Finite Element Analysis Of Steel LNG Storage Tank And Development Of Calculation Software Package

With the continuous development of the world economy,protecting the environment is getting more and more attention.As a clean and efficient energy source,liquefied natural gas(LNG)is increasingly used,and more and more LNG storage tanks have been designed and built.Once the LNG storage tank in operation were destroyed,it would often cause huge economic losses and even disasters.Therefore,the research on the safety of LNG storage tanks has great significance for guiding engineering design and manufacture.In addition,there is no specialized software for the calculation of tank strength at home and abroad.As structural calculations require personnel with professional knowledge,the project progresses slowly and costs a lot.Therefore,it is particularly urgent to develop a software used for strength calculation of LNG storage tank.In this paper,the 7500 m~3 LNG metal full-capacity tank is taken as the research object.The computation and simulation of the temperature field and stress field of the LNG storage tank in operation are carried out by using finite element method,and the safety evaluation results are given.The main contents of this paper are as follows:According to the provided project book and design drawings,the finite element model was established by ANSYS,including the axisymmetric model for thermal analysis and the solid model for strength analysis,and the corresponding boundary conditions and load conditions were applied according to the requirements of related specifications.All thermal and structural calculations and analysis has been completed.A thermo-structural coupling calculation method combining two-dimensional axisymmetric model and three-dimensional solid model is proposed specifically for thermal stress calculation of storage tanks which are used to store cryogenic chemicals such as LNG.Considering the different characteristics of thermal insulation material and structural material,the metal shell material with high thermal conductivity is neglected in the axisymmetric thermal analysis model.Otherwise,in the three-dimensional structural model,the insulating material(such as elastic cotton)with low elastic modulus is neglected.Thermal analysis and structural analysis implement automatic coupling calculations using node coordinate correspondence and ANSYS/APDL.This method has the superior advantage of reducing the computational scale and saving computational cost.Through computations of self-made example and actual tank,it is verified that this method has high calculation accuracy and ease of use.After analyzing the result of finite element calculation,it is found that the temperature field distribution of LNG storage tanks under normal operating conditions in summer is normal,the thermal angle protection system plays a good role in heat insulation,and according to the leak analysis results,it can effectively reduce the thermal shock of the low-temperature LNG liquid when touching the outer tank.The liquid-solid coupling vibration model established by ANYSY is in accordance with the engineering practice.Under the SSE earthquake,the stress value of the LNG storage tank is larger,and the most unfavorable part is at the bottom of the tank.This is consistent with the actual investigation results of the destruction of LNG storage tanks in the actual project.Based on ANSYS,a finite element analysis software package for cryogenic pressure vessels was developed using Matlab program.The software package includes steady-state and transient temperature field analysis,normal-use stress and strength analysis,and load-bearing limit state stress and strength analysis functions.It uses graphical interface input and file interaction input methods.So that,even without professional knowledge,the staff can complete the finite element calculation of the LNG storage tank in the actual project.