Steel tanks

[scuba6559]

Question - why is it that many stell tanks have only like a 2250 PSI rating vs aluminum at 3000 psi? Steel is supposed to be stronger - so WHY are they LP vs aluminum?
Confused on this!

 

[roakey]

Two answers to your question. They're a lot of HP steels too that operate at 3500psi. You're right, steel is stronger. If you cut steel and AL cylinders in half, you'd find that the ALs are about 1/3" in thickness whereas the steels are only about 1/8" in thickness because, as you pointed out, steel is stronger.

Also LP steels are typically 2400psi (+10%), not 2250. The old 72s were commonly 2250 (+10%).

Roak

 

[Rick Murchison]

In general, a Scuba tank is easiest to handle in the water if it's pretty close to neutrally buoyant or a few pounds negative. The higher the pressure, the thicker the walls and the less water displaced per pound of tank, therefore the more negatively buoyant the tank. LP steels have [in my opinion] excellent buoyancy characteristics.
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An easy visual on the strength issue is to stand a steel 72 and an aluminum 80 side by side - the aluminum 80 is visibly larger, but the steel 72 has a larger interior volume (that is, when both tanks are filled to the same pressure, the 72 has more gas than the 80 in it)... the difference is in the thickness of the metal.
Rick