EDGE DETECTION ON EDDY CURRENT IMAGE TO INCREASE DEFECT CHARACTERIZATION B. Benoist, P. Attaoui, R. La Commissariat Ii I'Energie Atomique (CEA) Centre d'Etudes et de REcherches sur les Materiaux (CEREM) Service des Techniques Avancees (STA) CE Saclay, 91191 Gif-sur-Yvette Cedex, FRANCE R. Lengelle, P. Gaillard Universite de Technologie de Compiegne (UTC) URA 817, Compiegne, FRANCE J. Reuchet Commissariat Ii I'Energie Atomique (CEA) Institut de Protection et de Silrete Nucleaire (IPSN) Departement d'Etudes de Silrete (DES) CE Fontenay-aux-roses, 92265 Fontenay-aux-roses Cedex, FRANCE INTRODUCTION As the nuclear yard ages, the control of steam generator tubes (SGT) must deal with new problems. In fact new defects appear, especially in the area of the tube sheet, of the tube support or at the U-bend area. Eddy current testing using Rotating Probe Coil (absolute mode) gives a better resolution. These measurements allow smaller defects to be detected along different orientations, especially defects along the circumference in the rolling transition. Signals collected during the exploration of the tube internal wall with this coil contain the useful information which is represented in the form of a cartography (or image) for each of the signal complex components. For example, defect characterization in kiss rolling zone (i.e. primary wall Stress corrosion cracking) consists of assessing its orientation, size and depth. Among safety regulations for SGT inspection, circumferential defect or longitudinal defect (free length above the tube sheet is less than 13 mm) result in the plugging of the tube. Expertise of SG of 900 MW PWR's using eddy current multifrequency (F 1 =500 kHz, F2=240 kHz, F3=100 kHz and F4=30 kHz) testing using Rotating Probe Coil (RPC) consists of scanning the inner surface with an absolute coil (diameter equal to 1 mm). The scanning is helical (the step is 0.5 mm, figure 1). The expertise consisted of examining the images of each component (X or Y) and of each frequency response (Fl, F2, F3 and F4). The paper deals with the automatic characterization of defects through the application of image processing tools. The aim is to produce a planar representation of the Review of Progress in Quantitative Nondestructive Evaluation, Vol. 15 Edited by D.O. Thompson and D.E. Chimenti, Plenum Press, New York, 1996 829 CORE Metadata, citation and similar papers at core.ac.uk Provided by Digital Repository @ Iowa State University