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chucri
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Posted: Tue Sep 23rd, 2008 07:31 am |
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which material is least desirable ( stainless steel or copper) to use with aluminum
if you follow the galvanic table copper is the farthest. i dont know why in Ballast sample test they say stainless steel is the least desirable
please advise
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xcentric
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Posted: Tue Sep 23rd, 2008 02:38 pm |
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I don't know which source you have your galvanic table from. Here's one I pulled up on the web. Notice that the aluminum and copper are relatively close, with only one type of stainless steel between them. Most of the stainless steel types are further from the aluminum than the copper.
http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm
and way more than you wanted to know here, with some discussion of why stainless steel corrodes less than the galvanic table might indicate:
http://www.auf.asn.au/scratchbuilder/corrosion.html
(the second link shows copper closer to aluminum than any of the stainless steel varieties)
And yet, here's a link that shows the stainless steel closer to aluminium than copper:
http://www.fourseasonsroofingandsiding.com/mixmetals.htm
I even saw a comment somewhere that copper should be used as a spacer between aluminum and steel to prevent galvanic action. Seems kinda silly after the examples shown in the last link. Hmm.
In conclusion, I'd say the answer is debatable and may depend largely on what kind of stainless steel you are using (of course Ballast probably didn't specify).
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wannabe2
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Posted: Tue Sep 30th, 2008 04:29 am |
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I was going to try to somewhat memorize the galvanic list, but I see that my PPI book and ALS books even have different lists. 1997 ALS lists: 1. Aluminum, 2. Zinc, 3. Iron and Steel, 4. Stainless steel, 5. tin, 6. lead, 7. brass, 8 copper, 9. bronze, 10. gold. PPI version 4 lists: 1. Zinc, 2. Galv. steel, 3. Aluminum, 4. Steel and Iron, 5. Stainless steel, 6 lead, 7. Tin, 8. Copper Alloys (brass, bronze) 9. Copper.
So, I am going to go with just knowing that gray metals (zinc, aluminum, steel) don't like anything with copper. So, don't use copper flashing for an aluminum window, and don't use steel fasteners for copper (if you must, use neoprene or rubber spacers). And, galvanic action is most severe in humid and marine environments.
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