The application and characteristics of new water supply pipes
Release date：2017-09-11
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The water supply pipe network has three characteristics that make the cycle long (30 years or longer), repair and renovation difficult, the accident is not easy to detect (buried in the ground). The safety and reliability of the water supply pipe network has two meanings: First, the pipeline network uninterrupted water supply, try to avoid the pipeline rupture, leakage, and even burst pipe; the second is the pipeline water quality, not because of the pipeline itself Pipe rust), affecting the water quality pipe network. That is, in the pipe network water distribution process, the pipe network water quality can not have much change; from the water plant to the user, a smooth arrival, while meeting the water and water supply service pressure. In the pipeline project, there are a variety of different materials pipes, a wide range of applications. As a result of technological progress, the use of materials used in the production of water pipes continue to develop, the performance of new water supply pipe has been greatly improved. From the water supply pipe network safety and reliability of the two requirements, one is uninterrupted water supply, the second is the pipe network water quality should be safe and reliable), this requirement is also practical application requirements, in order to discuss the new water supply pipe application and development.
First, metal pipes
In the early construction of the pipeline network, the use of lead pipe, which is a better corrosion resistance of the metal pipe. The oxide film formed on the surface of the lead tube has been considered to be non-toxic. With the progress of analytical instruments, you can determine the trace elements, and finally find out the lead will be isolated from the lead pipe. When the presence of oxygen, PH value of less than 7, there will be a trace of lead precipitation. Subsequently, the small-caliber galvanized steel pipe replaced the lead pipe. Now the analysis of pipe network water distribution process changes in water quality, can be found, leading to pipe network water quality is mainly due to the reduction of small diameter galvanized steel pipe, especially the user internal pipeline. On the one hand, in the use of small-caliber galvanized steel pipe, rarely used lining protective measures, the user's internal pipe pipe quality is poor; the other hand, small-diameter pipe in the pipe network at the end of the pipeline flow rate is slow, Long stay time, secondary water supply facilities management and poor maintenance. As a result, small-caliber galvanized steel pipes have been replaced by plastic pipes and composite pipes.
1, cast iron pipe
Is the most familiar, but also the use of a wider pipeline. Cast iron is iron (Fe) and carbon alloy, carbon in the cast iron in the mass fraction is higher than 2.11%, carbon content below this ratio, is low carbon steel. The use of low-carbon steel pipe, processing and installation more convenient. The mechanical properties of the steel pipe is better than other pipes, but its corrosion resistance is very poor. Steel pipe life of 20-30 years, cast iron pipe life of up to 80 to 100 years. As the surface of the steel pipe corrosion treatment is too much trouble, high cost of corrosion, generally only in special areas using steel pipe (now widely used).
2, ductile iron pipe
Is through the heating and cooling of the overall heat treatment method to change the performance of the pipe. For example, the ductile iron pipe is placed in a heating furnace, heated to 830 ° C, and then the pipe and the furnace are cooled to room temperature at the same time. This pipe and the furnace with the furnace cooling the overall heat treatment method, called "annealing". This method improves the impact toughness of ductile iron pipes. Comparison of ductile iron pipe and gray cast iron pipe metallographic analysis of photos, you can see the ball of graphite (carbon) and filamentous graphite (non-spheroidized carbon): gray cast iron pipe due to raw materials and production processes, A lot of cementite and ball, pipe fracture can see the white mouth organization (commonly known as gray), pipe performance is not as ductile iron pipe.
3, ordinary cast iron pipe and ductile iron comparison
With the development of cast iron pipe production technology and technological progress, today, centrifugal ductile iron pipe has become the world's most important cast iron pipe production process. Domestic use of gray cast iron pipe has been gradually to the centrifugal ductile iron pipe transfer. Ductile iron pipe should not only have a high tensile strength, but also should have a higher elongation. In accordance with the requirements of the international standard IS02531, ductile iron pipe tensile strength ≥ 420MPa, DN40-DNl00mm pipe, elongation ≥ 10%, DNl200-2600mm pipe, elongation ≥ 7%. The gray cast iron pipe has a wide range of control of the harmful components of the molten iron raw material because it does not require the elongation of the pipe. As follows:
Ductile iron pipe and gray cast iron pipe chemical composition comparison (%) Table 1,
Carbon (C) silicon (Si) manganese (Mn) phosphorus (P) sulfur (S)
Ductile iron pipe 3.5 ~ 3.61.6 ~ 1.80.2 ~ 0.4≤0.04≤0.02
Gray cast iron pipe 3.3 ~ 3.81.4 ~ 2.60.6 ~ ~ 0.9 ≤ 0.3 ≤ 0.10
Second, plastic pipe
Commonly used in the water pipe network in the plastic pipe can be divided into two categories: one is polyolefin materials: polyethylene (PE), polypropylene (PP), polybutylene (PB), such plastic pipe for fusion (heating )connection.
The other is vinyl chloride material: polyvinyl chloride (PVC), rigid polyvinyl chloride (U-PVC), chlorinated polyvinyl chloride (C-PVC), suitable for bonding (glue) connection. Is now divided as:
1, PVC plastic pipe
PVC and PE pipelines in the 20th century, 60 years, also used in water supply pipeline project. In the early stages of application, PVC pipe connection is relatively simple, small diameter PVC pipe with glue, bonding connection, medium diameter PVC pipe socket interface, the use of rubber ring seal, is an ideal flexible interface. So in the 20th century, 90 years before the wider application of PVC pipe. For the promotion of the initial PE pipe, the use of heating connection method, the construction is not convenient. Early PE pipe, due to material performance constraints, compressive strength and anti-cracking performance is not good. In order to withstand external pressure and internal pressure, PE pipe diameter larger, the thicker the wall. Because the thicker pipe wall to ensure that the pipeline has enough rigidity. Large diameter PE pipe, pipe wall is relatively thick, the amount of material used to increase the cost. Therefore, the promotion of the initial PE pipe, generally not more than DN300mm, mainly for indoor piping and water distribution network.
Polyvinyl chloride (PVC) is usually a multi-component plastic, PVC in the heat, oxygen, light, the structure will change. Therefore, PVC processing must be added to the stabilizer. In order to improve the surface properties of PVC pipes, reduce the shrinkage of the pipeline performance and coloring purposes, need to join other processing aids, fillers and pigments. Pipes commonly used in the U-PVC, is to improve the PVC brittle and hard performance, in the production by adding plasticizer. Plasticizer content in the 0-12% range of PVC pipe, known as U-PVC pipe.
C-PVC is made by the further chlorination of PVC products, C-PVC and PVC material is the difference between the different chlorine content, C-PVC chlorination of a higher degree. General PVC chlorine content of 56.7%; C-PVC chlorine content of 63-74%. This is the manufacturer of chlorination and production technology caused by different levels of technology. As the C-PVC chlorine content increases, C-PVC pipe anti-aging performance and pressure resistance are greatly improved. It can be seen, C-PVC pipe is the traditional U-PVC pipe improvement and improvement.
PVC pipe due to the construction of simple, good hydraulic conditions, in the water supply pipe network has been widely used. With the increasingly stringent environmental requirements, water quality indicators increased, taking into account the health and safety factors, PVC pipe in the following two aspects are questioned: 1.PVC pipeline additives used in heavy metals, there is a stabilizer such as phthalic acid, Which contains metal lead, lead may be into the water; 2. PVC pipe chlorine content is too high, may have a negative impact. The above two aspects of the problem, so that other plastic pipe, such as PE (polyethylene) and PP (polypropylene) to expand the market.
2, PE plastic pipe
PE (polyethylene) is rich in raw materials, from the molecular structure (C2H4), PE molecular structure is the most simple one of the polymer. PE pipeline in the development, and constantly overcome their own shortcomings. PE pipe heating welding, requires a certain operating space and skilled operation techniques. Later, the invention of the thermocouple casing: that is, two pipe or pipe fittings, through an electric welding sleeve connected. This connection is used
In the pipe within the PE pipe connection, or construction space is small place. PE pipe material performance is also improved, from PE63, PE80, to PEl00, the future will be developed to PEll5. PEl00 refers to the lowest strength (MRS) of 10 MPa after 50 years of use of this grade of PE material at 20 ° C; PE80 is 8.0 MPa.
With the PE material grade increase, the same pipe, the use of PEll5 pipe wall thickness, lower than the use of PEl00 pipe wall thickness. In meeting the requirements of the premise, PE pipe wall thickness thinner, reducing the amount of PE material, reducing costs, is conducive to PE pipe in large diameter pipe applications. PE pipe connections need to heat, but also requires a certain cooling time, each welding will take about 20 minutes. The larger the diameter of the pipe, the longer the heating and hot and cold time. Therefore, the PE pipe installation period is relatively long.
PE pipe in the pipeline-free excavation and the old pipe renovation, there is a high market share, therefore, PE pipe is often used in pipe-free excavation project; due to PE (polyethylene) comprehensive performance is good, Aluminum-plastic composite pipe and steel-plastic composite pipe) the main raw material. Composite pipe will be a reasonable combination of metal materials and plastic, you can make full use of metal good mechanical properties and plastic corrosion resistance, so as to ensure the safety and reliability of water supply network.
Third, the development of different types of pipe
In order to meet the requirements of safe operation of water supply pipe network, the development of pipe has two aspects: First, the choice of new pipe, limit and phase out the old pipe does not meet the development requirements. The development of good performance, good corrosion resistance of the new pipe, according to the actual requirements, select the appropriate metal or non-metallic pipe; Second, the pipeline surface to take protective measures, external corrosion and internal lining to ensure the safety of water pipe network. Is as follows:
l, cast iron pipe
In the pipeline project, still occupies an important position, especially steel production in the next few decades will not decline (the current world output 7-8 million tons). Cast iron pipe performance has been greatly improved. International standard IS02531, centrifugal ductile iron pipe tensile strength ≥ 420MPa, and low alloy steel and the strength of almost, but the centrifugal ductile iron pipe corrosion resistance is better than steel. In order to resist corrosion and ensure the quality of pipe network, cast iron pipe inside and outside the lining and anti-corrosion materials, are improved and improved.
2, plastic pipe
There will be greater development, PVC pipe material performance will also be improved, to avoid the use of heavy metals containing the stabilizer. A variety of new technologies on the new plastic, are constantly promoting the use. But the stability and aging of the plastic pipe is still a concern.
3, advanced composite pipe
In the 20th century has been greatly developed, such as prestressed steel and reinforced concrete pipe, PCCP pipe (steel tube concrete pipe) and resin-based composite material (glass pipe sand pipe GRP) in large diameter water pipeline project has been applied. Steel-plastic composite pipe and aluminum-plastic composite pipe, in the small-caliber user pipeline market has a great demand. The development of new water supply pipe is not a simple technological progress, but also take into account the market competition conditions and market orientation. Meet the development and environmental requirements of the new pipe, is still being developed.
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