With the improvement of people’s living standards, environmental protection awareness and health concerns, a green revolution in the 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 pipe

﹝一﹞Polypropylene 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, and the pipe diameters are specifically divided into DN20, DN25, DN32, DN40, DN50, DN63, DN75, DN90, 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. DN<50, the hot melt depth is 1-2MM, and DN<110, the hot melt depth is 2-4MM. When connecting, put the pipe end without rotating Insert into the heating jacket to reach the predetermined depth. At the same time, push the pipe fittings onto the heating head without rotation for heating. After the heating time is reached, immediately remove the pipes and pipe fittings from the heating jacket and the heating head at the same time, and insert them to the required depth quickly and evenly without rotation. 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 prohibited 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 extent. When the PP-R pipe is connected with the metal pipe fitting, a PP-R pipe with a metal insert should be used as a transition. The pipe fitting and the PP-R pipe are connected by hot-melt socket and connected with the metal pipe fitting 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.

﹝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 is generally up to 30 to 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. 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 is to prepare a resin solution with epoxy resin and curing agent. 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 FRP 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.