Tank Rust Removal Aternatives to Tumble

[ScubaLew]

Has anyone on the board have any DIY alternatives to tumbling for removing rust from a steel tank? It's out of hydro and I took it to the LDS for VIP and

Their opinion was to buy a new tank since the cost of tumbling and a hydro was close half the cost of a brand new aluminum tank and that because of the age of the tank, it was not worth the expense.

I personally think the tank still has a lot of use, but don't want to spring for the $ 35 cost of tumbling and then it would fail hydro.

Any suggestions?

 

[detroit diver]

I just ordered a bottle of this for another project, but it might work for you. Not a whole lot cheaper, but it would last quite a while:

http://www.ultraoneusa.com/shopdisplayproducts.asp?id=10&cat=Safest+Rust+Remover

Whatever you do, you're going to want to rinse it very well.

 

[Bob3]

You can bring the tank in for a hydro first, before tumbling.
Check the "master list" of hydro joints at: http://hazmat.dot.gov/files/approvals/hydro/hydro_retesters.htm
Your local shop is probably going to just bring it in by one of those places themselves anyway.
Just tell the hydro guys you need it tested to see if it's worth sticking any more time & effort into.
Heck, my local tester throws in a tumble for free.
If you're in San Antonio I know a guy with a tumbler...

 

[mddolson]

GLASS BEAD OR SILICA SAND BLASTING WORKS WELL.

Mike D

Has anyone on the board have any DIY alternatives to tumbling for removing rust from a steel tank? It's out of hydro and I took it to the LDS for VIP and

Their opinion was to buy a new tank since the cost of tumbling and a hydro was close half the cost of a brand new aluminum tank and that because of the age of the tank, it was not worth the expense.

I personally think the tank still has a lot of use, but don't want to spring for the $ 35 cost of tumbling and then it would fail hydro.

Any suggestions?

 

[Ontario Diver]

Look in the tank and you should be able to make a pretty good guess. If there is pitting - it will fail. If the rust is "goopy" and dark - it should be tumbled and then hydro'd. It will probably pass. If the rust is light in colour and covers the whole inside of the tank, it is probably flash rust. In that case, a light tubling with sand will polish it just fine. It will pass hydro.

I've hydro'd a lot of tanks and the steels can handle a tumble very well.

 

[derwoodwithasherwood]

How about electrolytic rust removal? Kind of like chrome plating except that you are coating an electrode with the rust from your cylinder.

You need a 10 amp battery charger, a box of salt, water, a funnel, a piece of steel rod, electrical tape, methyl hydrate and light oil. I adapted it from a technique used by antique outboard restorers, and use it quite successfully on motorcycle gas tanks. I have never tried this on a SCUBA cylinder but I don't see why it couldn't work.

Pre-mix the saline electrolyte using 1/4 box of table salt to 2 1/2 gallons of water, and fill the tank. Tape up the end of a steel rod (I was told re-bar, but use all-thread ready rod which works just fine) so it cannot short out against the tank bottom. Connect the negative lead of a 10 amp battery charger to bare metal on the tank. Place a wide-mouth plastic (non-conducting) funnel in the opening and put the rod in the tank through the funnel. Connect the positive lead to the electrode. It's best to use a charger with an ammeter. Mine just has a silly voltmeter gauge, so I connect the positive lead through a separate ammeter. Add salt as required to bring the current up to 10 amps. (The best I get is 9.4 amps, more salt doesn't help after that). Check every 2 minutes, and stop when the rust is gone. (It gets so murky, I can't see inside after a while unless I slosh out some of the water and tip the tank. I don't know how they do this with a marine tank and still check it ;-)

Total time for me on a gas tank is usually about 10 minutes.

First time I tried it, I was amazed at the results. Where there was heavy rusting, clean shiny metal magically appeared. I used a piece of cad-plated ready-rod for the electrode, and it turned black. The saline turned a weird shade of green, with chunks of rust floating around.

I flush everything out thoroughly with water after, followed with methyl hydrate. Even so, I often see a faint patina of rust starting to form again within 15 minutes. I quickly coat the inside with oil, but I don't think that would be a good idea for a SCUBA cylinder. Perhaps a shot of phosphoric acid (the stuff in Coca-Cola that eats rusty nails).

 

[derwoodwithasherwood]

Of course, there's also the old-fashioned "brit-iron" way of derusting. This involves using an acidic solution to remove the rust. I enclose the info given to me some years back below. This will remove the rust and stabilize the surface, preventing it from rusting in the foreseeable future. The acid treatment is OK, but even better is Wrangl solution, used to remove oxides from steel:

1000 ml HCl (Hydrocloric acid aka Muriatic acid) ,specific gravity: 1.19
20 g Sb2O3 Antimony Oxide
50 g SnCl4 Stannous Chloride

Throw a buch of old nuts and bolts into the tank, pour in the solution, and shake the tank vigorously for 1-25 min at 20-25 C.

The data is taken from ASTM, treatment designation C.3.1.

Rinse out with *lots* of water, alternatively one second treatment with 2 spoons baking soda in water. The chemicals are not toxic in diluted quantities and may be aquired at the chemist, but do not drink the stuff.

The additives (Antimony Oxide & Stannous Chloride) are supposed to prevent flash rusting after the treatment.

Phosphoric acid can be substituted for the Muriatic acid, but it will work slower. It is also less prone to flash rusting than the Muriatic acid.

 

[ackattacker]

OK I realize this is extreme necro-posting, and my first post to boot, but I felt compelled to log in and post and make sure that NOBODY follows derwoodwithasherwood's advice above about electrolytic rust removal. Electrolytic rust removal works very well and if you have the battery charger already it's super cheap. I've used it extensively for vintage car restoration. BUT YOU MUST NOT USE SALT. You use "washing soda" found in the laundry aisle.

Salt, under electrolysis, produces CHLORINE GAS aka chemical warfare. DO NOT USE SALT. Also do not use stainless steed rods for the electrodes, plain steel only. Stainless steel introduces hexavalent chromate into your electrolysis solution, which is extremely toxic and carcinogenic.

I would also hesistate to put antimony chloride and stannous chloride in my breathing air tank...

 

[lucca brassi]

Of course, there's also the old-fashioned "brit-iron" way of derusting. This involves using an acidic solution to remove the rust. I enclose the info given to me some years back below. This will remove the rust and stabilize the surface, preventing it from rusting in the foreseeable future. The acid treatment is OK, but even better is Wrangl solution, used to remove oxides from steel:

1000 ml HCl (Hydrocloric acid aka Muriatic acid) ,specific gravity: 1.19
20 g Sb2O3 Antimony Oxide
50 g SnCl4 Stannous Chloride

Throw a buch of old nuts and bolts into the tank, pour in the solution, and shake the tank vigorously for 1-25 min at 20-25 C.

The data is taken from ASTM, treatment designation C.3.1.

Rinse out with *lots* of water, alternatively one second treatment with 2 spoons baking soda in water. The chemicals are not toxic in diluted quantities and may be aquired at the chemist, but do not drink the stuff.

The additives (Antimony Oxide & Stannous Chloride) are supposed to prevent flash rusting after the treatment.

Phosphoric acid can be substituted for the Muriatic acid, but it will work slower. It is also less prone to flash rusting than the Muriatic acid.

you get clean , and passivated inner surface which is also perfect porous and retrieved ????

if you do not believe me do a metallurgical analysis !

the most gentle cleaning rust with baking soda

 

[rcontrera]

We used a good old tank brush set with great success. A side brush on a 3/8" drill spins fast enough to do a good job of cleaning and you have to remember to pull it all the way through the threads so it will get to the top dome as well. It takes a different bottom brush to get the very bottom of the tank, though. They run about $150 a set or less. I get about 50 tank cleanings per set out of mine.