PE (polyethylene) material is widely used in the field of water supply pipe manufacturing because of its high strength, corrosion resistance and non-toxicity. Because it will not rust, it is an ideal pipe to replace ordinary iron water supply pipes. The polyethylene water supply pipe shall conform to the national product standard GB/T 13663-2000 "Polyethylene Water Supply Pipe".

Benefits of PE water supply pipe:

corrosion resistance

(1) polyethylene has excellent corrosion resistance, good sanitary performance and long service life.

Polyethylene is a non-inert material. Except for a small amount of strong oxidant, it can resist the corrosion of various chemicals and is not easy to breed bacteria. As we all know, the reason why steel pipes and cast iron pipes are replaced by plastic pipes is not only because of their lower energy consumption, lower domestic energy consumption, lighter weight, smaller water flow resistance, simpler and faster installation, lower cost, longer service life and thermal insulation function, but also because plastic pipes have better corrosion resistance than steel pipes and cast iron pipes and are not easy to breed microorganisms.

The service life of polyethylene pipe is more than 50 years, which is not only confirmed by international standards and some advanced foreign standards, but also proved by practice.

Another reason why polyethylene can be popularized and applied is that PVC is under increasing pressure of environmental protection. First of all, the sanitary performance of PVC itself: as we all know, the production of PVC pipes can ensure the sanitary performance under regular production and strict control, and it is allowed to be used in the drinking water field. However, some people still worry that problems may occur in places with lax control, such as PVC resin.

Vinyl chloride monomer exceeds the standard, and toxic additives are misused in the formula of PVC pipe for water supply. Non-toxic PVC pipes and fittings for drainage are misused as water supply pipes and fittings. Second, the recycling of PVC pipes.

Problem: PVC, like polyethylene, is a thermoplastic, which can be used in theory, but countries have proved that the proportion of old plastic products can be recycled is limited, and the main treatment method is incineration to recycle energy.

Because PVC contains chlorine, it may produce harmful substances if it is not well controlled during incineration, while polyethylene only contains hydrocarbons, which will produce water and carbon dioxide after incineration.

Flexibility (= flexibility)

Polyethylene has unique flexibility and excellent scratch resistance.

The flexibility of polyethylene pipeline system has great technical and economic value. The flexibility of polyethylene is an important factor.

Performance, greatly improving the value of this material in pipeline engineering. Good flexibility enables polyethylene pipes to be coiled and supplied in a long length, avoiding a large number of joints and fittings. For example, in the national urban water improvement demonstration.

Nantong Water Supply Company made full use of the coiled characteristics of PE small diameter pipes when selecting materials in the transformation of one household and one meter. For users, there is no need for a pipe joint from the water meter to the end of the pipeline, which not only saves costs, but also saves money.

And the working efficiency is improved. This feature of PE small-caliber pipe has been recognized by water supply companies with outdoor water meter projects in cities all over the country and has become their first choice for water improvement. At the same time, it has flexibility, light weight and excellent scratch resistance.

Ability, so that it can adopt a variety of economic installation methods that can reduce the impact on the environment and social life, such as excavation-free construction technology. Excavation-free construction technology refers to the use of various geotechnical drilling and excavation technologies, which can not be opened on the surface.

Construction technology of laying, replacing or repairing various underground pipelines under trench (trough) conditions. Various trenchless construction technologies are very suitable for polyethylene pipelines, such as horizontal directional drilling and pilot drilling for laying new pipelines, and more in-situ drilling.

The expansion method for replacing old pipelines, the interlining method for repairing old pipelines and various improved lining methods (folding deformation method, hot stretching method and cold rolling method).

The unique flexibility of polyethylene also enables it to effectively resist underground movements and end loads. On the surface, strong

In terms of rigidity and rigidity, plastic buried pipes are not as good as cement pipes and metal pipes, but from the practical application point of view, plastic buried pipes belong to "flexible pipes". Under the correct design and laying construction, plastic buried pipes bear the same burden as the surrounding soil.

Therefore, the plastic buried pipe can meet the mechanical performance requirements for underground use, but it will not reach the same strength and rigidity as the "rigid pipe". At the same time, the pressure relaxation characteristics of polyethylene can be effectively consumed by deformation.

Force, its actual axial stress level is much lower than the theoretical calculation value, its elongation at break is generally greater than 500%, and the bending radius can be as small as 20 ~ 25 times of the pipe diameter. It is a kind of high toughness material, which is uneven to the foundation.

Settlement adaptability is very strong, and it is the best pipeline to resist earthquake, foundation settlement and temperature difference expansion. For example, in the Kobe earthquake of 1995, PE water supply pipes and gas pipes were the only surviving piping systems.

Low temperature tolerance

Polyethylene has outstanding low temperature resistance.

The low temperature embrittlement point of PE pipe is -70℃, which is superior to other pipes. Pvc during field construction in winter

(PVC-U) pipes are easy to brittle fracture. An experience gained from the pilot project of laying PVC- U buried water supply pipeline in Beijing, China is that PVC-U pipeline is not suitable for the environment below zero.

U) Pipeline laying has been completed. There is also an obvious evidence that in order to improve the toughness and low-temperature impact resistance of PP, ethylene and propylene monomers can be polymerized into random polypropylene (PP-R), and iPP is generally used.

In this paper, by polymerizing the mixed gas of propylene and ethylene, the polymer with irregular distribution of propylene and ethylene segments in the main chain (that is, PP-R pipe) and the ethylene content in PP-R pipe were obtained.

Mostly around 3%. However, the improved low temperature resistance of PP-R is still not satisfactory, and its embrittlement point is about-15℃, which is much higher than the embrittlement point temperature of polyethylene pipe -70℃.

Fracture toughness

Polyethylene has good fast crack propagation fracture toughness.

When the rapid crack propagation failure occurs, the crack can rapidly propagate several hundred meters at the speed of100 ~ 45 m/s.

When it reaches more than ten kilometers, it will lead to long-distance pipeline damage, large-scale leakage accidents, and subsequent burning and explosion (natural gas transportation) or flood (water transportation) accidents. This kind of accident is unlikely to happen, and once it happens, it will be extremely harmful.

For the sustainable development of plastic pressure pipes, it is very important to prevent the rapid expansion and destruction of cracks.

Sexual life has exceeded the requirements of long-term life intensity performance. The reason is that under the same SDR (ratio of pipe diameter to its thickness), the calculated long-term life-long-term strength and

It doesn't matter to increase the pipe diameter (in fact, large pipe diameter may be safer than small pipe diameter), but with the increase of pipe diameter, the risk of rapid crack propagation also increases. In the existing large-scale plastic experiment methods, such as polyethylene, polypropylene and polyvinyl chloride pipes,

When it reaches a certain pipe diameter, the allowable pressure determined to prevent the rapid expansion and destruction of cracks is always lower than that determined by the long-term strength problem. That is to say, according to the requirements of preventing the rapid expansion and destruction of cracks, it is decided that

After the allowable pressure, the long-term life (such as 20℃, 50 years) requirements can be met by themselves; Materials with fast crack growth and poor fracture toughness will be eliminated, regardless of their long-term strength properties. Such as polyvinyl chloride

(PVC-U) gas pipe has been basically replaced by polyethylene (PE) gas pipe. The trend that PVC-U water supply pipes in Europe are replaced by pe pipes is obvious.

China has not established a testing device to monitor the rapid crack growth and failure. China's standards for plastic pressure pipes do not involve this problem, which shows that the level of plastic pressure pipes in China is at least one development stage behind the general level in the world.

Connection mode of PE water supply pipe:

Polyethylene pipes and pipes, pipes and PE pipes,

There are many connection modes between pipes and fittings, and between polyethylene pipes and metal pipes. Different connection methods have their own advantages and disadvantages. Users can choose the appropriate one according to the environment such as pipe diameter, working pressure and place of use.

How to connect. The most commonly used connection methods of urban water supply polyethylene pipeline are: hot melt connection, electrofusion connection, socket flexible connection, flange connection, steel-plastic transition joint connection and so on.

1, hot melt connection

Hot-melt connection is to use a special heating tool to heat the parts of polyethylene pipes or pipe fittings to be connected under pressure, after melting them, remove the heating tool, apply pressure to connect the two melted surfaces together, and keep them under stable pressure for a period of time until the joint cools down. Hot-melt connection includes hot-melt butt connection, hot-melt socket connection and hot-melt saddle connection. [ 1]

2. Electric fusion connection

Electro-fusion connection means that the special electro-fusion pipe fitting with embedded resistance wire is in close contact with the connection part of pe pipe or pipe fitting, and the PE pipe heats the connection part through embedded resistance wire, so that it is fused and connected into a whole until the joint is cooled. Electrofusion connection can be used to connect polyethylene pipes or sockets with different types and different melt flow rates. The electrofusion connection is divided into electrofusion socket connection and electrofusion saddle connection.

3. Socket type flexible connection

The socket-type flexible connection of polyethylene pipes is a new type of connection developed with reference to the principle of socket-type flexible connection of cast iron pipes and polyvinyl chloride pipes (PVC-U). The PE pipe is welded with a reinforced polyethylene socket at one end of the polyethylene pipe. Socket-type flexible connection is that one end of polyethylene pipe is directly inserted into the special socket of pipeline or pipe fitting, and the purpose of connecting pe pipe and pipe fitting is achieved by reversely pulling down the locking ring in the socket and pressing the sealing rubber sealing ring.

4, flange connection

Flange connection is mainly used to connect polyethylene pipeline with metal pipeline or valve, flowmeter, pressure gauge and other auxiliary equipment. Flange connection mainly consists of polyethylene flange joint, steel or aluminum back pressure loose sleeve flange, steel or aluminum flange sheet, gasket or sealing ring, bolt and nut. Flange connection is to make the flange connector and flange piece closely contact by fastening bolts and nuts to achieve the purpose of connection.

5, steel-plastic transition joint connection

Steel-plastic transition joint connection is to connect polyethylene pipeline and metal pipeline with steel-plastic transition joint prefabricated by cold pressing or other means. Steel-plastic transition joints have pull-out locking rings and sealing rings, which usually require good sealing performance, and the pull-out and pressure resistance are greater than those of polyethylene pipes in the system.

The above is the connection mode of PE pipe. It should be noted that it is strictly forbidden to directly penetrate polyethylene pipes and fittings in any form and use threaded connection; It is forbidden to bake directly connected polyethylene pipes and fittings with open flame.