Friday, March 23, 2012

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

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