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Analysis of Magnetic Flux Leakage Testing for Longitudinal Discontinuities in Sucker Rods

The detection of sucker rod discontinuities is an urgent, scientifically difficult problem to be solved in the oil industry. In this paper, the modeling and testing technologies for longitudinal discontinu-ities in sucker rods were studied using finite element analysis software. The magnetic flux leakage (MFL) testing simulation was carried out, and a double-coil direct current (DC) magnetization model was established. The simulation results showed that the magnetizing field is stable and close to a uniform magnetic field. The testing model for the longitudinal discontinuity was set up, and the axial MFL signals were extracted at different heights above the discontinuity. Meanwhile, the MFL data were analyzed and compared, and the effects of magnetization level and discontinuity size on the MFL testing were discussed for enhancing detection reliability. Finally, the peak of leakage magnetic field was obtained under different liftoff values, and the relation curve between the liftoff value and the peak of leakage magnetic field was achieved. In this way, the key data between the sensor and detection device could be measured. Study results indicate that the MFL double-coil magnetization approach can be used to detect longitudinal discontinuities in sucker rods.

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