PE pipe has corrosion resistance (no need for anti-corrosion), good flexibility (can be laid along deep gully, and has anti-seismic, anti-settling, easy to bypass obstacles), simple construction (electricity, hot-melt connection), It is widely used because it is easy to install and at least safe for 50 years. PE pipe needs to pay attention to many matters in the welding process, and it is controlled and used according to the corresponding methods and principles, so that it can produce good performance and operation value in the specific use process. China's existing national standards and industry standards provide a basis for us to use polyethylene pipes, pipe fittings and construction technology.
First, the characteristics of PE pipe
PE pipe exhibits important performance in the installation and use of pipes. Good product performance characteristics make it have important value and contribution in use. It is in a good development position and trend in the same industry, and can produce important changes. And development space. PE pipes have many product characteristics superior to other building materials in specific use, and have made important contributions and values ​​in the industry.
1. PE pipe is corrosion-resistant and has a long service life. In China's coastal areas, the groundwater level is high and the land moisture is high. The use of seamless steel pipe must be anti-corrosion and installation of outward-angle tempering, and the service life is only 30 years, while the PE pipe can withstand The erosion of a variety of chemical media does not require preservative treatment. In addition, it does not promote the growth of algae, bacteria or fungi, with a service life of 50 years. Good resistance to stress cracking: PE pipe has low notch sensitivity, high shear strength resistance, and environmental stress resistance. Low temperature impact resistance: PE tube has a very low temperature embrittlement temperature and can be safely used in the temperature range of -60 degrees Celsius.
2, PE pipe circulation capacity is large, economically cost-effective. The inner wall of the PE pipe is smooth and does not scale. The absolute roughness ratio of the inner surface of the PE pipe is 1/20 of that of the steel pipe. The PE pipe with the same pipe diameter, the same length and the same pressure has a flow capacity of about 30% larger than that of the steel pipe, so the economic advantage is obvious. Excellent physical properties. The performance of medium density polyethylene is between high and low density polyethylene, which not only maintains the rigidity and strength of high density polyethylene, but also has good flexibility and creep resistance, and the higher density polyethylene is hotter. The excellent fusion connection performance is beneficial to the installation of plastic pipes. Compared with metal pipes, PE pipes can reduce engineering investment by about one-third, and small-diameter pipes that can be coiled can further reduce project cost.
3, PE pipe is easy to connect, simple construction and various methods. PE pipe body is light, easy to handle, easy to weld, and has few welding ports. When the pipeline is long, the pipe can be used to lay the PE pipe trench. The requirement is much lower than that of the steel pipe trench. When the construction conditions are limited, the electrofusion welding can be used. . Good sealing. The PE pipe itself is welded and welded, which essentially guarantees the interface material, the structure and the identity of the pipe body itself, and realizes the integration of the joint and the pipe material. The tensile strength and bursting strength of the interface are higher than that of the pipe body, which can effectively resist the axial stress induced by the internal pressure. Therefore, compared with the rubber ring type or other mechanical joints, there is no risk of leakage caused by the coupling distortion, and the sealing performance is very good. Easy maintenance, no water, gas maintenance and installation. In addition, the method of pipe sinking can be used to lay the bottom of the water, which greatly reduces the construction difficulty and engineering cost.
Second, the advantages of PE pipe
1. Polyethylene (PE) pipelines have good application prospects due to their ability to withstand internal pressure, strong corrosion resistance, and good weld joint tightness. At present, it has been used in the field of tap water supply pipes in China, ensuring the transportation of water quality to avoid secondary pollution. It has also been widely used in the fields of gas pipelines, chemical raw materials and industrial oil and cooling equipment.
2. Polyethylene (PE) pipe has reliable connection, no leakage, good chemical corrosion resistance, good resistance to application cracking, good low temperature impact performance, good aging resistance, long service life of 50 years, good wear resistance. Excellent performance such as good routable.
Good sealing performance:
3. PE pipe adopts electrofusion connection, hot melt butt joint, hot melt socket, welding and mechanical pipe connection. The strength of the interface is higher than that of the pipe itself, and will not break due to soil movement or load. The PE pipe directly presses the pipe through the weight without causing the pipe to rupture. In the process of use, the adaptability to the pipeline foundation is strong, and it is not easy to be damaged when the pipe base is unevenly settled and misplaced. At the same time, because the requirements on the pipe base are low, the cost can be greatly saved. It is reported that in the 1995 Kobe earthquake in Japan. PE gas pipes and water pipes are the only pipes that have not been damaged.
Good flexibility:
4, PE pipe has a unique flexibility, its elongation at break exceeds 500%, the bending radius can be as small as 20 to 25 times the diameter of the pipe, it is easy to move, bend and intersperse during laying. At the same time, due to the axial load of the welded joint, leakage and disengagement do not occur, so that it is not necessary to carry out "anchor" at the joint and the bend at the time of laying.
5, PE pipe has a good use advantage in use, can be fully in accordance with certain standards, can show good use value and contribution, fully used in the industry, showing certain use characteristics.
Third, PE to be welded pipe fittings testing and welding method time
1. The rapid and practical detection method and qualified judgment of PE pipe hot-melt connection and electrofusion connection welding joint are also a bottleneck of PE pipeline construction. In the aspect of electrofusion connection, it is incomplete and inaccurate to judge the quality of the welding only by the ejection of the observation hole on the final electrofusion tube. The observation hole is only used as a basis for judging the welding effect, and the final of the electrofusion welded joint. The quality is mainly controlled by strict control during the operation. Therefore, the rapid and practical detection method of polyethylene (PE) pressure pipe joints has been studied, which is of great significance to ensure the quality of the project. Taking the hot-melt connection as an example, the current test method is to visually test the appearance of the weld ring to verify its quality. Although some problems can be found by the appearance of the weld ring, some inherent problems cannot be reflected from the surface. "The appearance is similar to the qualified appearance, but the long-term strength cannot be guaranteed. Harbin Gas Company has formed "false welding" due to the fusion of PE pipe fusion ports. The other pipelines destroyed the gas pipeline foundation during construction, and the gas pipeline was under the action of unbalanced external force. It was crushed and cracked to cause a major leak.
2. Whether the end face of PE pipe to be welded is clean, if there is impurity, the effect of final welding is definitely affected; the scraping of the oxide layer, not scraping or insufficient scraping may cause 100% failure of welding; The correct assembly of the pipe or fitting to be welded will also affect the quality of the final weld. In addition, whether the storage conditions of the electrofusion pipe fittings before welding and the process of cooling after welding are appropriate are factors that affect the quality of the final weld. However, the regulation and necessary construction technology support in these aspects in China is lagging behind the development and application of PE pipes, which restricts the promotion and application of PE pipes to some extent. Therefore, professional training for engineering and technical personnel and construction personnel, and gradually achieving the certification is an effective way to make PE pipeline construction to a regular and good development.
3. As far as the PE pipe connection construction is concerned, although the operation is simple and easy to grasp, the operation steps of the hot-melt connection and the electrofusion connection must be strictly controlled, that is, the process control of the operation, and not the single final welding port. To judge the quality of the joint. For example, the milling of the end face to be welded, how to keep the end face clean and the cooling process and time of the final weld, etc., these problems are neglected and may not be manifested from the final weld, but the intrinsic performance of the weld is not guaranteed. Therefore, the correct and efficient execution of the welding process and operating procedures is critical and is closely related to the stability of the welding equipment and the responsibility of the operator. In terms of electrofusion connection, it is not enough to ensure the stability of the voltage and the welding time of the electrofusion tube and the welding time.
4. Taking hot-melt welding as an example, temperature, time and pressure are the three most important factors in the welding process. Because PE pipe hot-melt welding is very susceptible to environmental changes and human-induced operating factors, there is no uniformity in the world. The setting value, but in some countries using PE pipelines earlier, a relatively complete and mature calculation method of operation rules and parameter settings has been formed. In the construction of many PE pipeline projects in China, three important factors The setting is generally provided by a polyethylene (PE) manufacturer, so there is a big difference. In addition, in many places, quality accidents caused by the brutal construction of construction workers have also occurred from time to time. Despite the importance of three important factors: temperature, time and pressure, other details of the entire process are often overlooked.
Fourth, PE pipe characteristics and social benefits analysis
China's plastic pipes are developing rapidly and the quality is constantly improving. At present, the plastic pipe industry mainly consists of polyvinyl chloride (PVC-U) pipes, polyethylene (PE) pipes and polypropylene (PP-R) pipes. Among them, polyethylene (PE) pipes are widely used in building water supply, building drainage, buried drainage pipes, building heating, gas pipelines, electrical and telecommunications protection casings, industrial pipes, agricultural pipes, etc. due to their unique advantages. . It is mainly used in urban water supply, city gas supply and farmland irrigation.
In the northern part of China, when polyethylene is buried in the wild in the winter, it is concluded that an experience is not suitable for laying below zero, because the polyethylene pipe is easily brittle. Good wear resistance. The comparison of the wear resistance of polyethylene pipes and steel pipes shows that its wear resistance is four times that of steel pipes. PE pipe has good toughness and flexibility. PE pipe is a kind of high-toughness pipe with elongation at break of more than 500%. It has strong adaptability to uneven settlement and dislocation of pipe foundation and good earthquake resistance. Therefore, it is most suitable for earthquake-stricken areas and practice around the world. It is confirmed that the PE pipe is the best shockproof pipe. It is said that in the Kobe earthquake in Japan in 1995, PE pipes and water pipes were the only pipes that were not destroyed. In addition, the flexibility of the PE pipe is that the PE pipe can be coiled, reducing a large number of connecting pipe fittings. The direction of the PE pipe is easily changed according to the requirements of the construction method. During construction, the obstacle can be bypassed within the bending radius allowed by the pipe to reduce the construction difficulty.
There are still large gaps in various special resins required for plastic pipes. Although the output of PE and PP resin is very large in China, there are not many resins suitable for pipe, especially for urban water supply and PE water supply. PE pipe special materials and PP-R special materials for building hot and cold water are less, and a certain amount of special resin for plastic pipes is also required to be imported.
Since the 1990s, China's synthetic resin industry has flourished, and its output and consumption have maintained a good growth momentum. At present, China's synthetic resin raw PE water supply capacity reaches 10 million tons, ranking the top five in the world after the United States, Japan, Germany and South Korea.
Polyethylene is an inert material that, in addition to a small amount of strong oxidant, is resistant to a variety of chemicals and is less prone to bacteria. It is well known that steel pipes and cast iron pipes are replaced by plastic pipes not only because plastic pipes have lower energy consumption than water, low energy consumption, light weight, low water flow resistance, simple and quick installation, low cost, long life and heat preservation. Etc., but also because plastic pipes are more resistant to corrosion and less prone to microorganisms than steel pipes and cast iron pipes.
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