The presence of weld lines can cause a significant reduction in the mechanical properties of injection molded plastic parts, especially when they contain minerals additives or fiber reinforcements, and it is a common reason for their failure. In this work a method for modifying the flow pattern in the weld line zone using a 'flow disruptor" is proposed to strengthen the weld lines of fiber reinforced polypropylene. The flow disruptor is a small insert introduced inside the injection molding cavity, in the weld line area, and its objective is to mix the melt and disrupt fountain flow in order to blur and erase the weld line. The method is simple and low cost, does not require special machines or molds and does not affect the part shape or surface. Flow disruptors were designed, their effects analyzed by using simulation software, fabricated from different materials and encapsulated within injection molded tensile test samples for mechanical properties evaluation. The results of this work demonstrate that the mechanical properties in the weld line can be improved by the use of a well designed flow disruptor, made from suitable materials.