Study On Thermal-stress Numerical Simulation Of Multilayer Directly Buried Thermal Pipeline

Compared with the traditional thermal pipeline,the directly buried thermal pipeline has many irreplaceable advantages,among which the typical advantages are less land occupation,fast construction,easy maintenance,long service life and so on.Therefore,the development momentum of direct buried pipeline is very good in recent years.However,the relevant research and technical regulations have not fully kept pace with the development of buried pipelines.Therefore,it is necessary to study directly buried thermal pipelines.In this paper,"Technical Regulations for Direct Buried Steam Pipeline for Urban Heating" is used as the norm to analyze a certain type of direct buried thermal pipeline produced by Dalian Kehua Thermal Pipeline Co,Ltd.under various operating conditions.Firstly,the relationship between the thickness of air layer and the thermal conductivity of air layer is analyzed.This step is realized by theoretical analysis and numerical analysis.Through the results of air layer flow field analysis,the thickness of air layer which needs to consider the convective heat transfer of air is obtained.Combining with the relevant theory,the relationship between the thickness of air layer and its thermal conductivity can be obtained,which provides guidance for the calculation and selection of the equivalent thermal conductivity of air layer.Then,the equivalent thermal conductivity is determined according to the thickness of the air layer,and the thermal conductivity of other materials is considered.The temperature fields of different pipeline cross-section schemes under three different temperature conditions are obtained by finite element simulation.Then,the law of temperature fields of different schemes and the reasons for the formation of this law are analyzed.Finally,the best thermal insulation scheme is selected.The temperature of the inner and outer pipes is loaded into the "L" type natural compensation pipeline model and the "Z" type natural compensation pipeline model.At the same time,internal pressure and earth pressure are applied to the pipeline,and then the stress analysis of the inner working steel pipe is carried out.In this paper,the stresses of pipelines with different types of natural compensation under different working conditions and different loads are analyzed,and the results are analyzed,and the suggestions for laying and compensation of pipelines are given.In this paper,the results under various working conditions are analyzed,and the influence of different insulation layer setting methods on the insulation effect of pipelines and the stress of pipeline elbows with different types of natural compensation are obtained.It has a certain guiding role on how to choose the compensation type of directly buried pipelines.