Detecting flaws in steel tube or bar with a rotating coil in a magnetic saturating field

The equipment is unusual in that either eddy current or magnetic flux leakage is employed for flaw detection. A planetary scanning coil is rotated at high speed around the periphery of the tube, the incre mental permeability of which is reduced to approaching unity by using an intense magnetic field. Flaws 0.002 in. deep are detected under suitable conditions. The relative results of the two techniques are discussed against a background of laboratory trials using this equipment.