Ultrasonic and structural characterization of anisotropic austenitic stainless steel welds: Towards a higher reliability in ultrasonic non-destructive testing

The non-destructive testing of austenitic stainless steel welds of the primary coolant piping system is a significant problem for the nuclear industry. Ultrasonic techniques would be very helpful to detect, locate and size potential defects. Unfortunately, austenitic welds are coarse-grained, heterogeneous and anisotropic. This leads to aberration and scattering of the ultrasonic waves. In this paper, we present several experimental results of ultrasonic testing of two austenitic welds exhibiting high anisotropy. In order to explain the observed display of wave propagation phenomena such as beam deviation, we use finite element modeling. The modeling is associated with a complete characterization of the inspected welds. Two essential characteristics of the welds are determined: the average elastic constants of the weld and the grain orientations. The capability of the model is illustrated in different testing configurations. This work associating structural characterization and modeling shows that a better understanding of the phenomena of ultrasonic propagation should allow the interpretation and reliability of the industrial inspections of heterogeneous anisotropic welds to be improved.