6.10 PLASTIC PIPES
6.10.1 General
Plastic pipes are produced by extrusion process followed by calibration to ensure maintenance of accurate internal dia with smooth internal boxes. These pipes generally come in lengths of 6 meters. A wide range of injection moulded fittings, including tees, elbows, reducers,caps ,pipes saddles, inserts and threaded adaptors for pipe sizes 15-150mm are available.
6.10.2 PVC Pipes
The chief advantage of PVC are:
- Resistance to corrosion
- Light weight
- Toughness
- Rigidity
- Economical in laying, jointing and maintenance
- Ease of fabrication
The PVC pipes are much lighter than cast iron or A.C pipes. Because of their light weight PVC pipes are easy to handle, transport, and instal. Solvent cementing techniques for jointing PVC pipe lengths is cheaper, more efficient and far simpler. PVC pipes do not become pitted or tuberculated and are unaffected by fungi and bacteria and are resistant to a wide range of chemcials. They are immune to glavanic and electrolytic attack, a problem frequently encountered in metal pipes especially when buried in corrosive soils or near brackish waters. PVC pipes have elastic properties and their resistance to deformation resulting from earth movements is superior compared to conventional pipe materials especially asbetos. Thermal conductivity of PVC is very low compared to metals. Consequently water transported in these pipes remain at a more uniform temperature.
Rigid PVC pipes wiegh only 1/5 of conventional steel pipes of comparable sizes. PVC piepes are available in sizes of outer dia 20,25,32,50,63,75,90,110,140,160,250,290,315mm at working pressure of 2,5,4,6,10Kg/cm2.
Since deterioration and decomposition of plastics are accelerated by ultraviolet light and frequent changes in temperature which are praticularly severe in our country if is not advisable to use PVC pipes above ground. The deterioration starts with discolouration,surface cracking and ultimately ends with brittleness and the life of the pipe may be reduced to 15-20 years.
6.10.3 Precautions in Handling and storage
Because of their light wieght, there may be a tendency for a PVC pipes to be thrown much more than their metal counterparts. This should be discourged and reasonable care should be taken in handling and storage to prevent damage to the pipes. On no account should pipes be dragged along the ground.Pipes should be given adequate support at all times. These pipes should not be stacked in large piles, specially under warm temperature conditions, as the bottom pipes may be distorted thus giving rise to difficulty in pipe alignment and jointing. For temporary storage in the field, where racks are not provided, care should be taken that ground is lefel, free from loose stones. Pipes stored thus should not exceed three layers and should be stacked as to prevent movement. It is also recommended not to store one pipe inside another.