Why no carbon fiber tanks?

[rjack321]

Galvonic coupling is a thing I've learned about. It still seems like there has to be damage to the outside of the tank for especially salt water to get in, and then it actually has to corrode bad enough to fail.

Carbon fiber cylinders are made by wrapping the fibers around an aluminum liner (shell). Then the epoxy is applied and dried. So there is an inherent flaw in this design for underwater purposes, water penetrates along the aluminum - composite interface and galvanic corrosion sets in there. So it's not just through exterior nicks in the epoxy that water gets "in"

SCBA's in fire service aren't subjected to more than 1 ATA so there's a lot less water trying to force its way into that Ali-composite bond. They get plenty of exterior abuse, but also frequent inspections

 

[rjack321]

How do you get a 6000 psi fill? Most scuba shops i know of can fill to the high 3000's at best. Do fire departments just have different compressors?

You'd be shocked to learn that most air service compressors pump way higher than dive shops are willing to fill.

 

[rjack321]

Seems you are referring more to SCBA than SCUBA. What about using them for diving?

not rated for underwater use.
consider it a semi disposable cylinder - that takes a boatload of lead to sink

 

[MikeHoncho]

How do you get a 6000 psi fill? Most scuba shops i know of can fill to the high 3000's at best. Do fire departments just have different compressors?

Our MAKO fill compressors filled a bank of steel bottles to 6000 psi. The composites I’m talking about at that pressure are compressed gas tube intermodal which are CNG and other industrial use compressed gas systems.

 

[MikeHoncho]

not rated for underwater use.
consider it a semi disposable cylinder - that takes a boatload of lead to sink

I’ve never heard of a specific rating for under water use for a bottle but the SCBA they attach to are not ( but work). Physics wise a tank would be more stable at depth than a sea level I would think.

 

[211ratsbud]

Yes, I have two of them for rebreather bailout tanks. They are not DOT approved. Because they are bailout tanks, I don't need to get them filled very often. Here is my writeup on them:

Carbon Fiber Twins (or, maximizing bailout gas efficiency)

(NB: experienced technical rebreather divers might find this post “boring” while beginning technical divers might find it interesting and provide you something possibly new to think abo…

wreckedinmyrevo.com

- brett

I have some. I did not care for how light they got so quickly once I started huffing on them in bailout drills. I am reluctant to put a weight on it myself. Some of my buddies have the 12l versions with nx50+ in them and a good chunk of lead.

They're also pricey.

But that's another thread

 

[rjack321]

I’ve never heard of a specific rating for under water use for a bottle but the SCBA they attach to are not ( but work). Physics wise a tank would be more stable at depth than a sea level I would think.

ISO 11119-2 is adopted by reference by US DOT.

Carbon fiber SCBA cylinders are not subjected to the saltwater immersion testing requirements for underwater use (due to the corrosion caused by the drying salt). So they are not approved (by the manufacturer nor DOT) for that use.