cleaning tanks using acid wash?

[Brutus23]

Hello all,

I'm new here and I am wondering if anyone has tried and/or heard of cleaning tanks using an acid wash (50/50 Muriatic- Water) solution?
Thanks for any input

 

[luvdiving]

The only way I know of is to "tumble" them with an abrasive inside the tank, then rinse very well.

It seems that the acid might leave a residue?:boom:

 

[captain]

I have done this several times over the years on my old steel 72's
You have to protect the galvanizing on the exterior from the acid solution. Neutralize the acid with baking soda, rinse and dry the inside as fast as possible.

Captain

 

[Genesis]

Muriatic is way, way too strong and not what you want chemically anyway.

If you're going to do this use Phosphoric acid (e.g. "ospho"), cut fairly heavily.

It will EVENTUALLY eat zinc exterior galvanizing, but the inside isn't galvanized, and for galv in good condiition it would take hours to remove it. Now for galv that's trashed, that's another matter, but if its THAT bad you want the powder and gunk its turned to OFF anyway so you can put some ZRC on clean metal, and the ospho will do it for you.

One warning - you need to rinse this stuff out REAL WELL, and beware flash rust. The trick is to either use Nitrogen to dry the tank (no oxygen, no rust) or if you use air, use SCUBA AIR (very dry) and make the last rinse EXTREMELY HOT water, so the tank is nice and hot and thus dries very quickly. Oh, and don't be shy about the air either - invert the tank, take a reg, remove the second stage, stick that LP hose up in there and let 'er rip IMMEDIATELY when you're done. Not wide open, but pretty heavy flow. I use about 1/3rd of an AL80 drying a steel this way and I get NO rust due to the speed of the drying, and the tank is bone dry within 1-2 minutes.

DO NOT use this method (acid wash) on aluminum tanks.

EVER.

YOU WILL DESTROY AN ALUMINUM TANK WITH THIS METHOD!

 

[Brutus23]

Good evening,

Just seen the update on this thread and wanted to say thanks for the tips.

Safe Diving,
Brutus

 

[pescador775]

I prefer the phosphoric. The muriatic acid will eat rust but is difficult to control. If used, the soda rinse is a must. BTW, where can one buy ortho phosphoric acid?

As Genesis says, muriatic will eat holes in aluminum. Fizz, fizz.

Almost forgot, acid causing hydrogen embrittlement but takes a long time and mainly applies to chrome plating. Don't plate your tank.

Pesky

 

[Genesis]

is readily available at Home Depot in gallon jugs; it is sold for rust removal and works quite well.

It is green in color and appears to have a small amount of surfactant (detergent) in their formula, although that is not mentioned on the label - only that it contains phosphoric acid.

Beware that you must get it ALL out of the tank, because surfactants are really ugly things to be inhaling (far worse than the acid!) Do not just put water in the tank to rinse it - instead, rig up the necessary adapters to stick a hose INSIDE the tank and blast the interior with a flood of clean water; this provides lots of agitation and insures you get ALL of the stuff out. Don't be stingy with the rinse process!

Also, rubber gloves and eye protection are mandatory when working with stuff like this; getting it in your eyes can ruin your whole day and a lot more, and it will burn the skin.

"Neat" (uncut) is probably stronger than you need for any "rescuable" tank inside. I typically cut it about 4:1 or so with water (add acid to water, not the other way around!) for light flash rust and for external corrosion may use it up to full strength; be aware that if you've got a galvanized tank and need to "dip" it for this purpose you will probably need to use ZRC or something similar to protect the metal when you're done, as if the galvanizing is that bad it'll need help.

Phosphoric acid's beauty is that it pretty much leaves "good" metal alone, but is extremely aggressive in removing oxides (rust). The problem with muriatic acid (Hydrochloric) is that it is way too aggressive towards good metal and its almost impossible to control for that reason, with a high probability of damage to the base metal which may not be immediately obvious on inspection. Phosphoric acid will produce a very thin black oxide layer which is actually protective if left on for a bit longer than necessary, although I don't go that far because at some point you run some risk for hydrogen embrittlement, which is bad news - and I don't feel like finding out exactly where that line is.

Again, NEVER USE ANY ACIDIC CLEANER ON AN ALUMINUM TANK, inside or out!

 

[Ontario Diver]

Of course, if you clean out the tank using acid or tumbling the tank; you have altered the structure of the tank and DOT/TC rules require that you re-hydro the tank before use....

but you already knew that

 

[Bootybreath]

Hi there...

Has Anybody tried using citric acid for removing flash rust?
Well I have and works a dream...only it takes me 2 mins to rinse it out and by the time I dry it ( using a blast of scuba air) it almost instantly develops a light flash rust again...

Any ideas from old seadogs please ??
Oh and my tanks are seeing high FO2

Global recomends a last rinse using formula O which is a diethanolamine compound which I found to be highly cancerous even in miniscule ammounts.What the hell is goin on ere???Another diving paradox?

 

[DA Aquamaster]

I would not bother removing flash rust at all unless it begins to get quite prolific and/or has some area where the rust starts to look a little thicker.

in that case however, you are far better off having the tank tumbled. Tumbling removes rust from the highest spots downward so eventually when the rust has been removed, any pits in the surface of the tank will be clearly evident as they will still contain rust in the bottom of the pit.

This is not the case with an acid where the rust is removed from the surface of the metal with no real regard for the topography of the surface. In the case of a tank cleaned with acid a pit is much harder to see as it is usually much cleaner in the bottom and matches the color of the surrounding surface. A pit really should be grounds for condemning the tank and you don't want to miss one if it is present.