Plastic Pipes Conference Association # 2010 Vancouver
J.Bowman
Polyethylene (PE) resins are known to be sensitive to both sunlight and high ambient temperatures, such that excessive exposure can degrade the material. The inclusion of stabiliser packages into the polymer controls this potential for damage from outdoor aging. Reported in this paper are results on the stability and jointability of PE pressure pipes extruded with and without an integral and protective outer polypropylene (PP) skin, in the as-extruded form and after outdoor exposure in the Arizona desert to 3 GJ.m2 and 10 GJ.m2 of total radiation.
The stability of the resin trom the outer wall of the PE pipe was assessed after aging by measuring the oxidation induction time (OIT). The PP skin, even at 0.4mm thickness, provided protection for pipes receiving 10 GJ.m” of total radiation, as the OIT of the surface of the PE core pipe immediately below the skin was similar in value to the as-extruded and un-aged PE pipe. In contrast the OIT drops to close to zero for PE pipes without a protective skin when outdoor exposed to 3 GJ.m* of total radiation. Studies on the quality of electrofusion (EF) joints formed onto pipes after aging showed plain pipes (with no protective skin), prepared for EF joining by the use only of a cleaning cloth, had poor quality EF joints for 3 GJ.m* of total radiation, the de-cohesion tests being brittle in nature. In contrast, the skinned pipe subjected to 10 GJ.m” of total radiation prior to the peeling off of the PP skin, yielded high quality EF joints when the EF coupler was joined to the core PE pipe after removal of PP skin. The skin preserved the potential for high quality EF joints.
With ProFuse pipes the PP skin provides real protection from the effects of UV radiation and hign ambient temperatures, which then benefits the jointability of the core PE pipe, when joined by electrofusion. Utility companies in regions of high ambient temperatures and high UV radiation levels have much to gain from the use of skinned pipes of the correct structure, the skin protecting the core PE pipe to preserve or raise the integrity of water and gas distribution networks
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