The popularization practice of heat-resistant polyethylene (PE-RT) pipe in China 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)

The special material for heat-resistant polyethylene (PE-RT) pipes was first introduced by Dow Chemical Company in March 2002 under the brand name DOWLE9X2344E9LLDPE. The raw material is a stable medium density polyethylene, which is copolymerized by ethylene monomer and octene monomer. The raw material has excellent heat resistance and long-term hydrostatic resistance.

When the PE-RT material withstands stress at high temperature and high pressure, C8 molecule absorbs some energy during the extension process, which can prevent the lattice from being destroyed. By reasonable design, C8 monomer can be evenly distributed in the polymer molecule, so that the stress of the polymer can be uniformly distributed. By controlling the number of C8 monomer, the thermal stability and long-term hydrostatic resistance of the polymer can be improved.

In the early stage of PE-RT material development, Dow Chemical Company first developed DOW2344E pipe material, and then developed DOW2388 pipe material. The performance of 2388 pipe material is better than that of 2344E pipe material. As the PE-RT pipe market continues to expand, many international petrochemical companies have also developed their own brand PE-RT pipe special materials, such as YUCLAIRDX800 PE-RT pipe special materials developed by SK Chemical Company, SP980 pipe special materials developed by LG Chemical Company, 4731B pipe special materials developed by Basell Company, XP9000 pipe special materials developed by Korea Dalin Company, etc.

With the progress of polymer polymerization technology, PE-RT materials have been developed from copolymerization of ethylene and octene to copolymerization of ethylene and hexene, ethylene and butene, thus expanding the choice space of pipe manufacturers.

With the large-scale application of low-temperature ground radiation heating (referred to as "ground heating") system, the manufacturers of geothermal pipes have increased their investment in geothermal pipes. At present, the commonly used pipes in geothermal systems include PE-X pipes, PE-RT pipes, PB pipes, etc. Because of the advantages of strong repairability, good flexibility in construction, good recyclability, environmental protection and low price, PE-RT pipes have developed rapidly in recent years.

Selection of PE-RT Pipe Material

The quality of pipeline system depends not only on the pipe itself, but also on the conditions used, such as temperature and pressure. Improper selection of pipes often leads to serious quality accidents. When choosing pipes, we should use condition level 4 and floor heating according to ISO10508 "Thermoplastic Pipes and Fittings for Cold and Hot Water Systems". The design stress is 3.34 MPa. With the continuous development of the geothermal industry, many domestic plastic pipes manufacturers that did not originally produce PE-RT pipes have increased their investment in this product. At present, PE-RT pipes manufacturers have been replaced by the original ones. Several have grown rapidly to hundreds.

In the initial stage of PE-RT pipe development, because the temperature and pressure resistance of PE-RT material itself is weaker than that of cross-linked polyethylene pipe and aluminium-plastic pipe, the application of PE-RT product is mainly concentrated in the ground heating system, and seldom 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 two types of PE-RT pipes on the market at present, i.e. _-type and_-type. The temperature and pressure resistance of_-type PE-RT pipes has met the requirements of domestic radiator heating system. The classification of PE-RT materials by international standards is also continuing in the national standard of PE-RT being formulated.

By comparison, it can be found that the inflection point of_-type PE-RT pipes appears at 80, 90 and 95 (?) C for a long time, and its temperature and pressure resistance is lower than that of_-type PE-RT pipes.

Due to the change of installation mode, the domestic hot and cold water system has changed from the original two-pipe parallel connection to the water supply with water diverter. This installation mode requires higher flexibility of pipes because of the more random pipeline direction. Because of the flexibility of PE-RT pipe, coil supply can greatly reduce the use of fittings in the pipeline, and reduce the cost for users while facilitating construction.

Existing problems

Driven by economic interests, fake and inferior PE-RT pipes have emerged in the market. Their counterfeiting means are mainly embodied in the following two aspects:

1. Adding linear low-density polyethylene such as Yangzi 7042 linear low-density polyethylene to reduce costs. This kind of pipe is often difficult to pass the short-term hydrostatic strength test. At present, it is mainly used by some small manufacturers. These small manufacturers generally do not have testing equipment.

2. Producing PE-RT pipes with non-PE-RT special medium density polyethylene materials, such as medium density MP3410 and 3082 produced by a European company. At present, the main companies selling this raw material are trading companies, and manufacturers often do not know the inside story. The short-term performance of pipes produced from these raw materials may not pass the test. Because of its relative specialty and strong recessiveness, this mode of production is likely to lead to quality accidents in 5 years or 10 years.

The quality of PE-RT pipe depends not only on raw materials, but also on the quality control of pipe from production to factory. In the production process, we should pay close attention to the wall thickness and appearance of pipes to ensure that the wall thickness of pipes is relatively uniform. In addition, there should be no impurities or other stripes on the surface of the pipe wall that affect the performance of the pipe. Because PE-RT pipes are generally produced in the form of coils, pressure tests should be carried out on the whole coil during factory inspection to ensure that the whole coil is qualified products. But some small PE-RT tubes in China