Rust Issue

[Ed Hatfield]

Once a tank has been checked and there is rust visible inside - is the tank garbage or can it be cleaned/serviced. It is a 120 steel used for nitrox. I tried to search for a quick answer but nothing jumped out at me.

 

[masterof0]

Depending on how bad the rust is, it can be tumbled and cleaned. Do you know how long it has been rusted and if there was a significant amount of moisture in the tank? If it is just flash rust, then there shouldn't be any issues with getting it tumbled. If moisture has pooled in the tank and been sitting for a long time, then the longerthe tank sits and continues to rust, the greater the risk you will have to scrap the tank.

 

[tfsails]

It can also be whipped if it isn't too badly rusted. Whipping and tumbling are the main ways to de-rust a steel tank. If you think there's heavy rust on the bottom as mentioned above, I suppose you could have the tank hydro tested to see if there's any weakness in the metal. That's an option I would consider if my tank were badly rusted.

 

[Ed Hatfield]

The rust is minimal but the tank is also out of date and would require hydrostatic testing. Is it more common to have the test and the tank rolled or to replace the tank. I have no idea of the cost factor for this proceedure. Located in SW Ontario.

 

[tgsmith]

Have it tumbled and get it hydro'd after. There's some in the cylinder business on these boards that have seen some tanks lose serious amounts of mass due to rust but still pass hydro just fine after getting cleaned up, so I would put my money on refurbishing your cylinder if the rust is only minimal.

I would have it hydro'd after anyways if you're taking physical mass away from the cylinder, so to me that's a non-issue.

BTW, what's "whipping" a cylinder?

 

[halocline]

I'd have someone who you know to be an authority (unfortunately this eliminates some LDS employees) have a peek inside the tank, and then proceed. A good hydro guy will know after looking for 2 seconds whether the tank can be tumbled. Around here a hydro is around $20-25 and a tumble is around $10.

You didn't mention what kind of 120 it is. If it's a LP, chances of failing hydro are probably pretty slim if it passes a vis. HP tanks are subjected to much higher test pressures and there seems to be a smaller margin for passing hydro. I have no real evidence of that, you just tend to hear about HP tanks failing hydro more than LP tanks.

 

[cwkline]

Is it flash rust, or deeper rust with pitting? Very few steel tanks have no rust at all in them, as they are exposed to some moisture during the inspection process. I would have the cylinder hydro'd and VIP'd. The inspector will let you know if it needs tumbling. I have found that different inspectors have different standards on acceptable rust in a steel cylinder. BTW, if you take the cylinder to a hydro facility and bypass the shop, you can save some cash.
I'm sure others more qualified than me will chime in here. But that is my take on the rust thing.
Hope it works out
Safe Dives
Charlie

 

[Underwater Ogre]

RUST!!...no way...don't use it...get rid of it...I will take it off your hands. Send it to me and I recycle it properly.

U/O

 

[DA Aquamaster]

Very few steel tanks have no rust at all in them, as they are exposed to some moisture during the inspection process.

That is not exactly the case. With steel tanks used in O2 service the target is indeed zero rust due to both the fact that rust is flamable and due to the potential for sparks due to entrained particles.

The tank is tumbled (often with dry media) to remove any flash rust then tumbled several more minutes with the O2 cleaning solution and then rinsed/briefly tumbled with compound O or a similar O2 compatible rust inhibitor. That inhibitor is rinsed out with a very brief spray of water and the tank is then immediately dried. If done properly there will be no rust in the tank at all. Even with high 02 percentages rusting will not occur unless moisture is present so with high quality gasses that are suitably dry rust is not an issue in service either.

Some manufacturers also create what amounts to a phosphate coating with a mild phosphoric acid solution that also inhibits rust.

So a clean and shiny steel tank is not as uncommon as many people believe.

 

[drbill]

Is it a PST HP120 tank? I've lost two of them to rust... beyond repair. Hopefully yours is not.