城镇供热直埋保温塑料管道的应力分析

Stress Analysis of Directly Buried Insulation Plastic Pipeline for Urban Heating

结合工程实例,对城镇供热直埋保温塑料管道PE-RTⅡ的单位长度摩擦力、过渡段长度、应力状态、热伸长量、保温层应力验算进行研究,得出以下结论:过渡段长度、轴向应力和过渡段伸长量与管道的弹性模量、运行温差有关,而直埋保温塑料管道的弹性模量随温度的增加而减小,即塑料管的弹性模量与运行温度负相关,且变化很大。因此要求得这些量的最大值,就必须找出这些量为最大时的工况。将弹性模量关于温度的拟合公式代入这些量的计算公式,然后对管道工作温度求导,即可找到这些量为最大时的温度工况。由于PE-RTⅡ管道的弹性模量比钢质管道小很多,所以塑料管道的轴向力比相同管径钢质管道小很多,从而塑料管道过渡段最大长度比钢质管道小很多,即塑料管道只需很短的直管段就能锚固。在适用供热工况(压力小于或等于1.0 MPa、温度小于或等于75℃)下,PE-RTⅡ管道处于弹性状态,且最大当量应力远小于其所在工况的拉伸屈服强度。在适用供热工况下,PE-RTⅡ管道可以采用无补偿冷安装的敷设方式;膨胀量很小,可以不考虑热补偿。在适用供热工况下,PE-RTⅡ直管段的应力验算合格,满足要求。在适用供热工况下,只需要根据PE-RTⅡ管道的最大工作压力和设计应力来选择管系列,就可以保证其直管段应力验算合格。PE-RTⅡ直埋管道保温层应力符合规范要求。保温层实际承受压力为最大可承受压力的9.09%~25.07%,实际轴向剪切力为最大可承受轴向剪切力的13.63%~37.61%。说明保温层在正常覆土深度情况下是安全的。

Combined with engineering examples,the unit length friction force,length of the transition section,stress state,thermal elongation and insulation layer stress calculation of direct buried insulation plastic pipeline PE-RTⅡfor urban heating are studied.The following conclusions are drawn:1.The length of the transition section,the axial stress and the elongation of the transition section are related to the elastic modulus and the operating temperature difference of the pipeline,and the elastic modulus of the directly buried insulation plastic pipeline decreases with the increase of temperature,that is,the elastic modulus of the plastic pipeline is inversely related to operating temperature and varies greatly.Therefore,in order to obtain the maximum value of these quantities,the operating conditions when these quantities are maximum must be found out.2.Because the elastic modulus of PE-RTⅡpipeline is much smaller than that of steel pipeline,the axial force of plastic pipeline is much smaller than that of steel pipeline of the same diameter,so the maximum length of transition section of plastic pipeline is much smaller than that of steel pipeline,that is,plastic pipeline only needs a short straight section for anchoring.3.Under applicable heating conditions(pressure less than or equal to 1.0MPa and temperature less than or equal to 75℃),PE-RTⅡpipeline is in elastic state,and the maximum equivalent stress value is far less than the tensile yield strength of its working condition.4.Under applicable heating conditions,PE-RTⅡpipeline can be laid with no compensation for cold installation,and the expansion is very small,so thermal compensation can be disregarded.5.Under applicable heating conditions,the stress check calculation of PE-RTⅡstraight pipe section is qualified and meets the requirements.6.Under applicable heating conditions,it is only necessary to select the pipe series according to the maximum working pressure and design stress of the PE-RTⅡpipeline,which can ensure that the stress checking of its straight pipe section is qualified.7.The stress of PE-RTⅡdirectly buried pipeline insulation layer meets the requirements of the code.The actual bearing pressure of the insulation layer is 9.09%to 25.07%of the maximum bearable pressure,and the actual maximum axial shear force is 13.63%to 37.61%of the maximum bearable axial shear force.It indicates that the insulation layer is safe under the condition of normal soil depth.