One of the advantages of PE pipe is acid corrosion resistance, so there is no need to do corrosion treatment when buried underground. However, the disadvantage of PE pipe is that the compressive strength and oxidation resistance are not enough. Creep occurs when the temperature increases, and embrittlement occurs when the temperature decreases. PE pipe construction is mostly buried.
What are the regulations and how to track the buried PE pipes?
Regulations for directly buried laying
As the compressive strength of polyethylene pipe is lower than that of metal pipe, and it is more sensitive to temperature change, it must be deeply buried, avoid heating pipe, and minimize the same trench with other pipes and power lines. Under special circumstances, we should keep a certain distance from the top, bottom, left and right according to the standard, and take unique countermeasures.
As the coefficient of linear expansion of polyethylene pipe is more than 10 times higher than that of metal, it can be laid according to the flexible winding and bending of polyethylene pipe, but the bending radius should meet the requirements. If 50 mm ≤ pipe diameter D ≤ 160 mm, the allowable bending radius R shall be 50 D of the pipe diameter. And if there is connection on the pipe section, it shall not be less than 125 D.
Regulations for backfill:
After the polyethylene pipe is laid in the ditch, the pipe shall be immediately covered with fine soil or sand, and its thickness shall not be less than 30 cm, so as to ensure that the polyethylene pipe will not be damaged by external force.
To backfill the pipe trench, first backfill the bottom of the pipe, then backfill both sides of the pipe, and then backfill the soil to 50 cm of the top of the pipe. If there is water in the trench, it must be emptied and refilled.
Under the safe condition of engineering construction, it should be ensured that the fulcrum of pipe trench should be removed according to the backfill schedule. After the vertical sheet pile is removed, the gap shall be filled with sand and soil.
The backfill on both sides of the pipe top and within 50 cm above the pipe top shall not contain debris, bricks, garbage and other materials. Frozen soil shall not be used as backfill. A small amount of backfill is allowed above 50cm between pipe tops. The amount of rock and frozen soil not exceeding 10 cm in diameter shall not exceed 15% of the total volume of backfill. The backfill should be compacted in several layers, each layer should be 20-30 cm thick. The backfill on both sides of the pipeline and within 50cm from the top of the pipeline must be compacted manually. When the backfill is more than 50 cm from the top of the pipe, small machines can be used for compaction.
The compactness of each part of the trench shall meet the following requirements:
- Pleural filling (I) was 95%;
- 85% within 50cm above the tube (II);
- More than 50 cm from the top of the pipe to the ground (III) 95% of the urban area and 90% of the cultivated land.
In order to keep the pipeline from accidental damage due to human activities during port operation, a warning tape is laid at a vertical distance from the pipeline. The warning tape is used to remind the third party to pay attention to the polyethylene pipeline below during the project. Be careful to open the cavity to prevent damaging the polyethylene gas pipeline.
Because of its unique material, non-conductive, non-magnetic and low density, common metal detectors can not track PE.
So how to accurately locate the underground position of PE pipe?
Tracer line system
The basic principle of the tracer line system is to locate the position of the metal tracer line with the help of the metal line paved by the parallel pipe and the magnetic field change caused by the current crossing the metal line, so as to infer the position of the PE pipe.
- The products are relatively mature.
- The engineering construction method is simple.
- The workers are easy to operate.
- There is little difference with the original copper steel pipe system tracing method.
- It is easy to integrate with the current system.
The Disadvantages: The amount of construction is large. If the tracer line is damaged, the tracer line system between the two nodes will be invalid. The integration with the intelligent system is not close, the inspection work intensity is high, and it is greatly affected by the strong electromagnetic natural environment.
Types and characteristics of tracer line
1. Steel wire plastic film tracer line.
It is a kind of steel wire or other metal wire and PE plastic film inhibition, often integrated with warning tape, the diameter of steel wire is about 0.5mm.
Steel wire as conductor. Because of small cross-sectional area, it is not easy to connect, the resistance is large, the detection spacing is limited, only more than ten meters to dozens of meters. It is easy to break in the specific engineering construction, the electrical reasonable connectivity is easy to be destroyed, and the specific needs can not be considered.
2. Wire tracer wire.
Copper or aluminum cables are used as tracer wires, and 2.5-4mm cross-section is selected.
Because of the selection of wires or cables, the inspection distance is long and easy to use, but the project cost is relatively expensive. The outer surface insulation layer of the wire is PVC, which is easy to be aged after tmac. The relative PE material is insufficient. The metal core of the wire is mostly made of copper or aluminum, and the tensile strength is limited. When it is used for basic pavement and trenchless pavement, the fracture probability is high.
3. The special-purpose metal tracer wire
It is composed of special-purpose metal core (copper clad steel) and PE outer protective layer, with 205-7mm section.
Metal tracer wire, PE as the outer protective layer, insulation layer, anti-corrosion, moisture-proof, anti-aging, copper layer in the core layer properly improve the conductivity, improve the electrical signal, communication department reasonably improve the compressive strength of the wire, the conductivity is slightly weak, but the compressive strength and mechanical properties are excellent. The metal tracer line has been used for more than 20 years in European and American countries and has good economic effect. At present, the metal tracer line is used as the tracer line of PE pipe in China.