This document specifies the dimensions, the method of sampling, the preparation of the test specimens and the conditions for performing the tensile test with waisted test specimens in order to determine the tensile energy welding factor. A tensile test with waisted specimens can be used in conjunction with other tests (e.g. bend, tensile, tensile creep, macro, etc.) to assess the performance of welded assemblies, made from thermoplastics materials. The test is applicable to co-axial or co-planar heated tool butt welded assemblies made from thermoplastics materials filled or unfilled, but not reinforced. It is not applicable to tubular assemblies with a nominal outside diameter less than 90 mm.