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Cliff,
There is no direct correlation between the MAWP
(maximum allowable working pressure) for a pressure vessel subjected to
internal pressure and the crush strength of the vessel. The potential failure
modes are just to different. To utilize an existing pressure vessel, you
would have to remove one of the heads and install standard "T" shaped internal
stiffeners and reweld the head. ABS rules for Building and Classing
Underwater Vehicle, Systems, and Hyperbaric Facilities" has a chapter on
Metallic Pressure Boundary Components. For a given hull diameter and
stiffener design, these equations can be used to calculate the maximum design
depth for a stiffened hull. Given that you have to cut a head off one of
these vessels to install stiffeners and the uncertainty of the steel
used in the vessel, most psubers choose to purchase pressure vessel plate steel
like A516-70, have it cut on a plasma flat bed cutter and then have it rolled
and TIG welded. This way, you know exactly what you have. As
mentioned before, it difficult to remove odors from process fluids that
impregnate the steel in used vessels . These days, most places that would
have a bed plasma cutter large enough to handle the plate steel required
for a hull also are set up with a large roll. The biggest differences
in external and internally pressurized pressure vessels is the pressure
derating that occurs on externally pressurized vessels due to even slight
out of roundness during fabrication. Eccentricity in internally
pressurized vessel in no big deal but for externally pressured vessels, it is
significant. The bottom line is that, even though initially it might
look like a fast way forward to use a used oil field pressure vessel, when
you get into the details of the design, most pushers, after a bit of research,
choose to have their hull rolled from plate.
Cliff
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