Analysis On The Formation Of Sealing Preload And Short-term Deterioration Of Spherical Pipe Fittings Under Assembly Deviation

A highly reliable pipeline system could provide precise control and safety assurance for the aerospace equipment’s lubrication,transmission,braking and cooling.The 24° double-ball joint pipeline connection structure is widely used in rocket engines and satellites for its good sealing performance,strong pressure resistance and obvious weight reduction effect.At present,most of the failures of aerospace equipment are leakage failures,of which the leakage of the pipeline connection structure accounts for more than half.There are many factors affecting the sealing performance of the pipeline connection structure,including materials,assembly technique,assembly deviation,storage environment and working environment,etc.The urgent problems to be solved in the engineering are that the assembly technique of the pipeline connection structure is hard to get a precise control of the sealing preload and the sealing performance of the pipeline connection structure has deteriorated under storage conditions.In view of the above problems,this paper takes the 24° double-ball joint pipeline connection structure as the research object,and studies the deformation relationship of the pipeline connection structure.At the same time,the assembly deviation is introduced into the tightening process of the pipeline connection structure to study the influence of sealing preload,and on this basis,the changing law of the influence of short-term deterioration with assembly deviations on sealing performance was studied during storage.Firstly,this paper takes the DN4 24° double-ball joint pipeline connection structure as the object,establishes a parametric finite element model,adopts the torque method to explore the deformation relationship and the sealing formation process during the tightening process of the pipeline connection structure,and reveals the influence law of input torque and material parameters on sealing preload.Then the assembly deviation was introduced,and the changes of the angular assembly deviation and the radial assembly deviation on the deformation coordination relationship in the tightening process were analyzed,and then the change law of the sealing preload and contact parameters of the pipeline connection structure under different assembly deviations was revealed.Finally,the sealing contact test of the pipeline connection structure verifies the accuracy of the model for the simulation of the sealing contact parameters.Based on the above work,aiming at the deterioration of the sealing performance of the pipeline connection structure during the storage stage,the effect of short-term stress relaxation on the sealing preload and contact parameters of the pipeline connection structure was studied through finite element simulation,meanwhile the assembly deviation was introduced,the variation law of the influence of stress relaxation phenomenon on the sealing performance is revealed under the assembly deviation,and the accuracy of the finite element simulation is verified by the short-term deterioration test of the pipeline connection structure.In this paper,the deformation coordination relationship in the tightening process of the pipeline connection structure is studied,the assembly deviation is introduced into the tightening process,and its influence on the sealing performance is studied,and the influence of the assembly deviation on the short-term deterioration after the tightening is further studied.From assembly stage to storage stage,the influence law of assembly deviation on the sealing performance of pipeline connection structure is analyzed continuously,which has certain guiding significance for the design and formulation of the assembly techniques of pipeline connection structure.