Contact examination of components with complex geometry by a smart flexible phased array transducer
G. Cattiaux, O. Casula, C. Poidevin, G. Fleury,
4th International Conference on NDE in relation to Structural Integrity for Nuclear and Pressurized Components, London, December 6-8, 2004
Rapport DSR 48
The inspection of many components on nuclear equipments is mainly performed in contact by ultrasonic transducers coupled to solid wedges. The irregular surfaces and complex geometries of components (butt weld, nozzle, elbow) can not be fitted by the fixed shape of wedges during the scanning. This mismatch creates an irregular coupling layer between the wedge and the local surface, leading to beam distortions and losses in sensitivity. Previous studies  have shown that these two phenomena contribute to reduce the inspection performances leading to shadow area, split beam, ….
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, measures the local surface distortion allowing to compute in real-time the optimized delay laws to compensate the 2D or 3D distortions. 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.
To validate the concept of the Smart Flexible Phased Array Transducer, two prototypes have been integrated to detect flaws included in mock-ups with realistic irregular 2D and 3D shapes.
Inspections have been carried out on samples with a realistic irregular profiles and artificial flaws to estimate the enhancement performances of the "smart phased array transducer" compared to conventional contact probes.