Research On The Fatigue Cycle Of Direct Buried Heating Pipeline In Regional Hot Water Boiler Room Based On Fuzzy Mathematics

With the development of central heating technology and engineering in China,many heating pipelines are operating under complicated and changeable working conditions,and the instability factors are increasing,that leads to the occurrence of fatigue failure accidents.As is a statistic data of the fatigue life of pipe network,the maximum temperature difference fatigue cycle of heat supply network can not only fully consider the thermal stress caused by the temperature difference of the size cycle,but also it is of great significance to reduce the damage of pipe network and improve the life of pipe network.The operation accident frequency and cycle temperature difference of heating pipe network have an important and direct effect on its fatigue life.However,most studies have focused on the study of the overall pipe network or the thermal power plant for heating,and there is little research on the fatigue life of the heating pipe network in the regional hot-water boiler room as the heat source.Owing to this,this paper is based on the accident frequency and operation parameters of the pipe network in hot water boiler room as the heat source,then the fuzzy mathematics theory is used to analysis of the fuzzy phenomena in the pipe network deeply,and with the data processing of the operating temperature difference,the maximum temperature difference fatigue cycle of heat supply network is obtained.So,the research results have theoretical and practical significance for the safe operation of central heating direct buried pipeline.Firstly,this paper classifies the load and stress of the heating direct buried pipeline,and analyzes the stress and damage of the pipeline under the four limit states of the pipe.It is concluded that the low cycle fatigue failure has a greatly influence on the fatigue life of directly buried heating pipe,and that can be calculated by analyzing the temperature difference cycle of the pipeline.Secondly,this paper analyzes the fuzzy phenomenon in heating direct buried pipe network for ?whether the thermal stress causes an damage?,and the fuzzy mathematics theory is investigated to analyze the fuzzy phenomenon about the fatigue life of directly buried heating pipe.Also,the corresponding general membership function is given.The results show that: 1)The parabolic membership function is applicable to the prediction of the fatigue life of direct buried pipelines than others,and the universal membership function is obtained,which is applicable to the fatigue analysis of heating direct buried pipeline;2)It is also verified that the Palmgren-Miner formula in?Gegional Heating Manual ? is a kind of common membership function in fuzzy mathematics;3)The selection of membership function parameters has a great influence on the prediction accuracy of fatigue life.In addition,this paper investigates the accident situation of direct buried pipe network with hot water boiler room,and SPSS is used to describe dates and establish the model effectively.The results show that: 1)the heating system is divided into four grades and the frequency of accidents is subject to poisson distribution;2)for the main transmission line,the transmission line and the branch line in hot water boiler room as heat source,the frequency of accidents and the confidence level are between 99% within the service life of 30 years;3)The position of high frequency accident includes elbow,compensator,fixed pier and valve,mainly.Finally,according to the different outdoor computing temperature and heating time,the paper selects Taiyuan,Shijiazhuang,Datong and Yuncheng as representative heating cities,and collects the temperature of water supply and water return during the operation of the hot water boiler room in four cities.Cycle temperature difference is divided by the daily,weekly and monthly,then the maximum temperature difference fatigue cycles in the design life span of 30 years were calculated and analyzed with the general membership function,respectively.There are some research results as follows: 1)The fatigue life cycle interval of the transmission water supply and backwater pipe section in the regional hot water boiler room,ranges from high to low order are Datong,Taiyuan,Shijiazhuang,Yuncheng;2)The ranking of cycle times of fatigue life cycle is directly proportional to the design heating time of four representative cities,but it is inversely proportional to the average outdoor temperature of the heating season in these four representative cities;3)For the central heating cities which have lower the outdoor calculated temperature of heating and the longer the heating time,have the greater the fatigue damage on the main regional hot water boiler room,so,we should strengthen the buried heating pipe network security performance between the design and the operation stage in the future.