Duplex Systems

We have posted about the benefits of duplex systems many

times in this blog.  Being a galvanizer and powder coater,

we strongly encourage this type of system for many 

different types of projects.  But don't just take our word

for it, consider the opinion of Melissa Lindsley, the 

Marketing Director at the American Galvanizers Association.

Below is an article she authored, which was published in the 

August, 2013 issue of The Construction Specifier.  After 

reading the article, please give us a shout if you have any

questions:  (800) 244-4258, info@whyrust.com

http://www.kenilworth.com/publications/cs/de/201308/files/42.html

New Kettle!

A message regarding the galvanizing portion of our operation:

Hubbell Galvanizing would like to formally announce that our

new kettle is now operational.  The new kettle dimensions

are as follows:

46'L x 5'W x 10'D

Please contact us with any questions regarding size/fit, or to 

place your next order -- we look forward to assisting you!

Hubbell Galvanizing

1-800-244-4258

(315) 736-8311

info@whyrust.com

Duplex System Compatibility

What Paints and Powders are compatible with Galvanizing?

A partial listing of available paint, paint systems,

and powder coatings that are compatible with

galvanizing are listed in the following table. The
paint manufacturer can provide more thorough
information about the compatibility of specific
systems with galvanized steel. Always consult
the paint manufacturer prior to painting galvanized
steel. Different physical and chemical characteristics
for the same types of paint may have varied reactions
with a galvanized surface. The paint manufacturer and

galvanizer can assist in the creation of a successful

duplex system.

Type	Compatibility	Comments
Acrylics	Sometimes	If the pH of the paint is high,  problems may occur due to ammonia reacting with zinc
Aliphatic Polyurethanes	Yes	If used as a top coat for a  polyamide epoxy primer, it is considered a superior duplex system
Alkyds	No	The alkaline zinc surface causes the alkyds to saponify, causing  premature peeling
Asphalts	No	Petroleum base is usually not recommended for use on galvanized steel
Bituminous	Yes	Used for parts that are to be buried in soil
Chlorinated Rubbers	Yes	High VOC content has severely limited their availability
Coal Tar Epoxies	Sometimes	Rarely used, only if parts are to be buried in soil
Epoxies	Sometimes	If paint is specifically manufactured for use with galvanized steel
Epoxy-Polyamide Cured	Yes	Has superior adherence to galvanized steel
Latex-Acrylics	Yes	Has the added benefit of being environmentally friendly
Latex-Water-based	Sometimes	Consult paint manufacturer
Oil Base	Sometimes	Consult paint manufacturer
Portland Cement in Oil	Yes	Has superior adherence to galvanized steel
Silicones	No	Not for use directly over  galvanized steel, can be beneficial in high temperature systems w/ base coat
Vinyls	Yes	Usually requires profiling, high VOC’s have severely limited their availability
Powder Coating	Yes	Low temperature curing powder coatings work exceptionally  well over galvanized steel

HOW A DUPLEX SYSTEM WORKS

Before deciding how to protect steel from

corrosion, it is important to understand how steel

corrodes. Corrosion takes place because of

differences in electrical potential between small

areas on the steel surface that become anodic and

cathodic. When an electrolyte connects the anodes

to the cathodes, a corrosion cell is created.

Moisture in the air forming condensation on the

steel surface is the most common electrolyte. In

the electrolyte, a small electrical current begins to

flow. The iron ions produced at the anode

combine with the environment to form the loose,

flaky iron oxide known as rust.

In order to protect steel from corrosion,

something must interfere with the corrosion cell,

either by blocking the electrolyte or by becoming

the anode. Two common methods of corrosion

protection are cathodic protection (the formation

of another anode) and barrier protection (blocking

the electrolyte from the steel surface). Hot-dip

galvanizing alone affords both types of protection,

and painting or powder coating over hot-dip galvanizing
adds an additional barrier layer on top of the zinc coating,
thus enhancing the protection afforded to the steel.  Duplex
coatings also offer the element of color to your project,
making it more aesthetically pleasing.

Fortress Fusion Coatings specializes in duplex coatings,
specifically in powder coating over galvanizing.  We
would be happy to discuss your project with you and
answer any questions you may have.

Fortress Fusion Coatings, Inc.
1-800-244-4258
(315) 736-8311
info@whyrust.com
http://www.whypowder.com

Galvanizing Post Treatments & Paint/Powder Adhesion

Poor adhesion of paint or powder coating to galvanized
parts is a common issue - but it doesn't need to be.
There are a few factors that affect the adhesion between
the surfaces. One of these factors is the post-treatment of 

the galvanized steel.

After a piece of steel has been galvanized,
it is sometimes quenched or treated by the
galvanizer, in order to halt the reaction
between the iron and zinc (and to facilitate
immediate shipment of the galvanized steel).

The most common post-treatments are
water quenching and chromate quenching,

Both quenching methods (water and

chromate) can adversely affect the

bond between the galvanized steel

and the paint or powder coating, causing
adhesion issues. Communicating with the
galvanizer prior to galvanizing helps avoid
post-treatments that can be detrimental to
paint or powder adhesion.

At Fortress Fusion Coatings, we are very familiar with the factors affecting proper
adhesion between galvanized steel and paint or powder coating.  If you have any
questions about this, or any other coating-related issue, we would be happy to
discuss it with you.  Please give us a call:

(315) 736-8311 - Office
(800) 244-4258 - Toll-free
(315) 736-0381 - Fax
http://www.whypowder.com

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.

DUPLEX SYSTEMS: Powder coating or Painting Over Hot-dip Galvanized Steel

INTRODUCTION

For years, protecting steel from corrosion

typically involved either the use of hot-dip

galvanizing or some type of paint system.

However, more and more corrosion specialists

are utilizing both methods of corrosion

protection in what is commonly referred to as a

duplex system. A duplex system is simply

painting or powder coating steel that has been

hot-dip galvanized after fabrication. When paint

and hot-dip galvanizing are used together, the

corrosion protection is superior to either

protection system used alone.

Painting galvanized steel requires careful

preparation and a good understanding of both

painting and galvanizing. Many products have

been galvanized and painted successfully for

decades; two examples are automobiles and radio

towers. Past experience provides excellent

historical data for how best to achieve good paint

adhesion. Studying past adhesion failures and

successes led galvanizers, paint companies,

researchers, paint contractors, and other sources to

create ASTM specification D 6386, Preparation of

Zinc (Hot-Dip Galvanized) Coated Iron and Steel

Product and Hardware Surfaces for Painting.

When the galvanized surface is prepared correctly,

paint adhesion is excellent and the duplex system

becomes a highly successful method of corrosion

protection.