Interconnecting aluminum w/ SS

[Jim Karr]

I have a forty gallon kettle that I'm about to initiate. I plan on having a pipe nipple welded onto the bottom which will drain out at a shallow slope. Both kettle and pipe are aluminum.

I plan on using either a pickled brass or stainless valve on the exit end.

Will I encounter any problems from the dissimilar metals, exposing them to an acid solution, or will there be a galvanic reaction of any sort I should be concerned with?

 

[Sawdustguy]

There is the potential of a corrosion problem when mating Stainless Steel and Aluminum when a potential electrolyte is introduced. This is called Galvanic Corrosion. Basically when intoducing two different metals into an electrolyte, electrons will be stripped from the less noble metal (a metal that is more willing to give up it's electrons) and flow to the more noble metal (a metal that is less willing to give up it's electrons). This electron flow is a current and in essence is the same way your car battery works. In a car battery the two dissimilar metals are Lead and Lead Dioxide and they reside in an electrolyte of Sulfuric Acid. Another good example is electroplating.

If you look at the chart below Aluminum is much less noble than Stainless so the Aluminum would give up electrons and corrode. Now, there is a caveat. There always is. You may not have too big a problem because the Aluminum pot is much larger may not be so will to give up electrons to the little Stainless Steel valve. If it were me. I would go with a Brass Valve because while Brass is more noble than Aluminum it is much less noble than Stainless.

 

[Joe Camel]

If you were drilling a hole and using a bulkhead fitting, you could insulate the two metals from each other with rubber, this would in effect be a dielectric union and prevent corrosion. Since you're using a welded fitting, I'm not sure how I'd go about insulating the two metals.

 

[lamarguy]

I have a forty gallon kettle that I'm about to initiate. I plan on having a pipe nipple welded onto the bottom which will drain out at a shallow slope. Both kettle and pipe are aluminum.

I plan on using either a pickled brass or stainless valve on the exit end.

Will I encounter any problems from the dissimilar metals, exposing them to an acid solution, or will there be a galvanic reaction of any sort I should be concerned with?

In your case, no. You have absolutely nothing to worry about.

When the less noble metal (e.g., aluminum) has significantly more surface contact area than the more noble metal (e.g. brass or SS), the corrosion will be so slow you'll never notice it in the lifetime of the equipment.

Now, if you installed non-anodized aluminum fittings on an SS pot, your aluminum fittings would have a significantly shorter life expectancy.

 

[Brewers Hardware]

Like everyone already said; yeah, it'll corrode but so slight and slow you'll never know.

The only thing I have to add is wrapping the threads with Teflon tape will pretty well insulate the two metals as well. Not completely, but to the point it just won't matter.

 

[mmb]

If you keep things clean and dry when not using the pot, you'll be fine.

Wort will act as an electrolyte but you'll have so little time of contact you should be fine for some time.