The defect depth evaluation based on the dual-sensor strategy: Resisting the lift-off disturbance in magnetic flux leakage testing

The quantitative evaluation of defect information is the key issue in magnetic flux leakage (MFL) nondestructive testing on ferromagnetic materials. For the multi-sensor strategy with the same lift-off values, the arrayed layout of probes improves the testing efficiency, but the evaluation precision is still susceptible to the lift-off disturbance. This paper recommends a dual-sensor strategy with a given lift-off difference to resist the lift-off disturbance. Here, the reason for the possible overestimating and underestimating evaluation is clarified for the traditional single-sensor strategy using the magnetic dipole theory in MFL testing. In this paper, the effectiveness of the proposed dual-sensor strategy is demonstrated by comparison with the traditional single-sensor strategy. Analysis shows that the proposed dual-sensor strategy in MFL testing can overcome the lift-off disturbance and improve evaluation precision of the defect depth in cases with uncertain lift-off values. This study provides a path for the quantitative evaluation of MFL testing based on the dual-sensor strategy.