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Hot-Dip Galvanizing for Corrosion Protection

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Hot-Dip Galvanizing for Corrosion Protection (3 hours) Introduction Hot-Dip Galvanizing for Corrosion Protection is presented by the American Galvanizers Association (AGA). Founded in 1935, the AGA has remained the first and last source of information for the hot-dip galvanizing industry. One of the AGA’s primary missions is to provide information and assistance to the specifying community on topics such as specification interpretation, project applications, design issues, and any technical research or support that may be required. In addition to this course, you are encouraged to take advantage of the following free resources and services that will make the job of designing and specifying a corrosion protection system much easier: Specification Hotline Architects, engineers, fabricators, and specifiers throughout North America can call with any questions pertaining to hot-dip galvanizing after fabrication and speak with an AGA technical representative. Call the AGA toll-free at 1-800-468-7732. Literature and Library If our technical representatives are unable to immediately answer your questions, they have access to an extensive library to research various technical topics, as well as different hot-dip galvanizing applications. Galvanizing on the Web The AGA website can be found at www.galvanizeit.org. There, you can get instant access to a wealth of technical information on hot-dip galvanizing, download or order the AGA’s newest publications, and have access to a listing of member galvanizers, their kettle sizes, locations, phone numbers, etc. The website also has numerous links to members and other affiliated associations. Galvanizing Insights The association’s specifier newsletter is designed and published specifically for you. Each issue focuses on major subjects pertinent to the industry; past issues have focused on reinforcing steel, painting over hot-dip galvanized steel, turnaround time, and coating appearance, to name a few. Register for a free subscription to Galvanizing Insights on the AGA’s website, at www.galvanizeit.org/newsletter/. If you have questions throughout this course, please contact the AGA technical department at aga@galvanizeit.org or call 800-468-7732. Section 1: Tour of the City Corrosion is an incessant and costly problem. A recent study funded by the FHWA (Federal Highway Administration), NACE International and CC Technologies determined the total direct cost of corrosion is $279 billion per year, or 3.2 percent of the U.S. gross domestic product (GDP). Indirect costs (to the users/society) such as traffic delays, lost business, wasted energy are estimated to be almost five to ten times the direct cost, meaning the overall cost to society could be as high as 30 percent of the GDP.

The following is a corrosion tour of the city. Here you will see things you cross paths with everyday and, most likely, take for granted as natural, unavoidable, uncontrollable sights.

Pictured here is an obvious lack of maintenance of this corrosion prevention system — leading to ultimate project failure with apparent safety concerns.

This is a very common sight — the complete failure of parking blocks due to unprotected reinforcing steel corroding.

This sign says “IRS Problems,” but it clearly indicates “Corrosion Problems!” This sign shows the common occurrence of corner and edge corrosion, where, with a barrier corrosion protection system such as the one seen here, the paint tends to be thinner.

This painted railing shows severe red-rust clumping. Not only is this unsightly, but it is extremely hazardous because the rusting is so extensive the railing is completely deteriorated in many locations.

This series of photos depicts two different corrosion situations: First, the concrete steps show staining and cracks in different areas. In the third photo, it is apparent the concrete was patched, which is an obvious repair of spalled concrete. Unfortunately, the patched area has stained and cracked again. Second, while it’s difficult to see in the photos, the railing going up the steps is painted-over black steel with visible blistering, peeling, and rusting.

Here is a shot of a light pole with an unprotected base plate and fasteners. The corroded base plate and fasteners are causing staining on the underlying concrete base, but notice the hot-dip galvanized pole — it looks the same as the day it was hot-dip galvanized.

Last on our city tour is a severely corroded beam from the famous Williamsburg Bridge — located in New York City and built in 1903. When this photo was taken, the bridge was still in use and traveled daily by over 100,000 vehicles; the lower level also accommodated train traffic. After more than 30 instances of this extensive corrosion were identified, the bridge was closed. The direct cost of the repair soared to over $750 million. The indirect costs are even more expansive: the loss of productivity due to the resultant traffic congestion, the loss of income by the businesses in the affected area, and the environmental impact from blasting are estimated to exceed the bridge repair’s direct costs by about ten times or close to $7.5 billion.

Section 2: Why Unprotected Steel Corrodes So, why does unprotected steel corrode? Corrosion can simplistically be viewed as the tendency for any metal — in an elevated energy state such as a steel beam, plate, or bar — to revert back to its lower, more natural energy state of iron ore. This tendency is known as the Law of Entropy. Here is a bimetallic couple model to help explain the corrosion process:

A bimetallic couple is the connection of two different metals (typical examples include brass or bronze valves connected to steel or cast iron pipes, stainless steel fasteners connected to steel or cast iron, etc.). Metals corrode via an electrochemical process; an electrochemical process is corrosion accompanied by a flow of electrons between cathodic and anodic metallic surfaces. Four elements must be present at the same time for corrosion to occur: a cathode, anode, electrolyte solution, and a return current path (these terms are defined next). If you take away any one of these elements, corrosion will not take place.

• A cathode is an electrode* at which positive ions** are discharged, negative ions are formed, or other reducing actions occur.

• An anode is an electrode at which negative ions are discharged, positive ions are formed, or other oxidizing reactions occur.

• An electrolyte is a conducting medium in which the flow of current is accompanied by movement of matter — most often an aqueous solution of acids, bases, or salts, but may include many other media. An electrolyte is also a substance that is capable of forming a conducting liquid medium when dissolved or melted.

• The return current path is the metallic pathway connecting the anode to the cathode. It is often the underlying substrate metal.

*An electrode is a conductor through which current enters or leaves an electrolytic cell. **An ion is an electrified portion of matter. So, in a bimetallic couple model with zinc and steel as the dissimilar metals, corrosion occurs at the anode (zinc). The cathode (steel) is protected from corrosion. This is how the term cathodic or sacrificial protection (zinc sacrifices itself to protect steel) is derived. The term anode corrosion may also be familiar to you.

By using any two dissimilar metals, it could be possible to have anodic corrosion or cathodic protection. Different metals can protect other metals, according to the order of metals listed in the Galvanic Series of Metals – a list of metals and alloys arranged according to their relative potentials in a given environment. To explain, this table shows the Galvanic Series of Metals arranged in order of electrochemical activity in a seawater electrolyte. Metals high in the scale provide cathodic or sacrificial protection to the metals below them. Since zinc is higher than steel, zinc will protect steel.

The scale indicates that magnesium, aluminum, and cadmium also should protect steel. In most normal applications, magnesium is highly reactive and is rapidly consumed. Aluminum forms a resistant oxide coating and its effectiveness in providing cathodic protection is limited. Cadmium provides the same cathodic protection for steel as zinc, but for technical and economic reasons, its applications are limited. The corrosion process when two dissimilar metals are in contact was just explained using the bimetallic couple. But what about corrosion that occurs on one piece of steel with no other dissimilar metal in contact? Following is an explanation of how corrosion occurs in that instance: Rust, a corrosion by-product (and the more natural state of iron), can be the result of a chemical and/or an electrochemical process. Just like other metals, steel begins to corrode immediately upon contact with air, trying to revert to its natural state of iron oxide through the chemical reactions of iron and oxygen. Electrochemical reactions begin when there is a difference in electrical potential between small areas on the steel surface involving anodes, cathodes, and an electrolyte. The potential differences come from different states of iron oxide from steel impurities as well as other surface defects. This electrochemical process accelerates the change in steel from iron to iron oxide. The anodic and cathodic areas on a piece of steel are microscopic. Moisture in the air provides the electrolyte and completes the electrical path between the anodes and cathodes on the metal surface. Due to potential differences, a small electric current begins to flow as the metal is consumed in the anodic area. The iron ions produced at the anode combine with the environment to form the loose, flaky iron oxide known as rust.

As anodic areas corrode, new material of different composition and structure is exposed. This results in a change of electrical potentials and also changes the location of anodic and cathodic sites. The shifting of anodic and cathodic sites does not occur all at once. In time, previously uncorroded areas are attacked and a uniform surface corrosion is produced. This process continues until the steel is entirely consumed. The rate at which metals corrode is determined by factors such as the electrical potential and resistance between anodic and cathodic areas, the pH of the electrolyte, temperature, and humidity. Section 3: The Solution to Corrosion The problem of corrosion is clear. What is the solution? As depicted earlier with the bimetallic couple, if all four required elements (anode, cathode, electrolyte, and return current path) are present, corrosion can occur. But, by isolating the metal from the electrolytes in the environment, the steel will be protected, and corrosion will not occur. This is known as barrier protection. Two important properties of barrier protection are adhesion to the base metal and abrasion resistance. Paint is perhaps the best known example of a barrier protection system, but has many limitations. Hot-dip galvanizing, applies an impervious zinc metal to steel, has extreme adhesion to the steel (3600 psi), and is highly abrasion resistant. However, it is not only a terrific barrier protection system, but also a cathodic protection system. As has already been explained, zinc is anodic to steel; the galvanized coating will provide cathodic protection to exposed steel. When zinc and steel are connected in the presence of the electrolyte, the zinc is slowly consumed, while the steel is protected. The zinc’s sacrificial action offers protection where small areas of steel may be exposed due to cut edges, drill holes, scratches, or as the result of severe surface abrasion. Cathodic protection of the steel from corrosion continues until all the zinc is consumed. Hot-dip galvanizing is a factory-controlled process in which steel is protected against corrosion by a zinc coating applied by dipping the steel into a bath of molten zinc. This galvanizing process produces a durable, abrasion-resistant coating of zinc and zinc-iron alloy layers metallurgically bonded to the base steel and completely covering (inside and out) the piece of steel. There are four basic phases to the galvanizing process:

1) Pre-inspection When steel comes into the galvanizing plant, the material is first inspected to ensure proper vent and drainage holes have been provided (proper venting will be discussed in more detail shortly). Another part of the pre-inspection phase includes hanging the steel pieces on some sort of rack, chain, or wire system that will carry the material through the galvanizing process. The racks are lifted and moved through the process by an overhead crane system.

2) Cleaning

The steel must be thoroughly cleaned before it is galvanized, or the zinc will not bond to it. In this second phase of the galvanizing process, the steel goes through several cleaning steps.

The first step, caustic cleaning, consists of a hot alkali solution used to remove organic contaminants like dirt, water-based paint, grease and/or oil from the steel surface. All epoxies, vinyls, or asphalt must be removed by grit blasting, sandblasting, or other mechanical means before galvanizing. Removal of these materials is usually the responsibility of the fabricator, however, the galvanizer will do this if necessary. After caustic cleaning, the article goes through a clean water rinse. Next in the cleaning process, mill scale and rust are removed from the steel surface by pickling it in a dilute solution of heated sulfuric acid or an ambient-temperature hydrochloric acid solution. After this step, the article goes through another clean water rinse. The final step of cleaning, called fluxing, removes oxides and prevents further oxides from forming on the steel surface prior to galvanizing. Fluxing also promotes bonding of the zinc to the steel surface. The process of applying the flux to the steel depends upon whether the “wet” or “dry” galvanizing method is used. Dry galvanizing, the most common method, requires the steel to be dipped in an aqueous zinc ammonium chloride solution and then thoroughly dried before galvanizing. The wet galvanizing process uses a flux ‘blanket’ floating on top of the molten zinc. The final cleaning occurs as the material passes through the flux blanket before entering the galvanizing bath.

3) Galvanizing

The galvanizing phase of the process requires the steel material to be immersed in a molten zinc bath consisting of a minimum of 98% pure zinc. The bath temperature is maintained at approximately 850 F (approx. 455 C), and the metallurgical reaction and bonding of zinc to steel occurs when the material reaches the bath temperature.

4) Final Inspection The fourth and final phase of the process occurs when the quality of the galvanized coating is determined through visual inspection and measurement of the zinc coating. As explained previously, if the steel surface is not properly and thoroughly cleaned, zinc will not react with and adhere to the steel and bare spots will be evident. During measurement the thickness of the zinc coating is magnetically calculated to ensure adherence to specifications.

Section 4: The Galvanized Zinc Coating Now that you’ve learned about the galvanizing process, it’s time to examine the actual zinc coating. Galvanizing is a superior coating protection system because, unlike any other coating, zinc forms a metallurgical bond with steel. During galvanizing, molten zinc reacts with the steel’s surface to form a series of zinc-iron alloy layers. Pictured here is a photomicrograph of a cross-section of a galvanized steel coating.

• The first zinc-iron alloy layer, the Gamma layer, is approximately 75% zinc and 25% iron • The Delta layer, is approximately 90% zinc and 10% iron • The Zeta layer, is approximately 94% zinc and 6% iron • The Eta layer, which forms as the material is withdrawn from the molten zinc bath, is

100% pure zinc

As you can see, the Gamma, Delta and Zeta layers form approximately 60% of the total galvanized coating. All of the layers created through galvanizing – Gamma, Delta, and Zeta – have different hardness values. The Diamond Pyramid Number (DPN) is a progressive measurement of hardness; the higher the number, the greater the hardness.

• The base steel has a DPN of approximately 159 • Even though the Gamma layer is a thin compact layer, it has a DPN of approximately 250 • The Delta layer has a DPN of approximately 245 • The Zeta layer has a DPN of approximately 180 • Lastly, the pure zinc layer (Eta) has a DPN of approximately 70 and is very ductile

providing good impact resistance for the bonded galvanized coating

Therefore, the Gamma, Delta and Zeta layers are actually harder than the base steel. These high hardness values provide good abrasion resistance. A zinc coating prevents steel from corroding, and as has been stated before, zinc is less noble than steel. The long-lasting protection zinc affords steel is based on three factors:

• The zinc coating acts as a barrier against the penetration of water, oxygen, and atmospheric pollutants

• The zinc coating cathodically protects the steel from coating imperfections caused by accidental abrasion, cutting, drilling, or bending

• Zinc protects steel due to the formation of zinc corrosion by-products, or what is collectively termed the zinc patina.

Like any other metal, zinc begins to corrode when exposed to atmospheric conditions. When galvanized steel is removed from the zinc bath, its galvanized coating will

immediately begin to oxidize as it is exposed to air. A corrosion-resistant film of zinc oxide is formed usually within 24 hours of galvanizing. The silvery-metallic appearance of galvanized material changes to a light, matte-gray color as the zinc oxidizes. Zinc oxide is a white powdery material and its development is the first step in the creation of the protective zinc patina. The zinc oxide develops into zinc hydroxide. When the barely-discernable, whitish layer of zinc oxide is exposed to freely moving air, it reacts with moisture in the atmosphere – such as dew, rainfall, or even humidity – to form a porous, gelatinous, grayish-white zinc hydroxide. Depending on the type of exposure, the zinc hydroxide can form anywhere from hours to several months after galvanizing. During the normal wetting-drying cycle galvanized steel is exposed to in natural weather conditions, the zinc hydroxide reacts with carbon dioxide in the atmosphere and progresses into a thin, compact, tightly-adherent layer of basic zinc carbonate. This grayish-white film can take anywhere from three to twelve months to form. This progression to zinc carbonate provides the excellent barrier protection afforded by the galvanized coating. Because the zinc carbonate is relatively insoluble, it prevents rapid atmospheric corrosion of the zinc on the surface of galvanized steel. The rate of formation of the zinc patina depends not only on the amount of moisture in the atmosphere, but also on the period during which the zinc surface remains wet.

Now, remember the “IRS Problems” sign presented at the beginning of this presentation? This photomicrograph shown here is a cross-section of the edge of a galvanized object. Since the galvanizing reaction between zinc and iron is a diffusion process, the coating grows perpendicular to the surface. Thus, galvanizing produces coatings that are at least as thick, if not thicker, at the corners and edges as the coating on the rest of the part. As coating damage is most likely to occur at the edges of an object, this is where added protection is needed most. Unlike galvanizing, brush or sprayed barrier coatings and plated materials have a natural tendency to thin at the corners and edges, as depicted in the “IRS Problems” sign. Specifiers often ask if it is possible to tell the galvanizer how much zinc to put on the steel. But since the galvanized coating thickness is primarily determined by the chemical composition and surface conditions of the steel, determining what a product’s final coating thickness will be is almost entirely out of the hands of the galvanizer. There are many additional benefits of hot-dip galvanized steel, including the complete coverage afforded. Because the galvanizing process involves total immersion of the steel

material into the molten zinc bath, all surfaces are coated, meaning galvanizing provides protection both inside and outside of hollow structures. This is a great benefit because corrosion tends to occur at an increased rate on the inside of some hollow structures where the environment can be extremely humid. Painted hollow structures have no corrosion protection on the inside. A wide variety of shapes and sizes – ranging from small nuts, bolts, and fasteners to larger structural pieces, to even the most intricately detailed artistic pieces – can be galvanized. Processing time is another benefit derived from specifying hot-dip galvanizing as the corrosion-prevention method for steel. While other methods are dependent upon proper weather and humidity conditions for correct application, hot-dip galvanizing can be accomplished rain or shine, with service meeting most delivery schedules. There are also no installation delays due to curing times some corrosion protection systems require. Since zinc solidifies upon withdrawal from the zinc bath, it is possible for the material to be galvanized, transported to the job site, and installed all in the same day. And there’s no problem with leaving the galvanized steel out at the job site because, unlike other corrosion protection methods, UV rays do not compromise the integrity of the galvanized coating. Section 5: Galvanized Steel vs. the Environment Environments in which hot-dip galvanizing is commonly used include outdoor and indoor atmospheres, to contain/carry hundreds of different chemicals, fresh water, sea water, soils, concrete, and in contact with other metals. Since at least 1926, the American Society of Testing and Materials (ASTM) and other organizations have been continuously collecting records on the behavior of zinc coatings under various atmospheric conditions throughout the world. Exposure atmospheres have been divided into the following:

• Industrial • Suburban • Temperate Marine • Tropical Marine • Rural

The first and harshest atmosphere is industrial; most city or urban-area atmospheres are classified as industrial. (Keep in mind, of course, these atmospheres are generalized; there may be very harsh micro-environments within some atmospheres or applications, such as in the middle of a chemical plant). Visit the American Galvanizers Association web site, http://www.galvanizeit.org/, and click on the “Zinc Coating Life Predictor.” By entering known atmospheric data for any specific location in the world, you can accurately predict the durability of galvanized steel in that specific location. Suburban atmospheres are generally less corrosive than industrial areas, and as the term suggests, are found in largely residential, perimeter communities. Temperate marine atmospheres are usually less corrosive than suburban atmospheres. The length of service life of the galvanizing coating in marine environments is influenced by proximity to the coastline and prevailing wind direction and intensity.

Tropical marine atmospheres are similar to temperate marine atmospheres, except they are found in warmer climates. Rural atmospheres are usually the least aggressive of the five atmospheric types. This is primarily due to the relatively low level of sulfur dioxide and other emissions found in the other four atmospheres. Atmospheric classifications are a guide to predicting corrosion rates for general environmental conditions. However, since applications and atmospheres vary, the appropriate classification should be carefully selected on a job-by-job basis. Using the Service Life Chart, look at the protective life of galvanized coatings in keeping with the five atmospheres just described. A galvanized coating’s protective life is determined primarily by the thickness of the coating and the severity of the exposure conditions. The thickness of a galvanized coating is expressed in mil thickness (one mil is equal to a one-thousandth of an inch).

For example, consider a galvanized structure in a tropical marine atmosphere. According to the ASTM A 123, for a piece of steel with a thickness of 1/4 inch or greater, the minimum mil thickness requirement is 3.9 mils. Typically, the zinc coating thickness is greater than the minimum requirement; the average coating thickness is often between 5 and 7 mils. So, with a coating of 5 mils followed up to the tropical marine environment line and across, the chart indicates it will take approximately 100 years to create five percent surface rust. This doesn’t mean the project will be completely corroded in 100 years, but rather that in 100 years, 5 percent of the steel will be exposed. Ninety-five percent of the steel surface is still being protected by the zinc coating Five percent surface rust, as shown on the chart, indicates it is time to think about coating the galvanized surface by cleaning and preparing it, then brushing or spray-applying a different corrosion prevention method — if disassembly for regalvanizing is not a feasible solution. (Note: There is a difference between rust and brown staining that the human eye can rarely detect. Brown staining is occasionally visible when all of the free zinc (Eta) layer is consumed. Brown staining is the iron oxide corrosion by-product from the iron content percentages found in the zinc-iron alloy layers of the Gamma, Delta, and Zeta layers of the galvanized coating. Since it’s hard to tell the difference by just looking at it, use a

measurement gauge. If there is any mil thickness measurement, then brown staining has occurred and corrosion protection will continue to be provided by the remaining zinc coating.) When galvanized steel is used in contact with liquids, a different set of conditions determines its corrosion resistance. A liquid’s degree of acidity or alkalinity is the factor of greatest importance. This is usually expressed on a logarithmic scale as the pH number. Zinc coatings corrode faster in liquids with a pH below 4.5 or above 12.5. This should not be considered a “hard and fast rule” because factors such as agitation, aeration, temperature, polarization, and the presence of inhibitors may also affect the rate of corrosion. However — generally at intermediate pH values — a protective film is formed on the zinc surface, and the rate of corrosion is very slow. Since many liquids fall within this pH range, galvanized steel containers are widely used in storing and transporting many chemical solutions. Galvanizing is also successfully used to protect steel in fresh water exposure. The term “fresh water” is used loosely here to refer to all forms of water, except seawater. Water with relatively high free oxygen or carbon dioxide content is more corrosive than water containing less of these gases. Hard water is much less corrosive toward zinc than soft water. Galvanized coatings also provide considerable protection to steel immersed in seawater and exposed to salt spray. However, it is the dissolved salts (primarily sulfides and chlorides) in seawater that are the prime determinants of the corrosion behavior of the zinc immersed in seawater. Although anticipated galvanized coating life is shorter in seawater than in many other exposures, galvanized steel performs much better than many other coating systems in this environment. Section 6: All Zinc Coatings are not Created Equal Many people use “galvanizing” as a generic term for all types of zinc coatings, but all zinc coatings are not the same. In fact, their physical, chemical, and corrosion resistance properties can be extremely different. This section will explore the differences in the several types of zinc coatings available. Refer to the photomicrograph of various zinc coatings:

Metallizing (or zinc spraying) is feeding zinc – in either wire or powder form – through a spray gun, where it is melted and sprayed onto the steel surface by using combustion gases and/or auxiliary compressed air to provide the necessary velocity. Metallizing allows coating of fabricated items that cannot be galvanized because of their size, because the coating must be applied on the job site, or as a means of touching-up or repairing a hot-dip galvanized coating. This form of zinc coating is normally sealed with a thin coating of a low-viscosity polyurethane, epoxy, or vinyl resin. There are some limitations as to how thorough the zinc coverage is due to the inaccessible areas of some structures, such as recesses, hollows, or cavities (painting offers a similar limitation). Coating consistency is dependent on operator experience, and coating variation is always a possibility. Like paint, coatings may be thinner at corners and edges. Metallizing provides a minimum amount of cathodic protection, but with no zinc-iron alloy layers to provide abrasion resistance. The black areas on the photomicrograph above are voids. Metallizing is 85 percent as dense as hot-dip galvanizing. Zinc-rich paint, often inaccurately called “cold galvanizing,” consists of zinc dust in organic or inorganic binders. The white particles in the photomicrograph are zinc oxides; the black areas are the binders. Zinc-rich coatings are barrier coatings that also provide limited cathodic protection. The binder must be conductive, or the zinc particles must be in sufficient percentage of the overall paint and in contact, in order to provide cathodic protection. Suitable zinc-rich paints provide a useful repair coating for damaged galvanized coatings. However, uneven film coats may develop if applied by brush or roller, and mud cracking may occur if the paint is applied too thickly. Continuous galvanizing (galvanized sheet) is a hot-dip process, although usually limited to steel mill operations. The process consists of coating sheet steel, strip, or wire on machines over 500 feet in length, running the materials through the molten zinc at speeds of over 300 feet per minute. The resulting mil thickness is minimal compared to hot-dip galvanizing – with minimal zinc-iron alloy layers – but barrier and cathodic protection are provided. Continuously galvanized sheet steel is generally suitable for interior applications or for exterior applications where paint is applied over the zinc coating. Electroplating (or electrogalvanizing) refers to zinc coatings applied to steel sheet and strip by electro-deposition in a steel mill facility. There are no zinc-iron alloy layers, but barrier and cathodic protection are provided. The finish of electroplated steel is very smooth, however, the thin coating which is produced is generally not very appropriate for exterior applications. Electroplated fasteners are most commonly used in interior environments. Section 7: Specifying for Design Now that today’s severe corrosion problems and its various solutions have been discussed, it’s time to examine how to specify hot-dip galvanized steel in project designs. Protection against corrosion begins on the drawing board. No matter what corrosion prevention system is used, it must be factored into the design of the product. Once the decision has been made to use hot-dip galvanizing, the design engineer should ensure the steel pieces can be suitably fabricated for high-quality galvanizing. Certain rules must be followed in order to design components for hot-dip galvanizing after fabrication. Adopting the design practices shown in the next couple of pages, along with those listed in ASTM A 385 Practice for Providing High Quality Zinc Coatings (Hot-Dip), will

produce optimum quality galvanizing, reduce costs, assist with the timely processing of the product, and ensure the safety of the galvanizing personnel. The most important rule of designing for hot-dip galvanizing is the designer, fabricator, and galvanizer work together before the product is manufactured. This three-way communication will eliminate issues that could delay or prevent superior galvanizing quality. Most ferrous materials (those containing iron) are suitable for hot-dip galvanizing. Cast iron, malleable iron, cast steels, and hot- and cold-rolled steels all can be protected from corrosion by hot-dip galvanizing. Structural steel shapes, including those of high-strength, low-alloy materials are hot-dip galvanized to obtain long-lasting protection. Though most ferrous materials can be hot-dip galvanized, the chemical composition of the material affects the characteristics of the galvanized coating. During galvanizing, the ferrous material reacts with the zinc to form a series of zinc-iron alloy layers normally covered by a layer of pure zinc. For most hot-rolled steels, the zinc-iron alloy portion of the coating will represent 50 to 70 percent of the total coating thickness. Steel compositions vary depending on strength and service requirements. Major elements in the steel, such as silicon and phosphorus, affect the galvanizing process, as well as the structure and appearance of the coating. For example, certain elements present in the steel may result in a coating composed almost entirely, or completely of zinc-iron alloys. Per ASTM A385, Section 3.2, certain elements found in steels are known to have an influence on the coating structure. Carbon in excess of about 0.25%, phosphorus in excess of 0.04%, or manganese in excess of about 1.3% will cause the production of coatings different from the normal coating. Silicon concentrations between 0.05 - 0.15%, or above 0.25% have a profound effect on the nature of the coating produced (see chart below).

Optimum galvanizing appearance is seldom obtained when combining different materials and surfaces. Whenever possible, the varying materials previously described should be galvanized separately and assembled after galvanizing. When steels of special chemical composition or varying surface finishes are joined in an assembly, the galvanized finish generally is not uniform in appearance (though the variation in the color and texture of the coating has no affect on the corrosion prevention provided by the galvanized coating).

You should try to avoid designing articles that have extreme differences in steel thickness. The different thicknesses of steel will reach the zinc bath temperature at different times, as well as have different cooling rates. This uneven heating and cooling can cause stresses or the relieving of stresses that lead to warping or distortion. When welded items are galvanized, both the cleanliness of the weld area and the metallic composition of the weld itself affect the galvanizing quality and appearance around the weld. Galvanized materials may be welded easily and satisfactorily by all common welding techniques. Weld slag and weld flux should be removed by the fabricator prior to galvanizing (weld flux residues are chemically inert in the normal pickling solutions used by galvanizers, therefore, their existence will produce rough and incomplete zinc coverage). The specifics of welding techniques can best be obtained from the American Welding Society or your welding equipment supplier. When designing articles to be galvanized, it’s best to avoid narrow gaps between plates, overlapping surfaces, and back-to-back angles and channels. When overlapping contacting surfaces cannot be avoided and are separated by 3/32 inch or less (the thickness of a penny), all edges should be completely sealed by welding. The viscosity of the zinc prevents it from entering any space narrower than this. If there is an opening, the less viscous cleaning solutions will enter. Solutions may leach out of the opening later on, causing brown weep staining on the galvanized coating. Also, trapped solutions will “flash” to steam when the part is immersed in the 850 F molten zinc-galvanizing bath. When the trapped steam is released, it can prevent zinc from adhering to the steel adjacent to the lap joint. Likewise, pickling acid salts can be retained in these tight areas due to inadequate rinsing. The galvanized coating may be of good quality in the adjacent area, but humidity encountered weeks, even months, later may wet these acid salts. This will cause brown staining to seep out on top of the galvanized coating. Brown staining can be removed easily by scrubbing the stained area with a soft, nylon bristle brush. Do not use steel wool because steel particles will be imbedded in the zinc coating and cause more brown staining. Many structures and parts are fabricated using cold-working techniques. In some instances, severe cold-working may cause the steel to become strain-age embrittled. While cold-working increases the incidence of strain-age embrittlement, it may not become evident until after galvanizing. Strain-age embrittlement occurs because the aging of a piece of steel is relatively slow at ambient temperatures, but becomes more rapid at the elevated temperature of the galvanizing bath. Any form of cold-working reduces the ductility of steel. Operations such as punching holes, notching, producing fillets of small radii, shearing, and sharp bending may lead to strain-age embrittlement of susceptible steels. To avoid strain-age embrittlement, cold-worked steel may be stress-relieved per ASTM A143 prior to galvanizing. Cold-worked steels less than 1/8 inch thick, which are subsequently galvanized, are unlikely to experience strain-age embrittlement. With the increase in the sizes and capacities of galvanizing kettles, facilities can accommodate fabrications in a significant range of shapes and sizes. Galvanizing kettles up to 42 feet in length are available in most industrial areas. There are many kettles ranging from 50 and 60 feet in length. Widths and depths vary but are generally 6 – 7’ wide and 8 – 12’ deep. Designing and fabricating in modules suitable for the available galvanizing

facilities can allow for most components to be galvanized. However, it is wise at an early stage to verify kettle constraints with the local galvanizer. A list of galvanizing kettle locations throughout North America, and their sizes, can be found on the American Galvanizers Association website (www.galvanizeit.org/galvanizers/). When an item is too large for total immersion in the kettle of molten zinc – but more than half of the item will fit into the kettle – the piece may be progressively dipped. During this process, each end or portion of the article is dipped sequentially in order to coat the entire item. Always consult the galvanizer before planning to progressive dip. Designers should also consider the material-handling techniques used in galvanizing plants (hoists, cranes, pulleys, racks, wire, etc.). Large assemblies are usually supported by chain slings or by lifting fixtures. All articles are immersed into the galvanizing kettles from overhead, so chains, wires, or other holding devices are used to support the material unless special lifting fixtures are provided. The weight of fabrications should also factor into the design of products. The crane/hoist capacity required to move items from step to step in the galvanizing facility will sometimes vary from plant to plant. Contact your galvanizer to determine weight-handling capacity if it appears weight will be a factor in the design considerations. For effective galvanizing, cleaning solutions and molten zinc must flow into, over, through, and out of the fabricated article with undue resistance. Failure to provide for a free, unimpeded flow is frequently the cause of problems for the galvanizer and the customer. Improper drainage design results in poor appearance of the galvanized surface, bare spots, and excess build-ups of zinc, which are unnecessary and costly. Where gusset plates are used, generously cropped corners provide for free drainage. When cropping gusset plates is not possible, holes at least ½ inch in diameter must be placed in the plates as close to the corners as possible. Because of safety issues, tubular fabrications and hollow structural steel must be properly vented. Any solutions or rinse waters that might be trapped in a blind or closed joining connection will be converted to superheated steam and can develop a pressure of up to 3800 psi when immersed in molten zinc at 850 F. This presents a serious hazard to galvanizing personnel and equipment, as the steam may directly burn or cause zinc to be violently emitted from the kettle. Ample passageways allowing unimpeded flow in and out must be designed into assemblies. Keep in mind items to be galvanized are immersed and withdrawn at an angle, so vent holes should be located at the highest point and drain holes at the lowest point in each piece. Base plates and end plates must also be designed to facilitate venting and draining. Fully cutting the plate provides minimum obstruction to provide a full, free zinc flow into and out of the pipe. The most desirable fabrication is one that is completely open at both ends. Since this is not always possible, the use of vent holes in the plate often provides the solution. These are examples of equal substitutes if opening the full diameter is not allowed. Tanks and enclosed vessels should be designed to allow acid cleaning solutions, fluxes, and molten zinc to enter at the bottom and trapped air to flow upwards through the enclosed space and out through an opening at the highest point. This prevents air from being trapped as the article is immersed. The trapped air would, of course, prevent zinc from reaching the entire inside surface of the tank. The design must also provide for complete drainage of both interior and exterior details during withdrawal.

Some fabricated assemblies may distort at the galvanizing temperature as a result of stresses induced during manufacturing of the steel and in subsequent fabrication operations. Guidelines for minimizing distortion and warpage are provided in ASTM A 384 Safeguarding Against Warpage and Distortion During Hot-Dip Galvanizing of Steel Assemblies. To minimize distortion, design engineers should observe the following recommendations:

• Where possible, use symmetrical, rolled sections in preference to angle or channel frames. A non-uniform shape will tend to pull away from its axis

• Use parts in an assembly of equal or near-equal thickness • Accurately pre-form members of an assembly so it is not necessary to force, spring,

or bend them into position during joining • Try to avoid designs that require progressive-dip galvanizing

Hot-dip galvanized fasteners are recommended for use with hot-dip galvanized sub- assemblies and assemblies. Galvanized nuts, bolts, and screws in common sizes are readily available from commercial suppliers. Bolted assemblies should be sent to the galvanizer disassembled. When assemblies to be galvanized incorporate threaded components, the tolerance normally allowed on internal threads must be increased to provide for the thickness of the galvanized coating on external threads. Standard practice is to tap nuts oversized after galvanizing. Uncoated internal threads are acceptable since the zinc coating on the external thread provides full corrosion protection. For economic purposes, nuts are sometimes galvanized as blanks and threads are tapped after galvanizing. Recommendations for overtapping of threads may be found in the American Galvanizers Association publication The Design of Products to be Hot-Dip Galvanized After Fabrication. Identification markings on fabricated items should be carefully prepared before galvanizing so they will be legible after galvanizing and will not jeopardize the integrity of the zinc coating. Do not use paint, grease, or oil-based markers to apply addresses, shipping instructions, or job numbers on items to be galvanized. Pickling acids do not remove oil-based paints and crayon marks, thus resulting in extra work by the galvanizer to properly prepare the steel for galvanizing. Detachable metal tags or water-soluble markers should be specified for temporary identification. Where permanent identification is needed, there are three suitable alternatives for marking steel fabrications to be hot-dip galvanized. Each enables items to be rapidly identified after galvanizing and at the job site:

• Deep stencil a steel tag and firmly affix it to the fabrication with a minimum #9 gauge steel wire. The tag should be wired loosely to the work so that the area beneath the wire can be galvanized and the wire will not freeze to the work when the molten zinc solidifies.

• Stamp the surface using die-cut deep stencils or a series of center punch marks. They should be a minimum of ½ inch high and 1/32 inch deep to ensure readability after galvanizing. This method should not be used to mark fracture-critical members.

• A series of weld beads may also be used to mark letters or numbers directly on the fabrication. It is essential that all weld flux be removed in order to achieve a quality-galvanized coating.

Galvanized products should be specified in accordance with the appropriate standards. Standards have been developed to ensure optimum performance of galvanized products. Industry professionals specifying hot-dip galvanizing should become familiar with the following: ASTM A 123, A 143, A 153, A 384, A 385, A 767, A 780, and D 6386. ASTM A 123 Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products:

• Covers the requirements for galvanizing by the hot-dip process on iron and steel products made from rolled, pressed, and forged shapes, castings, plates, bars, and strips

• Covers both unfabricated products and fabricated products. This includes, for example, assembled steel products, structural steel fabrications, large tubes already bent or welded before galvanizing, and wirework fabricated from uncoated steel wire. This specification also covers steel forgings and iron castings incorporated into pieces fabricated before galvanizing or those too large to be centrifuged (or otherwise handled to remove excess galvanizing bath metal)

• Does not apply to wire, pipe, tube, or sheet steel, which is galvanized on specialized or continuous lines, or to steel less than 22-gauge thick. Indicates required minimum mil thickness

• Steps of the coating thickness inspection ASTM A 153 Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware:

• Covers zinc coatings applied by the hot-dip process on iron and steel hardware (bolts, nuts, nails, screws, clamps, etc.)

• Is intended to be applicable to hardware items centrifuged or otherwise handled to remove excess zinc

• Provides for a standard minimum coating thickness regardless of fastener dimensions.

ASTM A 385 Standard Practice for Providing High-Quality Zinc Coatings (Hot-Dip):

• Indicates procedures that should be followed to obtain high-quality hot-dip galvanized coatings

• Highlights many items that should be addressed when specifying hot-dip galvanizing, such as assemblies of different materials and/or different surfaces, steel selection, venting and drainage hole design issues, and marking parts for identification.

ASTM A767 Standard Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement:

• This specification covers concrete reinforcing bars with protective zinc coatings applied by dipping the properly prepared reinforcing bars into a molten bath of zinc

• If reinforcing bars are bent cold prior to galvanizing, they must be fabricated to a bend diameter equal to or greater than those specified in Table 2 in ASTM A767. The bend diameter’s range – depending on the bar number – is typically from six to ten times the bar’s diameter

• When bending reinforcing bars after galvanizing, there may be slight cracking and flaking of the free layer of zinc in the bend area, but this should not be cause for rejection because the integrity of the corrosion protection is still provided

ASTM A 780 Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings: This standard describes methods used to repair damaged hot-dip galvanized coatings. The damage may be the result of welding, in which case the coating will be damaged predominantly by burning, or by severe abrasion caused by excessively rough handling during shipping or erection. There are three types of touch-up and repair methods, according to ASTM A 780:

• Zinc-based solder alloys • Zinc dust paints • Metallizing

Please refer to ASTM A 780 for specifics on when these techniques are appropriate and how to apply them. ASTM D 6386 Standard Practice for Preparation of Zinc (Hot Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting: This standard describes surface preparation methods for painting new and weathered hot-dip galvanized steel that has not been painted previously, specifically so that an applied coating system can develop the adhesion necessary for a satisfactory service life. As a final step in the galvanizing process, the hot-dip galvanized coating is inspected for compliance with specifications. Interpretation of inspection results should be made with a clear understanding of the causes of the various conditions that may be encountered, and their effects on the ultimate objective of providing corrosion protection. Galvanizing’s service life is directly related to the thickness of the protective zinc coating. Corrosion prevention is greatest when the coating is thickest. The coating thickness is the single most important inspection check to determine a galvanized coating’s quality. Coating thickness, however, is only one inspection aspect. The coating’s uniformity, adherence, and appearance should also be checked. Inspection of the galvanized product, as the final step in the process, can be most effectively and efficiently conducted at the galvanizer’s plant where questions can be asked and answered quickly. There are a number of simple magnetic gauges used to give a convenient and reliable measurement of the zinc coating thickness, provided the instruments are properly calibrated. Bare spots are small, localized flaws that are usually self-healing due to the sacrificial action of the zinc and have little effect on the life of the coating. Where considered necessary, such spots may be patched using one of the repair methods discussed in ASTM A 780. When failing to thoroughly clean the steel’s surface, such as by not blast-cleaning paint off the steel’s surface, zinc will not metallurgically bond to the steel. Also, if sand remains embedded in castings, zinc will also not bond to the steel. Rough, “heavy” coatings refer to galvanized components showing markedly rough surfaces. This can include coatings that have just a rough surface and can, in some cases, involve some

groove type surface configurations. High phosphorus and/or high silicon content in the steel can lead to this condition. The coating pictured will provide quality corrosion prevention and is not grounds for rejection. A matte gray coating can appear as a dark gray circular pattern, a localized dull patch, or may extend over the entire surface of the product. This finish indicates an extended zinc-iron alloy phase caused by steels that are unusually reactive with molten zinc. Although not as shiny as a galvanized coating with free zinc on the outer surface, a matte gray coating provides similar corrosion prevention. As per ASTM A 123, Note 2, the presence of some elements such as silicon, carbon, and phosphorus – in certain percentages in steels and weld metal – tend to accelerate the growth of the zinc-iron alloy layers so the coating may have a matte finish with little or no outer zinc layer. The galvanizer has only limited control over this condition. Wet storage stain is the voluminous white or gray deposits formed by accelerated corrosion of the zinc coating when closely-packed, newly-galvanized articles are stored or shipped under damp and poorly ventilated conditions. Wet storage stain primarily consists of zinc oxide and zinc hydroxide. Due to improper ventilation and no circulating carbon dioxide, the final stage of the protective zinc patina – the zinc carbonate – cannot form. Weathered zinc surfaces that have already formed their normal protective layer of corrosion products are seldom attacked. The bulky white or gray corrosion product associated with wet storage stain should not be confused with the protective layer of zinc corrosion products that form under normal atmospheric exposure. Even though the corrosion products on fully exposed galvanized surfaces may be white or light gray, they are not the product of wet storage stain. Their color is solely a function of the environment and the zinc-iron alloy content of the galvanized coating. When wet storage staining is found on galvanized materials, it is not usually in sufficient quantity to be detrimental to coating protection. It normally disappears with weathering, however, with ill-advised transportation, handling, and storage methods, it can build up to the point where it should be removed before the steel is put into service. A light brushing with a nylon bristle brush will remove most wet storage stains, but if the buildup is excessive for the application, a 10:1 water and alkaline solution followed by rinsing may be warranted.

This picture indicates what is assumed to be the typical hot-dip galvanized surface. The surface is silver-gray and has spangles (zinc crystals) with a range of sizes. Different surface appearances may be noticed on different galvanized products. Cooling rate and additives to the galvanizing bath have a direct effect on the surface brightness and spangle size. Faster cooling usually results in a brighter coating with a smaller spangle size. Additive such as lead and antimony change the surface tension of the zinc and cause spangle as well.

Section 8: Duplex Systems For years, protecting steel from corrosion typically involved either the use of hot-dip galvanizing or some type of paint system. However, more and more corrosion specialists are utilizing both methods of corrosion protection in what is commonly referred to as a duplex system. A duplex system is simply painting or powder-coating steel that has been hot-dip galvanized after fabrication. When paint and galvanized steel are used together, the

corrosion protection is superior to either protection system used alone. Painting galvanized steel requires careful preparation and a good understanding of both painting and galvanizing. The ASTM specification for preparing galvanized steel surfaces to be painted is D 6386. The galvanized coating protects the base steel, supplying cathodic and barrier protection. Paint, in turn, grants barrier protection to the galvanized coating. The paint slows down the rate at which the zinc is consumed, greatly extending the life of the galvanized steel. In return, once the paint has been weathered or damaged, the zinc is available to provide cathodic and barrier protection so rust will not develop on the substrate steel. There are many reasons for using a duplex system, ranging from financial to safety. Each individual project raises unique reasons why a duplex system could be utilized.

Extended corrosion resistance The most obvious – and important – reason for using a duplex system is the added corrosion prevention. No single corrosion prevention system can match the corrosion resistance afforded for most applications by painting over hot-dip galvanized steel.

Economic benefits Because duplex systems greatly extend the life of a product, maintenance costs are significantly decreased. Additionally, a product lasts longer before it must be replaced, thus decreasing the life-cycle cost. The cost of a product protected by galvanizing and painting is lower over the entire life of the product than most single system methods of corrosion prevention. Life-cycle costs are only one form of economic benefits. Take, for example, a petrochemical plant. Here, a duplex system is used to combat not only the harsh atmospheric conditions, but also the extremely high shutdown costs required to replace and/or repair corroded parts.

Synergistic effect It is typical for a duplex system to provide corrosion protection 1.5 to 2.5 times longer than zinc or paint individually. For example, if a galvanized coating is expected to last 40 years, and a paint system is expected to last 10 years, galvanizing and paint together should last 75 years with minimal maintenance, or a minimum of 1.5 times the sum of both systems.

One example is provided in the photo below where powder coating adds extra durability and corrosion protection to these hot-dip galvanized utility poles in Europe. These poles were powder-coated immediately after galvanizing and then packaged for shipping.

Ease of repainting As paint weathers, the zinc in the galvanized coating is present to provide both cathodic and barrier protection until the structure is repainted.

The exposed zinc surface then can be repainted with minimal surface preparation. The galvanized guardrails in this photo are being prepared for repainting.

Safety marking The use of a duplex system allows galvanized steel to be painted in order to conform to safety color regulations. The best example of this is the Federal Aviation Administration regulation requiring structures over 200 feet high to be painted in the alternating pattern of white and international orange.

Section 9: Rebar Corrosion and repair of corrosion damage are multi-billion dollar problems. Observations on numerous structures show that corrosion of reinforcing steel is either a prime - or at least an important – factor contributing to the staining, cracking, and eventual spalling of concrete structures. These effects of corrosion often require costly repairs and continued maintenance during the life of the structure.

This figure depicts what would be visible if a core sample of concrete and rebar was cut so one can take a look inside. As the unprotected rebar begins to corrode, iron oxides (steel corrosion by-products) form. The increased volume of the iron oxides causes pressure on the surrounding concrete. To relieve this increased stress or pressure, the concrete will crack. At first the cracks will be small, only noticeable by the staining color of the rust rising to the surface of the concrete covering. But as the corrosion continues, a snowball effect is created. More cracks allow more electrolyte solution to reach the reinforcing steel, thus causing more corrosion and build-up of iron oxides. While rust-colored staining is the first visible sign of corrosion, it’s more than just an aesthetic problem. Once staining and cracking occur, there is an easy path for more moisture to reach the steel, creating more iron oxides and accelerating the corrosion process. Depending on the thickness, porosity, and initial cracking of the concrete cover, this type of staining may be evident in a year or less, with spalling to follow in the next couple of years. Red rust staining occurs parallel to the rebar and provides an indication of

where the corroding bar or bars are located. Spalling also occurs parallel to the rebar. The first signs of spalling indicate the structural integrity of the concrete is rapidly deteriorating. Epoxy-coated rebar can experience the same type of corrosion at places in the concrete where the epoxy coating is defective, or at exposed cut ends of the rebar. When the rebar is exposed to the environment, the structure has totally failed and rebuilding is necessary, as was the case with this bridge support along I-15 in Utah. The Utah DOT recently undertook the $1.6 billion dollar overhaul of a 17-mile stretch of I-15 that looks like this.

This picture was taken about 20 years after installation; the steel was never coated for corrosion prevention. In a climate like Utah’s – with strong freeze-thaw cycles, and where chlorides build-up from high use of de-icing salts – galvanizing the rebar would have significantly increased the protection from corrosion. Here is a picture of spalling concrete where unprotected rebar has been used. As has been discussed, the spalling is caused by the increased pressure build-up from the dense iron oxides resulting from the corroding bare steel.

When hot-dip galvanized rebar is used, the zinc corrodes in the same process as bare steel, but at a much slower rate. Unlike the very dense corrosion by-products of bare steel, zinc corrosion by-products are significantly less dense than iron oxides. The zinc corrosion by-products are powdery, non-adherent, and capable of migration from the surface of the galvanized coating into the matrix of the concrete, highly reducing the likelihood of zinc corrosion-induced spalling. Aside from the unique properties of the galvanized coating, there are numerous other reasons why galvanized rebar is a preferred method of corrosion protection. The galvanized coating is very tough and durable. It can be walked on, driven over, and exposed to the everyday hazards of the construction site without compromising the integrity of the coating. Even when there is a small scratch, about 1/16 of an inch, the sacrificial action of the zinc

will protect the steel. The galvanized coating requires no special handling; no soft gloves or nylon strapping are needed when handling galvanized rebar. It is easy to ship, haul, move around the job site, and install galvanized rebar. It can even be stored outside on the job site because the coating will not be damaged by ultraviolet (UV) rays from the sun (which does damage epoxy coatings). Galvanized rebar can be handled in the same manner as black rebar. In contrast, there is a 10-plus-page brochure published by the Concrete Reinforcing Steel Institute for handling epoxy-coated rebar. The brochure, entitled Reference Guide for Field Handling Techniques For Epoxy-Coated Rebar, covers numerous requirements which must be adhered to at the job site in order to maintain an adequate coating. All these requirements add significant cost to a project. Galvanized rebar can be fabricated before or after galvanizing. Or, when following bend radius recommendations as specified in ASTM A 767, the rebar can be fabricated on the job site without worrying about touch-up or coating failure. The rebar can also be welded before or after galvanizing using the same ventilation precautions as when welding black rebar, and using touch-up and repair procedures/methods as recommended in ASTM A 780. Galvanized steel, including rebar, is easy to inspect. The metallurgical bond will not occur during the galvanizing process unless the bar is thoroughly cleaned. Any bare spots would be visible immediately after galvanizing. Due to the fact the rebar is totally immersed in the molten zinc, there is 100 percent coverage on formed and bent bars. In addition, compared to epoxy systems that are generally very thin on edges and ends, all edges and ends of the galvanized coating will have the same, if not greater, thickness of zinc. Should there be cutting or torching on the job site, after cleaning the parts, a zinc solder or a zinc-rich paint will adequately protect exposed black steel. Follow the procedures in ASTM A 780 for touch-up and repair of galvanized coatings. Unlike epoxy systems, no inspection for inconsistencies or bare spots needs to be performed. Long periods of storage on the job site and exposure to harsh elements will have little or no effect on the galvanized rebar performance. Galvanized rebar has superior bond strength essential for reliable performance of reinforced concrete structures. These studies performed by the University of California - Berkeley show galvanized rebar to have greater bond strength, measured by stress in pounds-per-square-inch, than deformed black steel. The majority of the pullout strength comes from the ribs on the bar, but these studies show extra pullout strength can be realized with galvanized rebar.

The Boca Chica Bridge in Florida is a great example of hot-dip galvanized reinforcing steel at work. For over 30 years, galvanized rebar has provided this bridge near Key West with maintenance-free corrosion protection. Despite heavy traffic and humid salt-water conditions, core samples taken in 1991 showed the galvanized rebar to have an average thickness of four mils. No signs of corrosion are detectable.

This unique structure - known as “The Egg” is a wonder of modern construction. The “shell” is shaped by a heavily reinforced concrete girdle, which helps keep “the Egg’s” shape and directs the weight of the structure to the supporting pedestal and stem. Adding even more durability to this structure are miles of galvanized rebar weaving in and out of the shell and stem. “The Egg” was constructed in 1966 and took 12 years to build. Today it remains a beautiful piece of rust-free architecture.

This parking garage at Princeton University was built in 1991 using galvanized rebar. The multi-level structure used a variety of rebar sizes to provide long-lasting corrosion

prevention to the parking garage, which is exposed to a host of environmental conditions. In winter climates, a parking garage is a harsh environment due to road salts deposited on the decking by vehicles.

Section 10 - Hot-Dip Galvanized Steel in Our World With the economic solution and unrivaled barrier and cathodic protection from corrosion hot-dip galvanized steel provides, it's no wonder it is used in thousands of applications throughout the world. Almost any steel exposed to the elements in some fashion (directly or indirectly), is a prime candidate for hot-dip galvanizing. Some common steel products hot-dip galvanized include: pipe and tubing, fasteners, structural steel, reinforcing bar, utility poles, grating, expanded metal, guardrails, trash cans, fencing, and automobile underbody parts. Industries and markets utilizing hot-dip galvanized steel include: electrical utilities (towers, poles), cellular and land-line utilities (towers, poles), pulp and paper, water and wastewater, bridge and highway (bridge girders, stringers, columns, deck steel, guardrail, light poles), transportation (rail, automotive), agriculture, chemical & petrochemical (tanks, vessels, walkways, handrail) and recreation (stadiums, arenas, playground equipment). The following projects help to further demonstrate some specific examples of hot-dip galvanized steel in action:

INDIANAPOLIS MOTOR SPEEDWAY A towering metal structure featuring more than 500 tons of galvanized steel, the Indianapolis Motor Speedway (IMS) is one of the largest sport facilities in the world. Since IMS chose hot-dip galvanizing for corrosion protection of the Speedway’s Northwest Vista Addition in 1992, all subsequent steel additions to the metal behemoth have been specified to be hot-dip galvanized – a testament to the cost effectiveness and staying power of the zinc coating.

MI/M-102 BRIDGE RAIL RECONSTRUCTION The MI/M-102 Bridge Reconstruction demonstrated how a project can be both environmentally conscious and save taxpayers money. After attending a Galvanize It! seminar, Sue Datta of the Michigan Department of Transportation (MDOT) learned how many states have been taking old guardrail, stripping, regalvanizing, and returning it to service - so MDOT decided to regalvanize the existing steel guardrail panels. Thanks to the initially galvanized pieces used in the structure, this project was able to recycle 80% of the original material – saving enough money for the city to begin a new project originally slated for next year.

KUUUJUAQ, NUNAVIK AIRPORT This project, which had to be completed over the span of two summer seasons, utilized galvanized steel because of the rapidity and flexibility the process allows during onsite construction. Galvanizing was an excellent fit for this project, as it allowed the incomplete structure to be left exposed throughout the arctic winter without damage.

CTA BROWNLINE SEDGEWICK STATION Built in June 1900, this elevated station was incorporated into Chicago Transit Authority’s (CTA) $530 million Brown Line Capacity Expansion Project. To secure this large investment, CTA specified galvanizing for corrosion protection, just as it was selected originally in 1900. With the ability to withstand exposure to the elements without developing unsightly and dangerous rust, galvanized steel will allow the station’s renovations to last another hundred years.

NASHVILLE CHILDREN’S THEATRE DRAGON Located adjacent to the Nashville metro buildings downtown and highly visible from the street, the dragon guarding the Nashville Children’s Theatre will be viewed by approximately 300,000 people each year. With such high visibility, the artist wanted to ensure the sculpture would remain aesthetically pleasing, so galvanizing was chosen to prevent unsightly rust from marring the look of the sculpture. All components of this elaborate sculpture were galvanized, from the anchor apparatus for the dragon support, to the curling tips of the dragon’s wings – totaling more than 3,000 pounds of galvanized steel.

AERO SOLUTIONS POLE-MAX Pole-Max is a system used to add antennas onto existing cell phone towers. Special purpose, high-strength galvanized channel is used for this add-on product, capitalizing on the quick turnaround of the galvanizing process. Because galvanizing is not a weather-dependent process, it can be completed year round without common delays. With quick delivery and fast installation, Pole-Max takes advantage of this benefit.

NATIONAL GYPSUM National Gypsum’s Mount Holly plant is a $125 million high-speed wallboard manufacturing facility that recycles waste material rather than sending it to landfills. In keeping with the “green” spirit of recycling waste material, galvanized steel prevents the waste and expense of corrosion maintenance and repair, and is also recyclable; thus making it an environmentally friendly choice for this massive project. As is often the case, the initial cost and life-cycle cost of galvanizing the 3,461 tons of steel offered superior economics when compared to painted steel. The entire structure (with the exception of the outer skin of the building) is hot-dip galvanized for corrosion protection - a necessary requirement to withstand the damaging effects of an industrial environment.

Conclusion Any exterior environment is prime for the use of hot-dip galvanized steel. Common applications include theme park rides, stadiums, utility towers, bridge girders and decks, ornamental fences, docks, boat trailers, anchoring rods, bolts and nuts, handrail, grating walkways, and stairs. In addition to the long-term corrosion protection it offers, hot-dip galvanizing is chosen because it provides maintenance-free performance for decades.

Website: www.galvanizeit.org Toll-free phone: 1-800-468-7732 Email: aga@galvanizeit.org