Polyethylene pipes: types, characteristics, marking, scope

If earlier, when installing a water supply system, sewerage, when conducting gas, only metal or cast-iron pipes were always used. There was simply no alternative. Today, polymer products are increasingly being used, and, in particular, polyethylene pipes. They are increasingly replacing metal counterparts from the market, and all thanks to their low price, ease of handling, and long service life. The ease of installation adds to the polarity of PE pipes – there are fittings that are installed by hand. This is very convenient, for example, when installing a water supply or irrigation system in the country. 

Properties, advantages, disadvantages

Polyethylene pipes are used to transport various liquid and gaseous substances. In the literature, you can find an abbreviated designation: in the Russian version it is PE, in the international version it is PE or PE-X for cross-linked polyethylene.

They have excellent properties:

• The material is chemically neutral, does not react even with hydrochloric acid. As a result, they are used in manufacturing processes.
• In the normal state, it does not emit any substances, does not affect the taste of transported liquids. This allows them to be used in the construction of pipelines through which liquids that can be eaten circulate.
• The inner walls of polyethylene pipes are very smooth, no substances linger on them. Even after many years there will be no deposits on them.
  

• Smooth walls offer less resistance to water flow. Less resistance – requires a less powerful pump for pumping, less electricity is spent.
• The service life under normal operating conditions is about 50 years. But this figure decreases sharply with increasing temperature or pressure.
• Easy to cut, light weight, easy to install.
• Do not conduct currents, do not corrode.
• Polyethylene pipes with a diameter of up to 160 mm can be connected using special fittings. They are simply installed without any equipment, which is convenient in the “field conditions”, for example, in the country. Large diameters are welded with a special apparatus, but they are usually used in industry.
  

• Polyethylene does not conduct sounds well. So such a pipeline or heating system is “quiet”.
• The price of a pipeline made of polyethylene is 30-40% cheaper than a similar steel one.
• A ready-made plumbing or heating system is easy to remake. In the right place, the pipe is cut, the required fitting is installed, to which you can connect another branch or some device.

An excellent set of properties has led to the fact that polyethylene pipes are becoming more and more popular. But in order to avoid surprises, it is necessary to know their shortcomings. There are not very many of them, but they are quite serious.

• Polyethylene burns, and when burned, it releases harmful substances.
• Poor UV resistance. Under the influence of the sun, the material becomes brittle and brittle. But pipes made of cross-linked polyethylene are not affected by this disease; they have recently become leaders in sales.
• Large thermal expansion – it is 10 times greater than that of steel. To neutralize this shortcoming, a compensator is installed.
• If the liquid in the pipeline freezes, the polyethylene can break. Therefore, when using polyethylene pipes to organize the water supply of a private house or cottage, it is laid below the freezing depth or insulated from above, additional heating methods (heating cables) are used.

These are all shortcomings. Now for the varieties. According to the production method, there are three types of polyethylene pipes:

• high pressure;
• low pressure;
• made of cross-linked polyethylene (often red, as in most cases they are used for laying heating and hot water systems).
  

There is a certain paradox in these names. When talking about high or low pressure polyethylene pipes, they mean the way they are produced. But often this is perceived as an area of ​​​​use. In reality, it’s the other way around. Pipes produced at high pressure are less durable. They can only be used for non-pressure systems (no pumps). They are made for pressure water supply systems, but the strength is increased due to the thickness of the walls. With a normal wall thickness, their area of ​​uXNUMXbuXNUMXbuse is sewage, drainage systems, stormwater, etc. Here their qualities are optimal.

In pressure pipelines, where there is high pressure, low-pressure polyethylene pipes are used. They are more durable but, at the same time, more fragile, bend much worse. This is also not very good. But they can withstand significant pressure drops without any harm. And I must also say that both of these types of polyethylene pipes are only suitable for cold water – they cannot withstand hot water, they can melt.

But the third type – made of cross-linked polyethylene – is an option with high strength, flexibility. Such products withstand high pressure (up to 20 Atm) and temperatures up to +95 ° C, that is, PE-X pipes can be used for hot water supply, as well as for heating systems. By the way, metal-plastic pipes make them of this type of polymer. However, there is one “but” here – this type of material is not welded. When installing a pipeline made of cross-linked polyethylene, fittings with gaskets are used. The second type of assembly is adhesive, when the joints of the elements to be joined are smeared with glue.

Markings and diameters

Polyethylene pipes are usually black or bright blue, XLPE pipes can be bright red. They are painted this way on purpose – to make it easier to distinguish them from other polymers. Blue stripes can be applied along the wall if it is intended for cold water, yellow if it is used for a gas pipeline. The release form is in coils from 20 to 50 meters long (usually small diameters) and in pieces of 12 meters (or the desired length by agreement).

The diameters of polyethylene pipes vary in a wide range – from 20 mm to 1200 mm. Products of small section (up to 40 mm) are used mainly for water supply and heating systems in private houses and apartments, more serious ones (up to 160 mm) go to the risers of water supply, heating and sewage systems. Large diameters are already an industrial and manufacturing area. It is practically not used for private buildings and apartments.

Density of polyethylene

For the manufacture of pipes, polyethylene of different densities is used. The density is indicated by the numbers that come after the abbreviation:

• PE32 – appeared first, has the lowest density. Today, it is practically not used for the production of pipes.
• PE63 – has a rather large distance between the chains of molecules, which is why it does not tolerate pressure surges, it can break. Scope – internal wiring in non-pressure systems (irrigation systems from a barrel, outdoor shower, etc.), occasionally installed in private houses for wiring a water supply system inside the house. Sewer systems can be made from this type of polymer.
• PE80 – has high strength, can be used in cold water supply systems inside and outside the house, but with mandatory insulation. With a large wall thickness, they can be used for industrial purposes.
• PE100. At the moment, pipes made of such material are the most durable, but also the heaviest. It can be used in any area, for the transport of liquids and gases under high pressure. Cross-linked polyethylene grades with a density of 100 can be used in the distribution of hot water and heating.
  

What else may be interesting: polyethylene pipes can also be reinforced. In general, they are produced by extrusion – in a softened state, the material is squeezed out through a nozzle, then sent for calibration, where it is given the required section and size. In the production of reinforced polyethylene pipes, nylon, polystyrene or polyvinyl chloride (PVC) fibers are sealed inside the wall. The equipment for this process is much more complex, and therefore the price of reinforced PE pipes is much higher.

The diameter of polyethylene pipes and what is SDR

There is a significant difference in the marking of polymer pipes – the outer diameter is indicated. But the wall thickness varies within wide limits, so that the inner diameter has to be calculated – subtract twice the wall thickness from the outer one. The wall thickness in the marking is prescribed after the indication of the outer diameter (usually they put * or the “x” sign). For example: 160 x 14,6. This means that this pipe has an outer diameter of 160 mm, a wall thickness of 14,6 mm. You can also calculate the inner diameter of a polyethylene pipe: 160 mm – 14,6 mm * 2 = 130,8 mm.

The marking also contains the abbreviation SDR and some numbers. The numbers are the ratio of the outside diameter to the wall thickness. This indicator reflects the strength of the walls and their ability to withstand pressure surges.

The lower the SDR, the stronger (but also heavier) the pipe. True, this is true within products of the same density. For example, PE 80 SDR11 is stronger than PE 80 SDR 17.

Pipe series and pressure rating

The next parameter that may be important when choosing is the series. Denoted by the letter S, followed by numbers. Displays the ability of the walls to resist pressure. This is the ratio of the pressure that it can withstand (determined in the laboratory) to the working one. The larger the number, the stronger the pipe.

In practice, this indicator is rarely taken into account, since it is more “laboratory” than practical. Much more important may be the nominal pressure for which the walls are designed. These data are shown in the photo above. The pressure is at the intersection of columns and rows, indicated in Atmospheres. For example, for a PE 80 SDR 13,6 pipe, the working pressure is PN10 (10 Atm). This means that when transporting media with a temperature of no more than +20°C and a pressure of no more than 10 atm, the service life of this pipe is 50 years.

Regulations

GOSTs and industry standards were developed to standardize manufactured products. The regulatory framework for this type of materials appeared not so long ago – already in the current millennium – after 2000. The label usually indicates the standard that this type of product meets. The scope is determined by the name of the GOST (from the names of the GOSTs), but it is easier for non-professionals to focus on the presence of stripes of the corresponding color (blue for cold water, yellow for gas).

Here are the standards for Russia:

• GOST 18599-2001 Polyethylene pressure pipes.
• GOST R 50838-2009 Polyethylene pipes for gas pipelines.
• GOST R-2008 Multilayer pressure pipes for water supply and heating systems.
• GOST 32415-2013 Thermoplastic pressure pipes and fittings for them for water supply and heating systems. General specifications
  

There are standards for Ukraine:

• DSTU B V.2.7-151:2008 “Polyethylene pipes for cold water supply”
• DSTU B V.2.5-322007 “Free-flow pipes made of polypropylene, polyethylene, non-plasticizable polyvinyl chloride and fittings for them for external sewerage networks of houses and structures and cable ducts”
• DSTU B V.2.7-73-98 “Polyethylene pipes for the supply of combustible gases”

You can explore them all if you wish. For the most part, they are tables in which the entire range of products is indicated with an indication of the parameters.

An example of marking a PE pipe

For identification, polyethylene pipes are marked. The inscriptions are applied at every meter or so. The name of the manufacturer is indicated first, the campaign logo may be placed. This sign is optional, but it is a good sign that the company is not afraid for its product.

Followed by:

• pipe material designation, in this case – PE – polyethylene;
• the density of polyethylene is for this example 80;
• then SDR pipes – 11;
• the following is the outer diameter and wall thickness: 160 mm pipe diameter, 14,6 mm – wall thickness;
• the last position indicates GOST or DSTU, which corresponds to this type of pipe.

The pipe shown in the photo – for gas pipelines this is emphasized three times – with yellow stripes, the inscription “gas” in the marking and the name GOST – 50838-2009 – this is the standard by which plastic pipes for gas pipelines are produced.