Development of RFECT System for In-Line Inspection Robot Considering Extendibility of Receiving Sensors based on Parallel Lock-in Amplifier

박재하,송성진,유희령,김대광,김학준,조성호,김희민,박관수,노용우 한국정밀공학회 2017 International Journal of Precision Engineering and Vol.18 No.2

This paper proposes a new and effective approach to design a remote-field eddy current testing (RFECT) system equipped with a large number of sensors in order to provide full circumferential coverage of pipelines larger than 6 inches. By developing a parallel digital lock-in amplifier (LIA), the extendibility of receiving sensors can be achieved, and therefore, the modification of RFECT systems, which should be accompanied by sufficiently securing the receiving sensors whose number increases with the pipeline size, can be minimized. Using the design method for an RFECT system based on a parallel digital LIA, a new non-destructive testing (NDT) platform that can be applied to RFECT systems of various sizes without modifying the system architecture is developed. It is then applied to an RFECT system that can be mated with an in-line inspection (ILI) robot and has 36 receiving sensors to inspect unpiggable gas pipelines. The performance of the RFECT system is verified with respect to the sensitivity and the accuracy of defect characterization though the pull-rig test having a number of artificial defects.

Enhanced Detection of Defects Using GMR Sensor Based Remote Field Eddy Current Technique

J. W. Park,J. H. Park,S. J. Song,M. B. Kishore,S. G. Kwon,H. J. Kim 한국자기학회 2017 Journal of Magnetics Vol.22 No.4

Remote field eddy current testing (RFECT) can detect defects in ferromagnetic pipes without requiring a couplant and contact with the pipe wall. Because the response in the remote field zone is extremely low, testing requires high-sensitivity detection to sense low magnetic fields. Therefore, a magnetic circuit design comprising a RFECT system is necessary for excitation and reception. In this study, a RFECT system using a giant magnetoresistance (GMR) sensor is proposed, and magnetic circuits with magnets and/or yokes are designed and optimized for improved reception. To investigate the characteristics of the designed RFECT system, finite element analysis (FEA) and experiments are performed on various magnetic circuit system configurations. System performance is verified with respect to sensitivity and the detectability of defect characterizations in 4-inch ferromagnetic pipelines having different defect sizes. Consequently, the magnetic circuit system using the permalloy yoke shows the highest sensitivity, thus achieving effective RFECT detection.

핵연료 피복재 튜브의 원격장와전류 탐상을 위한 차폐된 관통형 탐촉자의 수치해석적 설계

신영길,신상호 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.6

본 논문에서는 핵연료 피복재 튜브를 검사하기 위한 차폐된 관통형 원격장와전류 탐촉자의 설계과정을 설명하고, 이 탐촉자에 의한 결함신호의 특성을 조사하였다. 먼저, 자기 에너지가 튜브 내부로 관통될 수 있도록 여자코일 외부를 전기적으로 절연된 얇은 철 박판을 적층시켜 차폐시켰다. 그리고 유한요소 해석을 통하여 차폐의 효과와 탐상주파수를 연구하였으며, 센서코일의 위치를 결정하였다. 그러나 이렇게 설계된 탐촉자를 사용하여 예측된 결함신호는 센서코일이 결함을 지날 때의 결함지시가 명확하지 않았으며, 여자코일이 결함을 지날 때의 결함지시도 차폐체로부터의 영향이 나타나는 등 여자코일로부터 자속이 직접적으로 센서코일에 영향을 미친다는 사실을 알게 되었다. 따라서 센서코일도 여자코일과 같은 형태로 차폐시켰는데 이 차폐의 효과는 놀라울 정도로 결함신호의 특성을 향상시켰다. 최종적으로 설계된 탐촉자를 사용하여 수치 모델링을 수행한 결과는 관내삽입 원격장와전류 탐촉자를 사용하였을 때의 신호와 매우 흡사한 신호특성을 보였다. 즉, 위상신호는 내부결함과 외부결함에 대하여 거의 동일한 민감도를 보였으며, 위상신호의 세기와 결함의 깊이 사이에 선형적인 관계가 있음이 관찰되었다. This paper explains the process of designing a shielded encircling remote field eddy current (RFEC) probe to inspect nuclear fuel cladding tubes and investigates resulting signal characteristics. To force electromagnetic energy from exciter coil to penetrate into the tube, exciter coil is shielded outside by laminations of iron insulated electrically from each other. Effects of shielding and the proper operating frequency are studies by the finite element analysis and the location for sensor coil is decided. However, numerically simulated signals using the designed probe do not clearly show the defect indication when the sensor passes a defect and the other indication appeared as the exciter passes the defect is affected by the shape of shielding structure, which demonstrates that the sensor is directly affected by exciter fields. For this reason, the sensor is also shielded outside and this shielding dramatically improves signal characteristics. Numerical modeling with the finally designed probe shows very similar signal characteristics to those of inner diameter RFEC probe. That is, phase signals show almost equal sensitivity to inner diameter and outer diameter defects and the linear relationship between phase signal strength and defect depth is observed.

시뮬레이션을 활용한 유동층보일러 수냉벽튜브 검사용 원격장 와전류 탐상 센서 설계

길두송,권찬울,조용상,김학준,Gil, Doo Song,Kwon, Chan Wool,Cho, Yong-Sang,Kim, Hak-Joon 한국전력공사 2019 KEPCO Journal on electric power and energy Vol.5 No.1

화력발전은 국내 발전량 중 가장 높은 비율을 차지하고 있으며, 그 중 석탄보일러 발전이 가장 높은 비율을 차지하고 있다. 석탄보일러는 석탄 연소 중 유해 물질 및 미세먼지가 발생하여 대기오염에 심각한 영향을 미친다. 이에 친 환경 석탄보일러로 유동층보일러가 도입 되었으며, 이는 유동매체를 활용하여 기존의 석탄보일러보다 약 1/10정도 적은 오염물질을 배출한다. 수냉벽튜브는 이 유동층보일러에서 중요한 역할을 하는 구조물로, 유동층보일러의 특성상 기존의 보일러보다 외벽손상이 심하다. 하지만 아직까지 이에 대한 정량적인 유지보수 기법이 없다. 원격장 와전류 탐상은 튜브형태의 내, 외벽 검사에 많이 사용되는 비파괴평가 기법으로, 비접촉이며 빠른 검사가 장점이다. 하지만 원격장 와전류 탐상은 본래 배관 내부에서 진행하는 검사이며, 수냉벽튜브는 특성상 내부 진입이 불가능하다. 이에 본 연구에서는 시뮬레이션을 활용해 유동층보일러 수냉벽튜브에 적합한 외부 원격장 와전류 탐상 센서에 대한 설계를 진행하고, 시뮬레이션을 수행하였으며, 기존 원격장 와전류 탐상과 유사한 신호를 얻음으로써 추후 실제 제작 될 원격장 와전류 탐상 센서에 대한 기준을 제시하였다. 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.

강자성체 배관 탐상용 RFECT System의 설계에 관한 연구

이유기(Yu Ki Lee),김희민(Hui Min Kim),박관수(Gwan Soo Park) 한국자기학회 2014 韓國磁氣學會誌 Vol.24 No.6

Remote Field Eddy Current Testing (RFECT), one of the ways which is a nondestructive testing using electromagnetic fields, can make up for Magnetic Flux Leakage (MFL) weaknesses and general Eddy Current Testing (ECT) weaknesses which is an occurrence of a huge friction force or disadvantage of detecting defects on the outer wall. So many of institutes and laboratories have studied on RFECT for the past 50 years. But There is a lack of discussion about a study on eddy current and magnetic field distributions in a pipe wall and designing of RFECT exciter coil. In this paper, eddy current and magnetic field distributions in a pipe wall and influence of altering variables are analyzed. Also, the optimal design algorithm about the RFECT Exciter coil are proposed, and influence on defect signals caused by alteration of its shape is analyzed.

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.

Defect Detection of Oil and Gas Pipeline using Remote Field Eddy Current Technology

Mingjiang Shi,Lin Feng,Zhiqiang Huang,Mengfei Zhang,Hao Wen,Qing Liu 한국자기학회 2019 Journal of Magnetics Vol.24 No.3

To solve the problem of wall thickness reduction and defects of oil and gas pipeline caused by corrosion or erosion, a remote field eddy current (RFEC) testing method with coaxial double coil structure is proposed to detect corrosion residual wall thickness of oil and gas gathering pipelines. Based on electromagnetic field theories, RFEC technology is theoretically analyzed. The theoretical model of RFEC detection for coaxial double coil structure is established. The relationship between the voltage phase of detection signal and the wall thickness of pipeline is derived, and an evaluation method of the residual wall thickness of the pipeline based on the phase trough time of the RFEC detection signal is proposed. The parameters of RFEC probe are optimized by Finite Element Method, and the detection system is designed on the basis of it. The practicability and the correctness of the theoretical model of the detection system are verified by experiments. It can be used to detect the residual wall thickness of pipelines in real time under different media conditions.

연속된 배관의 결함 검출을 위한 개폐식 와전류 탐촉자 개발

김영주,안봉영,이승석 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.2

서로 연결되어있는 강관의 결함을 검사할 수 있도록 하기 위한 개폐식 탐촉자를 제작하였다. 본 탐촉자는 기존의 외삽형 와전류 탐촉자로서는 탐상이 불가능한 설치 가동중인 튜브류의 검사를 위한 것이다. 리본 케이블과 커넥터로 구성된 여기 코일은 접합/단락이 가능하게 하였으며 감지 코일은 튜브 외벽 근처에 원주 방향으로 어레이 형태로 배치하였는데 여기 코일로부터 튜브 직경의 1.5배정도 떨어진 위치이다. 제작된 탐촉자를 강관에 적용한 결과, 감도나 결함 크기 구분 등의 성능은 자기 포화형 탐촉자에 미치지 못하나 비교적 큰 결함의 발견이나 위치 파악 등에는 적용 가능한 것으로 나타났다. 크랙 형태의 표면 결함의 경우 두께의 19% 이상의 결함을 찾을 수 있었다. The open-connect type eddy current transducer for the flaw detection in continuously connected pipelines was developed. This eddy current transducer is for the on-line inspection of the tubes in industries, to which commercial emcircling proves are not applicable. The excitation coil that consists of a ribbon type cable and a flat connector can be opened and closed on purpose. The sensing coils of this transducer are circumferentially arrayed near the outside of the tube wall but axially displaced from the exciter by about one and half tube diameter. In application to steel tubes, and the performance of this transducer was evaluated as a little behind those of magnetic saturation type in signal to noise ratio and flaw size decision, but usable to detect or to locate large size flaws in steel tubes. Surface cracks deeper than 19% of the tube thickness could be detected with good signal to noise ratio.

가스 파이프라인 상의 압력 부식에 의한 흠집 검사를 위한 원격 와전류 탐상 기술

김대원(Daewon Kim) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.6

Magnetic flux leakage (MFL) pigs are traditionally used for the detection of gross corrosion on steel pipelines used for the transmission of natural gas. Alternative nondestructive evaluation (NDE) modalities are required for the detection of stress corrosion cracking (SCC) which tends to exist in colonies oriented axially along the length of the pipeline. This paper describes the use of multiphase rotating magnetic fields in the remote region of the probe as a possible SCC detection mechanism. Details of a prototype pig and test rig are given and the challenges associated with the finite element modeling of the device are discussed. Initial experimental results show that this novel NDE modality is sensitive to axially oriented tight cracks.