thick steel liner 



glass fiber epoxy laminate 



decreases the pressure-containing capability of such a vessel. When one considers 

 that in a multilayer lining ( 1 ) some layers are already in compression while 

 others are in tension, and (2) that the amount of prestress to be expected from 

 very heavy overwrap is not a precisely predictable quantity, it must be concluded 

 that the interaction between the strains in the multilayer liner and the overwrap 

 will be unpredictable. 



The cost of a steel— fiber glass laminate vessel has been estimated to be 

 in the $5 to $10 per pound range. The rather high cost of such a construction 

 can be traced to the fact that there are two different fabrication processes 

 involved, each one of them requiring a different fabricator. Each fabricator's 

 profits, overhead, and transportation charges will make such a tank more 

 expensive than it would be if only one fabricator was involved. Furthermore, 

 quality glass-fiber— epoxy laminate is an expensive material, justifiable only 



where rigidity or weight reduction 

 is desirable. When to the already 

 high cost is added the premium 

 that the fabricator of the overwrap 

 will demand to cover uncertainties 

 of the process when applied to a 

 large vessel, the price of a pressure 

 vessel constructed in this manner 

 probably becomes uncompetitive 

 with other fabrication processes. 



The composite vessel 

 consisting of a compressed steel 

 liner with a pretensioned glass- 

 fiber— epoxy laminate overwrap 

 (Figure A-7) can be fabricated 

 today if modifications are made 

 to existing glass-fiber wrapping 

 and curing facilities. The 10- foot 

 internal diameter is already pushing 

 existing facilities to the limit, and 

 if there were a requirement for a 

 40- foot-diameter vessel, it would 

 necessitate the erection of new 

 fabrication facilities located in a 

 place from where the vessel could 

 be transported by ship to its loca- 

 tion in some seashore installation. 



\ /////// ff; 



W^ 



unpressurized pressurized 

 Distribution of Hoop Stress 



Figure A-7. Pretensioned-glass-fiber— epoxy- 

 laminate concept of pressure 

 vessel construction. 



54 



