A recently novel strain-based approach recently proposed by Remes (Remes 2013) for the fatigue strength modelling of welded steel joints is extended here to consider multiaxial loading conditions and three dimensions finite element models. Only the first step of the approach to initiate a crack is presented in this paper. The multiaxial fatigue number of cycles to initiate a crack of full-scale tube-to-plate specimens in S690QL steel is assessed and compared to experimental results. As fatigue cracks are initiating at the weld toe, the statistical distributions of the main geometrical parameters of the weld are defined by the mean of 3D laser scans and used to perform parametrical analyses. In addition, variations in the material characteristics due to the welding process, i.e. in the heat affected zone and the base material, are considered. Effects of the residual stresses are also considered. Results of the parametrical analyses and comparisons with the experiments are presented and discussed.