One of the challenges in the offshore exploitation of ultra-deep oil resources is to keep the oil at a temperature sufficiently high so that it flows, despite the low water temperature. For that, metallic pipes are thermally insulated by a thick multilayered coating (70 mm) based on polypropylene with hollow glass microsphere (GSPP). The coating extremities of the 12 meter long pipe sections are removed to permit the welding of the metallic tubes. A polypropylene-polyethylene blend is injected to ensure the continuity of the coating in the welding area and thus the thermal insulation. A perfect weld between the two thermoplastic polymers is necessary. Cracks may be observed especially between the coating and the weld and this will damage thermal insulation but also induce corrosion of the metallic tube. To evaluate and characterize the industrial welding, a laboratory scale test has been established. A thick block of GSPP (70×50×25 mm) is placed in a mold. One surface is heated by contact with a hot plate. The polypropylene-polyethylene blend is then injected to form the welding. The samples are instrumented with thermocouples to determine the thermally affected zone which depends of the temperature and time of the heating phase and of the injected polymer. Computational simulation is used with Abaqus© software to establish the experimental protocol and predict the evolution of the thermally affected zone. The mechanical properties of the welding are analyzed by tensile tests performed at different temperatures corresponding to different locations in the thickness of the pipe coating. The morphology of the thermally affected zone is studied by scanning electron microscopy, X-ray diffraction and differential scanning calorimetry. The optimal welding conditions between these two thermoplastic are investigated and will be adapted to the industrial process. Keywords: Welding, Injection molding, Thermally affected zone, Thermoplastic.