The seals associated with the free-floating end closures generally rely 

 for their sealing action on radial compression of the seal body between the 

 end closure and the interior of the vessel body. The design ingenuity of such 

 seals lies primarily in the provision for sealing the increasingly wider gap between 

 the end closure and the interior of the vessel as the vessel expands radially under 

 the internal hydrostatic pressure. Without provision for this gap during the 

 pressurization of the vessel, the seal will extrude into the gap and out of the 

 vessel, losing all of its sealing ability. For this discussion, it is obvious that an 

 ordinary 0-ring under radial compression would retain its sealing ability under 

 very low hydrostatic pressure only, as the presence of a gap of several thousands 

 of an inch would make it impossible to retain pressures of even 2,000-to-3,000-psi 

 magnitude. Obviously, other approaches to the seal design besides an ordinary 

 0-ring in radial compression had to be sought and evaluated. 



The seal designs that were evaluated in the seal-test vessel (Figure B-2) 

 were the wedge ring seal, 0-ring with continuous antiextrusion wedge ring, 

 0-ring with a split antiextrusion wedge ring, and twin 0-ring seal in a self-energized 

 elastic follower ring (Figure B-3). Each of these seal designs was thought to be 

 promising and worthy of investigation; the most desirable one was to be selected 

 on the basis of its performance under hydrostatic pressure in the vessel. 



Figure B-2. Location of seals 

 in the pressure 

 vessel during their 

 evaluation under 

 hydrostatic pressure. 



65 



