Influence of the uncertainty of elastic constants on the modelling of ultrasound propagation through multi-pass austenitic welds. Impact on non-destructive testing

Ultrasonic NDT is used on austenitic stainless steel welds in PWRs. Propagation modelling facilitates diagnostic concerning the detection of a possible defect if a realistic description of those heterogeneous anisotropic welds is introduced. A macrography, or MINA model, coupled with the ultrasonic code ATHENA, reproduces the deviations and divisions of the beam. In certain cases, some discrepancies between theory and experimentation are observed, and this study shows that they can be partly attributed to the uncertainty of the elastic constants Cij, complex to evaluate and measured on specimens sometimes little representative of the welded metal. We chose the seismogram as descriptor of phenomena to keep a maximum amount of information, to generate sensitivity and uncertainty maps. The zones sensitive (or not) to the variations of each Cij are revealed, helping in the choice of the test configurations. The analytical uncertainty propagation method is used to quantify the influence of Cij variability on the propagation simulation. The deviation in position and in time of flight of a classical ultrasonic test (NDT) is clearly shown.