It says right on my tanks - DO NOT OVERPRESSURIZE

[Ted Judah]

A year ago, I bought tanks for my wife and I. In that year we have used them on 16 dives and had them filled at 5 different dive shops. The pressures after each fill seem to vary wildly and is often overfilled.

Here are the markings on the tanks:

FABER MADE IN ITALY M8303 21/0154/ 073 02•21+
TC - 3AAM - 184/DOT - 3AA2400 DO NOT OVERPRESSURIZE REE67 BS85S


Below are the start fill pressures for each dive:

2400 lbs.
3400 lbs.
2600 lbs.
2500 lbs.
2500 lbs.
2500 lbs.
2200 lbs.
2800 lbs.
2800 lbs.
2800 lbs.
2950 lbs.
2400 lbs.
3000 lbs.
2750 lbs.
3250 lbs.
3525 lbs.

Am I missing something? should I be concerned? Should I request a certain pressure from dive shops?

 

[Divin'Papaw]

Perhaps Faber could give us a definitive answer? They surely know something about the issue at hand.

Seriously? They stamp DO NOT OVERPRESSURIZE right on the blasted cylinder!!! What do you think they are going to say?!

Every single manufacturer that has ever manufactured a tank will tell you to not over-pressurize. Faber, Luxfer, Catalina, Worthington, PST, etc. They all say the same thing. If you buy their rationale, than by all means make sure your own personal tanks are not overfilled. In the meantime, the majority of us will continue to do what we've been doing for literally decades.

 

[tursiops]

Repeated overfilling does cause metal fatigue, doesn't it?

Yes, but the issue is worrisome only for many 1000's or 10's of thousands of cycles, not the few our cylinders undergo, and even then it is for stressing to near maximum, towards the elastic limit, not the lower levels we use in scuba.

 

[goldfishtornado]

My recollection of this thread, is that it IS possible to get above the fatigue limit in steel with significant overfills.

If you believe the calculation there, you are at a 40k cycle lifespan. It doesn't look like anyone ever managed to dig up representative curves for the specific alloys in question though. I think it also doesn't account for the fatigue from the expected hydros, damage, or rough handling of the tanks. The representative curve is also log-scale in number of cycles, so 1000's is probably closer to a reasnoable-ish safety limit than counting on 10's thousands.

 

[ScubaSquatch]

OP, never get a fill in north central Florida...........you'll have a panic attack.

 

[DeepSeaExplorer]

The 2400 stamped on the tank is actually the turn pressure.

 

[rx7diver]

A guy I often dive with has some LP72's that date to the mid '90s, they still have a "+" rating

My only old-school 72 was manufactured in 1970. (I traded a still-new Al 80 for it ~2000.) It is my favorite cylinder for some types of diving. Each time I have had it hydroed, I have requested and received a "+" hydro. My most recent "+" hydro was a couple of months ago.

rx7diver

 

[rvojr]

My recollection of this thread, is that it IS possible to get above the fatigue limit in steel with significant overfills.

If you believe the calculation there, you are at a 40k cycle lifespan. It doesn't look like anyone ever managed to dig up representative curves for the specific alloys in question though. I think it also doesn't account for the fatigue from the expected hydros, damage, or rough handling of the tanks. The representative curve is also log-scale in number of cycles, so 1000's is probably closer to a reasnoable-ish safety limit than counting on 10's thousands.

Those numbers ought to about cover my tanks usage for my lifetime and the next couple people that use them. My LP50s haven't been filled under 3k at a variety of shops over the last couple months. I'm sure someone will at some point, but I think the fill is set for at least 3k or 3900 to cool to 3500 at most shops.

 

[Superlyte27]

My recollection of this thread, is that it IS possible to get above the fatigue limit in steel with significant overfills.

If you believe the calculation there, you are at a 40k cycle lifespan. It doesn't look like anyone ever managed to dig up representative curves for the specific alloys in question though. I think it also doesn't account for the fatigue from the expected hydros, damage, or rough handling of the tanks. The representative curve is also log-scale in number of cycles, so 1000's is probably closer to a reasnoable-ish safety limit than counting on 10's thousands.

When OMS started importing Faber in the late 90's the marketing sticker on the tank and in the media read: "Guaranteed for 10,000 fills at 4000psi" While the govt made them pull the marketing, it did not change the structure of the tank. That is all!

 

[goldfishtornado]

Guaranteed for 10,000 fills at 4000psi

Interesting, that S-N curve from the old thread would put the cycle life in the 10,000-20,000 range at that pressure. It's still a mystery to me where the data for the plot comes from. The Wikipedia entry is a dead end. The kink at the fatigue plateau also corresponds suspiciously close to where a 10% +fill would land.

 

[rob.mwpropane]

Just in case you got left out in the cold and didn't get the "plus" on a tank.. can always invest about $8 in one of these, lol