Composite fiber tanks

wrongjohn · Post by **wrongjohn** » Mon Jul 23, 2007 9:00 am

I did a search of the board, and didn't come up with anything, so I thought I would ask.

Why aren't divers using composite fiber epoxy tanks, specifically ones with metallic linings like those used by firefighters.

When I lived in CA, I did some web work for a company that manufactured them, several of their products seemed IDEAL for scuba diving, I asked, they saw no reason they couldn't be used for that application, they some of the tanks in question are specifically used for Scott packs, SCBA systems for firefighters. Those packs take a BEATING, firefighters LITERALLY throw them around, they get wet, they get toxic chemicals on them, they get really really hot in their working environment and they often in the winter get covered in ice cold water at the same time they are getting cooked. It seems to me if they can handle the torture of entering a burning building, they can handle a simple recreational dive?

Most of the tanks used by firefighters now that are composite are 4450psi.

Have composite tanks hit the scuba market and I just haven't spotted them or are they not here, and if not, is there a technical reason?

I mean composites are proving themselves to be a great technology for pressurized gas and cryo-gas storage so why aren't they getting use for something as simple as diving?

Cost?

Nwbrewer · Post by **Nwbrewer** » Mon Jul 23, 2007 9:09 am

My understanding is there are two major issues with using these tanks in diving applications.

One is cost, they are more $$$ than a steel tank. The other is that they are very positively bouyant. Light tanks are great for firefighters, not for divers, you'll just have to add lead back to compensate for that nice light tank. Steel gives you the best bag for your buck in tanks.

Jake

CaptnJack · Post by **CaptnJack** » Mon Jul 23, 2007 9:11 am

1) There is one composite tank approved for scuba diving, I don't have time to find it right now, but the 4500 psi fill pressure is definately hard on equipment

2) most SCBA tanks are not approved for scuba

3) most composite tanks have a 15 year lifespan, after that they must be discarded and are no longer legal to fill.

So in a nutshell:
Hard for manufactures to get composites DOT approved for scuba use
Hard to get 4500 psi fills
Limited lifespan
High cost

The cost benefits of composites just aren't there, esp. since you would just need to load up on lead to compensate for their light weight.

Richard

Sounder · Post by **Sounder** » Mon Jul 23, 2007 9:28 am

I think one reason we're not seeing them used in diving is their buoyancy characteristics. Scott SCBAs are wonderful for firefighting and HAZMAT operations because they were designed to maximize high air capacity to low weight while being as strong as possible.

I imagine the water displacement in the larger capacity bottles is about that of a HP80. I'd bet the SCBA tanks are fairly positively buoyant when they're even half full (pure speculation on my part) due to their light weight... again having been DESIGNED to be as light weight as possible.

So, would they work for SCUBA applications? Sure, but you'd have to compensate for their displacement with more weight on your belt (or where ever you put it) than what is probably comfortable.

I don't know what the expense factor is for them, but they're using the same manufactuing process for some paint-ball gun bottles. Granted, they're the expensive choice for gas bottles, but they're still affordable enough to be a consideration of many players.

My 2psi.

Sounder · Post by **Sounder** » Mon Jul 23, 2007 9:29 am

Wow, everyone responded at once!

wrongjohn · Post by **wrongjohn** » Mon Jul 23, 2007 11:12 am

CaptnJack wrote:1) There is one composite tank approved for scuba diving, I don't have time to find it right now, but the 4500 psi fill pressure is definately hard on equipment

2) most SCBA tanks are not approved for scuba

3) most composite tanks have a 15 year lifespan, after that they must be discarded and are no longer legal to fill.

So in a nutshell:
Hard for manufactures to get composites DOT approved for scuba use
Hard to get 4500 psi fills
Limited lifespan
High cost

The cost benefits of composites just aren't there, esp. since you would just need to load up on lead to compensate for their light weight.

Richard

I didn't think about the life span, that's news to me, I know they are making tanks that last longer than that, at least they were when I was doing the work for them almost 10 years go. Some of the cryo tanks had service lives of over 40 years. If we are going to use Hydrogen as a energy carrier for all these h2 Fuel Cell cars, we are going to be using composite tanks in cars. Then again, I don't expect a H2 fuel carrier economy anytime soon, I was told when I was young, I would have a nuclear powered flying car by now and a personal jet pack.

I also didn't know about the expense. I even when I worked the site, everything was by quote so I had no idea about the actual cost of their wares.

I have never thought about the relative density to water of the various composite material formulations, as it's never been a matter I have needed to factor in.

Well, I was just wondering. I constantly am wondering about such things, and now I know.

Thanks,

Steel it is.

Sounder · Post by **Sounder** » Mon Jul 23, 2007 11:22 am

Mmmm... steeeel. $\:D/$

CaptnJack · Post by **CaptnJack** » Mon Jul 23, 2007 1:12 pm

Sounder wrote:Mmmm... steeeel. $\:D/$

Around here steel is definately the way to go. Down in the tropics AL has its benefits - the few steels I have seen in MX are downright scary! Too much corrosion for poorly rinsed gear in 80F (water) - 95F (air)

airsix · Post by **airsix** » Mon Jul 23, 2007 2:46 pm

The composite scuba cylinders were a system sold by Interspiro (the makers of the 'gold-standard' AGA full-face mask), but I don't know who manufactured them for Interspiro. I used to have an AGA and it came with literature about the composite tank system. They were skinny cylinders mounted as either triples or quads. I forget which. Bob Thiry (I think his screen name is Bob3 on decostop and scubaboard) has a set. He's a nice guy and will answer questions if you care to ask him.

-Ben

CaptnJack · Post by **CaptnJack** » Mon Jul 23, 2007 3:55 pm

Luxfer's 2 composite scuba cylinders are at the bottle of this page.
http://www.luxfercylinders.com/products ... rial.shtml

Not super positive - fairly similar to an AL80, but they are a wrapped AL+fiber tank. Don't know the cost. Don't know if they have a service life or what it is. I bet VIPs are a pita, special rules for carbon fiber tanks, etc.

Since AL80s suck in a drysuit already there doesn't seem to be much local demand for these. Slightly heavier than a steel HP100 but positive at the end of the dive by +3

Overall not very useful do-dad.

wrongjohn · Post by **wrongjohn** » Mon Jul 23, 2007 5:49 pm

CaptnJack wrote:Luxfer's 2 composite scuba cylinders are at the bottle of this page.
http://www.luxfercylinders.com/products ... rial.shtml

Not super positive - fairly similar to an AL80, but they are a wrapped AL+fiber tank. Don't know the cost. Don't know if they have a service life or what it is. I bet VIPs are a pita, special rules for carbon fiber tanks, etc.

Since AL80s suck in a drysuit already there doesn't seem to be much local demand for these. Slightly heavier than a steel HP100 but positive at the end of the dive by +3

Overall not very useful do-dad.

I would presume Aluminum linings are the norm for composite tanks. The aluminum lining I suspect IS the mandrel/mold during the lay-up/laminate process. Otherwise making a composite tank would get very very complicated as it would have to be laid-up in multiple parts and joined. I don't think that would offer the structural integrity necessary to pump 200-300 bar worth of gas in one. I understand how Steel tanks are made and well it amazes me that they are so consistent, but they are. They are just press formed out, it's quite amazing.

I have done layups and made some pretty complicated forms for layup, it's no fun, weeks or months of work can go into making a semi-durable form that can be screwed up very very easily. Having a cheap form that goes with the tank seems the only logical choice to me for commercial manufacturing. The lining I suspect also significantly reduces the chance of de-lamination by gas intrusion if there are imperfections in the inner most layers of the lay-up surface. I certainly would want SOMETHING extremely gas tight between the HP gas (particularly an enriched 02 gas or H2) and the composite.

Also looks like they use a less than typical (for application) thread fitting, which means you have few valve options. I wonder if they make them or if they are outsourced.

My curiosity really ended with wondering why they weren't in wide spread use. And there seems to be a number of factors that could be contributing to that, including most fundamentally the aren't as ideal as "older" technologies for the application. I am sure cost, life-span, FUD, and DOT red-tape doesn't help either.

I have no particular want of CF tanks, unless they offered a real advantage to the shore part of the excursion at no expense to the underwater portion. And that is sort of true:

Compare the S100 (steel?) and S106W (composite) tanks (capacity and operating pressure aside):

On land you are going to have to 41.0lbs with the S100 and just 33.8 with the S106W.

The S106W is likely going to be lower drag in the water, it's smaller in diameter and about the same length. But it's going to be MUCH lighter on the surface, a full six pounds lighter. Either way you are going to have to stick around the same amount of weight on your backplate to offset the eventual buoyancy of the tank. But with the composite, your total load out weight on land is still six pounds lighter (12 if you are lugging a second), and from where I learned to dive, where we may walk a half-mile from where we can park, to where we start the 5 story run of stairs down to the beach, that's not insignificant. Because after the dive, you have to go back up those stairs, with all your gear, and walk that half-mile back to your car.

But I am still solidly sold on the idea of low pressure twins, they are what I know. I may explore something larger than the 70's I had, and with a higher operating pressure, I am nearly certain I am going to go with a isolation valve. Who knows I may wind up using some big HP steel tank, I have no idea. That's why I plan on asking a bunch of questions.

Dmitchell · Post by **Dmitchell** » Mon Jul 23, 2007 6:55 pm

CaptnJack wrote: I bet VIPs are a pita, special rules for carbon fiber tanks, etc.

VIP procedure isn't any different than any other cylinder. CF tanks are allowed certain amount's of damage just like AL tanks are. Nice thing about CF tanks is that you can repair minor damage.

The whole idea of CF tanks seemed cool, but the reality was that they are too expensive (something like $400+), too high pressure (4350), not buoyancy friendly, and they have a limited life.

Dave

CaptnJack · Post by **CaptnJack** » Tue Jul 24, 2007 12:24 am

Most scuba shops won't have the specs to VIP Luxfer's lone composite tank. If there were a bunch out there from various companies (e.g. Scott) I could see VIPs being a big problem. Heck shop staff have a hard enough time understanding 6351 issues, eddy current tests and the differences between their personal fill decisions and DOT laws/rules. I don't see composite tanks as entering easily into the scuba market. Not when steels last for decades, have good bouyancy characteristics, and are suitably cheap.

Dmitchell · Post by **Dmitchell** » Tue Jul 24, 2007 9:34 am

CaptnJack wrote:Most scuba shops won't have the specs to VIP Luxfer's lone composite tank.

That's totally bogus!

You obviously know nothing about VIP and the training to become an inspector.

When you take the course you are taught to visually inspect all cylinders, the process is the same 19 steps for a composite cylinder as it is for any other cylinder. Scuba shops frequently visual SCBA bottles as well as Paintball, Oxygen, and other cylinders.

The only difference in the visual process is that on a composite cylinder you look for damage to the fibers and there are generic spec's for how much damage is repairable.

If I recall correctly a scrape in the epoxy can be repaired but if there are broken fibers, it's condemned.

DM

airsix · Post by **airsix** » Tue Jul 24, 2007 9:42 am

If you have a look in person at the Luxfor fiber-wrapped tank you'll see that it's not a true composite cylinder at all. It's basically an AL80 that just has a fiber & epoxy reinforcing belt around it to increase the pressure rating. I can't imagine the VIP procedure being any different for this cylinder. If you are just looking at the inside you could not distinguish this cylinder from any other AL cylinder. The other thing to note is that the tank has a stamped disposal date so regardless of VIP or hydro, when it hits that date it goes in the bin.

-Ben

CaptnJack · Post by **CaptnJack** » Tue Jul 24, 2007 10:27 am

Dmitchell wrote:
CaptnJack wrote:Most scuba shops won't have the specs to VIP Luxfer's lone composite tank.
That's totally bogus!

You obviously know nothing about VIP and the training to become an inspector.

When you take the course you are taught to visually inspect all cylinders, the process is the same 19 steps for a composite cylinder as it is for any other cylinder. Scuba shops frequently visual SCBA bottles as well as Paintball, Oxygen, and other cylinders.

The only difference in the visual process is that on a composite cylinder you look for damage to the fibers and there are generic spec's for how much damage is repairable.

If I recall correctly a scrape in the epoxy can be repaired but if there are broken fibers, it's condemned.

DM

Nice try bud. Composite cylinders have a variety of allowed (and disallowed) damage limits. Some scrapes can be repaired, some not - yes there are generic limits but it also depends on the tank's construction. I don't VIP them.

Since shops can't get the stupid 6351 issues straight, often calling them "illegal", use eddy current testers on 6061 or worse steel tanks unnecessarily, etc. - assuming that they will competently VIP and/or repair composites when they've never or rarely seen one is awfully wishful thinking.

And yes I am a PSI inspector.

CaptnJack · Post by **CaptnJack** » Tue Jul 24, 2007 10:29 am

airsix wrote:If you have a look in person at the Luxfor fiber-wrapped tank you'll see that it's not a true composite cylinder at all. It's basically an AL80 that just has a fiber & epoxy reinforcing belt around it to increase the pressure rating. I can't imagine the VIP procedure being any different for this cylinder. If you are just looking at the inside you could not distinguish this cylinder from any other AL cylinder. The other thing to note is that the tank has a stamped disposal date so regardless of VIP or hydro, when it hits that date it goes in the bin.

-Ben

Do you have one? Do they have a 5 year hydro cycle or something different (like 3)? How much do they cost?

Dmitchell · Post by **Dmitchell** » Tue Jul 24, 2007 11:37 am

Inspecting these tanks is simple and no different than inspecting a Scott bottle which very well may be made by luxfer.

Tanks have a 15 year life and cost ~$400 each.

Here's the inspection criteria PSI revised it's course in 2003 to teach inspectors to inspect these tanks.

http://www.luxfercylinders.com/download ... manual.pdf

Looks the same as what I was taught by PSI.

Ben's right, looking inside a composite cylinder looks just like looking inside an AL cylinder.

BTW, if you are up to date on your equipment you should have a Visual Plus 3 and should be eddy current inspecting 6061 cylinders as well as 6351.

DM

CaptnJack · Post by **CaptnJack** » Tue Jul 24, 2007 12:01 pm

Eddy current tests are not required on 6061. Yes the Visual Plus3 can do them. A great way to keep making those tools and services now that all the 6351s have been deemed "illegal" by misinformed shops. I don't see any real need to have a VP3 since they may improve the quality of my VIPs but more technology/stuff does not necessarily = safer tanks.

(Granted I actually agree with the risk management decision not to fill 6351 tanks. However shops should just come out and say that they are not worth the risks and not try to hid behind DOT on this issue.)

Whether any of the above types of confusion would actually extend to composite scuba cylinders is certainly debatable. But I don't know anyone considering a 100cf,
3+ positive when empty,
limited lifespan,
comparatively damage sensitive
$400 tank in lieu of a

$320 lp95/hp100 with vastly better bouyancy, robustness, and lifespan. So whether you'd get hassled by a shop at VIP time is kinda a moot point, around here at least.

rcontrera · Post by **rcontrera** » Wed Jul 25, 2007 10:21 am

You guys are missing one important part in the equation ... filling them! 4300 PSI is a bunch of pressure! And there are a lot of shops that can't pump that high. There are even more that shouldn't pump that high.

A compressor that is rated to run for about 2000 hours before a full overhaul while running at 3000 PSI will most likely need the same service at 1000 hours or less if run at 4500 PSI.

Shops that fill to 4500 should be charging a lot more for fills than they do to fill 3000 because they tear up their compressor. Many dive shops charge $3-5 for a standard 3000 fill on an 80 and the same $3-5 on a paintball 4500 PSI bottle which is usually only about 8 cubic feet. But the fill does about the same amount of damage.

That's one of the reasons that many fire departments change out compressors every 3 to 5 years and dive shops only ever ten to fifteen years.

OK ... I'll climb down off my soapbox now.

CaptnJack · Post by **CaptnJack** » Wed Jul 25, 2007 10:27 am

There seem to be a few local shops pumping quite a bit over 3000psi routinely. At home, I do some limited pumping to keep my 4500 psi bank bottles filled to about 4300. I don't often dip into them but they are nice to have.

As a compressor guy, I'd expect you ecourage HP fills Ray!

rcontrera · Post by **rcontrera** » Wed Jul 25, 2007 10:47 am

As a compressor guy, I highly encourage regular oil and filter changes ... but they don't happen as often as they should either.

You might think that I like compressors breaking down, but I don't. It always seems to happen at the most in opportune moment for the shop. Our compressor mechanic isn't cheap and many shops are usually out of or low on cash at the time of breakdown (at least that is what they say). So I get stuck paying the mechanic and the parts and then have to wait for payment on the repair.

On the other hand, when they are going to buy a new compressor, they always have either their financing in order or have the cash. It is a much easier deal for me!

No, my biggest concern is our divers. I have a ton of friends that use dive shop air and THEY are the ones I worry about. While nobody (that I know of) pumps unsafe air, the quality ranges from OUTSTANDING to OUTHOUSE! Pumping to higher pressure is a faster road to the outhouse.

Sounder · Post by **Sounder** » Wed Jul 25, 2007 10:49 am

No, my biggest concern is our divers. I have a ton of friends that use dive shop air and THEY are the ones I worry about. While nobody (that I know of) pumps unsafe air, the quality ranges from OUTSTANDING to OUTHOUSE! Pumping to higher pressure is a faster road to the outhouse.

Simply poetic!