Detection of Corrosion Under Paint Using Magneto-Optic Imaging Methods
Small Business Information
Physical Research, Inc.
25500 Hawthorne Blvd., Suite, 2300, Torrance, CA, 90505
Gerald L. Fitzpatrick
AbstractConventional NDI methods for surface corrosion are difficult. For example, because magnetic field- gradients associated with surface corrosion in steel are far smaller than those associated with cracks, magnetic-particle methods are ineffective in this context, even on smooth painted-surfaces. Ultrasonic methods requiring area-scans are too time-consuming. Similarly, NDI for aluminum surface-corrosion using scanned eddy-current coils is too time-consuming. Moreover, variable paint- thickness can easily mimic eddy-current corrosion signals. Real-time NDI techniques that are unaffected by standard thickness' of paint would be a major advance. Magneto-optic imaging is such a technique. The magneto-optic/eddy current imager (MOI) is widely used in NDI of (painted) aluminum airframes. Hence, MOI detection of aluminum surface-corrosion should be possible. Recent developments also permit MOI-imaging of surface corrosion on (painted) steel. This was accomplished by combining rotating in-plane magnetization with magneto-optic imaging. Hence, a single "hybrid" instrument, which is capable of performing surface-corrosion NDI on steel and aluminum should be possible. This proposal describes how "hybridization" will be accomplished, and presents experimental results confirming technical feasibility. The end-product of Phases I, II and III will be a portable, battery-operated, field-instrument which is designed to be used by relatively- inexperienced shipboard-personnel to accomplished surface-corrosion NDI on both steel and aluminum.
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