Though many specifiers are familiar with one type of corrosion protection or another, few realize the intrinsic value of utilizing two corrosion protection systems together, known as a duplex system. A duplex system is formed by painting or powder coating over hot-dip galvanized steel. When used together, the corrosion protection of the two systems combined is far superior to either protection system used independently. However, the most important element to a successful duplex system is proper surface preparation. Once again, this begins at the drawing board and requires communication among the designer, fabricator, galvanizer, and painter/coater throughout the process.
Why Coat Galvanized Steel?
There are a number of reasons why utilizing a duplex system is advantageous. As more specifiers understand the importance of corrosion protection, galvanized steel used in conjunction with paint/powder coatings has risen. In addition to extended life (synergistic effect), here are some other benefits of specifying a duplex system:
- Color Coding/Safety
- Extended Corrosion Resistance
- Ease of Repainting
- Economic Benefit
Paint and galvanizing work in synergy. The paint prevents atmospheric attack on the zinc and the zinc prevents underfilm corrosion from cracking the paint. According to several studies conducted in Europe, the synergistic effect means the zinc-paint combination will last 1.5 to 2.3 times longer than the sum of the paint and galvanizing systems alone. So, for a 70 year galvanizing life and a 10 year paint life, the system will last from 120 220 years. Practically speaking, no paint lasts that long without being repainted. But what the synergistic effect means is paint lasts longer, generally 1.5 to 2.3 times longer than if applied over black steel and the repaint cycle is thus extended. This represents a significant cost savings over the life of the project.
Duplex System Case Study
Salvador Dali Museum- St. Petersburg, FL (2010)
A fitting tribute to an iconic artist, the Salvador Dali Museum is a work of art reflective of the artists characteristic juxtaposition of classical and fantastic elements. The structure, designed by Yann Weymouth and Novum Structures, features an undulating, abstract 75-foot glass structure that flows from the plaza up and around the cubist treasure box museum. The innovative structure of this popular museum will receive worldwide attention, as the geometry of the glass structure is groundbreaking in the architectural world.
The structure, located in the highly corrosive Floridian coastal environment, faced several development challenges. All steel elements of the museum needed a durable, low-maintenance corrosion protection system to guard against unsafe and unsightly corrosion; however, the appearance of the structure must also be pleasing to the eye, without distracting from the glass structure. Finally, the complexity and scale of the architecture required the steel elements be fabricated, processed, and delivered to the jobsite in order and without loss.
Incorporating a duplex system of powder coating over hot-dip galvanized steel for corrosion protection was the ideal solution for addressing all of these concerns. A duplex system combines the superior protection of galvanized steel with the additional benefits of another corrosion protection system, such as powder coating or paint, to extend the maintenance-free life of the project. The powder coated finish allowed a color selection that would blend with the facility, while the galvanized steel beneath ensured the pieces would be protected by the most durable corrosion protection system available the best of both worlds.