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Poliplex PE100 Pipe

Polyethylene (PE) pipes have been produced in Australia since the mid 1950’s, whilst initially in smaller diameters for industrial and agricultural applications, PE pipe and fittings are now available in diameters up to 2000mm. Usage has grown rapidly over this period and polyethylene resins are evolving from the tradition PE100 from the growing demand for higher performance, longer-life PE pipes that will provide reliable service for 100 years or more.

Material Properties

Mechanical Properties
Property Value & Unit
Density (Specific Gravity) 955kg/m3
Yield Strain 10%
Yield Stress 25MPa
Compressive Strength 32MPa
Tensile Modulus 900MPa
Hardness Shore D 63
Poisson’s Ratio 0.4
Ring bending modulus (3 mins) 950MPa
Ring bending modulus (50 yrs) 260MPa
Thermal Properties
Property Value & Unit
Coefficient of Thermal Expansion 1.8 x 10-4/°C
Thermal Conductivity 0.38W/m.K

Typical Fire Resistance Properties

Property Value & Unit
Ignitability 13
Smoke Development 3
Spread of Flame 7
Heat Evolved 6
Temperature effect on pressure rating

The co-efficient of thermal linear expansion of polyethylene varies with temperature but at ambient lies in the range 1.2 to 2.4 x 10-4 per degree C. In broad terms, this is about twenty times that of steel. and therefore unrestrained pipe will expand or contract much more than the steel structure that may be supporting it.

Should the pipe be fully restrained, the strain due to thermal change will generate stress in the material. However due to °the relatively low tensile deformation modulus of polyethy ene and assuming a typical ambient temperature fluctuation of less than 40 C, it can be assumed that the safe allowable stress will lnot be exceeded. Over the longer term, stress relaxation will increase the ability of polyeth­ylene to accommodate high thermal strains.

The conductivity of polyethylene varies with temperature almost linearly and is typically O .4 7W/m.K at o•c to 0.37W/m.K al 70°C.

The specific heat of polyethylene varies with temperature from 1800 Joules/kg.Kat o•c to 2200J/kg.K at 60°C.

All temperatures above 25°C it is necessary to rerate polyethylene pressure pipe systems. The table below provides guidance as to the maximum operating pressure of PE100 pipes at temperature. It should be noted that at constant temperatures greater than 40°C, the 50-year design life of POLlplex ® pipes may be reduced.

Thermal rerating of PE100 polyethylene POLIplex® pipe

Maximum allowable operating pressure - PE100 Water pipe (m head)

Temp°C PN4 PN6.3 PN8 PN10 PN12.5 PN16 PN20 PN25
20 40 63 80 100 125 160 200 250
25 36 58 73 91 115 145 182 227
30 36 58 73 91 115 145 182 227
35 33 53 67 83 106 133 167 208
40 33 53 67 83 106 133 167 208
45 (35 y)* 31 49 62 77 99 123 154 192
50 (22 y)* 29 46 57 71 91 114 143 179
55 (15 y)* 29 46 57 71 91 114 143 179
60 (7 y)* 27 43 53 67 85 107 133 167
80 (1 y)* 20 32 40 50 63 80 100 125

i. The values tabled are for POLlplex® pipe manufactured to AS/NZS 4130 and fittings made from compounds complying with AS/NZS 4131.

ii. The times given in years as (35y) are allowable extrapolation limits obtained by applying the factors in Table 1 of ISO 9080 to two years of test data at 80°C. Where appropriate. specific advice should be obtained from the manufacturer. and data provided shall be derived from testing to ISO 9080.

Thermal expansion and contraction

The co-efficient of thermal linear expansion of polyethylene varies with temperature but at ambient lies in the range 1.2 to 2.4 x 10-4 per degree C. In broad terms, this is about twenty times that of steel, and therefore unrestrained pipe will expand or contract much more than the steel structure that may be supporting it.

Should the pipe be fully restrained, the strain due to thermal change will generate stress in the material. However due to the relatively low tensile deformation modulus (E) of PE and assuming a typical ambient temperature fluctuation of less than 40°C it can be assumed that the safe allowable stress will not be exceeded. Over the longer term, stress relaxation will increase the ability of PE to accommodate high thermal strains.

Flammability

On the application of heat, polyethylene melts at between 120°C and 135°C and will catch fire at 340°C in the presence of name. Combustion is not self supporting if there is less than 17% oxygen present.

Under the appropnate conditions, polyethylene burns in air with a faintly luminous yellow flame to yield carbon dioxide and water. In uncontrolled fire conditions, other compounds can be produced including carton monoxide, aliphatic and aromatic hydrocarbons together with various oxygen containing substances.

Permeability

This property refers to the passage of either liquids or gases through the molecular structure of a material. Polyethylene resin, being hydrophobic, has a low permeability to water vapour, It is also relatively impermeable to gases such as carbon dioxide. ethylene, natural gas, oxygen, methane, air and nitrogen.

It does, however, exhibit significant permeability to some other gases and liquids such as aliphatic, aromatic and chlorinated solvents which are soluble with polyethylene. As a general rule, the larger the vapour molecule or the more dissimilar in chemical structure to polyethylene, the lower will be the permeability. To calculate the loss of gas from a PE pipe Fick's first law is applicable. This can be written:

Volume of permeating gas (m3) = g ΠDLPT/t

where

g = permeability coefficient (m3 per m.MPa.day)

D = outside of diameter (m)

L = length of pipeline (m)

P = partial pressure (MPa)

T = time (days)

t = thickness (m)

Poisson’s Ration

When any elastic material, including polyethylene, is extended by a longitudinal force it will simultaneously contract in the lateral direction. The ratio of the (smaller) transverse strain to the longitudinal strain is the Poisson's Ratio for the material and ranges from 0.3 for metals to 0.5 for rubber polymers. For PE, a value of 0.4 is accepted for calculation purposes.

Because of the comparatively high circumferential strain in a PE pipe under normal operating pressures, the longitudinal contraction may be significant where there is no restraint. This can occur in above ground installations or where slip liners are not grouted. In these circumstances the pipeline may require anchoring to prevent separation, The ultimate circumferential strength of the pipes will increase slightly when axial contraction is prevented.

Worked Example

Problem: By what amount will a POLIplex One Hundred pipeline shorten due to Poisson's effect when operating at class PN head?
Solution:

Circumferential (hoop) strain= Design Stress(MPa)/Long-term Modulus (MPa)

8.0/200 or 4%

Longitudinal = Poisson's Ratio x hoop strain

= 04 x 0.04

= 0.016

or 1.6% of length of pipeline

That is at maximum working head an unrestrained pipeline 100 metres long will shorten 1.6 metres and a 6 metre length joined with a mechanical coupling will contract 96 millimetres.

PE100 Material Composition

The PE100 polyethylene resin used in POLIplex® pipes and fittings are pre-compounded, either black or coloured with pigment, complying with AS/NZS 4131. Anti-oxidants are used to inhibit oxidation of the polymer at the compounding stage and during subsequent processing.

Carbon black is used in all black POLIplex® pipe at a concentration of 2.25 ± 0.25% by mass as an ultra violet radiation absorber.

In natural and coloured POLIplex® materials, hindered amine light stabiliser (HALS), ultra violet absorber. is used in lieu of carbon black.

Chemical Resistance

Polyethylene is a polyolefin resin, in chemical terms a non-polar high molecular weight paraffin of the hydrocarbon family. Hence it is very resistant to (non-oxidising) strong acids, strong bases and salts. It is mildly affected by aliphatic solvents although aromatic and chlorinated solvents will cause some swelling. Polyethylene is affected by strongly oxidising substances such as halogens and concentrated inorganic acids. POLIplex® pressure pipes should not be used to convey water disinfected with chlorine dioxide at any temperature which has been found to rapidly deplete the antioxidant additives at elevated temperature.

View the Iplex Chemical Resistant Tool