Marc Piriou

Enhancement of open-crack detection in flying-spot photothermal non-destructive testing using physical effect identification

This paper considers the images provided by a photothermal camera (flying-spot camera) dedicated to open-crack detection. In this type of active thermography, both thermal and optical effects contribute to the elaboration of photothermal images. Here the thermal effect is relative to the presence of open-cracks and the optical effects are due to surface conditions. In the case of open-cracks detection, the optical effects induce high magnitude perturbation signals, possibly masking the presence of open-cracks. In this contribution a signal processing method is proposed in order to identify both thermal and optical effects separately. The method lies uses multiple principal component analysis combined with a continuous wavelet transform. It is used to enhance the open-crack detection for the inspection of an industrial mock-up showing open-cracks and various surface conditions. The enhancement of the detection performance is characterized thanks to Receiver Operating Characteristic curves. The proposed method shows high detection performances and could be extended to a classification scheme.

Inspection of Bottom Mounted Instrumentation (BMI) J-Weld

Reactor Pressure Vessel (RPV) Bottom Mounted Instrumentation (BMI) primary nozzle ultrasonic (UT) inspections have been performed by AREVA for more than 15 years. EPRI demonstrations were performed in 2004 and an RSEM qualification was obtained in 2005, This UT inspection detects and characterizes cracks in the base metal of the penetration and its interface with the weld. A complementary Visual Examination of the weld or an Eddy Current examination may also be performed but these tests are understood to be marginal with a possibility to miss indications or to mistake inclusions or weld voids for in-service cracks and therefore could force an unnecessary repair. Difficulties associated with examination of this area include: • Unpredictable ultrasonic behaviour in the weld material; • Wavy and complex OD weld surface profile; • Restricted accessibility around the weld surface. AREVA’s Non Destructive Examination Technical Center (NETEC), has developed and/or evaluated several techniques to improve surface and volumetric inspection of this weld including: • A TOFD ultrasonic (UT) probe to detect and characterize cracks within the weld metal from the ID surface of the nozzle. • A flexible UT Phased Array probe to accommodate the wavy and complex weld surface, in partnership with CEA, • Reduced surface ET probes and flexible ET multi-coils (in partnership with CEA), for improved surface inspection, • Infrared Photo-Thermal Camera examination of the weld surface. This paper discusses the designs and performances of these specific probes and NDT techniques as applied to the BMI nozzles, J-welds, and other similar components.Copyright

HTR Fuel Integrity With Electromagnetic, Vision and Radiographic Nondestructive Evaluation Methods

In order to ensure HTR fuel qualification, as well as reactor safety, particles need to satisfy a set of specifications including particle integrity. To achieve this goal, AREVA NP has been engaged for several years in a R&D program aiming at the development of innovative industrial non destructive evaluation methods for HTR fuel as alternatives to destructive methods. After investigating a number of potential techniques, development has been focused on vision and eddy currents, both aiming at crack detection. High resolution Phase Contrast X-Ray imaging was also studied for structural defects characterization. For all these techniques, besides the development of HTR fuel dedicated control methods, equipment and probes were specifically designed, tested and optimized thanks to experiments conducted on real and artificial flaws, yielding for some of the methods to potential industrialization and quality control performed over 100% of the fuel production.Copyright

Photothermal NDE of CRD Penetration J-Groove Welds

A programmatic inspection of both old and replacement Reactor Pressure Vessel (RPV) heads is required by US nuclear utilities in response to the observed cracks and in some cases, leaks. Flaws can initiate either in the nozzle pipe, or in the J-Groove weld between the nozzle and the head. Inspection of the J-groove weld surface has historically been performed by eddy current (ET) or die-penetrant (PT) methods (Reference 1). Both approaches require complex robotic delivery mechanisms, are time consuming to perform, and are subject to false positive indications, or missed calls due to the very complex geometry. A new field-deployable photothermal non-destructive examination (NDE) system has been developed that offers distinct advantages over the ET or PT approach. A laser is scanned to heat a short line (∼20mm) on the material surface. Heat propagation perpendicular to the line is tracked with an IR imaging device. By appropriate signal processing, the image can enhance temperature change gradients indicative of cracks or material flaws. The method can be applied from up to 2 meters away from the surface and the detailed surface scans can be an optical scan rather than a complex-motion contacting tool scan of the surface. This paper outlines laboratory performance of the photothermal NDE system, discusses potential advantages over existing technology for RPV head J-groove inspection, and outlines additional developments for full field implementation.Copyright