Difference between high-density heat-resistant polyethylene insulation pipe and steel pipe is reflected in the thermal expansion and contraction characteristics, PE-RT II PE pipe has a large amount of expansion, but the expansion force is very small; while the steel pipe, on the contrary, has a very small amount of expansion, the expansion force is very large.
Therefore, under the same application conditions, the expansion force of PE pipe is generally less than 1/50 of the steel pipe. for centralized heating secondary pipe network with prefabricated thermal insulation PE pipe, the pipe axial stress mainly includes thermal expansion and contraction of pipeline thermal expansion stress, thermal insulation layer and the working pipe between the shear stress and friction between the outer pipe and the soil stress. When the friction between the outer protection pipe and the soil is greater than or equal to the thermal expansion force generated by the pipe, the pipe section will not produce thermal displacement.
The axial thermal expansion force of the working pipe is much smaller than the shear force between the working pipe and the insulation, so there will be no delamination between the working pipe and the insulation. This means: therefore the pipe can be completely laid in a direct burial without compensation, and there is no need to use additional fixing measures, which can reduce the investment and construction difficulties.
High-density heat-resistant polyethylene pipe also has the following characteristics compared with ordinary steel pipe:
(1) good thermal insulation performance, the inner layer of thermal conductivity is only 0.42W/m.K, heat loss is much lower than the steel pipe, long-term operation can save a lot of energy, significantly reduce energy costs.
(2) has a strong waterproof and corrosion resistance, reliable sealing, no seepage and no leakage; no corrosion, no pollution of water quality, no scaling and clogging, in the daily management and maintenance of heat pipe network has a greater advantage.
(3) In low temperature conditions also has good corrosion resistance and impact resistance, material embrittlement temperature of -70 ℃, can easily cope with the use in cold areas.
(4) Pressure and temperature resistance, reliable performance, 70 ℃ service life of up to 50 years.
(5) Convenient hot-melt docking and electrofusion welding, firm and reliable.
(6) The construction process is simple and fast, easy construction and installation, no need to attach a pipe trench, can be directly buried in the ground. This feature greatly saves the construction cost of PE-RT II pipeline and shortens the construction period. Considering the labor cost, material cost and mechanical equipment cost, the construction cost of PE-RT II pipeline can save 30% compared with steel pipe.
(7) This kind of pipeline has excellent resistance to rapid cracking and slow crack growth, and can be recovered after flattening; once the pipeline is fractured, broken, etc., the pipe presser can be used to realize local water-blocking operation, which is convenient for emergency repair and saves cost and time.
(8) Economic feasibility: 90mm diameter, high-density heat-resistant polyethylene pipe material costs are comparable with the steel pipe; 110mm or more, 10-20% higher than the steel pipe. If combined with the construction and operation, high-density heat-resistant polyethylene pipe in the dn355 below the economy is higher than the steel pipe.