Water can also get into the tank if there's water in the valve when you are connecting the first stage.
Does a nitrox tank rust more inside?
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Water can also get into the tank if there's water in the valve when you are connecting the first stage.
Care to explain this one a bit further? If there is air/gas in your tank that is pressurized, even when you have water sitting at the valve opening (trapped by the first stage), when you open your valve the ai/gas is going to push the water away from the opening and it won't be able to enter the tank. Now the water will get pushed into your regulator and that can cause other issues but I can't see how it would get into your tank.
Does a tank that is used for nitrox tend to rust more inside requiring more maintenance compared to a tank used exclusively for air?
Never been studied, so all you'll get are people's unsubstantiated personal opinions. Remember that anecdotal evidence ("This is what happened to me....") is the LEAST reliable form of evidence.
There has not been a definitive, controlled study with a large sample size to investigate the question of Nitrox and corrosion.
HOWEVER:
Back in the 1970s the University of Rhode Island did some small studies regarding steel and aluminum scuba cylinder storage. Small, meaning 8 to 10 cylinders, sometimes comparing single matched cylinders.
To make a long story short, one of their conclusions was that, during long-term storage, increased cylinder pressures resulted in increased internal corrosion, which they concluded was from the increased partial pressure of oxygen (pO2). However, there were many other confounding factors such as the composition of the water that caused the rust, the types of valves and snorkel used, (cathode-anode stuff), etc.
My take on the studies is that aluminum cylinders are much less susceptible to corrosion at higher pO2 than steel sylinders.
The studies are controversial because of their methods and small sample sizes.
If you want to read my detailed review of all of these studies, do a search on long-term cylinder storage.
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SparticleBrane
Contributor
Perhaps they meant "when connecting it to the fill whip" ?
Especially with a DIN valve, if you don't blow any residual water out of the threads in the valve before connecting the fill whip, that water can be forced into your cylinder during the fill process.
Does a tank that is used for nitrox tend to rust more inside requiring more maintenance compared to a tank used exclusively for air?
Yes, cylinders used for nitrox tend to oxidize more quickly than their brethren that are only used for air. Within a year or so, the inside of a cylinder dedicated for high ox use, even if it's aviator grade O2, is easily identifiable when compared to a "normal" cylinder, by way of example. The important thing is that although they will oxidize more quickly, everything is relative and they won't oxidize so much faster that it really makes any difference, especially for recreational mixes.
Yes, cylinders used for nitrox tend to require more maintenance than their brethren that are used only for air. That's not usually because of the oxygen content of the mix, however. At the easy end of the scale there is the whole bumper sticker silliness, at the more expensive end is oxygen servicing for pp blending.
There's nothing wrong with lurking. Sometimes it's even a good idea.
It probably depends on the valve and reg designs but it would theoretically be possible for any water that does not get blown past the HP seat to drip its way back through the reg and valve back into the tank during an extended period where the reg is pressurized but not used. Not the most likely scenario in the world, but remotely possible as there is no pressure differential between the HP portions of the reg and the tank.
However it is an intersting idea. It got me thinking that the same thing would be much more likely to occur with a first stage thoroughly flooded in a dip tank and then re-attached to a tank the next morning, pressurized, but not purged.
In particular with a diaphragm reg design, there may be virtually no flow past the seat when the reg is pressurized leaving a fair amount of water that could soak its way back past the filter and back down the valve to the tank.
The required chain of events is a bit long and the number of neccesary conditions is a bit high, but it is a plausible way to get water in a tank.
OP
scubadude79
Contributor
What was in error?
OP
scubadude79
Contributor
Not sure how the discussion got from higher PPO2 causing faster oxidization in the tank to the tank having water in it, but thanks for all the great comments. It sounds like a formal investigation, even a MythBusters test on this topic. Everyone, be sure to suggest it as it would be a great episode. Then they can blow the crap out of the tank!
If we lead off the suggestion by saying they can blow the crap out of a tank, the Mythbusters will be even more likely to tackle it.
As I recall, they've already blown the crap out of a couple of scuba tanks. Of course, they just like to blow stuff up anyway, so I get the feeling any excuse, no matter how tenuous, is sufficient for them.
As I recall, they've already blown the crap out of a couple of scuba tanks. Of course, they just like to blow stuff up anyway, so I get the feeling any excuse, no matter how tenuous, is sufficient for them.
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