Forced Magnetic Field Leakage (FMFL) - A new Approach to Non-Destructive Detection of Embedded Ferromagnetic Materials in Non-Magnetic Hosts

摘要

A new technique is proposed to detect magnetic defects and inclusions embedded in non-magnetic materials by magnetising the host with same polarity magnets. In this case, there is a forced magnetic flux leakage (FMFL) at the centre of the specimen which can be detected externally. The magnitude of the leaked flux at the position of the embedded magnetic material is higher than that of the case where there is no magnetic material there, and the difference between them can be accounted for by the presence of magnetic materials. Both Finite Element simulation and experiment have been performed on a control sample where the presence of a magnetic material at a welding site is imitated by introducing a thin Mild Steel (magnetic) ring in the inner circumference of Austenitic Steel (non-magnetic) pipe. The agreements between the simulated and experimental results are excellent, confirming that this new technique can be used for detecting magnetic materials embedded in non-magnetic hosts. The Forced Magnetic Flux Leakage (FMFL) technique can effectively be used in industries like oil, gas, chemical and civil engineering.