on site with tine lioists or cranes used for the removal of end closures or 

 placennent of test objects during the regular operation of the pressure vessel 

 after assembly. Because of this, even the heaviest stacked-ring pressure vessel 

 component weighs less than 20% of the total pressure vessel weight. The 

 economies accruing from transporting and placing such a pressure vessel are 

 considerable. Instead of having to transport the complete pressure vessel by 

 barge or ship, when its assembled weight is over 250 tons, the vessel compo- 

 nents can be shipped to its permanent location by rail or truck. At the 

 permanent location, the many vessel components are then easily placed 

 sequentially into the vessel pit without recourse to special hoisting equipment. 

 For the assembly of a stacked-ring pressure vessel, only an overhead crane is 

 required that later, after the assembly is completed, becomes part of the pres- 

 sure test facility. Pressure vessels that must be lowered fully assembled into a 

 pit require a group of specialized hoists and cranes. This requirement becomes 

 more stringent when the weight of the assembly exceeds 250 tons. This 

 weight is generally exceeded by pressure vessels 10 feet in diameter or larger, 

 with an operational pressure of 13,500 psi. 



Inspection and Safety. The additional desirable features of a stacked- 

 ring pressure vessel design during its operational life are the ease of inspection 

 of the load-carrying structural members, and the ease with which they can be 

 individually replaced in case of actual or incipient failure. In the stacked-ring 

 pressure vessel, every component, except the liner, is removable and replaceable 

 without cutting or welding. This ease of maintenance is bound to save many 

 dollars over the life of the vessel, which because of this component replace- 

 ability feature, is much longer than for monolithic vessels. The inspection of 

 individual structural components for incipient cracks is relatively easy, as the 

 individual tie rods, end closures, and retaining rings are easily accessible for 

 inspection on all of their surfaces. The stacked rings are accessible only from 

 the external surface, but because of their homogeneity and isotropic character, 

 accessibility from one surface is sufficient for ultrasonic or radiographic 

 investigation to locate incipient cracks. 



There is one further facet of vessel operation that is not often discussed, 

 but merits further investigation: the stacked-ring design is safer than multi- 

 layer or unilayer design. Although pressure vessels are designed with safety 

 factors to prevent failure in service under load, they nevertheless do fail once 

 in a while; when failure occurs, damage to equipment and injury to personnel 

 is extensive. The safety feature of stacked-ring pressure vessel design lies in 

 the separateness of each load-carrying structural member. Since it is quite 

 unlikely that an incipient crack would become self-propagating in more than 

 one structural member at the same time, the internal hydrostatic pressure will 



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