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PB-1 | Pipe Comparison

When long-term performance characteristics of plastics materials is compared, Polybutene-1 offers the total package for piping systems. Whether it is compared for flexibility, resistance to chemicals, creep, pressure and CLTE stress (Cyclic Linear Thermal Expansion); acoustic capabilities, product weight or toughness, Polybutene-1 delivers the long-term performance required for today's hot and cold pressurised piping systems.
 

Polybutene piping extrusion process allowing huge scope in pipe wall sections and diameters


PB-1 Piping Profile

Comparison of polymers used in piping systems
  PB-1 PP-R PE-X PVC-C
Impact Toughness +++ ++ +++ +
Chemical Resistance +++ +++ +++ +++
Flexibility ++++ ++ +++ +
Creep Resistance ++++ +++ +++ +++
Pressure Resistance ++++ ++ +++ +++
Weldability ++++ ++++ + ++
Resistance to Temperature & Pressure ++++ ++ +++ ++
Thermal Stress in Installations ++++ ++ +++ +
Sustainability
of System
++++ +++ +++ +++
Speed of Joint
Small Ø
++++ + +++ ++
Large Joint Ø Availability ++++ ++++ ++ +++

    Excellent  ++++    Good  +++    Fair  ++    Poor  +
 

The unique morphology and crystallisation behaviour of PB-1 gives it unrivalled properties for pressurised piping systems.

The ideal choice for pressurised piping systems

The property combination setting PB-1 apart from competitive materials is its high flexibility combined with outstanding resistance to internal pressure creep resistance over a wide range of temperatures.

All polyolefinic materials tend to creep when exposed to continuous stress over a long periods of time.

This cold flow behaviour can be suppressed by creating a 3-D network in the polymer structure such as the physical and chemical linking utilised in the manufacture of Polyethylene (PE-X). Polybutene-1 however, displays superior inherent creep resistance (see table below) without the need to apply any additional cross linking, copolymerisation or compounding modification.

In its simplest homopolymer form, the property profile of Polybutene-1 makes it the ideal choice for satisfying the demands of hot and cold pressure piping systems applications.
 


Pressure Resistance

The performance comparison of PB-1 and alternative plastics materials

Parallel standards to ISO 12230 exist which present the effect of time and temperature on the expected strength of the materials listed below. The data presented in these standards provides a useful means of comparison of the performance of these alternative plastic materials used for piping systems.

The following figure shows the performance reference lines (pressure resistance properties) for the following materials at 70°C on an equivalent scale:

Best performing materials

  • PB-H | ISO 12230 (2012)
  • PB-R | ISO 12230 (2012)

Medium performing materials without knee point

  • PE-X - ISO 15875 (2003)
  • PP-RCT - ISO 15874 (2013)
  • PE-RT type II - ISO 12230 (2012)

Low performing materials with knee point

  • PE-RT type I - ISO 22391 (2009)
  • PP-R - ISO 15874 (2013)

After 10 years of exposure to continuously applied stress, the best performing Polybutene-1 (PB-H & PB-R) retains over 50% more strength than the medium performing materials (PE-X, PP-RCT & PE-RT type II) and 70% - 90% more strength than the lower performing materials PE-RT type I and PP-R.


Design stress

After 10 years of continuously applied stress, PB-1 retains over 50% more strength than PE-X, PP-RCT and PE-RT type II, and 70-90% more strength than PE-RT type I and PP-R.

By employing standardised dimensional criteria presented in ISO 10508 it is possible to calculate the maximum allowable hoop stress of these alternative polyolefin pipes for the various standardised applicational temperature classes. This calculation of design stress results in the comparison presented in the table below which shows that PB-1 polymers achieve the highest hoop stress values across all standardised application classes. The intrinsic stress bearing advantage of PB-1 is between 35% and 90% higher, depending on application class and material. This effectively means that at equivalent thickness, PB-1 pipes offer a significant safety factor over these alternative plastic materials for installed systems.
 

Design Stress
@10 bar
Class 1
HWS 60°C
Class 2
HWS 70°C
Class 3
Low Temp UFH
max 50°C
Class 4
UFH & LT Heat
max 70°C
Class 5
HAT Heat
max 90°C
20°C/50y
PB-H 5.73 5.04 7.83 5.46 4.31 10.92
PB-R 5.17 5.13 7.82 4.34 4.13 10.93
PE-X 3.85 3.54 4.61 4.08 3.24 7.60
PP-R 3.09 2.13 4.68 3.30 1.90 6.93
PP-RCT 3.64 3.40 5.73 3.67 2.92 9.24
PE-RT I 3.32 2.68 4.65 3.27 2.38 6.68
PP-RT II 3.53 3.37 5.12 3.38 2.88 7.46
PVC-C 4.38 4.16 10

From the maximum allowable hoop stress, we can calculate a minimum allowable wall thickness. It is clear from the calculation that Polybutene-1 pipes can be produced with a significantly reduced wall thickness when compared to other materials dependent on applicational standards limitations. 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.

*PE-RT denotes Raised Temperature Resistance polyethylene


Creep Resistance

Superior long term creep resistance

In contrast to other thermoplastics used in piping applications, performance modification via compounding, cross-linking or copolymerisation is  not necessary for PB-1 piping systems to fulfil the stringent performance standards applied to their use.

In comparison with other polyolefin materials, Polybutene-1 has a higher level of resistance to strain under continually applied stress over long periods of time. This is known as creep behaviour and the graph illustrates the superior performance of PB-1 at times in excess of 100 hours.

In addition to its excellent mechanical and thermal properties, PB-1 provides a high level of resistance to chemical attack and also offers a level of flammability resistance meeting the demands of most applications.

PB-1 can be processed via standard injection moulding or extrusion processes into a broad range of products. In its most simple homopolymer form, the balance of properties of PB-1 make it the technically preferred material for the production of pressurised hot and cold water piping systems.
 


Weight, Flexibility
and Hydrostatics

Pipe weight and hydrostatic efficiency


Calculated for application class 2, 10 bar design pressure, based on published data.

 


Acoustic Properties

Sound dampening

The thinner pipe walls, high elasticity and low specific density in PB-1 pipes leads to high absorption of operating noises.

Among the superior properties of Polybutene-1 in comparison with other materials its excellent sound dampening. The combination of thinner pipe wall construction, low elastic modulus and low specific density in Polybutene-1 pipes (ρ = 0.9 g/cm3) leads to high absorption of “water hammer” and other noises associated with heating and cooling in pipe systems. Tests showed a 90% reduction of pipe-borne noise in the Royal Albert Hall in London after the installation of PB-1 pipes.
 

Sound velocity of materials
  Density (g/cm3) Elastic Modulus (MPa) Sound Velocity (m/s)
Soft Rubber 0.90 90 320
PB-1 0.93 350 620
PE-X 0.95 600 800
CPVC 1.56 3,500 2,350

Water hammer

A column of moving water within a pipeline contains stored kinetic energy arising from its mass and velocity. Since water is essentially incompressible, this energy cannot be absorbed when a valve is suddenly closed. The result is a high instantaneous pressure surge normally referred to as 'Water Hammer'.

The low elastic modulus of Polybutene-1, combined with reduced wall thickness gives rise to a low surge pressure for a given pipe OD and pressure rating. The table below compares maximum surge pressure for 38.1 mm (1-1/2") OD pipes of different plastic materials, designed for the same pressure service.

Five factors determine the severity of water hammer

  • Velocity
  • Modulus of elasticity of the pipe material
  • Inside diameter of the pipe
  • Wall thickness of the pipe
  • Valve closing time

The maximum surge pressures caused by water hammer can be calculated using the following equation taken from the 'Handbook of Thermoplastic Piping System Design', Thomas Sixsmith and Reinhard Hanselka, Marcel Dekker Inc., pp 65-69

Ps = V((3960 E t)/(E t + 3 x 105 DI))½
where:
Ps = surge pressure (psi)
V = water velocity (ft/sec)
DI = inside diameter of the pipe (mm)
E = modulus of elasticity of the pipe material (psi)
t = pipe wall thickness (mm)
 

  E E DI t V Ps Ps
  [psi] [MPa] [mm] [mm] [ft/s] [psi] [bar]
PB-1 65000 450 32.5 (1.28") 3.8 (0.15") 5.0 49.5 3.4
PE-X 87000 600 28.9 (1.14") 5.6 (0.22") 5.0 72.4 5.0
PP 116000 800 26.7 (1.05") 6.6 (0.26") 5.0 93.0 6.4
CPVC 507000 3500 30.9 (1.22") 4.6 (0.18") 5.0 140.6 9.7

 

Polybutene is often referred to as Polybutene-1, Polybutylene, PB-1 or PB.

Polybutene is not sold by PBPSA members for use in pipe applications intended for use in North America, and those parties require their customers or distributors not to sell products made from Polybutene into pipe applications for North America.