All thermoplastics essentially act like elastic when stressed for a short period of time and will return to their pre-stressed 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 (hot water plumbing systems in particular) are subject to continuous hoop stress from the pressure of the water within the pipes and to elevated temperatures from the transport of hot water, the creep resistance of the materials used within these systems is of vital importance.
Polybutene-1 is the material of choice for pipes used in hot water plumbing, as it is a very high molecular weight polymer, and the bulky ethyl radicals in its structure provide an extremely strong interaction between the molecules – all of which provide a high resistance to creep, even at elevated temperatures.
Thus Buteline Polybutene-1 (PB-1) pipe has excellent creep resistance that cannot be attained by any other polymer used for plumbing purposes today. This means that PB-1 pipes maintain their unique pressure performance over very long service lifetimes.
All the plastic materials used in the manufacture of Buteline fittings are also selected because of their outstanding resistance to creep. Both Buteline hot and cold system fittings are tested and suitable for use at elevated temperatures.