The types of municipal water supply and drainage pipes mainly include plastic pipes, metal pipes and reinforced concrete pipes. 
1.Plastic pipesPlastic pipes mainly include PVC-U pipes, PE pipes, FRPP pipes, and RPM pipes. The design service life of plastic pipes should not be less than 50 years.
The plastic pipe for municipal drainage should be designed according to the pressure-free gravity flow, constructed and calculated according to the flexible pipe design theory, and should be buried below the frozen line. 1.1 PVC—U pipePVC-U pipe is a hard PVC pipe, and the pipe wall is constructed with double-walled ripple pipes, reinforced pipes, flat-walled pipes and steel-plastic composite winding pipes. Steel-plastic composite spiral wound pipes are often connected by inner casing bonding. Double-walled ripple pipes, reinforced pipes and flat-walled pipes are commonly connected by sockets and sealed with rubber rings. For flat-walled pipes, when the pipe diameter is less than 200 mm, they are mostly connected by bonding. 
When the PVC-U pipe is used as a drainage pipe, the concentration of hydrogen sulfide gas in the pipeline is much higher than that of the hydrogen sulfide gas in the concrete drainage pipe, and the PVC pipe has good sealing performance for odor. When PVC-U is used as a drainage pipe, its production energy consumption accounts for 20% of the same diameter drainage cast iron pipe, low cost, aging resistance, good thermal insulation effect and long life, so it is widely used in municipal drainage. The material of PVC-U pipe is brittle and not resistant to external pressure, so when the pressure requirement is high, the reinforced pipe with good compressive performance or steel-plastic composite winding pipe is used. 1.2 PE pipesPE pipes are polyethylene pipes, mainly including double-walled ripple pipes, winding structural wall pipes, steel-plastic composite winding pipes, and steel-belt reinforced spiral ripple pipes. 
Double-walled ripple tubes are generally connected by socket type or double socket connection, and sealed with rubber rings. In addition to the connection method of double-wall ripple pipe, the winding structure wall pipe can also be often welded, and can also be connected by clamp, Huff and flange. Steel-plastic composite winding pipes and steel belt-reinforced spiral ripple pipes are often connected by welding or welding. PE pipes are divided into low-density, medium-density and high-density polyethylene pipes, and high-density polyethylene pipes (HDPE) are more widely used in the field of municipal water supply and drainage, which have strong impact resistance, heat and wear resistance, acid and alkali corrosion resistance, and the smallest permeability. The rapid cracking resistance is obviously better than that of PVC-U, and the thermal insulation performance is good, so it is widely used in municipal water supply, drainage and rainwater. Especially in municipal water supply applications, it has the advantages of high pressure resistance, small head loss and less leakage. 
1.3 frpp pipesFRPP pipe is a reinforced polypropylene pipe, which is connected by socket connection and sealed with rubber ring, mainly used for municipal drainage pipes, and its maximum pipe diameter can reach 1500mm. 
The pipeline should be laid on the undisturbed soil foundation or backfilled dense foundation after slotting, and the net width of the bottom of the trench can be determined according to the size of the pipe diameter, soil conditions, and buried depth construction technology. When excavating trenches, the elevation of the base should be strictly controlled, and the base surface should not be disturbed. 1.4 rpm tubeThe rpm pipe is a glass fiber reinforced plastic sand pipe, and the connection method is generally socket connection or double socket connection, and it is sealed with a rubber ring. The sand pipe is generally used for large-diameter drainage pipes with high requirements, and the commonly used is the FRP sand pipe, which has the advantages of strong corrosion resistance, good physical and mechanical properties, and good thermal resistance, so it is used more when transporting industrial wastewater. The disadvantage is that it is easy to become brittle and its strength decreases at low temperatures, so it is necessary to take measures to keep warm in colder areas. 
When the plastic pipe is sealed with an elastic rubber ring, when the diameter of the pipe is not more than 400mm, it can be directly inserted manually, and when the diameter of the pipe is greater than 400mm, a special tool should be used to seal the pipe interface with a rubber ring. Plastic pipes larger than 800mm are welded on both sides inside and outside. 2.Metal pipesThere are three main types of metal pipes in municipal water supply and drainage: ductile iron pipes, cast iron pipes for drainage and steel pipes. Buried metal pipelines are prone to chemical decay due to the action of acid, alkali, salt and groundwater in the soilUnder the action of the underground potential difference, it will also be subject to electrochemical decay. These pipes have a lifespan of 25 years. In general, the more oxygen in the water, the more severe the decay;The lower the pH, the faster the decay;The higher the salt content, the faster the decay, which is the result of oxidation and electrolysis. After the metal pipeline is laid, pay attention to the construction specifications when backfilling, and select the most suitable filling machine for soil backfilling in strict accordance with the project design plan. Before the trench is backfilled, the water should be drained, and some impurities in the raw materials should be eliminated, and liquefied fine sand and silty sand should not be used as backfilling. Backfill soil should be handled in layers, and wait until the soil compactness of the first layer of backfill has met the engineering requirements, the second layer can be carried out, and the fill should be carried out on both sides of the pipeline at the same time, and the compactness of the fill should meet the requirements of the specification. In the process of construction, the water ramming method or backfill with water can not be used, so as to avoid water accumulation, resulting in accidents. 2.1 Feed water ductile iron pipeFeed water ductile iron pipes have mild high wall, thin wall, pressure resistance, impact resistance, corrosion resistance, seismic resistance and other properties. 
The pipe interface adopts a flexible interface, and there is a certain elongation rate and deflection angle, which has the advantages of pig iron pipe and steel pipe material. The coating of the water nodular graphite cast iron pipe is selected according to the internal and external conditions at the time of use. The existing inner coating is epoxy resin, polyurethane inner and outer coating, PE film coating and other new ductile iron pipe products. Where the ductile iron pipeline connected by socket must be calculated and set up piers, and the T-type interface pipeline should be set up at the vertical or horizontal turn, and the size of the pier should be determined according to the pipe diameter, corner, working pressure and other factors. The external anti-corrosion coating of ductile iron pipes should be selected according to the soil conditions, galvanized and epoxy asphalt coating or higher requirements of the coating.
2.2. Drain cast iron pipesDrainage cast iron pipe has been basically replaced by PVC-U now, when the drainage cast iron pipe is used for a long time, the microorganisms attached to the inner wall of the water pipe are much more than those attached to the inner wall of the PVC pipe of the same diameter, which affects the water flow capacity, so the application is relatively less. 
2.3 steel pipesSteel pipe mainly refers to welded steel pipe, steel pipe pressure resistance is good, used in municipal water supply, the inner wall anti-corrosion is often made of cement mortar, the outer wall anti-corrosion using epoxy coal asphalt paint anti-corrosion, and the appropriate anti-electrochemical corrosion measures. When the steel pipe is used for drainage, it is mainly used for the inlet and outlet pipes of sewage plant structures, and it is necessary to do a good job of internal and external anti-corrosion.
3.concrete and reinforced concrete pipesConcrete and reinforced concrete pipes have the unique advantages of high compressive strength, good durability, long service life, easy manufacturing, low production cost and low price, and are widely used to lay drainage pipelines in China's urban construction, industrial and mining company construction, and farmland water conservancy construction, and have achieved good economic and social benefits.
The water flow speed of concrete pipe is relatively slow, the resistance is large, and the corrosion resistance is relatively weak. Under the condition of small pipe diameter, plastic pipes are relatively more used. After economic comparison, it is more reasonable to use plastic pipes under the condition of smaller pipe diametersUnder the condition of larger pipe diameter, the concrete pipe is more reasonable. With the continuous progress of urbanization, the demand for large-diameter rainwater pipes and drainage pipes is increasing, and the characteristics of low production cost, good durability and high compressive strength of concrete pipes meet the needs of market development. In order to overcome the shortcomings of high resistance and weak anti-corrosion ability, PVC lining is often widely used in large-diameter concrete pipes. Analysis of the application trend of municipal water supply and drainage pipesIn the future, the application trend of municipal water supply and drainage pipes will reflect the following characteristics:1.The development trend of high durability directionThe municipal water supply and drainage pipes used in China are not long, and there is still a lack of data in the research of their design life, but in terms of corrosion resistance, plastic pipes are better than metal pipes, so plastic pipes are more used in municipal water supply and drainage pipes than metal pipes. 2.The flexible interface type is more widely usedThe future development trend of municipal water supply and drainage pipelines is to use flexible joint mouth water supply and drainage pipes, which are convenient to install and have a small probability of water leakage. 3.The development trend of large-caliber and multi-varietyIt is more likely that reinforced concrete will be used for oversized drainage pipes, and it is also possible to use sand pipes, but it is limited in areas with low winter temperatures. The 12th Five-Year Plan has made it clear that industrial waste will be used in concrete, so it can be used in reinforced concrete with large pipe diameters.