: 스프링클러 구리배관의 공식 파손 억제
- Erratum to: CORROSION SCIENCE AND TECHNOLOGY, Vol. 19, No. 2(2020), pp. 89~99
DOI: https://doi.org/10.14773/cst.2020.19.2.89
The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting
the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray
photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion
pit. - KEYWORDs : Copper sprinkler tube, Pitting corrosion inhibition, Nitrogen bubbling, Sodium sulfite, Benzotriazole
- AUTHORs : 서상희†, 서영준, 이종혁, 권혁상
|
-
Page : 163 - 173
DOWNLOAD
- 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†
|
-
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
|
-
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 : 196 - 202
DOWNLOAD
- 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†
|
