Summary for galvanic corrosion chimney cap Discussion
Galvanic corrosion between the stainless steel chimney cap and the powder coated aluminum shroud is the main concern in this thread, especially because the home is only 2000 feet from the Atlantic Ocean. Don McCullough explains that the shroud will be aluminum with powder coating, while the smaller cap over the pipe will be stainless steel, and he worries that scratches during installation could expose bare metal at the contact point. The discussion notes that salt air can accelerate corrosion and asks whether caulk or a rubber isolator would be practical near the hot pipe. The practical takeaway is that the risk depends on whether the metals are electrically connected in the presence of moisture and salt, and that the coating may help but scratches or exposed edges could still matter. The thread is framed as a real-world coastal installation question rather than a definitive engineering test case.
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
November 20, 2017