Recommendation. There is no requirement for thicl<, flat end closures 

 for large vessels, since with the continuous-yoke restraint system, a thin end 

 closure suffices. Investigations into economical end closures for large-diameter 

 vessels need to be concentrated on hemispherical shapes, particularly of layered, 

 welded construction. 



Seals 



High-pressure seals should be; 



1. Simple to assemble 



2. Self-energizing (sealing ability increases with pressure) 



3. Unlikely to jam 



4. Easy to install 



Although a host of proven seal designs is commercially available, none 

 of them are ideally suited to large-diameter vessels for high internal pressure. 

 Their shortcomings lie principally in their requirement for either a high precom- 

 pression or fine dimensional tolerances between seal surfaces for proper sealing. 

 Those seals that can tolerate rough sealing surfaces and loose dimensional 

 tolerances on the vessel flange require such a high precompression to seal effec- 

 tively at 10,000-psi hydrostatic pressure that they are inapplicable to high 

 pressure vessels of 10-foot diameter. Almost all the axial compression seals 

 (Figure A-10) fall in this category. Those seals, on the other hand, that do not 

 require axial precompression to seal properly at 10,000-psi hydrostatic pressure 

 require such fine finish and dimensional tolerances on the internal diameter of 

 the vessel that it cannot be satisfied with ordinary machining tolerances for 

 cylinder openings of 10 feet. Only by premium surface finishing techniques 

 and meticulous attention to diameter tolerances on the internal surface of the 

 vessel can those seals be made to work successfully at 10,000 psi. Most radial 

 compression seals fall into this category. 



Conclusions. It appears that no currently available sealing system is 

 ideally suited for 10-foot-diameter vessels with 10,000-psi hydrostatic pressure 

 where repeated removal of end closure is required. However, of the two classes 

 of seals available, the radial compression seals are more applicable. It is not 

 feasible to mechanically apply sufficient pretensioning to the end-closure 

 restraint system to insure sufficient compression of axial seals to seal at 10,000- 

 psi operational pressure unless the very cumbersome thermal shrink technique 

 is applied. 



58 



