Detection of Corrosion Under Paint Using Magneto-Optic Imaging.

: This report describes developments in magneto-Optic imaging that make possible practical real-time imaging of surface corrosion under protective coatings in both steel and aluminum. The technology can also be applied to the detection of cracks. To accomplish imaging in steel a new method for producing rotating in-plane magnetization in steel parts was developed and combined with real-time magneto-optic imaging. Imaging in aluminum is accomplished by using an eddy-current excitation device for producing rotating in-plane eddy-current excitation. Small, relatively light-weight self-contained inspection systems suitable, in principle, for field applications have been produced. This project focused primarily on developing technology needed to accomplish inspections in steel. The resultant laboratory-prototype system for inspecting steel consists of a compact two-channel power-supply for "driving" novel surfaceconforming "quadrature' magnetic-yokes, a hand-held imaging probe that "nests" inside the yoke. and a CCD camemra-display system that provides real-time image monitoring and/or recording. Magneto-optic images of cracks or notches in steel pipes and steel plate, in addition to images of surface corrosion in both steel and aluminum are also illustrated. The potential for replacing some magnetic-particle based inspections (in steel) with the new magneto-optic imaging technology is briefly discussed.