Copper pipes, coolant & aluminium engines

The difinative (sic) answer is to proceed with caution.

For your aluminum radiator with copper pipe separated by rubber it is NOT safe to assume that the only concern would be direct contact between these dissimilar metals. Galvanic or bimetallic corrosion of aluminum can occur without physical content. You may get away with this combination in normal service in antifreeze, but might not if the system is cleaned using a solution that can corrode the copper slightly.

There is a good discussion of galvanic (bimetallic) corrosion in the Guides to Good Practice in Corrosion Control series in a big 579K file at

Look at Section 4.0, which is titled ABimetallic corrosion without physical contact.@ This is known under the term Adeposition corrosion.

National Association of Corrosion Engineers, Houston, Texas, 1984, page

99:

"DEPOSITION CORROSION is a form of pitting corrosion that can occur in a liquid environment when a more cathodic metal is plated out of solution onto a metal surface. It generally occurs with the more anodic metals such as magnesium, zinc, and aluminum. Common cathodic Aactivators@ are mercury and copper ions in solution.

For example, soft water passing through a copper water pipe will accumulate some copper ions. If water is then admitted to a galvanized or aluminum vessel, particles of metallic copper will plate out, i.e., deposit on the surface and stimulate pitting by local cell action.

Deposition corrosion can be avoided by preventing the pick-up of cathodic ions that will enter the equipment, or by scavenging them by passing the contaminated product through a tower packed with more anodic metal turnings on which the ions can deposit."

There is an enormous web site from the European Aluminium Association (EAA) on Training in Aluminium Application Technologies (Talat)

Se pages 12 and 13 of the Talat lecture #5103, "Corrosion control of aluminium - Forms of corrosion and prevention": where it is pointed out that only 0.02 to 0.05 ppm of Cu++ ion in solution can kick off galvanic corrosion from deposited copper.

Also see page 7 of Talat lectures #5104, "Basic approaches to prevent corrosion of aluminium"

Pittsburgh Pete

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