retaining ring 



sliding seal ring with 

 self-energizing radial seal 



convex end closure 



of modular construction 



(orange peel shaped polygons) 



stacked rings 



split nut l<eeper 



assembly to carry tensile stresses, 

 a concept is required that would 

 pernnit the hemispherical end 

 closure to carry only compressive 

 stresses. If the end-closure modu- 

 lar assemblies do not have to 

 carry any tensile stresses, the 

 capability of the closure to retain 

 internal hydrostatic pressure is 

 not diminished in any way by the 

 presence of the joints between the 

 individual spherical polygon 

 modules, particularly since a thin 

 liner makes the joints watertight. 

 In such a case, the bolted joints 

 between the individual modules 

 serve only to hold them together 

 for handling of the end closure by 

 a hoist during the opening and 

 closing of the pressure vessel. To 

 achieve this, a concept has been 

 proposed (Figure 8) which trans- 

 forms tensile stresses of the end closure to compressive stresses by substituting 

 a convex hemispherical end closure (as seen from the inside) for a concave 

 one. In this position, the end closure acts like a dome under external hydro- 

 static pressure and the axial force acting on it is absorbed by the retaining 

 ring pressing against its base. 



Besides the above-mentioned advantages accruing from the use of 

 convex (as the pressurizing medium "sees" it) end closures, there are also 

 some disadvantages. The major disadvantage is the decrease of internal usable 

 space in the pressure vessel, as the convex hemispherical end closures take up 

 one diameter of internal length. This constitutes a severe weight, and cost 

 penalty, if the pressure vessel must be lengthened to compensate for the loss 

 of the internal space. But for pressure vessels of such large diameter that 

 fabrication of monolithic hemispherical end closures is impossible, the space 

 taken up by the convex end closures is more than compensated for by the 

 fact that without the use of a modular end closure, a vessel of such a large 

 diameter would not be feasible at all. 



Assembly. The assembly of the stacked-ring pressure vessel from many 

 structural components without recourse to welding permits the vessel to be 

 transported to its installation site in the disassembled state, and to be assembled 



Figures. Typical segnnented-clonne 

 end closure. 



12 



