Fast Examination of Steam Generator Tubes by the means of the SET Eddy Current Probe
B. Benoist, T. Sollier, H. Schepens, M. Talvard, CEA Saclay, France; D. Boulanger, J. Reuchet CEA/IPSN-DES, Fontenay aux Roses, France
ABSTRACT A new probe has been developed i), to reduce the inspection time of SG areas usually inspected by rotating probes ii), to improve detection of circumferential cracks and iii), to enhance defect detection and characterisation in tube rolling area. The acronym SET stands for « Sonde à Excitation Tournante » which uses a rotating excitation concept. The SET probe is made of 16 Transmit/Receive units located on a single section of its body. This configuration was chosen to overcome disturbing effects on EC data due to speed variations of the probe. The main challenge with a reduced number of data collected per turn (16) compared to more conventional EC rotating probes (easily 200) is to obtain a good detection efficiency for small flaws and especially for small longitudinal cracks, the transversal configuration of the coils being clearly more suited for circumferential cracks. To overcome this limitation and to extend the spatial range of the conventional impedance coils, we have optimised 3 driving modes. Mode 1 is similar to the conventional impedance probe mode but is more convenient in an electronic view point. Mode 2 looks like a basic transmit/ receive mode with 2 transmitters to enlarge the sensitive area. It is particularly convenient for the detection of transverse cracks. Mode 3 has been optimised for the detection of longitudinal cracks : 3 adjacent coils are simultaneously driven to induce a larger eddy current pattern which better interacts with longitudinal flaws. Moreover, the orientation of the crack can be obtained from a comparative phase analysis : longitudinal cracks are detected with a 180° phase shift between mode 2 and mode 3. Those three modes are simultaneously active and produce a pattern electronically switched over the circumference of the probe.The SET has been operated at a translation speed of 200 mm/s and is excited with two frequencies simultaneously. Preliminary comparison with commercial rotating probes demonstrate the soundness of the SET concept. Experimental results obtained both on longitudinal and on transversal defects will be thoroughly presented. The latter prove the advantage of using electronic scanning to replace the mechanical rotation of the present day expertise probes.
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission.
Publisher: Woodhead Publishing Limited
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