We consider how to predict defect sizes, depth and width, from wave forms of the leakage flux obtained by the magnetic leakage flux method. Measurements of leakage flux were carried out using plane specimens with various values of depth and widthof the defect and the lift off which is the distance between the specimen surface and the probe, and a quasi-weld reinforcement specimen. The absolute value of maximum leakage flux was affected by the plate thickness or the shape of reinforcement not butby the defect shape. Therefore the absolute value method used by many researchers is not suitable for estimating the sizes of defect in a joint in which the average flux is not known. However, the wave form of leakage flux is almost unaffected by factorsother than the defect sizes. The depth and width of the defect are estimated by the proposed method that the two feature points of the wave form, for example the maximum leakage flux and one-tenth of the maximum value, of experimental value are combinedto the above feature points of the wave form calculated from the dipole modeling.
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