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FAQ

QUESTION: How large of a piece can we galvanize?
ANSWER: Our kettle is 5 feet wide, 46 feet long and 10 feet deep. Our kettle is large enough to handle just about any piece of metal, but please contact us about how large the piece is that you would like galvanized.


Q: Can I paint right over the galvanized coating? If so, what procedure should be followed?
A: Galvanized coatings can be easily and effectively painted, not only for aesthetics but also to extend the structure's service life. The age and extent of weathering of the galvanized coating dictate the extent of surface preparation required to produce a quality paint system over galvanized steel. ASTM D 6386, Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting, should be consulted for suggested surface preparation methods for galvanized coatings of varying ages. You can also consider powder coating, which requires less maintenance than paint.

Q: I'm interested in specifying hot-dip galvanizing for reinforcing steel. Are there any concerns with fabricating rebar after galvanizing?
A: Rebar is commonly fabricated after galvanizing. In order to minimize the possibility for coating damage, avoid bending the rebar more than eight times its radius. ASTM A 767, Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement, has a table that provides maximum bend diameters for various-sized rebar.

Q: What if the article to be galvanized is larger than the dimensions of the galvanizer's kettle? Can it still be galvanized?
A: Galvanizers can progressively dip such a fabrication. They dip one half in the molten zinc bath, remove it, turn it around or over and immerse the other half in the zinc. This method is often erroneously referred to as “double dipping.”

Q: Why do galvanized steel appearances differ from project to project and is there any difference in the corrosion protection offered by the different appearing coatings?
A: The steel chemistry is the primary determinant of galvanized coating thickness and appearance. Continuously cast steel produced by the steel companies has a wide variety of chemistries, thus the different coating appearances.

Q: What causes wet storage stain and how can it be prevented?
A: Zinc on newly galvanized steel is very reactive and wants to form zinc oxide and zinc hydroxide corrosion products that eventually become the stable zinc carbonate. When galvanized steel is tightly stacked or stored in wet boxes that don't allow for free flowing air, the zinc forms excessive layers of zinc hydroxide, otherwise known as wet storage stain. Most wet storage stain can be easily removed with a cleaner or nylon brush. To prevent wet storage stain, store galvanized steel indoors or block it so that there is ample free flowing air between each galvanized article.

Q: How long can I expect my galvanized steel project to last in service?
A: It is not uncommon for hot-dip galvanized steel to last more than 70 years under certain conditions. To get a good idea of how long your project will last, see the service-life chart.

Q: What is "cold" galvanizing?
A: There is no such thing as cold galvanizing. The term is often used in reference to painting with zinc-rich paint. Galvanizing by definition means a metallurgical reaction between zinc and iron to create a bond between the zinc and the steel of approximately 3,600 psi. There is no such reaction when zinc-rich paints are applied and the bond strength is only several hundred psi.

Q: Are all zinc-coated systems the same as hot-dip galvanizing?
A: There are several ways to apply zinc to steel but none offers the protection of HDG.

  • Metallizing is an expensive process in which zinc in wire or powder form is sprayed onto the steel. Because the zinc is sprayed onto the steel instead of migrating into the steel like HDG, it only provides barrier and limited cathodic protection.
  • Zinc-rich Paint is a paint that contains up to 78 percent zinc by weight and is one of the approved repair methods for HDG in ASTM A780, the repair specification for HDG. However, as with most paint coatings, the quality of the application is a major factor in determining the long-term performance. Consideration must be given to the initial steel surface condition (is it new, rusty or contaminated?), proper surface preparation, weather conditions (properly controlled temperature and humidity), the skill of the painter, the curing process and handling.
  • Continuous Galvanizing is typically used for very thin sheet products. Coils of steel sheet metal are fed as ribbon through a molten metal bath where it reacts to leave a protective surface coating. It has similar properties to hot-dip galvanizing, but the coating is thin since one of the factors affecting how much zinc will bond to the steel is the thickness.
  • Electroplate Galvanizing is the process whereby zinc is electrochemically applied to the steel. The coating thickness is very thin.

Q: What type of corrosion protection does HDG provide?
A: HDG Offers Three Types of Protection Against Corrosion

  • BARRIER: The four-layer galvanized coating provides superior barrier protection to prevent corrosion. The harder alloy layers mean the coating is very difficult to compromise.
  • CATHODIC: The electrochemical relationship between zinc and steel in the presence of an electrolyte, like moisture, means that if the galvanized coating is ever compromised down to the bare steel that the electrons in the zinc will “sacrifice” themselves to prevent corrosion. A “flash” rust will occur on the surface. But then the corrosion stops. Over time zinc from the top layer will flow into a cut up to ¼-inch in the coating to “heal” it.
  • ZINC PATINA: The zinc patina is a hard, thin film that forms on the galvanized coating when it reacts with the oxygen, moisture and carbon dioxide in the air. The zinc patina acts a barrier for the galvanized coating and must wear off before the galvanized coating can begin to wear.

Q: Why is HDG superior to paint for corrosion protection?
A: Although the paint industry has made great improvements in paint systems HDG is still superior to paint for corrosion protection providing decades not just for years. Here’s why:

  • HDG is not just a coating like paint. HDG bonds zinc to the steel at the molecular level.
  • In addition to the metallurgical bond, HDG provides two other types of protection - Cathodic Protection and the Zinc Patina. Paint does not provide these extra protections.
  • Despite improvements in paint in recent years the most serious drawback of paint systems is that if the coating is damaged and bare steel is exposed it will immediately begin to corrode. As the rust increases, it spreads under the remaining paint coating and separates it from the steel. That causes flaking and peeling. As the paint peels, more steel is exposed and the corrosion accelerates. Repair to paint can be expensive, difficult to make, hard to remove the rust from the surface and harder still to verify that the surface was prepped and painted properly for the new paint to stick.

Q: How does the cost of hot-dip galvanizing compare to other corrosion protection systems, such as paints?
A: When compared with paint systems, hot-dip galvanizing after fabrication has comparable initial application costs and, almost always lower life-cycle costs. In fact, the lower life-cycle costs of a hot-dip galvanized project make galvanizing the smart choice for today and tomorrow.

Q: What are the specifications governing hot-dip galvanized steel?
A: Structural steel (plate, wide-flange beams, angles, channels, pipe, tubing) are galvanized to ASTM A 123/A 123M. Fasteners and small parts that fit into a centrifuging basket are galvanized to ASTM A 153/A 153M. Reinforcing steel is galvanized to ASTM A 767/A 767M.

Q: What are the steps in the galvanizing process?
A: There are four steps:

  1. Pre-inspection - The fabricated structural steel is viewed to ensure it has, if necessary, the proper venting and draining holes, bracing, and design characteristics necessary to yield a quality galvanized coating
  2. Cleaning - Steel is immersed in a caustic solution to remove organic material such as grease and dirt, followed by dipping in an acid bath (hydrochloric or sulfuric) to remove mill scale and rust, and finally lowered into a bath of flux that promotes zinc and steel reaction and retards further oxidation of the steel. (Steel will not react with zinc unless it is perfectly clean.)
  3. Galvanizing - The clean steel is lowered into a kettle containing 850-degree Farenheit molten zinc where the steel and zinc react to form three zinc-iron alloy layers and one pure zinc layer.
  4. Final inspection – The newly galvanized steel is sight-inspected, followed by measurement of coating thickness with a magnetic thickness gauge.

Q: Why is zinc used in the hot-dip galvanizing process?
A: Although several metals could be used to galvanize steel, zinc has properties that make it the best choice by far. Zinc is a natural element and is essential for healthy human life. Zinc is included in vitamins, used in the prevention of sun burn, used to promote healing of wounds and minimizing diaper rash. Zinc is also 100 percent recyclable without any loss of characteristics or elemental change. Zinc also acts as an anode to steel, meaning the zinc will sacrifice itself to prevent corrosion of steel. Not every metal can do all that.

Q: How does galvanizing protect steel from corrosion?
A: Zinc used in the galvanizing process provides an impervious barrier between the steel substrate and corrosive elements in the atmosphere. It does not allow moisture and corrosive chlorides and sulfides to attack the steel. Zinc is more importantly anodic to steel - meaning it will corrode before the steel.

Q: What is Hot-Dip Galvanizing (HDG)?
A: Hot-Dip Galvanizing or HDG is a process in which zinc bonds to steel at the molecular level to produce a four-layer corrosion-resistant finish. The first three layers are zinc-iron alloy layers that are actually harder than the base steel. The fourth or top layer is pure zinc.

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