Duncan Galvanizing Blog

Why Specify Duplex Coatings?

Posted by Casey Shearns on Fri, Apr 09, 2021 @ 10:45 AM

 

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Duplex coatings are a great way to add reliable and long-lasting corrosion protection to your steel, as well as improve its aesthetics. We broke down the facts about duplex coatings, and a few reasons to specify Duncan’s duplex coating system on your next project:

What is a Duplex Coating System?

A duplex coating system is the use of two coating systems - hot dip galvanizing and either a liquid or powder coating over the galvanized steel. The combination of these two processes  provide excellent protection against corrosion, and far better protection than using just one alone. This allows for less maintenance over time, a more polished appearance, and other benefits.

Benefits of Duplex Coating

  • Synergistic Effect

Duplex coatings provide enhanced protection for steel. When hot-dip galvanized steel is topcoated with paint or powder, this duplex system provides a more enhanced level of corrosion protection known as the synergistic effect. Paint or powder coating provides a protective barrier for hot dip galvanizing, as the exterior layer slows down corrosion from reaching the underlying zinc. If the exterior layer is worn down, the zinc from the hot dip galvanizing still provides excellent corrosion protection. This combined system is more than the sum of their parts. Both parts extend life of each other, they do much better and last much longer than if they were isolated. Additionally, the hot dip galvanizing primer virtually eliminates underfilm corrosion and paint peeling. It also extends the maintenance cycle of black steel by up to 2x. Duncan Duplex Coating Systems offer a 20 year warranty against corrosion, so your project will be protected against corrosion for decades to come.

  • Aesthetics

Duplex coatings  are also great for the aesthetics of your projects. Sometimes, the silver finish of hot dip galvanizing alone is not appropriate for certain projects. Duplex Coatings allow for a number of different finishes on steel to achieve your desired appearance. Duncan’s Colorgalv allows steel to be finished with a wide variety of colors. Some projects may require a vibrant color for safety reasons, need to blend in with surroundings, or other have other specific aesthetic needs. Duplex coatings  use paint or powder to make this possible.

  • Economic Benefits

There are also economic benefits when duplex coatings are specified. When a duplex coating is used, galvanized steel will often stay in good shape for decades until maintenance is needed. The less maintenance required, the less money that needs to be spent on the project after completion. Because of the synergistic effect dramatically increasing the time before maintenance, the initial cost pays off over the life of the project and ends up costing far less than coating bare steel.

 

LITTLE KNOWN FACTOID:

Did you know that Duncan Galvanizing was the first galvanizer in the country to do Hot Dip Galvanizing and factory applied coatings when it introduced Colorgalv in the mid-1970’s?

Contact Duncan Galvanizing

For high-quality duplex coating systems, hot dip galvanizing, color galvanizing, and more, Contact Duncan Galvanizing at (617) 389-8440 or fill out an online form to get started.

Tags: Colorgalv, Hot Dip Galvanizing

Why Specify Galvanizing?

Posted by Casey Shearns on Tue, Mar 09, 2021 @ 04:46 PM

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Steel corrosion can be costly, dangerous, and unsightly.  It’s important to make sure the steel used in your project is utilizing an effective method for protection against corrosion, abrasion, and weather conditions. Hot dip galvanizing is the process of factory dipping of fabricated steel into a kettle of molten zinc with the goal of preventing this corrosion, and creating a steel product that stays structurally sound and aesthetically pleasing for years to come. Hot dip galvanizing is often the preferred method of corrosion protection for steel for a number of its unique benefits, including:

Durability & Corrosion Protection

First, hot dip galvanizing is a great investment because of its durability and protection from even the harshest environments. This protective zinc alloy becomes tightly bonded to the steel, creating a layered protection with a bond strength of around 3,600 psi. In addition to the corrosion protection in any environment, this alloy also provides excellent abrasion resistance that is harder than the steel, protecting it from any damage that might occur during the shipment or construction process. 

Additionally, hot dip galvanizing is the ONLY system that protects the steel on the inside and the outside. Ensuring that the inside of fabricated steel is galvanized can be crucial to the integrity and life of the steel.  Also, because the steel is completely submerged in our zinc bath, there is a uniform protection on the entirety of the fabricated steel, while other methods such as liquid coatings often cause the protective coating along the edges to be thinner. Utilizing hot dip galvanizing is the only process that ensures this complete and uniform protection for steel.

Cost

Hot dip galvanizing also has several cost benefits. The overall material and application generally costs less than other corrosion protection methods. It also can be completed in less time due to the factory immersion process, saving construction time costs as well.

It also has lifetime cost benefits, as hot dip galvanized steel requires much less maintenance over time. In this chart, you can see the impressive amount of time hot dip galvanizing protects the steel from corrosion before first maintenance is required. 

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Sustainability

Both zinc and steel are 100% recyclable, making hot dip galvanizing a very ‘green’ process. Zinc is natural, abundant, and essential to life. Therefore, the use of steel is not introducing any harmful substances into the environment. Zinc and steel can also be recycled to be used many times over in different projects, so even at the end of a building or structure’s life, that material can be used again. In fact, 30% of the world’s zinc supply is recycled. This way, you can ensure that the materials used will not create waste. Hot dip galvanizing also uses less natural resources and creates less harmful emissions into the atmosphere, contributing to the overall environmental friendliness of your construction job.

Availability & Versatility

Hot dip galvanized steel is both readily available and accessible, as well as versatile for a variety of projects. Steel of many different shapes and sizes can be galvanized. Because of the total immersion in the zinc bath, even intricate shapes can be fully galvanized and protected from corrosion. This makes hot dip galvanizing a great choice for steel components that have a unique or complicated shape.

Additionally, because galvanizing occurs factory in a controlled environment, the process can be completed in any weather conditions, while other processes can’t. This allows construction projects to move quicker when the galvanizing can be completed any day, any time of year. The average turnaround time for hot dip galvanized steel ready for use is about 3-5 days, quicker than many other processes.

Contact Duncan Galvanizing

Duncan Galvanizing is the Northeast’s trusted provider of hot dip galvanizing, color galvanizing, and more. Contact Howie Levine for help with specifications or Seth Dubinsky to request a quote at (617) 389-8440 or fill out an online form to get started. 

Tags: Corrosion Protection, Hot Dip Galvanizing, Duncan Galvanizing

HOT TOPICS IN HOT DIP GALVANIZING: Galvanizing Slip Factor, Hydrogen Embrittlement & A-490 Bolts

Posted by Howard Levine on Fri, May 29, 2015 @ 03:42 PM

Galvanizing Bolts

In 1837, Stanislaus Sorel received a patent for galvanizing. Even though the process has been around for over 175 years, it’s not your great, great, great grandfather’s galvanizing!

Of course, many of the same principles still apply…outstanding corrosion protection, metallurgical bonding,100% surface protection of the interior and exterior of steel fabrications, but the galvanizing industry has adapted to the demands of the 21st century by recognizing that there is more to it than stopping rust. This article will highlight some of the technical trends in galvanizing benefitting the engineering community.

There are several issues currently being addressed by the industry with the charge being lead by the American Galvanizers Association.  Of particular note and impact on the engineering community are Slip Factors for Slip Critical Connections and Hydrogen Embrittlement /Galvanizing  A-490 Bolts.

A slip factor study by the American Galvanizers Association is in the final stages of research. The goal of the study is a guideline or specification with instructions on preparing a galvanized surface to achieve a Class B slip coefficient. With a higher slip coefficient, designers will be able to use galvanized steel in applications previously not considered or decrease costs by using less connections. Previous phases of testing indicate that obtaining the required 0.50 slip coefficient through roughening or other treatments is not possible. Therefore, the testing is focused on the use of a zinc-rich paint over the galvanized surface to obtain the Class B slip coefficient. The final phase of testing is slated to occur early this year.

Hydrogen Embrittlement Study

Another study deals with the feasibility of hot-dip galvanizing A490 bolts without a danger of hydrogen embrittlement. Hydrogen embrittlement originates in the cleaning step of the hot-dip galvanizing process. During the process, the heating of the steel causes some of the atomic hydrogen absorbed from the pickling acid to migrate into “trap sites” within the steel matrix. Once in the trap site, the hydrogen atoms can cause a premature failure of the steel fastener when installed in the field. Removing the source of hydrogen atoms (pickling acids) from the galvanizing process essentially eliminates the concern for hydrogen embrittlement failure. To accomplish this, the time the steel spends immersed in the pickling acids must be eliminated as this is the only source of hydrogen atoms in the process.  Mechanical surface preparation (blasting or wheel abrading) of the steel after the degreasing stage will solve the problem. The study tested several bolts galvanized with this modified process for compliance with ASTM and other standards. Results of these tests were typical for hot-dip galvanizing, showed no adverse effect on the coating from the modified process, and met the requirements of ASTM A153. The A490 bolt study has been completed and is being introduced to ASTM for inclusion in the specification. There may be further testing to explore other steel base materials to prove there is no difference in their hydrogen threshold after galvanizing.  More tests will be done in 2015 and the total report will be published and a change will be proposed to the new specification on high strength bolts. It should be noted that these practices have been utilized in Europe for many years and the use of hot-dip galvanized A490 bolts is an accepted practice in design and construction.

Why is this Important?

Educating the next generation of architects and engineers is a priority. Many have little or no knowledge of the galvanizing process. Their college curriculum skims over (or ignores) the need for corrosion protection. Visits to college campuses and A/E/C offices across the United States and Canada are being held to educate future architects and engineers about hot-dip galvanized steel. Through these presentations, students and “emerging professionals” will learn about the galvanizing process, design, sustainability, performance, specification, cost, and inspection.

Contact Duncan Galvanizing

If you or your office would be interested in a presentation, click here. For more info, give us a call at 617-389-8440.

Tags: Hot Dip Galvanizing, Engineering Topics

Galvanized Steel in Parking Structures

Posted by Howard Levine on Thu, Feb 21, 2013 @ 10:10 AM

 

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Steel is an exceptional building material. It has come into its own as a recognized, aesthetically pleasing part of the built environment. Since parking garages are no longer viewed simply as secondary structures in a project’s master plan, there is a need for a well designed architecturally impressive building. By working together, the entire building team can create work that is cost effective, long lasting, and beautiful.  

Unfortunately, most areas where fabricated steel products are used are subject to hostile atmospheric conditions or direct contact with aggressive chemicals. Deicing salts, vehicle emissions and acid rain are the most common culprits. For the steel to last and do its designed work, it must be protected from this corrosive attack.  

Hot Dip Galvanizing has been protecting steel from corrosion for centuries. Galvanizers understand the problems and have developed creative solutions. The problems of the parking industry are severe, but solutions achieved in other industries have enabled galvanizers to meet the challenge.  

Some of the advantages of hot dip galvanizing in parking structures are:

  • The life expectancy of hot dip galvanized coatings is a proven, measurable factor. As zinc protects steel by sacrificing itself, the life of the coating can be accurately predicted by dividing the existing coating thickness by the average coating loss per year. The longevity calculations are based on empirical data, not theoretical. The result is the life to first rust (not failure). In most cases, the calculated life of most areas exceeds 40 years.

  • Hot dip galvanizing has been extensively used in the industry. Sign supports, landscape components, highway architecture, noise barriers and many other items are currently specified to be galvanized.

  • When galvanized, the galvanizer has sole responsibility for the coating system. As no recoat will be required, the problem of "mixed systems" for maintenance doesn't occur. Maintenance of records for prior coatings is simple ---it was galvanized.

  • The coating adherence and quality are simple to inspect and verify. If the base steel isn't properly cleaned and prepared, it will not coat. Hot dip galvanizing is the only corrosion protection system that guarantees that the steel is perfectly clean before application of the coating. There cannot be a metallurgical bond between the steel and zinc unless the steel is 100% contaminant free.

  • Hot dip galvanizing is the only system available that protects the steel on the inside as well as the outside. This is especially important in the case of tubular materials which cannot be maintained on the interior. Left untreated, the corrosion can rapidly spread from the interior of the tube to the outside ultimately resulting in a structural failure of the component. By coming in contact with moisture, the untreated steel will "bleed" onto the ground, concrete or other appurtenance. Occurring long before a loss of structural integrity, however, will be an aesthetic failure.

  • Galvanizing is a factory process and is not dependent on weather or other external conditions. This allows fabricators and contractors the ability to accurately schedule site deliveries, erection times and eliminate delays.

There is an inherent difference between hot dip galvanizing and other protective coating systems.  Basically, steel is protected from corrosion through either barrier or cathodic methods. Barrier protection occurs when the protective mechanism acts to prevent the steel from coming into contact with the contaminant. How well it does its job is totally dependent upon the three “legs” of the coating triangle: Surface Preparation, Application, and Material. If the steel has not been prepared properly or if the application is done in less than ideal conditions, the coating will fail and corrosion will result. Paint is one example of the barrier method.  

Cathodic protection is a process whereby the metal is protected from corrosion by changing an element of the corrosion circuit. A form of cathodic protection is called the sacrificial anode method. In this system, a metal that is anodic to the metal to be protected is introduced into the corrosion circuit and becomes the anode. The protected metal then becomes the cathode and will not corrode. Zinc is anodic to iron and steel and by forming a metallurgical bond between the coating and the underlying steel, hot dip galvanizing provides cathodic protection as well as barrier protection.  

Furthermore, since the hot dip galvanizing process calls for the steel to be immersed into a bath of molten zinc and other earthly metals, it is being protected on 100% of its surface. This protection is critical and unavailable in other types of corrosion protection. It really serves no useful purpose to have a wonderful design, fabricated perfectly, with "rust bleed" staining the steel or adjacent material. This discoloration will lead to the public’s perception of inferior workmanship and lack of maintenance. As much attention must be paid to this particular issue as to the proper fabrication techniques. Since many garage components are tubular, it is important to specify a corrosion protection system that will not only protect the steel on the outside, but on the inside as well.   In addition to providing corrosion protection, galvanizing’s pleasing gray color meets many visual requirements as well. Typically, galvanized steel will oxidize to a uniform patina. However, when the need for color is required for safety reasons or the design calls for a particular color scheme, galvanized steel can be successfully topcoated.

Contact Duncan Galvanizing

By following a proven formula, Duncan can add the beauty and additional longevity of a high performance coating system over galvanizing. For more information on the available paint and powder coating systems, and their warranties, please contact us at 617-389-8440 or fill out a contact form.

 

Tags: Corrosion Protection, Hot Dip Galvanizing, Duncan Galvanizing

What is the Production Process for Hot-Dip Galvanizing?

Posted by Popi Papadonta on Wed, Dec 21, 2011 @ 01:15 PM

Step 1: Surface preparation

Thorough cleaning is necessary as zinc will only adhere to clean steel. This gets accomplished by:

  • Degreasing: a hot alkaline cleaner is used to remove oil, grease, dirt, loose particles, and any other contaminates that may exist on the surface of the material

  • Acid pickling: an acid bath is used to remove mill scale and oxides

  • Fluxing (dry kettle): pre-fluxing in a zinc ammonium chloride solution to remove oxides and to prevent oxidation prior to dipping into molten zinc

Step 2: Immersion in bath of molten zinc

During this step, the steel is immersed in a bath of molten zinc at approximately 830˚F. The mix in the bath consists of ~98% pure zinc and 2% additives (Al, Bi, Ni). The zinc reacts with the iron in steel and it forms a coating which is metallurgically bonded to the steel. Also, the zinc flows into recesses and other areas difficult to access, coating all areas of complex shapes thoroughly for corrosion protection. Hot dip galvanizing is the only coating system that protects tubular steel on the inside. The zinc goes “in, around, over, under and through” the fabrication. 

hot dip galvanizingThe size of zinc baths varies from galvanizer to galvanizer and this restricts the size of steel that can be galvanized. When choosing a galvanizer, make sure that the size of the zinc bath is big enough to accommodate the size of your products such as large structural shapes. 

The final product is protected against corrosion as zinc creates a barrier between steel and the environment and also cathodically protects the base metal. 

Step 3: Finishing


After the steel is withdrawn from the galvanizing bath, excess zinc is removed by draining, by vibrating or for small items, by centrifuging. The galvanized item is then cooled in air.


Step 4: Inspection

Steel is inspected after galvanizing to verify conformance with specs

 

Contact Duncan Galvanizing

For high-quality hot dip galvanizing, color galvanizing, and more, contact Duncan Galvanizing at (617) 389-8440 or fill out a contact form.

 

Sources: Duncan Galvanizing Corp., American Galvanizers Association

Tags: Corrosion Protection, Hot Dip Galvanizing, Duncan Galvanizing