Polyethylene is used to produce and cover various types of pipes in various applications such as drinking water, sewage, gas, heating and plumbing pipes for homes, solid material transfer pipes, drip irrigation, protective pipes (wire and cable and glass fiber passage, etc.).

Polyethylene pipes have been in use for about 40 years, and gradually, with the recognition of the advantages and functions of this pipe and the gradual improvement of the characteristics used in many applications, they replaced various types of concrete, steel, cast iron and PVC pipes.

The flexibility of polyethylene pipes has made the movement and installation of pipelines much easier and less expensive than steel pipelines. The flexibility of these pipes allows for the bypassing of obstacles and the reduction of joints and connections. These pipes are much more resistant to natural disasters such as earthquakes than other types of pipes.

Polyethylene pipes have a wide range of applications, the most common of which are as follows:

Drinking water networks
Urban water supply networks
Urban and rural sewage networks
Pressure irrigation
Urban and rural sewage
Cable coating, metal pipe
Industrial water supply

Advantages of polyethylene pipes:

High resistance to breakage and cracking
Very high chemical resistance
Resistance to corrosion
High flexibility
Function at temperatures from minus 40o c to 70o c
Ability to use on uneven terrain
Long life
Easy and fast execution
High hydraulic resistance
Sound insulation
Excellent earthquake resistance
Impact resistance
Resistance to abrasion and scratching:
Polyethylene pipes are very suitable for transporting liquids that are abrasive or scratch-resistant due to the following polymer properties:

Low modulus of elasticity
High impact resistance
Friction coefficient Low
High chemical inertia The lifespan of polyethylene pipes against liquids containing abrasive particles and scratches is up to 10 times higher than that of metal and clay pipes.
The resistance of polyethylene pipes to natural disasters such as earthquakes is much higher than that of other types of pipes. The figure below shows the damage rate in the 1995 Japanese earthquake for different types of pipes.

Types of polyethylene raw materials:

PE63

PE80

PE100

Pressure classification of pipes according to the ISO I2I62 standard:

In the production of polyethylene pipes, the higher the pressure classification (PE63 to PE100), in addition to saving on material consumption, it increases the cross-sectional area of ​​the pipe at a constant outer diameter, which increases the pipe’s transfer capacity. If we assume that the transfer capacity is constant, the transfer speed can be reduced and, as a result, smaller pumps can be used for transfer. This reduces costs. In addition, when repairing pipes and using Amster pipes in the previous pipe – the loss of transmission capacity will not be large.

PE100 has advantages in non-pressure pipes, apart from pressure pipes, as it has a higher internal strength than standard heavy polyethylene (1250MPA versus 950MP), a higher modulus, greater radial stiffness, which is a great advantage in pressure and non-pressure sewage networks.

The most important functional characteristics of pressure polyethylene pipes:

1- Long-term strength:

Long-term strength or the basis of the hydrostatic design of the pipe determines the life of a pipe at a given pressure and temperature and is usually carried out by a series of tests at different pressures and temperatures over a specified period of time. To check the 50-year life of the pipe, the pipe must be obtained without creep tension.

2- Rapid crack growth:

Rapid crack growth is a very important defect that is frequently seen in transmission lines. The largest crack reported for a steel pipe was 11 km long, and for polyethylene, the largest crack was observed in a gas pipeline in Hungary with a diameter of 315 mm and a length of 700 m. Resistance to rapid crack growth is a term used to examine impact strength. These tests are used at a specific temperature to determine the pressure above which rapid crack growth occurs. This pressure is called the critical pressure.
The probability of rapid crack growth in pipes increases with increasing diameter and thickness of the pipe at low temperature and high ambient pressure. The term crack growth is used when the crack length is 4.7 times greater than the nominal outside diameter of the pipe.

3- Slow crack growth:

The slow crack growth characteristic shows the long-term and environmental resistance of the pipe. The initiation of crack growth depends on the internal stress residual from the processing time in the pipe and the installation pressure of the pipe. The crack test examines the long-term creep properties of the material, these tests are known as ESCR.
If a crack grows and a crack forms in the pipe, it is said that the pipe is bent. Pipes made of first-generation polyethylene bend in 100 hours, but the next generation bends in 1000 hours and the current generation lasts nearly 100 years.

4- Permeability:

This is important for the transmission of natural gas. Because it is possible for it to penetrate through polyethylene. Of course, the measured leakage rate is so low that it does not affect the transmission of gas.

Gas leakage rate from polyethylene

5- Expansion coefficient of polyethylene pipes:

The expansion coefficient is necessary for calculations related to the specific diameter and the amount of pressure on the pipe joints and the surrounding soil.

6- Thermal conductivity:

The amount of heat that a plastic pipe can transfer through its wall depends on the thermal conductivity of the pipe. The thermal conductivity of polyethylene is 0.43     w/mok. ASTM C177

7- Hygiene issues

For the transport of beverages, the hygiene of the materials in the pipe is important. The hygiene standards related to polyethylene are:
1- FDA, CFR, Title 21 (1994) 177. 1520. Olefin polymers     (USA)
2- NS

According to the “Nippon News Agency”, quoted by Platts, informed sources said:

China’s Jiutai Energy plans to launch its coal-based heavy polyethylene/light polyethylene linear production complex with a production capacity of 250,000 tons per year and a polypropylene production unit with a capacity of 350,000 tons per year in Ordos, China, in the Inner Mongolia region of the country.

Market sources predict that the full commissioning and start-up of the said complex will take until early 2019.

This is a common issue for all polymer production units and generally requires some time before starting up.

The Chinese company currently operates a polyethylene production complex with a capacity of 250,000 tons per year.

It also has a coal-based methanol production unit with a capacity of 1 million tons per year and a dimethyl ether production facility with a capacity of 100,000 tons per year on the same site.
China’s rich coal resources have encouraged many of the country’s chemical and petrochemical manufacturers to significantly reduce their need for other types of feedstock by utilizing this feedstock.