Old air

[dannobee]

The gas was analyzed. Oxygen was significantly reduced (down to 15.0%), carbon monoxide was elevated (10 ppm). Carbon dioxide was normal (0.01%).


Can anyone tell me what rust formation has to do with carbon monoxide??

Obviously the CO came from somewhere else. They should have explicitly stated that.

15% O2 will still support life while diving.

But back to the "study." 500ml of salt water is a LOT and totally unreasonable. The tank would need to be empty (or nearly so), then taken to a deeper depth, then the purge held open. That's not going to happen on any primary tank where the diver came back to the surface alive.

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[rstofer]

So, can (should) an end user gather up the tools and do their own visual inspections just before they take their tanks to the LDS for the annual VIP?

For the same reason that a diver analyzes their own Nitrox fills, it seems to me that taking a look inside the tanks is also a personal requirement. Though the diver (me) may lack the skills to really inspect the tanks, an overview could be quite informative.

Richard

 

[Luis H]

So, can (should) an end user gather up the tools and do their own visual inspections just before they take their tanks to the LDS for the annual VIP?

For the same reason that a diver analyzes their own Nitrox fills, it seems to me that taking a look inside the tanks is also a personal requirement. Though the diver (me) may lack the skills to really inspect the tanks, an overview could be quite informative.

Richard

A good LDS should show you the inside of your cylinder if you request to see it and should give you some feedback to what they are seeing and looking for.

I do all my own VIP (I started doing them while working at a shop in 1971). I also got certified recently from PSI/PCI and therefore have my own PSI stickers. Anyone can take a PSI cylinder inspection class, but not all LDS recognize all individuals' stickers, even if they are certified.


Some of my steel tanks have air that is probably close to a year old or more, but I know they got a good clean fill to start with and the tanks are in good shape. I am not at all concern.

I have analyzed the O2 content of steel tanks that have not been used in some 40 years and the air was as good as when it was filled. I would have dived if it would have been closer to full.


If in doubt, I would not risk a bad fill. But if it analyses with a good O2 content and there is no smell, it should be fine. It also helps a lot (confidence wise) if you know the source of the air and the original condition of the cylinder.

 

[rstofer]

A good LDS should show you the inside of your cylinder if you request to see it and should give you some feedback to what they are seeing and looking for.

What typically happens is that my LDS, which is a branch of another shop, sends the tanks to the mother ship for service. This is about 120 miles round trip if I want to see inside.

I'm going to look into the PSI course and see what I can find out. I don't want to do tank inspection for a living (in fact, I'm retired and have no intention of working) but I would like to know what to look for.

Richard

 

[Couv]

Hello Richard,

If you are just interested in some of the details of VIP inspections, go to this site and download the inspection manual.

Luxfer: Downloads


Edit: Here is another page you may find of interest: http://www.catalinacylinders.com/neckinspect.html

couv

 

[Doc Harry]

To rstofer,

What DA Aquamaster said. Moisture in the cylinder is usually from a wet cylinder valve. The fill station operator sometimes doesn't dry the valve before he/she hooks up the whip, and - poof - you got some droplets sprayed into your cylinder. Not 500 ml, the study went a little overboard with the volume of water to speed up the study.

You can also get moisture in the cylinder from saturated compressor filters. The fill station has to change the filters periodically!

As to the 3 month period - the Rhode Island study duration was 3 months, and the fatality that I mentioned was 3 months. There simply haven't been any other studies. That's all the data we have. So 3 months it is. It you want to to fund another study, we would all appreciate it......

The fatality that I mentioned... what else do you want to know? There isn't a whole lot more information to be gleaned from the literature. And I got copies of all of the original articles to review for myself. The guy hadn't been inspecting his steel cylinder. It was really badly corroded. And yes, in 3 months the oxidation process in his cylinder reduced the oxygen content to 2%-3% and he died. From a thermodynamics perspective, the amount of rust in his cylinder generally agreed with the calculated amount of rust that would be produced by such an oxidative process.

Fishpie,
Aluminum cylinders just don't have the problems that steel cylinders do. The oxidation process generally forms a protective barrier (aluminum oxide) and corrosion progresses much more slowly in aluminum. Additionally, aluminum cylinders are so much thicker than steel that it would take a very deep corrosion pit to compromise the cylinder wall strength. Nonetheless, aluminum cylinders need care and inspections, too.

Graeme Tolton,
Carbon monoxide is a product of oxidation of steel (after all, steel is carbon). I didn't mention it, but the carbon monoxide levels in the control (uncorroded) cylinders were normal, so the CO did not come from the compressor.

DA Aquamaster,
The suggestion that steel cylinders be stored nearly empty is not misguided. In fact, it's a suggestion based on the "best evidence" and consensus of industry experts. Now, we can argue on whether or not the "best evidence" is any good, and then you may have a point!!....

It's all an interesting topic, and it's especially interesting to go back to the original data that prompted industry experts to make their recommendations. If you haven't read my link Cylinder Storage: Fact and Fiction, then I suggest that you go there and look back over the original data to judge for yourself what it all means.

 

[DA Aquamaster]

What typically happens is that my LDS, which is a branch of another shop, sends the tanks to the mother ship for service. This is about 120 miles round trip if I want to see inside.

I'm going to look into the PSI course and see what I can find out. I don't want to do tank inspection for a living (in fact, I'm retired and have no intention of working) but I would like to know what to look for.

Below is the link to the PSI course schedule:

PSI Course Schedule

There is an instuctor in Modesto CA, so you should have options within an hour or so of home within the next couple months.

TDI has a VIP inspection course as well and they worked with PSI to develop the syllabus and course materials. It may provide you with another VIP course option.

Either way it could work out well for your local dive shop as well if they send tanks off to the mother shop due to the lack of a trained VIP inspector. They may not have Visual Plus / Eddy Current inspection equipment on hand at the local shop, but you could inspect all their steel and 6061-T6 alloy aluminum tanks for them and then only send the ones back to the mother ship that are need of tumbling, etc.

The tools and materials needed for visual tank inspection are not that extensive or expensive. A tank tumbler and related supplies would also be under $400-$500.

 

[rstofer]

The fatality that I mentioned... what else do you want to know? There isn't a whole lot more information to be gleaned from the literature. And I got copies of all of the original articles to review for myself. The guy hadn't been inspecting his steel cylinder. It was really badly corroded. And yes, in 3 months the oxidation process in his cylinder reduced the oxygen content to 2%-3% and he died. From a thermodynamics perspective, the amount of rust in his cylinder generally agreed with the calculated amount of rust that would be produced by such an oxidative process.

I would also like to know more about the tank: manufacturer, coating process, last hydro, last ViP, last fill, where filled, history of the fill station (compressor, filters), etc. Basically, I want to know enough to convince myself that it can't happen to my tanks.

We don't know that all of the rust was created during that last fill. The thermodynamics may appear to match by making some assumption as to the timing of the corrosion and the depletion of oxygen but it is the assumption that is problematic. The corrosion could have been building over dozens of fills. I'm not sure the report includes this level of detail.

I prefer to think of it as homicide. Nitrogen was introduced to the tank while maintaining the pressure and reducing the O2 content. Did anyone follow the money?

It seems to me that if 3 months were the universal truth, we would have a bunch of people dying from hypoxia. Yet, in all of recorded history, we have just one documented case (that we know of) or, at least, there are no CPSA warning labels required on every steel tank. In fact, other than this thread and the previous link, I have never even heard of a problem with steel tanks as long as they are not abused.

You would think that if rust was forming at such a rate, tanks would fail hydro in high percentage. In fact, you would expect to hear horror stories of steel tanks exploding while being filled. Yet steel tanks seem to live forever. Fourty years is common, fifty is likely. Maybe they do last forever... Just look at the hundreds of LP 72s cluttering the aisles around the pool at the local LDS. These tanks are ancient!

Unfortunately, I can't afford to fund a current study. In fact, I wonder why there hasn't been a follow on study with modern tanks. The universities study everything else!

I can look into the PSI tank inspection program and begin monitoring my own.

Richard

 

[rstofer]

Below is the link to the PSI course schedule:

PSI Course Schedule

There is an instuctor in Modesto CA, so you should have options within an hour or so of home within the next couple months.

The tools and materials needed for visual tank inspection are not that extensive or expensive. A tank tumbler and related supplies would also be under $400-$500.

Thanks! I signed up for the VCI program in May. I may add on the Eddie Current component when the class gets closer.

I don't intend to get into the business of servicing tanks but I am willing to invest a little money in my own education.

Richard

 

[Doc Harry]

Perfect timing, here's link to an interesting article, maybe a little off topic but...

Compressed breathing air - the potential for evil from within