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Characteristics of plastic pipe use and precautions
Abstract: Compared with traditional metal pipes, plastic pipes have the characteristics of light weight, corrosion resistance, high compressive strength, sanitary safety, small water flow resistance, long service life and convenient installation. The pipe diameter is one size larger than the nominal diameter . For example, PPR32 is equivalent to DN25. The hot water pipe is a green tube, and the hot water pipe is a red tube. Pay attention to the conversion of the pipe diameter when budgeting and drawing. As shown in the paper sheet, the DN20 is to be piped (piece) of PPR25. Be sure to use the same manufacturer's products, because the proportions of the ingredients in the products of different manufacturers will cause the bonding to be weak or not adhered to the original.
Key words: polypropylene tube, rigid polyvinyl chloride tube, rigid polyvinyl chloride silencer tube, plastic bellows, suction valve
With the improvement of people's living standards, environmental awareness and health concerns, a green revolution in the building materials industry has been set up in the water supply and drainage field. According to a large number of water quality monitoring data, after the cold-galvanized steel pipe is used, the general service life is less than 5 years , and the rust is severe. Residents have complained to the government departments, causing a social problem. Compared with traditional metal pipes, plastic pipes have the characteristics of light weight, corrosion resistance, high compressive strength, health and safety, small water flow resistance, energy saving, metal saving, improved living environment , long service life and convenient installation. The engineering community's favor and occupy a very important position, forming an unpredictable development trend.
Plastic pipe characteristics and applications
 Polypropylene pipe (PPR)
(1) In the current construction and installation works, most of the heating and water supply are PPR pipes (pieces). The utility model has the advantages of convenient and quick installation, economical and environmental protection, light weight, hygienic non-toxicity, good heat resistance, corrosion resistance, good heat preservation performance and long service life. The pipe diameter is one size larger than the nominal diameter. For example, PPR32 is equivalent to DN25, PPR63 is equivalent to DN50. The pipe diameter is divided into DN20, DN25, DN32, DN40, DN50, DN63, DN75, DN90, DN110. The pipe fittings are various in three-way, elbow, pipe hoop and variable diameter. , pipe plugs, pipe clamps, brackets, hangers. The hot water pipe is divided into two parts, the cold water pipe is a green strip pipe, and the hot water pipe is a red strip pipe. The valve has PPR ball valve, globe valve, butterfly valve, gate valve, and copper core inside the PPR material.
(2) Pipes are connected by welding, hot melt and threaded connections. The PPR tube has the most reliable hot-melt connection, convenient operation, good air tightness and high interface strength. The pipe connection uses a hand-held fusion splicer for hot melt connection. Remove dust and foreign matter from pipes and accessories before connecting. When the red light of the machine lights up and stabilizes, align the pipe to be connected (piece) DN<50 hot melt depth is 1-2MM, DN<110 hot melt depth is 2-4MM. When connecting, the pipe end is rotated without rotation Insert into the heating jacket to a predetermined depth. At the same time, the tube is pushed to the heating head without rotation to heat, and after the heating time is reached, the tube and the tube are immediately removed from the heating sleeve and the heating head, and the shaft is quickly inserted into the required depth without rotation and evenly. A uniform flange is formed at the joint. The newly welded joint can be calibrated within the specified heating time, but rotation is strictly prohibited. When the pipe and the pipe are heated, excessive heating should be prevented to make the thickness thin . The pipe is deformed within the pipe fitting. Rotation is strictly prohibited during hot melt cannula and calibration. There must be no open flame at the operation site, and it is strictly forbidden to bend the pipe with open flame. When the heated pipe and pipe are vertically aligned, the force should be light to prevent the elbow from bending. After the connection is completed, the pipe and the pipe must be tightly held for a sufficient cooling time, and after cooling to a certain extent, the hand can be released. When the PP-R pipe is connected with the metal pipe fitting, the PP-R pipe with the metal insert should be used as the transition. The pipe fitting and the PP-R pipe are connected by the hot melt socket, and are connected with the metal pipe fittings or the hardware fittings of the sanitary ware. When using a threaded connection, a polypropylene raw tape should be used as the sealing filler. If the faucet is connected to the mop pool, the inner elbow (threaded inside) is installed at the end of the upper PPR tube. During the installation of the pipeline, do not use excessive force to avoid damage to the threaded fittings and cause leakage at the joint. Tube cutting can also be cut by special pipe: the pipe cutter blade should be adjusted to match the diameter of the pipe to be cut. When the rotation is cut, the force should be evenly applied. After cutting, the complete round of the complete rounder should be applied to the fracture. When the pipe is broken, the section should be perpendicular to the pipe axis and free of burrs.
(3) During the pipeline installation process, the hydraulic test may be carried out in layers or in a single set. The working pressure and test pressure of all pipelines are: low working pressure is 0.4Mpa, test pressure is 0.6Mpa, high and medium working pressure is 0.6Mpa, and test pressure is 0.9Mpa. After the pipeline system is installed, Comprehensive inspection, check the installed pipes, valves, gaskets, fasteners, etc., all in accordance with the design and technical specifications, remove the fittings that are not suitable for testing with the pipeline, replace them with temporary short pipes, and close all openings. And irrigate from the lowest place and deflate from a height. Purge the pipeline that has passed the test pressure until the dirt is washed out, and do all the work of purging and cleaning records and pressure test records. The test pressure is 1.5 times the working pressure of the system, but not greater than the allowable pressure of the pipe. Water should be injected slowly during the test. Sealed inspection should be done after filling. The pressure should be gradually increased to the test pressure by hand pump, stabilized for 1h, the pressure drop is less than 0.05Mpa, and then reduced to 1.15 times of the working pressure for 2 hours, the appearance inspection, no leakage and no leakage pressure does not exceed 0.03Mpa is qualified.
(4) When installing and paying attention, avoid touching sharp objects when handling and installing pipes to prevent damage to the pipes. During the installation of the pipeline, organic pollutants such as paint should be prevented from coming into contact with the pipes and fittings. The opening where the installation is interrupted or completed must be temporarily closed to prevent debris from entering. The water supply pipe system should be flushed with water before acceptance. The flushing water flow rate should be greater than 2m / s. When flushing, the dead angle should not be left. The taper should be opened at each water distribution point. The lowest point of the system should be equipped with a water discharge port. The cleaning time is controlled at the outlet of the flushing outlet. After the drinking water system is rinsed, 20-30 mg/l of free chlorine water is used to fill the pipeline for disinfection. Chlorine-containing water should be retained in the tube for more than 24 hours. After the pipeline is disinfected, it is rinsed with drinking water and sampled and tested by the health management department. The water quality complies with the current national standard “Sanitary Standard for Drinking Water” before it can be delivered. Within 30 minutes, two boosts were allowed and raised to the specified test pressure. Pay attention to the conversion of the pipe diameter when budgeting and drawing. As shown in the paper sheet, the pipe (piece) of PPR25 is required for DN20. Be sure to use the same manufacturer's products, because the proportion of ingredients in different manufacturers' products is different. Will cause the bond to be weak or not bonded.
 Hard polyvinyl chloride pipe (UPVC)
(1) UPVC pipe (piece) is used for drainage. Due to its light weight, corrosion resistance and high strength, it is widely used in pipeline installation. Under normal circumstances, the service life is generally 30 to 50 years. The inner wall of UPVC pipe is smooth and the frictional resistance of the fluid is small, which overcomes the defect that the cast iron pipe affects the flow due to rust and scale. The pipe diameter is also larger than the nominal diameter. For example, DN100 is U-PVC110.DN150 is U-PVC160. Pipe fittings are divided into oblique three-way, four-way, elbow, pipe hoop, variable diameter, pipe plug, trap, pipe clamp and hanger.
(2) Drainage glue for connection. The adhesive must be shaken before use. Pipes and sockets must be cleaned. The smaller the gap between the sockets, the better the sanding of the joints with abrasive cloth or saw blade. The inner part of the socket is evenly brushed once, and the outer part of the socket is brushed twice, and the glue is dried for 40~60s. After inserting into place, it should be noted that the glue drying time should be appropriately increased or decreased according to climate change. Do not touch the water when bonding. After the pipe is in place, it must be placed in the ditch. After the joint is dry, backfilling should be started 24 hours after the joint is dry. When backfilling, the pipe will be filled with sand to leave the joint and then backfilled in large quantities. Use the same manufacturer's products. When the UPVC pipe is connected with the steel pipe, the steel pipe joint must be cleaned and glued. The UPVC pipe is heated and softened (but not burnt) and then placed on the steel pipe and cooled down. If the pipe clamp is added, it will be better. For the large-area damage of the pipe, it is necessary to replace the whole pipe, and the pipe joint can be used to replace the pipe. For the treatment of leakage at the solvent bond, a solvent method can be employed. At this time, the water in the tube is drained first, and a negative pressure is formed in the tube, and then the adhesive is injected on the pores of the leaking portion. Due to the negative pressure inside the tube, the adhesive will be sucked into the pores to achieve the purpose of stopping leakage. The lining method is mainly for the leakage of pipe through holes and joints. At this time, the same diameter pipe with a length of 15 to 20 cm is selected, and the longitudinal pipe is cut longitudinally, and the inner surface of the casing and the outer surface of the pipe to be supplemented are roughened according to the method of bonding the joint, and the sleeve is tightly attached to the water leakage after being glued. The glass fiber method is formulated into a resin solution by using an epoxy resin and a curing agent, and after impregnating the resin solution with a glass fiber cloth, it is uniformly wound around the surface of the pipe or the joint leakage, and is solidified to become a glass steel. Because the method is simple in construction, easy to master in technology, good in plugging effect and low in cost, it has high promotion and use value in anti-seepage trapping.
(3) The hydrostatic test of the pipeline or pipe network system must be carried out after bonding and drying for 24 hours. The water pressure test of the pipeline must comply with the national pressure test rules for non-metallic pipelines. For the test of the pipeline without joints, the length of the test is ≯1.5km, and the test length of the pipe with the joint is ≯1km. The test pressure of the pipeline or pipe network shall not exceed 1.5 times of the design working pressure, the minimum ≮0.5MPa, and the test pressure shall be kept for 2h or satisfied. The special requirements of the design, no leakage is qualified. Budget, pay attention to the conversion of pipe diameter when cutting. Also be sure to use the same manufacturer's products to prevent the proportion of ingredients in different manufacturers' products. Will cause the bond to be weak or not bonded.
I have encountered many specific problems and accumulated some experience in participating in the construction and engineering of plastic pipe construction management.
First, the expansion and contraction of plastic tubes
The ends of the modified hard PVC pipe are plugs, the pipe fittings are sockets, most of them are connected by socket bonding method, which is an immutable permanent connection, while the linear expansion coefficient of plastic products is large, and the pipeline is subject to The length of expansion caused by changes in ambient temperature and sewage temperature,
Second, UPVC drainage pipe construction needs attention
(1) The arrangement of the drainage and outlet pipes has a great influence on the design flow of the system. The connection between the riser and the discharge pipe is to use a different diameter elbow. The outlet pipe is preferably larger than the riser pipe. The outlet pipe should discharge the sewage as far as possible without any elbow or B-tube. Many projects have confirmed that the thinner drainage outlet pipe and the increased pipe fittings on the outlet pipe will adversely change the pressure distribution inside the pipe, reduce the allowable flow rate value and prone to poor drainage of the toilet in the future use.
(2) UPVC spiral pipe drainage system In order to ensure the spiral flow of the spiral pipe, the riser cannot communicate with other risers. Therefore, an independent single riser drainage system must be adopted, which is one of the characteristics of UPVC spiral pipe. Never add a snake, copy the drainage system of the cast iron pipe, and add the exhaust pipe in the high-rise building. If the exhaust pipe is added, the material is wasted and the drainage characteristics of the spiral pipe are destroyed.
(3) Three-way or four-way pipe fittings for side water inlet used with spiral pipe, belonging to nut extrusion rubber ring sealing sliding joint, generally allowing the distance of telescopic sliding to be within the temperature difference range of conventional construction and use stage, according to UPVC The pipeline expansion system allows the pipe length to be 4M, which means that no matter whether it is a riser pipe or a transverse branch pipe, as long as the pipe segment is within 4M, no additional expansion joints should be provided.
(4) Connection of pipes. UPVC spiral pipe uses nut extrusion rubber ring sealing joint. This joint is a sliding joint that can be used for expansion and contraction. Therefore, the proper clearance should be considered according to the procedure after the pipe is inserted. Avoiding the trouble of individual operators in the construction process, the reserved clearance is too large or too small, and the temperature changes in the future, and the pipeline deformation causes leakage. The prevention method is to first determine the reserved gap value according to the construction temperature at that time. In the construction of each joint, insert the mark on the insertion tube first, and the insertion mark can be achieved during the operation.
(5) In some high-rise building designs, in order to strengthen the anti-water flow impact capability of the bottom of the riser of the spiral pipe drainage system, the flexible elbow pipe is used for the steering elbow and the discharge pipe. The outer wall of the plastic pipe inserted into the socket of the cast iron pipe shall be roughened to increase the friction and fastening force of the filler with the caulking.
(6) The snorkel that protrudes from the roof is affected by the temperature difference between indoor and outdoor and the storm. It is often the case that the joint between the snorkel tube and the roof waterproof layer or the heat insulation layer produces a telescopic crack, which causes the roof to leak. The prevention method is that a water blocking ring of 150MM-200MM above the top layer can be made around the roof vent pipe.
(7) Two problems frequently encountered in the construction of buried drain pipes: One is that the laying of pipes below the indoor floor is not carried out after the backfilling is completed. After the backfilling soil is compacted, although it is qualified before the tamping, the pipe joint is cracked and leaked after use: the other is the hidden pipe, the left and right sides and the upper part are not covered with sand, causing the pointed hard object or the stone to directly touch the pipe. The outer wall causes damage or leakage of the pipe wall.
(8) The installation of indoor UPVC spiral pipe should be carried out continuously after the completion of the civilized wall flour decoration. In fact, due to the construction period, most of them are synchronized with the decoration after the completion of the main structure. This will cause the smooth and beautiful surface to be contaminated. The best solution is to use the plastic cloth to wrap and protect the UPVC spiral tube in time, and then remove it after completion. Furthermore, it is necessary to strengthen the finished product protection of the UPVC spiral pipe during the construction process. It is strictly forbidden to climb on the pipe, fasten the rope, use the scaffolding board, use it as a support or use it for other purposes. The water level of the floor drain The top level of the floor drain should be 5~10mm below the ground, and the depth of the floor drain seal should not be less than 50mm. The purpose is to prevent the harmful gas in the sewage pipe from entering the indoor pollution indoor environment after the water seal is destroyed. However, it is rarely mentioned in the design of water supply and drainage that construction and construction units use low-cost floor drains in order to reduce the cost. Such floor drain seals are generally no more than 3 cm, which cannot meet the requirements of water seal depth. In addition, the residents used the stainless steel floor drain on the decoration market to replace the original plastic floor drain when decorating the house. Although the exterior is bright and beautiful, the internal water seal is also very shallow. When draining, the water seal of the floor drain is destroyed due to positive pressure (lower floor) or negative pressure (higher floor), and the odor enters the room. A lot of residents reflected the smell in the home, and the kitchen hood was more serious when it opened, which is why the water seal was damaged due to pressure fluctuations. Some residential kitchens have floor drains. Because there is no water for a long time, especially in winter, the water seals are easy to dry, and the floor drain should be replenished frequently. It is recommended to use high water seal or new anti-backflow floor drain during design and construction. There is less splashing water on the floor in the kitchen, and no floor drain can be set.
Third, the pipeline foundation laying
(1) In order to ensure that the bottom of the pipe is in close contact with the foundation and control the axis elevation and slope of the pipe, the PVC-U pipe should still be used as a cushion foundation. For the general soil, usually only a layer of 0.1m thick sand cushion can be used. For soft soil foundation, and when the bottom of the tank is below the groundwater level, it is advisable to lay a layer of gravel or gravel with a thickness of not less than 0.15m and a particle size of 5 to 40mm.