A Study On The Application Of Steel-plastic Composite Pre-insulated Pipe In Heat Supply System

Steel-plastic composite pre-insulated pipe is no longer the supplement of centralized heat-supply network.It is a subversion of the old system of heat-supply network,a new breakthrough and a revolution.Enjoying the advantage of excellent performance and good value for money,steel-plastic composite pre-insulated pipe with a great prospect represents the future of pipeline industry.It provides a platform for stimulating the organizational reformation of heating system in China,achieving the goal of energy-saving and consumption reduction,and modernizing centralized heat supply.With its prominent superiority,mature technic and remarkable economic efficiency,steel-plastic composite pre-insulated pipe has replaced the traditional heating pipes.There are many practical steel-plastic pre-insulation pipe cases in the heating domain,but its theoretical research is insufficient.In order to securely and reliably applied steel-plastic composite pre-insulated pipe in heating systems,this passage mainly focuses on researching its mechanical properties,heating buried pipeline design and its energy consumption.Followings are main research content and conclusions:(1)Conforming the pipe mechanical performances,parameter elastic module and coefficient of linear expansion of practical steel-plastic pre-insulation pipes.Basing on theoretical derivation of finite element analysis methods,laboratory tests(small size tests),outdoor tests(large-size tests)and engineering practices,analysis results show that.theoretical calculations meet engineering requirements.Therefore,it is safe and reliable which can be used as engineering design basis.But parameter elastic module and coefficient linear expansion only concerns steel-plastic composite pre-insulated pipes while fails to consider the impact of thermal insulation layer and protective outer shell.The fact is that the elastic modulus of steel-plastic composite pre-insulated pipe is smaller compared with that of steel pipe.Therefore,it is impossible not to consider the impact of thermal insulation layer and protective outer shell.(2)Mainly analysis yield and instability,the theory of direct pipeline wall thickness,straight pipeline stress checking calculation and thermal elongation,lateral deformation instability,vertical stability problems that occurred when applying steel-plastic composite pre-insulated pipe into directly buried installation.Results show that the existing wall thickness is smaller than the minimum theory wall thickness provided that the design pressure is].0 MPa,the maximum installation temperature difference is below 85 ?,the pipeline is in the elastic phase,there is no risk of yield and instability in directly buried installation and stress checking calculation also meets the requirement.On road class I and ?,there will be no bucking instability.And if it meets the regulation of minimum depth,there will be no risk of vertical instability.Considering the length of transition section of buried pipe and calculation results of thermal elongation,there is few displacement of the whole pipeline.It is possible to neglect impact of pipeline displacement on brach,elbows and reducers security.(3)Steel-plastic composite pre-insulated pipes are used in the secondary network.Its fluid flows in a turbulent transition zone which is different from steel pipes that transporting hot water in turbulent rough area.Therefore the calculation of frictional resistance varies.By comparing analysis,it is clearly to see that Alite Su Li equation is suitable for hydraulic calculation;by comparing and contrasting the hydraulic power through steel pipelines,it can be inferred that transportation energy consumption could approximately reduce a half once inside diameter and current capacities are certain;if the insider diameter and specific frictional resistance are fixed,the transmission capacity would increase 34.2%?54.3%.