Application status and analysis of plastic pipes i

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The application status and analysis of plastic pipes in water supply system

since 1998, in the implementation of the national "Ninth Five Year Plan" for the promotion and application of chemical building materials and the outline of the 2010 development plan, as well as the provisions on accelerating the promotion and application of chemical building materials and restricting and eliminating backward products, all localities have taken into account the actual situation of the region, Great progress has been made in actively promoting various plastic pipes and plastic composite pipes to replace galvanized water supply pipes that affect the quality of drinking water for residents. Many articles also introduce plastic pipes and plastic composite pipes from different angles. The author will analyze the existing plastic pipes and plastic composite pipes from the perspective of the whole water supply system. 1. Application status of pipes in water supply system for convenience, we simplify the supply system of water for urban residents as shown in. According to this division, we also call the pipes from the water source to the water plant and from the water plant to the pipe as water transmission pipes, the pipes and the pipes from the pipe to the user's building as distribution pipes, and the pipes entering the user's building as water supply pipes. The water supply system for urban residents in room h at present, the pipes used in the water supply pipe system mainly include cast iron pipes, ductile iron pipes, steel pipes, galvanized steel pipes and reinforced concrete pipes. The application of plastic pipes is not widespread. At present, only UPVC pipes (PVC-U pipes) and high-density polyethylene pipes (HDPE pipes) are specified in the national standards. Generally speaking, the mechanical properties of steel pipes are good, but the external anti-corrosion treatment is also required when laying underground, and the cost is high; The mechanical properties of cast iron pipe are not as good as steel pipe, but the corrosion resistance is stronger than steel pipe, and the price is cheaper; Ductile iron pipes have roughly the same mechanical properties as steel pipes, and their corrosion resistance is better than steel pipes, but at present, the domestic production is not large enough and the price is relatively expensive; Reinforced concrete pipes have low mechanical properties, good corrosion resistance and low price. The disadvantages are high density, high damage rate during handling and lack of supporting pipe fittings. The above pipes, except for concrete pipes, can pollute the water quality transmitted internally. At present, the preventive measures are to treat them with cement mortar or plastic lining, but these two methods are not suitable for small u-diameter pipes. Table 1 shows the types, standards, nominal diameters and working pressures of commonly used pipes at present. 2 application status of plastic pipes in water supply system at present, the plastic pipes and plastic composite pipes that can be used in water supply system mainly have the following points for reference: ◆ whether the clamps are convenient and safe to use should include PVC-U pipes, HDPE pipes, cross-linked high-density polyethylene pipes (hdpx pipes), polypropylene pipes (PP pipes), polybutylene pipes (Pb pipes), ABS pipes, metal lined plastic pipes, aluminum plastic composite pipes, etc. The main features of these pipes are introduced below. The deep research on PE pipes is attributed to the demand for gas transmission. With table 1, the types, standards, nominal diameters Working pressure pipe type standard number nominal diameter/run prestressed concrete pipe one stage three stages self coagulation stress concrete steel pipe reinforced cast iron pipe continuous casting hydrostatic test pressure laab2.0 centrifugal sand mold hydrostatic test pressure pg2.02.51.52, 0 ductile iron pipe continuous casting centrifugal sand mold hydrostatic test pressure 3.0 hydrostatic swab pressure 3.0 steel pipe spiral welded steel pipe galvanized welded steel pipe hydrostatic test pressure 2, 5 hydrostatic test pressure: 2.5, 3.0 Hydrostatic test pressure: 2.5, 3.0 with the development of technology, PE performance has been greatly improved in more than 10 years. HDPE pipes are widely used in iso12162 and ISO plastic water supply systems because of their excellent physical and mechanical properties. PE pipes are non-toxic, corrosion-resistant, flexible, low temperature resistant, convenient for construction and installation, and can be connected by fusion welding in a variety of ways, with overall tightness * *. In recent years, in some industrial developed countries in Europe and the United States, PE pipes began to surpass PVC-U pipes in the first place. The proportion of various plastic water supply pipes in Europe in 1997 is shown in Table 2; Table 2 the proportion of various plastic water supply pipes in Europe in 1997. In the 4427 standard for drinking water heating/indoor pipes, PE materials are classified into five grades according to the * low allowable strength (MRS) of pipes. From PE32 to PE100, the properties of the material have been greatly improved, not only the short-term mechanical properties, but also the long-term pressure resistance and rapid crack growth resistance (RCP). The research shows that the lower the temperature, the larger the pipe diameter and wall thickness, and the higher the working pressure, the greater the risk of rapid crack expansion of thermoplastic pipes. Compared with other thermoplastic pipes, PE pipes have * good long-term pressure resistance and fast crack expansion resistance. Therefore, PE pipes have unique advantages in the field of large-diameter pipe transmission. From the perspective of international standards, the diameter range that PE pipes can use * is wide. The * large working pressure during service life is 1.6mpa At the same time, it is stipulated that PE pipes can be used in the temperature range below 40. If the service temperature increases, the working pressure should be reduced with a reduction factor. The selection of reduction factors is clearly stipulated in iso13761 and iso4427. PE material has poor temperature resistance and cannot be used as hot water pipe, which limits the application of PE pipes. PVC-U pipe has strong advantages as a water supply pipe because of its excellent mechanical properties and economy. In some industrial developed countries, the consumption of PVC-U pipes has accounted for 80% of the plastic pipe market The consumption structure of PVC-U pipes in Europe in 1997 is shown in Table 3. At 25 ℃, when PVC-U pipes have a 50 year expected service life, * the large working pressure is 2.5mpa At the same time, it is stipulated that PVC-U pipes can be used in the temperature range below 451. If the service temperature increases, the working pressure should be reduced by a reduction factor. PyC resin has poor temperature resistance, and PVC pipes cannot be used as hot water pipes, which is the main defect of PVC pipes as water supply pipes. In addition, PVC-U has poor anti crack rapid expansion performance, and there have been reports of water hammer effect leading to the rupture of water transmission pipeline. Therefore, PVC-U pipes should be used cautiously in the transmission of large diameter and high pressure. In order to improve the temperature resistance of PE material, it is modified by crosslinking technology. Crosslinking changed the force between PE macromolecules, from the original only crystal lattice force and van der Waals force to chemical bond force between some macromolecules. Therefore, its macro properties have also changed greatly, mainly reflected in the great improvement of the creep resistance, temperature resistance, environmental stress cracking resistance, chemical resistance, wear resistance and notch sensitivity of the material. In particular, due to the improvement of creep resistance, its hydrostatic performance, especially high-temperature hydrostatic performance, has been greatly improved. After long-term research, HDPE pipe crosslinking and stabilization technology has been relatively mature, and relevant technical standards have been formulated. According to this standard, hdpe-x pipe can be used continuously for 50 years under 70. At the same time, it is stipulated that, Hdpe-x pipe can also be used in the range of 70~11 (TC), but its service life will be reduced after the temperature rises. Obviously, the performance of hdpx pipe is much better than that of HDPE pipe, which can not only meet the requirements of cold water supply, but also meet the requirements of hot water supply. From the perspective of existing cross-linking technology, the waste products produced in the production process have formed "insoluble and non molten" Therefore, it is difficult to use it after re crushing, which increases the production cost. In addition, from the perspective of environmental protection, hdpx pipes cannot be reused. After scrapping, except for reports that they can be used as fillers and then modified PE after being crushed and fully refined, they can only be sent to be cracked into monomers for reuse. PP pipe because of its excellent performance, especially compared with PVC and PE pipes, PP pipe not only has high strength, but also has certain temperature resistance. Therefore, it is a promising pipe in water supply/hot water pipe system. 15874 standard m, whether homopolypropylene (pp-h), block copolymer polypropylene (PP-B), or random copolymer polypropylene (the installation distance of P sample can be adjusted freely; P-R), can be used to process water supply pipes, but the performance of these three kinds of PP is different, so we should pay attention to the difference. Pp-h has poor low temperature resistance, which should be paid attention to when the ambient temperature is low; The long-term hydrostatic performance of PP-B, especially at high temperature, is poor. If it is to be used in hot water pipes and meet the service life of 50 years, the wall thickness must be increased, which will bring adverse economic factors. Pp-r. year has better comprehensive performance. Due to the short development and application time of PP pipe, which can avoid scratching when washing the car, the research on the anti rapid crack propagation performance of large-diameter PP pipe is not enough. Therefore, there are still doubts in the transmission application of large-diameter high pressure. Tube Pb as a material * appeared in the early 1970s. It is a semi crystalline plastic polymerized from butene-1 monomer. The pipe made of Pb has good hygienic performance, non-toxic and harmless, chemical resistance of * *, good flexibility, high and low temperature resistance, excellent creep resistance, environmental stress cracking resistance and wear resistance. According to is0/dis15876 standard W, Pb tube can be used continuously for 50 years under 70 ℃. The report of the PB pipe rupture accident, which sells pipe grade Pb resin and pays huge compensation to users, has attracted great attention of insiders. This event will definitely have a great impact on the promotion and application of Pb pipes. 2.6 aluminum/plastic composite pipe aluminum/plastic composite pipe is a kind of composite pipe, which is welded into a closed tube by thin aluminum plate in the middle, and bonded with plastic on the inner and outer walls by hot-melt adhesive. Both inner and outer walls can be PE (mostly HDPE) or (PEOC), or the inner wall can be PX and the outer wall can be hdpe As a new type of composite pipe, aluminum/plastic composite pipe is undoubtedly an excellent pipe with characteristics. In addition to the similar advantages of other plastic pipes, it also has the advantage of good gas barrier, which can be bent and shaped at will in construction without elbows. Moreover, it has special advantages in terms of flexible touch screen. According to astmf1282 standard W, pe/a1/pe composite pipe has a * large working pressure of 1.38MPa at 23 and 1.10mpa at 601 when it has a 50 year expected service life; According to astmf1281 standard, when pex/a1/pe-x composite pipe has a 50 year expected service life under 231, the * large working pressure is 1.38MPa, the * large working pressure under 60 is 1.10mpa, and the * large working pressure under 83 is 0.86mpa However, aluminum/plastic composite pipe has some fatal weaknesses, which should be paid attention to. The first is the difficulty of recycling. According to the requirements of aluminum/plastic composite pipe, in order to ensure sufficient adhesion between aluminum layer and plastic layer, an adhesive layer needs to be added. This makes it difficult for people to separate plastic from aluminum. In addition, even if the method of separating plastic skin and aluminum skin is developed in the future, it will be difficult to reuse the plastic layer due to the mixing of adhesives. At present, there is no report of good recycling. Secondly, in a large scope, the economy loses competitiveness. Therefore, the * large pipe diameter specified in astmf1281 and f1282 standards is 32mm, and the * large pipe diameter specified in astmf1335 is 50mm 3 selection and analysis of plastic pipes in water supply system from the perspective of the whole water supply system, what kind of plastic pipes can prevail? Different pipes should be selected for different applications and different requirements. The main basis for selection is: the performance requirements of pipes, the size and price of diameters, as well as the impact of materials on human living environment. For plastic pipes, the use requirements mainly include: (1) the mechanical properties under the premise of the required service life of the project, for example, for general civil buildings, whether they can meet the requirements of water supply pressure, temperature, external load and impact under the requirements of 50 years of service life; (2) Whether the construction and installation are convenient and whether the integrity of the system is good

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