Zinc Dust Zinc Oxide Paint Versus Zinc Rich Coating

Whether to use a zinc dust/zinc oxide paint or a zinc-rich coating depends on a number of factors, including cost of surface preparation, paint application, and anticipated length of surface. Zinc dust/zinc oxide coatings are ideal for rural or semi-industrial atmospheres. They are particularly effective on galvanized surfaces.

The widely used zinc dust/zinc oxide primers based on ordinary drying oil media do not give general electrolytic protection against corrosion and therefore do not fall in the category of zinc-rich paints.

Zinc-rich coatings are preferred for the protection of steel or galvanized steel structures exposed to marine environments or immersed in seawater. Applications include interiors of floating roof tanks, cooling tower piping, pipe racks and exterior piping in refineries, stacks, chemical plant maintenance, offshore drilling platforms, aboveground pipelines, structural steel before erection, exterior of pressure vessels, ammonia tanks, ship holds, and air conditioning equipment.

A top coat finish may be necessary in aggressive atmospheres. The top coat must adapt to the environment and must guarantee compatibility with, and adhesion to, the zinc-rich primer.

Advantages and Limitations of Zinc-Rich Paints. Zinc-rich primers offer a more versatile form for applying zinc to steel than galvanization; large, continuous complex shapes and fabricated new or existing structures can be easily coated at manufacturing shops or in the field. Their performance has earned them a prominent place in the field of corrosion protection coatings. However, the limitations of zinc-rich paints include cost, difficulty in applying, and the requirement of clean steel surfaces. They must be top coated in severe environments (pH under 6.0 and over 10.5).

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