The interpretation of on-sites inspections of austenitic or bimetallic welds is particularly difficult due to their internal structures. Indeed, skewing and splitting of the ultrasonic beam caused by inhomogeneity and anisotropy of the material may occur. This paper describes a ray-based model for simulating the ultrasonic wave propagation in such structures. The formalism based on dynamic ray tracing system in Cartesian coordinates along a known ray consists in solving eikonal and transport equations. The ray trajectories are obtained through the resolution of a system of linear ordinary differential equations of the first order, whereas the computation of ray amplitude requires solving the so-called paraxial ray tracing system. This method can be applied using a smooth cartography of the weld material properties obtained thanks to image processing techniques. In this case, the orientation of grains at each point of the weld is extracted by interpolation from the cartography. We present here simulation results using this method and comparison to finite element and experimental results.