How did optimisation reduce contact stresses by 48%? Read on...
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A project was undertaken to investigate the design & optimisation of a metallic seal ring as part of an end cap for a 140 tonne
pressure vessel (shown below). A vessel loading condition of 4483 bar (65,000 psi) internal pressure was stipulated. The design of a metallic seal of 762 mm (30”) bore diameter provided a challenging task, due to the extremely high pressure application.
A detailed Finite Element Analysis (FEA) was carried out to evaluate the seal and the initial conclusion was that it required complete re-design. In this work, analysis and interpretation was used to establish the modelling method for the seal. A 15 degree slice FEA model that was developed for seal optimisation which contained elasto-plastic material response, frictional contact modelling, advanced pressure field application and thermal modelling. A von Mises stress plot is shown below at 65,000 psi.
To maintain sealing contact pressure, the seal has to overcome differential radial movement between the vessel and the end cap during pressure loading. The optimisation process developed a novel profiled seal contact that reduced contact stresses by 48%, eliminating seat damage occurring during pressure loadings.
Structural deformations cause the seal contact point to shift, providing the opportunity for liquid to penetrate up to the contact point. Limitations were recognised within the FE software, which allowed unidirectional pressure penetration only. To overcome this limitation, a bespoke user subroutine was written to revise the contact algorithms within the Abaqus FE program. This enabled ‘contact pressure zones’ to correctly progress and (for the first time) regress in real time, with seal and seat movements. Video of seal ring shown below.
The paper will be presented at the 2014 SCC (Rhode Island),
Hope to see you there!
Adam Slee
