Aluminum and stainless mixed

OK, hope I don't get shot over this, or worse, live beer free!
I have seen many builds that show aluminum pots being fitted with ss washers and such. Per Hschool class, you mix dissimilar metals, add acid/base and water, you now have a battery. The electrolysis corrodes the aluminum. I have never seen this brought up. As an electrical Ingineer, I run into this quite often. Also studied spelin.
David

I did bring up that exact subject recently in a discussion about pot material choices. I prefer SS on SS for that exact reason.

Stainless/aluminum is fine. Not all dissimilar metals have electrolysis issues.

As an electrical Ingineer, I run into this quite often. Also studied spelin.

Click to expand...

I majored in spelin

S_M

Stainless and aluminum are a bad mix. Years ago license plates used to fall off cars because of the ss bolts. In pool equipment, the mix of aluminum and stainless steel always causes the aluminum to loose. I paid $$ for that one!

boiling water in Al pots isn't a prob, but I prefer SS for wort boiling... see how well hot wort cleans copper? not sure that Aluminium won't get a bit dissolved.... they say not , but.....( ps the dissolved copper ain't an issue, the yeast gets rid.)

Bonding Al to Ss will cause corrosion in the Al. Especially in a wet environment. Al and Ss are on opposite sides of the galvanic spectrum, and the further apart they are the more/faster the corrosion will happen. There are many factors involved. Such as mass. If you add a Ss connector to an Al pot, the Al has much more mass. Which will cause it to corrode slower. The inverse of the two with cause faster corrosion of whichever metal is lower on the galvanic chart.

This is all actually beyond my education, but I have read quite a bit about it due to my profession and location of work. I work on the coast and have seen what Ss can do to Al over a short period of time. (Months)

Here is a Quick link to a little more info.

I had an aluminum pot with many SS fittings for a long time before upgrading to stout-tanks. Made good beer, and I haven't died (yet), but toward the end there was some strange stuff happening. To the stainless, actually, not the aluminum.

All of the internal stainless developed a very tough to clean hard coating of what was the same general color as rust, but I do not think it was. With a LOT of hard scrubbing, I could get them clean. I never let it bother me too much, but perhaps I should have. It wasn't the stainless corroding, it was something being deposited on it.

The AL pot looked alright, aluminum always tends to end up looking a little cruddy with its oxidation layer.

I talked to my Dad about this a few years back. He's a metallurgist. Yes, there will be some corrosion, but it's not something that will happen overnight. It's a long, slow process.

Like Facinerous said, mass is a factor. A large AL pot with some SS fittings will behave differently than a SS pot with AL fittings. If you're going to mix metals, the way we're doing it is the best option.

Also, look at the actual exposure time in the presence of an electrolyte. If the equipment was sitting in wort all day, every day it would probably be a huge issue. That's most likely why a brewery would never consider mixing metals the way some of us do. However, I use my pots about 1-2 times per month for an hour or so. Them they are cleaned, dried, and put away.

I'm not too worried about it. If I have to buy a new ~$40 pot every 5-10 years, I can live with it.

I have an aluminum pot with SS fittings. Heating element and SS nut for that and a SS valve with SS nut for that. I have no issues. The element isn't even rusting at the base.

I'll let you know in 40 years if its still good