Introduction to Polyethylene of Raised Heating Resistance Materials
Polyethylene of Raised Temperature Resistance (PE-RT) is obtained by copolymerizing with olefins such as hexene to obtain excellent long-term heat resistance stability and excellent long-term hydrostatic strength; Excellent welding performance (hot melt butt welding, electrofusion connection), low-temperature impact resistance (as low as -40 ℃), excellent crack resistance (whether scratches will cause rapid brittle failure) and other characteristics.
Application of PE-RT Ⅱ Pipe
At present, heat-resistant polyethylene has been developed into high-density heat-resistant polyethylene II. High-density heat-resistant polyethylene (PE-RT Ⅱ), like all polyolefin materials, is a high molecular polymer composed of carbon and hydrogen, with good chemical stability and good resistance to common acids, alkalis, and salts. of corrosion resistance. The properties of polyolefin materials depend on the structure of the material, and the main influencing factors include molecular weight distribution and the type of comonomer. The comonomers of polyethylene polymers include hexene, butene, and octene. The longer the comonomer molecular chain, the more connecting chains can be formed. From the point of view of molecular weight distribution, there are unimodal distribution and bimodal distribution. The bimodal molecular weight distribution has better comprehensive performance because the low molecular weight part ensures good processing performance of the material, and the high molecular weight part makes the material very good. Good pressure resistance and long-term stability. In addition, PE-RT type II material is a viscoelastic material with dual properties of elasticity and viscosity, so it has good plasticity and reduces external stress damage.
Features of high-density heat-resistant polyethylene insulation pipe PE-RT II
The high-density heat-resistant polyethylene insulation pipe is formed by mixing and extruding heat-resistant polyethylene (PE-RT Ⅱ) resin and special color masterbatch into the working inner pipe, with polyurethane material as the insulation layer, and high-density polyethylene pipe as The outer protective pipe, the nominal pressure is not more than 1.0MPa, and the outdoor central heating composite pipe with the hot water temperature not exceeding 80℃. It is suitable for thermal prefabricated direct buried pipes and high-temperature hot water piping systems, especially in the secondary pipe network of urban heating systems and hot spring thermal insulation piping systems in the north.
Another difference between PE-RT II insulation pipe and steel pipe is reflected in the characteristics of thermal expansion and cold contraction. PE-RT II type PE pipe has a large amount of expansion, but a small expansion force; on the contrary, steel pipe has a small amount of expansion and a small amount of expansion. Powerful. Therefore, under the same application conditions, the expansion force of PE pipe is generally less than 1/50 of that of steel pipe. For the prefabricated thermal insulation PE pipe used in the secondary pipe network for central heating, the axial stress of the pipe mainly includes the thermal expansion stress caused by the thermal expansion and contraction of the pipeline, the shear stress between the thermal insulation layer, and the working pipe, and the external protective pipe and the outer protective pipe. Frictional stress between soils. When the friction force between the outer protective pipe and the soil is greater than or equal to the thermal expansion force generated by the pipe, the pipe section will not generate thermal displacement. The axial thermal expansion force of the working tube is much smaller than the shear force between the working tube and the insulating layer, so there will be no delamination between the working tube and the insulating layer. This means: Therefore, the pipeline can be laid directly without compensation, and no additional fixing measures are required, which can reduce investment and construction difficulty.
According to the data, the high-density heat-resistant polyethylene pipe also has the following characteristics compared with ordinary steel pipes:
(1) Good thermal insulation performance, the thermal conductivity of the inner layer is only 0.42W/m.K, and the heat loss is much lower than that of steel pipes. The long-term operation can save a lot of energy and significantly reduce energy costs.
(2) It has strong waterproof and corrosion resistance, reliable sealing, no seepage, and no leakage; no rust, no water pollution, no scaling and blockage, and has great advantages in the daily management and maintenance of the heat pipe network.
(3) It also has good corrosion resistance and impact resistance under low-temperature conditions, and the material embrittlement temperature reaches -70 ℃, which can easily cope with use in cold areas.
(4) Pressure and temperature resistance, reliable performance, the service life can reach 50 years at 70 ℃.
(5) Hot-melt butt and electro-fusion welding are convenient, firm, and reliable.
(6) The construction process is simple and fast, the construction and installation are convenient, and there is no need to attach a pipe trench, and it can be directly buried in the ground. This feature greatly saves the construction cost of the PE-RT II pipeline and shortens the construction period. Taking into account labor costs, material costs, and mechanical equipment costs, the construction cost of PE-RT II pipelines can be reduced by 30% compared to steel pipes.
(7) This type of pipeline has excellent resistance to rapid cracking and slow crack growth, and can be recovered after being flattened; once the pipeline is broken or damaged, the pipe pressure can be used to achieve local water blocking operations, which is convenient for emergency maintenance. Save cost and time.
(8) Economic feasibility: For diameters below 90mm, the material cost of high-density heat-resistant polyethylene pipes is equivalent to that of steel pipes; above 110mm, it is 10-20% higher than that of steel pipes. If combined with construction and operation, high-density heat-resistant polyethylene pipes are more economical than steel pipes below dn355.
Precautions for the use of high-density heat-resistant polyethylene insulation pipe PE-RT II in heating and hot sping
(1) Raw materials should be strictly controlled, and attention should be paid to distinguishing between PE-RT type II products and PE-RT type I products.
(2) During welding, when the nominal outer diameter of the work pipe is less than 90mm, electrofusion pipe fittings should be used for connection; when the nominal outer diameter of the work pipe is greater than or equal to 90mm, hot-melt butt joints should be used.
(3) If there are some pipe sections in the thermal pipe network that use high-density heat-resistant polyethylene insulation pipes, it should be noted that the connection between the steel pipe and the plastic pipe cannot be converted from steel to plastic, and flanges and heat-resistant sealing rings should be used for the connection.
(4) PE material will accelerate its aging when exposed to ultraviolet rays. It should not be used on the ground but should be buried in the ground. Sunlight should be avoided during storage and construction.