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Shenzhen underground gas pipe network transformation in the application of PE pipe
Guangdong Dapeng LNG imports, marking the Shenzhen City has begun to enter the era of natural gas, liquefied petroleum gas replacement. Replacement process needs to carry out maintenance on the pipeline network, while the Shenzhen Special Economic Zone is running an underground gas pipeline network construction, mostly in the early adoption of a steel pipe, which has been part of the tube aging or with a hidden running or leaking, repair it [1] and replacement is imperative. In order to ensure the city gas safety requirements and to meet the smooth replacement of natural gas, Shenzhen mainly used PE pipe for direct replacement of pipe.
Shenzhen, a commonly used type of PE pipe PE pipe also known as polyethylene pipe, polyethylene as raw material production based on transmission and distribution pipeline system is the Ministry of Construction, "85" and "national chemical building material industry," Tenth Five-Year "plan and the 2010 Development Plan" key to promote the use of the energy-saving products and materials and plastic pipes.
PE pipe [2] is customarily divided according to density, low density polyethylene (LDPE) pipes, linear low density polyethylene (LLDPE) tubes, medium density polyethylene (MDPE) pipes and high-density polyethylene (HDPE) pipe. As the material advances, according to the different stages of development and performance, resulting in the level of differentiation of the material, density polyethylene as the pipe does not reflect the nature of performance, so the current international on the basis of long-term polyethylene pipe hydrostatic strength (MRS) of the pipe and its raw materials classified and named.
The long-term hydrostatic strength is continuously applied to the polyethylene resin when the pipe wall for 50 years when calculating damage caused by pipes in the wall of the circumferential tensile stress, the International polyethylene pipe materials will be divided into PE32, PE40 , PE63, PE80 and PE100 five grades.
Shenzhen, PE80 and PE100 generally used two types of PE pipes. PE80 The MRS value 8MPa, its resin comonomer content is relatively high, with a higher long-term hydrostatic strength and resistance to environmental stress cracking performance. PE100 The MRS value of 10MPa, the resin has a bimodal molecular distribution, hexene copolymer, high density and stiffness, a strong creep resistance, while enhancing the long-term hydrostatic strength also increased resistance to slow crack growth and resistance to rapid crack extension performance. SDR11 series of natural gas pipeline, PE80 and PE100 respectively, the maximum allowable working pressure of 0.4MPa and 0.5MPa; SDR17.
6 series of natural gas pipeline, PE80 and PE100 respectively, the maximum allowable working pressure of 0.2MPa and 0.3MPa. Shenzhen, PE pipe in DN110 and below the adoption of SDR11 series, namely, ordinary series, DN160 and above using SDR17.6 series.
2 PE pipe properties [3-4] PE pipe is the most mature application of the current international pressure pipe of plastic, one of the performance test and practical application have been a reliable verification. Although the PE pipe heat, pressure and other properties of inferior steel, but it is anti-corrosion, construction and the strong anti-geological changes still has obvious advantages, mainly in:
(1) Density: With the increase of the density polyethylene, polyethylene materials, increased rigidity, tensile strength increases.
(2) Temperature: Polyethylene is a polymer composite material, more sensitive to temperature, the temperature dropped, increased the tensile strength of polyethylene, PE pipe up to low-temperature brittleness temperature of -80 ℃.
(3) flexibility: PE has a unique flexible pipe laying is easy when you move, bend, and interludes.
(4) anti-corrosion: PE pipe chemical stability is good, has a strong resistance to a variety of acid, alkali, salt, corrosion resistance, thus laying of PE pipes in the underground anti-corrosion treatment is not required.
(5) can be melting: PE pipe is thermoplastic and has a good may be melting, PE pipe welding joints can withstand axial load without leakage and release, so in the pipeline junction and the bend do not need to anchor fixed, set buttress, the construction cost greatly reduced, pipe network is also more secure.
(6) Health Sexual: PE pipe in the production and processing does not add any toxic additives, pipe wall smooth, non-scaling, non-breeding bacteria.
(7) economy: PE pipe in the city, low-pressure pipe applications, compared to steel pipe in the economic advantages are obvious, many cities in China are reflected.
3 PE Pipe Technologies
3.1 PE pipe connections
PE pipe application technology is mainly reflected in the corresponding construction technology, construction of PE pipe connection technology is key to the quality of their installation. PE pipe in Shenzhen city, construction of gas pipeline network connecting the main use of hot melt and fused connections. Fused connection is required to connect two end into the buried electric wire casing, replace the electric wire to pass current, will be connected to pipe fittings heated to melting temperature of the cooling fixed to the interface to form a solid tight joints ; hot melt connection is with the tube axis perpendicular to the two corresponding face contact with the heated plate to the melting temperature, melting mouth pressed to connect the two.
Shenzhen, PE pipe in DN110 and below the adoption of fused connection, DN160 and above connection with hot melt.
3.2 PE pipe construction [5-6]
PE pipes are mainly embodied in construction technology:
(1) The positioning put line and trench excavation:
First, determine the control bit, and then press the drawings will pile, actinomycetes. Pay-off when the excavation is not guaranteed tube bit offset, post-excavation required to form the bottom of the trench should be flat dense. If the ditch in case of obsolete structures, hard stone, wood and garbage and debris must be removed, and then deposited a layer of a thickness of 10cm of sand or prime territories and leveling compaction. Newly built road, Shenzhen, the provisions of the three years can not be excavated, so the new amendments to the road within three years to conduct gas need to use directional drilling techniques, to the laying of pipe jacking techniques.
(2) PE pipe installation and testing:
PE pipe materials of construction should first conduct a test, and then welded PE pipe, the pipe trench and connected to the next, and then purging of the pipeline, strength and air tightness test, the final backfill compaction. In the material testing process, pipe, pipe fittings should have the quality inspection department of product quality inspection report and the production plant certification. The pipe, pipe fittings for appearance and geometry inspections of pipes, pipe fittings inside and outside the cleanliness of the surface is smooth, whether there are grooves, scratches, dents, impurities and color of inequality. PE pipe welding process, welding parameters must be recorded, and self-test weld, qualified to enter the next Weld. Gas pipeline media for blowing compressed air, blowing winds of not less than 20m / s, need to purge several times to determine when you blow air in the non-stolen goods qualified. Strength and gas-tight test test medium is compressed air, the medium suitable temperature does not exceed 40 ℃. Shenzhen underground pipe network construction, reconstruction, PE pipe strength test pressure of 1.5 times the design pressure, the pressure regulator observed after 1 hour; airtight test pressure of 1.15 times the design pressure, regulators determine the pressure drop after 24 hours to meet the requirements for compliance. Trench backfilling, the fine sand to fill the top tube 10cm, and then layered mixed sand and gravel backfill 40cm, the final compaction of the pavement.
4 PE pipe application prospect
In Shenzhen underground gas pipe network transformation projects, PE pipe PE pipe properties decided to adopt a direct replacement of existing problems or risks of the pipe is feasible, and are conducive to underground gas pipe network construction and maintenance. PE pipe in Shenzhen gas pipeline network is widely used, technology is relatively mature, the development of gas industry in China has very broad prospects. |
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