Balanced Field Electromagnetic Pipeline Crack Detection Method With Multiple-Correlation Demodulation

Balanced field electromagnetic technique (BFET) is an effective method for in-line internal inspection of pipeline cracks. To address the issue of tilted lift-off noise from sensors during the inspection process, this paper proposes a multiple correlation demodulation method that uses frequency-correlated processed detection signals for phase correlation calculations. In this paper, the crack detection principle of balanced electromagnetic technology is studied. The electromagnetic propagation characteristics of the crack detection signal and tilt lift-off noise are analysed. The reasons for the difference between the two waveforms and the signal characteristics are clarified. A multi-correlation demodulation model is established. Simulation and experimental results show that the phase peak of tilted lift-off noise remains constant. When the correlation coefficient is 0.33, multiple correlation demodulation can effectively remove tilted lift-off noise while preserving the amplitude and phase information of the crack detection signal. The phase peak of the crack detection signal after multiple correlation demodulation increases approximately linearly with increasing crack depth and also increases linearly with crack angle. After multiple correlation demodulation, the peak of the induced voltage increases linearly with increasing crack depth, but first decreases and then increases with increasing crack angle. This characteristic provides a foundation for further quantification of crack parameters and serves as a reference for noise elimination and signal identification in electromagnetic non-destructive testing of pipeline cracks.