This paper presents a 3D thermo-mechanical model of arc-welding applied to tubular K-joints susceptible to fatigue cracking. The 3D torch trajectory is reproduced to simulate both temperatures and stresses during welding and ultimately the 3D residual stress distribution after cooling. The influence of latent heat, of the increase of thermal conductivity to simulate the fluid convection within the weld pool, the activation of finite elements to simulate the use of filler wire and the number of passes on as-welded residual stresses is assessed using ABAQUS. Actions taken to simplify the problem and reduce the computation time are presented and discussed. Comparisons of fusion zones obtained numerically and using optical macrographs as well as comparisons between calculated and measured residual stresses are presented. This numerical analysis highlights high tensile residual stresses occurring at the gap zone which is the most critical location where fatigue cracks initiate and propagate in tubular bridge K-joints.