At present, plastic water supply pipes include:
- rigid polyvinyl chloride (PVC-U),
- high-density polyethylene (HDPE),
- cross-linked polyethylene (PE-X),
- polybutene (PB),
- acrylonitrile,
- butadiene,
- styrene (ABS),
- chlorinated polyvinyl chloride (PVC-C),
- aluminum-plastic composite pipe (PE-AL-PE, PE-X, AL-PE-X),
- modified polypropylene (PP-R, PP-C) .
Plastic water supply pipes have the advantages of light weight, convenient construction, smooth inside of the pipe, good hydraulic conditions, no scaling, no corrosion, and long service life. However, the plastic water supply pipe itself has the shortcomings of brittleness, impact resistance, and low resistance to mechanical damage.
With the high-grade housing, concealed concealed installations are often used to conceal the pipes under the ground, and the wall grooves are easy to be concealed for work, decoration, and construction. It is difficult to complete the water tightness test of plastic water supply pipes at one time due to the damage caused by work such as cleaning the ground, and the water tightness test of the pipe is an effective method to prevent the pipeline from leaking. Following we will introduce the PE water supply pipe construction plan.
Excavation of Pipe Trench
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The excavation of the pipe trench should be straight, and the excavation width of the trench bottom is DN+0.30m. When the pipeline is connected underground, the width of the groove bottom at the interface should be appropriately increased. The width of the groove bottom of the pipeline should not be less than DN+0.50m to facilitate installation and connection.
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When the pipeline is buried, the minimum pipe top covering depth shall meet the following requirements:
- a. When buried under the carriageway, it should not be less than 0.80m.
- b. When buried under the sidewalk, it should not be less than 0.60m.
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When crossing the carriageway does not reach the design depth, measures of laying steel casing shall be taken for protection.
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When the pipe groove must be turned, the turning angle should not be too large, and the bending radius should meet the following requirements:
PE pipeline allowable bending radius R (mm) D≤50 30D; 50D≤160 50D; 160D≤250 75D; D>250 100D.
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When excavating the pipe groove manually, the bottom of the groove is required to be flat and dense, without sharp objects. The bottom of the trench can be undulated, but the pipe must be supported smoothly. If there is over-excavation, it must be backfilled and tamped.
Pipeline Connection
PE water supply pipe connection has hot melt connection and electrofusion connection; hot melt connection is divided into hot melt socket connection and hot melt butt connection, electrofusion connection is divided into electrofusion socket connection and electrofusion saddle connection. We adopt the hot melt butt connection method for construction, and its main steps are as follows:
- Material preparation: Put the pipe or pipe fittings in a flat position and place them on the butt joint machine, leaving enough cutting allowance of 10-20mm.
- Clamping: According to the pipes and fittings to be welded, select suitable slip fixtures, clamp the pipes, and prepare for cutting.
- Cutting: Cutting the impurity and oxide layer on the end faces of welded pipe sections and fittings to ensure that the two butt joint end faces are smooth, clean and free of impurities.
- Alignment: The end faces of the two welded pipe sections should be completely aligned, the smaller the wrong side, the better, and the wrong side should not exceed 10% of the wall thickness. Otherwise, the docking quality will be affected.
- Heating: The temperature of the butt joint is generally between 210-230℃. The heating time of the heating plate is different in winter and summer, and the melting length of both ends is preferably 1-2mm.
- Switch: Take the heating plate away, quickly let the two hot melt end faces adhere and pressurize. In order to ensure the quality of the melt butt joint, the shorter the switching period, the better.
- Melting butt joint: It is the key to welding. The butt joint process should always be carried out under melting pressure, and the appropriate width of the crimping is 2-4mm.
- Cooling: Keep the docking pressure constant, and let the interface cool down slowly. The length of the cooling time is based on the hard curling by hand, and no heat is felt.
- Docking is complete: After cooling down, release the slips, remove the docking machine, and prepare for the next interface connection again.
Installation and Construction
- Check whether the pipe groove meets the installation requirements before installation, and then check the appearance of the pipe for obvious dents, cracks, scratches, or scratches, and replace it in time if there are hidden quality hazards.
- C20 concrete is used to set up concrete supports at pipe elbows, tees, tapered joints, fire hydrants, etc., and flange valves are reinforced with brick supports.
- When connecting PE water supply pipes with metal pipes, valves and fire hydrants, steel-plastic transition joints or special flange connections must be used.
- Exhaust valves should be installed at the uplift part of the pipeline or on the uphill section to reduce the impact of the gas and water mixed pressure on the pipeline. The ratio of the pipe to the exhaust valve is designed to be
1:8. - Because the PE pipe itself has good flexibility and flexibility, all pipe installations have not considered the installation of expansion joints.
Backfill and Compact
After the pipeline is installed and laid, it should be backfilled immediately after the concealed project is checked and accepted, and the following requirements should be met during backfilling:
- Prevent the pipeline from floating due to the accumulation of water in the tank. If there is accumulated water, find a way to drain it.
- When backfilling pipe troughs in stone, soil and rock mixed sections, first load and transport clay or sand to backfill to the top of the pipe 200-300mm, and then backfill other miscellaneous soil after tamping.
- Backfilling must be backfilled from both sides of the pipe at the same time, with one layer backfilling and one layer compacted.
- Before the pipeline pressure test, under normal circumstances, the backfill should not be less than 500mm.
- Large-area backfilling after the pipeline pressure test should be carried out when the pipeline is full of water, and the pipeline should not be left empty for a long time after the pipeline is laid.
- Exhaust cuts should be installed at the uplift of the pipeline or on the upslope to reduce the impact of the mixed pressure of air and water on the pipeline.
Backfilling must be backfilled from both sides of the pipeline at the same time, backfilling one layer to compact one layer. Before the pipeline pressure test, under normal circumstances, the backfill should not be less than 500mm. After the pipeline pressure test, the large area backfill should be carried out when the pipeline is full of water. After the pipeline is laid, it is not suitable to be in an empty pipe for a long time.