Research On A Two-stage Self-balancing Sealing System For Oil And Gas Pipelines Under Pressure

Compared with the biggest domestic plugging system((?)1219mm),the natural gas pipeline plugging system with diameter 1422mm increases 36%in plugging area,and when the plugging pressure increases from 10 MPa to 12 MPa,the supporting reaction force of the plugging system from the high pressure medium increases 63%.For the monolayer cup leather packing,excessive supporting reaction can lead to plastic deformation of pipelines which is prone to accidents on one hand;on the other hand,the sealing ability between the leather cup and the pipeline will decline,due to the existence of elliptical degree,straight weld,spiral weld and other factors of the pipe,and in fact,the maximum plugging pressure is 10 MPa at present.Based on the upcoming Sino-Russian eastern front (?)1422mm natural gas pipeline engineering,this paper studied the corresponding (?)1422mm plugging system with pressure,the plug-tee and two-stage plugging devices were designed accordingly and the Finite Element Method was applied to strength analysis and failure assessment.We focused on the following aspects:(1)A general plan and a detailed structure design to the plugging device were carried out the Solidworks software and the Adams kinematics analysis software were applied to the size design and optimization for the plugging device to solve the rotational interference problem.Finally,a two-stage plugging device which can be smoothly down into the pipeline was developed.(2)The detailed stress and strain distribution of the plugging tee joint assembly was obtained by ABAQUS finite element analysis software.The security of the assembly before and after plugging operation was assured by linear assessment of danger cross sections.(3)Based on ASME BPVC VIII-2 Standard,a three-dimensional model was established and finite element analysis was carried out with the elasticity-plasticity stress analysis method for the designed two-stage pressure plugging system.The stress and strain distribution of each component in plugging state was obtained.The numerical solutions of local maximum equivalent plastic strain was compared with the allowable values through standard calculation,the safety and rationality of the structure were verified.(4)The seal ability between the cup leather and the pipeline was analyzed emphatically,according to the pressure self-balance principle.The influence of the cup leather structure,operating differential pressure,weld reinforcement and pipe ovality on the sealing property of the leather cups was studied by using the finite element method to ensure the sealing safety of the key parts.