Theoretical Analyses of MFL Signal Affected by Discontinuity Orientation and Sensor-Scanning Direction

To improve the accuracy of the magnetic flux leakage (MFL) nondestructive testing in practical applications, we analyzed the MFL signal characteristics affected by discontinuity orientation and sensor-scanning direction. On the basis of magnetic dipole theory, the descriptions for the MFL field distributions of discontinuities in arbitrary orientations were established, indicating that the MFL density increases with the discontinuity orientation increasing from 0 to $\pi $ /2 and that magnetic flux always flows through the discontinuity perpendicularly, which was verified by relevant experiments. Further, the influence of the sensor-scanning direction on MFL signal features was analyzed and it was found that the MFL component signal parallel to scanning direction increases, the MFL component signal perpendicular to scanning direction falls, the MFL component signal perpendicular to discontinuity stays the same, and the widths of test signals become narrow, when the angle between the discontinuity orientation and sensor-scanning direction increases.