Duncan Galvanizing Blog

CORROSION PROTECTION FOR ROOFTOP DUNNAGE

Posted by Howard Levine on Fri, Jun 19, 2015 @ 03:29 PM

Rusty Rooftop Dunnage

The expression “out of sight, out of mind” is particularly appropriate for rooftop dunnage. Rarely, if ever, is any attention paid to the steel supporting the mechanical equipment supports, HVAC, solar and cooling tower.

Even though this material doesn’t have the same cachet as Architecturally Exposed Structural Steel, it is an integral part of the building. While initial cost of the dunnage is part of the overall construction budget, replacement or maintenance is not. That cost comes directly out of the Owner’s pocket!

How can the steel be protected from corrosion in the aggressive New England environment? The answer is simple: Hot Dip Galvanizing. Galvanizing is a metallurgical bond between the zinc and steel that provides protection against virtually any corrosion causing element. 

Hot Dip Galvanizing lasts longer and protects better than paint and is a “green” process and will help in reaching your LEED goals. Paint is NOT enough to protect your rooftop steel.

Think about it: You don’t want to rent a crane in five years to repair a problem caused today.

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.

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.

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.

If you or your office would be interested in a presentation, click here.

Tags: Hot Dip Galvanizing, Engineering Topics

Do You Want This?

Posted by Howard Levine on Tue, Sep 30, 2014 @ 03:07 PM

Colorgalv by Duncan

Or This?

NOT Colorgalv!

Rainbow Terrace Apartments in Salem, MA
Click each image for an enlarged view.

A Long-Lasting Coating System
That Looks Good Too

Duncan Colorgalv Thermoset 10

  • Anti-Graffiti Coating Available

  • No Maintenance Required

  • 20 Year Warrantee

  • Meets All "Green" Standards

What Our Customers Say

"I specified Duncan Colorgalv Thermoset 10 for Rainbow Terrace Apartments in Salem and Willowood Gardens in Gloucester because I wanted my clients to have a long-lasting, durable coating system for their exposed steel."

"Having done design work for many of the region's Housing Authorities, I was aware of the need for a maintenance-free product to control operational costs. Duncan Colorgalv Thermoset 10 was my choice!"

~~ Robert Mitnik, A/A

Would you like more information? Call Duncan at 617-389-8440 or email info@duncangalvanizing.com.

 

Tags: Colorgalv Thermoset

Spotlight On Colorgalv

Posted by Howard Levine on Tue, Sep 30, 2014 @ 02:45 PM

Colorgalv by Duncan

Click each image for an enlarged view.

NOT Colorgalv!

Riverfront Fencing Hartford Connecticut

Colorgalv®. There is NO equal.
And this proves it!

The picture on the top was taken in December of 2003, almost 10 years after the fencing was installed. It still looks great!

The picture on the bottom, also taken in December of 2003, has only been installed since 1999, and it has failed completely.

The only similarities between these two installations is the location. They are adjacent to each other on the Connecticut River.

Why would one fail and the other look as good as new 10 years later? The answer is simple: The installation on the top was Colorgalv® by Duncan. The one on the bottom was an “or equal”. Even though Colorgalv® was specified for the fencing on the bottom, the contractor submitted an “or equal”.

Why accept a substitution?
Is it cheaper? No. Is it better? No. Will it last longer? No.

The initial cost of Colorgalv® is virtually equal to painting over galvanizing, so there really is no appreciable “first cost” savings by going with an “or equal”. And when you look at life cycle costing, well, the savings are astronomical.

Colorgalv® is a complete process. All work is done in one factory controlled environment. Nothing is left to chance and all the variables that could possibly lead to a failure have been eliminated. So, Colorgalv® is truly a better process than an “or equal”.

And, since Colorgalv® is warranteed for 20 years, you will have the peace of mind knowing that a company in business since 1890 will be standing behind the work to ensure the longevity of the installation.

Want more information? Call Duncan at 617-389-8440 or email info@duncangalvanizing.com.

Tags: Corrosion Protection, Colorgalv

Galvanized Steel in Parking Structures

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

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.  

32.RedStairwayParkingG (2) resized 600Furthermore, 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. 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.


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. 

 

Sources: Duncan Galvanizing Corp., American Galvanizers Association

Tags: Corrosion Protection, Hot Dip Galvanizing, Duncan Galvanizing