The following grades of low pressure polyethylene are used for gas pipelines: PE100+, PE100, PE80. PE63 is usually not used. Permissible pressures are respectively 2.0, 1.6 MPa, 1.25 MPa (with maximum wall thickness, with other thickness may be lower values of nominal pressure). Numbers 100 and 80 indicate the minimum long-term strength in bar (0.1 MPa).
Products with a diameter of up to 180 mm are available in coils, larger diameters – only in pieces of 6 and 12 m.
Gas polyethylene pipelines are produced either in yellow color or in black with a yellow stripe. The products are marked every 1 m, including the name of the product, then the material, the size ratio of diameter and wall thickness (SDR), diameter, purpose.
Characteristics of PE pipes for gas pipelines
The main characteristics of polyethylene gas pipes:
- The density is 0.94-0.95 g/cm³.
- Tensile strength is 100-170 kgf/cm².
- Melting point – 130…135 °С.
- Working temperature – up to +60 °C.
- Maximum operating pressure – 2.0 MPa.
Polyethylene can last 50 years or more if it is used properly. The first pipes have already lasted fifty years. It is only necessary to lay polyethylene gas pipelines in a place concealed from ultraviolet light. In addition, the PE gas pipeline is poorly resistant to alternating loads.
Scope of application
PE pipes are only used for medium and low pressure gas distribution pipelines in underground laying. PE cannot be used for outdoor application due to its sensitivity to ultraviolet light.
PE is also not used for underwater laying and in earthquake-prone areas.
Advantages and disadvantages of PE pipes for gas pipelines
Advantages of PE pipes for gas pipelines:
- Resistance to corrosion, including electrochemical – an undeniable advantage compared to steel communications.
- Polyethylene is a dielectric, and it is not affected in any way by stray currents in the ground.
- Durability – 50 years and more.
- Durability, chemical inertness, resistance to hydraulic shocks, alkalis and acids, water.
- Plasticity, absence of brittleness.
- Eco-friendliness. Relatively harmless production, harmless disposal, recyclability.
- Non-toxicity to people.
- Low cost.
- Freezeproof to -60 ° C;
- The workpiece can be easily bent by hand or on a mandrel. Polyethylene products can be easily cut, bent, welded, and simply mounted.
- Ability to install PE pipes of small diameter in one long piece, without joints or with a minimum number of joints and fittings. Any joint reduces tightness and increases the chance of leakage.
- Smooth inner surface, its low adhesion.
- Low weight facilitates installation, transportation and storage.
Disadvantages of PE pipes for gas pipelines:
The main disadvantage – not resistant to UV radiation. Also note:
- Low resistance to elevated temperatures. The maximum parameter should not exceed 60 … 60 ° C; long straight sections of the pipeline when heated can stretch and sag.
- Maximum allowable pressure for polyethylene pipes is limited to 2.0 MPa.
- Black with a yellow stripe polyethylene is not too aesthetic for laying indoors, bright yellow pipes look better.
Features of installation of gas PE pipes
Gas polyethylene pipes should be laid in the ground or indoors, so that they do not get sunlight. PE communications can not be laid near chimneys and heating pipes – when overheated PE “leads”, in case of abnormal situations with the chimney, PE structures can ignite.
Polyethylene utilities should be well anchored to the walls with a small pitch. Polyethylene is an almost ideal material for laying utilities in the ground.
The most important feature of the installation of gas pipes is that you can not install gas communications yourself, even if you know how to do it. Gas is a source of high danger, and the slightest leak can lead to death.
Therefore, for the installation, you should engage a specialized firm with a license for installation work on the laying of gas communications and installation of equipment.
Ways of connection
You can connect polyethylene gas pipes with press fittings, butt welding, electrofusion welding (with the help of thermistor couplings). Crimp, or compression fittings can not be used, as well as sliding and push-fittings – they give insufficient tightness of the connection.
How to weld correctly
The most reliable and tight connection is obtained by welding with thermal-resistance couplings. Such sockets have heating elements inside. Two fittings are inserted into the socket, the fitting is connected to the welding machine, the socket itself and the fittings are heated, then cooled and polymerized. Such couplings are quite expensive. Large diameter trunk pipelines (over 315 mm) are welded only this way.
For pipes with a wall thickness of at least 5 mm butt welding is used. The connection is less reliable than when welding with thermistor couplings. Jointed ends are evenly cut, cleaned, dirt is removed, degreased, inserted into a special soldering iron, joints are heated and tightly squeezed.
Sustain for about 10 minutes until the polyethylene polymerization, then do not move the joint at least another half an hour until the soldering place is completely cooled. There is special equipment for butt welding large pipelines.
It is necessary to pay attention to the preparation of the welded ends – the quality of the weld depends on it.
Works on the laying of gas communications require special care. I hope this article comes in handy as a source of information on polyethylene gas piping and proper installation of utilities.
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