Eddy current detection of defects on metal components

Defects such as corrosion on either the inner or outer surface of a covered metal component 44 are detected through eddy current inspection, using at least two magnetising yokes 10a, 10b held fixed with respect to each other by a common excitation coil 20. The yolks are scanned over the cover of the component 44. A magnetic flux sensor 30 preferably on the leg of each yoke 10a, 10b detects changes in the magnetic flux that penetrates different depths into the covered metal component 44, depending on the relative position of each magnetizing yoke 10a, 10b. Sensors 30 may be located on one or both legs of the yolks, and each yolk may have more than two legs, each leg having its own sensor. Sensor coils may be differentially connected.