Thermo-structural Coupling Analysis Of L-shape HV-MLI Cryogenic Pipes

With the rapidly development of science and technology,High Vacuum Multilayer Insulation(HV-MLI)cryogenic pipes are widely used in many fields such as energy,chemical industry,aerospace science and technology and nuclear industry.Due to working in the cryogenic environment and bearing liquid pressure,the HV-MLI cryogenic pipe will bear complex loads because of thermo-mechanical coupling effects.The bellows and insulation supports are delicate components in the pipe which could have many kinds of damage under complex loads.The structure integrity of each part in the HV-MLI cryogenic pipe has a significant impact on the safety of the pipe.To investigate the response of all parts in the pipe under complex loads,Finite Element(FE)method was used in the thermo-mechanical coupling analysis process of a certain L-shape HV-MLI cryogenic pipe.The temperature distribution of the pipe and heat leakage of each part were obtained by thermal analysis.Based on the thermal analysis results as well as the loads and constraints that the L-shape HV-MLI pipe bears when it works,the structural analysis was conducted,and the stress of inner tube,outer tube,thermal bridge,bellows and insulation supports were calculated.The relationship of the stress on each part with loads was analyzed.The following findings were concluded based on the analysis results.First,In the structure analysis process,an equal-section pipe model was used to replace the bellows.Through the data which was analyzed,it was found that the equal-section pipe modelis reasonable and effective.Compared to the model that contains bellows,the efficiencyof equal-section pipe model is 300 times as high as before,and it could also guarantee the accuracy of simulation.Therefore,the equal-section pipemodel is suitable for the multi-fields coupling analysis of HV-MLI cryogenic pipe.Second,heat in the environment gets into the L-shape HV-MLI cryogenic pipe through three ways including thermal bridges,insulation supports and multilayers.Insulation supports and thermal bridges are the main factors of the pipe’s heat leakage.When the pipe was used to transport LN2,the heat leakage through the above three ways accounts for about 49.07%,49.32% and 1.61% in the whole pipe’s heat leakagerespectively.Third,the stresses of inner tube,outer tube,elbow and thermal bridge are relatively small and lower than the yield strength,and they are very safe when the pipe works.The stress of bellows increases with the fall of cryogenic liquid’s temperature or the increase of the length of inner tube that the bellows compensated.The bellows in the horizontal pipe is the most dangerous part of the whole pipe because of the high stress.Finally,the internal pressure of inner tube is the main factor impacting the stress of insulation supports.The stress of insulation supports closed to the elbow increases with the internal pressure of inner tube,but the variation of the stress on insulation supports far away from the elbow is very small.So,increasing the thickness of insulation supports closed to the elbow and reducing the thickness of insulation supports far away from the elbow could guarantee the insulation supports’ strength and reduce heat leakage of the pipe.