After a general dicussion of factors which lead to zinc becoming cathodic to steel in hot water tanks the author relates instances pointing to the presence of copper as being a principal agent in the rapid dissolution of zinc protective coatings exposed to heated water. The copper appears to deposit as small metallic particles on the surface of the zinc, forming galvanic cells which lead to rapid pitting. As little as 0.1 ppm copper causes a definite increase in corrosion rate. Examples of six galvanized water tanks in use for periods from 431 to 667 days are given. The author concludes lower corrosion rates can be secured by using all-galvanized systems, by removing carbon dioxide, by removing copper from water or lowering operating temperature to prevent potential reversal. Discussion relates case histories tending to place blame for rapid corrosion in galvanized water heaters on copper piping.

Subject
Pits, Water, Materials, Piping, Corrosion rate, Iron, Rods, Tubercles, Steel, Magnesium, Carbon dioxide, Copper, Zinc
Copyright 1953 by the National Association of Corrosion Engineers.
1953
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