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Magnetic leakage flux testing with probes - physical principles and restrictions application

: Dobmann, G.; Hoeller, P.; Walle, G.

Non-destructive testing international : NDT international 20 (1987), Nr.2, S.101-104
ISSN: 0308-9126
Fraunhofer IZFP ()
defect size estimation; magnetic flux leakage testing; probe lift-off

This article reviews various factors which affect magnetic flux leakage testting with probes. The author's results for quasi-stationary magnetization are compared with results obtained by other authors for the DC magnetization. In particular, lift-off effects of the probe in combination with the influence of the defect width are discussed. For lift-off values much larger than the crack widths, which is the case in practice, the leakage field amplitude increases with the crack width for a fixed crack depth. This effect is responsible for uncertainties in defect size estimation and demands better criteria than amplitude criteria alone. (IZFP)