Carbon Fiber tanks

[pasley]

I just checked the Luxfer website http://www.luxfercylinders.com/products/scuba/specifications/us_imperial.shtml and they claim to have a Hoop Wrapped 4350psi SCUBA cylinder. Now I don't know if the Gods at TC have approved this puppy but the 106 cu ft weighs in at 34 lbs (Compared to 32 for a AL80) empty. Salt water bouyance is 3lbs positive when empty and about 5 lbs negative when full.
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Their tank is a hybrid mix of thin metal cylinder with fiberglass wrap to increase strength. At present there are no approved by the DOT pure fiberglass or carbon fiber cylinders out there for SCUBA.

Can you imagine how fragile a pure fiber cylinder would be? Just picture yourself being slammed into a rock tank first by surge. In fact, take a look at any well used tank and the abuse it takes. My clear coated AL80 has lots of blemishes in the finish where I have been banged into a rock or two by surge, or surf, or who knows what.

I would not use one for SCUBA. These are tanks designed specifically for SCBA which is on dry land use only by fire departments etc.

 

[Ontario Diver]

Can you imagine how fragile a pure fiber cylinder would be?

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I would not use one for SCUBA. These are tanks designed specifically for SCBA which is on dry land use only by fire departments etc.

Actually, yes I can. I have seen, hydro'd, vis'd and repaired both Hoop wrapped and full composite cylinders as part of my company's business for fire companies, emergency training (lots of abuse) and others.

Both the hoop wrapped and the fibre composite are build by winding either fiberglass or carbon fibres around an aluminum shell. The difference is that hoop wrapped goes around the tank laterilly leaving bare aluminum at the top and bottom and the full wrap goes around the entire cylinder. In both cases the fibers are encased in resin (like fiberglass) and the finished product is covered in a coat of epoxy.

Neither 3HWM or 3FCM are as tough as aluminum or steel - but they aren't tissue paper either. Thier biggest drawback is abrasion and hard cuts and the higher amount of maintenance required in terms of more visual inspections and repairs to the expoxy coating.

These tanks when used are expected to take a beating but they are also expected to be trashed when they have taken a beating or reached the end of thier life cycle.

In fact this is one of the tests required..

9.13.5 Gunfire Test
One representative cylinder, filled with air or nitrogen to service pressure, shall be impacted by a 7.5 mm
calibre armour-piercing projectile having a velocity of approximately 850 m/s. The cylinder shall be so
positioned that the projectile impact point is in the cylinder sidewall wrapping at approximately a 45°
angle and aimed to exit at the cylinder sidewall. The distance from the firing location to the test cylinder
shall not exceed 45 m. The tested cylinder shall reveal no evidence of a fragmentation failure. The
approximate size of entrance and exit openings shall be recorded.

Yes, the cylinder would take the abuse of being smashed against the rocks - after the dive the cylinder would have to be inspected and if damaged - condemed.

 

[pasley]

...Yes, the cylinder would take the abuse of being smashed against the rocks - after the dive the cylinder would have to be inspected and if damaged - condemed.

Thank you. That was interesting.

Bottom line is that SCUBA has a lot of hard hits on sharp rocks and other items that would result in abrasion. The typical SCUBA user is a private party with limited wallet depth. The typical SCBA user is a municipality or other Government Agency with considerably deeper depth to their wallet and a paid inspector on staff. IMHO wrapped tanks are not practical for SCUBA for the typical private party.

 

[Ontario Diver]

The typical SCBA user is a municipality or other Government Agency with considerably deeper depth to their wallet and a paid inspector on staff. IMHO wrapped tanks are not practical for SCUBA for the typical private party.

Well, you haven't dealt with some of the volunteer fire depts that I have seen.

We agree on your points though. Much like the the use of rebreathers requires a higher standard of care and maintenance, the use of composite cylinders require the diver to recognize the demands of a product with a defined lifecycle and the discipline to condem the tank when appropriate. There may be places for them, but I do not think that they will become mainstream.

 

[derwoodwithasherwood]

Well, you haven't dealt with some of the volunteer fire depts that I have seen.

Speaking as one who has tried the express floorboard ride to the basement while wearing one of those "bombs", I gotta go with Ontario Diver with this one -- those composite cylinders are a lot tougher than they look. However, they don't make a lot of noise bouncing off steel beams so forget about attracting attention by banging your knife against it.

BTW: I have used one underwater. Ok, it wasn't that deep -- just a loading dock +1', but it worked ;-) My captain tried his out in a swimming pool shortly thereafter (who the h&!! puts a swimming pool on the 2nd floor anyway?). In both cases, the cylinder survived a hit on something hard underwater.

That said, the arguments about cost are valid. They must be hydroed every 3 years and decomissioned after 15 under TC rules.

 

[ChrisA]

Can you imagine how fragile a pure fiber cylinder would be? Just picture yourself being slammed into a rock tank first by surge. In fact, take a look at any well used tank and the abuse it takes. My clear coated AL80 has lots of blemishes in the finish where I have been banged into a rock or two by surge, or surf, or who knows what.

I think a pure fiber tank _could_ be designed for SCUBA. It is just that none are. Yes, carbon/epoxy would not take to abuse but what about a spectra or kevlar tank? Kevlar failure mode is not like carbon. Carbon tends be like a glass jar-- strong and ridgid, untill it fails completly but if you were to make a kevlar tank and then seriously abuse it with a 15 pound sledg hammer the tank would become a sack, still on one piece. I used to work with the stuff and have done the sledge hammer test on samples

I've seen kevlar/epoxy white water kayak on a Ford Bronco roof rack after the Ford bronco rolled on the road. We had to use a screw jack to push the Bronco's roof back up but the kevlar boats survived with only some skid marks on the decks. Boats were made with 12 layers of 9 oz saten weave fabric, epoxy and a vacuum bag process in a basic "garage shop" type factory. Nothing High Tech.

A filiment wound kevlar tank designed with thick walls could likely servive extream abuse such as falling off a truck at freeway speeds
and being hit be the car behind. (I've seen this too) but the cost would be over $1k per tank and you'd need loads of weight to make it sink, so what's the point?

 

[android]

I took a composite material course when I was a jet mech in the Navy. The stuff is strong and light. It also needs frequent inspection by a qualified inspector.

I love composite sports gear such as tennis rackets and golf clubs, but I just don't think it's a good idea for consumer products that can cause a fatality if the part fails.

That includes bicycle frames and forks and scuba cylinders. The bicycle forks are the scariest to me. I've seen pictures of failures and they are usually immediate and catastophic. The rider is almost guaranteed an ambulance ride.

If you get a fiber tank, learn to inspect it and do it frequently. This is usually going to be a "tap test" and visual for abrasion, scratches and broken fibers but get the mfg's recommendations.

 

[Xanthro]

Composite tanks can take punishment far greater than you might expect.

In paintball, composite tanks are the norm for compressed air. AL is used, but is heavier and generally considered low end.

I've seen 4500 pis tanks get dropped from cars and land on concrete, get run over by a car, get slammed into bunkers, slammed into the dirt, rocks, walls, etc.

I've never seen a failure other than a ruputed burst disk.

You can shot them with a high powered rifle and they don't explode, the will simply vent the air, and even that venting is not really powerful.

A hole AL cylinder goes flying across the room, as the pressure pushes the hole open and the metal tears. That doesn't happen with a composite cylinder. The hole doesn't really expand.

The big draw back, other than buoyancy, is abrasion. The tanks can tear, and while this tear might not leak at the time, it is a weak point. It would be better for the tank to slam hard against a rock than rub across it.

Also, as far as I know composite tanks are measured differently. The internal volume of the tank is measured in inches or feet at standard air pressure, then the PSI is listed.

For instance, I have a 119 cubic inch tank rated for 4500 PSI. I also have a 68 cubic inch rated at 4500 psi.

Xanthro

 

[shaneevans1]

Ok, Xanthro,
how bout a fiber tank with a neoprene cover, just like the paintballers use?
The 88ci tanks are not THAT expensive.. I seem to have the crap shot out of me regularly by a bunch of teenagers w/carbon tanks at our local field.. one of them, in fact is on my 12 year olds christmas list.
They look pristine after a couple of years of play in a neoprene sock.. just an idea.

 

[cdennyb]

Hi all,

Has anyone out there used carbon fiber tanks for a SCUBA application? If you have used them, how did they work? If not, why not?

I understand that they have some advantages(really lightweight), but also some serious drawbacks as well(large bouyancy swing).

Any thoughts?

well Hiram, as a fellow traveler who has seen "third base" I have to tell you. These tanks are cool, the only drawback is they're rated at 4350 psi but most compressors won't pump that high so the 106 cuft tank only fills to 80 cuft at 3000 psi but the good part is that I can pump it to 3300 psi without having to watch the gauge! Cool huh?
I have been given two tanks to use, (pictures enclosed), and find them both incredible units. They are made form 7000 series alum. and are wrapped with fiberglass to get their high pressure capability. As you can see from the pictures they are very pretty tanks and to tell the truth, I can't find anything wrong with them. They came O2 cleaned in sealed bags with thermo valves (DIN Style) (in sealed bags as well)and we loaded them right from the startw ith 36% nitrox. Using them as singles was no problem at all with buoyancy but I dive a dry suit and don't really notice the difference between them and the 80 cuft tanks.
To be honest, I don't see a big advantage unless you can pump to 4350 and use them till they're empty or close to it... 4350 psi gives you 106 cuft in the same size package as a standard 80 cuft tank, so there's an added benefit from that alone. They also are labled with a service life limit, which means in the year 2017 no one will fill them except for me personally if I still own them.
So there you go, right from someone who uses them. (Oh, I also own 6 other 80 cuft tanks, a set of doubles, and the rest singles and our own compressor.)
db