What if the majority of the components of the vessel are radically different from the standard components of and ASME Section VIII vessel? How is initial section sizing determined? For the high-pressure vessel featured in this case study, FEA was an integral tool in finding a starting point for component sizing and geometry as well as certifying the final design.
It is common for pressure vessels to have non-standard geometry that requires ASME Section VIII, Division 2 analysis. For example, maybe a cone requires an angle that exceeds standard code limits. General sizing of the member can be determined using design guidelines and the component can be shown to meet code allowables using FEA.
Figure 1: Original cryogenic ASME pressure vessel CAD geometry
The client provided the starting point geometry in the form of a 3D parasolid geometry model. This model was then converted into a surface model suitable for FEA plate meshing.
Figure 2: Final vessel design as a collection of surfaces ready for FEA plate meshing
The geometry shown above is the final sheet geometry as created in Femap. This process requires some engineering since the idealization from 3D to sheet geometry is not intuitive and some adjustments must be made to account for engineering principles of pressure vessel design.
Figure 3: An exaggerated deformation of the vessel under high pressure loading
The FEA model was exercised under positive and negative pressures to meet the ASME Section VIII, Division 2 requirements for stress and buckling.
Figure 4: Plate element mesh with ASME Section VIII, Division 2 stress intensity contour.
The model was interrogated per ASME Section VIII, Division 2 specifications for stress intensity and membrane stresses. The stress results were compared against ASME stress allowables at the cryogenic temperatures.