Numerical modelling is widely used in the framework of inspection qualification processes, since it offers the capability to study a wide scope of configurations and at a lower cost compared to a full experimental campaign. In this context, the reliability of simulation models is of the highest importance. In order to evaluate this reliability and determine the field of application of CIVA simulation tools, a long-range collaborative work has been engaged between the CEA-LIST & EXTENDE. This is based on comparisons between experimental results and CIVA predictions on configurations representative of industrial NDT applications. After an overview of the validation works initiated, this paper focuses on the presentation of results obtained in tandem mode, a UT technique commonly used for the detection of side wall weld defects, such as in the zonal discrimination method. In this configuration, a pair of single element transducers located one after the other scans the part, one being the transmitter and the other being the receiver. This technique can also use a phased-array probe with two separate groups of elements. The comparisons between experimental and simulated results obtained on such configurations are presented in this paper.