Pipe Performance

Long-term Burst Performance

The resistance of pipes to deformation and burst is determined by testing to international/ national standards. The test results are then used to calculate the maximum permitted hoop stress for hot water transportation according to a defined set of conditions, referred to as temperature classes. These temperature classes are compiled to reflect the likely cross-section of service conditions for a 50-year period for a range of different heating and water supply applications. The internationally accepted temperature classes are stipulated in ISO Standard 10508, and referred to in other systems standards for plastic piping systems.
Classification of Service Conditions for 50 Years CEN/ISO Classes
Service Conditions
Class Application Normal Maximum Malfunction
    Temp
°C		 Time
years		 Temp
°C		 Time
years		 Temp
°C		 Time
hours
1 Hot Water Supply @ 60°C 60 49 80 1 95 100
2 Hot Water Supply @ 70°C 70 49 80 1 95 100
4 Underfloor Heating Low Temp. Heating Systems 40 20 70 2.5 100 100
60 25
5 High Temp. Heating Systems 60 25 90 1 100 100
80 10

By employing standardised dimensional criteria, it is possible to calculate the maximum allowable hoop stress of competitive polyolefin pipes for each of these temperature classes as follows:

Maximum allowable Hoop Stress (MPa) (Design Stress) of Polyolefin Pipes For Hot Water Transportation
PB-1 PEX PE-RT PP-R
Temperature Class Polybutene-1
(ISO 15876-2)		 Cross-linked Polyethylene
(ISO 15875-2)		 Raised Temperature Resistance Polyethylene
(ISO 22391-2)		 Polypropylene Random-Copolymer
(ISO 15874-2)
1 (HWS 60°C) 5.73 3.85 3.30 3.09
2 (HWS 70°C) 5.06 3.54 2.70 2.13
4 (UFH and low temperature radiators) 5.46 4.00 3.26 3.30
5 (High temperature radiators) 4.31 3.24 2.4 1.90

These calculations indicate that the required wall thickness of Polybutene-1 pipes could be less than the other candidate materials for equivalent stress resistance performance. However the calculation of wall thickness depends on other additional standardised requirements with the result that with pipe diameters of less than 20 mm, all polyolefin pipes must comply to a minimum fixed thickness standard defined for a specific material. Consequently the performance benefit of Polybutene-1 pipes leads to an increase in the design factor of +35% in comparison with cross-linked polyethylene and +50% when compared with PE-RT, rather than in corresponding material savings.

For pipe diameters greater than 20 mm however, it is allowable to calculate pipe thicknesses according to standardised performance criteria where the advantages of using Polybutene-1 can be realised in terms of lower pipe weight and hence less raw material consumption and cost.

The following table illustrates the benefits of using Polybutene-1 in comparison with competitive materials in a 40 mm diameter pipe for a 50-year life expectancy at 70°C continuous operating temperature including design factors.

50 Years life (70°C curve) including safety factor
  PB-1 PEX PP-R PVC-C  
Pipe dimension 40 mm OD x thickness (mm) 3.7 5.5 6.7/8.0 4.5 mm
ID (Inner diameter) (mm) 32.6 29.0 26.6/24.0 31.0 mm
Pipe inner surface (mm2) 834 660 555/462 754 mm2
Pressure rating PN 16 PN 20 PN 20/PN 25 PN 25  
 
Flow speed at V = 2.0 l/s 2.4 3.0 3.6/4.4 2.7  
Loss of pressure  V = 2.0 l/s 18.4 32.5 49.5/81.3(SVGW/DVGW) 23.6  
Ratio of Linear pipe weight 1 1.44 1.66 1.57  
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