calculation of stresses in the flat end closure and bearing pad are rather routine; 

 in the case of tie-rod restraint the calculations are difficult because there are 

 stress concentrations whose magnitude nnust be both analytically and experi- 

 mentally determined during the design phase. 



Because ( 1 ) very little was known about design and operation of vessels 

 with tie-rod end restraints at the beginning of this exploratory study while the 

 design of yoke restraints and associated end closures was quite well understood, 

 and (2) the application of yoke restraint severely handicaps the access to vessels' 

 interiors and slows down the use of such vessels for hydrostatic tests, it was 

 decided to explore experimentally only the tie-rod restraint system. (The 

 tie-rod restraint system promises to alleviate those difficulties.) It was felt that 

 by exploring it experimentally ( 1 ) some design and stress distribution data 

 would be generated where none was available before, and (2) some experience 

 would be gained in the operation of the tie-rod restraint system that would 

 permit rational comparison between the operational desirabilities of tie-rod- 

 and yoke-restrained systems. After selection of the tie-rod restraint for 

 investigation within the objective and scope of this exploratory study, no 

 further discussion of the yoke-restraint subsystem will be made until the section 

 on conclusions and recommendations. 



Construction. The fact that the stacked-ring pressure vessel relies for 

 its strength not on any welds, but on isotropic homogeneous forgings permits 

 the use of high-strength steel alloys for which the welding techniques have not 

 yet been developed, or are only in the development stage. Specifically speaking, 

 it permits the construction of a pressure vessel from structural components 

 forged from maraging steels with yield points of up to 250,000 psi. 



Although the stacked-ring pressure vessel design and fabrication technique 

 permits the assembly of rather large high-pressure-capacity pressure vessels 

 from smaller structural components, there is a limit to how large a pressure 

 vessel can be assembled in such a manner. This limit on the size of a stacked-ring 

 pressure vessel is determined by the forging capability of the steel industry. 

 The largest structural components in a stacked-ring pressure vessel are the 

 retaining rings and the end closures; therefore the maximum size of these com- 

 ponents that can be forged by the steel industry will determine the maximum 

 diameter and pressure capability of a stacked-ring pressure vessel. To determine 

 the largest retaining ring or end closure the industry can forge at any given date 

 is almost impossible without a detailed survey of each forging press in the world. 

 A limited inquiry has shown, however, that the steel industry can easily forge 

 structural components of such size as to permit the assembly of pressure vessels 

 with an operational pressure of about 13,500 psi, a 10-foot internal diameter, 

 and a 30-to-40-foot length. 



