Best chemical rust remover for inside a tank

[in_cavediver]

OK, I have never really needed to deal with significant rust removal on any tanks but with the gift of a pair of steel 72's, I want to remove the flash rust to look for any pitting.

I have heard phosphoric acid is a good choice followed by copious rinsing and then o2 cleaning to remove any acid residue.

I'd like to do the quick rust check prior to sending them for hydro to catch an obvious flaw. generally speaking - they are in excellent condition considering they are older than I am. (hydros in 1970)

Anything better to use?

[captain]

You can also use diluted hydrocloric (muratic acid) available at Home Depot,Lowes, etc just as well. Keep it away from the galvanize on the outside. Flash rust shouldn't hide pitting deep enough to kill a tank. I have 10 72 between 50 and 35 years old that I rarely tumble and they pass every time. Just be sure the hydro station follows PST D100 procedure. I know of cases where the hydro shop bought cylinders for a customer because they didn't follow it and failed good cylinders.

[in_cavediver]

Originally Posted by captain

You can also use diluted hydrocloric (muratic acid) available at Home Depot,Lowes, etc just as well. Keep it away from the galvanize on the outside. Flash rust shouldn't hide pitting deep enough to kill a tank. I have 10 72 between 50 and 35 years old that I rarely tumble and they pass every time. Just be sure the hydro station follows PST D100 procedure. I know of cases where the hydro shop bought cylinders for a customer because they didn't follow it and failed good cylinders.

Thanks!

[cummings66]

Use Phosphoric acid, it's the best way to do it. It won't damage the good steel like you can with muriatic acid. If it's just flash rust you can use a very minor amount, start with something like 2% and see how it goes. You'll need about the same amount you would use with a cleaner.

Phosphoric acid also gets rid of oils. To get rid of it, use a VERY hot water rinse after the rolling around bit. Roll it around a bit and then look into the cylinder. Might take 5 minutes or 15, but don't go longer than 15. When done you should find it looks better than ever before. You will probably get black and if so just keep at it with the acid mix and you will eventually get rid of it too. The Phosphoric acid will make the rust turn black as it's getting rid of it. If it's heavily rusted you could try a 4 or 6% mix and then drop down. Hot water rinse when done gets rid of the phosphate coating.

[cummings66]

Here's the link to the receipe for the mixes I use. The thread by the way has some very good information in it.

The Deco Stop