Corrosion of carbon steel structures and structural members is a costly problem for pulp and paper mills. This corrosion is usually prevented by the use of protective coatings, and costs arise when these coatings need to be maintained or replaced, or fail altogether. Maintenance costs per square foot of steel range up to $1 for preventive maintenance of a good quality coating system; up to $4 for recoating a failed system, and up to as much as $20 when steel replacement and coating of severely corroded members are required. In new construction, the cost of original two- or three-coat paint systems usually ranges from $1.00 - $2.00 per square foot and galvanized coatings cost in the area of $1.00 per square foot.
Zinc coatings have been used for decades to protect structural steel from corrosion. Zinc by itself or zinc- rich primers that are used alone or in multi-coat protective systems have been widely used because of their special properties. They provide both barrier protection against corrosion and galvanic (sacrifical) protection of steel substrates. The former occurs because zinc corrodes more slowy than carbon steel in a wide range of atmospheric environments - as long as the pH is between 5 and 12. Galvanic corrosion protection can be obtained whether the zinc is used as a metallic coating or if high levels of zinc dust are formulated into coatings, using various vehicles.
The purpose of this document is to generally describe the various zinc and zinc-rich coatings available for use in pulp and paper mills and to provide a clear enough understanding of the various different zinc-based coatings to allow selection of the appropriate type of zinc coating for a variety of purposes.
