Field application of eddy-current data processing

Eddy current examination of tubes in PWR steam generators aims at the detection and sizing of the highest amount of flaws. Due to considerations of time consumption, it was not realistic to perform several tests on the same tube using every time a different probe to cover the whole range of foreseeable defects. The circumferential bobbin coil was accepted as the best compromise and as far as French and Belgian plants are concerned, the performance of the equipment designed at that time allowed a travel speed of the probe of 0.5 m/s. Signal analysis has been based on phase measurement and the use of phase versus depth calibration curves. The correct use of multifrequency principles allowed the suppression of unnwanted signals and a level of confidence in the results of flaw sizing higher than that given by the use of a single frequency. However, as the drawbacks of the solutions adopted were not ignored, it has become necessary to develop new tools in order to meet new requirements. Fundamental works carried out by French Atomic Energy Commission have been adapted to the field and two application are described here