Question about my new steel tank (new to me).

[markmud]

At that point, the tank will no longer be O2 clean, and no longer safe for nitrox fills, but will still have nitrox stickers on it!

For example, my tanks have a different-colored visual inspection sticker that says it was O2 clean at the time of the inspection, as well as a 6-inch green-and-yellow sticker that goes around the tank. These stickers are commonplace among rec divers in my area, but are not necessarily universal.

I am either not reading your post correctly or your message isn't quite right.

One of my tanks is O² clean, and the others are not but I regularly have them filled with pre-blended nitrox or nitrox made with a NuVair system. These non 0² tanks are safe up to 40% Nitrox.

OP, your tank needs to be hydroed and VISed. Your valve probably needs to be overhauled. Ask the tech to use components that are safe up to 40% or have the tech O² clean your tank and valve for partial pressure blending, if partial pressure blending is the only available option for you. As Brett wrote, don't let your O² clean tanks get contaminated with hydrocarbons from a crappy compressor. It is critical for O² clean tanks and a good idea for all scuba tanks. But, with tanks safe up to 40% a person won't get killed and you won't breath CO.

I recommend replacing the valve with a modern valve. New modern valves are almost universally safe for nitrox to 40%. I don't think there are any modern valves today that aren't safe for preblended Nitrox up to 40%.

Again, my tanks are either O² clean for partial pressure blending or safe for pre-blended nitrox or NuVair Nitrox. I have been dealing with this issue for 15 years. I have not seen the VIS sticker that says "safe for preblended Nitrox" in almost a decade. One of my tanks does not have the 6" green Nitrox sticker but it is filled with EANx. There is a piece of green tape that labels the tank "Nitrox 32%".

The main difference between O² clean and Nitrox-ready are Viton verses Buna-N O-rings, Cristo lube verses silicone grease, and a more thorough cleaning of the tank components to ensure there are no hydrocarbons.

What I have written is a thumbnail explanation. Ask your VIS inspector for more details.

Good luck,
m

 

[rnln]

too much info now
MarkMud,
I think you are mixing up with my old/first tank the LP72 with my second LP85 on the topic of Nitrox. The LP85 was Nitrox ready. The OP use it at 30%, he said. when I bought it, it's still had a tat of air in there and he said it was Nitrox.

The question is how often you have to do O2 cleaning, every time you have VIP annually or only once and keep up using clean air? If it's once only, then the shop really ruined my tank Nitrox grade. If it needs to be done annually with VIP, then I am ok because I will have to do it again in the future when I am ready to use Nitrox anyway.

Thanks

 

[Brett Hatch]

I am either not reading your post correctly or your message isn't quite right.

Hi Mark. Either of these could be true, or both, or I could just be flat-out wrong -- let me clarify and we shall see.

The scenario I'm trying to address goes like this: on Monday you have an O2 clean tank with O2 stickers. On Tuesday you bring it in for a fill and receive Grade E air (aka safe-to-breathe air from a crappy compressor with the wrong kind of lube). Now you have a tank which is safe to dive, and labelled O2 clean, but may not actually be. On Wednesday you bring it in for a nitrox fill.

It is my understanding that an O2 cleaning (or at least a VIP from a nitrox-trained op) is required prior to Wednesday's fill; is this correct? If yes, then I think you would agree that Tuesday's operator probably made a mistake putting Grade E air in the O2-labelled tank?

OP, your tank needs to be hydroed and VISed. Your valve probably needs to be overhauled. Ask the tech to use components that are safe up to 40% or have the tech O² clean your tank and valve for partial pressure blending, if partial pressure blending is the only available option for you. As Brett wrote, don't let your O² clean tanks get contaminated with hydrocarbons from a crappy compressor. It is critical for O² clean tanks and a good idea for all scuba tanks. But, with tanks safe up to 40% a person won't get killed and you won't breath CO.

<snip>

Looks like you may not have realized that the first half of this thread was about one tank, and the recent posts are about a different tank that is in better shape maintenance-wise.


@rnln by the way, Mark has brought up a point which I was neglecting, but might be relevant here. There are 2 different relevant cleanliness standards for oxygen: O2 clean vs safe up to 40%. There are also different ways of making nitrox. For our purposes there 1) partial pressure filling, and 2) filling with pre-mixed gas*.

With a partial pressure fill, the operator fills the tank in 2 steps: first with pure O2, second with plain air. So they take your tank at say 500 psi of 21% (air), your target pressure of say 2400 psi, and your target gas mix of say 32% O2. Then they do some math, which tells them how much pure O2 to squirt in before topping off with air. At the end, your tank should be pretty close to the target. After they put the O2 in but before they put more air in, the tank will be at a high temperature with a high percentage of O2 (possibly close to 100%). Certain contaminants are likely to ignite under these conditions, hence the problem. If your tank is O2 clean then partial-pressure filling is safe. If it is safe up to 40%, then only pre-mix filling is safe. And if there is sufficient contamination, then only filling with air is safe.

The different methods require different equipment, so some shops can do one but not the other, or vice versa. Talk it over with your operator, you might actually be in fine shape here, or you might need an O2 cleaning. It depends on what kind of gas they put in when you got the fill, and what kind of equipment they have for nitrox fills.

* There are various types of pre-mixed gas: banked gas, membrane mixers, stick mixers, gas purchased from a third party, and so on. However for the present purpose I think it's safe to ignore these differences and lump them together as gas-which-is-not-partial-pressure-filled.

 

[Brett Hatch]

This website seems to have some good info on this: Nitrox Fills and O2 Cleaning Cylinders - The Scuba Doctor
Although note that they are in Australia, so the "legal" section of course won't apply everywhere.

 

[rnln]

Brett,
thanks for more info and the article. I understand now. Honestly, too much to remember and easy to make mistake. This is why people tend to like to keep coming to the same scuba shop which he knows about huh.

 

[Brett Hatch]

It's also why they tend to recommend taking the nitrox course

 

[rnln]

yeah. I will if I decide to go into it. Right now, I just need to understand enough to decide how/what to do with the new tank.
Thanks again.

 

[Scared Silly]

I just check the VIP sticker. It doesn't say anything about what type of air, It only says inspected interior/exterior for rust and such. Another sticker sticker does said this tank was clean such and such from manufacture for enriched air... I guess this is the manufacture sticker. Also, the biggo yellow/green band on top saying Nitrox is gone. I am going to ask them on this.
Thanks.

Post up pictures. One sounds like the original mfg which does not really matter now and the new VIP which does.

FWIW when doing a proper inspection all stickers need to be removed as corrosion can be hidden underneath.

 

[dead dog]

“You’re” not “your”. At least get your grammar right if you’re going to accuse me of buying bog-roll.

If you read it right you would have seen it was a spelling mistake not a grammar mistake.

 

[Scared Silly]

I regularly have them filled with pre-blended nitrox ...

There is no such thing as pre-blended nitrox. The basic definition of NITROX is a mixture of oxygen and nitrogen. So what does it mean to pre-blend a mixture? There is, however banked NITROX.

These non 0² tanks are safe up to 40% Nitrox.

Except there is no industry standard for that. Just made up BS as you will not find it from any cylinder mfg.