Tiiird, the use of tie rods and retaining flanges for restraining the 

 hemispherical end closure proved to be feasible. As anticipated, this restraint 

 was easy to operate in opening and closing the vessel. However, from the 

 structural viewpoint, this restraint left much to be desired as the stress level in 

 the structural components was higher than calculated. The high level resulted 

 from stress concentrations introduced by the geometry as well as by the 

 machining tolerances. This was shown quite clearly by the failure of tie rods 

 and segmented retaining flanges at hydrostatic pressures considerably lower 

 than those for the stacked rings. The stress concentration in the tie rods 

 appeared to have a magnitude of 3 based on the comparison of hydrostatic 

 pressure, at which tie rods and stacked rings failed. In view of this, it would 

 appear that in order for tie-rod restraint to operate properly, the nominal 

 stress level in the tie rods would have to be decreased by a factor of 3 through 

 enlargement of the tie-rod diameter, or the tie-rod head would have to be 

 redesigned so that the stress raiser effect is considerably decreased. 



The same applies to the hemispherical end closure that failed at 

 approximately one-third of its predicted failure pressure. There the problem 

 can also be resolved either by lowering the average stress level in the end closure 

 by a factor of 3 through increase in thickness of the hemisphere, or the transition 

 zone between the end-closure flange and the hemisphere would have to be 

 redesigned. In either case, it appears that the design of the hemispherical end 

 closure with the tie-rod restraint system requires more than nominal engineering 

 stress calculations, and that the weight of this system would have to be increased 

 considerably. 



Fourth, in view of the previous discussion, it appears that the tie-rod 

 restraint system with hemispherical end closures, even though proven to be 

 successful operationally, leaves a lot to be desired from the structural viewpoint. 

 It appears, therefore, that the tie-rod restraint system with which the stacked- 

 ring and segmented-wall vessel designs were equipped is less desirable and 

 structurally safe than the continuous-yoke system with bearing blocks and flat 

 end closures discussed earlier in this report. 



Fifth, the radial seals utilized on the end closures of the stacked-ring 

 and segmented-wall vessel designs performed satisfactorily without any leakage 

 during all of the hydrostatic tests to which the acrylic models were subjected. 

 For higher pressures, such as those that would be encountered in the steel 

 vessels, the self-energizing radial seals experimented with in this study should 

 be utilized (Appendix C). Thus, it appears that radial seal designs experimented 

 with in this study adequately meet the operational needs of large vessels with 

 10,000-psi or higher operational pressure. 



39 



