Research On Directly Buried Hot-water Heat-supply Pipeline Under Non-compensating And Cold Installation Conditions

In recent years，the directly burying technology of heat-supply pipeline isdeveloping rapidly and is first applied in Northeast China. Obvious economic andsocial benefits were obtained because of using directly buried method in most ofreconstruction, extension and newly built hot-water supply networks. In1998,Technical specification for directly buried heating pipeline engineering incity (CJJ/T81-98), the industry standard of the People’s Republic of China which canprovide guarantee for design and construction of directly buried heat-supply pipeline,was issued and implementing. At the same time, the standard offered relativecalculation methods for non-compensating directly burying. In2011, Design codefor city heating network (CJJ34-2010) was issued and implementing. Streetheat-supply pipeline networks are required to be buried by non-compensating methodwhen design pressure is no more than1.6MPa and design temperature is no more than95oC in the design code above. This code provided more basis for the use ofnon-compensating design.Recently, the directly burying method of heat-supply pipeline is widely adopted,but the real application of directly buried hot-water pipeline under non-compensatingand cold installation conditions shall be further developed and disseminated. Thoughits basic theory (using shakedown analysis) had reached a consensus, there are hugenumbers of ever-changing and thorny problems in practical applications. According toshakedown analysis, it’s possible to use directly non-compensating burying methodeven though designed water temperature reaches140oC in pipeline networkscompared with elastic theory. In this respect, the shakedown analysis can extend theapplication of directly non-compensating burying, simplify construction technology,shorten construction period and save construction cost.In the strength design of directly buried heat-supply pipeline, different technicalmeasures shall be applied to avoid different damages caused by differentcharacteristics stress forces. Therefore, in different situations and sections, flexiblychoosing different installation methods is significant for safe and economicaloperation of directly buried heat-supply pipeline networks.It is well known that the corrugated compensator is the most accident-causingcomponent. Pipelines with no corrugated compensator can guarantee safe operation ofpipeline networks under calculation allowed conditions. There’s only relative regulations for designs whose heating pipes’ diameters are no more than DN500.While, most of pipeline networks exceed the limit and some of them have reachedDN1200in actual projects. In this research, the project’s diameter is DN600, designpressure is2.5MPa, heat medium is hot water, supply and return water temperature is130℃/90℃, peak water temperature is135℃. The real supply water temperaturewas maintained between130~135℃. Choosing directly non-compensating buryingmethod with above heat-supply parameters and standard-exceeding pipe diameter is achallenge for both design calculation and installation. In this paper, basic theory wasjust discussed in the aspect of pipeline strength, weak links in practical project werealso studied and calculated according to theory requirements in detail to determinereasonable arrangement form. With the calculation for meeting strength requirements,hydraulic calculation and insulation thermodynamic calculation were doing, thusconstituted complete design and research system of the project.