In order to keep the time required to open and close the vessel within 

 practical limits, independent sealing of each tank is precluded. Closure would 

 have to be provided by a common end closure, or closures. 



Desirable Features 



1. By using several vessels separated by a small, fluid-filled annular space, the 

 wall thickness of the individual shells is reduced. Fabrication operations 

 including forging, rolling, welding, etc., are less expensive for the thinner vessels. 



2. Individual vessels could be fabricated elsewhere and assembled at the site. 

 However, for such on-site assembly, it is desirable to reduce welding operations 

 to a minimum. 



3. The inner vessel could be constructed of a corrosion-resistant steel while 

 other vessels could be of different material. 



4. Compared with the multilayer construction, the separated layer concept 

 provides more flexibility in controlling the stresses in the vessel. If the annular 

 space pressurization proceeds simultaneously with the test chamber pressuri- 

 zation, it becomes unnecessary to obtain large compressive hoop stresses near 

 the interior by prestressing. 



Undesirable Features 



1. Complicated systems for initial or continuous pressurization of the annular 

 fluid spaces are required. 



2. Differences in strains between individual vessels (for example, unequal axial 

 shortening) could lead to difficulties in sealing. 



3. Dynamic behavior of a separated layer vessel resulting from implosion of a 

 test object or other causes would require careful analysis. 



4. Whereas in a monobloc or multilayer shell the plastic flow of the interior 

 portion of the shell is restrained by the elastic outer portions until yield has 

 proceeded through the shell wall, the behavior of a separated layer vessel at 

 pressures above that required to cause yielding of the interior tank has not 

 been established. For instance, the compressibility of the fluid between tanks 

 might allow the inner vessel to burst with little restraint being offered by the 

 outer layers. Hence, the factor of safety against burst would not be significantly 

 larger than the factor of safety against initial yielding. 



5. Sudden depressurization of the test volume could lead to buckling of the 

 vessel, so that this factor would require consideration in design of the inner 

 vessel. This would require thorough study of the annular space pressures 

 resulting from depressurization of the test chamber. 



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