Aluminium diesel tank with bronze elbo and copper pick up tube. Corrosion potential?

[Eastward ho 24]

And thanks for the link it's exactly what I need I'm gonna use that puppy...I didn't have an after pic of the inside of the tank . It came very clean and they are very thick I think it'll be ok

[billgewater]

Never seen an alloy or plastic tank on a truck, earth moving machinery or SUV. They use steel! Wonder why? I have helped to remove alloy and SS fuel and water tanks with pin hole corrosion with short life spans. Probably dependent on the particular alloy/welding used which you have little control over. Mixing metals is usually just asking for trouble IMHO.
However, I would be concerned over the use of tyre tube rubber as a gasket material. I would be asking around for a standard industrial material advocated for the purpose.
A leaking water tank does little harm as water eventually evaporates, but diesel in the bilges? Anything it touches will probably be contaminated for ever and the clean up would probably lead to the creation or extension of your own personal vocabulary.

[Eastward ho 24]

The tire rubber is a no no? Fuel hoses are rubber I thought? Rubbers rubber?

[Scout 30]

Originally Posted by a64pilot

Why did you replace them? Why not plastic?

I replaced them because one started leaking. For a boat built in '86 I think that's a pretty good lifespan. I considered polyethylene but I think aluminum is stronger. In addition polyethylene tanks have had problems with permeation resulting in fuel smells escaping into boats. However, with aluminum tanks installation is really important. Nothing that holds moisture can be up against them & direct exposure to saltwater will really shorten their lives. While I think aluminum fittings make a lot of sense the brass fittings on my old tanks did not cause any corrosion at all.

[Sailmonkey]

Originally Posted by billgewater

Never seen an alloy or plastic tank on a truck, earth moving machinery or SUV. They use steel! Wonder why? I have helped to remove alloy and SS fuel and water tanks with pin hole corrosion with short life spans. Probably dependent on the particular alloy/welding used which you have little control over. Mixing metals is usually just asking for trouble IMHO.

However, I would be concerned over the use of tyre tube rubber as a gasket material. I would be asking around for a standard industrial material advocated for the purpose.

A leaking water tank does little harm as water eventually evaporates, but diesel in the bilges? Anything it touches will probably be contaminated for ever and the clean up would probably lead to the creation or extension of your own personal vocabulary.

Ummmm, what?

Heavy trucks almost universally have aluminum fuel tanks, tractors come with plastic fuel tanks, most vehicles have a plastic tank (flex fuel is an exception). Aluminum has a good lifespan if properly installed, so does steel. Plastic will as well.

[a64pilot]

Originally Posted by billgewater

Never seen an alloy or plastic tank on a truck, earth moving machinery or SUV. They use steel!.

Actually almost all modern automotive tanks are plastic.
My last three trucks were anyway.
Plastic doesn’t rust and is easily moldable into complex shapes and more crashworthy than steel tanks.
Now big machines are made from steel and they have the materials and tradesmen necessary, and likely need excessively strong tanks.

[a64pilot]

Originally Posted by Scout 30

I replaced them because one started leaking. For a boat built in '86 I think that's a pretty good lifespan. I considered polyethylene but I think aluminum is stronger. In addition polyethylene tanks have had problems with permeation resulting in fuel smells escaping into boats. However, with aluminum tanks installation is really important. Nothing that holds moisture can be up against them & direct exposure to saltwater will really shorten their lives. While I think aluminum fittings make a lot of sense the brass fittings on my old tanks did not cause any corrosion at all.

I asked cause mine are now 30 yrs old. If I replace them, it’s the last Achilles heel I have, but they are stupid expensive to replace on my boat, usually the water tank goes first, and fuel tanks usually last until eaten away from the outside, fuel I don’t think ever deteriorates them, but water on the outside does.

[sailorchic34]

Aluminum is an anode to SS, copper, even black iron, so the aluminum tank will corrode using ss hardware . If it were my tank, I would find Nylon bolts and nuts for the access covers and use thick gasket paper to isolate the cover from the aluminum tank. That with the nylon bolts and nuts will prevent galvanic corrosion on the tank.

For the fuel line connections, I might tap the SS cover. As the cover would already be isolated from the aluminum tank it would not be a major issue. Copper and SS are close in the galvanic tablet to not be a major issue. Though I would use something (loctite or teflon tape which will help isolate the single copper thread to ss.

You can also coat the SS bolts and nuts with something that isolates the SS from the aluminum, but aluminum will corrode where the bolts connect to the tank.

Using plastic diptube and elbow would also prevent corrosion.

[Scout 30]

Originally Posted by a64pilot

I asked cause mine are now 30 yrs old. If I replace them, it’s the last Achilles heel I have, but they are stupid expensive to replace on my boat, usually the water tank goes first, and fuel tanks usually last until eaten away from the outside, fuel I don’t think ever deteriorates them, but water on the outside does.

If there's a chance that the tanks will come in contact with saltwater I would absolutely not use aluminum when replacing them.

[boatpoker]

Originally Posted by Scout 30

If there's a chance that the tanks will come in contact with saltwater I would absolutely not use aluminum when replacing them.

Many aluminum boat owners will be surprised by this statement.

[james247]

Originally Posted by billknny

Copper and Aluminum? Bronze and Aluminum?



That is an easy one... no, NO, and NOOOOOO! Just do NOT do it.



Even a trace of salt water will dissolve the Al. I have seen a copper penny dropped on top of an Aluminum tank dissolve its way right down into the tank, leaving a hole behind, in months, not years. You can find pictures in corrosion texts of the same problem.



If you use stainless, be VERY sure you have all the connection points well insulated (PROPER gaskets, (no inner tube crap) Tef-Gel on screws, etc) and you can get away with it. Best not to do on top or bottom of a tank where water can pool, vertical sides are better.



Do this RIGHT or you will be ripping the tank out after it saturates the bilge with spilled diesel.

Yes a coin dropped in a bilge of an aluminium yacht. The bilge was dry but the hole was as if cut by laser.
Weld the filling point and vent in aluminium. Also weld an elbow at the base of the tank. Half inch put a clear plastic tube over it with a clamp. Then a valve on the other end hold it up to the tank and open the valve. The resultant level is the level of the tank. A bit of maths will calculate the volume of the fuel or water in the tank.
All fittings to a mast where unlike metals must be isolated by Sicka or the like.

[mitiempo]

Originally Posted by Eastward ho 24

I should thinking about that tuff gel stuff and in my opinion it's just snake oil. If the threads are engaged your gonna have metal to metal the snake oil will just squeeze out.

TefGel is not snake oil. It enables removal of the fittings in the future. Without it they become effectively welded in place.

I agree with the others lose the inner tube gaskets. Oil eats rubber - same reason you cannot use a rubber impeller in an oil pump, it has to be nitrile.

[Compass790]

I'd use garlock ( availiable from gasket material suppliers ) or a bead of silicone ( allow to go off) for yr inspection gasket. Silicone is cheapest & works well.

[Jim Cate]

Nothing that holds moisture can be up against them & direct exposure to saltwater will really shorten their lives.

One wonders how aluminium hulls last so long, considering that they float in saltwater full time.

Jim

[RaymondR]

You need nitrile rubber for gaskets which are in contact with diesel fuel.

You can avoid the dissimilar metal problems by going to TIG welded alloy tube and alloy flanges. SS or monel bolts and studs and chromate paste.