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Old 26-06-2013, 20:09   #1
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Galvanic corrosion question

I have a 300 gallon fiberglass water tank with an access plate for cleaning, but had to cut out a piece of the fiberglass baffle to access both sections. I am going to bolt a piece of G10 epoxy fiberglass into that hole in the baffle, but am trying to choose an appropriate alloy. My main concern is getting corrosion on the pick-up pipe which I can see but not access. It appears to be galvanized steel, and has been there for 30 years. So, I do not want any galvanic corrosion introduced from the bolts I use on the G10. I can get 316 stainless bolts, which are supposedly astentetic (approximate spelling). I can also get silicon bronze bolts. These bolts will be in drinking water most of the time. What would be the best choice? Any experience?
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Old 26-06-2013, 20:39   #2
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Re: Galvanic corrosion question

Consider using Nylon hardware. It will absorb some water but should not compromise the strength. And it has no galvanic issues.
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Old 26-06-2013, 20:53   #3
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Re: Galvanic corrosion question

The copper in bronze would be more reactive with the zinc anodizing than would the nickle in the stainless.

I like Dan's idea.
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Old 26-06-2013, 21:32   #4
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Re: Galvanic corrosion question

Silly question but why don't you glass the hole up again !!! ?
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Old 26-06-2013, 22:20   #5
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Re: Galvanic corrosion question

Fresh water is not an electrolyte. Any galvanic corrosion may have in the tank will be very slow.

Emmalina sez why not glass up the hole. I ask why not leave it there? You will have to clean the tank again. The baffle is to reduce swash and provide stiffness. Swash will likely not be affected unless the hole represents a large percentage of the surface area of the baffle. Stiffness should not be significantly affected in a tank that large if you cut out a hole big enough only for cleaning access.
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Old 18-07-2013, 19:47   #6
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Re: Galvanic corrosion question

Thanks for the good replies. I think I will use the 316 hardware at the top of the baffle plate, since it will be out of the water most of the time. I will look into using nylon hardware on the lower part of the plate, though I have heard that nylon submerged in water will eventually loose strength. I need to have the plate to subdue the slosh of 300 gallons.
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Old 19-07-2013, 05:46   #7
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Re: Galvanic corrosion question

Bill,

If you are worried about pressure on the plate consider putting some holes in the plate to let some water through. It will still work as a baffle. Also, consider putting identical plates on either side of the baffle plate. Like a sandwich where the plates are the bread and the baffle plate is the cheese. That way whichever way the pressure is from it will force a plate against the baffle. Leave at least one hole at the bottom of the new plate(s) so water doesn't get trapped and become a science experiment.
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