Aluminum Fuel Tank Build Question

[jpendoley]

Looking to clear up a question regarding building fuel tanks with aluminum. I just replaced my rusty 50 gallon tank with a shiny new custom built aluminum tank. I have read on boat building forums that aluminum from the factory has a “mill scale” that should be removed prior to service. It’s presence can lead to corrosion down the line. It can be removed by lightly sanding or by acid etching. My fabricator says not so, but I read a couple of pretty well written articles that were convincing. What’s the consensus? My steel tank gave many years of service, I need this to be my last tank install-it’s an arduous project.
Jim

[Rucksta]

Check with your fabricator why he says it is not required to descale.
It may be he has already done so.

Removal of the mill scale - shiny coating on new aluminium - is done prior to MIG welding to prevent porosity of the weld.

Since the wire brush and or acid wash is already out for the weld prep it would be good practice to descale all surfaces.

The corrosion problem is pronounced when deoxygenated water sits next to shinny aluminium.

[jpendoley]

Thank you-just confirms everything I read. I called the fabricator and asked and he said it has no mill scale because it’s aluminum. Not feeling real confident about his answer...
And the surfaces are shiny-when the surface should be flat and appear dull. I guess I will learn how to descale aluminum after fabrication now....

[sailah]

Im a garage aluminum welder with my TIG so take that into consideration....

You remove the oxide layer on aluminum prior to welding to prevent contaminating the weld. I do this with dedicated stainless brushes then wiping down with acetone. Same with the filler rods. Aluminum will oxidize naturally and quickly in the presence of air and this forms a protective layer. If you remove this, it will simply oxidize again. Not sure why you'd want to remove this layer as it will just keep coming back. Unless you coated it with something.

Ive seen plenty of people coating tanks with coal tar epoxy though.

That's all i got.

[sailah]

Mill scale is something i would refer to when talking about hot rolled steel, not aluminum. Cold rolled steel doesn't have this as much.

Im tending to lean in your fabricators side but open to being wrong.

My 44 gal aluminum tank is bare on my 1986 Dickerson and still looks new.

[sailah]

I don't think i made my case clear... sorry before coffee. I would not attempt to remove what you are referring to scale. Aluminum oxide layer is beneficial. It's removed prior to welding just to prevent porosity and contamination of welds and it will reform in minutes protecting the metal.

If that were my tank, I'd clean and abrade ther tank in order to get a good bond with an epoxy but that's all i would do.

Maybe call an aluminum tank builder in Florida and ask a third party? I think your welder is correct

[Dougtiff]

I had Aluminum water and diesel tank's fabricated for a customer, that have been in place for about 5 year's now, with no issues, never heard of mill scale on aluminum, as already stated, alu oxidizes.

[captjamied]

Man this thread...where do I start...?
As a journeyman shipwright and aluminum boat builder I have built literally hundreds of aluminum fuel tanks. The "Mill-scale" (it's not mill scale exactly)...technically, mill scale are iron oxides...but let's not digress.
What, I believe, you are referring to are aluminum oxides, and your fabricator is spot on. Aluminum oxide layer on the surface protects the aluminum from corrosion. These oxides need only be removed at the weld zones prior to welding, you should be more concerned about the clean up of the finished tank as weld spatter, smoke, and microscopic debris in the tank can get into suspension and pass through the fuel lines and, hopefully, into your filter.
Happy sailing.

[georgeg305]

On the subject of aluminum fuel tanks, I would expound on my boat tank. If you live in a humid climate ( such as North Florida where I live ) you should check for water in your tank. You can buy a water detecting grease from your NAPA dealer. Smear some on a stick and "stick" your tank. That's assuming your tank, like the one on my Catalina 30 has an access plate on top. The grease will turn orange when water touches it. The problem with water is that there is a bacteria that lives in the water and eats diesel fuel. Its commonly called "algae". Algae pee is acetic and will eat holes in the bottom of your tank. My boat had been abandoned by the previous owner. I found my problem when the tank started to leak. Water can come from three sources: contamination when you buy fuel ( only buy from hi volume dealers ), leakage from the "O" ring on the deck fill plate cover, ( check your "O" ring for nicks )and condensation during the winter ( keep your tank full).
Algae looks like long strings of green snot. The first line of defense is that your pickup tube should be 1/2 to 3/4" up off the bottom of the tank. The algae will grow attached to the bottom of the tank but if you are low on fuel and get in some rough water, it will break loose. My boat had a coarse screen in the bottom of the tank pick up tube. which algae had clogged. Remove it. . ( Its easier to let the stuff come up and clog other places that are more accessible.) My boat ( Catalina 30 ) also has a coarse screen in the bottom of the off engine electric fuel pump. The bottom of the pump has a twist off cap ( with the three little tits ) Just twist off the cap and check the screen. Check the glass bowl of your Racor fuel/water separator. There should be a drain at the bottom that you can pull some content and check for water. If water reaches the fuel injectors, it will ruin them. By the way, my 85 vintage bowl was NOT glass but some polycarbonate material that was intolerant to alcohol. ( when I cleaned it, with alcohol, the bowl shattered.

[old pirate]

Consider where you place your tank in the boat, making sure that it is dry at all times. Last week one of our aluminium tanks leaked all 50 gals into the bilge. Underneath it had rubber strips, presumably to stop movement ! But these strips absorbed moisture which coroded into the tank. So when I filled it a hole developed. Now I have the other 50 gal tank to look forward to.

[blubaju]

Carbon fiber mast with an Aluminum rail, for a good bonding (NO SCREWS) and avoiding these nasty blisters on old aluminum, it was well sanded and immideatly glued with epoxy before oxydizing.

If you worry you could do a coating with food grade epoxy paint.
I would do! Follow the special instructions for Aluminum!

Clorine in water is not Aluminums friend!!! Sometimes it ends up in white powder! Depends on chlorine level and Aluminum alloy and sometimes stray currents.

Being a retired stainless steel fabricator with plenty Aluminum works too, my water- and diesel tanks are made of >>> Epoxy! 1985 till today never had a problem, never repainted, nothing.

[kmcshane]

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I have both aluminum water and fuel tanks. Fuel tanks are spotless, and terry cloth clean when empty.
Not so with water tanks, and would appreciate comments as to reason(s) why. The tanks themselves are bulletproof and are housed in the aluminum keel aft of the 5000# poured lead that would take any grounding.
What I would like to point out: there is a build up (probably benign) of a gnarly solid deposit on the bottom of all three water tanks.
I'm reading it has to do with adding dilute bleach to the water in hopes of mild purification.
True? False? What else may have cause this build up in solid clumps about 2 cm thick, looks like aluminum lava.
This posting is in hopes your tanks won't develop this seeming minor, but annoying, condition.
(don't have photos of the deep bilge water tanks, but here's where they are)

[old pirate]

Cant help with you water tanks. Ours are plastic.
We do have a build up of black fungal matter in the aluminium diesel tanks which we intend attacking with biocide.

[KP44]

I replaced the 55 and 60 gallon black iron tanks on our Kelley-Peterson with 71 and 94 gallon custom-built aluminum tanks about 10 years ago. They are still "like new".

[jhulmer]

Originally Posted by jpendoley

Looking to clear up a question regarding building fuel tanks with aluminum. I just replaced my rusty 50 gallon tank with a shiny new custom built aluminum tank. I have read on boat building forums that aluminum from the factory has a “mill scale” that should be removed prior to service. It’s presence can lead to corrosion down the line. It can be removed by lightly sanding or by acid etching. My fabricator says not so, but I read a couple of pretty well written articles that were convincing. What’s the consensus? My steel tank gave many years of service, I need this to be my last tank install-it’s an arduous project.
Jim

I've been manufacturing aluminum products for 30+ years. There is no such thing as mill scale on aluminum, you can only find mill scale on steel. Its a carbide precipitous that floats to the surface during the mill process.
Aluminum has an aluminum oxide layer that protects it and it forms on its own in the presence of oxygen. You only have to remove the oxide layer to weld it. Your fabricator is correct. The tank will be fine as is as long as it doesn't sit in water or on wood barrers or any thing that will hold moisture. If you want more protection then that have it alodined or anodized, but not necessary. BUT, don't waste your time sanding bare aluminum.
Jim