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Galvanizing Steel

Galvanizing steel is the process of submerging steel in a bath of molten zinc which creates a protective layer that prevents future corrosion. Rust is potentially dangerous and can cause metal parts to become stiff and weaken the integrity of the metal and thus the structure.

Repairing deteriorated steel bridges after decades of use is time-consuming, expensive, and difficult to keep up with.

Hot-dip galvanization for steel not only protects metals from corrosion but also improves maintenance-free longevity. Thus, in the long run, businesses are saving money by keeping their steel galvanized and protected. In addition, the galvanization process is environmentally-friendly and resistant to conditions.

Galvanizing Steel: Three Main Steps

Step 1: Surface Preparation

The first and most crucial step is preparing the surface of the material for the coating process. Zinc will not react to unclean metal, so a successful surface prep is a must. Preparing the steel begins by removing all the dirt, grease, and other contaminants from the metal surface. This method is completed by degreasing the metal in a hot alkali solution or other acidic baths.

Pickling

Then the steel material is pickled through a diluted acidic solution for the removal of mill scales and any rust buildup. Depending on the company, this process is either replaced with or accompanied by abrasive cleanings, such as air blasting sand or metallic shot.

Fluxing

The final process for surface prep is fluxing. This procedure eliminates oxides while simultaneously creating a protective coating for the prevention of the formation of any additional oxides.

Step 2: Galvanizing Steel

After the surface of the metal has been prepped, it’s submerged in a large bath of 98% pure molten zinc at 830° F. The zinc reacts to the clean metal and generates a protective layer.

When the steel has reached the same temperature as the zinc bath, it is then withdrawn, drained, and cooled off before moving to the final step. Depending on the size and thickness of the material, this process could take up to 10 minutes or less.

Post-Treatment

It’s possible that a post-treatment coating will be applied to the metal. This process is called quenching. The steel is dipped in mostly water and some chemicals to create a protective layer. Frequently, finishing steps will include grinding off zinc drips for a smooth finish.

Step 3: Inspection

During the inspection phase, the coating thickness, weight, and appearance is meticulously analyzed and compared against the ASTM Standards. There are two different procedures that can be performed to measure the coating’s level of thickness: magnetic gauges or optical microscopy. Magnetic thickness gauge is the most simple and non-destructive thus making it the most popular method.

Analyzing Coating Weight

The second element that is analyzed is the material’s coating weight. The coating weight refers to the volume of zinc coating on the metal surface. Like the coating thickness inspection process, coating weight has two different methods for measuring the weight. Both the weigh-galvanize-weigh and the weigh-strip-weigh procedure should only be applied to single specimen inspection. These methods have their pros and cons so it’s important to choose the procedure that works best for you.

Final Galvanizing Steel Step

The last component that is inspected is the steel’s appearance and coating finish. All sections of the material are inspected to ensure that it meets the proper standards. As mentioned before, zinc will not react to unclean metal. Thus, the steel’s appearance and finish provides useful information such as revealing any errors that occurred during the galvanization process.

U.S. Bridge is a Certified Steel Fabricator

U.S. Bridge has been serving communities for more than 80 years, building steel bridges that withstand time. We’re a steel fabricator by the AISC for Certified Bridge Fabrication — Advanced (Major) and continue to be a leader in the American steel industry.

Still unsure if galvanizing steel is the right step for your bridge construction? Check our other blogs on the galvanization process and construction services for more information. Contact us today and let’s talk about how we can make your bridge project a long-lasting success.

Hot Dip Galvanized

A new bridge is a piece of infrastructure that will serve communities and transportation for decades. They must be built to last with the strongest and most durable materials. With hot-dip galvanizing, U.S. Bridge builds bridges that minimize maintenance and long-term durability regardless of the environment.

We’ve been galvanizing bridges since 1987, and we were the first to hot-dip galvanize an entire welded truss bridge. By bonding zinc to our U.S.-manufactured steel, we’re building long-lasting, reliable bridges with a sustainable process.

The Galvanizing Process

To galvanize steel, thorough cleaning of the steel is absolutely necessary. This is because zinc will only react with clean steel during the hot-dip process. Areas that are not perfectly clean will interfere with the process.

Before the Hot-Dip

Before hot-dip galvanizing, the surface must be prepared. This process includes degreasing, pickling, and fluxing.

Degreasing is the first step in cleansing the steel. It remotes dirt, oils, and organic residue. Next is pickling, which removes the iron oxides and scales from the steel’s surface to expose a bare area for galvanizing. Finally is the fluxing process, which prepares the steel for the hot-dip phase by applying a protective saline layer.

Hot-Dip Galvanizing

After the cleaning process, the steel is immersed in a kettle bath of 85% pure molten zinc at 830° F. The zinc reacts with the iron steel to form metallurgically-bonded coating. Once the steel reaches the bath temperature, the bonding is complete.

Once the steel cools down, an inspection verifies that it conforms to specifications. This includes a visual inspection and a magnetic thickness gauge that measures the coating.

Galvanizing Improves Bridge Life Cycle

The cost of hot-dip galvanized steel is roughly the same as painting a bridge. While a quality paint coat must be touched up, zinc-coated steel does not need maintenance over the bridge’s life.

However, the galvanized steel eliminates corrosion for up to 100 years in many cases. According to one study, the future maintenance of bridges can be reduced by 50% with galvanizing. With galvanized steel, the average service life is 8.5% longer. In fact, at U.S. Bridge, we have a 35-year warranty on our galvanized steel beam bridges — we’re that confident in lasting quality of galvanization.

Environmentally-Friendly

There are several environmental advantages to hot-dip galvanizing, beyond just the financial and durability impact. The key to sustainable construction of bridges is to continually lower the environmental impact of producing products. This is possible with zinc and steel.

Both zinc and steel are two naturally occurring, abundant elements. Ore — which steel is composed of — is the fourth-most abundant element on Earth. Zinc is 24th. Both are infinitely recyclable without the loss of physical or chemical properties. These materials can be used over and over without compromising their integrity.

With less maintenance, galvanizing will also prevent potentially harming environments during maintenance and traffic delays.

Build Sustainable Bridges with U.S. Bridge

In summary, hot-dip galvanizing steel is about the savings on the life-cycle of your bridge and the environmental benefits. With decades of experience in hot-dip galvanizing, we guarantee the highest level of quality in our steel bridge parts.

U.S. Bridge has been serving communities for more than 80 years, building bridges that withstand time. Our bridge experts will advise you on the best option for your bridge. Contact us today and let’s talk about how we can make your bridge project a long-lasting success.