Zinc metallizing with a high purity zinc wire has been utilized for external corrosion control of iron pipe for over 50 years, and supplied by U.S. Pipe for over 20 years.. While most publications on metallic zinc coated iron pipe are based on experience and case histories from England and Europe, it should be noted that metallic zinc is, and has been used extensively for external corrosion protection of ductile iron

 

pipe by China, India, the Middle East, Latin America, Africa, Korea, Japan, and others. Zinc coating for external corrosion protection of ductile iron pipe is such a recognized and established worldwide practice that there is an international standard, ISO 8179-1(Ductile Iron Pipes-External zinc-based coating-Part 1: Metallic Zinc with Finishing Layer) which was first issued in 1985 (ISO, 2004).

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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 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.

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STANDARDS

- ANSI/AWWA C151/A21.5 Ductile Iron Pipe, Centrifugally Cast for Water.
- ANSI/AWWA C104/A21.4 Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water.
- ANSI/AWWA C111/A21.11 Rubber-Gasket Joints for Ductile-Iron Pressure Pipe and Fittings.
- ANSI/AWWA C105/A21.5 Polyethylene Encasement for Ductile Iron Pipe Systems.
- ASTM A746-03 Standard specification for Ductile Iron Gravity Sewer Pipe.
- ASTM A716-08 Standard Specification for Ductile Iron Culvert Pipe.
- ASTM A536 Standard Specification for Ductile Iron Castings.
- ISO 8179-1, Ductile Iron Pipes-External Zinc-based Coating-Part 1: Metallic Zinc with Finishing Layer (ISO 2004)

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