This type of
coating is recommended for indoor use in relatively dry areas. This process
deposits a coating
of zinc on the
steel or iron by electrolysis from a bath of zinc salts. This coating is pure
zinc and
adheres to the
steel or iron with a molecular bond. A maximum of .5 mills of zinc can be
applied using
this method.
Pre-Galvanized Zinc (ASTM A653)
This type of
coating is suitable for extended exposure in dry or mildly corrosive
atmospheres, but not generally
recommended
for outdoor use, or in industrial environments. This coating is also referred to
as “mill
galvanized” or
“hot-dip mill galvanized”. This process continuously rolls steel coils or sheets
through
molten zinc.
The steel is then cut or slit to size. Coating thickness of .90 ounces per
square foot of steel
surface
(referred to as G90). Cut edges are not zinc coated, however, zinc near the
uncoated steel becomes a
sacrificial
anode, which protects the bare areas after a short period of time.
Hot-Dip Galvanized (ASTM 123)
This type of
coating provides extended corrosion protection for steel and iron products
exposed to
extreme
humidity commonly evident in outdoor exposure or in uncontrolled atmospheric
conditions. This
coating
provides superior corrosion resistance to that of electro-plating. The process
calls for the steel or
iron product
to be completely immersed into a bath of molten zinc, which creates a
metallurgical bond.
The minimum
coating thickness is 1.5 ounces per square foot per side (3 ounces per square
foot of steel
or iron).
Caution should be taken when specifying Hot-Dip Galvanizing on certain products.
Products
with threaded
components should either have the threads protected from the galvanizing process
or
chase the
threads subsequent to hot-dipping. Products with critical size tolerances should
account for the
thickness of
the coating.
COPPER-GARDfinish
for copper tubing installations.
The finish provides
superior corrosion protection and insulates against dissimilar metal contact,
thus preventing
electrolysis. The
process applies a baked-on epoxy paint to steel stampings and iron castings. In
the three-step
process, the parts
are zinc plated to .0002” thick, an epoxy copper colored powder is then applied
by an
electrostatic
method, and finally, the coated parts are baked at 180 degrees for 20 minutes.
This coating is
designed for copper tubing installations. The coating is intended to identify
the product size
only. This finish
is not intended for corrosion resistance.
This coating is
intended to support chrome plated pipe and provides corrosion resistance for
commercial
installations such
as hospitals, schools and prisons.
Galvanic Corrosion
Galvanic corrosion potential is a measure of how dissimilar
metals will corrode when placed against each other in an
assembly. Metals close to one another on the chart generally do
not have a strong effect on one another, but the farther apart
any two metals are separated, the stronger the corroding effect
on the one higher in the list. This list represents the
potential available to promote a corrosive reaction, however the
actual corrosion in each application is difficult to predict.
Typically, the presence of an electrolyte (eg. water) is
necessary to promote galvanic corrosion. Please see chart below.
