Corbec, Hot-dip Galvanizing
Hot-dip Galvanizing FAQ

Galvinizing's FAQ

What is hot-dip galvanizing?

Hot-dip galvanizing is a method whereby freshly cleaned steel is immersed in a kettle of molten zinc at 450 C, creating a metallurgically bonded zinc alloy coated with pure zinc. The first of these two steel alloys is harder than the base metal. This gives the hot-dip galvanizing its excellent abrasion resistance property. The outer layer, smooth and pure zinc, absorbs shocks; the underlying alloy layers offer effective protection for the base metal.

How does Corbec ensure that the galvanizing meets industry standards?

Corbec uses standards and processes that meet the specifications for hot-dip galvanizing issued by the Canadian Standards Association (CSA) and the American Society for Testing and Materials (ASTM).

The test results and certificates of compliance for selected specifications are available, provided the request is made on the original order, delivered before galvanizing.

What are the possible sizes?

It is important to note that due to our safety equipment on our kettles, it is impossible to double-dip galvanize. If your parts exceed the size of our kettles, please contact us and we will discuss the possible solutions with you! They may be more affordable than you think!

It happens that in some places, the zinc layer is brighter than elsewhere: Why?

The chemical composition of the steel used largely determines the final appearance of the galvanized product and the thickness of the coating. Steels produced by foundries have a wide range of compositions, and consequently, the galvanizing results differ.

Also, galvanizers can choose the additives to be mixed in the zinc kettle, which, according to their "recipe", will produce a shiny, matte or marbled (spangled) appearance. The appearance does not affect the anticorrosive properties of galvanizing.

What should I do to minimize the risk of distortion of my parts?

You can easily reduce these risks by selecting your steel so that the thicknesses are equivalent within each sub-assembly to be galvanized. By avoiding the use of thick 1/16" steel and promoting symmetrical designs (where possible), you greatly reduce the risk of deformation and distortion of your parts.

What is white rust and how can it be avoided?

This term is often used incorrectly instead of the more common term "wet storage stain", which is a slight corrosion, much less serious than white rust. Storage stains can be avoided by storing freshly galvanized steel according to guidelines, avoiding exposing unprotected surfaces to moisture or water, or by applying a surface passivation treatment. Note that these spots will disappear once the galvanized steel is exposed.

What is the "cold galvanizing"?

There is no such thing as a cold galvanizing process. This term is used to refer to zinc rich paint, suitable for repairing galvanized surfaces. Galvanizing is defined as a metallurgical reaction between zinc and iron that produces a zinc-steel bond of approximately 3,600 psi. There is no chemical reaction when applying a zinc-rich paint and the bond's strength is only a few hundred psi.

Why must parts be perforated before galvanizing?

The reason is simple: the ventilation holes are required when immersing the parts for venting air and drain holes are required to enable the full flow of liquid when cleaning and during galvanization. Since the material must be fully protected, zinc must circulate freely in all cavities of a part or structure.

Is it possible to paint galvanized steel? If so, what procedure should be followed?

Galvanized structures can be easily painted. While in some cases aesthetics are what is sought, it is important to note that painting done according to standards will extend the service life of galvanized materials. The condition of the material (aging) indicates the surface preparation required to ensure an optimal paint treatment. The document ASTM D 6386, Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Products and Hardware Surfaces for Painting should be consulted for this purpose.

What is the approximate service life of galvanized parts?

The zinc corrosion rate and the duration of protection is determined by the quality of the coating (thickness) and the amount of corrosive elements present in the immediate environment. For example, in a rural environment where vehicle traffic is reduced, the virtual absence of corrosive emissions allows galvanizing to easily last for 100, even 150 years without maintenance.

Conversely, in an industrial/marine environment where the presence of corrosive elements (chlorides, sulfides) is significant, galvanized steel can last 50 to 100 years.

This will be explained more in depth and documented on the AGA website.

Is it possible to "order" a particular thickness of zinc on my material?

No. The chemical composition of the steel and the condition of the surface will determine the thickness of the zinc coating which is obtained by hot-dip galvanizing. Leaving the steel longer than prescribed in the molten zinc kettle may result in: 1) an increase in the thickness of the coating, but only marginally so, or 2) a significant increase in the thickness of the coating will weaken the top layer of zinc and may result in flaking.

What is "double-dipping"?

Double-dipping is a progressive immersion procedure for parts that are too large for in a single dip in the kettle. This procedure cannot be used to obtain additional coating.

Do I need to be worried about contact between the steel and other metals?

Zinc is called a "noble" metal, it will sacrifice itself (in other words, it will corrode, give up its electrons and create a bimetallic couple) to protect most metals. Therefore, it is recommended to isolate the galvanized steel so it will not be in direct contact with different metals. Rubber or plastic, two non-conductive substances, are often used to provide this insulation. Furthermore, if assembly is required after galvanizing, it would be appropriate to use galvanized hardware, and if welding is required, be sure to cover weld seams with zinc rich paint protection.