Fuel Tanks and ethanol....

[Ike]

Why does aluminum corrode when phase separation occurs?

A quote form an article on my web site:

What about other types of tanks? It has been known for years that aluminum tanks can corrode from the inside out due to alcohol in the fuel. If the tank is left in storage for many months phase separation can occur, resulting in separate layers of fuel, alcohol and water in the tank. Acidic compounds form at the boundary between the water and alcohol
and this corrodes the tank.

I have been trying to find the source of that info in the last sentence, but I do recall it was in a research paper on alcohol problems in aluminum tanks. Give me a few days and I'll find it.

Also, yes, drains are not permitted in gasoline fuel tanks but nothing in the USCG regulations, ABYC standards, or ISO prohibits a secondary pickup and a means to pump out the water in the bottom of the tank. Tank pickups generally do not go all the way to the bottom of the tank just for that reason. You would pick up all the misc. crude that collects, as well as water. But you can pump it out if you want to. The fitting would have to be on top of the tank and the pump would have to suck the fluid out. It would have to be an ignition protected pump if it is electrical, unless it was outside the fuel tank compartment or the engine space, and the pump was not exposed to fumes.

And in spite of what that EPA paper says the people at the EPA who were dealing with boats didn't have a clue. I was the USCG liaison to the EPA on this issue and they didn't know squat about the effects of alcohol on fuel systems in boats and didn't even believe that it could damage the engines. I, and quite a few other people, quickly acquainted them with the realities of it. But it took a while for it to sink in. As far as the people in the EPA who deal with clean air, they never did get the picture. However NMMA and others are keeping after them on the E-15 and E-85 proposals.

[Bigfoot1]

To accurate twrs, Tom
I was trying to find my most recent copy of the ABYC standards but must have put lent them out.
They specifically state that fittings that are to be used in contact with an aluminum tanks must be aluminum or 300 series stainless due to galvanic corrosion that can take place between dissimilar metals.
If I find my book in the next few weeks, I will forward you the exact wording of the standards.

[Ike]

Actually it doesn't say that anymore.

here's the text of H-24 Gasoline fuel systems;

24.18.1 Tank Materials
24.18.1.1 Material thickness shall be at least the minimum thickness as listed in H-24 TABLE IV.
24.18.1.1.1 Materials not listed in H-24 TABLE IV shall be tested to demonstrate corrosion resistance in a marine
environment equivalent to those materials listed.
24.18.1.2 Steel sheet tanks, when constructed for gasoline, shall be galvanized on the inside and outside by the
hot dip process.
24.18.1.3 Fuel tanks shall not be constructed of terneplate steel.
24.18.1.4 Non-metallic materials are considered acceptable for corrosion resistance; however, all other
requirements of this standard must be met.
24.18.1.5 The copper-base alloys normally used for fuel fittings and lines are considered acceptable for direct
coupling with all fuel tank materials listed in H-24 TABLE IV, except aluminum.
24.18.1.6 Copper base alloy components shall be separated from contact with aluminum tanks or fitting plates by
means of a galvanic barrier such as 300 series stainless steel.
24.18.1.7 Fastenings used to couple fittings, such as fuel senders, to aluminum tanks shall be of 300 series
stainless steel or its equivalent in corrosion resistance.


H-33 - Diesel Fuel Systems, is almost identical wording..

[Bigfoot1]

Ike
24.18.1.6
says that you cannot screw a copper, brass fitting into an aluminum tank, (without a galvanic de-coupler) so I dont understand your comment, that it "actually does not say that any more"
as well as 24.18.1.5 copper is acceptible for fittings to fuel tanks EXCEPT ALUMINUM,
Bottom line, copper or brass based fittings are not allowed for direct connection with aluminum tanks

[Ike]

You said ;

specifically state that fittings that are to be used in contact with an aluminum tanks must be aluminum or 300 series stainless

What I meant is that the standard is a bit broader, allowing for other galvanic barriers. It's still a good idea to use stainless.

[TollyWally]

How do the plastic pipe bushings etc. fare?

[Ike]

I haven't actually observed them in use. Almost everything I've seen is metal usually Stainless steel, even on plastic tanks.

[Bigfoot1]

TollyWally, ( must be a tollycraft owner ha ha)
It appears that non metallic fittings are allowed as per the specs that IKE put in his response. We have seen the plastic caps used on the 5 gallon gerry cans, crack due to embrittlement which can be caused by UV light, maybe ethanol in the gas etc. The strength of plastic cannot equate to stainless or aluminum. On the other side, in the boats that we build, we often use an aluminum fitting that has a plastic draw tube attached to the fitting and we have never had an issue with these. Mind you the plastic is spec'd for this application, where as an ABS or
PVC plastic fitting may not be resistant to embrittlement from the marine environment.
I would expect that if you bought plastic fittings from a marine supplier that had the fitting specified as a plastic fuel fitting, then they might be ok.
Again for the price of a $2.00 fitting, why take the risk.

[CDK]

Glass filled PVC is an acceptable fitting material, although it slowly deteriorates in bright sunlight. It is not harmed by gasoline or alcohol. It is used on a large scale for all kinds of small industrial products. Carbon filled polyethylene is the material black jerrycans are made of, it is very durable in any environment, even with aggressive acids. Without the carbon (from recycled tires) it rapidly gets brittle in UV.
Polyethylene terephtalate (PET) is probably the best choice, both for a marine environment, Coca Cola and beer!

[TollyWally]

Thanks for the input guys. Bigfoot, Not much gets by you. CDK, talk about harsh environment.