• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.321-331
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• 2015

A study on the application of cooling defect detection was performed on the basis of a preceding study on the heated defect detection in nuclear piping loop system, using lock-in infrared thermography. A loop system with piping defects was made by varying the wall-thinning length, the circumference orientation angle, and the wall-thinning depth. The test was performed using an IR camera and a cooling device. Distance between the cooling device and the target loop system was fixed at 2 m. For analyzing experimental results, the temperature distribution data for cooling, and phase data were obtained. Through the analysis of this data, the defect length was measured. The reliability of the measurements for cooling defect conditions was shown to be higher in the lock-in infrared thermography data than the infrared thermography data.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.364-371
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• 2003

In this paper, a review of the current status, on the use of long range cylindrically guided wave modes, and their interaction with cracks and corrosion damage in pipe-like structures will be discussed. Applications of cylindrically guided ultrasonic wave modes have been developed for inspection of corrosion damage in pipelines at chemical plants, flow-accelerated corrosion damage (wall thinning) in feedwater piping, and circumferential stress corrosion cracks in PWR steam generator tubes. It has been demonstrated that this inspection technique can be employed on a variety of piping geometries (diameters from 1 in. to 3 ft, and wall thickness from 0.1 to 6 in.) and a propagation distance of 100 meters or more is sometimes feasible. This technique can also be used in the inspection of inaccessible or buried regions of pipes and tubes.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.900-907
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• 2000

The three-dimensional turbulent flow in curved pipes susceptible to flow-accelerated corrosion has been analyzed numerically to predict the pressure and shear stress distributions on the inner surface of the pipes. The analysis employs the body-fitted non-orthogonal curvilinear coordinate system and a standard $ {\kappa}-{\varepsilon}$ turbulence model with wall function method. The finite volume method is used to discretize the governing equations. The convection term is approximated by a high-resolution and bounded discretization scheme. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of a modified version of momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The numerical calculations have been performed for two curved pipes with different bend angles and curvature radii, and discussions have been made on the distributions of the primary and secondary flow velocities, pressure and shear stress on the inner surface of the pipe to examine applicability of the present analysis method. As the result it is seen that the method is effective to predict the susceptible systems or their local areas where the fluid velocity or local turbulence is so high that the structural integrity can be threatened by wall thinning degradation due to flow-accelerated corrosion.

• 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.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.437-442
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• 2010

Flow-accelerated corrosion (FAC) leads to thinning of steel pipe walls that are exposed to flowing water or wet steam. From experience, it is seen that FAC damage to piping at fossil and nuclear plants can result in outages that require expensive repairs and can affect plant reliability and safety. CHECWORKS have been utilized in domestic nuclear plants as a predictive tool to assist FAC engineers in planning inspections and evaluating the inspection data so that piping failures caused by FAC can be prevented. However, CHECWORKS may be occasionally ignore local susceptible portions when predicting FAC damage in a group of pipelines after constructing a database for all the secondary side piping in nuclear plants. This paper describes the methodologies that can complement CHECWORKS and the verifications of CHECWORKS prediction results using numerical analysis. FAC susceptible locations determined using CHECWORKS for two pipeline groups of a nuclear plant was compared with determined using the numerical-analysis-based FLUENT.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.7-14
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• 2011

Soft copper tube is one of the popular materials which are used for shipbuilding, automobiles, and freezing and HVAC equipment. However, these materials have problems that they cause occasionally outside wrinkle, spring back, wall thinning phenomena. In this study, to avoid these phenomena, was manufactured a mild materials devoted bending machine, which selected a bending method where the mandrel presses the pipe along with the sliding guide rail during bending process. During the course of confirming this performance, it was found that as the diameter of copper tube used for materials became smaller, the spring back phenomenon increased. And as the bending angle became larger, it became larger. In addition, we could manufacture mold products which scarcely generated wrinkle when bending copper tubes.

• 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.

• 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%.

• Corrosion Science and Technology
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• v.18 no.2
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• pp.61-71
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• 2019

Flow-Accelerated Corrosion (FAC) is a phenomenon in which a protective coating on a metal surface is dissolved by a flow of fluid in a metal pipe, leading to continuous wall-thinning. Recently, many countries have developed computer codes to manage FAC in power plants, and the FAC prediction model in these computer codes plays an important role in predictive performance. Herein, the FAC prediction model was developed by applying a machine learning method and the conventional nonlinear regression method. The random forest, a widely used machine learning technique in predictive modeling led to easy calculation of FAC tendency for five input variables: flow rate, temperature, pH, Cr content, and dissolved oxygen concentration. However, the model showed significant errors in some input conditions, and it was difficult to obtain proper regression results without using additional data points. In contrast, nonlinear regression analysis predicted robust estimation even with relatively insufficient data by assuming an empirical equation and the model showed better predictive power when the interaction between DO and pH was considered. The comparative analysis of this study is believed to provide important insights for developing a more sophisticated FAC prediction model.