Although, in recent years, there has been a tendency for municipal water managers to favour the use of polyvinyl chloride (PVC) for repairs to their pipeline systems, high-density polyethylene (HDPE) systems still have a distinct advantage in terms of their long-term performance. While the higher internal diameters possible with PVC and its compatibility with existing ductile-iron pipework are obvious benefits, HDPE welding provides a seal that does more than merely reduce leakage to within certain allowable limits; it eliminates leaks altogether So what is the secret of these exceptionally durable joints?
Metal pipes can either be welded or bolted together and sealed with a gasket, while PVC pipes can be fused or joined with adhesives. However, in each case, the resulting joints tend to be porous. This is responsible for typical leakage rates of between 10 and 20%. What is different about the HDPE welding process is that the joints it produces are totally watertight and thus their allowable water leakage is zero.
The process itself is quite straightforward and no weld-filler rod is involved. After cleaning the cut ends, the two sections of high-density polyethylene pipe are placed close together and their ends are heated until they become soft and pliable. At this point, the two sections are pushed together and pressure maintained for about three minutes while they cool. What is important to note about HDPE welding is that fusion will only be complete once the material has cooled below 120 °C, which should only take a further 10 minutes. By this time, the fused pipe is ready for installation. No thrust blocks or restraints are needed, as the fused joints are self-restraining and so installation is cheaper than for the alternatives.
In summary, while PVC may be cheaper and available in a wider range of diameters, what is significant about the use of HDPE and fusion welding is, because it can eliminate leaks completely, the long-term cost of this systems make it a highly competitive option that can offset the possible advantages offered by alternative systems.