Electro-Plated Zinc (ASTM B633)

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-GARD finish 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.


 
Electric current
flows from
plus to minus
Anodic
(least
noble)
Corroded

Direction
of attack

Cathodic
(most noble)
Protected

Magnesium
Magnesium Alloys
Zinc
Beryllium
Aluminum 1100, 3003, 3004, 5052, 6053
Cadmium
Aluminum 2017, 2024, 2117
Mild Steel 1018, Wrought Iron
HSLA Steel, Cast Iron
Chrome Iron (active)
430 Stainless (active)
302, 303, 321, 347, 410, 416 Stainless Steel(active)
Ni-Resist
316, 317 Stainless (active)
Carpenter 20Cb-3 Stainless (active)
Aluminum Bronze (CA687)
Hastelloy C(active) Inconel 625(active) Titanium(active)
Lead/Tin Solder
Lead
Tin
Inconel 600 (active)
Nickel (active)
60% Ni 15% Cr (active)
80% Ni 20% Cr (active)
Hastelloy B (active)
Naval Brass (CA464), Yellow Brass (CA268)
Red Brass (CA230), Admiralty Brass (CA443)
Copper (CA102)
Manganese Bronze(CA675), Tin Bronze(CA903, 905)
410, 416 Stainless(passive) Phosphor Bronze(CA521, 524)
Silicon Bronze (CA651, 655)
Nickel Silver (CA 732, 735, 745, 752, 754, 757, 765, 770, 794
Cupro Nickel 90-10
Cupro Nickel 80-20
430 Stainless (passive)
Cupro Nickel 70-30
Nickel Aluminum Bronze (CA630, 632)
Monel 400, K500
Silver Solder
Nickel (passive)
60% Ni 15% Cr (passive)
Iconel 600 (passive)
80% Ni 20% Cr (passive)
Chrome Iron (passive)
302, 303, 304, 321, 347 Stainless (passive)
316, 317 Stainless (passive)
Carpenter 20Cb-3 Stainless (passive), Incoloy 825 (passive)
Silver
Titanium (passive), Hastelloy C & C276 (passive)
Graphite
Zirconium
Gold
Platinum