补偿弯臂长度对Z形补偿管段应力的影响

Effect of Compensating Bending Arm Length on Stress of Z-shaped Compensation Pipe Section

针对工作管(材质为Q235B)规格为D1220×14的保温管,在被补偿弯臂取循环温差作用下的过渡段长度,补偿弯臂分别取1～14倍弹性臂长的条件下,对水平埋设Z形补偿管段的最大等效应力(范式等效应力,基于第四强度理论)进行有限元模拟,分析Z形补偿管段最大等效应力出现最小值时对应的补偿弯臂长度。Z形补偿管段最大等效应力(出现在弯头外壁)随着补偿弯臂长度的增大先减小后增大。补偿弯臂长度由1倍弹性臂长增加到4倍弹性臂长时,最大等效应力迅速减小。补偿弯臂长度为4～9倍弹性臂长时,最大等效应力随补偿弯臂长度的增大而减小,但变化幅度不大。当补偿弯臂长度大于9倍弹性臂长后,最大等效应力随着补偿弯臂长度的增大逐渐增大。最大等效应力的最小值出现在补偿弯臂长度为9倍弹性臂长时。由模拟结果可知,当补偿弯臂长度小于1. 5倍弹性臂长时,弯头的最大等效应力大于3倍钢材许用应力(钢材许用应力取125 MPa),此时弯头应力较大,易发生疲劳破坏。

For the insulation tube with working tube (material Q235B) specification of D1220×14,the compensated bending arm takes the length of the transition section under the cyclic temperature difference,and the compensating bending arm takes 1 to 14 times of elastic arm length respectively.The finite element simulation of the maximum equivalent stress (von Mises stress,based on the fourth strength theory) of buried horizontally Z-shaped compensation pipe section is performed.The length of the corresponding compensating bending arm is analyzed when the maximum equivalent stress of the Z-shaped compensation pipe section appears at the minimum value.The maximum equivalent stress of the Z-shaped compensation pipe section decreases first and then increases with the increase of the length of the compensating bending arm.When the length of the compensating bending arm increases from 1 time of the elastic arm length to 4 times of the elastic arm length,the maximum equivalent stress rapidly reduces.When the length of the compensating bending arm is 4 to 9 times of the elastic arm length,the maximum equivalent stress decreases with the increase of the length of the compensating bending arm,but the variation range is not large.After the length of the compensating bending arm is more than 9 times of the elastic arm length,the maximum equivalent stress increases gradually with the increase of the length of the compensating bending arm.The minimum value of the maximum equivalent stress occurs when the length of the compensating bending arm is 9 times of the elastic arm length.The simulation results shows that when the length of the compensating bending arm is less than 1.5 times of the elastic arm length,the maximum equivalent stress of the elbow is more than 3 times of the allowable stress of the steel (the allowable stress of the steel for 125 MPa).At this time,the elbow stress is large,and the fatigue damage easily occurs.