• 비파괴검사학회지
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• 제30권4호
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• pp.330-337
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• 2010

본 논문은 원전 증기발생기(SG, steam generator) 세관의 정밀 진단을 위한 차세대 탐촉자인 배열형 와전류 탐촉자의 특성 해석에 대한 3차원 전자기 수치해석을 수행하였다. 다양한 결함 해석을 위해 ASME(American Society of Mechanical Engineers) 표준시험편과 X-probe combo 표준보정시험편(inline EXP/spiral groove combo standard)을 선정하여 탐상신호를 획득하고, 실제 실험 신호와 비교하여 결과의 타당성을 검증하였다. 표준 보정 시험편의 해석 결과를 바탕으로 원전 SG 세관에서 주로 발생하고 있는 pitting, SCC(stress corrosion cracking), multiple SCC, wear 결함에 대하여 탐상신호를 획득하였다. 해석 대상으로는 원자력발전소 SG 세관으로 사용하고 있는 Inconel 600 도체관을 사용하였고, 이때의 시험주파수는 300 kHz이다. 본 논문을 통하여 각각의 결함에 대한 신호 특성을 파악하여 배열형 와전류 탐촉자의 결함의 종류에 따른 신호 특성을 확인할 수 있었다. 본 논문의 결과는 배열형 와전류 탐촉자의 와전류 탐상 신호 평가시 도움이 될 것이다.

• 비파괴검사학회지
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• 제26권2호
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• pp.90-98
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• 2006

원전 증기 발생기 세관의 MRPC probe 신호를 검사하고 평가하기 위해서는 일반적으로 Combo 표준 보정 시험편 신호가 신호 보정을 위해 사용된다 이렇듯 Combo 표준 보정 시험편 신호는 신호 평가에 중요한 영향을 미치지만, probe 상태나 관 주위의 여러 요소에 의해 쉽게 영향을 받기 때문에 결함 평가 요소인 신호의 크기 값과 위상각을 왜곡시킬 수 있다. 따라서 본 연구는 이런 문제점을 극복하기 위해 Combo 표준 보정 시험편의 실제 신호를 모사 신호로 대체하는 가능성을 알아보기 위해 실험을 해 보았다 이를 위해 MRPC probe와 Combo 표준 보정 시험편의 특성을 조사하였으며 계산 수행을 위해 체적 적분 방법으로 계산되는 상용 전자기 해석 프로그램인 VIC-3D를 사용하였고 모사 신호를 생성한 후 실험 신호와 비교를 통해 신호의 정확성을 확인하였다. 마지막으로, 모사 신호를 이용한 결함 평가를 위하여 실제 결함과 가공 결함에 대해 위상각과 크기 값의 항목으로 평가하여 실제 결함 평가자에 의한 결과와 비교하였다.

• 대한기계학회논문집B
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• 제27권12호
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• pp.1699-1707
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• 2003

Coriolis mass flowmeter(CMF), which can measure the mass flow directly, is getting rapid attention for the industrial and custody transfer purpose. In order to study the characteristics and the applicability of CMF, it is tested with the national flow standard system. Two types of sensing tube, U-type and straight type, are employed in the test. Water, spindle oil and viscosity Standard Reference Material whose viscosities are 1, 20 and, 67 $\textrm{mm}^2$/s, respectively, are studied. It is shown that the linearity of CMF is getting deteriorated as the fluid viscosity increases, which is due to the zero drift and the relaxation time of the fluid. To test its applicability in the case of high pressured gas, it is calibrated using compressed air, It shows 1∼l.6 % deviations compared to the calibration results using water. It concludes that the fluid velocity in CMF should be lower than the sonic velocity. In addition, the effects of the vibration from the pipeline and pump on CMF as well as the long term stability are studied.

• 한국압력기기공학회 논문집
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• 제10권1호
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• pp.75-81
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• 2014

A simulation of eddy current testing has been utilized for predicting the signal characteristics to the various defects and developing the probes. Especially, CIVA which is a simulation tool dedicated to nondestructive testing has a good accuracy and speed, and provides a three-dimensional graphical user interface for improved visualization and familiar data displays consistent with NDE technique. Although internal validations have been performed by the CIVA software development specialists, an independent validation study is necessary for the accuracy assessment of the software prior to practical use. For this purpose, in this study, eddy current testing signals of ASME FBH calibration standard tube for bobbin probe were simulated using CIVA and the results were compared to the experimental inspected signals based on the relationship between each flaw signal in terms of amplitude and phase, and the shape of the Lissajous curve. And then we verified the accuracy of the simulated signals and the possible range for simulation. Overall, there is a good qualitative agreement between the CIVA simulated and experimental results in the absolute and differential modes at the two inspection frequencies.

• Journal of Microbiology and Biotechnology
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• 제18권9호
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• pp.1550-1554
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• 2008

A hydrogen sulfide $(H_2S)$ detecting tube was developed for the quantitative determination of $H_2S$ produced by yeast during laboratory scale wine fermentations. The detecting tube consisted of a small transparent plastic tube packed with an $H_2S$-sensitive color-indicating medium. The packed medium changed color, with the color change progressing upward from the bottom of the tube, upon exposure to $H_2S$ produced by yeast during fermentation. A calibration study using a standard $H_2S$ gas showed that the length of the portion that darkened was directly related to the quantity of $H_2S$ (${\mu}g$) with a high correlation coefficient ($r^2$=0.9997). The reproducibility of the $H_2S$ detecting tubes was determined with five repetitive measurements using a standard $H_2S$ solution [5.6${\mu}g$/200 ml (28 ppb)], which resulted in a coefficient of variation of 3.6% at this level of $H_2S$. With the sulfide detecting tubes, the production of $H_2S$ was continuously monitored and quantified from laboratory scale wine fermentations with different yeast strains and with the addition of different levels of elemental sulfur to the grape juice. This sulfide detecting tube technology may allow winemakers to quantitatively measure $H_2S$ produced under different fermentation conditions, which will eventually lead winemakers to better understand the specific factors and conditions for the excessive production of $H_2S$ during wine fermentation in a large production scale.

• 비파괴검사학회지
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• 제28권4호
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• pp.339-345
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• 2008

원자력발전소 열교환기 튜브의 대부분은 구리, 티타늄, 인코넬합금 등의 비자성체로 제작되어 있으나 2차 터빈계통의 습분분리재열기(moisture separator & reheater), 급수가열기 등의 튜브는 고압, 고온 등의 열악한 운전조건에서 상대적으로 고온 강도가 우수한 탄소강 또는 페라이트계열 스테인레스강 등의 자성체로 제작되어 있다. 특히 습분분리재열기 튜브와 같은 열교환 매체가 증기인 경우 열전달 능력을 증가시키기 위해서 핀 튜브를 사용한다. 탄소강 또는 페라이트계열 스테인레스강 등의 자성체 튜브는 고온, 고압에서 강도가 우수하지만 운전 중에 증기 커팅, 침식, 기계적 진동 마모, 응력부식균열 등의 사용 중 결함이 발생하여 발전소 정상운전에 지장을 초래할 수 있기 때문에 전열관의 건전성 평가를 위한 주기적인 비파괴검사의 수행이 필요하다. 하지만 자성체 열교환기 튜브는 투자율이 높은 전기적 특성으로 인하여 기존의 와전류검사기술로는 비파괴검사가 어렵기 때문에 원격장검사기술을 적용해야 한다. 따라서 본 연구에서는 원자력발전소 습분분리재열기세관의 현장적용에 필요한 검사기술을 개발하기 위해서 원격장탐촉자, 인공결함 시험편 및 탐촉자 구동장치를 설계하였으며, 이를 활용하여 발전소 현장 검사에 적용하였다.

• 대한기계학회논문집B
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• 제30권6호
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• pp.497-504
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• 2006

A Coriolis mass flowmeter(CMF), which has U-Shaped unique measurins tube was developed fo. direct mass flow measurement. In order to convert the time difference between two measuring tubes motion into mass flowrate and flow quantity, a signal processing circuit, as a part of CMF, was also developed. The CMF was designed as the 15 mm nominal diameter of pipe connection and the 8 mm stainless steel(sus 316) pipe was used for measuring tube. To maximize the flow signal(time difference) from the measuring tubes, the natural frequency of measuring tube was adjusted as 220 Hz, which is same as the frequency of exciter. The maximum displacement at the end of the measuring tube was measured as 0.05 mm and the maximum time difference between two measuring tubes was observed as $20{\mu}s$, which was proper for discrimination and measuring range of CMF. The developed CMF was tested against the gravimetric flowmeter calibrator in the range of 3 kg/min and 30 kg/min. The results showed that the CMF has good linearity and repeatability in the tested flow range. Large size of CMF base on the current study experience will be developed.

• Nuclear Engineering and Technology
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• 제46권5호
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• pp.619-632
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• 2014

The Best Estimate Plus Uncertainty (BEPU) method has been widely used to evaluate the uncertainty of a best-estimate thermal hydraulic system code against a figure of merit. This uncertainty is typically evaluated based on the physical model's uncertainties determined by expert judgment. This paper introduces the application of data assimilation methodology to determine the uncertainty bands of the physical models, e.g., the mean value and standard deviation of the parameters, based upon the statistical approach rather than expert judgment. Data assimilation suggests a mathematical methodology for the best estimate bias and the uncertainties of the physical models which optimize the system response following the calibration of model parameters and responses. The mathematical approaches include deterministic and probabilistic methods of data assimilation to solve both linear and nonlinear problems with the a posteriori distribution of parameters derived based on Bayes' theorem. The inverse problem was solved analytically to obtain the mean value and standard deviation of the parameters assuming Gaussian distributions for the parameters and responses, and a sampling method was utilized to illustrate the non-Gaussian a posteriori distributions of parameters. SPACE is used to demonstrate the data assimilation method by determining the bias and the uncertainty bands of the physical models employing Bennett's heated tube test data and Becker's post critical heat flux experimental data. Based on the results of the data assimilation process, the major sources of the modeling uncertainties were identified for further model development.

• 비파괴검사학회지
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• 제32권1호
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• pp.56-63
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• 2012

본 연구에서는 가공된 오스테나이트계 STS 316L ASME 표준 교정시험편을 이용하여 튜브 두께 감소율과 잔존두께에 대한 와전류 신호와 IRIS 신호특성을 비교하여 리보일러 튜브의 현장 적용성을 평가하였다. 그 결과 두께감소율의 경우 와전류탐상검사는 $20%{\times}4$ 평저공, 10% 외면 그루브, IRIS는 80%홈, 10%외면 그루브에서 ${\pm}15%$ 이상의 편차가 발생하였다. 잔존두께의 경우 와전류탐상은 측정치가 모두 허용범위를 만족하였으나, IRIS는 80% 인공홈에서 ${\pm}15%$ 이상의 편차가 발생하였다. 따라서 와전류탐상검사 후 의사지시에 대한 해석, 두께감소율 측정을 위해 IRIS를 수행한다면 신뢰성이 향상될 것으로 판단된다.

• 한국대기환경학회지
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• 제34권3호
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• pp.393-405
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• 2018

Volatile organic compounds (VOCs) are representative air pollutants due to their detrimental effects on human health and their role in formation of secondary organic aerosols. Assessments and monitoring programs of VOCs using periodic grab sampling like Tedlar bags, canisters, and sorbent traps provide limited information, often with delay times of days or weeks. Selected ion flow tube mass spectrometry (SIFT-MS) is an emerging analytical technique for the real-time quantification of VOCs in air. It relies on chemical ionization of the VOCs molecules in air introduced into helium carrier gas using $H_3O^+$, $NO^+$, and $O_2{^+}$ precursor ions. Real-time monitoring method of 60 VOCs in the ambient air was developed using TO-15 standard gas mixture. Calibration curves, method detection limit, and quantitation reproducibility of the target compounds were tested. Dynamic dilution system was used to dilute standard gas from 0.174 ppbv to 100 ppbv, where calibration curves showed good linearity with $r^2$> 0.95 in all target analytes. Limit of detection (LOD) all compounds were sub ppbv, and some halogenated compounds showed pptv levels. Seven consecutive analyses of target compounds showed good repeatability with relative standard deviation of less than 10%. One day monitoring of VOCs in ambient air was conducted in Geoje. Average concentration of target VOCs in Geoje were relatively lower than other regions, among which formaldehyde showed the highest concentration ($15.4{\pm}5.78ppbv$). SIFT-MS provided good temporal resolution data (1 data per 3.2 minute), which can be used for identifying ephemeral short-term event. It is expected that SIFT-MS will be a versatile monitoring platform for VOCs in ambient air.