Craig, Every metal has an associated potential, or voltage property. Here are simplified examples of potential values in sea water: -0.05: 304 Stainless -0.30: Copper -0.76: Aluminum The greater the difference in potential between metals, the faster the rate of corrosion of the metal with the lower number. The lower one is the one with the most negative number. There are three combinations of metal of interest: 1) Stainless and aluminum will cause corrosion in the aluminum. 2) Stainless and copper will cause corrosion in the copper. 3) Copper and aluminum will cause corrosion in the aluminum. However, the rate of corrosion of (3) is less than (1). The fact that the higher metal (stainless) is smaller in size than the lower metal (aluminum) is helpful. If the situation were reversed, that is if you had some sort of aluminum fasteners in a stainless spar, it would corrode faster than an aluminum spar with stainless fasteners. steve Steve R. M-15 #119 Lexington, KY ********************************************* I'd like to know more about galvanic corrosion, if any M-List metallurgists can explain: Why would copper prevent galvanic corrosion between steel and aluminum, and why wouldn't copper cause galvanic corrosion to both?
Thanks, Steve! I'm not a science person, at least, I don't have the empirical mind of many of the M-List engineer types, but for some reason, metal properties fascinate me. I've looked at stainless + bronze previously because I've retrofitted so much of my M17's hardware with bronze ... If I remember correctly, bronze wouldn't be far from copper, making it the less likely to suffer galvanic corrosion when paired with stainless, but stainless and bronze get along okay, and I know are paired by some manufacturers, for instance, in turnbuckles and winches. I wonder if I need worry about galvanic corrosion at all since I'm a freshwater sailor (?) ... --Craig ----- Original Message ----- From: Steve R. To: montgomery_boats@mailman.xmission.com Sent: Tuesday, August 02, 2005 3:07 PM Subject: M_Boats: re: galvanic Craig, Every metal has an associated potential, or voltage property. Here are simplified examples of potential values in sea water: -0.05: 304 Stainless -0.30: Copper -0.76: Aluminum The greater the difference in potential between metals, the faster the rate of corrosion of the metal with the lower number. The lower one is the one with the most negative number. There are three combinations of metal of interest: 1) Stainless and aluminum will cause corrosion in the aluminum. 2) Stainless and copper will cause corrosion in the copper. 3) Copper and aluminum will cause corrosion in the aluminum. However, the rate of corrosion of (3) is less than (1). The fact that the higher metal (stainless) is smaller in size than the lower metal (aluminum) is helpful. If the situation were reversed, that is if you had some sort of aluminum fasteners in a stainless spar, it would corrode faster than an aluminum spar with stainless fasteners. steve Steve R. M-15 #119 Lexington, KY ********************************************* I'd like to know more about galvanic corrosion, if any M-List metallurgists can explain: Why would copper prevent galvanic corrosion between steel and aluminum, and why wouldn't copper cause galvanic corrosion to both? _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
Craig, I've never seen any corrosion problems on freshwater boats. When I was looking around at bigger project boats, I saw that the difference between the saltwater boats and the fresh ones is huge. While the metal parts of the 30 y.o. freshwater boats are smooth and clean while the same boat in salt water has pits all over it's fittings and looks as though it's been through the mill. Tod -----Original Message----- From: montgomery_boats-bounces+htmills=bright.net@mailman.xmission.com [mailto:montgomery_boats-bounces+htmills=bright.net@mailman.xmission.com] On Behalf Of Craig F. Honshell Sent: Tuesday, August 02, 2005 8:39 PM To: For and about Montgomery Sailboats Subject: Re: M_Boats: re: galvanic Thanks, Steve! I'm not a science person, at least, I don't have the empirical mind of many of the M-List engineer types, but for some reason, metal properties fascinate me. I've looked at stainless + bronze previously because I've retrofitted so much of my M17's hardware with bronze ... If I remember correctly, bronze wouldn't be far from copper, making it the less likely to suffer galvanic corrosion when paired with stainless, but stainless and bronze get along okay, and I know are paired by some manufacturers, for instance, in turnbuckles and winches. I wonder if I need worry about galvanic corrosion at all since I'm a freshwater sailor (?) ... --Craig ----- Original Message ----- From: Steve R. To: montgomery_boats@mailman.xmission.com Sent: Tuesday, August 02, 2005 3:07 PM Subject: M_Boats: re: galvanic Craig, Every metal has an associated potential, or voltage property. Here are simplified examples of potential values in sea water: -0.05: 304 Stainless -0.30: Copper -0.76: Aluminum The greater the difference in potential between metals, the faster the rate of corrosion of the metal with the lower number. The lower one is the one with the most negative number. There are three combinations of metal of interest: 1) Stainless and aluminum will cause corrosion in the aluminum. 2) Stainless and copper will cause corrosion in the copper. 3) Copper and aluminum will cause corrosion in the aluminum. However, the rate of corrosion of (3) is less than (1). The fact that the higher metal (stainless) is smaller in size than the lower metal (aluminum) is helpful. If the situation were reversed, that is if you had some sort of aluminum fasteners in a stainless spar, it would corrode faster than an aluminum spar with stainless fasteners. steve Steve R. M-15 #119 Lexington, KY ********************************************* I'd like to know more about galvanic corrosion, if any M-List metallurgists can explain: Why would copper prevent galvanic corrosion between steel and aluminum, and why wouldn't copper cause galvanic corrosion to both? _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats _______________________________________________ http://mailman.xmission.com/cgi-bin/mailman/listinfo/montgomery_boats
participants (3)
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Craig F. Honshell -
htmills＠bright.net -
Steve R.