——Characteristics of FRP pipes

1. Good corrosion resistance, no impact on water quality. FRP pipes can resist the erosion of acid, alkali, salt, seawater, untreated sewage, corrosive soil or groundwater and many chemical fluids. It has a longer service life than traditional pipes, and its design service life is generally more than 50 years. For sand-filled FRP pipes, they are mainly used in municipal and urban transmission and distribution networks. They are welcomed by the water supply and drainage industry due to their advantages of non-toxic, rust-free, tasteless, no secondary pollution to water quality, no need for corrosion protection, greatly extended service life, and easy installation.

2. Anti-pollution and anti-moth. The surface of unsaturated polyester resin is clean and smooth, and will not be contaminated by crustaceans, fungi and other microbial stations in the sea or sewage, which will increase the roughness; Reduce the overflow section and increase the maintenance cost. FRP pipes are free of these pollutants and are clean after long-term use. At the same time, due to its smooth inner wall and excellent corrosion resistance, it will not produce scale and microbial growth, effectively ensure water quality and maintain the stability of water resistance. However, the traditional pipes still have the phenomenon of water resistance increasing and surface scaling in the future.

3. Good heat resistance and frost resistance. At - 30 ℃, it still has good toughness and extremely high strength, and can be used in the range of - 50 ℃ - 80 ℃ for a long time. The resin with special formula can also work at temperatures above 11O ℃.

4. Light weight, high strength, convenient transportation and installation. The sand-filled FRP pipe with tight filament winding is used, and its specific gravity is 1.65-2.0, which is only 1/4 of steel. However, the hoop tensile strength of FRP is 180-300MPa, and the axial tensile strength is 60-15OMPa, which is similar to alloy steel. Therefore, its specific strength (strength/specific gravity) is 2-3 times that of alloy steel. In this way, it can meet the requirements of users and be designed to meet the requirements of all kinds of pipes under internal and external pressure. For single weight of the same pipe diameter. FRP pipe is only 1/2.5 of carbon steel pipe (steel coil pipe), 1/3.5 of cast iron pipe, and 1/8 of prestressed reinforced concrete pipe, so it is very convenient for transportation and installation. The length of each section of FRP pipe is 12 meters, which can reduce the number of joints by two-thirds than that of concrete pipe. Its socket connection mode makes the installation fast and simple, while reducing the lifting cost and improving the installation speed.

5. Small friction resistance, good conveying capacity. The inner wall of FRP is very smooth, and the roughness and friction resistance are very small. The roughness coefficient is 0.0084, while the n value of concrete pipe is 0.014, and that of cast iron pipe is 0.013. Therefore, glass fiber reinforced plastic pipe can significantly reduce the fluid pressure loss along the way and improve the conveying capacity. Therefore, it can bring significant economic benefits: ① At the same conveying capacity, glass pipe with smaller inner diameter can be selected for the project, thus reducing one-time project investment; ② Using pipes with the same inner diameter, FRP pipes can reduce pressure head loss and save pumping costs compared with other pipes; ③ It can shorten pumping time and reduce long-term operating costs.

6. Good electrical and thermal insulation. FRP is non-conductive. The electrical insulation of the pipeline is excellent, and the insulation resistance is 1012-1015 Ω · cm. It is most suitable for use in transmission and telecommunication line dense areas and areas with frequent lightning; The heat transfer coefficient of glass fiber reinforced plastics is very small, only 0.23, which is 5 ‰ of that of steel. The thermal insulation performance of pipe construction is excellent.

7. Good wear resistance. Put water containing a large amount of mud and sand into the pipe to carry out a comparative test on the impact of rotary wear. After 300000 rotations, the wear depth of the inner wall of the pipe is as follows: 0.53mm for steel pipe coated with tar and enamel, 0.52mm for steel pipe coated with epoxy resin and tar; The surface hardened steel pipe is 0.48mm, and the glass steel pipe is 0.21mm. This shows that it is quite wear-resistant.

8. Low maintenance costs. Due to the above corrosion resistance, wear resistance, frost resistance and pollution resistance of glass fiber reinforced plastic pipe, the project does not need measures and maintenance such as rust prevention, pollution prevention, insulation and thermal insulation. No barrier protection is required for buried pipes, which can save more than 70% of engineering maintenance costs.

9. Strong adaptability. FRP pipes can be used according to various specific requirements of users, such as different flow, different pressure, different buried depth and load conditions; Designed and manufactured into pipes with different pressure classes and stiffness classes.

10. The project has a long service life and is safe and reliable. According to the simulation test in the laboratory, the suitable service life of FRP can be more than 50 years.

11. The comprehensive benefits of the project are good. Comprehensive benefits refer to long-term benefits formed by construction investment, installation and maintenance costs, service life, energy saving and steel saving and other factors. The comprehensive benefits of FRP pipes are desirable. Especially, the larger the pipe diameter, the lower the cost. When it is further considered that the buried pipe can be used for several generations without annual maintenance, and its superior comprehensive benefits can be brought into play.

——Characteristics of steel pipe

1. Compared with other traditional pipes, steel pipes are light in material, high in strength, good in toughness, can withstand high internal pressure, flexible in manufacturing and use, and can adapt to complex or harsh geological conditions.

2. However, the steel pipe has a high end rate in the process of use, which is mainly caused by the trouble of internal and external anti-corrosion treatment. First of all, the problem of external corrosion protection is very critical. The quality of external corrosion protection directly affects its service life. At present, the external corrosion protection of domestic steel pipes is mainly covered. For steel pipes, it is required to adopt strengthened or extra strengthened external corrosion protection, and cathodic protection is implemented in some areas. The covering type of external anti-corrosion method is generally coating such as petroleum asphalt, epoxy coal tar asphalt, etc. The latter is not easy to solidify at low temperature, and has more problems in the construction of welded joints on site. This chlorosulfonated polyethylene was used previously, because of the large number of solvents, it is easy to produce pinholes, and the resistance to penetration is unqualified, and it is clearly no longer used in some areas. The anti-corrosion effect of cathodic protection is relatively good, but due to the use of sacrificial anode, the anode must be replaced regularly in future operation, which increases the operating cost and work. In addition to the internal wall treatment, there are generally three methods: anti-corrosion coating, resin mortar and cement mortar. There are two problems in the three methods. The first is the bond strength between the anticorrosive coating and the steel pipe. The cement mortar has been mentioned before. For the two methods of anti-corrosion coating and resin mortar, the inner surface of the steel pipe can be completely derusted before construction, but this is difficult to be intact. Therefore, the rust spots cause the origin of delamination in the future, forming corrosion and scaling; The second is that most of the steel pipes are butt welded on site, and corrosion protection is carried out after welding. It can only be carried out manually. The quality is not easy to control. Moreover, for the pipes with small diameter, the corrosion prevention will not be carried out because the personnel cannot enter the construction site. It also causes the hidden danger of future weld damage. According to the analysis of several steel pipe explosion accidents, it is mainly caused by poor weld quality and weld corrosion.

3. The overall cost is high.

4. Poor hydraulic performance and high energy consumption. The internal roughness coefficient of the steel pipe is between 0.013-0.014, so for the pipeline with the same water transmission capacity and the same pipe diameter, the resistance along the pipeline is high, so the pump head needs to be increased, and the initial investment needs to be increased. At the same time, the operating cost also increases greatly due to the large power consumption.

5. The pipeline has the defect of poor bearing capacity for water hammer.