Old Fire Extinguisher as air tank

[cjkersh]

I saw a thread on here which is now closed that warned of the dangers of welding up an old fire extinguisher tank and using it for air.

Here are some thoughts. Some of these old tanks are rated for 1500 PSI. They also have 1" NPT fittings on top so there should be no need for welding of any kind nor is that a good idea. Finally a drain valve for moisture could easily be included in the plumbing and the tank mounted head down to allow it to drain.

I beleive that these heavy tanks are one of the safest tanks you will ever use if you can find one, however they are extremely heavy. You would be waiting a lifetime for one to rust through.

I'm wondering if these heavy older tanks were considered in the previous threads. Specifically I'm referring to older CO2 tanks rated at 1500 PSI. They get retired frequently and where build to last many lifetimes.

I work at a facility that does the testing certification and recharging of extinguisher tanks. Some of the older best built tanks of all time are retired because they are not current spec. In my opinion that in no way makes them dangerous quite the contrary they are more apt to pass the 1500 PSI test we put them through than most.

Obviously I'm anticipating that if these were converted to air it would be the 125-175 psi variety for auto / shop use.

 

[gr2vessels]

You are right as long as you use the API 579 correctly for re-rating.
Cheers,
gr2vessels

 

[chicopee]

It could be that cyclic loading of the improvised air tanks may have something to do for not allowing conversions. Also approved air tanks are build in accordance with NB unfired pressure vessel code, can it be said the same thing with these old fire extinguisher tanks?