How much rust is expected or allowable in a steel cylinder?

[Matt S.]

I recently had my steel 119s inspected and my LDS determined that they needed a tumble. Along with my inspection paperwork I got to see the rust removed from each tank... It was a very small amount of material, about as much as you'd get from a single grind on a pepper mill. (I can't show a photo, because the shop didn't want me to take the rust baggie home since it was "hazardous.")

When I asked how it happened, and what I could do differently to prevent it, I was told that you had to make sure that the valve area was always completely dried out, or water would work its way into the tank, even if pressurized. (Say what?)

The shop also wanted to blame a bad fill station too but I've only been using them for over a year, so they had to backpedal on that and blame my maintenance routine.

This is the second year running that this shop has needed to tumble my tanks. Before, when I went to different shops, I don't think I ever had it done.

I had thought that inside a steel cylinder some small amount of surface rust was expected, and in fact inevitable.

Anyway, how much rust is too much? I am wondering if I am getting tumbled over tumbling.

If there is something I should be doing other than a fresh water rinse, and blowing out the valve by releasing air, I'd love to know that too.

[CaptnJack]

Use a different shop. The whole rust chips in a baggie = hazardous means they are completely clueless. If its actually dangerous waste (State law does not use the term hazardous waste) ask to see their dangerous waste manifest, since they are surely not disposing of dangerous waste in the regular trash right?

Their fill station is blowing water into the tanks. Either by not blowing out the valve right before filling, their whips are getting water in/on them (from a nearby water bath), or their filters are saturated and water is blowing right on through. You should be blowing out the valves just before putting the regs on too.

[Nwbrewer]

Just did the first hydro on my 119. Only 3 compressors were ever used on that tank. vbcoachchris, NWSD when they were open, and a certain buddy who will remain nameless. It was still shiny inside.....

I agree with Richard, get a new shop, those guys are blowing smoke.

Also if all the rust that came out was just a tiny amount, why did it need a tumble? I've been pretty successful with using a whip to take out light surface rust on some used tanks that I've bought.

Jake

[BillZ]

Like Richard said - Most likely it's from person who fills your tanks not blowing out the valve before filling the tank. The other alternative, the shops compressor letting water get through their filtration system, would be a huge problem since the filtration media won't work if it's wet. That would mean you were probably getting compressor oil and potentially CO in your fills.

Just curious - when the shop tumbled your tanks how did they separate the rust, dry it out and bag it? I've tumbled many tanks and the rust gets washed out in a wet slurry when I remove the tumble media and rinse the tank.

[Dusty2]

Just curious - when the shop tumbled your tanks how did they separate the rust, dry it out and bag it? I've tumbled many tanks and the rust gets washed out in a wet slurry when I remove the tumble media and rinse the tank.

Yep

[H20doctor]

ive had flash rust in my tanks... but that was my fault for not blowing my tanks dry after rinsing them at home.. and also the shop should clear the valve before they fill.. my flash rust was cleaned at my dive shop with a drill bit , then air cleaned.. all better no biggie

[Jeff Kruse]

Light surface rust is fine. Even some fine dust/flakes are fine. If the rust makes a small bump/knob in the tank then the inspector needs to poke at it. If the inspector can’t determine that metal under it is fine then it needs to whipped or tumbled.

I took the PSI class and started doing a lot of vips for my tanks and my friends. My tanks were only filled by my compressor and year after year they were spotless inside. Then I would look at my friends tanks, some of those filled in Bothell were also very good, but quite a few of the other tanks were not very good. One tank I dumped out about a pennies worth of rust. Another had a nice film of oil and water all over the inside of the tank.

It was really an eye opener. Before I got my compressor I would have to have my tanks tumbled every couple of years. Now for the last 10 years the insides are great, unfortunately here in Puerto Rico the last 6 years has really rusted them on the outside around the boot.

That’s the question I have, how much rust around the boot is ok? The rust can be scraped/lightly sanded off and leaves pits from 5 – 10 thousandths. These tanks are 22 years old. Cold galv CRC spray just isn’t working here.

[CaptnJack]

That’s the question I have, how much rust around the boot is ok? The rust can be scraped/lightly sanded off and leaves pits from 5 – 10 thousandths. These tanks are 22 years old. Cold galv CRC spray just isn’t working here.

I can send you a pdf of the pit limits for 3AA and E9791 steel tanks when I get home tonight. Same email as before? I don't know them off hand, but the walls are thin and so the allowable pits are pretty small.

[Jeff Kruse]

Thanks but I probably I have those. The rust I am talking about is around the tank boot. It bubbles up and flakes off. It comes off when you scrape it and it's only a few thousandths thick but every time you clean the surface to bare metal it rusts up again. Spraying with CRC just comes off in a few weeks. The galvanization around the boot has been long gone.

[CaptnJack]

Thanks but I probably I have those. The rust I am talking about is around the tank boot. It bubbles up and flakes off. It comes off when you scrape it and it's only a few thousandths thick but every time you clean the surface to bare metal it rusts up again. Spraying with CRC just comes off in a few weeks. The galvanization around the boot has been long gone.

The limits for line corrosion like that are about 1/2 the limits for an isolated pit. Could you go without the boot?

[Matt S.]

Thanks for the help fellas. I think I am going to be switching fill stations anyway, we'll see if that makes a difference. I'll also be extra sure to blow out the valve again before I drop them off.

[kdupreez]

Thanks for the help fellas. I think I am going to be switching fill stations anyway, we'll see if that makes a difference. I'll also be extra sure to blow out the valve again before I drop them off.

Like others have said, when you tumble a tank and then remove the tumbling media, its impossible to really seperate the rust dust from the media and then when you wash out the tank, the rest of the fine (mostly media) dust is gone too..

I think you were taken for a bit of a ride.. They are saving that "rust baggie" for the next customer...

Only way to remove rust and put it in a baggie is to "whip" it with steel whipping brush and a drill.. and that takes all of 5-10min.. plus you need a fairly excessive amount of rust to get that much rust dust with a whip and at that point you need to really tumble..

sorry Matt.. maybe time to find a new LDS..

[Paulicarp]

Just did the first hydro on my 119. Only 3 compressors were ever used on that tank. vbcoachchris, NWSD when they were open, and a certain buddy who will remain nameless.

Nameless? All the kicka$$ fills I do for you, and all I get is "nameless"?

[Nwbrewer]

Just did the first hydro on my 119. Only 3 compressors were ever used on that tank. vbcoachchris, NWSD when they were open, and a certain buddy who will remain nameless.

Nameless? All the kicka$$ fills I do for you, and all I get is "nameless"?

I thought Nameless was the name of the compressor?

[Matt S.]

Only way to remove rust and put it in a baggie is to "whip" it with steel whipping brush and a drill.. and that takes all of 5-10min.. plus you need a fairly excessive amount of rust to get that much rust dust with a whip and at that point you need to really tumble..

Hmm, maybe they did say they whipped it. Whatever it was, it was something like $40-50 per cylinder which seemed excessive on top of the VIP fee.

In any case, same end story, I'll try another shop for fills.

[CaptnJack]

Only way to remove rust and put it in a baggie is to "whip" it with steel whipping brush and a drill.. and that takes all of 5-10min.. plus you need a fairly excessive amount of rust to get that much rust dust with a whip and at that point you need to really tumble..

Everyone has their own get feeling about when to whip vs just go for a tumble. Personally whipping is just for one little blotch of rust on the bottom or something like that. If there's more than 2 rust spots I tumble since I need to wash cylinders after whipping anyway to remove the dust and O2 clean.

[kdupreez]

Everyone has their own get feeling about when to whip vs just go for a tumble. Personally whipping is just for one little blotch of rust on the bottom or something like that. If there's more than 2 rust spots I tumble since I need to wash cylinders after whipping anyway to remove the dust and O2 clean.

Agreed! whipping becomes laborious for more than a few blotches. I'd rather at that point just throw on the tumbler and let it roll for a few hours while I enjoy a beer

[archisgore]

let it roll for a few hours while I enjoy a beer

I'm learning that a surprising number of divers love beer!