Multi-Frequency Eddy Current Testing of Ferromagnetic Welds
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Begun in 1973, the Review of Progress in Quantitative Nondestructive Evaluation (QNDE) is the premier international NDE meeting designed to provide an interface between research and early engineering through the presentation of current ideas and results focused on facilitating a rapid transfer to engineering development.
This site provides free, public access to papers presented at the annual QNDE conference between 1983 and 1999, and abstracts for papers presented at the conference since 2001.
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Abstract
Single frequency phase analysis eddy current techniques have limited potential for inspections for surface cracking in inhomogeneous ferromagnetic welded surfaces [1). Signals from these cracks are masked in noise produced by lift-off, probe wobble and local changes of the permeability of the weld, the most troublesome noise source. Surface cracks and changes in magnetic permeability create signals with phase angles that are too close to be discriminated from each other. Another method, in addition to phase discrimination, must be used to distinguish crack signals from signals created by changes in magnetic permeability. This paper explores the use of the comparison of phase and amplitude data from two probe frequencies to distinguish cracks from changes in local magnetic permeability.