Oxygen depletion

[john j]

I just spent a few minutes doing a rough calculation.  I made a lot of assumptions, but if you had a steel cylinder about the size of Al 80, filled with 80ft3 of air, and it rusted uniformly inside, consuming 1 millimeter of the tank wall, you would reduce the available oxygen atoms in the gas by 0.00001%.  It's a rough calculation and I invite others to perform their own and compare.  Even if I'm off by as much as a few powers of 10, that still puts it at a tiny loss.  1000 times my estimation is still 0.01% loss.  When the tank is pressurized, there is such a huge number of oxygen atoms in there, that losing some to rust is insignificant.  The numers here are huge, like ten to the power of 27 oxygen atoms in there.