• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.191-198
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• 2008

Flow accelerated corrosion (FAC) phenomenon of low alloy carbon steels in nuclear power plant has been known as one of major degradation mechanisms. It has a potential to cause nuclear pipe rupture accident which may directly impact on the plant reliability and safety. Recently, the equipotential switching direct current potential drop (ES-DCPD) method has been developed, by the present authors, as a method to monitor wall loss in a piping. This method can rapidly monitor the thinning of piping, utilizing either the wide range monitoring (WiRM) or the narrow range monitoring (NaRM) technique. WiRM is a method to monitor wide range of straight piping, whereas NaRM focuses significantly on a narrow range such as an elbow. WiRM and NaRM can improve the reliability of the current FAC screening method that is based on computer modeling on fluid flow conditions. In this paper, the measurements by ES-DCPD are performed with signal sensitivity analyses in the laboratory environment for extended period and showed the viability of ES-DCPD for real plant applications.

• Korean Journal of Food Science and Technology
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• v.20 no.6
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• pp.742-748
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• 1988

The macro-and microstructure of Chinese cabbage used for Korean Kimchi preparation were examined and the texture characteristics of raw cabbage leaf and salted or blanched leaves were evaluated by cutting test. The length and thickness of leaf stalk increased with the order of pyllotaxis, but the thinning effect of outermost leaves was observed. The microstructure of cut-profile of stalk showed densely compacted vascular systems aligned in the center of stalk and the outer space was filled with large parenchima cells. Due to this structure, characteristic cutting curves were obtained by cutting test, composing three peaks of cutting for inner surface skin, center vascular system and outer surface skin. Salting and blanching increased the cutting force mainly due to the increase of Gutted cell wall number caused by the structure collapse.

• Corrosion Science and Technology
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• v.6 no.6
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• pp.291-296
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• 2007

The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4270-4274
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• 2011

A method is proposed for determining chromium content in the carbon steel pipes of a nuclear power plant (NPP) to evaluate wall thinning caused by flow-accelerated corrosion (FAC). A flat file was used to obtain filings samples. To assess sampling quality, a disk form of SRM 1227 was ground with the flat file, and the amount of Cr in the filings was determined by ICP-AES. The content of chromium in the filings of SRM 1227 was estimated as six times higher than the certified value due to the contamination of chromium in the file. To eliminate chromium contamination from the file, it was coated with WC-12Co using high-velocity oxygen-fuel (HVOF) spraying systems. After obtaining filings samples using the coated file, Cr content in four types of disk-form SRMs was determined by ICP-AES. The recoveries of Cr in the disk-form SRMs were in the range of 95.4-102.6%, with relative standard deviations from 0.43 to 3.0%. The Cr contents in the filings collected from the used outlet headers of the nuclear power plants using the flat file coated were in the range of 0.11-0.19%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.7
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• pp.377-385
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• 2013

In this study, the performance of an impeller according to blade length and pitch angle was studied experimentally by building a variable pitch impeller while changing blade length to review the effect of blade length and pitch angle on a fan's performance. The pitch angle was changed in six steps from $20^{\circ}{\sim}45^{\circ}$ at intervals of $5^{\circ}$ while the blade lengths were changed to 90 mm, 100 mm, 110 mm and 120 mm with an identical airfoil shape while carrying out the experiment. The results are summarized as follows : The air flow per static pressure of axial fans increased linearly with increase of pitch angle, but the high static pressure showed a decrease at a pitch angle of $35^{\circ}$. The shaft power increased proportionally to the pitch angle at all blade lengths; the larger the pitch angle, the larger the measured increase of shaft power. This is because the drag at the fan's front increases with the pitch angle. In the axial fans considered in this research, the flow and incre.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.71-74
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• 2005

In manufacturing automotive parts, such as engine cradles, frame rails, subframes, cross-members, and other parts from circular tubes, pre-bending and pre-forming operations are often required prior to the subsequent tubular hydroforming process. During some pre-forming operations, the cross section of a bent circular tube is crushed into an oval-like shape to ensure proper geometry and sufficient clearance in the hydroforming dies. For such applications, the use of oval Instead of circular tubes could be an effective means of eliminating the pre-forming step. The oval tube could also be produced with less thinning and with less strain on the outside of the bend when controlled by a booster system without the use of mandrel. Hence, the understanding of the issues that occur in the bending of oval tubes is worthy of Investigation. This paper presents parametric studies on the bending of oval tubes without a mandrel. The finite element modeling technique is used to examine the deformation characteristics for both circular and oval tubes. In the simulations, the bending process parameters of bend radius, aspect ratio of the tube ovalness, and tube wall thickness are varied. Observations are made to obtain a hoop-buckle limit diagram in terms of a non-dimensional shape degradation factor. Suggestions based upon developed criteria are made on the acceptability of bend tubes suitable for hydroforming applications without the need ofa pre-forming step or the used of a mandrel.

• Journal of the Korean Wood Science and Technology
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• v.35 no.6
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• pp.152-158
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• 2007

Micromorphological and chemical characteristics of living Castanea spp. and Tamarix spp. attacked by a brown-rot fungus were examined. Micromorphological features of brown-rotted hardwood species were similar to those observed in softwoods such as losses in birefringence under polarized microscopy, preferential degradation of $S_2$ layer and cracks in the $S_3$ layer. Thinning of the secondary cell wall in fibers was also observed, although it did not seem to be the main symptom. FT-IR analysis showed that bands assigned to cellulose and hemicelluloses decreased or disappeared, whereas the bands assigned to lignin increased. X-ray diffraction analysis exhibited the decrease of relative crystallinity, indicating that degradation of hardwood by a brown-rot fungus was in the advanced stages.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.406-414
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• 2001

Ultrasonic guided waves were explored to apply them to the long range inspection of polyethylene coated steel gas pipes. The steel pipes have such dimensions as 190.7mm inside diameter and 5.3mm thickness. The outside surface of the pipe is coated by a polyethylene layer of $1.9{\pm}0.5mm$ thickness. Non-axisymmetric guided waves were excited on the outside surface of the polyethylene coated pipe by using a 0.5MHz transducer with a variable angle shoe. Frequency and phase velocity tuning was used to find optimum guided wave modes for the inspection. The dispersive characteristics of the modes were analyzed in time-frequency representation obtained by short time Fourier transforms. Sample results were presented for artificial defects such as wall thinning and hole.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.23 no.2
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• pp.255-264
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• 1993

The purpose of this study was to obtain some informations for the radiographic differential diagnosis between dentigerous cysts and unicystic ameloblastomas in the mandible. The authors observed and compared the clinico-radiographic features of 38 cases of dentigerous cyst and 32 cases of unicystic ameloblastoma associated with impacted mandibular molar. The obtained results were as follows: Dentigerous cysts occurred the most frequently in the 3rd decade, but unicystic ameloblastomas in the 2nd decade, and both lesions occurred with slight predilection in males. Average of lesional size of unicystic ameloblastomas was larger than that of dentigerous cysts, and lesions of over 25㎠ were only in unicystic ameloblastomas. Cortical thinning and expansion were more frequently observed in unicystic ameloblastomas at 72.9% than in dentigerous cysts at 15.8%. Dentigerous cysts showed smooth border at 89.5%, but unicystic ameloblastomas showed smooth border at 53.1% and scalloped border at 46.9%. Dentigerous cysts showed well-defined outline at 81.6%, but unicystic ameloblastomas showed well-defined outline at 53.1% and moderate-defined outline at 46.9%. In both lesions, the mandibular 3rd molar was the most frequent causative tooth. Average of distance between the cemento-enamel junction and lesional wall attachment of the causative tooth was longer in unicystic ameloblastomas than in dentigerous cysts. Severe displacement of causative tooth was more frequent in unicystic ameloblastomas at 62.5% than in dentigerous cysts at 23.7%. Dentigerous cysts showed homogeneous lesional radiolucency at 89.5%, but unicystic ameloblastomas showed inhomogeneous lesional radiolucency at 53.1%. Root resorption of adjacent tooth and displacement of mandibular canal were more frequent in unicystic ameloblastomas at 65.2% and 61.5% than in dentigerous cysts at 15.8% and 38.1% respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1097-1103
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• 2011

Liquid droplet impingement erosion (LDIE) is caused by the impact of high-velocity droplets entrained in steam or air on metal. The degradation caused by the LDIE has been experienced in steam turbine internals and high-velocity airplane components (particularly canopies). Recently, LDIE has also been observed in the pipelines of nuclear plants. LDIE among the pipelines occurs when two-phase steam experiences a high pressure drop (e.g., across an orifice in a line to the condenser). In 2011, a nuclear power plant in Korea experienced a steam leak caused by LDIE in a pipe through which a two-phase fluid was flowing. This paper describes a study on the design change of a pipe affected by LDIE in order to mitigate the damage. The design change has been reviewed in terms of fluid dynamics by using the FLUENT code.