A Numerical Model for Ultrasonic Time-of-Flight Diffraction (TOFD) Testing of Austenitic Welds

Austenitic stainless steel welded components are widely used in industrial applications. Due to the large grain size of these welds, ultrasonic testing of them is a difficult task. In this paper, the propagation of ultrasonic waves in austenitic stainless steel welds prepared by shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) processes is modeled by finite element method. The grain structure of welds prepared by these two processes are completely different. First, the exact grain structure of each weld is extracted by examining the weld grain structures on a welded specimen. The weld areas of the two welds are then divided into several domains and the grain orientation of each domain is extracted. The elasticity tensor of the orthotropic weld material is also measured. In meshing of the finite element model, the grain orientation in each domain is accounted for by rotating the elasticity tensor of the elements of that domain along the direction of grains. The propagation of waves in time-of-flight diffraction (TOFD) ultrasonic testing of the welds is then simulated by using this model. Actual TOFD tests are also conducted on the welded test specimen in which crack-like slots are implanted. The TOFD signals collected from welds are then compared with the results obtained from the finite element model. Very good agreement is observed between the simulated and measured results indicating that the proposed finite element model can accurately model the SMAW and GTAW austenitic welds.