A flexible phased array transducer for contact examination of components with complex geometry
16ème conférence mondiale sur les contrôles non destructifs, Montréal, 30 août-3 septembre 2004,
Rapport DSR 30
The inspection of many components on nuclear equipments is mainly performed with contact ultrasonic transducers. The surfaces of components involve that the shapes of the solid wedges are not matched to the irregular surface or to the shape of components (butt weld, nozzle, elbow). This mismatch creates an irregular coupling layer between the wedge and the local surface, and can lead to beam distortions and losses of sensitivity. These two phenomena contribute to reduce the inspection performances.
To improve such controls, a new concept of contact “smart phased array transducer” has been developed with the support of the French "Institut de Radioprotection et de Sûreté Nucléaire" (IRSN). The phased array is flexible to fit the complex profile and to minimize the thickness of the coupling layer. The independent piezoelectric elements composing the radiating surface are mechanically assembled in order to build an articulated structure. A profilometer, embedded in the transducer, allows to compute in real-time the optimised delay laws to compensate the distortions of 2D or 3D profiles. Those delay laws are transferred to the real-time UT acquisition system, which applies them to the piezoelectric elements. This self-adaptive process preserves, during the scanning, the features of the focused beam (orientation and focal depth) in the specimen.
Two prototypes are presented and inspections of realistic irregular profiles of 2D and 3D geometry mock-ups, including artificial flaws, have been carried out, to estimate the enhancement performances of the "smart phased array transducer" compared to conventional contact probes.