• Proceedings of the KSME Conference
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• 2001.11a
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• pp.61-66
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• 2001

Fracture behaviors of pipes with local wall thinning is very important for the integrity of nuclear power plant. In pipes of energy plants, sometimes, the local wall thinning may result from severe drosion-corrosion damage. However, effect of local wall thinning on strength and fracture behaviors of piping system were not well studied. In this paper, the monotonic bending tests were performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and fracture strength of locally thinned pipe were manifested systematically. The observed failure modes were divided into four types; ovalization, ovalization+cracking, local buckling and local buckling+cracking. Also, maximum load was successfully evaluated.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.90-95
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• 2003

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. In pipes of energy plants, sometimes, the local wall thinning may result from severe erosion-corrosion (E/C) damage. However, the effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. In this paper, the monotonic bending tests were performed of full-scale welded and unwelded carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. The observed failure modes were divided into four types; ovalization, crack initiation/growth after ovalization, local buckling and crack initiation/growth after local buckling. Also, the strengths of welded and unwelded piping system with local wall thinning were evaluated.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.622-628
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• 2003

The purpose of this study is to evaluate the effect of local wall thinning on the collapse of elbow subjected to internal pressure and bending moment. Thus, the nonlinear 3D finite element analyses were performed to obtained collapse moment of elbow containing various wall thinning defects under two loading; modes (closing and opening modes) and defect locations (intrados and extrados). From the results of analyses, the influence of wall thinning defect on the global moment-rotation behavior of elbow was discussed, and the dependance of collapse moment of elbow on wall thinning depth, length, and circumferential angle was investigated under different loading mode and defect location.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.21-38
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• 2009

The use of multi scale modeling concepts and simulation techniques to study the destabilization of an ultrathin layer of oxide interface between a metal substrate and the surrounding environment is considered. Of particular interest are chemo-mechanical behavior of this interface in the context of a molecular-level description of stress corrosion cracking. Motivated by our previous molecular dynamics simulations of unit processes in materials strength and toughness, we examine the challenges of dealing with chemical reactivity on an equal footing with mechanical deformation, (a) understanding electron transfer processes using first-principles methods, (b) modeling cation transport and associated charged defect migration kinetics, and (c) simulation of pit nucleation and intergranular deformation to initiate the breakdown of the oxide interlayer. These problems illustrate a level of multi-scale complexity that would be practically impossible to attack by other means; they also point to a perspective framework that could guide future research in the broad computational science community.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.3
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• pp.341-350
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• 2012

In this paper we observe the protective coatings carbon for steel, aluminium and titanium alloys were obtained by plasma electrolytic oxidation (PEO) under unipolar and bipolar conditions. The anticorrosion properties and the thermal stability of the surface layers were studied by electrochemical impedance spectroscopy and potentiodynamic polarization. It was found that the application of the bipolar PEO mode enables one to synthesize the surface layers that possess enhanced anticorrosion and mechanical properties. results of research of antiscale PEO - coatings for marine power equipment are presented. The combined method of prevention of corrosion and scale formation was tested at the industrial plants of Russian Shipyard "Zvezda".

• Journal of Welding and Joining
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• v.17 no.5
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• pp.89-96
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• 1999

The base metal and weld metal of alloy designed austenitic stainless steels were electrochemically tested in artificial sea water. Pitting resistance of 14 different stainless steels was evaluated by measuring pitting potential. The effect of alloy element to pitting potential was evaluated by changing chromium, nickel, sulfur content. The site of pitting initiation was observed by optical microscope. As a result of electrochemical test, pitting resistance of weld metal was higher than base metal, and rapidly cooled weld metal has higher pitting potential than slowly cooled weld metal. In case of primary δ-ferrite solidification, pitting potential was increased, but residual δ-ferrite was detrimental to pitting resistance. Chromium was more effective to pitting resistance than nickel, and sulfur was very detrimental element to pitting resistance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.8
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• pp.770-777
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• 2004

Fouling and cleaning tests are performed for a uniquely designed 7,000 ㎉/hr fluidized bed heat exchanger for exhaust gas heat recovery. Fuel rich condition is maintained in the combustor for a limited time period to generate soot that is to be deposited on the heat transfer surfaces (fouling) and 600 Um glass beads are circulated inside the heat exchanger system for cleaning and enhancing the heat transfer performance. According to the present experimental study, performance degradation mode could be monitored and the effect of particle circulation on the heat transfer improvement could be identified. Through the present study, it is demonstrated that circulating particles contribute not only to the fouling reduction in gas side, but also to the heat transfer enhancement of the unit, while other possible aging factors including water side corrosion seemed to contribute to the accumulated performance deterioration.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.629-637
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• 2017

Continuous concrete beams are commonly used as structural members in the reinforced concrete constructions. The use of fiber reinforced polymer (FRP) bars provide attractive solutions for these structures particularly for gaining corrosion resistance. This paper presents experimental results of eight two-span continuous concrete beams; two of them reinforced with pure glass fiber reinforced polymer (GFRP) bars and six of them reinforced with combinations of GFRP and steel bars. The continuous beams were tested under monotonically applied loading condition. The experimental load-deflection behavior and failure mode of the continuous beams were examined. In addition, the continuous beams were analyzed with a numerical method to predict the load-deflection curves and to compare them with the experimental results. Results show that there is a good agreement between the experimental and the theoretical load-deflection curves of continuous beams reinforced with pure GFRP bars and combinations of GFRP and steel bars.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.3
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• pp.259-264
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• 2000

The paper provides the characteristic analyses of porcelain suspension insulators. The comparisons of characteristics were made as a function of failed and unfailed insulators which had ben used in the fields. This paper also describes the failure modes occurred in the fields. The aging of cement corrosion of metal breaking of shed puncture in the head and separation of glaze are different failure modes for porcelain suspension insulators. Among these failure modes the puncture breaking and glaze problems were major concerns in this research. The cracks porosities of porcelain and micro-crystals on the graze were the causes of these failures. These results were confirmed by conducting various failure analyses.

• Journal of the Korean Society of Safety
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• v.19 no.1
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• pp.6-11
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• 2004

CNG buses were introduced in 2002 to reduce air pollution to the big cities. The durability and safety evaluation were performed for the NGV-2 type cylinders taken from two buses after 30 months of running. No external damage and no internal corrosion was observed on the container surfaces. Defect exceeding the allowable limit was not found in the UT test. Permanent volume expansion was about 1.2% which is much smaller than the required design limit. Cycling test showed no failure after 11,250cycles and burst pressures were still above the maximum design pressure. Both the longitudinal and circumferential failure mode were observed, where both the fracture strengths were far above the design limit. This study showed the present CNG fuel cylinders were safe enough for further usage.