| In recent years,the country has set the goals of "peaking carbon" and "carbon neutrality," which require relatively zero carbon emissions through the use of renewable energy and afforestation.Our country’s energy is mainly based on coal,which is neither renewable energy nor low carbon energy,at present has gradually been replaced by natural gas,natural gas belongs to low carbon fossil energy,with great development potential,so the rational use of natural gas has great significance for reaching the peak of carbon,carbon neutral goal smoothly realization.LNG storage tank is a device for storing liquefied natural gas,and the welding of the storage tank is the key to ensure the quality.9Ni steel is the main material of steel used in the inner tank of LNG storage tank.Manual arc welding is mainly adopted when welding the vertical weld of 9Ni steel and SAW is mainly adopted when welding the transverse weld.With the application of TIP-TIG(TT)welding in vertical welds of LNG storage tanks,TT welding is currently replacing cross welding SAW to become the main welding method for the inner tanks of LNG storage tanks.In this paper,three welding methods such as TT horizontal welding,TT vertical welding and SAW horizontal welding have been adopted for welding 9Ni steel.Based on the experimental results,Shrinkage method of the steel plate has been utilized for finite element analysis,and the simulation results are in agreement with the experimental results.Then,the verified model was used in a three-in-one module to study the influence of three welding sequences on welding deformation under two welding processes of vertical welding TT+TT and vertical welding TT+SAW(TT+SAW): vertical welding priority welding,horizontal welding priority welding and vertical welding and horizontal welding at the same time,as well as the influence of assembly constraints on welding deformation.In the simulation of the welding of the whole storage tank,the influence of multiple people simultaneous welding of TT+SAW and TT+TT on the welding deformation was studied,and the influence of welding sequence was studied as weld-on-load and integral welding on the welding deformation.The main conclusions are as follows:(1)The typical simplified joints of TT vertical welding,TT transverse welding and SAW transverse welding were analyzed by Visual-Assembly software with shrinkage method.The verified results were close to the stress and deformation results measured by experiments,which proved the reliability of the simulation results.Because the deformation data measured by SAW experiment was only the overall deformation data after welding,and the deformation after welding was large,in order to reduce the error,the w elding sequence of SAW was optimized.The results showed that the welding sequence of 1-2-6-7-8-3-4-5 had the smallest deformation,and the subsequent SAW model was simulated with this welding sequence.(2)The three-in-one module studied the influence of internal constraints and unloading time on welding deformation under TT+TT,and the results showed that the welding deformation caused by unloading internal constraints after the activation of the second weld was the minimum.Then on this basis,the influence of vertical welding preference,horizontal welding preference and vertical and horizontal welding on welding deformation is studied.The results show that vertical welding preference produces the smallest welding deformation.The influence of three welding sequences on welding deformation under TT+SAW was studied,and the results showed that the welding deformation of vertical welding was the least.(3)For the simulation of the tanks in the LNG storage tank,the grid of the three-in-one model was first tried to discretise the grids of the LNG storage tank,but it was found that the number of grids had exceeded 7 million.In order to optimize the number of grids,the number of welds needed to be simplified.Under the new model,TT vertical welding,TT transverse welding and SAW transverse welding need to be re-checked.The model verification results are close to the experimental results,which proves the reliability of the simulation.(4)In the TT+SAW welding process,the welding sequence was discussed as the deformation caused by weld-on-load welding and the deformation caused by the welding of 4,8 and 11 people in the same direction at the same time under the two welding sequences.According to the extracted deformation curve and deformation cloud map,the welding deformation produced by weld-on-load welding and weld-on-load welding with 4,8 and 11 people welding in the same direction at the same time is basically the same,but the efficiency of welding with 11 people is the highest.According to the deformation nephogram and extracted deformation curve,the welding deformation of weld-on-load and weld-on-assembly is basically the same.(5)In the TT+TT welding process,11 people were compared to weld-onload and weld-on-assembly at the same time.The results showed that there was basically no difference in deformation between weld-on-load and weld-onassembly.By comparing the radial deformation generated by the TT+TT welding process and the TT+SAW welding process,it can be seen from the deformation cloud map that the maximum deformation of TT+SAW is concentrated on the weld,while the maximum deformation of TT+TT is in the center of the upper steel plate,and the deformation of TT+TT decreases relative to that of TT+SAW. |
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