The promotion of heat-resistant polyethylene (PE-RT) pipes in my country shows that many people do not have a deep understanding of this product. Therefore, it is necessary to further introduce and analyze the concept, characteristics and related knowledge of this product. The concept of heat-resistant polyethylene (PE-RT)
Heat-resistant polyethylene (PE-RT) pipe special materials were first introduced by the Dow Chemical Company in the United States in March 2002, under the brand name DOWLE9X2344E9LLDPE. This raw material is a medium-density polyethylene with stable properties, which is copolymerized with ethylene monomer and octene monomer. The raw material has excellent heat resistance and long-term hydrostatic performance.
When the PE-RT material is under stress under high temperature and high pressure, C8 molecules absorb part of the energy during the stretching process, which can prevent the crystal lattice from being damaged. Through reasonable design, the C8 monomer can be evenly distributed inside the polymer molecule, so that the polymer is uniformly stressed, and by controlling its quantity, its thermal stability and long-term hydrostatic resistance can be improved.
In the early stage of PE-RT material development, the Dow Chemical Company first developed the DOW2344E pipe special material, and then developed the DOW2388 pipe special material. Among them, the performance of 2388 pipe special materials is better than that of 2344E pipe special materials. Due to the continuous expansion of the PE-RT pipe market, many international petrochemical companies have also developed their own grades of PE-RT pipe special materials, such as the PE-RT pipe special material developed by SK Chemical Company YUCLAIRDX800, and LG Chemical Company developed The special materials for SP980 pipes, the special materials for 4731B pipes developed by Basell, and the special materials for XP9000 pipes developed by Dalin Company of South Korea.
With the advancement of polymer polymerization technology, the current PE-RT material has been developed from the original copolymerization of ethylene and octene to the copolymerization of ethylene and hexene, ethylene and butene, thus expanding the pipeline manufacturer’s Choose a space.
With the large-scale application of low-temperature floor radiant heating ("floor heating") systems, floor heating pipe manufacturers have increased their investment in floor heating pipes. At present, commonly used pipes in floor heating systems include PE-X pipes, PE-RT pipes, PB pipes, etc. Because PE-RT pipe has the advantages of strong repairability, good construction flexibility, good recyclability and environmental protection, and low price, it has developed rapidly in recent years.
Selection of PE-RT pipe
The quality of the piping system is not only dependent on the pipe itself, but also closely related to the conditions used, such as temperature and pressure. Inappropriate selection of pipes often leads to serious quality accidents. When selecting pipes, it should be in accordance with ISO10508 "Thermoplastic pipes and fittings for cold and hot water systems". Use condition level 4 and floor heating. The design stress is 3.34MPa. With the continuous development of the floor heating industry, many domestic Plastic pipe manufacturers that produce PE-RT pipes have also increased their investment in this product. At present, PE-RT pipe manufacturers have rapidly grown from a few original manufacturers to hundreds.
In the initial stage of the development of PE-RT pipes, because the temperature and pressure resistance of PE-RT materials is weaker than that of cross-linked polyethylene pipes and aluminum-plastic pipes, the application fields of this product are mainly concentrated in floor heating systems, and are rarely used. In the radiator heating system. However, with the continuous development of polymerization technology, according to the established international standard ISO22391-2 for PE-RT pipes, there are currently two types of PE-RT pipes on the market, namely type Ι and type Π, of which type Π PE-RT pipe The temperature and pressure performance of the radiator has reached the current domestic radiator heating system requirements. The PE-RT national standard that is being formulated also continues the international standard classification of PE-RT materials.
Through comparison, it can be found that the type I PE-RT pipe has an inflection point when it is used for a long time at the typical temperature of 80℃, 90℃ and 95℃, and its temperature and pressure resistance is lower than that of the Π type PE-RT material.
Due to the change of the installation method, the domestic cold and hot water system has been transformed from the original double-pipe parallel type to the use of a sub-catchment water supply. This installation method requires a higher flexibility due to the random direction of the pipeline. Due to the good flexibility of PE-RT pipes, the use of coiled pipes can greatly reduce the use of accessories in the pipeline, which facilitates construction and reduces costs for users.
Driven by economic interests, fake and inferior PE-RT pipes have appeared on the market. The counterfeiting methods are mainly reflected in the following two aspects:
1. Add linear low-density polyethylene such as 7042 linear low-density polyethylene of Yangzi Company to reduce costs. Such pipes are often difficult to pass short-term hydrostatic strength testing. At present, it is mainly used by some small manufacturers. These small manufacturers generally do not have testing equipment.
2. Use non-PE-RT pipe special medium density polyethylene materials to produce PE-RT pipes, such as medium density MP3410 and 3082 produced by a European company. Currently, the companies that sell this material are mainly trading companies, and the manufacturers often don't know the inside story. The short-term performance of pipes produced from these raw materials may not pass the test. This production method is relatively professional and has a relatively strong concealment, which is likely to cause quality accidents in 5 or 10 years.
The quality of PE-RT pipes depends not only on the raw materials, but also on the quality control of the pipes from production to delivery. Pay close attention to the wall thickness and appearance of the pipe during the production process to ensure that the pipe wall thickness is relatively uniform. In addition, there should be no impurities or other stripes affecting the performance of the pipe on the surface of the pipe wall. Since PE-RT pipes are generally produced in the form of coiled pipes, the entire coil of pipes should be pressure tested during the factory inspection to ensure that the entire coil of pipes are qualified products. However, some small domestic PE-RT pipe manufacturers are negligent in management and rarely perform real-time inspections during the production process, which will inevitably produce a large number of unqualified products. In the factory inspections, these companies often only do sampling inspections, so that a large number of unqualified products enter the construction site, laying many hidden dangers to the floor heating project.
In addition, the PE-RT production line used by some manufacturers is modified from the PP-R production line. Because the melting point and fluidity of the two materials PP-R and PE-RT are different, the use of this production line to produce PE-RT pipes will have a greater impact on the performance of the pipes, and it will also bring more Many hidden dangers.