Properties of Polyethylene Pipe

HIGH & MEDIUM DENSITY POLYETHYLENE are non-toxic, flexible, highly resistant to UV radiation, lightweight, impact resistant and has a design life of 50 years at a specified design temperature and pressure rating of the medium. Abrasion resistance is better than any other rigid thermoplastics and considerably better than steel and other metal pipes, concrete and asbestos cement. Corrosion resistance of PE pipes is excellent and extremely resistant to chemicals, solvents and radioactive waste water.

Thermal Properties

PE has a coefficient of linear expansion of approximately 1.5 x 4-10 per degree Centigrade, which is in the order of ten times greater than that for iron or steel. The thermal conductivity of PE is approximately 0.4 W/mO K, so PE is a poor conductor of heat. Therefore, the water or any medium contained in PE pipe changes temperature more slowly than any other conventional pipe.

Color of Pipes

Due to the extreme weathering conditions in the Middle East and to counterattack Ultraviolet radiation, ATA PIPES are normally supplied in black color. A Co-extrusion system is responsible for producing pipe with color stripes depending on pipe application. International norms recommends Blue stripe for potable water, Orange for conduit, and Yellow for gas application. For electrical conduit and fiber optic applications, a two-color double layer pipe is available where the main layer is black and the thin outer layer can be blue, orange, or green depending of customers color specifications. Conduit pipes also has a pulling rope inside pre-installed during production to ensure easy insertion and pulling of fiber optics and electrical cable during installation. Other colors also can be produced depending on customer requirement.

Chemical Resistance

Polyethylene(PE) has a good resistance to a wide range of chemicals. For all practical purposes, PE is chemically inert within its normal temperature range of use. It does not rot, rust, pit, corrode or loose wall thickness through chemical or electrical reaction with the surrounding soil. It does not normally support the growth of algae, bacteria or fungi.

Fracture Resistance of Polyethylene Pipe

POLYETHYLENE pipe is tough and ‘brittle type’ fracture is difficult to achieve even in laboratory tests at low temperatures. The failure mode in stress rupture testing is ductile unless testing is carried out at low stresses at elevated temperatures for considerably extended periods of time to reproduce slow crack growth. PE pipe have excellent resistance to this mode of failure (demonstrated by tests such as the notched pipe test). For PE100 pipes, catastrophic failure due to rapid crack propagation (RCP) will not occur under normal service conditions. PE pipes that meet the Rapid Crack Propagation (RCP) test requirements for full resistance are suitable for operation at the nominal pressure rating. The many years of successful installation of polyethylene pipe has shown that PE is a tough and resilient material capable of withstanding the normal rigors of pipe laying and pipeline operation.

Abrasion Resistance of Polyethylene

Pipe rupture caused by the gradual decomposition of the pipe material as a result of corrosion and or abrasion is a problem that deserves prime consideration in the planning of pipe systems and the choice of pipe material. A number of investigations proved that PE pipe has a very strong resistance to abrasive media compared to other pipe materials.

Weathering Resistance of Polyethylene Pipe

Weathering due to prolonged outdoor exposure will cause degradation of most natural and plastic materials, particularly by the combined effects of short-wave ultra-violet (UV) rays from sunlight and atmospheric oxygen. PE pipes are protected from these effects by the addition of carbon black. Because carbon black is the most effective protection against UV, PE pipes are normally supplied in black. This ensures that black pipes made from this material can be stored or used outdoors over the period of time without any fear of a change in properties, which is not available from other thermoplastics.

Resistance of Polyethylene Pipe to Microorganism & Rodents

Research carried out by behavioral scientists shows that rodents ( and also gnawing insects such as termites) are compelled to maintain their teeth in good condition by gnawing objects that stand in their way. In the case of PE Pipe, there is the additional point that the smooth round surface does not give the teeth sufficient hold to bite properly. Large number of termites inhabited in countries like Australia & Africa have not reported so far any damage in PE pipelines. PE is not a nutrient medium for bacteria, fungi, spores, parasites, etc. So PE pipes are resistant to all forms of microbial attack. Further, it should be noted that sulphate reducing bacteria in the soil have no effect on PE pipes since the product is resistant to both sulphurous acid and sulphates.

Resistance of Polyethylene Pipe to High Energy Radiation

PE pipes are suitable for applications involving exposure to high energy radiation. This material has been used successfully for many years to remove radioactive effluent from hot laboratories and as cooling water lines in nuclear energy technology

Effect of Elevated Temperatures

As per DIN 8074, the nominal working pressure has been calculated for operational conditions at 20ºC. Since Polyethylene is a thermoplastic material, a loss in mechanical properties is to be expected as the temperature rises. PE pipe can be used under pressure at temperatures in excess of 20ºC with an appropriate reduction in its design pressure rating and Service life. A sample illustration for PE100 material taken from DIN8074 is shown below.

Table 2

Classification of PE Pipes

Table 3

STANDARD DIMENSION RATIOS (SDR) of PE Pipes