Why no carbon fiber tanks?

[Scared Silly]

Luxfer makes a hoop-wrapped composite SCUBA cylinder

 

[Bob DBF]

Luxfer makes a hoop-wrapped composite SCUBA cylinder

About the same weight as a steel 10, about 4# more buoyant empty. On the plus side, it is 300 bar.

 

[happy-diver]

A blast from the past of mine 20 yrs ago

travelled the one on the right, shown next to an SCBA and a 40, twinned, around the world
drysuit diving?

 

[rjack321]

carbon fiber is also EXTREMELY fragile and you should be very careful if using them in salt water. If any salt water gets into the resin matrix through a small scratch/crack it will seep into the carbon fibers themselves. Once the tank dries the water will leave but the salt crystals remain and will abrade through the fibers as the tank expands/contracts due to temperature/pressure changes and will radically reduce their life. They are not a smart choice for in-water applications, especially salt. Perfectly fine on land, but absolutely the wrong choice for water.

Also the mention of buoyancy. Have to use steel for this because AL80's are a bit weird in terms of the squared off bottom. Current Faber FX100 weighs 34lbs and is just a hair negatively buoyant so call it neutral when empty. If you made that same bottle out of a CF composite it would weigh less than 15lbs, so call it 14 for round numbers. That bottle is the same physical size, holds the same amount of gas, but is now 20lbs positively buoyant instead of neutral. That weight has to be made up somewhere, hell even in cave diving we aren't ever THAT negative.

9L carbon fibers are quasi standard for exploration sump diving. Many people buy soon to be expired ones let go from fire departments at year 13 of their 15yr life. They take 14lbs of lead to make them neutral in freshwater though....

On the plus side you can haul a 13 lbs tank in and out of the cave to refill it and leave the lead behind. Here's an al80, a 9L with no rigging, a 9L with 14lbs of lead on it, and an hp100 side by side. The al80 has no valve in it, at the time I took this I was weighing them empty.

At 300bar the 9L CFs hold about 100cf of gas depending on the mix and compressibility.

 

[tbone1004]

@rjack321 not saying they don't have any use, just saying that aside from the safety issues of long term use in the salt affecting their strength that the buoyancy characteristics suck for normal use. Sump diving is one of those areas where they have a unique use, but there's what 40 people in the world qualified to do that kind of work?

 

[Mod63]

While I wouldn't touch CF tanks with a barge pole for OC diving, I quite like them as bailouts. The Worthingtons available in Europe are under the same rules as steel and aluminium, and even after 15+ years diving them in salt water they are no worse than my steel tanks.

 

[rjack321]

@rjack321 not saying they don't have any use, just saying that aside from the safety issues of long term use in the salt affecting their strength that the buoyancy characteristics suck for normal use. Sump diving is one of those areas where they have a unique use, but there's what 40 people in the world qualified to do that kind of work?

40?
There are cavers all over the world doing sump dives everywhere from Austria to Canada, to Mexico, TAG to Thailand. The lp45 steel tank (5.5L?) is probably used far more, but 9L carbon fiber is definitely in the mix.

 

[Subcooled]

That makes sense, they would probably be too light. I was thinking that they would be less susceptible to corroding and therefore better for underwater use.

Aluminum oxide should protect aluminum tanks from further corrosion in salty waters.
Steel tanks are great for cold sweet water divers.
Shouldn't the paint protect the tank?

 

[myself]

Aluminum oxide should protect aluminum tanks from further corrosion in salty waters.
Steel tanks are great for cold sweet water divers.
Shouldn't the paint protect the tank?

The paint would certainly help, but I have seen plenty of painted steel objects rust, ie: cars.

 

[Subcooled]

The paint would certainly help, but I have seen plenty of painted steel objects rust, ie: cars.

Fair enough! No paint cover is perfect!