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概要

NDE techniques using magnetic methods such as hysteresis loop, Barkhausen noise, magnetoacoustic emission, permeability changes are used for characterization of ferromagnetic steels and eva luation of degradation of steels. Also, magnetic flux leakage testing is used for wall thinning on the tubes in various plants. In this paper, a feasibility of those magnetic techniques for applying evaluation of small defects with sub-mm size was examined. As the results, the techniques except MFL method have no ability of the detection of such small defects because those me thods detect the averaged value in the area depends on dimension of the probe, while MFL can detect very small defects with several hundred micrometers due to its local detection principle.

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