be relieved by failure of only one ring member. Thus the failure of any of 

 the individual stacked rings is a local failure, and not a general catastrophic 

 failure. The same applies in a limited measure to the end-closure tie rods. 

 If failure in one of the rods occurs, then only one or two more rods will fail 

 with it before the pressure inside the pressure vessel is relieved. Because of 

 this, the damage to the vessel, as well as to the facility, will be slight and the 

 vessel can be easily repaired. The failure of the end closure, or of the end- 

 closure retaining ring, needless to say, will be just as disastrous as in a 

 multilayer or unilayer vessel, but much easier to repair than in such vessels. 

 The top closure is replaceable in all types of pressure vessels, but the retaining 

 flanges and the bottom closure are not. The stacked-ring pressure vessel does 

 permit, however, the replacement of these structural components also. 



Segmented-Wall Pressure Vessel 



Although the stacked-ring pressure vessel concept alleviates most of 

 the fabrication and handling problems associated with large monolithic or 

 layered high internal pressure vessels, it does not eliminate them completely. 

 The limitation on the diameter of the vessel for stacked-ring vessel design 

 still remains the forging capability of the steel industry. To be sure, this 

 limitation is less severe for forging rings than for forging monolithic cylinders, 

 but it is nevertheless severe enough to make the stacked-ring construction 

 somewhat less than an optimum solution to the problem of large pressure 

 vessel construction. The sizes of forged rings that industry will produce in 

 the near future will, of course, increase from year to year, but even so it is 

 doubtful whether thick-walled rings of larger than 20-foot diameter and 1-foot 

 thickness will be feasible to fabricate. Consequently the segmented-wall module 

 design has been proposed for the fabrication of high-pressure vessels with 

 diameters beyond the capability of the stacked-ring fabrication technique.^ 



The basic attractiveness of the segmented-wall module design lies in 

 its reliance on small segmentlike modules for the construction of the cylin- 

 drical vessel wall. The segments, held together by shear pins extending the 

 length of the cylinder, permit the assembly of very large diameter thick-walled 

 pressure vessels from relatively small interchangeable structural modules 

 (Figure 9) that are easy to fabricate, transport, and assemble at the pressure 

 vessel installation site. In this type of design as with the stacked-ring design, 

 the axial loads on the end closure are carried by a series of tie rods or by an 

 external yoke. One further advantage of the segmented-wall design is that a 

 modular design can also be applied to the end-closure retaining rings, if a 

 tie-rod end-closure restraint system is used, eliminating size and weight of the 

 end closure as the limitation on the maximum diameter of vessel that could 



14 



