The method specified is based on determining the temperature at which a standard indenter, under a force of 50 N ± 1 N, penetrates 1 mm into the surface of a test piece cut from the wall of a pipe or fitting while the temperature is raised at a constant rate. Is applicable only to thermoplastics materials for which it is possible to measure the temperature at which the rate of softening becomes rapid. Is based on ISO 306:1994 which, however, applies to materials in the form of sheets.