| Tee structure is an important part of central heating pipe system,at run time,usually be suffered from water pressure?self-respect?soil load?temperature and other factors,stress and deformation overall complex.Meanwhile,compared with the straight pipe of the pipeline,tee belonging to the large opening structure and geometrical structure of discontinuous fitting,in the vicinity of intersecting lines had a great peak stress.Branch line is enerywhere in directly buried heating Pipeline Engineering,tee is used very common,therefore take measures to reduce tee peak stress,especially for large-diameter buried heating pipe tee,to reducing tee primary stress,secondary stress and peak stress equivalent stress,which has very important significance for buried heating pipe to operation safely One of the main ways to reduce peak stress is to enhance the local strength of the tee However,the current CJJ/T81-2013 "Technical specification for directly buried hot-water heating pipeline in city" lack of any way to strengthen the tee,Tee experience approach is targeted at less than or equal to the 500mm branch,Tee discipline did not give a stress calculation method and the failure judgment condition,both lack of theoretical support and mature engineering practice,which buried a serious hidden danger to the city safety operation of heating,tee to strengthen weak technical problems need to be solved.In response to this situation,we use ANSYS finite element analysis software to establish extruded tee?cape strengthen extruded tee model,Simulate and analysis the large diameter extruded tee?cape strengthen extruded tee equivalent stress distribution under the internal pressure load,temperature load and displacement,tee in anchorage,transition and tee branch under different arrangement mode.The main research content and results are as follows:(1)According to the common form loads and characteristics in buried heating pipe tee,classify pipelines stress and pipeline failure modes commonly,clearly pointed out that the main failure form of buried heating pipe tee is plastic deformation and low cycle fatigue damage.(2)Introduced the current "regulations" on the tee branch layout requirements,use Palmgren-Miner formula of European regulations and the S-N curve,determine whether different levels of the tee request meets the safety low cycle fatigue failure Claim.And gives a three-way method of strengthening and reinforcing theory from an engineering point of view.(3)Using the finite element analysis software ANSYS to establish extruded reducing non-reinforcing model and cape strengthen model.For the three regional arrangement,when in the anchorage section,extruded reducing tee the maximum equivalent stress is located in the inner wall of the tee abdominal region,adopts the cape strengthening method can effectively reduce the stress level of large diameter tee.(4)When the tee is in transition,vertical branches and spanning branches equivalent stress levels slowly at first and then rapidly increasing trend with the increase in the amount of displacement of main pipe;When the main pipe displacement is positive direction,parallel branch tee stress decreases approximately line with the displacement of main pipe;When the main pipe displacement is reverse direction,parallel branch tee stress decrease slowly at first and then rapidly increasing with the displacement of main pipe;"permitted displacement "as the diameter of main pipe increases.When taking cape to strengthen,stress increase rate of tee slowed with the increase of the displacement of main pipe,Tee' capacity of resist displacement of main pipe enhancement,,permitted displacement"has increased.(5)For equal diameter extruded tee strengthened difficult problem,from the engineering point of view,summarizes several reliable and secure ways of branching and engineering methods.(6)Established part database of reducer extrusion tee cape strengthen size,provides the basis data for the use of cape strengthen in the actual project. |
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