This will be a good one for American engineers.
But before I get to the equation? Some info....

> Make a solid propellant rocket-tube, 12 inches in diameter.

> The rocket-tube cylinder walls will be 1/20th of an inch thick.

> The tensile strength of the steel alloy would be 90,000 PSI

> And the internal combustion pressure may soar to say 80 atmospheres
[1200 PSI, more or less]

The standard equation I found for finding the "bursting/rupturing value" for cylinders is? >>>>

Internal pressure [PSI] x diameter of cylinder [Inches]
divided by tensile strength of material [PSI] x (4) x thickness of cylinder
walls [inches, or fraction thereof].

1200 PSI x (12 inches diameter) / 4 x (90,000 PSI) x (1/20th of an inch)

= 14,400 (pounds/inch) / 18,000 (pounds/inch).

18,000 (pounds/inch) is supposed to be the material strength at its given
thickness.
14,400 (pounds/inch) is supposed to be the internal tension force against those thin walls.
I think a variable or a constant is missing.

Because?...Because I seriously doubt that even high-grade steel alloy
cylinders, 12 inches in diameter, with cylinder walls ONLY one-twentieth of an inch thick would be able to withstand internal pressures of 80 atmospheres.

Check to see how thick the walls of scuba tanks are, if you don't believe me.
Don't you agree?

Jacob