Galvanic Corrosion Question

[dezirak]

If I had a system that uses aluminum, steel, and copper as different construction components, all in the presense of boiling saltwater, how would I go about protecting each individual part of the system from galvanic corrosion? I've read about a sacrificial anode composed of magnesium in water heaters. The copper and steel contact one another directly. The steel and aluminum contact one another directly. They all are contacted with eachother through salt water as well. I think it would probably be possible to use a magnesium sacrificial anode, but I don't really no how to go about doing that. I'm very ignorant when it comes to materials.

 

[EdStainless]

Ouch! Sounds like trouble. In hot seawater you will have corrosion issues with all of these materials.


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[mshimko]

From what you describe, you have three disimilar metals in electriocal contact, and all exposed to a hot electrolyte. Someone has designed a very strong battery!

Seriously, if the aluminum wasn't there I'd suggest sacrificial zinc anodes, but I don't think this will help the aluminum. A magnesium anode would protect all three metals, but I've no idea on it's properties at elevated temperatures, how long a certain mass of magnesium may last, etc.

There's a reason the FIRST AND BEST method of corrosion control is proper material selection.

 

[kenvlach]

Electroplate every component individually with nickel.
Assemble.
Plate the insides of the system by flowing electroless nickel plating solution through at 90-95 ^oC.

When the system eventually fails, scrap it and use only titanium or 70-30 Ni-Cu or something else appropriate (maybe enameled glass?).

FYI: The galvanic positions of zinc & iron reverse above about 70 ^oC (160 ^oF).

 

[TVP]

dezirak,

I'm not sure that only one exclamation point after Ouch sufficiently conveys the problem of these three metals in contact in boiling saltwater. I can't imagine this assembly having any type of usable life.