Basic knowledge of UPVC pipe
Basic knowledge of UPVC pipeUPVC pipe uses polyvinyl chloride resin as a carrier, which has excellent characteristics such as accurate temperature sensitivity, timed melting, and rapid absorption of active ingredients of additives when weakening the gravitational force between resin molecular chains. At the same time, it uses the world-famous calcium and zinc composite heat stabilizer. In the process of resin high temperature and melting, it can capture, inhibit, absorb and neutralize the release of hydrogen chloride, and perform double bond addition reaction with the polyene structure to replace the active and unstable chlorine atoms in the molecule. So as to effectively and scientifically control the catalytic degradation and oxidative decomposition of the resin in the molten state.
Chinese name UPVC pipes Foreign name UPVC pipes Definition Plastic pipe materials PVC production characteristics No plasticizers Advantages It is not easy to react electrochemically with acids, alkalis and salts Application areas Tap water piping engineering, etc.
table of Contents
1 Performance characteristics
2 Similar
3 Problems
4 Application areas
5 Technical standards
6 Development prospects
Performance characteristics
UPVC pipe is a kind of plastic pipe made of polyvinyl chloride (PVC) resin as raw material and without plasticizer. With the development of chemical industry technology, it is now possible to produce non-toxic grade pipes, so it has the performance of general polyvinyl chloride, and adds some excellent properties, specifically it has the advantages of good corrosion resistance and softness, so Especially suitable for water supply network. Because it is not conductive, it is not easy to electrochemically react with acids, alkalis, and salts. Acids, alkalis, and salts are difficult to corrode it, so no external anti-corrosion coating and lining are required. The good flexibility has overcome the shortcomings of the brittleness of the plastic pipe in the past, and it can yield under the load without breaking. Such a test has been done: a UDN DN50mm pipe was placed on the ground, and a Crown 3.0 car was driven on it. The pipe was flat but not broken. Then we let the Dongfeng car loaded with goods pass over the pipe, and the pipe was just deformed without cracking. In addition, UPVC pipes have a small modulus of elasticity and therefore can reduce the magnitude of pressure impact and thus reduce the impact of water hammer. The inner wall of U-PVC pipe is smooth, and the resistance is small (the resistance coefficient of UPVC pipe is 0.009, and the general galvanized pipe. The resistance coefficient of cast iron pipe is 0.012-0.013), so the good hydraulic conditions are obvious. When the same liquid is transported with pipes of the same diameter, UPVC pipes have a resistance of about 30% less than galvanized pipes and cast iron pipes; when the head loss is the same, the water transport capacity of UPVC pipes is more than 20% larger than cast iron pipes. Because the inner wall of UPVC pipe is smooth, the liquid will not scale in the internal flow, so its conveying capacity will not decrease with the increase of the running time. And this is exactly galvanized pipe and cast iron
UPVC pipe
The shortcomings that cannot be overcome. With the continuous deepening of reform and opening up, people's living standards continue to improve, and the requirements for the quality of tap water are becoming higher and higher. In addition to ensuring that the factory water meets domestic drinking water standards, the water supply industry must also qualify the water delivered through the pipe network. People strongly reflect the phenomenon of "yellow water" and "black water" in tap water, and the main reason for the deterioration of the water quality of the guiding pipe network is the corrosion of the water supply pipe, especially the cold galvanized pipe. Corrosion begins within a year and a half of use and does not last for a long time, resulting in irony smell and color in the water. The galvanized pipes buried underground are more corroded. UPVC pipes are corrosion resistant. No scaling, it can inhibit the growth of bacteria, which is conducive to protecting the water quality from the secondary pollution of the pipeline. Therefore, UPVC pipe has wide application prospects, especially a large number of buried pipes in front of users' water meters can use it.
In addition, UPVC pipes are also lightweight. Advantages of convenient transportation. The specific gravity of UPVC pipe is about 1.4 (the specific gravity of cast iron pipe is about 7.4), which is one-fifth of the weight of cast iron pipe. Using UPVC pipe can save 1 / 10-1 / 5 of transportation cost than cast iron pipe. Its handling, loading and unloading construction are very convenient. Often the construction environment of the water supply pipeline is relatively difficult, and the construction site is muddy. If it can reduce the labor intensity of the workers and shorten the construction cycle, it is the most ideal thing. UPVC pipe can achieve this ideal. UPVC pipe is light in weight and can be moved manually during the installation process, generally without the use of machinery. For example, a UPVC pipe with a length of 6m in DN200 has a weight of about 55Kg, and a cast iron pipe of the same diameter and length has a weight of 304Kg. When installing, the UPVC pipe can be carried by one person, and the cast iron pipe needs three people or machinery to drop the pipe. It reduces the labor intensity of workers and saves working hours and construction costs.
UPVC pipe connection methods include socket aprons connection, adhesive connection and flange connection. These types of connection methods can be directly installed in the pipe trench without digging another work pit. There is no need to use linseed or expansive cement to make an interface. You can use a manual hoist or manually put the end of the pipe socket on the rubber ring and insert it directly into the bearing. In the mouth, the depth of the inserted tube is marked by the tail mark.
Similar comparison
UPVC pipes and PE pipes are thermoplastic pipes. They share a common characteristic, but they are flexible. Heat resistance requirements. There are also differences in technical characteristics such as anti-aging. Now the technical characteristics of UPVC pipe and PE pipe are compared and analyzed as follows:
1. Performance comparison between UPVC and PE pipes
Types of pipes Advantages Disadvantages UPVC has strong corrosion resistance, is easy to connect, inexpensive and has a hard texture. It is not suitable for hot water transportation, the joint bonding technology requires high, and the curing time is longer. HDPE is lightweight, has good fatigue strength, good temperature resistance, good toughness, and good flexibility. Welding requires electricity; mechanical connectors are more expensive.
As can be seen from the table above, PE pipes are more expensive due to their joints, which restricts and hinders its wide application.
2. Linear expansion coefficient of UPVC and PE pipes
Pipeline linear expansion coefficient a (/ 0C) UPVC (hard polyvinyl chloride) 6 × 10-5 HDPE (high density polyvinyl chloride) 18 × 10-5 MDPE (low density polyvinyl chloride) 16 × 10-5
It can be seen that PE pipe has a larger linear expansion coefficient than UPVC pipe, so it should be paid attention to in the design.
3. Comparison of aging resistance of UPVC pipes
Developed countries on PVC. The comprehensive evaluation of PE pipes is as follows:
Content Evaluation value PVC HDPE MDPE Aging resistance value 20 13
It can be seen from the above table: from the perspective of aging resistance and long-term strength, PVC pipes are better than PE pipes; from the damage form, PE is better than PVC. As for easy rollability and weldability, it is only related to installation process. Transportation, etc., should not be used as the main indicators for evaluating the two materials.
4. Installation and connection of UPVC pipe and PE pipe
As mentioned before: UPVC pipe connection method has socket aprons connection. Adhesive connection and flange connection are more suitable for sockets with larger diameter. If the adhesive connection is used, it is difficult to ensure the absolute cleanliness of the pipe joint before bonding, and a grain of sand. A small bubble will be a hidden danger of water leakage at the interface. In addition, the bonding is also affected by the temperature and air, which makes it difficult to construct outdoors.
The connection forms of PE pipes are electrothermal fusion connection and thermal fusion butt connection. Especially for the electrothermal fusion connection, it uses a sleeve to cover the two pipe joints, and the sleeve and the two pipes are fused together by the heating wire inside the sleeve, which is easy to achieve and ensure that the interface is dense Leaky, but this sleeve joint is expensive.
There is a problem
Although the advantages of rigid PVC drainage pipes are very significant, there are still some problems in the design and construction use:
1. Temperature effect
UPVC pipes have poor heat resistance, and the tensile strength of the environment drops above 60 ℃ (applicable to domestic sewage with continuous discharge temperature not exceeding 40 ℃ and instant discharge temperature not exceeding 80 ℃). Therefore, the design should be far away from the heat source, such as greater than or equal to 400mm from the stove side, and greater than or equal to 200mm from the hot water pipe, and the hot water pipe should take thermal insulation measures, and must not pass through the flue and firewall.
The impact strength of the rigid PVC plastic drain pipe is reduced under low temperature environment. Therefore, in the conversion layer of the air-conditioned equipment, you can consider using cast iron pipes instead of rigid PVC drainage pipes to ensure drainage safety.
Due to the large influence of temperature and the large expansion coefficient, it is required to install expansion joints on each layer of riser and longer horizontal pipe. Therefore, the gap effect of UPVC pipes should be considered in other professional layouts. When laying parallel to other pipes, the plastic pipes are close to the side. When laying crosswise, the plastic pipes are below and should be staggered, and metal sleeve protection should be considered. In addition, the riser passing through the floor roof should be used as a fixed support point, and a flexible sheath should be added.
2. Effect of stiffness
UPVC pipe
UPVC pipe
For each layer of the riser, there should be a solid fixing bracket, which can control the direction of expansion of the pipeline, and can also share the weight of the riser. It also protects the head of the riser from the horizontal pipe from being overstressed. The pipeline ruptures and leaks, and at the same time, the bottom of the riser should also be equipped with supporting measures such as piers or hangers.
In outdoor construction, UPVC pipes are particularly vulnerable to damage. When UPVC and the outdoor integrated pipe network are crossed, manual and mechanical appliances are enough to cause different degrees of damage to them, and even the powder or breakage causes the pipeline to be impassable. When the pipeline is backfilled, the UPVC pipe is often damaged due to the partial overhead of the pipeline or being pressed by a large hard object. Therefore, the buried UPVC pipe requires the base to be tamped, with 100mm below the pipe and 300mm backfill sand above the pipe, and the total buried depth is not less than 900mm.
3. Building fire protection
China's research on PVC plastic flame retardant technology generally has a tendency to one-sidedly pursue the improvement of oxygen index and ignore the research on smoke performance. Statistics show that 79% of the fire is fatal. Some UPVC pipes have an oxygen index of more than 50%, but the amount of smoke generated during combustion is large, and the Vicat temperature is only between 70 ° C and 90 ° C. Therefore, although the UPVC pipe is difficult to burn, it is very easy to soften and deform, and the smoke smell is very strong. On the one hand, in the fire, lethal smoke is generated. On the other hand, the pipe softens and deforms when the temperature exceeds 90 ° C. The greater the wind speed of the drain or vent pipe passing through the roof, the faster the fire spreads. Therefore, whether UPVC pipes can be used in high-rise buildings has been a matter of debate, and the focus of the debate is its fire resistance.
UPVC pipes have been widely used in high-rise buildings, but they have not paid enough attention to the above fire protection issues, nor did they comment on the installation of UPVC pipes in the special acceptance of fire protection. Because the current "Code for Fire Protection Design of Buildings" GB 50016-2014, "Hard Polyvinyl Chloride Pipes for Building Drainage" GB / T5836. 1-92 and "Technical Specifications for Building Drainage Polyvinyl Chloride Pipeline Engineering" CJJ-96 are not available Clearly stipulate how to use UPVC pipes, so that this problem is "unregulated". While calling for the introduction of relevant national documents, some suggestions were made for colleagues' reference: (1) Rain, sewage and ventilation risers should be installed along the outer walls of the building as much as possible. (2) When rain, sewage and ventilation risers are in the building, they should be installed in the pipeline well, or protected with non-combustible materials such as bricks and concrete blocks. (3) The branch pipe discharged into the drainage riser shall be a metal drainage pipe, or strict fire prevention measures shall be taken for the branch pipe, such as steel casing and inorganic fire prevention casing. (4) Metal fittings should also be used for drainage accessories.
Also. The UPVC drainage pipe also has issues such as riser energy dissipation, noise reduction and condensation prevention, all of which limit the promotion and use of the existing UPVC drainage pipe to a certain extent.
Application field
1. The tap water piping project (including indoor water supply and outdoor municipal water pipes), because UPVC plastic pipes have the advantages of acid and alkali resistance, corrosion resistance, no rust, no scaling, protection of water quality, and protection of water quality from secondary pollution, it is strongly advocated Today, the production of environmentally friendly products, as an ideal "green building material" to protect human health, has been widely promoted and applied in China and the world.
UPVC pipe
UPVC pipe
2. For water-saving irrigation piping project, the use of UPVC spray drip irrigation system can save water by 50% -70% compared with ordinary irrigation, at the same time, it can save fertilizer and pesticide consumption, and increase crop yield by 30% -80%. In today's lack of water resources and the backward irrigation methods of agricultural production in China, this has great social benefits for promoting the development of water-saving agricultural production in China.
3. Plumbing works for construction.
4. UPVC plastic pipe has excellent insulation ability and is also widely used as a cable conduit for post and telecommunications.
5. UPVC plastic pipe is resistant to acid, alkali and corrosion, and many chemical plants are used as infusion piping. Others are also used in well drilling engineering, medical piping engineering, mineral brine transportation piping engineering, electrical piping engineering, etc.
technical standard
GB / T 5836.2-2006 "Hard polyvinyl chloride (PVC-U) pipe fittings for building drainage"
GB / T10002.1-2006 "Hard PVC pipes for water supply"
GB / T 10002.2-2003 "Hard PVC fittings for water supply"
GB / T 8801-2007 "Hard polyvinyl chloride (PVC-U) pipe fitting drop test method"
GB / T 8803-1988 "Test method for hot oven of injection-molded rigid polyvinyl chloride (PVC-U) fittings"
GB / T 8801-1988 "Hard polyvinyl chloride (PVC-U) pipe fitting drop test method"
GB / T 18993.3-2003 "Chlorinated Polyvinyl Chloride (PVC-C) Piping System for Cold and Hot Water Part 3 Pipe Fittings"
GB / T 24452-2009 "chlorinated polyvinyl chloride (PVC-C) pipes and fittings for sewage and wastewater (high and low temperature) in buildings"
GB 9644-1988 "Extraction methods and allowable values of lead, tin, cadmium, mercury for rigid polyvinyl chloride (PVC-U) drinking water pipes and fittings"
Prospects
In August 1998, the Xiamen Municipal Construction Commission issued a notice requiring that all new construction projects of less than 400mm water supply pipes and indoor and outdoor drainage pipes must use plastic pipes, indicating that plastic pipes have entered a wider application space. However, the shortcomings of UPVC drainage pipes in use are still urgently needed to develop products with high strength, low noise, good fire protection characteristics, low investment and low energy consumption to adapt to the deeper and broader development of the modern construction market need. Fortunately, many scientific research and production units outside China have continuously developed various new products, some of which have entered the market, and they represent the development trend of UPVC pipes.
Plastic and metal composite pipes with mature technology have appeared in the Chinese market, which are resistant to high temperature and low noise. However, due to the high price and small diameter, they are suitable for hot and cold water pipes in high-end decoration. Plastic-steel composite pipe, but the price is also relatively high, and it is not yet used in the drainage system; some units in China have developed double-layer plastic pipes to reduce noise indicators.
UPVC pipe
UPVC pipe
It is only one step away from entering the market; the Sichuan Fire Science Research Institute of the Ministry of Public Security has developed a flame-retardant PVC formulation using halogen-free and antimony-free flame retardant smoke suppressants five years ago, with an oxygen index of 51% -56%. The amount of smoke is low (smoke density level is about 54%) and the toxicity of smoke is very small, but for various reasons, the technology has not yet entered the market. Some advanced countries and regions abroad. For example, a large number of reinforced two-layer pipes are used in Japan, but a shell made of asbestos or reinforced fiber cement is placed on the outside of the ordinary UPVC pipe, which greatly improves the fire resistance. According to reportsThe pipeline made by this technology can withstand 800o-1010 ℃ high temperature. It will not generate smoke or soften and deform in the fire. It can be used at will in high-rise buildings. Plastic metal composite pipes and plastic steel composite pipes have been widely used in developed countries and regions.
Generally speaking, Chinese urban drainage projects are still dominated by drainage cast iron pipes, cement pipes, and reinforced concrete pipes. Although the promotion and application of current rigid PVC drainage pipes have achieved certain results, they are still in the early stages of development At this stage, compared with advanced foreign countries, there is still a big gap. China's drainage pipeline service area is less than 70%, planned. By the beginning of the 21st century, it will reach 80%, which will require a large number of rigid PVC plastic drainage pipes. The broad market provides better prospects for the development of plastic pipes.
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