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Page : 325 - 330 DOWNLOAD
원전 2차계통의 수화학 변화가 배관감육에 미치는 영향 분석
Pipe wall-thinning by flow-accelerated corrosion (FAC) is a significant and costly damage of secondary system piping in nuclear power plants (NPPs). All NPPs have their management programs to ensure pipe integrity from wall-thinning. This study analyzed the pipe wall-thinning caused by changing the amine, which is used for adjusting the water chemistry in the secondary system of NPPs. The pH change was
analyzed according to the addition of amine. Then, the wear rate calculated in two different amines was compared at the steam cycle in NPPs. As a result, increasing the pH at operating temperature (Hot pH) can reduce the rate of FAC damage significantly. Wall-thinning is affected by amine characteristics depending on temperature and quality of water.
KEYWORDs : flow-accelerated corrosion, wall-thinning, water chemistry
AUTHORs : 윤훈·황경모·문승재†

Page : 313 - 324 DOWNLOAD
시효열처리 및 UNSM 처리에 따른 316L 스테인리스강의 입계부식거동
Austenitic 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, stress corrosion cracking, pitting, etc. Since these types of corrosion are closely related to the formation of chromium carbide in grain boundaries, the alloys are controlled using methods such as lowering the carbon content, solution heat treatment, alloying of stabilization elements, and grain boundary engineering. This work focused on the effects of aging and UNSM (Ultrasonic Nano-crystal Surface Modification) on the intergranular corrosion of commercial 316L stainless steel and the results are discussed on the basis of the sensitization by chromium carbide formation and carbon segregation, residual stress, grain refinement, and grain boundary engineering.
KEYWORDs : 316L stainless steel, UNSM, Intergranular corrosion, Sensitization, Carbide formation, Carbon segregation, Residual stress, Grain refinement, Grain boundary engineering
AUTHORs : 이정희·김영식†

Page : 301 - 312 DOWNLOAD
Transmission Electron Microscopy Characterization of Early Pre-Transition Oxides Formed on ZIRLO TM
Corrosion of zirconium fuel cladding is known to limit the lifetime and reloading cycles of fuel in nuclear reactors. Oxide layers formed on ZIRLOTM cladding samples, after immersion for 300-hour and 50-day in a simulated primary water chemistry condition (360 oC and 20 MPa), were analyzed by using the scanning
transmission electron microscopy (STEM), in-situ transmission electron microscopy (in-situ TEM) with the focused ion beam (FIB) technique, and X-ray diffraction (XRD). Both samples (immersion for 300 hours and 50 days) revealed the presence of the ZrO sub-oxide phase at the metal/oxide interface and columnar grains developed perpendicularly to the metal/oxide interface. Voids and micro-cracks were also detected near the water/oxide interface, while relatively large lateral cracks were found just above the less advanced metal/oxide interface. Equiaxed grains were mainly observed near the water/oxide interface.
KEYWORDs : ZIRLO, oxide, pre-transition, primary water, in-situ transmissionelectron microscop
AUTHORs : Hoyeon Bae, Taeho Kim, Ji Hyun Kim and Chi Bum Bahn†

Page : 296 - 300 DOWNLOAD
Effect of Annealing Heat Treatment to Characteristics of AlDC8 (Al-Si-Cu) Alloy
ALDC8 (Al-Si-Cu) alloy has been often corroded with pattern of intergranular corrosion in corrosive environments. Thus, in order to improve its corrosion resistance, the effect of annealing heat treatment to corrosion resistance and hardness was investigated with parameters of heating temperatures such as 100 ℃, 200 ℃, 300 ℃, 400 ℃ and 500 ℃ for 1hr. The hardness was varied with annealing temperature and slightly decreased with annealing heat treatment. However, the relation between annealing temperature and hardness agreed not well each other. Corrosion potential was shifted to noble direction and corrosion current density was also decreased with increasing annealing temperature. Moreover, both AC impedance at 10 mHz and polarization resistance on the cyclic voltammogram curve were also increased with increasing annealing temperature. Furthermore, intergranular corrosion was somewhat observed in non heat treatment as well as annealing temperatures at 100 ℃, 200 ℃ and 300 ℃, while, intergranular corrosion was not nearly observed at annealing temperature of 400 ℃, 500 ℃. Consequently, it is considered that the annealing heat treatment of ALDC8 alloy may be an available method not only to inhibit its intergranular corrosion but also to improve its corrosion resistance.
KEYWORDs : intergranular corrosion, annealing heat treatment, cyclic voltammogram, AC impedance, corrosion current density
AUTHORs : Kyung Man Moon, Sung-Yul Lee, Myeong Hoon Lee, Tae-Sil Baek, and Jae-Hyun Jeong†

Page : 288 - 295 DOWNLOAD
Crevice Corrosion Study of Materials for Propulsion Applications in the Marine Environment
The present work addresses crevice and galvanic corrosion processes occurring at the cylinder head gasket/cylinder head interface and cylinder head gasket/cylinder liner interface of four-stroke medium-speed diesel engines for marine applications. The contact between these systems and the marine environment can promote formation of demanding corrosion conditions, therefore influencing the lifetime of the engine components. The electrochemical behavior of various metals and alloys used as head gasket materials (both ferrous alloys and copper alloys) was investigated. The efficacy of corrosion inhibitors was determined by comparing electrochemical behavior with and without inhibitors. In particular, crevice corrosion has been
investigated by electrochemical tests using an experimental set-up developed starting from the requirements of the ASTM G-192-08, with adaptation of the test to the conditions peculiar to this application. In addition to the crevice corrosion resistance, the possible problems of galvanic coupling, as well as corrosive reactivity, were evaluated using electrochemical tests, such as potentiodynamic measurements. It was possible to quantify, in several cases, the corrosion resistance of the various coupled materials, and in particular the resistance to crevice corrosion, providing a basis for the selection of materials for this specific application.
KEYWORDs : head gasket, crevice corrosion, galvanic corrosio
AUTHORs : F. Deflorian†, S. Rossi, M. Fedel, C. Zanella, D. Ambrosi, and E. Hlede

Page : 280 - 287 DOWNLOAD
Accelerated SCC Testing of Stainless Steels According to Corrosion Resistance Classes
The German Guidelines for stainless steel in buildings (Z.30.3-6) issued by the German Institute for Building Technology (DIBt) categorizevarious stainless steel grades into five corrosion resistance classes (CRCs). Only 21 frequently used grades are approved and assigned to these CRCs. To assign new or less commonly
used materials, a large program of outdoor exposure tests and laboratory tests is required. The present paper shows theresults of stress corrosion cracking (SCC) tests that can distinguish between different CRCs. Slow strain rate tests (SSRT) were performedin various media and at different temperatures. CRC IV could
be distinguished from CRC II and CRC III with a 31.3 % Cl- as MgCl2 solutionat 140 °C. CRC II and CRC III could be differentiated by testing in a 30% Cl- as MgCl2 solutionat 100 °C.
KEYWORDs : M. Borchert†, G. Mori, M. Bischof, and A. Tomandl
AUTHORs : M. Borchert†, G. Mori, M. Bischof, and A. Tomandl

Page : 273 - 279 DOWNLOAD
Effect of Chemical Passivation Treatment and Flow on the Corrosion of 304 Stainless Steel in Hydrochloric Acid Solution
Effects of passive film quality by chemical passivation and solution flow on the corrosion behavior of 304 stainless steel in HCl solution were investigated using a coloration indicator, and by corrosion weight loss, electrochemical polarization and element dissolution measurements. A high redness degree suggests a low passive-film integrity for 304 stainless steel following air exposure, while the minimum redness degree for the samples after chemical passivation suggests a high passive-film integrity. In the static condition, samples subjected to air exposure exhibited a high corrosion rate and preferential dissolution of Fe. Chemical passivation inhibited the corrosion rate due to the intrinsically high structural integrity of the passive film
and high concentrations of Cr-rich oxides and hydroxide. Solution flow accelerated corrosion by promoting both the anodic dissolution reaction and the cathodic reaction. Solution flow also altered the preferential dissolution to fast uniform dissolution of metal elements.
KEYWORDs : stainless steel, chemical passivation treatment, flow, corrosion, metal element dissolution
AUTHORs : Jie Zhao, Cong Qian Cheng†, and Tie Shan Cao

Page : 267 - 272 DOWNLOAD
Microbiologically Induced Corrosion of Three Tubular Materials
The performance of three tubular materials (C-90, L-80, and N-80) was evaluated in a synthetic brine inoculated with sulfate-reducing bacteria (SRB) in the absence and presence of biocides. A flow loop was used in the evaluation of the three alloys. Morphological examination of the alloy surfaces after exposure to SRB
and after biocide treatment was performed by scanning electron microscopy (SEM) to determine the nature of any localized corrosion. The SE images of the coupon samples showed a marked difference between the biocide-treated and untreated samples. Small pits were observed on the ultrasonically cleaned surfaces of the three alloys after exposure to SRB. The biocide treatment reduced the number of SRB on the surfaces of the alloys. Results indicated that C-90 and L-80 alloys exhibited better MIC resistance than N-80 under the conditions used in this study.
KEYWORDs : Flow loop, sulfate-reducing bacteria, pitting attack, biocide
AUTHORs : S. Mukadam† and A. Al-Hashem

Page : 261 - 266 DOWNLOAD
The Kinetics of Anodic Dissolution and Repassivation on 316L Stainless Steel in Borate Buffer Solution Studied by Abrading Electrode Technique
The capacity of passive metal to repassivate after film damage determines the development of local corrosion and the resistance to corrosion failures. In this work, the repassivation kinetics of 316L stainless steel (316L SS) was investigated in borate buffer solution (pH 9.1) using a novel abrading electrode technique. The
repassivation kinetics was analyzed in terms of the current density flowing from freshly bare 316L SS surface as measured by a potentiostatic method. During the early phase of decay (t < 2 s), according to the Avrami kinetics-based film growth model, the transient current was separated into anodic dissolution (idiss) and film formation (ifilm) components and analyzed individually. The film reformation rate and thickness were compared according to applied potential. Anodic dissolution initially dominated the repassivation for a short time, and the amount of dissolution increased with increasing applied potential in the passive region. Film growth at higher potentials occurred more rapidly compared to at lower potentials. Increasing the applied potential from 0 VSCE to 0.8 VSCE resulted in a thicker passive film (0.12 to 0.52 nm). If the oxide monolayer covered the entire bare surface (θ=1), the electric field strength through the thin passive film reached 1.6 × 107 V/cm.
KEYWORDs : repassivation, abrading electrode, anodic dissolution, passive film, high-field model
AUTHORs : H. S. Xu, D. B. Sun, H. Y. Yu†, and H. M. Meng

Page : 253 - 260 DOWNLOAD
Can the Point Defect Model Explain the Influence of Temperature and Anion Size on Pitting of Stainless Steels
The pitting behaviours of 304L and 316L stainless steels were investigated at 3 °C to 90 °C in 1 M solutions of NaCl, NaBr and NaI by potentiodynamic polarization. The temperature dependences of the pitting potential varied according to the anion, being near linear in bromide but exponential in chloride. As a result, at low temperatures grades 304L and 316L steel are most susceptible to pitting by bromide ions, while at
high temperatures both stainless steels were more susceptible to pitting by small chloride anions than the larger bromide and iodide. Thus, increasing temperature appears to favour attack by smaller anions. This paper will attempt to rationalise both of the above findings in terms of the point defect model. Initial findings are that qualitatively this approach can be reasonably successful, but not at the quantitative level, possibly due to insufficient data on the mechanical properties of thin passive films.
KEYWORDs : stainless steel, pitting corrosion, anion s
AUTHORs : Daniel J. Blackwood†

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