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KIO composite covers installed in NEW BOULEVARD
Path: Cable conduits | Physical, chemical properties
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Physical, chemical properties


The high density polyethylene is a thermoplastic resin.
At room temperature the density is between 0,94 and 0,96 g/cm³, about 60 % is crystalline the remaining is amorphous.
Between 125° - 135° C, polyethylene melts and the viscosity is molecular weight dependent. The melt density drops to 0,80 g/cm³.
The polyethylene resists to the most chemical products and solvents. Only some substances, such as the decahydronaphtalene or some aromatic or halogenated hydrocarbons, dissolve the polyethylene at high temperatures.
The chemical destruction of polyethylene can occur only under the action of strong oxidizing agents such as fuming nitric acid or fuming sulphuric acid.


MECHANICAL PROPERTIES

The most important mechanical characteristics of a conduit are:
a) resistance to deflection;
b) resistance to impact.


The first characteristic is the most important as the pipe is buried and subjected to the static and dynamic load.
Any load caused by stress (described later in this chapter) on the ground that covers the cable ducts must also be added.
The second characteristics regards the accidental stress caused by the stones in the ground falling onto the cable duct surface during pipe-laying.
For this reason, the ground layer around the cable duct must be free from stones bigger than 80-100mm.
No more low-temperature tests are required with polyethylene as it can resists to low temperatures (-50°C) without going fragile; nevertheless, tests are carried out just to comply with the standards required when cable ducts were only made of polyvinyl chloride (PVC).

a) Resistance to deflection.
The stiffness test, is based on the CEI EN 50086-2-4 variant A1. According to this standard, the 200 mm long conduit test piece is deflected between two 100 x 200 x 15 mm plates to reduce the outer diameter by 5%; the force required must exceed the settled value (450 N or 750 N).
At the end of the test, the cable duct test piece is not classified but simply declared compliant or non-compliant.

b) Resistance to impact.
The classification is made according to the impact test.
While the resistance to deflection characterises the conduit during its whole "underground" life, the resistance to impact concerns only its installation.
The test is carried out only for safety purposes. The test consists in a weight falling on the test piece according to the CEI EN 50086-1 and CEI EN 50086-2-4 variant A1.
The test piece is cooled at -5°C for 2 hours.
The test consists in letting a 5 Kg fixed weight beam fall down on the test piece from a height which varies depending on the pipe nominal diameter (see table "Impact test").
At the end of the test, no cracks that could make water pass from inside to outside must be detected. This result must be detected at least on 9 over the 12 test pieces tested.

Table "Impact test"
nominal diameter
of the tube (mm)
mass of the dart
(Kg)
height
(mm)
≤ 60 5 300
61 ÷ 90 5 400
91 ÷ 140 5 570
> 140 5 800