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-----Will aluminum and/or galvanized steel flashing touching copper pipe make it corrode?
My brand new solar hot water piping penetrates my tile roof. The installers used galvanized flashing on the bottom layer against the roofing felt. Then they used a second layer of maleable aluminum flashing on the top layer over the tiles. I raised the issue of galvanic corrosion caused by dissimilar metals. They smeared each layer of flashing with an asphalt based caulk after it was in position and told me that it would insulate everything so no galvanic problems. Later, I checked with an ohm meter and there is a very low resistance/high conductivity between the copper pipe and both of the flashings. The system manufacturer specified copper flashing but the installers went the less expensive route. Does the galvanized and/or aluminum flashing need to be replaced with copper or a non-conductive sleeve added?
Bruce RogersEngineer - Escondido, California, USA
June 26, 2008
Most dissimilar metals in electrical contact with each other and in the presence of an electrolyte (water) will corrode.
To prevent: use same metal, or insulate one from the other, or keep very dry!
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
June 28, 2008
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