Application of Modelling for Enhanced Ultrasonic Inspection of stainless steel welds

The ultrasonic inspection of the primary coolant piping of Pressurized Water Reactors (PWR) is a major concern for the nuclear industry. Numerous studies have been undertaken over some years by EDF R&D in collaboration with the French Atomic Energy Commission (CEA) to improve the non-destructive testing (NDT) process for these applications and to help towards their qualification. More particularly, a great deal of work was carried out on the inspection of austenitic stainless steel welds. Indeed, the anisotropic, heterogeneous and coarse granular structures of these welds lead to important disturbances of the ultrasonic propagation: beam skewing and splitting, attenuation, backscattering and ghost echoes. This paper presents the methodology developed for modelling the ultrasonic inspection of austenitic welds, which is based on an accurate characterization of the material. Two numerical approaches are presented: a finite elements code, ATHENA, developed by EDF, and a semi-analytical code that is a part of the CIVA simulation platform developed by the CEA. These codes simulate the propagation of the ultrasonic beam in the weld and calculate the defect-beam interaction. Ultrasonic beam disturbances are illustrated from experimental and numerical results for different applications. In particular, the influence of variations in the weld structure on NDT performance is discussed. This comparison between experiment and modelling shows the modelling methodology to be valid.