Journal of the Korean Society for Nondestructive Testing (비파괴검사학회지)

The Korean Society for Nondestructive Testing (한국비파괴검사학회)
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GMR Sensor Applicability to Remote Field Eddy Current Defect Signal Detection in a Ferromagnetic Pipe

강자성 배관의 원격장 와전류 결함 신호 검출에 GMR Sensor의 적용성 연구

  • 박정원 (성균관대학교 기계공학과) ;
  • 박재하 (성균관대학교 기계공학과) ;
  • 송성진 (성균관대학교 기계공학과) ;
  • 김학준 (성균관대학교 기계공학과) ;
  • 권세곤 (한국철도공사 기술연구처)
  • Received : 2016.11.10
  • Accepted : 2016.12.12
  • Published : 2016.12.30
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Abstract

The typical methods used for inspecting ferromagnetic pipes include the ultrasonic testing (UT) contact method and the following non-contact methods: magnetic flux leakage (MFL), electromagnetic acoustic transducers (EMAT), and remote field eddy current testing (RFECT). Among these methods, the RFECT method has the advantage of being able to establish a system smaller than the diameter of a pipe. However, the method has several disadvantages as well, including different sensitivities and difficult-to-repair coil sensors which comprise its array system. Therefore, a giant magneto-resistance (GMR) sensor was applied to address these issues. The GMR sensor is small, easy to replace, and has uniform sensitivity. In this experiment, the GMR sensor was used to measure remote field and defect signal characteristics (in the axial and radial directions) in a ferromagnetic pipe. These characteristics were measured in an effort to investigate standard defects at changing depths within a pipe. The results show that the experiment successfully demonstrated the applicability of the GMR sensor to RFECT signal detection in ferromagnetic pipe.

강자성 배관의 대표적인 비파괴검사 방법으로 접촉방식인 초음파탐상(UT)과 비접촉식 검사인 누설자속탐상(MFL), 전자기초음파탐상(EMAT), 원격장 와전류탐상(RFECT) 기법 등이 있다. 특히 원격장 와전류(RFECT) 기법은 배관의 직경보다 작은 시스템 구축 등의 장점이 있다. 이런 장점에도 불구하고 array system을 구성할 경우 coil sensor 각각의 민감도 차이와 유지 보수 등의 문제가 있다. 이런 문제점을 해결하기 위해 크기가 작고 교체성이 우수하며 같은 민감도를 갖는 GMR sensor(giant magneto-resistance)를 적용하였다. 본 연구는 강자성 배관에 GMR sensor의 축 및 반경 방향의 원격장 및 깊이 변화를 가진 표준결함 실험을 통해 원격장 및 결함신호 특성을 확인하였고 강자성 배관에 원격장 와전류를 이용한 GMR sensor의 적용 가능성을 확인하였다.

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References

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