In the extrusion of thermoplastic profiles, weld lines are formed whenever the profiles are hollow, being promoted by the spider-legs used to support the required torpedo(s), or when flow separators are used to help balancing the flow. In both cases, the flow is separated in two or more fronts, which rejoin downstream the physical obstacle (spider leg or flow separator). Close to these obstacles surface, the polymer melt flows at a very low speed, being abruptly accelerated after detaching from their rear end wall. This acceleration induces high molecular orientation along the flow direction, hindering the molecular diffusion that would attenuate the weld line detrimental effect. In this work, numerical and experimental approaches are combined, in an attempt to relate the thermomechanical conditions in which weld lines are formed and their mechanical strength. For this purpose, a prototype extrusion die (encompassing a moveable spider-leg, its positioning/fixing system, and a tool conceived to change the spider-leg location) was designed [1]. This special extrusion system was used to produce tapes under different flow conditions, by varying the location of the spider leg (i.e., its distance from the die outlet) and the flow rate. These tapes were then mechanically characterized through tensile and flexural tests. The experimental case studies used were numerically studied, with the help of the foam-extend branch of the open-source computational library OpenFOAM®, considering a viscoelastic Giesekus constitutive model. The numerical results were analyzed, targeting the identification of potential relationships between the flow conditions in which the weld lines were formed and their strength. The results obtained allowed to identify a clear correlation between those two factors. [1] CARNEIRO, O S, MOTA, A R, SITOTAW, Y, NÓBREGA, J M, Int Polym Proc Vol. XXXI (2016), pp 254-261 (DOI 10.3139/217.3200)