• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.25-30
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• 2013

The periodic inspection of piping and pressure vessels welds in nuclear power plant has to provide reliable result related to weld flaws, such as location, maximum amplitude response, ultrasonic length, height and finally the nature or flaw pattern. The founded flaw in ultrasonic inspection is accepted or rejected based on these data. Specially, the amplitude of flaw response is used as basic parameter for flaw sizing and it may cause some deviation in length sizing result. Currently the ultrasonic inspections in nuclear power plant components are performed by specific inspection procedure which describing inspection technique include inspection system, calibration methodology and flaw characterizing. To perform ultrasonic inspection during in-service inspection, reference gain should be established before starting ultrasonic inspection by the requirement of ASME code. This reference gain used as basic criteria to evaluate flaw sizing. Sometimes, a little difference in establishing reference gain between calibration and field condition can lead to deviation in flaw sizing. Due to this difference, the inspection result may cause flaw sizing error. Therefore, the objective of this study is to compare and evaluate the ultrasonic amplitude difference between air filled and water filled pipe in nuclear power plant. Additionally, the accuracy of flaw sizing is estimated by comparing both conditions.

• Journal of the Korean Society for Nondestructive Testing
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• v.8 no.1
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• pp.6-11
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• 1988

The comparison and analysis of flaw detectability, flaw sizing methods and allowable criteria in accordance with the applicable codes, ASME and RCC-M Code, in ultrasonic examination of pressure vessel in nuclear power plants were studied. Accordding to the codes, calibration blocks were made. The artificial flaws such as disc and band types in test specimens were machined. They were detected and evaluated with etch code requirements and measured values were compared with the actual flaws.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.155-160
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• 2001

This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.

• 한국가스학회:학술대회논문집
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• 2004.11a
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• pp.158-163
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• 2004

• Journal of Ocean Engineering and Technology
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• v.19 no.3
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• pp.1-10
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• 2005

The effect of rotation on the unsteady laminar flaw past a circular cylinder is numerically investigated in the present study. The numerical solutions for the 2D Navier-Stokes equation obtained, using two different numerical methods. One is an accurate spectral method and the other is a finite volume method(FVM). First, the flaw around a stationary circular cylinder is investigated to understand the basic phenomenon of flaw separation and bluff body wake. Next, the flow characteristics of the laminar flow, past a rotating circular cylinder, are investigated, using a FVM developed in this study. By the effect of rotation, it is seen that values of lift increase, while the values of mean drag decrease. Further, the criteria of angular velocity, at which the Karman vorteces disappear, is also determined.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.304-309
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• 2003

In this study, natural flaws in welding parts are classified using the signal pattern classification method. The storage digital oscilloscope including FFT function and enveloped waveform generator is used and the signal pattern recognition procedure is made up the digital signal processing, feature extraction, feature selection and classifier design. It is composed with and discussed using the distance classifier that is based on euclidean distance the empirical Bayesian classifier. Feature extraction is performed using the class-mean scatter criteria. The signal pattern classification method is applied to the signal pattern recognition of natural flaws.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.291-295
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• 1996

In CANDU reactor, each pressure tubes contain twelve fuel bundles and provide the inlet and outlet for the primary coolant. If a leak develops in the pressure tube, it is detected by Annulus Gas System which contains circulating dry $CO_2$ gas. Since the leaks caused by the flaws are resulted in pressure tube break, establishment of flaw assessment method is very significant in view of the fracture mechanics. In this paper, various criteria for assessing the flaws are presented to prevent the tube rupture and ensure the integrity of reactor operating.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1181-1185
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• 1990

A failure evaluation diagram to evaluate fatigue fracture was developed. The relation between the fatigue limit and the threshold stress intensity factor for the short-cracked specimens of various materials including a piping carbon steel can be rationally predicted by the proposed method. It is shown that the coupled failure evaluation diagram for fatigue and ductile fracture is expecially useful for evaluation of the flaw tolerance as well as the margin of the safety of the pressure vessel and piping. Further, accumulation of fatigue data will be needed to construct an accurate fatigue failure evaluation diagram.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.21 no.1
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• pp.133-143
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• 2018

In spite of the growing importance of landscaping trees, the rate of flawed and withered trees damaged by pest, disease, drought or frost is increasing. In order to evaluate the performance of the Tree Protective Pad, which are developed to reduce the failure ratio in landscape planting, the tree protective pad for 'digging', 'pest controlling', and 'insulating' are tested based on the five functional criteria; moisturizing effect, wither preventive effect, pest and disease control, thermal effect, tensile strength, and environmental performance. The result of this study is as follows. The moisturizing effect of the tree protective pad for digging is found to be outstanding. According to the result of testing the pad on trees, in particular, it is better than jute tape in wither preventive effect, which means it is expected to prevent flaw and wilt from planting during the improper seasons like summertime. The experiment of installing the protective tree pad for pest controlling to the trunk of Quercus mongolica shows that preventive effect of the pad from diseases and insects is superior, and it also has economical effect by reducing the use of agricultural chemicals. The comparative test of the pad for insulating and jute tape proves that the temperature of the pad is about $2^{\circ}C$ higher than outside. The rate of tensile strength and biodegradation of the pad exceeds the optimal level, so it is revealed that the pad may be the work efficient and environment-friendly product. Likewise, by timely irrigating trees, the tree protective pad economically prevents trees from pest, disease,drought or frost, which may be caused by improper seasonal or delayed planting. As a means of reducing the flaw and facilitating the growth of trees, the exceptional performance of the pad is expected to effectively used in landscape planting and management.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.103-111
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• 2002

In this study, the natural flaws in welding parts are classified using the signal pattern classification method. The storage digital oscilloscope including FFT function and enveloped waveform generator is used and the signal pattern recognition procedure is made up the digital signal processing, feature extraction, feature selection and classifier design. It is composed with and discussed using the distance classifier that is based on euclidean distance the empirical Bayesian classifier. feature extraction is performed using the class-mean scatter criteria. The signal pattern classification method is applied to the signal pattern recognition of natural flaws.