Optimal design of pipeline layout to increasing tightening rate of spherical sealing joint

Abstract

spherical sealing joint airtight sealing structure (hereinafter referred to as “screw joint”) is an important part of the spacecraft propulsion system to realize airtight connection between the pipes in different cabins and between the pipe and the thruster. The screw joint realizes aright sealing by deforming the metal of the spherical head and the conical surface, and it is very sensitive to scratches or indentation, so in operation, repetitive disassembly and assembly shall be avoided and it is necessary to realize airtight tightening in one shot. According to statistical results, in research and development of spacecraft, the success rate for one-shot tightening of the same screw joint differs with the type and the section of the spacecraft: in some sections, the success rate is close to 100%, but in some other sections, it reduces to 70%. This paper makes failure analysis for unqualified one-shot tightening of screw joints and sorts out the factors related to pipeline layout design that leads to the failures, on the basis of which it tries to optimize the design from the perspective of pipeline layout. By calculating the tightening force of the screw joint, this paper quantifies the requirements for degree of freedom (DOF) of the pipeline and the rigidity of the valve/pipeline supporting stand. It will be of great significance to ensure high reliability of the spacecraft propulsion system.