Research On The Equivalent Temperature Cycles Index Of Directly Buried Heating Pipe

What is often lacking,in Urban heating directly buried hot water pipeline technology procedures,is fatigue analysis cycle index for directly buried heating pipe.The first issue of fatigue analysis for directly buried heating pipe is the fatigue cycles of components,which deterrmines the fatigue limit.If the number of temperature cycling is underestimated,fatigue failure occurs and it will shorten the life time of pipe network.The number of temperature cycling is determined by the small difference in temperature cycles,the heat source start-stop and large difference temperature cycles of pipeline accidents.In view of the above problems,the directly buried heat-supply pipeline of two thermal power plant and two regional boiler rooms is investigated in this paper.The supply and return water temperature of four transmission lines,eight distribution pipelines and eight branch lines are investigated for five heating periods.Also their pipeline accident records are investigated,including compensator damaged,pipeline leak and local component failure(such as elbows,T-pieces and reducers etc..)First,the expectation,variance and the range of radius of four transmission lines,eight distribution pipelines and eight branch lines’daily,weekly and monthly maximum temperature difference are calculated based on t-controllable distribution functions.Second,the Small temperature difference between the equivalent temperature cycles index of four transmission lines,eight distribution pipelines and eight branch lines are calculated based on Palmgren-Miner formula.Third,the pipeline accident investigation and records show the four transmission lines accidents’ number ranges in the five years to two years at a time;the eight distribution pipelines accidents’ number ranges in the two years to half years at a time;the eight branch lines accidents’number ranges in the a year and a half to a year at a time;At last,the equivalent temperature cycles index of transmission lines,distribution lines and branch lines are calculated out by added the heat source start-stop frequency times in 30 years(the design life of pipelines).That is to say,the transmission lines’ equivalent temperature cycles and pipeline design life of 30 years of equivalent temperature cycles are calculated out by added the small temperature difference,and 1.2 times(added rev.stop every year large temperature difference and transmission lines occur an accident every five years)and 1.5 times(added rev.stop every year large temperature difference and transmission lines occur an accident every two years)each year of the transmission lines accident times.The distribution lines’ equivalent temperature cycles and pipeline design life of 30 years of equivalent temperature cycles are calculated out by added the small temperature difference,and 1.5 times(added rev.stop every year large temperature difference and transmission lines occur an accident every two years)and 1.75 times(added rev.stop every year large temperature difference and transmission lines occur an accident every a year and a half)each year of the transmission lines accident times.The branch lines’ equivalent temperature cycles and pipeline design life of 30 years of equivalent temperature cycles are calculated out by added the small temperature difference,and 1.75 times(added rev.stop every year large temperature difference and transmission lines occur an accident every a year and a half)and 2 times(added rev.stop every year large temperature difference and transmission lines occur an accident every year)each year of the transmission lines accident times.This method is used for the heating of the city transportation trunk line,distribution main line and branch line,can draw in different cities,all kinds of application level pipeline’s actual cycle times.Also this lays the foundation for each of the different level of the city pipeline using different fatigue analysis limit.Furthermore this research has important theoretical significance and engineering application value.