Abstract In the case of multi-pass welds, the material is very difficult to describe
due to its anisotropic and heterogeneous properties. Anisotropy results from the
metal solidification and is correlated with the grain orientation. A precise
description of the material is one of the key points to obtain reliable results with
wave propagation codes. A first advance is the model MINA which predicts the
grain orientations in multi-pass 316-L steel welds. For flat position welding, good
predictions of the grains orientations were obtained using 2D modelling. In case of
welding in position the resulting grain structure may be 3D oriented. We indicate
how the MINA model can be improved for 3D description. A second advance is a
good quantification of the attenuation. Precise measurements are obtained using
plane waves angular spectrum method together with the computation of the
transmission coefficients for triclinic material. With these two first advances, the
third one is now possible: developing an inverse method to obtain the material
description through ultrasonic measurements at different positions.