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"Will galvanic corrosion occur if SS chimney cap touches powder coated aluminum shroud?"

November 20, 2017

Q. Hi, I live 2000 feet from the Atlantic Ocean and need to have my chimney shroud (in my case, it's about 3'D x 4'W) replaced. The proposal says they will make the shroud from aluminum (and powder coat it) and cover the pipe with a stainless steel chimney cap (the smaller cage-like piece that only goes over the pipe). Pardon me if I am stating the obvious in my descriptions but I want to be clear since I'm not certain I'm using the correct names for the shroud and cap.

The fireplace is what I believe you call an "insert" and it has a small pipe as its "chimney." Basically, there is a big stucco box to look like a chimney through which the pipe goes. Typical 90s Florida practice.

My main question is, will the SS cap and aluminum shroud corrode where they intersect? Even though the shroud will be powder coated there are bound to be scratches in that area when installing. I mentioned my distance from the ocean because I know salt water speeds galvanic corrosion. Since the pipe gets hot, I assume caulk or some kind of rubber insulator isn't practical. I read all sorts of posts about corrosion from disparate fasteners but have never seen this issue come up.

In addition to the answer about corrosion, any other insights are welcomed as well. My thanks!

Don McCullough
- Atlantic Beach, Florida

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