SCINFERNL
+1y
Don't do it !!
Beer kegs are used to hold fluid, not air.
When in use, there is approximately 12-15 PSI CO2 in the keg.
If a beer keg should fail, the fluid will absorb the impact of the failure.
If it should fail being used for air storage, it will have nothing to absorb the failure and you will have aluminum shrapnel due to the thin aluminum that the keg is made from...
Steel is malleable, and therefore stretches. Aluminum is far less malleable and tends to fracture.