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-   -   Galvanic corrosion (http://www.houserepairtalk.com/f34/galvanic-corrosion-17232/)

suobs 01-20-2014 04:38 AM

Galvanic corrosion
 
I always thought aluminum and galvanized steel should not be in contact (e.g., galvanized nails in aluminum flashing), but the galvanic action table in the Florida code has them right next to each other (at least Aluminum 1100 whatever that is is next to galvanized):

http://publicecodes.cyberregs.com/st/fl/st/b1400v07/st_fl_st_b1400v07_ras111_sec004.htm

oldognewtrick 01-20-2014 06:06 AM

Galvanized nails and aluminum flashing are perfectly acceptable and used all the time in roofing. You run into problems where you use galvanized nails and copper flashing.

Wuzzat? 01-20-2014 10:54 AM

Quote:

Originally Posted by suobs (Post 98835)
but the galvanic action table in the Florida code has them right next to each other

Which means there will be little potential difference which means one is less likely to corrode.
I had another anodic series that showed the mV between metals; you could do <50 mV in humid environments (so you could have
Zinc, wrought; zinc-base die-casting alloys; zinc plated
-1.25v
Magnesium & magnesium-base alloys, cast or wrought
-1.75v
touching each other) and <150 mV in dry environments.

That's interesting about the water flow in your link since fresh water is not a very good conductor. Perhaps rain runoff from surfaces is more conductive.

I couldn't find mine but here's one from Wikipedia

Anodic index
Metal
Index (V)

Most Cathodic
Gold, solid and plated, Gold-platinum alloy
-0.00
Rhodium plated on silver-plated copper
-0.05
Silver, solid or plated; monel metal. High nickel-copper alloys
-0.15
Nickel, solid or plated, titanium an s alloys, Monel
-0.30
Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys
-0.35
Brass and bronzes
-0.40
High brasses and bronzes
-0.45
18% chromium type corrosion-resistant steels
-0.50
Chromium plated; tin plated; 12% chromium type corrosion-resistant steels
-0.60
Tin-plate; tin-lead solder
-0.65
Lead, solid or plated; high lead alloys
-0.70
2000 series wrought aluminum
-0.75
Iron, wrought, gray or malleable, plain carbon and low alloy steels
-0.85
Aluminum, wrought alloys other than 2000 series aluminum, cast alloys of the silicon type
-0.90
Aluminum, cast alloys other than silicon type, cadmium, plated and chromate
-0.95
Hot-dip-zinc plate; galvanized steel
-1.20
Zinc, wrought; zinc-base die-casting alloys; zinc plated
-1.25
Magnesium & magnesium-base alloys, cast or wrought
-1.75
Beryllium
-1.85
Most Anodic


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