Creep Resistance of Polyethylene
All thermoplastics essentially act like elastic when stressed for a short period of time and will return to their prestressed state when the stress is removed. However, when stressed continually over a long period, they will “creep”, as the deflection of the material will increase with time.
The amount of “creep” that any plastic part experiences is influenced by several factors – the material from which it is made, the stress under which it is used, and the temperature at which it is exposed to the stress.
Because all plumbing systems are subject to continuous hoop stress from the pressure of the water within the pipes and possibly to elevated temperatures from the transport of hot water, the creep resistance of the materials used within these systems is of vital importance.
Polyethylene molecules demonstrate very similar characteristics as Polybutene-1 molecules at temperatures below around 60°C. The molecular bonds become weaker at elevated temperatures, which in turn severely reduce creep resistance at higher temperatures, making Polyethylene an unsuitable material for the manufacture of hot water plumbing systems. Thus Buteline have adopted Polyethylene as a material for the manufacture of pipes and fittings for cold water plumbing.
All the plastic materials used in the manufacture of Buteline fittings, whether for hot or cold plumbing systems, are selected because of their outstanding resistance to creep. Both Buteline hot and cold system fittings are tested and suitable for use at elevated temperatures.