U. S. Pipe Introduces Zinc Coated Ductile Iron Pipe
U.S. Pipe has introduced Zinc Coated Ductile Iron Pipe to further advance corrosion control in ductile water pipelines. Although zinc is a relative newcomer to the domestic markets, U. S. Pipe has provided zinc coated material internationally for more than twenty years.
Zinc metallizing with a high purity zinc wire has been utilized for external corrosion control of iron pipe for over 50 years. Initially used in Europe, zinc coating is now becoming more widely used in the United States with many municipalities and water works boards standardizing on ductile iron with metallic zinc coating.
Metallic zinc coating on ductile iron pipe is applied using an arc spray process in which metallic zinc is heated to a molten state and projected in small droplets by spray guns onto the pipe surface. In the arc spray system, two high purity zinc wires are brought together under a high electrical potential which results in the wires being melted at the point of contact. The molten zinc droplets are then propelled to the surface by clean compressed atomizing air. Providing an active inner layer of 200 g/m2 of pure metllic zinc under the asphaltic topoat.
Numerous studies and publications from around the world over the last 50 years have demonstrated that both arc sprayed metallic zinc with topcoat and enhanced polyethylene encasement are economical and effective methods of external corrosion control for iron pipe. In environments where neither zinc nor enhanced polyethylene encasement are recommended individually, additional studies in Europe and the USA have shown that combining arc spray metallic zinc coating with polyethylene encasement produces a synergistic corrosion protection system.
In Europe, the primary method of corrosion control for iron pipe since 1958 has been an external coating of arc spray metallic zinc plus topcoat. In 1985, the first international standard on metallic zinc coating was issued as ISO 8179-1, Ductile Iron Pipes-External Zinc-based Coating-Part 1: Metallic Zinc with Finishing Layer (ISO 2004).
Additional studies in Europe have confirmed that combining metallic zinc coating with polyethylene encasement produces a synergistic corrosion protection system. The zinc will protect the pipe at unrepaired damage to the encasement, and the encasement will extend the life of the zinc, enhance the development of zinc corrosion products as the zinc sacrifices itself, create a homogeneous environment around the pipe with some biocidal characteristics, and allow the zinc to be utilized in some severe environments where it is otherwise not recommended.
Zinc coated pipe is recommended to be encased in AWWA C105 polyethylene or V-Bio® in the following environments: where the soil is acidic (pH ≤5) or very basic (pH >9), extremely low resistance soils (< 1,500 ohm-cm), peat soil, certain artificial backfill polluted by chemical products or cinders with sulfur, in sea or fresh water and subject to intensive running water, outside mechanical abrasive and corrosive conditions, areas with stray electrical currents, and installations where soil conditions are unknown.
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Metallic Zinc Coating for Ductile Iron Pipe