|
A tank of any sort, including a pressure hull, can't be judged by the
internal pressure it can hold.
If you take a tank, and add pressure to the inside to the point of failure,
the metal has "burst" and the tank blows out. That limit relates to the "burst"
threshold of the tank material, known as "yield"
(The AS 516-70 steel we are using has a limit of 70,000 psi)
External pressure is something VERY different. The metal doesn't burst, the
tank collapses. This has more to do with the shape of the tank and it's ability
to resist crushing.
Assuming there are no weak spots like seams, the pressure to crush a tank
is much less than the pressure required to burst a tank.
A simple way to demonstrate this difference would be to take a small tank
like a camp stove propane bottle and pump it up with a compressor. Put a 100 psi
charge in it, and it will hold.
Take that same tank with just one atmosphere of pressure in it , cap the
end, and put it in a chamber that is then pumped up to 100 psi. That little
propane tank will fold up like a beer can long before you reach the 100 psi.
That's why the design of your hull, and it's stiffeners, are so
crucial.
A square tank with flat surfaces can't take much external pressure, where a
curved tank of the same material can withstand a whole lot more, because the
pressure isn't concentrated on the center of a flat span, but rather is
transferred all around the curve. The strongest tank is a sphere. The pressure
is equal on all parts of the round surface. Frank D. Gas prices getting you down? Search AOL Autos for fuel-efficient used cars. |