超高压自增强厚壁弯管应力分析

Stress analysis of ultra-high pressure autofrettage thick-walled bend tube

超高压管式反应器由经过自增强处理的厚壁直管和厚壁弯管组合而成,自增强厚壁弯管的受力难以通过理论分析得出。基于有限元方法对自增强厚壁弯管的受力情况进行了分析,并将结果与基于平面应变模型的自增强厚壁直管的有限元计算结果进行对比。研究结果表明,厚壁弯管的回转半径对自增强厚壁弯管的受力情况有显著影响,回转半径越大、厚壁弯管的受力情况越接近厚壁直管。以自增强厚壁直管在工作压力下内表面的当量应力幅值为衡量基准,当厚壁弯管回转半径增大到一定值,可以认为自增强厚壁弯管的疲劳性能与厚壁直管基本一致。对于目前国内LDPE/EVA装置中常用规格的厚壁自增强弯管,如果以厚壁直管内表面当量应力幅值的10%作为厚壁弯管当量应力幅值的最大偏差,则回转半径R的取值应大于7D_(o),当偏差为5%时,回转半径R需大于10D_(o)。该研究结果与国外引进的超高压管式反应器设计参数相吻合。

The ultra-high pressure tubular reactor is composed of autofrettage thick-walled straight tubes and thick-walled bent tubes.The autofrettage stress of the thick-walled bend tube is difficult to be obtained by theoretical analysis.The finite element method was adopted to analyze the stress of the autofrettage thick-walled bend tube.Moreover,the analysis result was compared to that of the autofrettage thick-walled straight tube based on the plane strain model.The results show that the bending radius of autofrettage thick-walled bend tube has a significant effect on its stress condition.The greater the bending radius,the closer the stress distribution of thick-walled bend tube is to that of thick-walled straight tube.Taking the equivalent stress amplitude of the inner surface of the thick-walled bend tube under working pressure as the benchmark,it can be concluded that the fatigue performance of the thick-walled bend tube is basically equal to that of the thick-walled straight tube when the rotation radius increases to a certain value.For thick-walled autofrettage bend tube of the specifications commonly used in LDPE/EVA units,if 10%of the equivalent stress amplitude on the inner surface of the thick-walled straight tube is taken as the maximum deviation of the equivalent stress amplitude of the thick-walled bend tube,then the value of the radius of rotation R should be greater than 7 D_(o)at least.When the deviation is 5%,the radius of rotation R needs to be greater than 10 D_(o).The research results are consistent with the design parameters of the ultra-high pressure tubular reactor imported from abroad.