• Steel and Composite Structures
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• v.35 no.2
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• pp.171-186
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• 2020

This paper aims at providing insights on the use of thermosetting liner for the repair of offshore pipelines exposed to corrosion and leakage. The work which covers both experimental and numerical approaches were aspired due to the high cost of repair for pipelines, limitations of thermoplastic material and limited study of reinforced thermosetting liner. The experiment involves a destruction test called the burst test, carried out on an API 5L X42 carbon steel pipe under four case studies, namely (i) intact pipe, (ii) pipe with corrosion defect, (iii) pipe with corrosion defect and repaired with thermosetting liner and (iv) pipe with leakage and repaired with thermosetting liner. The numerical simulation was developed to first validate the experimental results and later to optimize the design of the thermosetting liner in terms of the number of layers required to restore the original strength of the pipe. The burst test shows an improvement in 23% of the burst capacity for the pipe with corrosion defects, after being repaired with a three-layer thermosetting liner. The parametric studies conducted showed that with an addition of thermosetting layers, the burst capacity improves by an average of 1.85 MPa. In conclusions, the improvement in strength can be further increased with increasing thickness of the thermosetting liner. The thermosetting liner was also determined to fail first inside the host pipe.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.

• Journal of Fisheries and Marine Sciences Education
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• v.10 no.2
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• pp.226-238
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• 1998

With the advent of high speed and high output diesel engines, cavitation erosion-corrosion of wet cylinder liners is one of the most prevalent types of failure. The cavitation erosion-corrosion at cylinder liners in water cooled diesel engines is considered to be to the collapse of cavitation bubbles attributed to the cylinder liner vibration. To suppress cavitation damage in cylinder liner, the addition of an inhibitor would be more general method and innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. In this study, photomicrographs from vibratory facility cavitation specimens and from an eroded liner of a field diesel engine are compared. The behavior of cavitation bubbles grown in fluid is observed under vibration conditions by taking direct photographs with high speed camera. In order to determine the contributions of pure cavitation erosion and of pure corrosion to the total cavitation damage are be studied by following an experimental programme which includes three types of test: (1)pure cavitation erosion test, (2)pure corrosion test, and (1)cavitation erosion-corrosion test. Also cavitation damage under vibratory cavitation is reduced by using flow in tap water.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.359-364
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• 2001

The purpose of this study is to develop the repair system for RC members with damaged by rebar corrosion using new corrosion inhibitor which was high nitrite content. In the experiments, the acceleration corrosion test of rebar was conducted using the specimen which was applied by various repair system. As a result, it was confirmed that the new repair system without concrete patching had high anti-corrosion property compared with other repair systems and was very effective as a spray type corrosion inhibitor in concrete containing chloride (0.1% of NaCl).

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.663-667
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• 2004

Underframes of rolling stock structure are made of hot rolled steel of SS400 or SM490A. While these underframe steels are designed to satisfy the mechanical requirements, their corrosion behavior also should taken into account. Underframes are coated to prevent corrosion, but they are often defected by external factors to result in local corrosion which may cause the weakness of mechanical strength. Thus, the corrosion of underframe steels was examined through atmospheric corrosion test to estimate service life and safety.

• Corrosion Science and Technology
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• v.3 no.5
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• pp.187-193
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• 2004

We have investigated the differences between the general corrosion and microbiologically influenced corrosion (MIC) of steels in terms of electrochemical behavior and surface phenomena. Corrosion potential of steels in the absence of SRB (sulfate-reducing bacteria) shifted to a low level and was maintained throughout the experimental period (40 days). The potential in the presence of SRB, however, shifted to a noble level after 20 days' incubation, indicating the growth of SRB biofilms on the test metal specimens and a formation of corrosion products. In addition, the color of medium inoculated with SRB changed from gray to black. The color change appeared to be caused by the formation of pyrites (FeS) as a corrosion product while no significant color change was observed in the medium without SRB inoculation. Moreover, corrosion rates of various steels tested for MIC were higher than those in the absence of SRB. This is probably because SRB were associated with the increasing corrosion rates through increasing cathodic reactions which caused reduction of sulfate to sulfide as well as formation of an oxygen concentration cell. The pitting corrosions were also observed in the SRB-inoculated medium.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.2
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• pp.173-181
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• 2007

Recently, galvanizing method is predominantly being used not only a economical point of view but also due to it s stability and long life. For example, guard rail of high way, all kinds of structures for ship etc. were protected with galvanizing and demand of galvanized structural materials was being increased with more and more. However, galvanized structures were inevitably being deteriorated with time eventually because they were corroded with solution of galvanizing film and exfoliation of it s film in the present severe corrosive environment. Therefore, it is necessary to improve the corrosion resistance of the galvanizing film through various methods such as variation of chemical composition of galvanizing bath, chromate treatment and coating treatment. In this study, three test specimens such as pure galvanizing, galvarium, and chromate treatment were submerged at tap water with inhibitor addition. And the effect of their corrosion resistance improvement was comparatively investigated with electrochemical method. Corrosion current density of the galvanized steel was the largest among three specimens, however, the galvarium steel showed the lowest corrosion current density. Futhermore, these three kinds of test specimens indicated considerably excellent corrosion resistance by dipped at tap water with inhibitor addition. Especially, the galvanized steel showed the best effect of corrosion resistance improvement than other test specimens.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.50-55
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• 2013

The purpose of this study was to investigate corrosion characteristics of Ti-xTa alloys with Ta contents. Ti-xTa alloys used as samples (x=30, 40%) were arc-melted under argon atmosphere of 99.9% purity. Ti-xTa alloys were homogenized for 12hr at $1000^{\circ}C$ and then water quenched. The surface characteristics of Ti-xTa alloys were investigated using optical microscopy (OM) and X-ray diffractometer (XRD). The anodic corrosion behaviors of the specimens were examined through potentiodynamic, potentiostatic and galvanostatic test in 0.9 % NaCl solution at $36.5{\pm}1^{\circ}C$. After corrosion test, the surface characteristics of Ti-xTa alloys were investigated using OM. The microstructure of Ti-Ta alloy showed the beta structure with Ta content. The corrosion resistance of Ti alloy was improved by increasing Ta content and the corrosion morphology of Ti-Ta alloy showed that the site attacked by chloride ion decreased from the active to passive region with Ta content. Potential of Ti-40Ta alloy increased as time increased, whereas, current density of Ti-40Ta alloy decreased as time increased compared to Ti-30 alloy.

• Corrosion Science and Technology
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• v.18 no.6
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• pp.267-276
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• 2019

The purpose of this study was to examine the influence of conditions for quenching and/or tempering on the corrosion and hydrogen diffusion behavior of ultra-strong automotive steel in terms of the localized plastic strain related to the dislocation density, and the precipitation of iron carbide. In this study, a range of analytical and experimental methods were deployed, such as field emission-scanning electron microscopy, electron back scatter diffraction, electrochemical permeation technique, slow-strain rate test (SSRT), and electrochemical polarization test. The results showed that the hydrogen diffusion parameters involving the diffusion kinetics and hydrogen solubility, obtained from the permeation experiment, could not be directly indicative of the resistance to hydrogen embrittlement (HE) occurring under the condition with low hydrogen concentration. The SSRT results showed that the partitioning process, leading to decrease in localized plastic strain and dislocation density in the sample, results in a high resistance to HE-induced by aqueous corrosion. Conversely, coarse iron carbide, precipitated during heat treatment, weakened the long-term corrosion resistance. This can also be a controlling factor for the development of ultra-strong steel with superior corrosion and HE resistance.

• Journal of Fisheries and Marine Sciences Education
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• v.12 no.2
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• pp.164-175
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• 2000

Port facilities and marine structures used in marine environment were encountered to corrosion damages because of the influence of Cl-. Generally, to protect these accidents, anti-corrosion paint and epoxy coating have been used. But they were still remained erosion-corrosion damage like impingement erosion, cavitation erosion and deposit attack. It is necessary to develope the new composite lining material in order to protective those corrosion damages. In this paper, polyester glass flake, vinylester glass flake lining and epoxy coating for SS400 were investigated by the electrochemical polarization test and the impingement-cavitation erosion test for corrosion behaviour under the sea water. The main results obtained are as follows ; 1) Epoxy coating appear potentiodynamic polarization behaviour, but polyester glass flake and vinylester glass flake lining do not appear potentiodynamic polarization behaviour. 2) Open circuit potential of polyester glass flake lining is more noble than that of epoxy coating and corrosion current density of polyester glass flake lining is less drained than that of epoxy coating in sea water. 3) Open circuit potential of vinylester glass flake lining is more noble than that of polyester glass flake lining and corrosion current density of vinylester glass flake lining is less drained than that of polyester glass flake lining in the sea water.