WELDING PROCEDURE The procedures stated below should be regarded as a general guideline only. The manufacturer of the HDPE pipe should be asked to supply specific recommendations for welding of their products or materials. Likewise, the welding machine supplier shall supply detailed welding procedure for their machines. Heat fusion bonding is a combination of temperature and force resulting in two mating surfaces flowing together to produce a joint. Fusion bonding occurs when the joint cools below the melt temperature of the material. There is a temperature range within which any particular material may be satisfactorily joined. The specified temperature used requires consideration of the properties of the specific material, the fusion equipment being used and the welding environment. The butt-welding is done in several phases and by using several parameters. The operations can be summarised as follows: - The alignment of the pipe - The shaving of the surfaces of the pipe ends - Cold matching of the HDPE pipes - Cleaning of surfaces - Heating of surfaces - Fusion of surfaces - Cooling of weld joint