>because these pressures are mostly
>balanced with only pressure differences
>of around 100 psi
John says:
"Nope. If you have ten walls, each of which is sized for a 100 psi differential, that is the exact thickness needed for a 1000 psi differential in a single wall. If the outer shells are increasingly larger to hold more volume, they need to be correspondingly thicker to handle the additional stresses."

Hmm, well that's not what I was talking about, but it's interesting & it's a topic I have wondered about before. It's true that the outer walls would be "correspondingly thicker to handle the additional stresses." A cylinder which was 6" in diameter could have a thinner wall to hold 100 psi as compared to a cylinder 12" in diameter- that would seem to be the reason why someone would *even* think of doing these multiple walls- though generally speaking, the added complexity and cost would seem to prohibit it.

>BUT a bundle of pipes welded together
>with a hollow center which also holds
>pressure should hold more volume at
>higher pressure than a single walled
>large pipe (cylindrical tank
John says:
"Also doesn't hold, because for it to contain any pressure in the center, the pipes on the outside will have additional stress trying to pull them apart, so they will need to be thickened."

Let's try an extreme example, say you had 20 cylindrical tanks which were strong enough to hold 1000 psi. Arrange them so they form cylinder wall and weld them together. And put a top and a bottom on it. Have center chamber able to hold 100 psi. Compare this to the 20 high pressure tanks with an additional separate tank which can hold the 100 psi of same volume.
Or another extreme example- this time limiting the dimension to two. Imagine a pipe a mile tall. Now you would want the pipe thicker at the bottom in order to support the weight above and any sheer forces and thinner at top (less weight). And keeping to the subject, "for whatever reason" this pipe will be pressurized, having more pressure at the bottom section than the top sections- say, 5 sections with 500, 400, 300, 200, 100 psi.
The bulkhead between sections would need to be able to hold 100 psi, so instead of the top needing to hold 500 psi, it could be designed to hold 100.
-gb