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Galvanic action in aluminum-lined steel gutters

A subcontractor was hired to replace some steel rain gutters on a metal building. Instead of removing and replacing the steel gutters as planned, he decided to "line" the existing steel gutters with aluminum gutters of approximately the same size. The aluminum gutters were fastened to the existing steel gutters with steel screws that have a small rubber gasket under the head. I am concerned about galvanic corrosion reducing the life of these gutters. The work is done in a very neat and workmanship like manner.
The building is located in a very humid, wet, warm (hot) climate. Also, the building is located within five (5) miles of a salt water lake; probability of acid rain in the area is probably low to moderate. The life expectancy of steel gutters in this area would normally be fifteen (15) to twenty (20) years. Can we reasonably expect the aluminum gutter liners to last as long?

C. Gene Rogers
Contractor/Engineer - New Orleans, Louisiana, USA
2007

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My Chemistry 101 says that aluminum is -1.70 below hydrogen and iron is -44 below hydrogen and that the two metals are 1.26 volts apart. I predict the iron is going to degrade but I will not predict how fast. Louisiana's thermal cycling will play a part.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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Actually, the aluminum will be the sacrificial anode in this galvanic couple. In my opinion, this was a very bad idea. Aluminum can corrode rapidly in contact with steel. I have seen aluminum components on trucks corrode through nearly 1/8 in. thickness in less than five years where the aluminum was in contact with steel. The corrosion will be less severe if the steel has a good paint coating.

Larry Hanke
Minneapolis, Minnesota
2007