Why use Polyethylene (PE)?
- The most developed water network built from PE is in the UK.
- Since the early 60’s UK Water Authorities have been replacing old DI and more recently modified grades of PVC pipework systems for water and gas supply with PE.
- What was the reason for this change considering that of the old legacy material Ductile Iron was always the preferred option.
- SAFETY & SECURITY of PE in relation to failures or leaks on piping systems.
- In the UK for each 1000 km of water network currently installed in Ductile Iron you have an average of 204 leaks but conversely in the case of PE piping systems the leaks are only a fraction of that figure at 26 No. or 1/12th.
PE Material Properties
We can consider a design life of 50 years for PE pipes based on the following parameters.
A working temperature of 20° C at a working pressure of 10 BAR.
At 50 years you might start to see some slow crack propagation.
However some PE polymers developed in the last 10 years have through accelerated testing proved that they are able to resist the slow crack growth well beyond the 50 year period.
PE has excellent resistance to rapid crack propagation.
Polyethylene piping systems are perfectly sealed thanks to the welding procedures and the homogenous bond formed between the two melted pipe surfaces.
Even though PE is considered a soft material its volume loss in cubic millimetres is only 21 when compared to the same figure for steel which is 138 (volume loss is the friction of liquids inside the pipe with the PE pipe surface which could cause abrasion of the pipe wall, thus reducing the wall thickness of the PE pipe and consequently the volume of the pipe. Instead of volume loss, mass loss can be considered which is 20mg for PE100 and 1081mg for steel).
The use of carbon black additives protects the pipe from oxidation and helps maintain the pipes mechanical properties.
In the UK British gas has checked the deterioration of pipelines installed in PE after 7, 12, 18 and 24 operating years. All pipe sections were checked for physical deterioration and without exception the values of the PE raw material were the same as those for newly extruded product.
To clarify, even after many years use the PE pipes are maintaining the same properties as those pipes of new production.
One of the strongest arguments for preferring PE to other metal materials is the absence of the effects of corrosion – it doesn’t happen.
Let the figures speak for themselves.
The following figures represent the growing % share of PE pipes used for water distribution in
1993 – 55%
2002 – 65%
2007 – 70%