| Undersea oil& gas pipeline is a key facility for the development of offshore oil and gas resources. The sealing with connection of flange and lens gasket is one of the key links in the connection of underwater pipelines. Due to it’s working environment between internal medium of high temperature and high pressure and external sea water of low temperature,lens gaskets are always in a high-stress state, which cause it easy to leakage and resulting in seal failure. Besides, effects of ocean currents, sediment and disturbance on pipes caused by activities of fish shoals and so on will produce bend moment on the pipeline, which will cause effects on the sealing with connection of flange and lens gasket in deep water pipeline.Therefore, it is significant to consider the leakage effect of working environment on the sealing with connection of flange and lens gasket.Firstly, the force analysis model was established in this paper according to the 6in connection joint for flange lens gasket used in deep water pipeline. And the calculation formula of the contact width and maximum contact pressure on the lens gasket is derived.Finite element simulation software is used to analyze the nonlinear contact of the flange lens gasket, the distribution of contact stress and deformation of the flange lens gasket are obtained, According to the fluid slit flow theory, the leakage rate model of the sealing surface and the rough surface is established.The contact sealing mechanism of the flange lens gasket from the micro level is analyzed in this paper, and a mechanical model for the contact stress of the micro convex bodies on the rough surface is established. And according to this model,the elastic and plastic contact mechanics model of rough surface based on statistical features is established,and the mathematical relationship between the average separation distance and the contact area and the contact pressure is derived. Combined with the leakage rate model of rough sealing surface,the relationship between the contact pressure and the leakage rate is studied and the sealing condition of the lens gasket is put forward in this paper.Simulation analysis method was used to analyze the influence on the contact stress of the lens gasket caused by temperature field distribution of the connection joint of flange lens gasket and coupling effect between temperature and structure. Considering the long time working under high temperature and high pressure, the influence of creep on the sealing connection of lens gasket was analyzed in this paper, and the rules of influence with time of creep on the contact stress of the lens gasket was obtained.Through Co-simulation with ANSYS and Fluent, the impact force generated by the flow of water flow around the suspended span pipeline is analyzed, translate into the bending moment applied to the flange lens gasket joint, the influence of bending moment applied on seal leakage of the flange lens gasket was analyzed.Finally, the experiment of lens gasket seal was designed, the formula of contact width of lens gasket was verified by experiment. The seal condition of the lens gasket with different roughness is verified,through theoretical contact stresses are compared with measured axial pressure and verify the lens gasket connection leakage model is correct. At the same time,according to the experimental results, the influence of temperature and flow field of lens gasket seal connection was analyzed, the correctness of the theory was verify indirectly. |
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