• 한국압력기기공학회 논문집
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• 제9권1호
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• pp.70-76
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• 2013

Several finite element models for the leak-before-break (LBB) assessment of overlay dissimilar metal weldment were constructed and analyzed to develop a simple finite element modeling method. The J-integral, crack opening displacement (COD) and J-integral distribution along the crack front in thickness direction due to the applied moment were obtained from the analysis results of the constructed finite element models, and studied compared to the previous literatures. It is concluded that the modeling with base material only is simple and produces a slightly conservative results compared to the complex modeling composed with weld metal and base metal in the calculation of J-integrals and COD values which are used for the calculation of fracture toughness and postulated leakage crack length respectively.

• 한국안전학회지
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• 제15권2호
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• pp.59-62
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• 2000

Almost accidents related with gas have started with the leakage of LPG(Liquefied Petroleum Gas) in the open air. But experimental data of LPG leak jet are difficult to find because the safety of experiment is hard to secure and its phenomenon is not steady but transitional. This study is focused on the phenomena of injection jet of liquid butane to the open air. Simple experiment shows that only liquid butane jet in the open air is possible due to the slow vaporization because of low temperature difference between the liquid and air and low vapor pressure of liquid butane. Comparing with the water, 25~40% more liquid butane flow through the tube under the same pressure difference driving.

• 설비공학논문집
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• 제26권2호
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• pp.91-96
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• 2014

An acoustical model for detecting the leak location in a buried gas pipeline has been developed. This model is divided into an experimental model for sound diagnosis, and a theoretical model for sound prediction, which is based on the transfer matrix method, representing the sound pressure and the volume velocity as state variables. The power spectrum is measured by attaching only one microphone to the closed end pipe. It has been shown that the response magnitude of acoustic pressure signals calculated by the acoustical model depends upon the thickness and diameter of a pinhole. The validity for the acoustical model has been verified through a comparison between the measured and calculated results.

• 한국화재소방학회논문지
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• 제27권1호
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• pp.26-30
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• 2013

초고층건물의 수계소화설비에 있어서 적정 방수압력을 제공하기 위해서는 감압밸브의 사용이 필수적이다. 하지만 많은 경우 밸브 내 누설로 인한 균압 현상으로 인해 감압 기능을 상실하는 경우가 많다. 본 연구에서는 최근 개발된 균압 현상을 자동으로 방지해 줄 수 있는 새로운 개념의 감압밸브에 대한 성능평가를 수행하였다. 그 결과 다양한 설정 조건에도 불구하고 설계 감압비가 최대 약 11% 범위 내에서 유지되었으며, 피스톤의 자동 셀프 록(self-lock) 기능에 의해 균압 현상도 방지할 수 있는 것으로 나타났다.

• 한국압력기기공학회 논문집
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• 제6권1호
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• pp.43-49
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• 2010

The piping failure probability of the reactor coolant system in Kori unit 1 was evaluated considering stress corrosion cracking. The P-PIE program (Probabilistic Piping Integrity Evaluation Program) developed in this study was used in the analysis. The effect of some variables such as oxygen concentration during start up and steady state operation, and operating temperature, which are related with stress corrosion cracking, on the piping failure probabilities was investigated. The effects of leak detection capability, the size of big leak, piping loops, and reactor types on the piping failure probability were also investigated. The results show that (1) LOCA (loss of coolant accident) probability of Kori unit 1 is extremely low, (2) leak probability is sensitive to oxygen concentration during steady state operation and operating temperature, while not sensitive to the oxygen concentration during start up, and (3) the piping thickness and operating temperature play important roles in the leak probabilities of the cold leg in 4 reactor types having same inner diameter.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.425-430
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• 2008

To verify the system performance of portable AE leak diagnosis system which can measure with moving conditions, AE activities such as RMS voltage level, AE signal trend, leak rate degree according to AE database, FFT spectrum were measured during operation on total 11 valves of the secondary system in nuclear power plant. AE activities were recorded and analyzed from various operating conditions including different temperature, type of valve, pressure difference, valve size and fluid. The results of this field study are utilized to select the type of sensors, the frequency band for filtering and thereby to improve the signal-to-noise ratio for diagnosis for diagnosis or monitoring of valves in operation. As the final result of application study above, portable type leak diagnosis system by AE was developed. The outcome of the study can be definitely applied as a means of the diagnosis or monitoring system for energy saving and prevention of accident for power plant valve. The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the major valves at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized temperature water and steam flowed through glove valve(main steam dump valve) and check valve(main steam outlet pump check valve) on the normal size of 12 and 18 ". The valve internal leak monitoring system for practical field was designed. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. To improve the reliability, a judgment of leak on the system was used various factors which are AE parameters, trend analysis, frequency analysis, voltage analysis and amplitude analysis of acoustic signal emitted from the valve operating condition internal leak.

• 한국진공학회지
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• 제15권4호
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• pp.347-353
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• 2006

국제도량형위원회의 질량 및 관련량 자문위원회 (CCM)가 주관하는 헬륨 투과형 표준리크(standard leak) 핵심측정표준 국제비교 (key comparison, KC)에 참여하기 위하여 기존의 정압형 리크표준기에 porous plug를 추가하여 측정범위를 $10^{-6}$ Pa L/s 까지 확장한 헬륨 미세리크 표준기를 개발하였다. 이를 위해 헬륨 기체에 대한 고진공 및 초고진공 표준기의 압력비와 porous plug의 콘덕턴스를 새롭게 측정하였으며, 개발된 장치를 이용하여 명목 값이 $5.6{\times}10^{-4}$ Pa L/s 인 투과형 표준리크를 직접 교정한 결과 표준기와 차이가 11.1 % 임을 알 수 있었다.

• 한국산학기술학회논문지
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• 제21권4호
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• pp.546-551
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• 2020

함정에는 격벽으로 구분되어 나누어지는 공간인 격실이 종류와 목적에 따라 수개 혹은 수십 개가 존재한다. 이러한 격실들은 화재 및 화재로 인한 연기의 전이방지, 침수 시 침수의 확산 방지 등 특정 격실에서 발생하는 특이 상황들이 타 격실로의 전이를 방지하여 생존성 향상에 목적을 두고 설계된다. 생존성 향상 목적 달성을 위하여 각 격실들은 기밀 또는 수밀을 유지하도록 건조하며, 각 격실의 기밀 또는 수밀 정도를 확인하기 위하여 함정 건조 단계에서 평가를 수행한다. 건조하고 있는 군함에 관한 평가는 해군 지침에 의거하여 함 건조업체 주관으로 해군 및 국방기술품질원이 입회하여 평가를 실시한다. 생존성과 직결되는 만큼 격실 기밀 평가의 중요성은 매우 높아 명확한 기준에 따라 수행되고 있으나, 1개 이상의 복수개 격실 기밀 평가 시 1개 압력센서로 압력을 측정하여 격실 압력을 실시간으로 확인하는 것과 각 격실별 미세한 압력 변동 사항 확인이 제한되는 것을 식별하였다. 따라서 본 연구에서는 현재 수상함정 중 군함에서 실시하고 있는 그룹 격실 기밀평가 방안에 대한 개선 방안 및 신뢰성 검증 방안에 대해 서술하였다.

• Ocean Systems Engineering
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• 제2권1호
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• pp.17-31
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• 2012

This study investigated the behavior of a non-isothermal $CO_2$ bubble formed through a leak process from a high-pressure source in a deep sea. Isenthalpic interpretation was employed to predict the state of the bubble just after the leak. Three modes of mass loss from the rising bubble were demonstrated: dissolution induced by mass transfer, condensation by heat transfer and phase separation by pressure decrease. A graphical interpretation of the last mode was provided in the pressure-enthalpy diagram. A threshold pressure (17.12 bar) was identified below which the last mode was no longer present. The second mode was as effective as the first for a bubble formed in deep water, leading to faster mass loss. To the contrary, only the first mode was active for a bubble formed in a shallow region. The third mode was insignificant for all cases.

• 대한기계학회논문집
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• 제19권3호
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• pp.731-740
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• 1995

The objective of this paper is to develop defect assessment technology for integrity evaluation of CANDU pressure tubes. In fracture mechanics analysis, three-dimensional and two-dimensional (line-spring model) finite element analyses were performed to obtain the stress intensity factor for axial and circumferential surface cracks. In leak before break (LBB) analysis, heat transfer analyses for through-wall cracks were performed by considering the cooling effect and the LBB application time was computed. It was shown that the analytical results obtained in this study provide less-conservative but accurate solution for defect assessment of CANDU pressure tubes.