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증기발생기 전열관 검사를 위한 차동형 원격장와전류 탐촉자 설계
신영길,신상호,정태언 국립7개대학공동논문집간행위원회 2001 공업기술연구 Vol.1 No.-
As steam generator (SG) tubes have aged, new and subtle flaws have appeared. Most them start growing from outside the tubes. To find outer diameter defects more easily, the author had shown that the remote field eddy current (RFEC) technique, which had shown equal sensitivity to inner diameter (ID) and outer diameter (OD) defects, is feasible for the inspection of SG tubes. Based on the results obtained in that study, this paper designed a differential RFEC probe and studied the characteristics of differential RFEC signal. Finite element modeling studies show that the differential signal still has the equal sensitivity to ID and OD defects and at the same time it is possible to distinguish one from the other. Also noticed is that there is few degrees of signal rotation but sensitive changes in signal length when the depth of small defect varies. If the volume of defect is large, the changing rate of signal length is higher than that of defect size variation. The characteristics of signal show that the proposed differential RFEC technique can be a good alternative for the initial inspection of SG tubes.
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.
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.
渦電流 標潗浸透 깊이·表皮效果와 缺陷信號 位相角의 關係解析
鄭泰彦,張基玉,朴大英 韓國非破壞檢査學會 1985 한국비파괴검사학회지 Vol.5 No.1
An experiment to invertigate the rate of change of phase angle of eddy current output signal caused by outer surface defect of nonferromagnetic tube by variation of standard depth of penetration and variation of percent of tube wall penetration was carried out. The results of the experiment show that the phase angle of defect signal is increased with decreasing the standard depth of penetration or the depth of defect. The results also show that the phase angle is decreased with increasing the skin effect of eddy current, and that the resolution is decreased with decreasing the depth of defect.