DECEMBER 17--CEDIP Infrared Systems (www.cedip-infrared.com) is under contract with Framatome ANP (www.framatome-anp.com), the French manufacturer of nuclear plants, for the development of a new kind of camera, called the flying spot or photothermal camera, that can solve the problem of surface-crack detection in the nuclear and aviation industries. The new generation of photothermal camera, based upon the Framatome-Onera patented principle of flying spot, is to be used by Framatome ANP and its subsidiary Intercontrole for the inspection of nuclear pressure vessels, in an attempt to replace dye-penetration techniques.
The detection of cracks is particularly important for safety in the aviation and nuclear industries. Traditional crack-detection methods, however, are rather slow. Visual testing methods are still the most widely used, especially during the processing and maintenance operations. Among them, dye-penetration testing is probably the most popular one because of its low cost and high versatility. Nevertheless, in some cases, this simple technique cannot be used for reasons including surfaces that require noninvasive analysis, surfaces that are unsafe to humans (nuclear vessels), or where high surface roughness can lead to a high risk of false crack measurement. In addition, dye penetration does not lend itself to automation or online measurements.
In this system, the exterior of a sample under investigation is heated by the absorption of a CW laser scanning the surface. Focalization of the heating beam provides for three-dimensional heat diffusion that is sensitive to defects perpendicular to the surface. These infrared emissions are monitored by an infrared camera, the image of which scans with an adjustable offset the surface at the same velocity as the laser.
Based upon this unique and patented adaptation of the active IR thermography technique, the Flying Spot camera permits the detection of surface flaws in metallic materials. This novel system has been proven in field trials to reliably reveal cracks of only a few micrometers width in a contactless way even on rough 'industrial' surfaces. Initial results indicate that the flying-spot camera may be considered a true viable industrial alternative to conventional NDE techniques (dye penetration, eddy current, magnetic flux) for fast and remote detection of surface damage.