PE (polyethylene) materials are widely used in the field of water supply pipe manufacturing due to their high strength, corrosion resistance and non-toxicity. Because it will not rust, therefore, it is an ideal alternative to ordinary iron pipe to pipe. Pe water supply pipe implementation product national standard: GB/T 13663-2000 "water supply polyethylene (PE) pipe."
Characteristic benefit
Corrosion resistance
(1) Polyethylene has excellent corrosion resistance, good hygienic performance and long service life
Polyethylene is an inert material that, in addition to a small amount of strong oxidant, is resistant to a variety of chemicals and is less prone to bacteria. It is well known that steel pipes and cast iron pipes are replaced by plastic pipes not only because plastic pipes have lower energy consumption than water, low energy consumption, light weight, low water flow resistance, simple and quick installation, low cost, long life and heat preservation. Etc., but also because plastic pipes are more resistant to corrosion and less prone to microorganisms than steel pipes and cast iron pipes.
The service life of polyethylene pipes is more than 50 years. This has not only been confirmed by international standards and some advanced foreign standards, but has also been proved by practice.
Another reason why polyethylene can be promoted is because PVC is increasingly subject to environmental protection. The first is the hygienic performance of polyvinyl chloride itself: it is well known that the production of polyvinyl chloride pipes under regular production and strict control can ensure hygienic performance and allow application in the field of drinking water. But still there are fears problems may occur in the strict control of places: such as polyvinyl chloride resin, vinyl chloride monomer is excessive, PVC pipe for water supply in the formulation of a misuse of toxic additives. Misuse of non-toxic PVC pipes and fittings for drainage to water supply pipes and fittings. The second is the recycling of PVC pipes: polyvinyl chloride and polyethylene are thermoplastics, which can be used theoretically, but the proof of each country, the proportion of old plastic products that can be recycled is limited, the main treatment It is incinerated to recover energy. Because of the chlorine content, polyvinyl chloride may produce harmful substances when it is not well controlled during incineration. Polyethylene contains only hydrocarbons, which generate water and carbon dioxide after incineration.
Flexible
Polyethylene has unique flexibility and excellent scratch resistance
Flexible polyethylene pipe system has great technical and economic value. The flexibility of polyethylene is an important property that greatly increases the value of this material for pipeline engineering. Good flexibility allows the polyethylene tube to be coiled and supplied over a longer length, avoiding a large number of joints and fittings. For example, when the Nantong Water Supply Company, a national urban water reform demonstration unit, selects materials in one household and one table, it fully utilizes the characteristics of PE small-diameter pipes that can be coiled. From the water meter to the user one pipe, there is no pipe joint in the middle. It not only saves costs, but also improves work efficiency. This characteristic of PE small-diameter pipe has been recognized by the water supply company with water meter households in various cities across the country, and has become the first choice for its water-removing operation. At the same time, it is flexible and lightweight, and has excellent scratch resistance, making it possible to use a variety of economical 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 construction technology of laying, replacing or repairing various underground pipelines under the condition that the surface is not trenched (slotted) by using various geotechnical drilling techniques. A variety of excavation-free construction techniques are very suitable for the use of polyethylene pipes, such as horizontal directional drilling and guided drilling methods for laying new pipelines, expansion pipe methods for replacing old pipelines in situ, and interspersed renewal lining methods for repairing old pipelines and Improved lining method (folding deformation method, hot drawing method and cold rolling method).
PE's unique flexibility also makes it effective against underground movements and end loads. On the surface, in terms of strength and rigidity, the plastic buried pipe is not as good as the cement pipe and the metal pipe. However, from the practical application, the plastic buried pipe belongs to the “flexible pipeâ€. Under the correct design and laying construction, the plastic buried pipe is Work with the surrounding soil to withstand the load. It need not reach the buried plastic pipes "steel pipe" rigidity of the same strength and mechanical properties to meet the requirements buried in use. At the same time, the pressure relaxation characteristics of polyethylene can effectively consume stress through deformation, the actual axial stress level is much lower than the theoretical calculation, and the elongation at break is generally greater than 500%, and the bending radius can be as small as the diameter of the tube. 20 to 25 times, it is a kind of high toughness material, which has strong adaptability to uneven settlement of foundation. These characteristics make it the most excellent pipeline to resist earthquake, foundation settlement and temperature difference expansion. For example, in the 1995 Kobe earthquake in Japan, PE water supply pipes and gas pipes were the only pipe systems that were spared.
Low temperature resistance
Polyethylene has outstanding low temperature resistance
The low temperature embrittlement point of the PE pipe is -70 ° C, which is superior to other pipes. Polyvinyl chloride (PVC-U) pipe is easy to be brittle during field construction in winter. One of the lessons summarized in the pilot project of laying polyvinyl chloride (PVC-U) buried water supply pipe in Beijing area is that it is not suitable for temperature below zero. The laying of polyvinyl chloride (PVC-U) pipes was carried out. There is also a clear evidence that in order to improve the toughness and low temperature impact resistance of PP, ethylene and propylene monomers can be copolymerized to form random copolymer polypropylene (PP-R), which generally adopts iPP process route and method. a mixed gas of propylene and ethylene are copolymerized to give a main chain is randomly distributed in the copolymer of propylene and ethylene segments (i.e., tube material PP-R), an ethylene content of PP-R pipe material mostly around 3%. However, the improved low temperature resistance of PP-R is still unsatisfactory, and the embrittlement point is about -15 ° C, which is much higher than the embrittlement temperature of the polyethylene tube -70 ° C.
Fracture toughness
Polyethylene has good rapid crack growth fracture toughness
When rapid crack growth occurs, cracks can rapidly expand from a few hundred meters to a dozen kilometers at a speed of 100 to 45 m/s, causing long-distance pipeline damage, large-scale leakage accidents, and subsequent combustion explosions (natural gas) or floods ( Water delivery accident. The probability of such an accident is not great, and once it occurs, it is extremely harmful. For the continuous development of plastic pressure pipes, the importance of preventing the occurrence of rapid crack growth damage exceeds the requirements for long-term life strength performance. The reason is: in the same SDR (ratio of pipe diameter to thickness), the calculated long-term life-long-term strength is independent of increasing pipe diameter (in fact, large-diameter pipes may be safer than small-diameter pipes), but the rapid crack growth risk The pipe diameter increases and increases. In the existing large-scale plastic experimental method pipe, such as polyethylene, polypropylene, polyvinyl chloride pipe, etc., when a certain pipe diameter is reached, the allowable pressure determined by preventing the rapid crack growth damage is always longer than the long-term strength. The permissible pressure determined by the problem is low. That is to say, after the allowable pressure is determined according to the requirement of preventing rapid crack growth and damage, the long-term life (such as 20 ° C, 50 years) can be satisfied by itself; the material with rapid crack growth and poor fracture toughness will be eliminated, regardless of it. Long-term strength performance is good or bad. For example, polyvinyl chloride (PVC-U) gas pipes have been basically replaced by polyethylene (PE) gas pipes. The trend of European polyvinyl chloride (PVC-U) water supply pipes being replaced by polyethylene (PE) pipes is clear.
China has not yet established a test device to monitor the rapid crack growth and damage. China's plastic pressure pipe standards do not involve this issue, which indicates that China's plastic pressure pipe level is at least one stage behind the world level.
Use regulations
General provisions
1 Pipes and fittings shall have the product quality inspection report of the quality inspection department and the certificate of the manufacturer.
2 When storing, transporting and transporting pipes, non-metallic ropes should be bundled and the ends of the pipes should be sealed.
3 When pipes, pipes are stored, transported and transported, they must not be thrown or cracked.
4 When pipes, pipes are stored, transported and transported, they shall not be exposed to sunlight or rain; they shall not be in contact with other chemical substances such as oil, acid and salt.
5 The storage period between pipes and fittings from production to use should not exceed one year.
Material acceptance
1 Receiving pipe and fittings must be accepted. First check the product manual, product certificate, quality assurance certificate and various performance inspection and acceptance reports and other relevant information.
2 When inspecting pipes and fittings, they should be sampled in the same batch and inspected for size and appearance according to the current national standard “PE for polyethylene (PE), and should be thoroughly tested if necessary).
Storage
1 Pipes and fittings should be stored in a well-ventilated warehouse or a simple shed with a temperature not exceeding 40 °C.
2 Pipes should be stacked horizontally on a flat support or on the ground. The stack height of not more than 1.5 m, when the tube bundles bundled into 1mx1m square, two opposite sides of the support and protection, may be appropriate to increase the stacking height, but not more than 3m, the tube should be neatly stacked in layers, it should ensure that it did not fall, and to facilitate Take and manage.
3 Pipes and fittings should be covered when they are temporarily stacked outdoors.
4 Pipes of different diameters and different wall thicknesses should be stacked separately when the pipes are stored.
Handling
1 When pipe is transported, it must be hoisted with a non-metallic rope.
2 When handling pipes and fittings, care should be taken carefully and neatly arranged. Do not throw and drag along the ground.
3 When transporting pipes and fittings in cold weather, it is strictly forbidden to strike sharply.
transport
1 When transporting pipes, vehicles should be placed on the bottom of the flat car. When transported, they should be placed in a flat cabin. When transporting, the full length of the straight pipe should be supported, and the coils should be stacked neatly. Both the straight pipe and the coil pipe should be bundled and fixed to avoid collision with each other, and the stacking contact should not damage the sharp protrusion of the pipe.
2 When transporting pipe fittings, they should be stacked and arranged in a row and fixed firmly.
3 Pipes and fittings should be covered during transportation to avoid exposure and rain.
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