Plants, animals, humans – all living creatures on earth need water to survive and thrive. This is why water systems remain one of the most important infrastructures today.
Of course, humans require more than just water. People need clean, potable water. This becomes even more crucial for those living in areas with desert climates, like the United Arab Emirates (UAE). After all, how can people survive the heat in a desert country without enough drinking water?
Besides the supply itself, one of the most critical elements of water pipe systems is the delivery – one that doesn’t compromise water cleanliness and safety. This is where high-density polyethylene (HDPE) pipes can save the day.
Here, you’ll learn HDPE Pipe Insertion Technology for Rehabilitation of Largediameter Water Supply Pipes.
HDPE Pipe Insertion Technology for Rehabilitation of Largediameter Water Supply Pipes
Determination of Repairing Method for Interpenetration in Pipeline
The repair technology of inserting high-density polyethylene (Hish Density Polyethylene, HDPE) pipe in the pipeline is to use the external energy of the original pipeline to resist impact and internal energy to withstand pressure, and the lining pipe is resistant to corrosion, wear, high temperature, Long service life and other characteristics, forming a "pipe-in-pipe" composite structure, so that the repaired pipeline has the comprehensive characteristics of the original pipe and the lined pipe. The difference between root pry diameter reduction methods can be divided into two different methods: ① "u" type method. Use a diameter reducer to align HDPE villages that are equal to or slightly larger than the inner diameter of the original pipe
The hdpe pipe for water supply is reduced in diameter and shaped into a "U" shape, and then slowly pulled into the cleaned target pipe, and the liner is restored by means of air pressure or water pressure. ②Isometric compression method. The hdpe pipe for water supply liner that is equal to or slightly larger than the inner diameter of the original pipe is subjected to multi-stage equal-diameter compression, and then slowly pulled into the cleaned and treated target pipe. After 24 hours, the hdpe pipe for water supply slowly recovers by itself. Through the scheme comparison, it is determined that the project adopts the equal-diameter compression method.
①Pipeline positioning. First use ground penetrating radar to detect the direction of the pipeline. After the first node is excavated, use an automatic crawling camera robot (CCTV) to start from the first node and determine its position, inner diameter and bends that are difficult to find on the ground from the inside of the pipeline. The exact location of the first class node. ②Pipeline cleaning. Use PIG physical cleaning technology to clean the original pipeline. For a small amount of solid scale and obstacles, you can continue to clean with the method of "skinning cow". After the pipeline is cleaned, the CCTV imaging system is used to check the cleaning effect. This process is an important part of the hdpe pipe for underground water supply repair technology. The cleaning effect is to determine whether the water HDPE pipe will not be scratched during the lining process, so as to ensure
One of the key factors for the safe operation of the pipeline. ③ HDPE water pipe welding. Use a special equipment hot-melt welding machine to butt the liner and check the quality. The butt joint process should strictly control the butt joint temperature, pressure, time and other parameters. The reasonable selection of each parameter during welding is one of the important factors that determine the quality of the joint. Therefore, each weld is numbered and the welding parameters and quality are recorded. After welding, conduct an air tightness test on the water HDPE pipe with a pressure of 0.1 MPa to check the tightness of the weld seam of the water HDPE pipe.
④ Interspersed test. The effect of pipe cleaning will directly affect the penetration quality of water pipes, so a penetration test should be carried out before formal penetration. When the scratch depth of the penetration test section is ≤1 mm and the penetration resistance is ≤150 kN/km, the cleaning is qualified. ⑤The liner is inserted. Use a reducer to reduce the liner pipe in four stages of equal diameter and uniform diameter, and the reduction range is controlled at 5% to 12%. Fix the tractor at the head end of the water HDPE pipe that has been reduced in diameter, and use a winch to pull the water HDPE pipe slowly through the cable Human original pipeline, the traction speed is controlled at 15-18m/min, and the traction force is less than 50% of the yield strength of water HDPE pipe. After the pipeline is penetrated, the recovery of the liner is checked again with CCTV to ensure the quality of the penetration. ⑥Joint processing. When inserting the liner, there should be a certain allowance for the length of each inserted section of HDPE pipe (both the allowance at the penetration end and the outlet end are 12 m).
The composite flange is connected, and the adjacent pipe sections or fittings are connected by bolts with loose flanges. ⑦ After the repair of each pipe section is completed, the strength and tightness test shall be carried out in sections according to the "Code for Construction and Acceptance of Water Supply and Sewerage Pipeline Engineering" (GB 50268-97).
Determination of the length of interspersed section
Generally, the length between two fittings is used as an intersecting section, but when the angle of the elbow is small and the distance is not long, it can be considered to pass directly through the elbow without segmenting, but generally it cannot pass through two elbows continuously. For the straight pipe section, according to relevant information, DN800 pipes can be penetrated 1000 m at a time, but the distance between the two fittings of the water supply pipe rarely reaches 1000 m. Therefore, the length of the interpenetrating pipe section mainly depends on the density of the pipe fittings.
Technical pros and cons
① Short construction time. According to the traditional "big excavation" construction, it takes about 35 d/km, and HDPE pipe repair only needs 23 d/km. Water HDPE pipe customization can be made in the factory during the pipeline flushing period, and no additional time is required. ② Less excavation earthwork. Using the traditional "big excavation" operation method, the amount of excavated earthwork needs to be more than 6 600m³/km; using HDPE pipe repair only needs to dig work pits, and the number of work pits depends on the number of interspersed sections (only at the intersected section nodes) excavation), each working pit the excavation volume is about 90 m³.
③Low cost. The cost of using hdpe pipe for underground water supply interpenetrating repair technology is about 55% of the traditional "big excavation" construction. ④HDPE pipe has good chemical stability, is not easy to corrode and scale, and will not breed bacteria, microorganisms or algae. ⑤Increase the conveying capacity. After pipeline repair, the inner diameter is reduced
24 mm, but its roughness coefficient (0.01) is low and the conveying capacity is greatly improved.
⑥Excellent wear resistance. The results of sand-mixed wear test in water show that the wear resistance of hdpe pipe for underground water supply is about 4 times that of steel pipe. ⑦ Good impact resistance. HDPE pipe has good pressure bearing capacity, which greatly improves the pressure bearing capacity of the original pipeline after lining repair. Tests have shown that steel pipes lined with HDPE pipes with a wall thickness of 8 mm can withstand a pressure of 7 MPa, while steel pipes not lined with hdpe pipe for underground water supply can only withstand a pressure of 5 MPa, and the pressure bearing capacity is significantly improved. ⑧Long service life, generally up to 50 years.
① There is a risk of the liner getting stuck. Due to the small isodiametric compression (about 5% to 12%), the liner may be stuck due to excessive resistance when the original pipe has a serious misalignment or an elbow is not found in the interspersed section. ②The hdpe pipe for underground water supply to be inserted after welding need to occupy a large space, and some lanes need to be closed for construction in urban areas. ③ When the inner diameter of the original pipe is quite different, because the liner with a smaller diameter is selected, the liner and the original pipe cannot be tightly attached to the larger inner diameter of the original pipe. ④ hdpe pipe for underground water supply welding has higher requirements on parameters such as temperature, pressure and time. ⑤ High requirements for cleaning the original pipe. ⑥After the liner is damaged, the water flows along the interlayer, so it is difficult to find the damage point, and it is inconvenient to maintain. ⑦When the pipeline repaired by the liner needs to be opened to receive water, a section of the original pipe must be removed after the water is cut off, and then the liner is disconnected, the flange is pressed, and the tee is connected to receive water. The construction is difficult. Therefore, this technology is suitable for water main pipes and should be used with caution in the repair of water distribution pipes.
① Save construction costs. Re-laying a DN800 ductile iron pipe, the construction cost is estimated to be about 2.643 million yuan/km (including the cost of road damage and environmental restoration); the original pipe is reconstructed with the repair technology of interspersed HDPE pipe, and the construction cost is 1.4 million yuan/km (including work pits and broken roads and borrowed land costs). ② Reduce the head of the raw water pump and reduce power consumption. According to empirical calculations, when the DN800 cement pipe is lined with 12 mm hdpe pipe for underground water supply, the water delivery can be increased by 41% under the premise that the pump outlet pressure remains unchanged and the head loss of the original water pipe before and after the transformation is the same. If the current flow rate is maintained, the head of the water pump can be reduced and the power consumption can be reduced by about 90×104 kW·h/a. ③Adopting the traditional "big excavation" operation method not only requires a large amount of earth excavation, but also requires a large number of land borrowing, cofferdams, drainage, soil transportation and other processes, which will inevitably greatly interfere with people's daily life, especially in construction in the downtown area. According to the current surrounding environment of the pipeline, when adopting the traditional "big excavation" construction, some buildings must be demolished, which will have a serious impact on the normal life of some residents. However, the reconstruction of the original pipeline by using the internal interpenetrating HDPE pipe repair technology only needs to excavate the working pit, and the excavation area is not large, which reduces the interference to the normal life of the citizens. In addition, the environmental impact, traffic impact, and commercial loss of the "big excavation" construction are much higher than those of repairing the original pipeline with the technology of interpenetrating hdpe pipe for water supply.