DISCUSSION OF CONCEPTS 



Stacked-Ring Pressure Vessel 



The stacked-ring pressure vessel is a very simple concept'' which relies 

 for its strength on two separate sets of structural members — one set for 

 carrying the axial stresses, the other for carrying the circumferential stresses. 



Radial Restraint. The set of structural members for giving the vessel 

 strength to resist radial forces generated by hydrostatic pressure consists of a 

 series of rings stacked upon each other and a liner inserted inside these rings 

 for sealing the joints between individual rings. Since the rings are only required 

 to carry circumferential stresses, no welding or mechanical bolting is required 

 between individual rings to hold them together. The minimum dimensions of 

 a ring for a given vessel diameter are determined by two parameters: ( 1 ) the 

 hoop and radial stresses inside the ring and (2) the twisting moment imposed 

 on the ring by the radial hydrostatic pressure. The maximum dimensions of 

 a ring are on the other hand determined by the forging capability of U. S. 

 industry and the weight handling capability of the crane at the pressure vessel 

 assembly place. 



Axial Restraint. The set of structural members for giving the vessel 

 strength, to resist axial forces generated by hydrostatic pressure consists of the 

 two end closures and the end-closure-retaining tie rods, or a yoke. The end 

 closures and their tie rods (or a yoke) constitute a separate structural assembly 

 in no way interconnected with the stacked rings that resist the radial forces on 

 the vessel. The end closures are of the free-floating type, that is, they displace 

 relative to the stacked-ring assembly when internal hydrostatic pressure is 

 applied. The tie rods (or a yoke) holding the end closures together are of the 

 nonprestressed design, so that upon locking in place there is no axial tensile 

 stress in them prior to pressurization of the pressure vessel's interior. Upon 

 pressurization, the stress in the tie rods (or yoke) is proportional to the hydro- 

 static pressure inside the vessel, and the resulting elongation of the tie rods 

 (or yoke) permits the end closures to float freely inside the pressure vessel 

 liner enclosed by stacked rings. 



Although both the tie rods and the yoke provide axial restraint on the 

 end closures, there is a considerable difference in their effect on the design of 

 end closures because of the manner in which the restraint is imposed upon the 

 end closures under an axial thrust generated by the hydrostatic pressure inside 

 the vessel. The3;ofee type of restraint girds the vessel along its longitudinal 

 axis, thus retaining both pressure vessel end closures at the same time. Since 

 the yoke passes directly over the vessel end closures, and since during the 



