First, the characteristics of PE gas pipe
1. Good hygienic performance: PE pipe processing does not add heavy metal salt stabilizer, the material is non-toxic, no fouling layer, no bacteria, and it solves the secondary pollution of urban drinking water.
2, corrosion resistance: in addition to a few strong oxidants, can withstand the erosion of a variety of chemical media; no electrochemical corrosion.
3. Long service life: PE pipes can be safely used for more than 50 years under rated temperature and pressure conditions.
4, better impact resistance: PE pipe has good toughness, high impact strength, heavy weight directly pressed through the pipeline, will not lead to violent pipeline.
5. Reliable connection performance: The strength of the PE tube hot melt or electrofusion interface is higher than that of the pipe body, and the joint will not be broken due to soil movement or live load.
6. Good construction performance: The pipeline is light in weight, the welding process is simple, the construction is convenient, and the comprehensive construction cost is low.
Second, PE gas pipe connection method
In the application process of PE gas pipe, a key factor in whether PE gas pipe can reach the specified long-term service life is the quality of laying. The HDPE pipeline has a variety of unique properties to make the pipeline more safe and fast, and the correct construction design and installation procedures will make these superior performance of the pipeline to a greater extent.
1. Technology before PE gas pipe construction
a should be familiar with and master the construction drawings before construction;
b Prepare the corresponding construction equipment;
c On-the-job training for the operators, after the training is qualified, the construction can be carried out;
d Accept the inspection of pipes and fittings according to the standard.
2. Excavation of PE gas pipe trench
The excavation of the trench must be carried out in strict accordance with the excavation route and excavation depth guided by the design drawings or project supervision, and may not be altered without the consent of the relevant department. Generally, the minimum pipe top cover thickness buried in polyethylene pipes is:
A. The buried depth of the pipe buried under the roadway shall not be less than 0.9 m;
B. It shall be buried under the sidewalk or the pipe branch shall not be less than 0.75 meters;
C. The branch under the green belt or in the residential area shall not be less than 0.6 m;
D. In the permanent frozen soil or seasonal frozen ground layer, the buried depth of the pipe top should be below the freezing line. In the solid and stable bottom of the trench, the width of the trench is determined by the operating space required for the construction. The size of the space must allow proper preparation of the bottom of the trench and the filling and compaction of the trench filling material, and also It is necessary to take into account the cost of trench excavation and the cost of purchasing landfill materials.
3. Preparation of PE gas pipe trench bottom
For pressure systems such as water supply, sewage or long-distance transfer lines, unless the design drawings have special requirements, the horizontal accuracy of the bottom of the trench is generally not very high. For gravity drainage systems, the grade of the slope must meet the specified requirements.
If the bottom of the trench is fairly straight and there are essentially no large rocks in the soil, then there is no need to level it. Of course, it would be better if it was a bottom layer of the trench that was not disturbed. However, if the bottom of the trench has been disturbed or must be disturbed during the excavation process, the compactness should at least reach the compactness of the surrounding material. The bottom of the trench is generally not more than 50 mm in diameter. Sharp stones with sharp edges and corners are mixed with some sand and clay. HDPE pipes of all sizes can generally accommodate the unevenness of a small number of local pipe bottoms. However, if the backfill material contains sharp-edged stones or hard shale, stress concentration areas may be generated on the pipe surface to cause damage. pipeline.
For excavation in shale and loose rock soil, in order to avoid contact with loose rock, it is necessary to provide a uniform ditch bed for the HDPE pipe. The general practice is to dig deeper than the specified level when opening the bottom of the pipe. At least 150mm, then backfill to the specified height with appropriate landfill material and compact to a compactness of 90% or higher.
4. Laying of pipes in PE gas pipe trench
Before the pipe is placed in the trench, the pipe should first be inspected thoroughly, and the pipe is allowed to hang or roll into the trench without any defects. The pipes are usually pre-connected on the ground. Sometimes the pipes may be pre-connected into a number of pipe sections of about 150 meters in length, stored in a certain place, transported to the installation site when they need to be lowered and connected, and then hot-melt connections are used. These sections can be connected by mechanical connection. Pipes with a nominal diameter of less than 20 mm can be manually pulled into the pipe trench; all large pipes, fittings, valves, fire hydrants and fittings should be carefully placed into the pipe trench with appropriate tools; for long-distance pipe lifting, A nylon rope is recommended.
5, the final pipe connection and assembly
The hot-melt connection of the pipe in the trench is the same as the hot-melt connection of the pipe on the ground, but it must be ensured that the connected pipe must be cooled to the ambient temperature of the soil before it is connected. When connected to metal pipes, water tanks or water pumps, flange connections are generally used. Flange connections are also possible when it is not convenient to connect by hot melt. When the flange is connected, the bolts should be evenly tightened in advance, and after 8 hours, re-tighten.
6, stress test
The pressure test can be carried out before or after the pipeline is backfilled. The pipeline should be covered with a certain interval. Especially for the meandering pipeline, the pipeline should be fixed in place during the pressure test. The flange connection should be exposed to facilitate inspection of leaks.
The test pressure of the pressure test shall not exceed 1.5 times the pressure level of the pipe pressure rating or the lowest pressure class of the system. At the beginning, the pressure shall be raised to the specified test pressure value and sufficient time shall be allowed to ensure sufficient expansion of the pipe. A process takes 2-3 hours. When the system is stable, raise the pressure to 1.5 times the working pressure, stabilize the pressure for 1 hour, carefully observe the pressure gauge, and patrol along the line if there is no visible leakage or occurrence during the test. With a significant pressure drop, the pipe passes the pressure test.
During the pressure test, the pressure drop is caused by the continuous expansion of the pipe. It is normal to produce a certain pressure drop during the test, and it cannot be proved that the pipe system must leak or break.
7, backfill and tamping
Under normal circumstances, the corner and initial backfilling requirements should be at least 90%, and the tamping layer should be at least 150mm from the top of the pipe. For less than 300mm from the top of the pipe, direct compaction should be avoided. The final backfill may use the original excavation of soil or other materials, but it must not contain frozen soil, agglomerated clay and stones with a maximum diameter of 200 mm.
Third, PE gas pipe application areas:
1. Urban water pipe network system.
2. Urban and rural drinking water pipelines.
3. Feed liquid transportation pipelines for chemical, chemical fiber, food, forestry, printing and dyeing, pharmaceutical, light industry, papermaking, metallurgical and other industries.
4. Agricultural irrigation pipelines.
5. Post and telecommunications lines, power line protection sleeves.
6. Mine mortar conveying pipeline.
7. Post and telecommunications lines and power line protection sleeves.
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