Magnetic field with different frequencies of spatial components for flaw detection

The advantages of non-steady magnetic fields with the direction-varying field lines are well known in non-destructive testing. Magnetic field with orthogonal spatial components of slightly different frequencies is suitable for identification of electro-physical parameters of local conductive objects. Also this field can show good informative properties in other areas of non-destructive testing, as flaw detection of metal tubes, bars and wires. Eddy-current probes, based on the magnetic fields with spatial components of different frequencies, are less sensitive to misalign and angular displacement of testing objects than usual probes with encircling coils and more sensitive to extended flaws with small properties variation in longitudinal direction. New eddy-current technique was tested at Russian tube-rolling mills on water and gas tubes with up to 60 mm diameters at a speed up to 4 meters per second.