Abstract

Although remote field eddy current had achieved successive application in pipes and tubes non-destructive testing, the poor ability and sensitivity to axial crack such as stress corrosion crack prevented its further application. A novel high resolution remote field eddy current detection method which can be suitable for axial crack especially stress corrosion crack detection was proposed and verified by simulation and experiment. First of all, conventional detection ability of remote field eddy current for crack in different directions was researched with detail. Aside from this, applicability of orthogonal magnetic filed in remote field eddy current was analyzed and simulated by finite element method, and appropriate configuration using to generating orthogonal magnetic fields for tubular structure was discussed and verified. Thirdly, design of detection system including key parameters selection and detection coil mode were researched. At last, proposed high resolution detection system were verified experimentally using various type defects, such as parallel axial crack and real stress corrosion crack. From the above research, conclusions were drawn as followed: the detection ability and sensitivity of proposed remote field eddy current detection system could be improved significantly compared with conventional system, especially for axial crack which was not easily to detect, and real stress corrosion crack could be detected and evaluated successively.

Highlights

  • Stress corrosion crack (SCC) is typical defect of industry tubular structures such as oil and gas pipes [1]

  • The effective method to improve performance of Remote field eddy current (RFEC) SCC detection is designing a novel sensor and detection system, which is more sensitive to tiny axial crack

  • (3) Sensor length reducing: In conventional RFEC, detection coil always fixed at 4~5 times tube diameter to avoid the jitter or off-center of sensor, and forbidden the ability to pass through the bend and elbow

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Summary

INTRODUCTION

Stress corrosion crack (SCC) is typical defect of industry tubular structures such as oil and gas pipes [1]. Non-Destructive Testing (NDT) is an effective method to detect it and avoid the occurrence of accident. Remote field eddy current (RFEC) is a “typical eddy current NDT method, which has advantages such as almost equal sensitivity to inner and outer defects, easy defect characterization and insensitivity to lift-off or wobble” [2, 3]. RFEC can detect many type defects of pipes and tubes, poor ability to detect SCC prevents its further application. It is mainly because of that conventional RFEC sensor using two solenoid coils as exciting and detection electromagnetic disturbance, and is more sensitive to circumferential defect than axial defect. The effective method to improve performance of RFEC SCC detection is designing a novel sensor and detection system, which is more sensitive to tiny axial crack

EXPERIMENT OF CONVENTIONAL RFEC NDT
Principle of Finite Element Method
Simulation of High Resolution RFEC
30 Hz sinusoid Axial
HIGH RESOLUTION RFEC DETECTION SYSTEM DESIGN
Excitation
Detection Coil
EXPERIMENT RESULTS
Results of Two Parallel Axial Cracks
Results of Real Stress Corrosion Crack
CONCLUSION
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