Synergistic Corrosion Protection of Ductile Iron Pipe Utilizing Metallic Zinc Coating in Combination with Enhanced Polyethylene Encasement

Zinc metallizing with a high purity zinc wire with topcoat has been utilized in Europe for external corrosion control of iron pipe for over 60 years. In the United States, polyethylene encasement has been the primary asset preservation method utilized for gray and ductile iron pipe since 1958. In that 60 year time period hundreds of millions of feet of iron pipe have been installed worldwide and successfully protected with each of these methods. Like any corrosion protection system, these methods have limitations. International studies over the last 47 years have verified that the limitations of both methods when utilized independently can be solved by combining them together as a system. More recent studies in a severely corrosive Florida Everglades environment have shown that the synergy of the two combined systems can be further improved by utilizing a polyethylene encasement enhanced with an anti-microbial and a corrosion inhibitor. This paper summarizes the results to date of 15 years of testing the following methodologies with and without intentional damage to the encasement film: standard polyethylene encasement (with and without galvanic cathodic protection), polyethylene encasement enhanced with an anti-microbial and a corrosion inhibitor, and both types of polyethylene encasements applied to arc spray metallic zinc coated ductile iron pipe.