Ok, 4000 psi it is... but out of curiosity, how will this device be used - how do you plan to generate an external 4000 psi loading? 8000' deep in the ocean or something else? If it's some explosion, then you have to consider that only one side will be exposed, and you are not dealing with hydrostatic loading conditions.
In any case, Section VIII won't be of use here. But at only 2" ID, and 12" long, I wouldn't necesserely expect a buckling failure. I'd start at 1" thick and use FEA to see how it'll behave. What material are you planning on using?
jt