Improving SNR of MFL detecting defect signal of drill pipe by using pole piece

The magnetic flux leakage (MFL) technique is generally considered to be an efficient and effective non-destructive testing (NDT) method and has been widely used in the oil field inspection industry for the examination of drill pipe. This paper studies the resistance distribution in the magnetic circuit of magnetic flux leakage detection probes and proposes the method of adding a pole piece to reduce magnetic resistance. The magnetic circuit model is simulated by using finite element analysis and the results show that the detection probe with a pole piece can strengthen the magnetic leakage signal for a drill pipe defect, and pole pieces with different thicknesses have little influence on the defect magnetic leakage signal in the circuit. Practical testing confirms that the probe with a pole piece can clearly improve the SNR of the MFL signal. The analysis results are of great value for improving defect identification rates and for the precise detection of defects.