Best composite material for gasoline tank 1

[Rink]

Can someone comment on the properties of the following materials with regard to use as a gasoline tank? In each case, a choice of resin must be made. I've made a matix below to help simplify your responses (hopefully).

References or links appreciated, in addition to experience or guesses...please identify

---------------------- Polyester---- Vinylester----epoxy----
E-glass | EP | EV | EE |
S-glass | SP | SV | SE |
Aramid/Kevlar | AP | AV | AE |
Carbon fiber | CP | CV | CE |
--------------------------------------------------------------

 

[avior]

In D.Gay, S.V.Hoa, S.W.Tsai ’s book “Composite materials - Design and application”, at page 172 speaking about efficiency they recommend kevlar/epoxy against glass/epoxy. More, in chapter 18.1.8 they calculates the stress, strain, etc. considering a thin tube under pressure made by filament winding of glass/epoxy with a winding angle 45, the fiber volume fraction is 0.6. speaking about winding angle in chapter 18.1.9 is calculated the winding angle and the wall thickness for a pressure vessel made of glass/epoxy rovings with 0.8 fiber volume fraction. There are more useful examples.

 

[samplesecond]

are you planning on having some sort of bladder within the tank, or is the gasoline in contact with the interior surface of the tank?

 

[Rink]

samplesecond,

No bladder. Gasoline in direct contact with the composite surface. That is the thrust of my question. My understanding is that one of the reinforcment materials I listed tends to soak up fluids more than the others, but I can't remember which one! CRS.

 

[MechanicalChef]

I see a fundamental issue with running a composite tank without any type of bladder. Composites generally don't like to deform. In the event of an accident, the tank won't simply bend or leak. Without a bladder, it's probably going to rupture and dump fuel everywhere. Sounds like a great way to get hurt or killed.

 

[samplesecond]

Above and beyond the safety consideration, I have had epoxy resins break down (with carbon substrate) under extended exposure to petroleum distilates (gasoline and diesel)- the mechanical strength of the composite diminished about 40% (in bending) after about 100 hours of continuous exposure to the fluids...Unfortunately, I never had the opportunity to determine the reason for failure (be it from material/resin imcompatibility with the fluids, or process/user error..)

That said, I would be very curious if there are any recommended coatings/alternative resins which might provide a longer service life

 

[MechanicalChef]

Also, in aerospace, many of the resins we deal with have ratings for exposure to petroleum distilates. In our case, hydraulic fluid, lubricating agents, etc.

Oh, I just dug this up:

http://www.ppg.com/prc-desoto/pdf/PPG AEROSPACE QUALIFIED AT BOEING for chromate-free primer.pdf

It's a primer used on the composite fuel tanks for 787.

 

[berkshire]

Rink (Automotive)
Do not forget that you will also need a means of discharging static build up from fuel filling the tank.
i.e copper tapes or mesh.
B.E.

 

[Rink]

samplesecond,

Interesting. I see motorcycle fuel tanks advertised that seem to be fiberglass, kevlar or carbon fiber, sometimes in combination. No mention of resin breakdown issues in their sales literature (no surprise I guess).

Here's a quote from one such website:
"Q. Do your tanks require a bladder and or do I have to apply a fuel proof coating on the inside such "Kreem"?

A. Neither. FuelCels are inherently fuel proof and leak free by creating an impervious shell matrix. In fact, a coating would have nothing to stick to and could peel off and get into your fuel system."

... and from the same site-
"Q. Will I have to drain my race fuel from my tank?

A. The epoxy matrix we use has never exhibited any problems with race fuels over extended periods of time."

----------------------------------------------------------------
Berkshire,

Thanks, I would not have thought about this until the first (and last?) discharge!

 

[RPstress]

If this gas tank is in a vehicle then crash-worthiness may be an important design driver. Non-metallic automobile fuel tanks are typically layered with a variety of materials so that they can withstand considerable deformations without leaking. If you use a liner or similar to contain leaks then bear in mind that any stiff fiber reinforcement like glass can make a nasty source of sharp edges if it breaks. If any liner is to be used for containment, then a flexible puncture-resistant layer outside it would also be desirable.

There are a great many glass/polyester and glass/vinyl ester pressure vessels out there with a big variety of corrosive fluids and solvents in them. Glass/epoxy is also sometimes used, but epoxy's superior properties are generally not worth its extra cost in this sort of application. (For most applications, epoxy isn't that much better than vinyl ester anyway.) The same applies to carbon fiber; it's really only used for weight-critical pressure vessels. S-glass is strong, but there's probably little reason to use it here. I would avoid Kevlar or other organic fibres in this context. Kevlar doesn't stick that well to polymer matrixes to start with, and having solvent around can't make things any better.

For all common matrixes I would not anticipate a great problem with gasoline, though orthophthalic polyester should not be used. The matrix near the wetted surface will be slightly plasticized, giving a slight reduction in compressive properties. You could use a liner to avoid this, but there is no great necessity. If the external surface is exposed to the elements it should be painted to have good durability (many years).