What Does Duplex System Mean?
A duplex system is the combination of two protective coating systems: a paint or powder coating applied as a topcoat to a galvanized coating. This is done to improve the corrosion resistance of a material, and can greatly extend a material's lifespan.
Corrosionpedia Explains Duplex System
Powder coatings as well as galvanization provide corrosion protection when used individually. A duplex system provides enhanced effects between the newly coated materials and zinc, which results in more effective protection than either individual method.
This coating method reduces the corrosion rate of zinc, extending the lifespan of galvanized steel. If the exterior paint-coated layer is damaged, the galvanized zinc coating beneath still provides corrosion protection. As a result, life of material is extended approximately 1.5 to 2.3 times the sum of either protection method individually.
In mathematical form, the synergistic effect is defined:
M-Duplex = 1.5 to 2.3 (M-galvanizing + M-paint), where M = time to first maintenance
For example, if a galvanized coating alone provides 70 years of maintenance-free protection and if a paint coating alone provides 10 years of maintenance-free protection, then the duplex system would provide maintenance-free protection for 120 to 180 years.
ASTM D6386 and ASTM D7803 standards specify the optimum conditions to develop successful coatings.
Advantages of the duplex system include:
- Cost saving
- Extended service life
- Reduced maintenance
- Reduced replacement expenses