using luxfer carbon fiber tanks on rebreathers

paulraymaekers

hello all, as a test, since a year some of us are using luxfer carbon full wrap tanks on their breathers: they are great for traveling: a 3l tank weights 1.9kg! but....

they are not rated for diving, only for SCBA. the explication I got is that there is not enough market for those little lightweight tanks to go trough the testing and certification proces for diving application.

are there other reasons why?? I heard of the dräger composite tanks that could not be used for diving because of porosity in seawater, but I think this does not apply for the luxfers w're using.

any idees???

paul

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.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

silent running

Vey cool idea Paul. The explanation of demand vs cost to certify might be plausable. I guess many OC divers count on the tank being heavy enough to figure into being neutral in the water and most don't travel with theirs, so the land weight is not an issue for them. But then again, what dive operator wouldn't prefer a lighter tank, even just for handling around the shop/boat?

What size are the luxfers you use? And what's the rated pressure?

gtzavelas

a couple of years ago I was investigating buying such tanks to transport quite far inside caves. I finally decided against it because after doing some research I found out that they are VERY sensitive to banging / hitting.
I will try to dig out the info.

divetheworld

We have made composites for diving applications for some years now and I can tell you that it is very difficult to get it right.
The problem is that the seawater travels/wicks up the bonded fibres when under pressure and finds its way into small cavities. The best you can expect is to find some cosmetic damage to the outer poly resin. The worst is a complete failure of the fibres.
Carbon fibres are actually crap for strength until they are boded with a resin media. If you get some raw carbon and rub it between your fingers, it will disintegrate into powder before your very eyes. If the resin is weakened then the whole structure is wastage.
For diving applications, the whole composite structure has to be sealed with an outer poly coat.

Draeger SCBA cylinders are sealed as far as I know. To what external pressure they will withstand before saltwater ingress occurs...I have no idea.

Brent

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ccr_ada

Will we be seeing them at the NEC Paul?

THANKS

ccr_ada

paulraymaekers

no, the standart rEvo will have steel tanks on it :-(

we use the 3 liter L29C 1.9kg, 300bar (test pressure 450, burst pressure mini 1100 bar) but we use them at 200 bar!

regards
paul

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www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...

jaap

Hi

Do you know if Luxfer are making the cylinders or if the buy them from some other manufacturer? I know that Interspiro composite cylinders are made by a ABB company.

I have dived with Interspiro composite twins on OC, and happened to teach a dive course for the company. So I picked up some info about some problems with composite cylinders in SCUBA applications.

Have you noticed that the cylinders drop in pressure if filled and not used for a few weeks? Gas is lost by diffusion.

If no, then you probably have a cylinder with a metallic liner? As I got it the liner can be a dangerous thing since the thermal expansion will likely not be the same as the composit and this can promote the formations of cracks. So cylinders with a liner might needs special inspections/handling procedures. I got that info from Interspiro and they don't use metallic liners so the information could be biased.

The testing for SCUBA approval of a composite cylindes is much stricter than for ordinary cylinders, the same goes for the inspection interval/procedure. This is due to several complications like that the material is much easier to damage, water affects the composite in several ways, the fabrication of the cylinders have a higher degree of defective units.

The seal between the valve and the cylinder is also a critical part since its metall to composite. The expected corrosion of the metal insert (valve to cylinder) and swelling of the material can be very different for a SCBA and SCUBA case. So a SCBA design may be unsuitable and dangerous for SCUBA.

Use of higher O2 contents can also be a real problem for composite cylinders. Interspiro is delivering composite cylinders that are approved for SCUBA with _Air_ to the Swedish Navy for use in semiclosed _nitrox_ Rebreather. But these are not really approved for general nitrox use since (if I got it right) the composite has properties like ignitions points that are too low. The Navy got around this since they can approve things for internal use according to their needs without having to follow EU rules and such things. But (again, if I got it right) they did alot of testing and found them to be safe for _premixed_ nitrox filling but _not_ for 100% O2.

So, lots of potential troubles.

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My initials: JAAP

J. V.

Luxfer SCBA carbon tanks have a thin aluminium liner wrapped by composit. Luxfer indication says to charge it at 30 bar /minute maximum to limit temperature elevation. Tanks seems OK for oxygen use, there is a sticker tagged "oxygen". But they have a limited life, 10 or 15 years (I don't remember exactly and I don't have my cylinders near me )

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Jacques
NPSFQQA-EDS IT # 007
(remué non agité)

Deepthought

I seem to remember an article a few years back involving a new design for a compact tank for firefighting.

This was a composite toroid tank (ring shaped like a doughnut) and it was reinforced using aramid fibres (AKA Kevlar - tensile strength 6 times that of steel for less weight!)

There's a lot of interesting technology out there but divers only get it 'second hand' - e.g. they didn't develop O2 sensors for us but for medical use, we're just lucky that the technology is suitable.

I know there have been warnings (and casualties!!) in the UK about not using SCBA tanks for Scuba. I seem to remember that the root cause was that though the valves were standard DIN outlets they were prone to corrosion and failure in saltwater.

paulraymaekers

lifetime 15 years, testing every 5 year, oxigen compatible

we do always fill them slower than steel tanks!

paul

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www.rEvo-rebreathers.com

.... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...