Dynamic Response Analysis Of Cryogenic Piping

The cryogenic piping is used for conveying fluid medium,transmitting fluid power and information in the cryogenic field.All kinds of power equipment connected to the cryogenic piping,such as reciprocating compressor or pump,run intermittently and periodically.The power equipment provides a certain excitation to the fluid in the tube,and leads to vibration of the fluid tube.Pulsating fluid exerts a periodical pulse excitation force on pipe elbows,reducing pipe,valves and other components,and then causes the vibration of piping.The vibration of piping would make piping connecting parts wear down and loosen,and bring about fatigue or fracture of the supports and hangers.The continuous vibration of piping would lower the accuracy of instruments and apparatuses,damage connecting pipe,tees and elbows,and even cause the destruction of the entire pipeline.In this paper,the piping vibration standards at home and abroad are used as references,and the piping of 20 000 m3 cryogenic storage tank(the cryogenic ethylene liquid transporting piping)of Lanke high-tech is taken as a research object.The cryogenic piping vibration problems caused by power equipment of cryogenic piping are studied.The cause and affecting factors of the cryogenic piping vibration are analyzed.The physical model of cryogenic piping is established using CADWorx and CAESARII software,and statics analysis and dynamic harmonic response of cryogenic piping under different working conditions are completed.In the end,the corresponding improvement measures are put forward based on the calculation results.The main work of this paper is detailed as follows:1.The static analysis of cryogenic piping are carried out,and the level of the primary stress,secondary stress and displacement of piping are checked according to the related standards.The result indicates that the current design of cryogenic piping is feasible.The considerations of model establishment of cryogenic piping supports and hangers as well as the way how to use them are introduced.The stress,displacement and constraint of pipping are analyzed by using CAESARII software.The results show that the maximum stress ratio of piping is less than 1,and the linear displacement of piping is relatively large.The forces on the horizontal and longitudinal of piping are bigger than others.Therefore,the nozzle connecting equipment and piping suffers much force because of the equipment weight and base sedimentation.Due to the insufficient supports and guidance,the stability of the piping is weak.In view of this,corresponding improvement measures are put forward to optimize the piping.2.The outlet piping of cryogenic submerged pump is taken as an example,the harmonic analysis is performed by using CAESARII software,and the harmonic response of the pipeline under the excitation of the fluid pressure pulsation is obtained.The result shows that the original piping basic frequency is extremely low,the stress exceeds the standard,and a severe vibration of piping is easy to happen under the pressure fluctuation.It's necessary to weaken the piping vibration by taking some protective measures.The vibration trend of the piping is weakened significantly by changing the tube bracing structure and layout,reducing additional displacement of the pipe nozzle,and adjusting the position of valves and other accessories in the piping.Primary stress ratio of piping is reduced by 38.8%,secondary stress ratio as three times as original,and the fundamental frequency is increased by 219.5%.The natural frequency of piping is avoided to go with the resonance region,the descend range of the largest amplitude attains 2 mm to 22 mm,and vibration trend of piping significantly is decreased.3.The dynamic analysis of the cryogenic ethylene liquid transporting piping is performed using CAESARII software,the displacement and stress of the piping under the discharging reaction force of relief valve s are checked to make sure that they conform to the specification,and the structure of the pipe is optimized.The result shows that,the basic frequency of the piping is extremely low,the piping stress exceeds the standard,the longitudinal amplitude of the piping elbow near to the relief valve is large,and the lateral vibration is obvious in the position of elbow on which the discharging reaction force of relief valve acted.The piping structure should be improved.First,the piping intermediate position constraint is changed into a fixed support to increase the stiffness of the piping.Second,the bearing support is changed into a spring support in the piping elbow near to the relief valve to bear the vertical opposing force.Third,a damping constraint is set in the inlet piping of the relief valve,a bearing support with a gap is added in the outlet elbow of the relief valve,and the best gap is found to be 6.63 mm by repeatedly adjusting the gap between the limit and the piping.The maximum amplitudes of X,Y and Z for the improved piping are respectively decreased by 88.12%,76.02% and 99.86% according to the simulation.