• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.5
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• pp.493-500
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• 2001

The detection of axial cracks using conventional MFL pig is a significant challenge in the gas pipeline inspection. In this study, a technique using interaction of circumferentially induced torrents with axial stress corrosion crack is presented. The feasibility of this technique is investigated using finite element modeling. Finite element analysis of such interaction is a difficult problem in terms of both computation time and memory requirements. The challenges arise due to the nonlinearity of material properties, the small sire of tight cracks relative to that of the magnetizer, and also time stepping involved in modeling velocity effects. This paper presents an approach based on perturbation methods. The overall analysis procedure is divided into 4 simple steps that can be performed sequentially. Modeling results show that this technique can effectively detect colonies of SCC as well as single SCC.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.7-14
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• 2005

본 논고에서는 microfocus X 선 발생장치와 평판형 영상센서를 이용한 micro-CT 시스템의 개발과 그 응용에 대해 소개하였다. 개발과 관련하여서는 영상센서 및 시스템의 동작원리뿐만 아니라 성능평가 결과에 대해서도 간단히 언급하였는데, 이와 같은 성능평가는 추후 개선된 혹은 새로운 설계 및 제작을 위해서는 필수적으로 수반되어야 할 부분이다. 개발된 micro-CT 시스템의 응용분야 소개와 관련하여서는 몇 가지 획득 영상을 토대로 바이오 영상과 산업용 영상에 관하여 언급하였다. 바이오 영상분야에서는 현재 세계적으로 유수 의료기기업체에서 이미 제작하여 판매하고 있으며, 대부분 X선 영상증배관 혹은 CCD(charge-coupled device)를 X 선 영상획득 센서로 사용한 반면, 본 논고에서 소개한 시스템은 평판형 영상센서를 사용했다는 점에서 차별성이 있다. Micro-CT 시스템의 산업용 영상분야로의 적용은 이제 시작 단계이며, 기존 라미노그라피 시스템을 대체하거나 혹은 새로운 응용으로 자리매김할 것으로 기대된다.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.5
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• pp.494-498
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• 2004

Fire accidents often happen in large buildings because large buildings are equipped with heavy electrical wiring and piping. When fire is to be occurred in those buildings, it is very dangerous to People and building structures. Therefore, multi-point wireless temperature sensors for large buildings are necessary in order to detect fire in the early time and thus to minimize the loss. A wireless device was composed of the transmitter and receiver. The specification of this device was as follows: 915MHz of transmitted frequency, 4 channels, 9600bps of the transmitted speed, and 10mW of the transmitted power. We confirmed through experiment that the temperature was well sensed and fire location was determined by the 4 channel sensors of the developed sensor system.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.427-435
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• 2009

Cylindrical structures such as pipes and shafts are widely used in various industrial facilities. Recently, researches on magnetostrictive transduction of torsional waves have been actively reported for the nondestructive evaluation of those cylindrical structures. However, the existing magnetostrictive patch transducer has somewhat inconvenient and time.consuming process like patch bonding to a structure since it should employ a magnetostrictive patch having strong magnetostriction. To overcome these limitations of the existing transducer, in this work, we develop a novel modular magnetostrictive transducer to generate and measure torsional waves to inspect a cylindrical structure. The proposed transducer can be applied as viscous liquid coupling with shear couplant or dry coupling without coupling media instead of patch bonding to a structure. We describe a detailed structure of the modular transducer and conduct some experiments to verify its performance.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.2
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• pp.165-170
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• 2014

Shear horizontal (SH) waves propagate as a type of plate wave in a thin sheet. The dispersion characteristics of SH waves can be used for signal analysis. Therefore, SH-waves are useful for monitoring the structural health of a thin-sheet-structure. An electromagnetic acoustic transducer (EMAT), which is a non-contact ultrasonic transducer, can generate SH-waves easily by varying the shape and array of magnets and coils. Therefore, an EMAT can be applied to an automated ultrasonic testing system for structural health monitoring. When used as a sensor, however, the EMAT has a weakness in that electromagnetic interference (EMI) noise can occur easily in the automated system because of motors and electric devices. Alternatively, a fiber optic sensor works well in the same environment with EMI noise because it uses a light signal instead of an electric signal. In this paper, a fiber Fabry-P$\acute{e}$rot interferometer (FFPI) was proposed as a sensor to receive the SH-waves generated by an EMAT. A simple test was performed to verify the performance of the FFPI sensor. It is thus shown that the FFPI can receive SH-wave signals clearly.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.1
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• pp.33-38
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• 2019

Thermal power generation accounts for the highest percentage of domestic power generation, among which coal-fired boiler generation accounts for the highest percentage. Coal boilers generate harmful substances and fine dust during coal combustion and have a serious effect on air pollution. So, fluidized-bed boilers have been introduced as eco-friendly coal boilers. It uses a fluid medium which affect the combustion temperature of coal. Because of it fluidized-bed boilers emit less pollutants than original one. Water-wall tubes play an important role in this fluidized bed boiler. Due to the fluid medium, the wall damage is more severe than the existing boiler. However, there is no quantitative maintenance technique in Korea yet. Remote field eddy current testing is a non-destructive evaluation technique that is often used for inspection of inner and outer wall of tube. it can inspect with non-contact and high speed. However, it is an inspection that proceeds from inside the pipe, and the water-wall tube is not able to enter the interior. In this study, we designed and simulated an external remote field eddy current sensor suitable for water-wall tube of a fluidized - bed boiler using simulations. By obtaining a signal similar to the existing remote field eddy current test, the criteria for the external remote field eddy current sensor design can be presented.