Improvement of the sensor system in magnetic flux leakage-type nondestructive testing (NDT)

In magnetic flux leakage (MFL)-type nondestructive testing (NDT) system, the sensitivity of MFL sensor depends on the change of the magnetic field, not just on the magnitude of the field. In this paper, the leakage parameter was defined to determine the operating point in saturation curves, and an optimum design method to determine the size of the magnet to maximize the MFL signals in NDT is described. For detecting the small depth defect, we also developed the back yoke sensor system. The sensitivity of the optimum sensor system is increased up to 200%. The computed MFL signals in the optimally designed system are verified by measurement using Hall sensors mounted on the six-legged PIG in an 8-in test pipe with defects. The rhombic defects could be successfully measured and identified from the weak defect signals