There are three methods for heating pipes for polyurethane direct-buried insulation pipes : no compensation method, one-time compensation method and compensation installation method. Because the urban heating district heating pipe network adopts hot water with temperature ≤120°C from the perspective of economic security, Polyurethane insulation directly buried pipe can withstand temperatures up to 120 ° C, so now we only discuss the first two direct burying methods. 1. Uncompensated direct burial laying method The polyurethane direct buried thermal insulation pipe is uncompensated and directly buried, that is, the pipe is fixed by the frictional resistance between the soil and the outer casing. When the sum of the frictional resistance of the soil and the pipeline is equal to or greater than the expansion force of the pipeline, the pipeline is no longer elongated, and no compensator is added. At this time, the displacement potential energy generated by the pipeline during the thermal expansion and contraction is stored in the pipeline wall. When there is no compensation for direct burial, there is no need to install compensator, sliding bracket, fixed bracket and other pipe fittings on the pipeline. The pipeline is basically in the stopped state in the straight pipe section, and the so-called “friction length†in the free end such as the elbow and the unearthing section. There is a displacement in the range of l"; according to the "Central Heating Design Manual", the stress value will not exceed the allowable stress within 15000 times of alternating current and the allowable temperature difference of 83 °C. This type of burying is suitable for low temperature heating lines below 95 °C. The concentrated air conditioning water temperature in Yueyang living quarter is 5°C~70°C, and it can be used without compensation for direct burial.
2, one-time compensation direct buried laying method polyurethane direct buried insulation pipe, its working principle is to weld the pipe on the product, remove the positioning angle steel, heat the pipe to the required temperature, the pipe heat elongation, the bellows expansion joint compensator is compressed accordingly In this state, the compensator outer sleeve saw-shaped lap weld is welded, and then the compensator becomes a rigid whole, no longer has the compensation ability. In operation, it is compensated by the tensile-compression elastic deformation of the pipe. In this way, the compensator compensates a part of the total deformation generated by the section of the pipeline under the design temperature difference, and its function is only to make the equilibrium point of the tension-compression in the pipeline operation at the midpoint of the total deformation under the design temperature difference. . The tensile and compressive stresses are substantially equal, which serves to reduce the tensile or compressive deformation stress of the pipeline. The one-time compensator is suitable for pipelines with working pressure ≤1.6MPa and working temperature ≤120°C, and its service life is over 30 years.
2, one-time compensation direct buried laying method polyurethane direct buried insulation pipe, its working principle is to weld the pipe on the product, remove the positioning angle steel, heat the pipe to the required temperature, the pipe heat elongation, the bellows expansion joint compensator is compressed accordingly In this state, the compensator outer sleeve saw-shaped lap weld is welded, and then the compensator becomes a rigid whole, no longer has the compensation ability. In operation, it is compensated by the tensile-compression elastic deformation of the pipe. In this way, the compensator compensates a part of the total deformation generated by the section of the pipeline under the design temperature difference, and its function is only to make the equilibrium point of the tension-compression in the pipeline operation at the midpoint of the total deformation under the design temperature difference. . The tensile and compressive stresses are substantially equal, which serves to reduce the tensile or compressive deformation stress of the pipeline. The one-time compensator is suitable for pipelines with working pressure ≤1.6MPa and working temperature ≤120°C, and its service life is over 30 years.
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