Rusty cylinders-need help!

[Waterbottle]

Hello,
I opened my scuba cylinders (sometimes air tastes like swamp) and I found couple very rusty spot from both bottles. Is this dangerous and what I could do for the rust? Cylinders stamped(for next 10years) one year ago and are 20 years old. I have only filled these in diving shop. How fast rust comes and why if I have used shop diving air? Here is a couple photos. Thank you. (Sorry bad english)

 

[Waterbottle]

Cylinders are d12 200bar

 

[Jonn]

You can get a cylinder stamped for ten years in Finland?

 

[Waterbottle]

You can get a cylinder stamped for ten years in Finland?

Yes

 

[AfterDark]

Tanks can be rolled with abrasives or power brushed with a brush for that purpose.
The location and depth of the rust makes a difference if the tank can be saved or scrapped. The bottom is the thickest part of the tank. Rust on the bottom is least likely to be a problem. A good reason to store tanks standing up so any water settles to the bottom.

Good Luck!

 

[grf88]

It is more likely that the swamp tasting air is causing the rust than the rust causing the swamp tasting air. You will need to have the tanks tumbled to remove the rust prior to a proper inspection being able to be made. If after tumbling the tanks pass inspection then get them filled elsewhere.

 

[rjack321]

They need to be tumbled then visually inspected for pitting. That is A LOT of rust.

 

[stretchthepenn]

Is this dangerous and what I could do for the rust?

The rust won't affect your breathing air. It may, however, affect the tank's ability to hold air without rupturing. In that sense, the rust is dangerous.

How fast rust comes and why if I have used shop diving air?

"Flash" rust -- a thin film, like in your third picture -- forms almost instantly. It often appears on the inside of a freshly oxygen-cleaned steel cylinder after the final rinse. The thick rust in your pictures, though, needs weeks or months to form.

Shop air itself is probably not the rust's source. If it is, then the shop's compressor has serious problems, and other customers would have rusty tanks, too. The source is likely water that either drifted into the tank or was forced into the tank.

Has your tank ever been completely empty?

If yes, then one of two common things could have happened:
1. When the regulator was removed, drops of water trickled in through the open valve.
2. While the tank valve was open, ambient air drifted inside and deposited water vapor.

If no, then water was probably forced into the tank during a fill. Sometimes water droplets can accumulate in a valve's aperture or on a fill whip's end, and the shop air will pick up the droplets and shove them into your tank.

 

[rob.mwpropane]

Sometimes water droplets can accumulate in a valve's aperture or on a fill whip's end, and the shop air will pick up the droplets and shove them into your tank.

Let's say that water did get in this way.... wouldn't the air that's "supposed" to be super dry absorb that small amount of water? And then in turn get breathed in / expelled back through the valve?

I honestly don't know, but that's a lot of rust. It just seems to me whatever is happening is happening on a more consistent basis than just "a little".

He said cylinders with an "s", so it's happening to both (or more).

 

[BRT]

Let's say that water did get in this way.... wouldn't the air that's "supposed" to be super dry absorb that small amount of water? And then in turn get breathed in / expelled back through the valve?

I honestly don't know, but that's a lot of rust. It just seems to me whatever is happening is happening on a more consistent basis than just "a little".

He said cylinders with an "s", so it's happening to both (or more).

The air is super dry, at atmospheric pressure. Not so dry at tank pressure. A -60 dewpoint at atmospheric pressure will allow condensation at 39F and 3500 PSI

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