Zinc Metallizing for External Corrosion Control of Ductile Iron Pipe

Zinc metallizing with a high-purity zinc wire has been utilized for external corrosion control of iron pipe for more than 50 years. This paper summarizes publications and experiences of metallized zinc on iron pipe over that time period and discusses advantages and limitations of this method of corrosion protection. Advantages include but are not limited to uniform cathodic protection of the iron pipe surface; thicknesses compatible with critical joint tolerances; no special considerations with respect to field cuts, tapping saddles, or corporation stops; no special handling or installation procedures required; ability to "self-heal" in many environments; minimal surface preparation required; and compatibility with current ductile iron pipe manufacturing processes. Limitations include that it is not recommended as a standalone method of corrosion control in severely corrosive soils or areas of stray electrical currents, it has limited cathodic protection at large areas of unrepaired damage in that it is a sacrificial coating that sacrifices itself to protect the iron substrate, and it is not compatible with some polymeric topcoats. In severely corrosive soils or areas of stray electrical currents, polyethylene encasement conforming to AWWA C105 is used to supplement the metallic zinc coating. Previously unpublished results of corrosion studies, with and without polyethylene encasement, are also presented.