Digital Processing for Ultrasonic Testing of Components Generating a High and Heterogeneous Structural Noise

Paul, Nicolas; EDF R&D PRISME; France

Paul, N.; EDF R&D PRISME; France
Foata, M; EDF CEIDRE SEND; France
Kassis, P.; EDF R&D PRISME; France

ID: ECNDT-0071-2018
Download: PDF
Session: Microstructural Scattering - UT 1
Room: J2
Date: 2018-06-13
Time: 09:00 - 09:20

This work focuses on non-destructive examinations using ultrasonic waves on complex materials generating a high and heterogeneous structural noise on the examined area. A first application of TOFD (Time Of Flight Diffraction) testing on Pressurised Water Reactor vessel penetration tubes is described here.

During an ultrasonic examination, multiple diffusion of the ultrasonic waves caused by grain boundaries makes the discrimination between structural noise and a potential defect intricate. The difficulty of the diagnosis can moreover be increased when the structural noise appears to be inhomogeneous on the examined area, which can be caused by evolutive coupling conditions or by a heterogeneous distribution of the grain sizes.

In order to facilitate the analysis of these acquisitions, EDF R&D in collaboration with EDF CEIDRE has designed and patented numerical processing methods embedded in the EDF software « CORUS ». The heterogeneity of the structural noise is handled via a local normalisation coefficient which allows to fully homogenize the acquisitions. Spatial filters are then applied to reduce the variability of the values taken by the structural noise on a C-scan, thus increasing the defects detectability.

CORUS has been successfully tested on several acquisitions from mock-ups and from many real vessel penetration tubes presenting a high and heterogeneous structural noise. The improvement in terms of signal-to-noise ratio depends on the defect depth. It varies from 6 to 14 dB.

The presented processing methods are not only dedicated to TOFD examinations of vessel penetration tubes. They also apply to any ultrasonic inspection of some heterogeneous material.