Conception, development and implementation of a non-destructive examination process for austenitic welds and austeno-ferritic materials by automated ultrasound with phased array transducer.

Bakhti, Samir; Omexom NDT; France

Bakhti, S.; OMEXOM; France
Fortineau, J.; OMEXOM; France
Mathieu, R.; OMEXOM; France
Ponton, J.; Omexom NDT Engineering and Services; France
Blachon, P.; OMEXOM; France

ID: ECNDT-0267-2018
Download: PDF
Session: PAUT-Nuclear Industry
Room: H2
Date: 2018-06-13
Time: 09:00 - 09:20

The primary loop of French nuclear power plants comprises a large number of weldings of components.
The assemblies have a singular area at the root of the welded joint of the parts. This stress concentration zone undergoes mechanical and thermal stresses which can cause the initiation and propagation of a failure crack, located on the side opposite to the scanning side.
Non-destructive testing (NDT) of these components is a major challenge for the safety of installations as well as for the optimization of preventive maintenance.
The welds of the primary loop have a highly anisotropic and heterogeneous structure, capable for degrading the performance of the control process by physical phenomena that disturb the ultrasonic beams (deflection and division of ultrasonic beams, variation in acoustic permeability, …).
This study treats the particular case of ultrasonic testing of a high thickness austenitic stainless steel welding of two molded austeno-ferritic steel parts constituting a nuclear power plant component. The structure of the base metal, on either side of the weld, makes examination more difficult because this material exhibits an heterogeneous coarse-grained structure : a large diffusion of the ultrasonic wave generates a high level of background noise which prevents an easy interpretation of the results.
Omexom NDT develops an automated ultrasonic inspection process of this type of component (including base metal and weld metal), using an original design of phased array transducer in order to scan this type of equipment, to make the interpretation of the results, to estimate the performance of the processes and to anticipate inspection difficulties (appearance of artifacts, beam deflection, high structural noise level, echoes of geometry, …).