WHY USE A DUPLEX SYSTEM?

Duplex systems, as we define them, are materials that
have been painted or powder coated after galvanizing.

Each individual project raises unique reasons as

to why a duplex system should be utilized, and the

advantages for choosing to do so are many:

Extended Corrosion Resistance

The most obvious and most important reason for

using a duplex system, is the added corrosion

protection it provides. Other systems
simply can't match the corrosion resistance

provided by painting or powder coating
over hot-dip galvanized steel.

Synergistic Effect

It’s typical for a duplex system to provide

corrosion protection 1.5-2.5 times longer than

the sum of the lifetime of zinc or paint, used

individually.  For example, if a galvanized coating

is expected to be maintenance-free for 40 years

and a paint system is expected to last ten years,

galvanizing and paint combined should protect the

steel substrate for at least 75 years, or 1.5 times the

sum of both systems.

Economic Benefit

Because duplex systems greatly extend the

service life of a product, maintenance costs are

significantly decreased.  Additionally, a product

lasts longer before it must be replaced, thus

decreasing the life-cycle cost. The cost of a

product that has been protected by galvanizing and

painting or powder coating, is lower over the entire
life of the product than most single system methods
of corrosion protection.

Ease of Repainting

As the paint film weathers, the zinc in the

galvanized coating is present to provide both

cathodic and barrier protection, until the structure

is repainted. The exposed zinc surface then can

be repainted with minimal surface preparation.

Aesthetics

Galvanizing has an attractive metallic-gray

appearance, suitable for a myriad of applications,

but painting or powder coating can offer aesthetic
advantages. One might choose to paint over a
galvanized coating so that a project matches its
specific environment—such as a stadium, theme
park, or natural habitat.

Safety Marking

A duplex system of galvanized

steel and paint or powder coating
may be used to conform to safety
regulations. For example, the Federal

Aviation Administration (FAA)

requires structures over 200 feet

tall to be painted in the alternating
pattern of white and orange.

Color Coding

Painting or powder coating over galvanized steel
also increases safety in many environments, by
color-coding gas, steam, or chemical pipes,
identifying hazardous work areas and walkways,
and marking high-voltage electrical lines and
equipment.

Extending the Life of Previously Galvanized Steel

Paint is a logical choice to extend the life of

galvanized structures, once the zinc coating has

substantially and naturally weathered away.

Instead of being completely replaced, the

galvanized structure can easily be painted,

extending its useful life. Organic zinc-rich paints

are specifically suited to this application.

Repair of Hot-dip Galvanized Steel

Zinc-rich paints can also be used to touch-up and

repair damaged areas on a galvanized coating, in

order to comply with ASTM A 780, Repair of

Damaged and Uncoated Areas of Hot-Dip

Galvanized Coatings. Repairing a galvanized

coating will significantly extend the useful life of

a product.