I. Internal sliding and external fixation
When polyurethane insulating steel pipe is heated and contracted, it will change its motion, and it is possible to produce displacement phenomenon. The insulating structure layer and outer casing are generally a kind of integral structure. External fixing means that the working steel pipe and the external maintenance pipe must be fixed together before they are considered good. Two large reinforced concrete piers should be installed at both ends of each section of the pipe and the compensator, so as to ensure the inconvenience of pipe fixing, it is still a little beneficial. Because of the need for reinforced concrete piers for external fixing, the construction area is large, the investment is large, and the construction period is sometimes longer, so it is better to pay attention to the comparison before. According to the difference of envelope, it can be divided into plastic envelope steel structure, FRP envelope steel structure and steel envelope steel structure. It has been proved theoretically that the plastic sleeve steel structure did not conform to the development trend of directly buried steam pipeline at present.
II. Internal sliding internal fixation
Fixed the working steel pipe on the external maintenance pipe through a certain construction mode, fully utilized the strength and stiffness of the external maintenance pipe, and the friction between the external maintenance pipe and the soil to further fix the internal pipe, without the use of reinforced concrete structure, the construction of reinforced concrete piers can be saved. As long as the steel pipe is used as the external maintenance pipe, it is possible to adopt the internal fixation method. The fixed end has heat insulation equipment to reduce the thermal bridge effect. At the same time, the external maintenance pipe should have sufficient strength to meet the requirement of pipeline thrust. It has great advantages to adopt internal fixing structure for "steel sleeve steel" thermal insulation structure. According to the difference of outer guard pipe, it can be divided into steel jacket structure and steel jacket composite structure.
3. Skillful application of external sliding internal fixation
The insulation data of polyurethane insulating pipe and working steel pipe are separated by a certain process, and then they will form a whole. The insulation structure and working steel pipe must move together when the pipe shrinks. There is a gap of 10-20 mm between the outer casing and the thermal insulation structure layer. Such a design structure can not only play a good role in thermal insulation, but also be a reliable channel for tidal discharge. The distance between the working steel pipe and the outer sleeve is separated by a set of heat-insulating guide brackets to stop the support, which can reduce the friction force when the pipe displaces and make it more tedious and fast when it moves.
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