Reasons for Duplex Coating
There are seven good reasons to paint or powder coat hot-dip galvanized steel:
- Extended Durability in what is called the synergistic effect between galvanized steel and paint, the zinc of the galvanized coating is a barrier protection to the substrate steel, cathodically protects it, and provides underfilm corrosion protection of the paint. Synergistically, the paint provides a barrier protection to the zinc coating.
- Economic because the zinc extends the life of the paint, less maintenance is required over the entire service life.
- Ease of Repainting when the paint of a duplex system completely weathers, the exposed zinc coating requires minimal surface preparation when repainting.
- Aesthetics desiring a color to match surrounding structure or for branding.
- Safety Marking the extremely high cost to maintain a very tall structure often means galvanizing is a requirement but those same tall structures are mandated to be painted safety orange and white for high visibility to air traffic.
- Extending the Life of Previously Galvanized Steel large in-place structures often cannot be regalvanized after decades of exposure and so a logical means of keeping the structure in service is to apply a paint, often an inorganic zinc-rich paint which provides barrier protection and some cathodic protection.
- Color Coding steam, water, and other fluid piping systems are often painting in industrial facilities to distinguish them for quick repair and safety concerns.
Guide to Preparing Hot-Dip Galvanized Steel for Paint
© 2023 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative information about after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competent professional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation or warranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.