Investigation of the parameters of samples that are used for eddy-current inspections

In order to eliminate errors that result from different properties of a calibration sample and a tested object when selecting the conditions for an eddy-current inspection, the electric and the magnetic properties of various steel grades were investigated that are necessary to analyze the positions of the hodographs on the flawless areas of the calibration sample and the test object and to make corrections for the expected changes in these properties that are caused by the effects of a gap for defective areas of a tested object. The study was carried out using samples that were manufactured of steel grades of different chemical compositions with a set of artificially made defects of known sizes. The test technique was evaluated on the basis of a reference specimen from D16 duralumin. The magnetic and electrical properties of the steel grades that are necessary to calculate the hodographs of the signals from the transition-type and lay-on eddy-current converters and to select test conditions are reported.