Linear Expansion Coefficient And Elastic Modulus Of Steel-plastic Composite Pipe Analysis

Steel-plastic composite pre-insulated pipe is a new heating pipe. It comprises of steel-plastic composite pipe (including pipe fittings), rigid polyurethane foam plastic insulation layer and the polyethylene protection shell. The steel-plastic composite pipe is the key of steel-plastic composite pre-insulated pipe. It compose of borehole net steel pipe and PE-RT. Borehole net steel pipe is enhanced framework, it is made from cold-rolled punched hole steel sheet. And heat-resistant polyethylene (PE-RT) is main material. Owing to using of an enhanced framework and the heat-resistant polyethylene, compressive strength and heat-resistance of pipe have been significantly improved. Steel-plastic composite pre-insulated pipes can be used as hot water pipes, the secondary heating network pipes etc.Steel-plastic composite pre-insulated pipe lacks of theory evidence and practical cases in application of direct-buried heating area. Effects of pipeline mechanical properties coming from insulation layer and insulation shell are also unknown. Therefore, analyzing mechanical properties of pre-insulated pipe as a whole is extraordinary essential. This paper studies two type steel-plastic composite pre-insulated pipes from three aspects, including finite element analysis, experimental research and composite materials micromechanics theory. The main contents and conclusions are:1. Using the finite element analysis software to analyze dn110 and dn200 steel-plastic composite pre-insulated pipes for thermal analysis and structural analysis. Imposed 20 degrees temperature load on the model outer wall and 50 degrees,70 degrees,90 degrees temperature load on inner wall separately. It simulates the radial temperature distribution in the pipeline. Then it takes temperature as boundary conditions to simulate the model axial thermal displacement and calculates the finite element value of linear expansion coefficient of steel-plastic composite pre-insulated pipes according simulation results. Moreover, Imposed pressure load and temperature load on the model, to calculate the finite element value of elastic modulus according simulation results.2. Designing laboratory bench for steel-plastic composite pre-insulated pipes. It obtains the experimental value of linear expansion coefficient and elastic modulus of dn110 and dn200 two types pipes by experiment. On the basis of composite materials micromechanics theory, it calculates the theoretical value of linear expansion coefficient and elastic modulus of different types pipes.Analyzing finite element values, the experimental values and the theoretical values of linear expansion coefficient and elastic modulus of dn110 and dn200 steel-plastic composite pre-insulated pipes by the Origin, it corrects micromechanics theory formula of composite materials. It derives modifier of linear expansion coefficient and elastic modulus of different types pipes. It provides designed and calculated parameters for steel-plastic composite pre-insulated pipes applying in the direct-buried heating area.3. Paper designs pit experiment of steel-plastic composite pre-insulated pipes. It simulates running condition of dn110 and dn200 two type pipes in the direct-buried heating engineering. Through observing experimentation, it obtains transition length, thermal expansion and axial force of the composite pipes. And comparing with the theoretical values of the maximal transition length, thermal expansion and axial force of the composite pipe, the result verifies the accuracy of the laboratory experiment for composite pipes.