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Characteristics of plastic pipes, operation steps and precautions

Posted by: steel world 2021-10-18 Comments Off on Characteristics of plastic pipes, operation steps and precautions

With the improvement of people’s living standards, environmental protection awareness and health concerns, a green building materials industry has been set off in the field of water supply and drainage. According to a large number of water quality monitoring data, cold-galvanized steel pipes generally rust after less than 5 years of service life, and the iron smell is serious. Residents complained to government departments one after another, causing a kind of social problem. Compared with traditional metal pipes, plastic pipes have the characteristics of light weight, corrosion resistance, high compressive strength, sanitation and safety, low water flow resistance, energy saving, metal saving, improved living environment, long service life, and convenient installation. Favored by the engineering community and occupies a very important position, forming an unreasonable development trend.
Characteristics and application of plastic pipes
(one) Poly pipe (PPR)
(1) In the current construction and installation projects, most of the heating and water supply are PPR pipes (pieces). Its advantages are convenient and quick installation, economical and environmentally friendly, light weight, sanitary and non-toxic, good heat resistance, corrosion resistance, good heat preservation performance, long life and other advantages. The pipe diameter is one size larger than the nominal diameter. For example, PPR32 is equivalent to DN25, and PPR63 is equivalent to DN50. Pipe diameters are specifically divided into DN20, DN25, DN32, DN40, DN50, DN63, DN75, DN90, and DN110. There are many types of pipe fittings, tees, elbows, pipe clamps, reducers, pipe plugs, pipe clamps, brackets, hangers. There are cold and hot water pipes, the cold water pipe is a green strip tube, and the hot water pipe is a red strip tube. The valves include PPR ball valves, globe valves, butterfly valves, gate valves, and those with PPR material and copper core inside.
(2) The pipe connection methods include welding, hot melt and threaded connection. PPR pipe uses hot melt connection to be the most reliable, easy to operate, good air tightness, and high interface strength. The pipe connection adopts a hand-held fusion splicer for hot-melt connection. Before connecting, remove dust and foreign objects from the pipes and accessories. When the machine’s red light is on and stable, align the pipes (pieces) to be connected with DN<50, the hot melt depth is 1-2MM, and DN<110, the hot melt depth is 2-4MM. When connecting, insert the end of the tube into the heating jacket without rotating to reach a predetermined depth. At the same time, push the tube to the heating head without rotation to heat. After the heating time is reached, immediately remove the tube and tube from the heating jacket and the heating head at the same time, and insert it to the required depth quickly and evenly without rotating A uniform flange is formed at the joint. During the specified heating time, the newly welded joint can be calibrated, but rotation is strictly prohibited. When heating pipes and fittings, prevent excessive heating and make the thickness thinner. The pipe is deformed in the pipe fitting. It is strictly forbidden to rotate during hot melt intubation and calibration. There should be no open flame at the operation site, and it is strictly forbidden to bake the pipe with an open flame. When aligning the heated pipe and fittings vertically, use light force to prevent the elbow from bending. After the connection is completed, the pipes and fittings must be held tightly to maintain sufficient cooling time, and the hands can be released after cooling to a certain degree. When the PP-R pipe is connected with the metal pipe fittings, a PP-R pipe with metal inserts should be used as a transition. The pipe fittings and the PP-R pipe are connected by hot-melt sockets, and are connected with the metal pipe fittings or the hardware fittings of sanitary ware. When using threaded connection, it is advisable to use polypropylene raw material tape as the sealing filler. If the faucet is connected to the mop pool, install a female elbow (threaded inside) on the end of the PPR pipe on it. Do not use excessive force during the pipeline installation process, so as not to damage the threaded fittings and cause leakage at the connection. Pipe cutting can also be cut by special pipes: the bayonet of the pipe scissors should be adjusted to match the diameter of the pipe being cut, and the force should be evenly applied when rotating and cutting. After cutting, the fracture should be rounded with a matching rounder. When the pipe is broken, the section should be perpendicular to the pipe axis without burrs.
(3) During the pipeline installation, the hydraulic test can be carried out in layers or in a single set. The working pressure and test pressure of all pipelines are respectively: the low zone working pressure is 0.4Mpa, the test pressure is 0.6Mpa, the high zone and the middle zone are calculated with 0.6Mpa, and the test pressure is 0.9Mpa. After the installation of the piping system is complete, check the installed pipes, valves, gaskets, fasteners, etc., and after all meet the design and technical specifications, remove the fittings that are not suitable for pressure testing with the pipeline and replace them with temporary shorts. Pipes, all openings are closed, and water is filled from the lowest point, and air is vented from a high point. Purge the pipes that have passed the pressure test until the dirt is flushed, and make various purge and cleaning records and pressure test records, etc. Work. The test pressure is 1.5 times the working pressure of the system, but shall not be greater than the allowable pressure of the pipe. Water should be filled slowly during the test, and the seal should be checked after filling. The pressure should be increased slowly to the test pressure with a hand pump, and stabilized for 1 hour, the pressure drop is less than 0.05Mpa, and then decreased to 1.15 times the working pressure, and stabilized for 2 hours. Visual inspection, no leakage, no pressure drop, no more than 0.03Mpa is qualified.
(4) When installing, pay attention to avoiding sharp objects when handling and installing the pipeline to prevent damage to the pipeline. During pipeline installation, prevent organic pollutants such as paint from coming into contact with pipes and fittings. The openings where the installation is interrupted or completed must be temporarily closed to prevent debris from entering. The water supply piping system should be flushed with water before acceptance. The flushing water flow rate should be greater than 2m/s. When flushing, no dead corners should be left. The faucet of each water distribution point should be turned on. The lowest point of the system should be set up with a water outlet. The cleaning time should be controlled until the water quality of the flushing outlet is equal to the inlet water. After flushing the drinking water system, the pipes should be filled with 20-30mg/l free chlorine water for disinfection. Chlorine-containing water should stay in the pipe for more than 24h. After the pipeline is disinfected, it is rinsed with drinking water, and the water quality meets the current national standard “Sanitary Standards for Drinking Water” after sampling and inspection by the health management department before it can be delivered to use. Within 30 minutes, allow two pressure rises to reach the specified test pressure. Pay attention to the conversion of pipe diameter when budgeting and lifting materials. The section of the chart is DN20 and PPR25 pipes (pieces) should be mentioned. Must use the same manufacturer’s products, because different manufacturers’ products contain different proportions of ingredients. It will cause weak bonding or failure to bond.
﹝二﹞ Rigid polyvinyl chloride pipe (UPVC)
(1) UPVC pipes (pieces) are used for drainage. Because of its light weight, corrosion resistance, high strength, etc., it is widely used in pipeline installation. Under normal circumstances, the service life can generally reach 30-50 years. The UPVC pipe has a smooth inner wall and low fluid friction resistance, which overcomes the defect that the cast iron pipe affects the flow rate due to rust and scaling. The pipe diameter is also one size larger than the nominal diameter. For example, DN100 is U-PVC110. DN150 is U-PVC160. Pipe fittings are divided into oblique tees, crosses, elbows, pipe clamps, reducers, pipe plugs, traps, pipe clamps, and hangers.
(2) Drain glue for connection. The adhesive must be shaken before use. The pipes and socket parts must be cleaned up. The smaller the socket gap, the better. Use emery cloth or saw blade to roughen the joint surface. Brush the glue thinly inside the socket and apply glue twice on the outside of the socket. Wait for the glue to dry for 40-60s. After inserting it in place, attention should be paid to appropriately increase or decrease the glue drying time according to climate changes. Water is strictly prohibited during bonding. The pipe must be placed flat in the trench after it is in place. After the joint is dry, start backfilling. When backfilling, fill the circumference of the pipe tightly with sand and leave the joint part to be backfilled in large quantities. Use products from the same manufacturer. When connecting the UPVC pipe to the steel pipe, the joint of the steel pipe must be cleaned and glued, the UPVC pipe is heated to soften (but not burnt), and then inserted on the steel pipe and cooled. It is better to add a pipe clamp. If the pipe is damaged in a large area and needs to replace the entire pipe, the double socket connector can be used to replace the pipe. The solvent method can be used to deal with the leakage of solvent bonding. At this time, drain the water in the pipe first, and make the pipe to form a negative pressure, and then inject the adhesive on the pores of the leaking part. Due to the negative pressure in the tube, the adhesive will be sucked into the pores to achieve the purpose of stopping leakage. The patch bonding method is mainly aimed at the leakage of small holes and joints in pipes. At this time, choose 15-20cm long pipes of the same caliber, cut them apart longitudinally, roughen the inner surface of the casing and the outer surface of the pipe to be patched according to the method of bonding joints, and cover the leaking area with glue. The glass fiber method uses epoxy resin and curing agent to prepare a resin solution. After impregnating the resin solution with glass fiber cloth, it is evenly wound on the surface of the leaking part of the pipe or joint, and becomes glass fiber reinforced plastic after curing. Because the method has simple construction, easy-to-master technology, good plugging effect and low cost, it has high promotion and use value in anti-seepage and leakage compensation.
(3) The water pressure 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 pressure test rules for non-metallic pipelines stipulated by the state. For the pressure test length of the pipeline without node connection ≯1.5km, the pressure test length of the pipe section with nodes ≯1km. The test pressure of the pipeline or pipe network shall not exceed 1.5 times the design working pressure, the minimum is ≮0.5MPa, and the test pressure shall be maintained for 2h or meet the special requirements of the design. No leakage is considered qualified. Pay attention to the conversion of pipe diameter when cutting the budget. It is also necessary to use the same manufacturer’s products to prevent different manufacturers’ products from different proportions of ingredients. It will cause weak bonding or failure to bond.
I encountered many specific problems and accumulated some experience when participating in the management of the installation of engineering plastic pipelines.
A telescoping plastic pipe
ends modified PVC drain pipe is a plug, socket fittings are, most bonding method using socket connection is a permanent connection invariable, the expansion line of plastic products The coefficient is large. The expansion and contraction length of the pipeline caused by changes in ambient temperature and sewage temperature can be calculated as follows:
where: ΔL——pipe temperature elongation, m; Δt——temperature difference, ℃; L ——The length of the pipeline, m; α——The coefficient of linear expansion, which is 7×10-5m/m℃.
Calculate the temperature elongation of a 3 m long pipeline at △t=50℃ as 10.5 mm, then this 10.5 mm elongation or contraction must be solved by the special fitting of the expansion joint, especially in northern China, where the environmental temperature difference is large. The expansion joint must be installed, otherwise there is the possibility of straining or bulging the elbow. However, the common fault in the installation process is that the insertion depth is marked at the pipe socket not according to the ambient temperature at the time. After installation, the insertion depth is not known, and the quality inspector cannot check it. It is easy to cause the rubber to fall out of the socket when it is cold. The protection range of the sealing ring. Odor leaks out; when the weather is hot, the pipe has nowhere to extend and the joints are swollen. There is also the installation of the expansion joint upside down, that is, the side of the rubber seal ring is used as a downward socket, causing undue leakage.
Second, the problems that need attention in the construction of UPVC drainage pipes
(1) The layout of the drainage pipe has a great influence on the design flow of the system. The riser and the discharge pipe should be connected with a reducing elbow. The exit pipe should be one size larger than the riser. The exit pipe should discharge the sewage as smoothly as possible outside, and there should be no elbow or B-shaped pipe in the middle. Many projects have confirmed that the thinner drainage pipe and the additional pipe fittings on the pipe will adversely change the pressure distribution in the pipe, reduce the allowable flow value and prone to poor toilet drainage during future use.
(2) UPVC spiral steel pipe drainage system In order to ensure the spiral steel pipe water flow falls spirally, the riser cannot be connected with other risers, so an independent single riser drainage system must be adopted, which is also one of the characteristics of the UPVC spiral steel pipe. Avoid superfluous, copy the drainage system of cast iron pipes and add exhaust pipes in high-rise buildings. If the exhaust pipes are added, materials will be wasted and the drainage characteristics of spiral steel pipes will be destroyed.
(3) The special tee or four-way pipe fittings for side water intake used with spiral steel pipes belong to the nut extrusion rubber ring sealed sliding joints. Generally, the distance of telescopic sliding is allowed to be within the temperature difference range of the normal construction and use stage. According to UPVC In the pipeline expansion system, the allowable pipe length is 4M, that is to say, whether it is a riser pipe or a horizontal branch pipe, as long as the pipe section is within 4M, no additional expansion joints are required.
(4) Connection of pipes. UPVC spiral steel pipe adopts nut extrusion rubber ring to seal the joint. This kind of joint is a kind of sliding joint, which can be used for expansion and contraction. Therefore, it is necessary to consider the appropriate reserved gap after the pipe is inserted in accordance with the regulations. Avoid excessively large or small reserved gaps due to individual operators’ trouble-free construction during construction, which may cause leakage due to seasonal temperature changes and pipeline deformation in the future. The prevention method is to first determine the reserved gap value according to the current construction temperature. When constructing each joint, make an insertion mark on the insertion tube first, and it is enough to reach the insertion mark during operation.
(5) In the design of some high-rise buildings, in order to strengthen the resistance of the bottom of the riser of the spiral steel pipe drainage system.

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