Cleaning tank rust

[Paladin]

I just got my tanks back from hydro, one AL80 and one steel 72. Both tanks were still damp inside and the steel 72 has a fine layer of rust inside. That tank is 33 years old and has been totally rust free for all those years. When I took the tank in for hydro three weeks ago, I checked inside and it was clean and free of rust. I called the shop and I was essentially told that, as they are the only place within a fifty mile radius that does this kind of work, they are swamped with jobs and cannot take the time to dry out tanks they hydro.

So, how do I clean this rust out before it does permanent damage?

 

[DA Aquamaster]

They are required to do a VIP as part of the requalification and I have a hard time believing any shop would feel it is ok to send a tank back into service that is still damp inside. I'd contact the DOT and suggest they send an inspector to see what else they are screwing up.

Rust will attract and concentrate mopisture so if it is anything more than light flash rust, you will want to remove it. Tumbling is the traditional method and works well but it obviously reqquires a tumbler. Most decent dive shops will have one.

A rinse with a suitably dilute solution of phosphoric acid also works well to remove the rust, followed by a thorough rinse. You can also finish the process with an even more dilute solution to give the tank a phosphated finish that will act as a rust inhibitor.

 

[Sailor612]

DA is right!!

I'd like to add a few thing though that I have learned from experience....
When a tank is tumbled, a tumble medium (similar to little pebbles BUT NOT ACTUAL PEBBLES!) is put in the tank with a cleaning/rust inhibitor solution and clean water. All it does its rotate in circles with those items inside...kinda like a rock tumbler. Once it has been tumbled long enough (usually a few hours unless it is REAL bad) it gets pulled off the tumbler, the medium/solution is rinsed out, and then it goes back on the tumbler for 15-25 min with DISTILLED or deionized water to make sure everything is rinsed well. The "final" rinse then gets dumped out and the tank gets put up to dry. Usually the drying phase is a no-heat, forced air dry. THat can take anywhere from a few hours to half a day. Once the tank is completly dry, the valve can be put on and the tank can get a fill....usually there is a internal visual done before the valve goes on to make sure it didn't flash rust, is dry, and the original rust wasn't covering up any issues.

It is not good to use regular tap water during the rinse phase because the minerals in tap water can cause the tank to flash rust very quickly and the process has to be done all over.

Compared to the whole process, there isn't really too much "labor" time involved, most of the time is waiting for each process to be complete.

 

[DA Aquamaster]

I usually dry my streel tanks with a blast of air from a scuba regulator. I cut the second stage end off a 40" hose that went bad and use the resulting rubber hose to blow the air into the tank while the tank is inverted. The air is dry and the high flow rate rapidly displaces the water and evaporates any remaining water on the surface before flash rusting occurs. It is also a 2-3 minute process, although I come back and do a quick flush a half hour or so later to ensure any humidity remaining in the tank is removed.

I also have my own tank tumbler, which I have been told is somewhat unusual. Personally, I think everyone should own one.

 

[Spimon]

Just out of interest, how did you discover the tanks were damp/rusting inside?
Once mine are back from testing I just use them. I never take the valves out.

 

[Doc Harry]

Dang! Find another place to get your hydros! Their actions are UNACCEPTABLE!!!

I agree with tumbling. Some people use a whip that attaches to a screw driver that basically flails the inside of your cylinder. This method looks leaves your cylinder looking like hell and does an extremely poor job of removing rust.

Drying a steel cylinder slowly can just lead to more rust. The rust inhibitors are a great idea.

A great way to dry your cylinders quickly is with good, clean compressed air.

Get an air gun like this:

and attach a long rigid metal extension pipe (I use brake line from an auto parts store that has been thoroughly cleaned and degreased).

This way you can reach all the way into your cylinder and blow it dry in less than minute.

 

[Cave Bum]

Dang! Find another place to get your hydros! Their actions are UNACCEPTABLE!!!

I agree with that!

I agree with tumbling. Some people use a whip that attaches to a screw driver that basically flails the inside of your cylinder. This method looks leaves your cylinder looking like hell and does an extremely poor job of removing rust.

I use a sand blaster to clean rust, with aluminum oxide 70 grit for steel tanks and a crushed walnut shell grit for aluminum tanks.

Drying a steel cylinder slowly can just lead to more rust. The rust inhibitors are a great idea.

A great way to dry your cylinders quickly is with good, clean compressed air.

The problem with compressed air is the low pressure compressor supplying the air is oil lubricated and doesn't have a seperator (Coalescer) to take out the oil and water that contaminates it.

You're better off re-rinsing with very hot water, then drying with either air out of a scuba tank (the best way) or a heat gun. They make an air gun/tire inflator adaptor for the inflator hose and Harbor Freight has an air gun with a long nozzle, 3 foot or so. That's what I use.

 

[Doc Harry]

The problem with compressed air is the low pressure compressor supplying the air is oil lubricated and doesn't have a seperator (Coalescer) to take out the oil and water that contaminates it.

That's a problem. That's why I specify good, clean compressed air.

Personally, I use a heated dryer, too, that I got on sale through Global when I bought my tumbler.

 

[oxyhacker]

A dangerous thing to specify, without being more specific. Most people don't have a clue what good, clean air is. I've had a lot of people assure me their shop compressor produces it, because it has a big filter on it, but I don't think any of us would suggest using air from a shop compressor on dive gear.

When talking about air for drying out tanks or regulators. I usually specify "scuba air" or "O2-safe scuba air". Anything that comes out of a scuba compressor is pretty sure to be clean enough, but anything coming from any other kind of compressor most emphatically isn't.

That's a problem. That's why I specify good, clean compressed air..

 

[Paladin]

Spimon,
I find out about the rust and the dampness inside the tank because when I got the tanks back, they were empty. I pulled the valves and dropped a light down in side to check tanks' interiors. The inside of the steel tank was covered with a fine, thin coating of rust and that tank had never had any rust in it since I bought it new in 1976. The place where I got my tanks hydroed wanted to charge me over thirty dollars per tank to fill them. This is not a dive shop, it is a company called Airgas that services gas welding equipment, fire extinguishers, medical oxygen cylinders, fire department breathing cylinders and such. They also do the scuba tanks of all the local fire and police departments and is the only place to have tanks tested within a hundred miles of me.

I got the rust out, though. I took the aluminum cleaning rod from one of my gun cleaning kits and attached lengths of "weed eater" trimmer line to it with duct tape to make a brush. I connected the rod to an electric drill and inserted it into the tank. With the brush spinning, I slowly worked it up and down inside the tank. The plastic trimmer line gently cleaned away the rust without damaging the clean metal underneath. About forty-five minutes of this and all the rust was removed. I removed the loose rust with a high capacity vacuum cleaner with an attachment tube small enough to go down into the tank. I took the tank down to the dive shop I've started going to to be inspected and filled. The tank passed inspection with flying colors, so to speak.

You may rest assured that I will never again take a tank to Airgas to be tested.