Wall Thickness & Design Stress
Due to the chemical properties of Polybutene-1 (PB-1) raw material, only Polybutene-1 (PB-1) piping can achieve high temperature and high stress but maintain lower wall thickness to ensure adequate water-flow through the pipe network.
Lower wall thickness also means a larger internal bore for a given external pipe diameter, resulting in reduced head pressure loss and lower flow speeds to deliver a fixed volume of water.
A comparison of the inside diameter/thickness of Polybutene-1 (PB-1) with other plastic materials is shown in the following graph:
Different material thickness (service life class 2 ISO 10508)
A more visual comparison can also be made using a series of cut-away diagrams:
Buteline pipe sizes are similar to traditional metal pipe sizing, making size-for-size substitution possible.
There is no need for upsizing, therefore Buteline pipe is an economical choice.
In addition to this, there is no scale build-up or corrosion with Buteline Polybutene-1 pipe.
|PB-1 Pipe||Outside Diameter (OD)||Wall Thickness (WT)|
|Type 18 PN 16||15.8mm - 16.0mm||1.6mm - 1.8mm|
|Type 22 PN 16||22.1mm - 22.3mm||2.1mm - 2.5mm|
|Type 28 PN 16||27.9mm - 28.2mm||2.7mm - 3.1mm|
Pipes made from Polybutene-1 have very high tensile strength even at higher temperatures resulting in high-pressure resistance and higher design stress than other plastic pipes that are also at elevated temperatures. For example, after 10 years exposure to continuously applied stress at 70°C, PB-1 pipe retains 40% more strength than PE-X pipe.
The standardised dimensional criteria presented in ISO 10508 makes it possible to calculate the maximum allowable hoop stress of various polyolefin pipes for the various standardised application temperature classes.
From the above table, the maximum allowable hoop stress for Polybutene-1 (PB-1) is found to be:
- At least 35% higher than for PE-X (cross-linked polyethylene) pipes
- At least 65% higher than for PP-R (polypropylene) pipes
- Over 50% higher than for PE-RT (polyethylene of raised temperature resistance) pipes
This effectively means that at equivalent thickness, Polybutene-1 pipes offer a significant safety factor over these alternative polymer materials for installed systems.