PE gas pipeline construction features, requirements, advantages and disadvantages and problems explained in detail!

PE gas pipeline construction features, requirements, advantages and disadvantages and problems explained in detail!

I. Introduction

In the design of gas transmission and distribution, urban gas pipelines include steel pipes and cast iron pipes. But with the passage of time, the shortcomings of poor corrosion resistance, high cost, and inconvenient transportation and installation of metal pipes have gradually emerged, so people have turned their attention to plastic pipes. Polyethylene pipe (hereinafter referred to as PE pipe) is a new generation of gas delivery pipe, which is made of polyethylene as the main raw material and extruded. It is corrosion-resistant compared with traditional metal pipes; light weight and density It is only 1/8 of steel; it has a long service life and can reach 50 years; it has high strength and good toughness, can withstand changes in formation without breaking; it has the advantages of simple construction, etc. It is a new product for the replacement of gas pipelines. PE pipes have been used abroad for decades. Developed countries in the world have started to study PE pipes since the late 1940s and applied them in gas engineering; since the 1960s, PE pipes have been used in gas transmission and distribution systems. Management; and the proportion of use is gradually expanding. At present, PE pipelines have all been adopted in developed countries and regions such as Europe, America and Japan. At the 1988 International Coal Federation (IGU) Transmission and Distribution Committee meeting in Munich, it was unanimously agreed: "Underground gas pipelines using polyethylene (PE) as raw materials are reliable in quality, safe in operation, easy to maintain, and cost-effective."

Although China started late in the buried PE pipeline industry for gas, it has a strong development momentum. In 1982, Shanghai entered the trial stage of the PE pipeline for the first time. In order to make the research work of PE pipe more important and to proceed smoothly, the National Science and Technology Commission listed the development of "the development and processing application technology of special materials for polyethylene gas pipes" as the national "Seventh Five-Year" key project in 1987. From the processing of special raw material pipes and fittings to engineering applications to the formulation of standards and regulations, systematic research has been conducted and fruitful results have been achieved. In 1995, the State Technical Supervision Bureau and the Ministry of Construction respectively issued national standards for polyethylene gas pipes and fittings and industrial procedures for engineering technology, marking the standardization of the application of polyethylene gas pipes in China. At present, gas PE pipes have been widely used in gas medium and low pressure pipe networks.


2. Construction characteristics of PE gas pipeline
1 Easy installation and maintenance, easy to operate

There are two kinds of PE pipe connection methods, one is electric fusion connection, generally suitable for pipe diameter less than De110; two is hot fusion connection, generally suitable for pipe diameter not less than De110, no sleeve pipe fittings are needed in butt joint. The above two connection operation methods can be mastered in short-term training, the welding quality can be guaranteed, and the construction progress is fast. In addition, it is possible to open three-way operation with gas in the existing gas pipeline network. In this process, it is impossible to use steel pipes as gas pipelines.

The weight of PE pipe is lighter, no lifting equipment is needed, and it is more convenient to carry and pipe down the groove. As long as the electric pipe fusion welding machine is used for PE pipe welding, the equipment is portable and the degree of automation is high. No manual welding is required. The installation and construction are convenient, the strength is small, and the efficiency is high. Buried PE pipelines for fuel gas mainly use hot melt connection or electric fusion connection, and the interface strength is generally higher than the strength of the pipe itself. Therefore, compared with rubber ring joints or other mechanical joints, there is no risk of leakage due to joint twisting. PE pipe has excellent flexibility, which greatly enhances the value of the material for pipeline engineering. Due to the flexibility of polyethylene, the polyethylene gas pipeline with a small diameter (generally not greater than D100) can be supplied in coils, which saves a lot of pipe fittings during construction and also avoids the possibility of joint leakage; Without slotted construction, the direction of the polyethylene gas pipeline is easy to change according to the requirements of the construction method, so that it can change the shape of the pipe before construction, and restore its original size and size after inserting the old pipe.

PE pipes are easy to maintain, and can be continuously opened or repaired on the pipes. In this regard, there are very mature technologies. Polyethylene pipes are good for emergency repairs and maintenance in the future. Due to the good flexibility of polyethylene pipes, in actual projects, gas pipelines with operating pressures below 0.1 MPa are clamped with flattening tools to repair gas and repair new pipelines. During the process, there is no open flame phenomenon, which reduces the risk of entraining operations in the gas system; because the flattening operation is used for emergency repairs or for the purpose of connecting new pipelines, this operation does not last long.

Therefore, the flattening operation of the polyethylene pipeline in a short time, when the stress is removed, the polyethylene gas pipeline itself should be able to basically restore its original shape. PE pipe has great advantages in trenchless pipeline construction. There are many cases of crossing roads and buildings when constructing gas pipelines in urban areas. When using trenchless technology, due to the relatively large disturbance of PE pipe, the welding speed is fast and the construction is convenient.

2 Anti-corrosion treatment

PE pipe is a polymer of polyethylene, which has stable chemical properties, is less corroded by the chemical substances in the soil and stray current, and has good acid and alkali resistance. Therefore, polyethylene gas pipes do not need to be treated for anticorrosion when laying , Its service life is up to 50 years. In particular, there are many kinds of anti-corrosion technical methods for buried steel pipes that use PE materials as anti-corrosion layers. According to relevant literature, foreign PEs are buried for 60 years and then dug out and re-welded. The welding and body quality can also reach PE pipes. The stipulated quality index requirements; PE pipes do not need anti-corrosion treatment. The design life of steel pipes is generally 20 years.

3 Strong adaptability of engineering

There are many professional pipelines in municipal engineering and residential community courtyards, and the pipeline position is tight. In this complex construction environment, PE pipe is flexible and flexible: it is not easy to break when the pipe base sinks slightly; PE can be used The flexibility of the pipe is laid in a meandering shape or curved along the terrain. The borrowing angle during construction is large. It is easy to bypass obstacles within the allowable bending radius, reducing the number of joints and reducing the difficulty of construction.

4 Low investment cost

Urban gas transmission and distribution pipeline network is an important part of urban gas engineering. The cost of gas pipeline network accounts for a large proportion of the total cost of gas engineering (about 40%). Therefore, it is very important to study the economic cost and economic operation of gas pipeline network. . The economic performance of PE gas pipelines and steel pipes is compared as follows:

(1) The price of the pipe is better than the commonly used gas steel pipes. It is well known that pipes below DN200, PE pipes are cheaper than steel pipes; PE pipes with small diameters generally use electric fusion connection, and the price of PE pipe fittings is high; for PE with large diameters Due to the thicker wall thickness, the pipe is more expensive than the steel pipe, but hot melt connection can be used to save the cost of pipe fittings, and the service life is long (the service life of the PE pipe is 50 years, and the service life of the steel pipe is based on the depreciation fee of the gas facility of the National Planning Commission The year is limited to 18 years), without anti-corrosion, its comprehensive price is still lower than the investment in steel pipes.
(2) Because the PE pipe has strong flexibility, it can be prefabricated on the ground, and then put into the pipe trench, without the need to make a work pit, so the earthwork volume of the PE pipe construction pipe trench is smaller than that of the steel pipe construction pipe trench .

(3) The medium-pressure steel gas pipeline must be subjected to a non-destructive inspection and other valuable expenses during installation and welding, and the detection procedure is relatively complicated; and the PE gas pipe inspection procedures, methods and methods are simple and effective, and the inspection fee is very small. In short, gas PE pipe materials and installation costs have obvious advantages over steel pipes. The comprehensive economic performance of PE gas pipes is far superior to steel pipes.



3. Construction requirements of PE gas pipeline

Due to the many advantages of gas PE pipes, our company uses a large number of PE pipes in the laying of natural gas new pipe networks and the transformation of old pipe networks. After years of PE pipe construction, we have accumulated some technology and construction experience, and construction personnel are also afraid of the original Construction PE pipes have become the current favorite construction PE pipes.

1 Groove

The current gas source of our company is natural gas, so trench excavation requires a good slope control. If over-excavation or soil replacement, the back soil must be tamped to prevent backwater accumulation due to the sinking of the pipeline. It can be lowered down.

2 PE pipe connection

The connection uses hot melt connection and electric fusion connection:

(1) Hot-melt connection: Before and after hot-melt connection, the dirt on the two heating surfaces of the heating plate of the connecting tool should be cleaned with clean gauze to prevent affecting the thermal efficiency and the quality of the joint. The heating time, heating temperature, holding pressure, and cooling time during connection should comply with the regulations of the pipe and pipe manufacturer. During the holding and cooling period, no movement and external force should be applied, otherwise the joints that have not yet reached the maximum compressive strength will not be uniform. Of the flange, which affects the joint even compression. The two ends of the butt joints should be pin milled to make the vertical joint of the two end surfaces good and ensure a good edge. Otherwise, the contact area is reduced and the strength is weakened.

(2) Electrofusion connection: When the electrofusion connection is made, make sure that the electrofusion tool is connected correctly, and the settings of the energizing current and energizing time should meet the requirements of the electrofusion accessories. The fused socket surface needs to be clean, and the two ends of the pin milling should be vertically joined. The oxide layer of the fused surface should be scraped off with a knife, and the fused surface should be roughened to increase the contact surface. Before inserting the pipeline, mark the position of the insertion length to ensure a sufficient length, ensure the area of the electric fusion connection, and enhance the quality of the connection joint.
The saddle-shaped fused connection also needs to clear the surface, and requires tightening the flat fixing screws of the pipe to make the contact surface coincide.

3 Backfill

The strength and stiffness of the gas PE pipe is not as high as that of the steel pipe. There should be no sharp and hard debris around the pipe, but now there are many sharp and hard objects in the underground of the old city. Therefore, sand should be placed before the down pipe. Sand to ensure pipeline safety.

4 Air-operated work

For PE pipes above De110 connected to straight pipes or open tees, special fixtures for PE pipes can be selected according to the gas source (single and double gas sources). After the gas source is clipped off, the fused sleeve is used for connection. If every time the pipe end is sealed with a flange head, the flange head can be used to connect the pipe without stopping the gas. When the branch pipe smaller than De63 is opened on the PE pipe above De110, the fused saddle tee is adopted without stopping the gas. After installing the saddle tee on the pipeline, the cutter is used to open the original pipe for ventilation.

4. The disadvantages and points of attention of gas PE pipes in application

1 PE pipe has low mechanical strength and is easily damaged by man-made

PE pipe is not as hard as steel pipe, so it is easy to be perforated when it is impacted by hard objects. In order to protect the PE pipeline from man-made damage, when the PE pipeline is laid, red bricks and warning tapes are generally added above the PE pipeline, and then the inspection of the pipeline is strengthened. When the gas PE pipe is pre-constructed or buried in a shallow depth, the gas PE pipe may be easily drilled through during the construction of other supporting pipe networks or road construction in the community, causing gas leakage. In order to avoid the occurrence of similar things, the gas PE that has been constructed should be strengthened in monitoring or constructed after other supporting pipe networks, and ensure sufficient burial depth.

2 PE pipe is more sensitive to thermal stability

The PE tube's compressive strength will decrease at higher temperature; too low temperature will cause it to become brittle. Therefore, the current PE pipe generally uses a pressure of 0.1 ~ 0.4MPa. Since PE pipes are easy to oxidize, bend and sensitive to temperature, they have certain requirements for storage, handling, transportation, storage period and construction of pipes. There are many PE pipe construction equipments, which are highly dependent on the construction equipments. It has high requirements on the external environment. It is inconvenient to construct in cold weather and strong winds and rains, so protective measures must be taken.

3 PE pipes and pipes have no conductivity, which brings great inconvenience to the detection and positioning of PE pipes. For this, the completion of construction materials must be strictly reviewed in the project, and it must be consistent with the drawings; after the pipeline is put into operation, If the construction near the pipeline changes, the original completion drawings should be updated in time to ensure that the accurate information of the underground natural gas pipeline can be grasped in time, thus laying a good foundation for the operation and management of the pipeline.

4 Matching problems of PE pipe and fittings

Due to the limitation of the chemical properties of the PE pipe, it cannot be used on the ground (cannot be used as an open pipe). The PE well has a large volume and is inconvenient to construct in the community pipe network. The price of PE pipe fittings is high.

V. Conclusion

The gas pipe network is constantly updated with the advancement of material science, from the original gray cast iron pipe, lead cast iron pipe, mechanical interface cast iron pipe, ductile iron pipe to the currently commonly used steel pipe, and the international advanced level of PE tube. In summary, although PE pipes still have some shortcomings, compared with metal pipes, PE gas pipes have the advantages of excellent performance, simple construction, reliable operation, convenient maintenance, long service life, low investment cost, and a set of perfect The operation and management plan of the company can fully realize the safe operation of the gas pipeline network. Therefore, the application prospect of PE gas pipelines in the city gas transmission and distribution pipeline network is very broad, and it is worthy of our vigorous promotion and application in the pipeline gas industry. 13 years of practice has proved that the application of gas PE pipes in Zhenjiang City's urban gas transmission and distribution pipeline network has practical significance for reducing the cost of gas engineering, improving the transmission and distribution capacity of the gas pipeline network, and ensuring the safe operation of the pipeline network. With the rapid development of China's natural gas industry, the application technology and construction technology of gas PE pipes are becoming more and more mature, and the proportion of gas PE pipes in urban gas transmission and distribution network projects will become larger and larger.If you want to know more about it please do not hesitate to contact me. WhatsApp:+86-15966835076