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자성체 가스관에서 복수의 결함에 의한 원격장와전류 신호특성 조사
신영길,이윤태,송성철,정희성 국립7개대학공동논문집간행위원회 2004 공업기술연구 Vol.4 No.-
Remote field eddy current testing signals have unique signal characteristics such as the equal sensitivity to ID and OD defects and the linear relationship between defect depth and phase signal strength. In this paper, those and new signal characteristics are studied by carefully prepared experiments with gas pipes. Many kinds of defects are designed and fabricated, such as ID and OD defects, axial and circumferential defects, and multiple defects on the same circumference. Multiple defects on the indirect paths and very long defects reveal the linear relationship between defect depth and phase signal strength. Equal sensitivity to ID and OD defects is also demonstrated. It is found that the phase signal is more sensitive to axial defects and the phase signals from circumferential defects tend to underestimate the total defect length.
지지대에 인접한 전열관 결함으로 인해 발생되는 보빈 와전류 신호의 예측 및 분석
신영길,이윤태 국립7개대학공동논문집간행위원회 2005 공업기술연구 Vol.5 No.-
In this study, eddy current signals from various anomalous defects in the heat exchanger tube are predicted and their signal slope characteristics are analyzed. The signal changes due to frequency increase are also observed. Based on the accumulated knowledge, the analysis of superimposed signal is attempted which includes the effects of support plate. Both differential and absolute bobbin probe signals are analyzed. For the prediction of signals, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful to locate the position of defect under the support plate and absolute signals are easy to predict and analyze even though they are superimposed signals. Combined use of these two types of signal will help us accomplish a reliable inspection.
유한요소해석에 의한 절대코일 와전류 신호의 임피던스 평면도 작성
신영길,이윤태,이정호,송명호 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.4
와전류 탐상에서 차동형 탐촉자는 신호에 영향을 미치는 변수들을 줄일 수 있어 흔히 사용된다. 그러나 차동신호는 인접한 두 코일의 임피던스 차이를 신호로 사용하기 때문에 신호예측이나 해석이 쉽지 않다는 단점이 있다. 반면에 절대코일에 의한 신호는 상대적으로 형태가 단순하므로 신호예측이나 해석이 더 수월하다. 따라서 서로의 장, 단점을 상호보완적으로 사용하면 검사 신뢰도를 향상시키는데 큰 도움이 될 것이다. 본 논문에서는 인코넬 평판과 튜브에서 절대코일 신호를 예측하기 위하여 유한요소해석을 수행하였고, 리프트 오프, 충전율, 전도도, 탐상 주파수, 피검사체의 두께, 내, 외부 결함 등이 신호에 미치는 영향을 계산하여 임피던스 평면도로 작성하고, 신호특징을 분석하였다. 그 결과, 절대신호에 대한 많은 실용적인 지식을 축적할 수 있었고, 절대신호와 차동신호 특성의 유사성을 이해하게 되었으며, 결함깊이와 주파수 변화에 따른 신호의 기울기를 대응곡선 그래프로 작성할 수 있었다. In eddy current testing(ECT), differential probes have been frequently used since they can reduce the number of parameters that influcence ECT singles. However, differential signal is actually the difference of the two coil's impedance so that signal prediction and interpretation are not easy. On the other hand, absolute coil signal is rather straightforward to predict and analyze. Therefore, combined use of the two types of signals would increase the test reliability. In this paper, absolute coil signals from Inconel plate and tubes are predicted by the finite element analysis and effects of lift-off, fill-factor, conductivity, operating frequency, test specimen thickness, inner diameter defects, and outer diameter defects are investigated. As a result, various impedance plane diagrams are drawn and analyzed. Significant practical knowledge about absolute signals is accumulated and similar characteristics of the two types of signal could be understood. Finally, slope angle versus defect depth calibration curves are prepared for three different frequencies.
직경 1˝ 자성관에서의 원격장와전류 탐상 실험 빛 결함신호 특성
신영길,이창준,이정호,이윤태,장권규,송성철,송성진,정태언 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
In this study, a remote field eddy current testing system is built to inspect 1˝ diameter ferromagnetic tubes and resulting experimental signals are investigated. To decide the operating frequency, the emf of sensor coil is monitored while the sensor coil is moved away from the exciter. At proper frequency, sudden change would occur in the signal pattern. This also indicates the location of remote field region, so that the distance between coils can be decided. The defect signal contains two defect indications, each appears as the sensor and exciter coil passes a defect. Experimental results show that defect depth can be estimated by comparing the two indications. Also, linear relationship between defect depth and phase signal strength is observed.
가스관의 원격장와전류 탐상실험에서 관찰된 결함신호의 특성
신영길,이정호,이윤태,송성진,정태언 국립7개대학공동논문집간행위원회 2003 공업기술연구 Vol.3 No.-
When the identical coils are used for the exciter and sensor in the remote field eddy current (RFEC) probe, two defect indications appear in a single defect signal. The two indications are expected to be the same according to numerical simulation study. However, in our previous experimental work on 1" diameter ferromagnetic tube, we had found that the two indications in a phase signal are not identical and it may be possible to estimate the defect depth by comparing the two indications in a single phase signal. In this paper, those findings are re-examined with gas pipes whose diameter is 48.8 mm. At first, the operating frequency and the coil spacing in a probe are decided. Secondly, defect specimens are designed and built after examining edge effects and the signal sensitivity to the distance between sensor and defect. The RFEC testing experiments using these specimens show the same tendency as appeared in 1" diameter tube, i.e., the defect indication that appears in a phase signal as the exciter coil passes a defect is smaller for shallow defects, but it becomes bigger than the other for deep defects. This finding seems to be very important since it enables us to estimate the defect depth without preparing calibration curves for various depths of defects.