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P D H en g i n eer .c o m

CourseMA-3002

Hot Dip Galvanizing for CorrosionProtection

To receive credit for this course

This document is the course text. You may review this material atyour leisure either before or after you purchase the course. Topurchase this course, click on the course overview page:

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Hot-Dip Galvanizing for Corrosion Protection (3 hours)

IntroductionHot-Dip Galvanizing for Corrosion Protectionis presented by the American GalvanizersAssociation (AGA). Founded in 1935, the AGA has remained the first and last source ofinformation for the hot-dip galvanizing industry. One of the AGAs primary missions is toprovide information and assistance to the specifying community on topics such asspecification interpretation, project applications, design issues, and any technical researchor support that may be required.

In addition to this course, you are encouraged to take advantage of the following freeresources and services that will make the job of designing and specifying a corrosionprotection system much easier:

Specification Hotline

Architects, engineers, fabricators, and specifiers throughout North America can call with anyquestions pertaining to hot-dip galvanizing after fabrication and speak with an AGA technicalrepresentative. 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 haveaccess 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 toa wealth of technical information on hot-dip galvanizing, download or order the AGAsnewest 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 otheraffiliated associations.

Ga lv a n i z i n g I n s i g h t s

The associations specifier newsletter is designed and published specifically for you. Eachissue focuses on major subjects pertinent to the industry; past issues have focused onreinforcing steel, painting over hot-dip galvanized steel, turnaround time, and coatingappearance, to name a few. Register for a free subscription to Galvanizing Insightson the

AGAs website, at www.galvanizeit.org/newsletter/.

If you have questions throughout this course, please contact the AGA technical departmentat [email protected] call 800-468-7732.

Section 1: Tour of the City

Corrosion is an incessant and costly problem. A recent study funded by the FHWA (FederalHighway Administration), NACE International and CC Technologies determined the totaldirect cost of corrosion is $279 billion per year, or 3.2 percent of the U.S. gross domesticproduct (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 theoverall cost to society could be as high as 30 percent of the GDP.


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The following is a corrosion tour of the city. Here you will see things you cross paths witheveryday 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 ultimateproject failure with apparent safety concerns.

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


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This sign says IRS Problems, but it clearly indicates Corrosion Problems! This sign shows thecommon 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 extremelyhazardous because the rusting is so extensive the railing is completely deteriorated in many locations.


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This series of photos depicts two different corrosion situations: First, the concrete steps show stainingand cracks in different areas. In the third photo, it is apparent the concrete was patched, which is anobvious repair of spalled concrete. Unfortunately, the patched area has stained and cracked again.Second, while its difficult to see in the photos, the railing going up the steps is painted-over black steel

with visible blistering, peeling, and rusting.


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Here is a shot of a light pole with an unprotected base plate and fasteners. The corroded base plate andfasteners 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 NewYork City and built in 1903. When this photo was taken, the bridge was still in use and traveled daily byover 100,000 vehicles; the lower level also accommodated train traffic. After more than 30 instances ofthis extensive corrosion were identified, the bridge was closed. The direct cost of the repair soared toover $750 million. The indirect costs are even more expansive: the loss of productivity due to theresultant traffic congestion, the loss of income by the businesses in the affected area, and theenvironmental impact from blasting are estimated to exceed the bridge repairs direct costs by about tentimes or close to $7.5 billion.


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Section 2: Why Unprotected Steel CorrodesSo, why does unprotected steel corrode? Corrosion can simplistically be viewed as thetendency 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 knownas 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 brassor bronze valves connected to steel or cast iron pipes, stainless steel fasteners connected tosteel or cast iron, etc.). Metals corrode via an electrochemical process; an electrochemicalprocess is corrosion accompanied by a flow of electrons between cathodic and anodicmetallic 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 youtake away any one of these elements, corrosion will not take place.

A cathodeis an electrode* at which positive ions** are discharged, negative ionsare formed, or other reducing actions occur.

An anodeis an electrode at which negative ions are discharged, positive ions areformed, or other oxidizing reactions occur.

An electrolyteis a conducting medium in which the flow of current is accompaniedby 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 iscapable of forming a conducting liquid medium when dissolved or melted.

The r e t u r n c u r r e n t p a t h is the metallic pathway connecting the anode to the

cathode. It is often the underlying substrate metal.

*An electrodeis 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, corrosionoccurs at the anode (zinc). The cathode (steel) is protected from corrosion. This is how theterm cathodic orsacrificial protection (zinc sacrifices itself to protect steel) is derived. Theterm anode corrosionmay also be familiar to you.


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By using any two dissimilar metals, it could be possible to have anodic corrosion or cathodicprotection. Different metals can protect other metals, according to the order of metalslisted in the Galvanic Series of Metals a list of metals and alloys arranged according totheir relative potentials in a given environment.

To explain, this table shows the Galvanic Series of Metalsarranged in order of

electrochemical activity in a seawater electrolyte. Metals high in the scale provide cathodicor sacrificial protection to the metals below them. Since zinc is higher than steel, zinc willprotect steel.

The scale indicates that magnesium, aluminum, and cadmium also should protect steel. Inmost normal applications, magnesium is highly reactive and is rapidly consumed. Aluminumforms 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 technicaland economic reasons, its applications are limited.

The corrosion process when two dissimilar metals are in contact was just explained usingthe bimetallic couple. But what about corrosion that occurs on one piece of steel with noother dissimilar metal in contact? Following is an explanation of how corrosion occurs inthat instance:

Rust, a corrosion by-product (and the more natural state of iron), can be the result of achemical and/or an electrochemical process. Just like other metals, steel begins to corrodeimmediately upon contact with air, trying to revert to its natural state of iron oxide throughthe chemical reactions of iron and oxygen. Electrochemical reactions begin when there is adifference in electrical potential between small areas on the steel surface involving anodes,

cathodes, and an electrolyte. The potential differences come from different states of ironoxide from steel impurities as well as other surface defects. This electrochemical processaccelerates the change in steel from iron to iron oxide.

The anodic and cathodic areas on a piece of steel are microscopic. Moisture in the airprovides the electrolyte and completes the electrical path between the anodes and cathodeson the metal surface. Due to potential differences, a small electric current begins to flow asthe metal is consumed in the anodic area. The iron ions produced at the anode combinewith the environment to form the loose, flaky iron oxide known as rust.


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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 andcathodic 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. Thisprocess 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 andcathodic areas, the pH of the electrolyte, temperature, and humidity.

Section 3: The Solution to CorrosionThe 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 themetal from the electrolytes in the environment, the steel will be protected, and corrosionwill not occur. This is known as barrier protection. Two important properties of barrierprotection are adhesion to the base metal and abrasion resistance. Paint is perhaps thebest known example of a barrier protection system, but has many limitations. Hot-dipgalvanizing, 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 barrierprotection system, but also a cathodic protection system.

As has already been explained, zinc is anodic to steel; the galvanized coating will providecathodic protection to exposed steel. When zinc and steel are connected in the presence ofthe electrolyte, the zinc is slowly consumed, while the steel is protected. The zincssacrificial action offers protection where small areas of steel may be exposed due to cutedges, drill holes, scratches, or as the result of severe surface abrasion. Cathodicprotection 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. Thisgalvanizing process produces a durable, abrasion-resistant coating of zinc and zinc-ironalloy layers metallurgically bonded to the base steel and completely covering (inside andout) 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 toensure proper vent and drainage holes have been provided (proper ventingwill 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 throughthe galvanizing process. The racks are lifted and moved through the processby an overhead crane system.

2) Cleaning

The steel must be thoroughly cleaned before it is galvanized, or the zinc willnot bond to it. In this second phase of the galvanizing process, the steel goesthrough several cleaning steps.


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The first step, caustic cleaning, consists of a hot alkali solution used toremove organic contaminants like dirt, water-based paint, grease and/or oilfrom the steel surface. All epoxies, vinyls, or asphalt must be removed bygrit 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 steelsurface by pickling it in a dilute solution of heated sulfuric acid or an ambient-temperature hydrochloric acid solution. After this step, the article goesthrough another clean water rinse.

The final step of cleaning, called fluxing, removes oxides and prevents furtheroxides from forming on the steel surface prior to galvanizing. Fluxing alsopromotes bonding of the zinc to the steel surface. The process of applyingthe flux to the steel depends upon whether the wet or dry galvanizingmethod is used. Dry galvanizing, the most common method, requires thesteel to be dipped in an aqueous zinc ammonium chloride solution and thenthoroughly dried before galvanizing. The wet galvanizing process uses a fluxblanket floating on top of the molten zinc. The final cleaning occurs as thematerial passes through the flux blanket before entering the galvanizing bath.

3) Galvanizing

The galvanizing phase of the process requires the steel material to beimmersed 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 thematerial reaches the bath temperature.

4) Final Inspection

The fourth and final phase of the process occurs when the quality of thegalvanized coating is determined through visual inspection and measurementof the zinc coating. As explained previously, if the steel surface is notproperly and thoroughly cleaned, zinc will not react with and adhere to thesteel and bare spots will be evident. During measurement the thickness ofthe zinc coating is magnetically calculated to ensure adherence tospecifications.


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Section 4: The Galvanized Zinc CoatingNow that youve learned about the galvanizing process, its time to examine the actual zinccoating. Galvanizing is a superior coating protection system because, unlike any othercoating, zinc forms a metallurgical bond with steel. During galvanizing, molten zinc reactswith the steels surface to form a series of zinc-iron alloy layers. Pictured here is aphotomicrograph 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 totalgalvanized coating.

All of the layers created through galvanizing Gamma, Delta, and Zeta have differenthardness values. The Diamond Pyramid Number (DPN) is a progressive measurement ofhardness; 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 lessnoble 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, andatmospheric pollutants

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

Zinc protects steel due to the formation of zinc corrosion by-products, or what iscollectively termed thezinc 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


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immediately begin to oxidize as it is exposed to air. A corrosion-resistant film of zinc oxideis formed usually within 24 hours of galvanizing. The silvery-metallic appearance ofgalvanized material changes to a light, matte-gray color as the zinc oxidizes. Zinc oxide is awhite powdery material and its development is the first step in the creation of the protectivezinc patina.

The zinc oxide develops into zinc hydroxide. When the barely-discernable, whitish layer ofzinc oxide is exposed to freely moving air, it reacts with moisture in the atmosphere suchas dew, rainfall, or even humidity to form a porous, gelatinous, grayish-white zinchydroxide. Depending on the type of exposure, the zinc hydroxide can form anywhere fromhours to several months after galvanizing.

During the normal wetting-drying cycle galvanized steel is exposed to in natural weatherconditions, the zinc hydroxide reacts with carbon dioxide in the atmosphere and progressesinto a thin, compact, tightly-adherent layer of basic zinc carbonate. This grayish-white filmcan take anywhere from three to twelve months to form. This progression to zinc carbonateprovides the excellent barrier protection afforded by the galvanized coating. Because thezinc carbonate is relatively insoluble, it prevents rapidatmospheric corrosion of the zinc onthe 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 zincsurface 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 coatinggrows perpendicular to the surface. Thus, galvanizing produces coatings that are at least asthick, if not thicker, at the corners and edges as the coating on the rest of the part. Ascoating damage is most likely to occur at the edges of an object, this is where addedprotection is needed most. Unlike galvanizing, brush or sprayed barrier coatings and platedmaterials 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 chemicalcomposition and surface conditions of the steel, determining what a products final coatingthickness will be is almostentirely out of the hands of the galvanizer.

There are many additional benefits of hot-dip galvanized steel, including the completecoverage afforded. Because the galvanizing process involves total immersion of the steel


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material into the molten zinc bath, all surfaces are coated, meaning galvanizing providesprotection both inside and outside of hollow structures. This is a great benefit becausecorrosion tends to occur at an increased rate on the inside of some hollow structures wherethe environment can be extremely humid. Painted hollow structures have no corrosionprotection on the inside.

A wide variety of shapes and sizes ranging from small nuts, bolts, and fasteners to largerstructural pieces, to even the most intricately detailed artistic pieces can be galvanized.

Processing time is another benefit derived from specifying hot-dip galvanizing as thecorrosion-prevention method for steel. While other methods are dependent upon properweather and humidity conditions for correct application, hot-dip galvanizing can beaccomplished rain or shine, with service meeting most delivery schedules. There are alsono installation delays due to curing times some corrosion protection systems require. Sincezinc solidifies upon withdrawal from the zinc bath, it is possible for the material to begalvanized, transported to the job site, and installed all in the same day. And theres noproblem with leaving the galvanized steel out at the job site because, unlike other corrosionprotection methods, UV rays do not compromise the integrity of the galvanized coating.

Section 5: Galvanized Steel vs. the EnvironmentEnvironments in which hot-dip galvanizing is commonly used include outdoor and indooratmospheres, 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 otherorganizations have been continuously collecting records on the behavior of zinc coatingsunder various atmospheric conditions throughout the world. Exposure atmospheres havebeen divided into the following:

Industrial

Suburban Temperate Marine Tropical Marine Rural

The first and harshest atmosphere is industrial; most city or urban-area atmospheres areclassified as industrial. (Keep in mind, of course, these atmospheres are generalized; theremay be very harsh micro-environments within some atmospheres or applications, such as inthe middle of a chemical plant).

Visit the American Galvanizers Association web site, http://www.galvanizeit.org/, and clickon the Zinc Coating Life Predictor. By entering known atmospheric data for any specificlocation 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 termsuggests, are found in largely residential, perimeter communities.

Temperate marine atmospheres are usually less corrosive than suburban atmospheres. Thelength of service life of the galvanizing coating in marine environments is influenced byproximity to the coastline and prevailing wind direction and intensity.


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Tropical marine atmospheres are similar to temperate marine atmospheres, except they arefound in warmer climates.

Rural atmospheres are usually the least aggressive of the five atmospheric types. This isprimarily due to the relatively low level of sulfur dioxide and other emissions found in theother four atmospheres.

Atmospheric classifications are a guide to predicting corrosion rates for generalenvironmental conditions. However, since applications and atmospheres vary, theappropriate 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 keepingwith the five atmospheres just described. A galvanized coatings protective life isdetermined primarily by the thickness of the coating and the severity of the exposureconditions. The thickness of a galvanized coating is expressed in mil thickness (one mil isequal to a one-thousandth of an inch).

For example, consider a galvanized structure in a tropical marine atmosphere. According tothe ASTM A 123, for a piece of steel with a thickness of 1/4 inch or greater, the minimummil thickness requirement is 3.9 mils. Typically, the zinc coating thickness is greater thanthe 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 doesnt mean the project will be completely corroded in 100 years, but rather that in100 years, 5 percent of the steel will be exposed. Ninety-five percent of the steel surface isstill 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 preparingit, then brushing or spray-applying a different corrosion prevention method if disassemblyfor regalvanizing is not a feasible solution.

(Note: There is a difference between rust and brown staining that the human eye can rarelydetect. Brown staining is occasionally visible when all of the free zinc (Eta) layer isconsumed. Brown staining is the iron oxide corrosion by-product from the iron contentpercentages found in the zinc-iron alloy layers of the Gamma, Delta, and Zeta layers of thegalvanized coating. Since its hard to tell the difference by just looking at it, use a


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Metallizing (or zinc spraying)is feeding zinc in either wire or powder form through aspray gun, where it is melted and sprayed onto the steel surface by using combustion gasesand/or auxiliary compressed air to provide the necessary velocity. Metallizing allows coatingof fabricated items that cannot be galvanized because of their size, because the coatingmust 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 howthorough the zinc coverage is due to the inaccessible areas of some structures, such asrecesses, hollows, or cavities (painting offers a similar limitation). Coating consistency isdependent 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 ofcathodic protection, but with no zinc-iron alloy layers to provide abrasion resistance. Theblack areas on the photomicrograph above are voids. Metallizing is 85 percent as dense ashot-dip galvanizing.

Zinc-rich paint, often inaccurately called cold galvanizing, consists of zinc dust in organicor inorganic binders. The white particles in the photomicrograph are zinc oxides; the blackareas 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 insufficient percentage of the overall paint and in contact, in order to provide cathodicprotection. Suitable zinc-rich paints provide a useful repair coating for damaged galvanizedcoatings. However, uneven film coats may develop if applied by brush or roller, and mudcracking may occur if the paint is applied too thickly.

Continuous galvanizing (galvanized sheet)is a hot-dip process, although usuallylimited to steel mill operations. The process consists of coating sheet steel, strip, or wire onmachines over 500 feet in length, running the materials through the molten zinc at speedsof over 300 feet per minute. The resulting mil thickness is minimal compared to hot-dipgalvanizing with minimal zinc-iron alloy layers but barrier and cathodic protection areprovided. 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 andstrip by electro-deposition in a steel mill facility. There are no zinc-iron alloy layers, butbarrier and cathodic protection are provided. The finish of electroplated steel is verysmooth, however, the thin coating which is produced is generally not very appropriate forexterior applications. Electroplated fasteners are most commonly used in interiorenvironments.

Section 7: Specifying for DesignNow that todays severe corrosion problems and its various solutions have been discussed,its time to examine how to specify hot-dip galvanized steel in project designs.

Protection against corrosion begins on the drawing board. No matter what corrosionprevention system is used, it must be factored into the design of the product. Once thedecision has been made to use hot-dip galvanizing, the design engineer should ensure thesteel pieces can be suitably fabricated for high-quality galvanizing.

Certain rules must be followed in order to design components for hot-dip galvanizing afterfabrication. Adopting the design practices shown in the next couple of pages, along withthose listedinASTM A 385 Practice for Providing High Quality Zinc Coatings (Hot-Dip), will


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produce optimum quality galvanizing, reduce costs, assist with the timely processing of theproduct, and ensure the safety of the galvanizing personnel.

The most important rule of designing for hot-dip galvanizing is the designer, fabricator, andgalvanizer work together before the product is manufactured. This three-waycommunication will eliminate issues that could delay or prevent superior galvanizing quality.

Most ferrous materials (those containing iron) are suitable for hot-dip galvanizing. Castiron, malleable iron, cast steels, and hot- and cold-rolled steels all can be protected fromcorrosion 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 thematerial affects the characteristics of the galvanized coating. During galvanizing, theferrous material reacts with the zinc to form a series of zinc-iron alloy layers normallycovered by a layer of pure zinc. For most hot-rolled steels, the zinc-iron alloy portion of thecoating will represent 50 to 70 percent of the total coating thickness.

Steel compositions vary depending on strength and service requirements. Major elementsin the steel, such as silicon and phosphorus, affect the galvanizing process, as well as thestructure and appearance of the coating. For example, certain elements present in the steelmay 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 aninfluence on the coating structure. Carbon in excess of about 0.25%, phosphorus in excessof 0.04%, or manganese in excess of about 1.3% will cause the production of coatingsdifferent from the normal coating.

Silicon concentrations between 0.05 - 0.15%, or above 0.25% have a profound effect onthe nature of the coating produced (see chart below).

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


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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, aswell as have different cooling rates. This uneven heating and cooling can cause stresses orthe 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 theweld. Galvanized materials may be welded easily and satisfactorily by all common weldingtechniques. Weld slag and weld flux should be removed by the fabricator prior togalvanizing (weld flux residues are chemically inert in the normal pickling solutions used bygalvanizers, therefore, their existence will produce rough and incomplete zinc coverage).The specifics of welding techniques can best be obtained from the American Welding Societyor your welding equipment supplier.

When designing articles to be galvanized, its best to avoid narrow gaps between plates,overlapping surfaces, and back-to-back angles and channels. When overlapping contactingsurfaces cannot be avoided and are separated by 3/32 inch or less (the thickness of apenny), all edges should be completely sealed by welding. The viscosity of the zincprevents it from entering any space narrower than this. If there is an opening, the lessviscous 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 moltenzinc-galvanizing bath. When the trapped steam is released, it can prevent zinc fromadhering 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 humidityencountered weeks, even months, later may wet these acid salts. This will cause brownstaining to seep out on top of the galvanized coating.

Brown staining can be removed easily by scrubbing the stained area with a soft, nylonbristle brush. Do not use steel wool because steel particles will be imbedded in the zinccoating 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 evidentuntil after galvanizing. Strain-age embrittlement occurs because the aging of a piece ofsteel is relatively slow at ambient temperatures, but becomes more rapid at the elevatedtemperature of the galvanizing bath. Any form of cold-working reduces the ductility ofsteel. Operations such as punching holes, notching, producing fillets of small radii,shearing, and sharp bending may lead to strain-age embrittlement of susceptible steels. Toavoid strain-age embrittlement, cold-worked steel may be stress-relieved per ASTM A143prior to galvanizing. Cold-worked steels less than 1/8 inch thick, which are subsequentlygalvanized, are unlikely to experience stain-age embrittlement.

With the increase in the sizes and capacities of galvanizing kettles, facilities canaccommodate fabrications in a significant range of shapes and sizes. Galvanizing kettles upto 42 feet in length are available in most industrial areas. There are many kettles rangingfrom 50 and 60 feet in length. Widths and depths vary but are generally 6 7 wide and8 12 deep. Designing and fabricating in modules suitable for the available galvanizing


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facilities can allow for most components to be galvanized. However, it is wise at an earlystage to verify kettle constraints with the local galvanizer. A list of galvanizing kettlelocations throughout North America, and their sizes, can be found on the AmericanGalvanizers 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 thisprocess, each end or portion of the article is dipped sequentially in order to coat the entireitem. 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 chainslings or by lifting fixtures. All articles are immersed into the galvanizing kettles fromoverhead, so chains, wires, or other holding devices are used to support the material unlessspecial lifting fixtures are provided. The weight of fabrications should also factor into thedesign of products. The crane/hoist capacity required to move items from step to step inthe galvanizing facility will sometimes vary from plant to plant. Contact your galvanizer todetermine weight-handling capacity if it appears weight will be a factor in the designconsiderations.

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. Whencropping gusset plates is not possible, holes at least inch in diameter must be placed inthe 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 joiningconnection will be converted to superheated steam and can develop a pressure of up to3800 psi when immersed in molten zinc at 850 F. This presents a serious hazard togalvanizing personnel and equipment, as the steam may directly burn or cause zinc to beviolently emitted from the kettle. Ample passageways allowing unimpeded flow in and outmust be designed into assemblies. Keep in mind items to be galvanized are immersed andwithdrawn at an angle, so vent holes should be located at the highest point and drain holesat the lowest point in each piece.

Base plates and end plates must also be designed to facilitate venting and draining. Fullycutting the plate provides minimum obstruction to provide a full, free zinc flow into and outof 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 notallowed.

Tanks and enclosed vessels should be designed to allow acid cleaning solutions, fluxes, andmolten zinc to enter at the bottom and trapped air to flow upwards through the enclosedspace and out through an opening at the highest point. This prevents air from beingtrapped as the article is immersed. The trapped air would, of course, prevent zinc fromreaching the entire inside surface of the tank. The design must also provide for completedrainage of both interior and exterior details during withdrawal.


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Some fabricated assemblies may distort at the galvanizing temperature as a result ofstresses induced during manufacturing of the steel and in subsequent fabricationoperations. Guidelines for minimizing distortion and warpage are provided inASTM A 384Safeguarding Against Warpage and Distortion During Hot-Dip Galvanizing of SteelAssemblies. To minimize distortion, design engineers should observe the following

recommendations:

Where possible, use symmetrical, rolled sections in preference to angle or channelframes. 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 readilyavailable from commercial suppliers. Bolted assemblies should be sent to the galvanizer

disassembled. When assemblies to be galvanized incorporate threaded components, thetolerance normally allowed on internal threads must be increased to provide for thethickness of the galvanized coating on external threads. Standard practice is to tap nutsoversizedafter galvanizing. Uncoated internal threads are acceptable since the zinc coatingon the external thread provides full corrosion protection. For economic purposes, nuts aresometimes galvanized as blanks and threads are tapped after galvanizing.Recommendations for overtapping of threads may be found in the American GalvanizersAssociation publication The Design of Products to be Hot-Dip Galvanized After Fabrication.

Identification markings on fabricated items should be carefully prepared before galvanizingso they will be legible after galvanizing and will not jeopardize the integrity of the zinccoating. Do not use paint, grease, or oil-based markers to apply addresses, shippinginstructions, 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 properlyprepare the steel for galvanizing. Detachable metal tags or water-soluble markers shouldbe specified for temporary identification.

Where permanent identification is needed, there are three suitable alternatives for markingsteel fabrications to be hot-dip galvanized. Each enables items to be rapidly identified aftergalvanizing and at the job site:

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

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

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


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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 thefollowing: 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 steelproducts made from rolled, pressed, and forged shapes, castings, plates, bars, andstrips

Covers both unfabricated products and fabricated products. This includes, forexample, assembled steel products, structural steel fabrications, large tubes alreadybent or welded before galvanizing, and wirework fabricated from uncoated steel wire.This specification also covers steel forgings and iron castings incorporated into piecesfabricated before galvanizing or those too large to be centrifuged (or otherwisehandled to remove excess galvanizing bath metal)

Doesnotapply to wire, pipe, tube, or sheet steel, which is galvanized on specializedor 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 toremove excess zinc

Provides for a standard minimum coating thickness regardless of fastenerdimensions.

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

Indicates procedures that should be followed to obtain high-quality hot-dipgalvanized 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 coatingsapplied 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 abend diameter equal to or greater than those specified in Table 2 in ASTM A767. Thebend diameters range depending on the bar number is typically from six to tentimes the bars diameter

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


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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. Thedamage may be the result of welding, in which case the coating will be damagedpredominantly 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 howto apply them.

ASTM D 6386 Standard Practice for Preparation of Zinc (Hot Dip Galvanized) Coated Ironand 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 appliedcoating 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 forcompliance with specifications. Interpretation of inspection results should be made with aclear understanding of the causes of the various conditions that may be encountered, andtheir effects on the ultimate objective of providing corrosion protection.

Galvanizings 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 thesingle most important inspection check to determine a galvanized coatings quality. Coating

thickness, however, is only one inspection aspect. The coatings uniformity, adherence, andappearance should also be checked.

Inspection of the galvanized product, as the final step in the process, can be mosteffectively and efficiently conducted at the galvanizers plant where questions can be askedand answered quickly.

There are a number of simple magnetic gauges used to give a convenient and reliablemeasurement of the zinc coating thickness, provided the instruments are properlycalibrated.

Bare spots are small, localized flaws that are usually self-healing due to the sacrificial actionof 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 inASTM A 780.

When failing to thoroughly clean the steels surface, such as by not blast-cleaning paint offthe steels surface, zinc will not metallurgically bond to the steel. Also, if sand remainsembedded in castings, zinc will also not bond to the steel.

Rough, heavy coatings refer to galvanized components showingmarkedly rough surfaces. This can include coatings that havejust a rough surface and can, in some cases, involve some


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groove type surface configurations. High phosphorus and/or high silicon content in the steelcan lead to this condition. The coating pictured will provide quality corrosion prevention andis not grounds for rejection.

A matte gray coating can appear as a dark gray circular pattern, a localized dull patch, ormay 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 notas shiny as a galvanized coating with free zinc on the outer surface, a matte gray coatingprovides similar corrosion prevention.

As perASTM A 123, Note 2, the presence of some elements such as silicon, carbon, andphosphorus in certain percentages in steels and weld metal tend to accelerate thegrowth of the zinc-iron alloy layers so the coating may have a matte finish with little or noouter zinc layer. The galvanizer has only limited control over this condition.

Wet storage stain is the voluminous white or gray deposits formed by accelerated corrosionof the zinc coating when closely-packed, newly-galvanized articles are stored or shippedunder damp and poorly ventilated conditions. Wet storage stain primarily consists of zincoxide 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. Weatheredzinc surfaces that have already formed their normal protective layer of corrosion productsare seldom attacked.

The bulky white or gray corrosion product associated with wet storage stain should not beconfused with the protective layer of zinc corrosion products that form under normalatmospheric exposure. Even though the corrosion products on fully exposed galvanizedsurfaces may be white or light gray, they are not the product of wet storage stain. Theircolor is solely a function of the environment and the zinc-iron alloy content of thegalvanized coating. When wet storage staining is found on galvanized materials, it is notusually in sufficient quantity to be detrimental to coating protection. It normally disappearswith 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. Alight brushing with a nylon bristle brush will remove most wet storage stains, but if thebuildup is excessive for the application, a 10:1 water and alkaline solution followed byrinsing may be warranted.

This picture indicates what is assumed to be the typical hot-dipgalvanized surface. The surface is silver-gray and has spangles(zinc crystals) with a range of sizes. Different surface appearancesmay be noticed on different galvanized products. Cooling rate andadditives to the galvanizing bath have a direct effect on thesurface brightness and spangle size. Faster cooling usually resultsin a brighter coating with a smaller spangle size. Additive such aslead and antimony change the surface tension of the zinc andcause spangle as well.

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


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corrosion protection is superior to either protection system used alone. Painting galvanizedsteel requires careful preparation and a good understanding of both painting andgalvanizing. The ASTM specification for preparing galvanized steel surfaces to be painted isD 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 therate at which the zinc is consumed, greatly extending the life of the galvanized steel. Inreturn, once the paint has been weathered or damaged, the zinc is available to providecathodic 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. Eachindividual 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 addedcorrosion prevention. No single corrosion prevention system can match thecorrosion resistance afforded for most applications by painting over hot-dipgalvanized steel.

Economic benefitsBecause duplex systems greatly extend the life of a product, maintenance costs aresignificantly decreased. Additionally, a product lasts longer before it must bereplaced, thus decreasing the life-cycle cost. The cost of a product protected bygalvanizing and painting is lower over the entire life of the product than most singlesystem methods of corrosion prevention.

Life-cycle costs are only one form of economic benefits. Take, for example, apetrochemical plant. Here, a duplex system is used to combat not only the harshatmospheric conditions, but also the extremely high shutdown costs required toreplace and/or repair corroded parts.

Synergistic effect

It is typical for a duplex system to provide corrosion protection 1.5 to 2.5 timeslonger than zinc or paint individually. For example, if a galvanized coating isexpected 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 aminimum of 1.5 times the sum of both systems.

One example is provided in the photo below wherepowder coating adds extra durability and corrosionprotection to these hot-dip galvanized utility poles inEurope. These poles were powder-coated immediatelyafter galvanizing and then packaged for shipping.

Ease of repaintingAs paint weathers, the zinc in the galvanizedcoating is present to provide both cathodic andbarrier protection until the structure is repainted.


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

Safety markingThe use of a duplex system allows galvanized steel to be paintedin order to conform to safety color regulations. The best example

of this is the Federal Aviation Administration regulation requiringstructures over 200 feet high to be painted in the alternatingpattern of white and international orange.

Section 9: RebarCorrosion and repair of corrosion damage are multi-billion dollar problems. Observations onnumerous 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 ofconcrete structures. These effects of corrosion often require costly repairs and continuedmaintenance during the life of the structure.

This figure depicts what would be visible if a core sample of concrete and rebar was cut soone can take a look inside. As the unprotected rebar begins to corrode, iron oxides (steelcorrosion by-products) form. The increased volume of the iron oxides causes pressure onthe surrounding concrete. To relieve this increased stress or pressure, the concrete willcrack. At first the cracks will be small, only noticeable by the staining color of the rustrising to the surface of the concrete covering. But as the corrosion continues, a snowballeffect 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, its more than just anaesthetic problem. Once staining and cracking occur, there is an easy path for moremoisture to reach the steel, creating more iron oxides and accelerating the corrosionprocess. 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 nextcouple of years. Red rust staining occurs parallel to the rebar and provides an indication of


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where the corroding bar or bars are located. Spalling also occurs parallel to the rebar. Thefirst 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 concretewhere 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 andrebuilding is necessary, as was the case with this bridge support along I-15 in Utah. TheUtah DOT recently undertook the $1.6 billion dollar overhaul of a 17-mile stretch of I-15that looks like this.

This picture was taken about 20 years after installation; the steel was never coated forcorrosion prevention. In a climate like Utahs with strong freeze-thaw cycles, and wherechlorides build-up from high use of de-icing salts galvanizing the rebar would havesignificantly increased the protection from corrosion.

Here is a picture of spalling concrete where unprotected rebar has been used. As has beendiscussed, the spalling is caused by the increased pressure build-up from the dense ironoxides 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, zinccorrosion 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 thegalvanized coating into the matrix of the concrete, highly reducing the likelihood of zinccorrosion-induced spalling.

Aside from the unique properties of the galvanized coating, there are numerous otherreasons why galvanized rebar is a preferred method of corrosion protection. The galvanizedcoating is very tough and durable. It can be walked on, driven over, and exposed to theeveryday 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


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will protect the steel. The galvanized coating requires no special handling; no soft gloves ornylon strapping are needed when handling galvanized rebar. It is easy to ship, haul, movearound the job site, and install galvanized rebar. It can even be stored outside on the jobsite because the coating will not be damaged by ultraviolet (UV) rays from the sun (whichdoes damage epoxy coatings). Galvanized rebar can be handled in the same manner asblack rebar. In contrast, there is a 10-plus-page brochure published by the Concrete

Reinforcing Steel Institute for handling epoxy-coated rebar. The brochure, entitledReference Guide for Field Handling Techniques For Epoxy-Coated Rebar, coversnumerous requirements which must be adhered toat the job site in order to maintain anadequate coating. All these requirements add significant cost to a project.

Galvanized rebar can be fabricated before or after galvanizing. Or, when following bendradius recommendations as specified in ASTM A 767, the rebar can be fabricated on the jobsite without worrying about touch-up or coating failure. The rebar can also be weldedbefore or after galvanizing using the same ventilation precautions as when welding blackrebar, 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 occurduring 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 themolten zinc, there is 100 percent coverage on formed and bent bars. In addition, comparedto epoxy systems that are generally very thin on edges and ends, all edges and ends of thegalvanized 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 ora zinc-rich paint will adequately protect exposed black steel. Follow the procedures in ASTMA 780 for touch-up and repair of galvanized coatings. Unlike epoxy systems, no inspectionfor inconsistencies or bare spots needs to be performed. Long periods of storage on the jobsite and exposure to harsh elements will have little or no effect on the galvanized rebarperformance.

Galvanized rebar has superior bond strength essential for reliable performance of reinforcedconcrete structures. These studies performed by the University of California - Berkeleyshow galvanized rebar to have greater bond strength, measured by stress in pounds-per-square-inch, than deformed black steel. The majority of the pulloutstrength comes fromthe ribs on the bar, but these studies show extra pulloutstrength can be realized withgalvanized rebar.


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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 onthe decking by vehicles.

Section 10 - Hot-Dip Galvanized Steel in Our WorldWith the economic solution and unrivaled barrier and cathodic protection from corrosionhot-dip galvanized steel provides, it's no wonder it is used in thousands of applicationsthroughout the world. Almost any steel exposed to the elements in some fashion (directlyor 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-dipgalvanized 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-dipgalvanized steel in action:


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INDIANAPOLIS MOTOR SPEEDWAYA towering metal structure featuring more than 500 tons of galvanized steel, theIndianapolis Motor Speedway (IMS) is one of the largest sport facilities in the world. SinceIMS chose hot-dip galvanizing for corrosion protection of the Speedways Northwest VistaAddition in 1992, all subsequent steel additions to the metal behemoth have been specifiedto be hot-dip galvanized a testament to the cost effectiveness and staying power of the

zinc coating.

MI/M-102 BRIDGE RAIL RECONSTRUCTIONThe MI/M-102 Bridge Reconstruction demonstrated how a project can be bothenvironmentally conscious and save taxpayers money. After attending a Galvanize It!seminar, Sue Datta of the Michigan Department of Transportation (MDOT) learned howmany 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 theinitially galvanized pieces used in the structure, this project was able to recycle 80% of theoriginal material saving enough money for the city to begin a new project originally slatedfor next year.


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KUUUJUAQ, NUNAVIK AIRPORTThis project, which had to be completed over the span of two summer seasons, utilizedgalvanized steel because of the rapidity and flexibility the process allows during onsiteconstruction. Galvanizing was an excellent fit for this project, as it allowed the incompletestructure to be left exposed throughout the arctic winter without damage.

CTA BROWNLINE SEDGEWICK STATIONBuilt in June 1900, this elevated station was incorporated into Chicago Transit Authoritys(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 anddangerous rust, galvanized steel will allow the stations renovations to last another hundredyears.


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NASHVILLE CHILDRENS THEATRE DRAGONLocated adjacent to the Nashville metro buildings downtown and highly visible from thestreet, the dragon guarding the Nashville Childrens Theatre will be viewed by approximately300,000 people each year. With such high visibility, the artist wanted to ensure thesculpture would remain aesthetically pleasing, so galvanizing was chosen to preventunsightly 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 curlingtips of the dragons wings totaling more than 3,000 pounds of galvanized steel.

AERO SOLUTIONS POLE-MAXPole-Max is a system used to add antennas onto existing cell phone towers. Specialpurpose, 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 quickdelivery and fast installation, Pole-Max takes advantage of this benefit.


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NATIONAL GYPSUMNational Gypsums Mount Holly plant is a $125 million high-speed wallboard manufacturingfacility that recycles waste material rather than sending it to landfills. In keeping with thegreen spirit of recycling waste material, galvanized steel prevents the waste and expenseof corrosion maintenance and repair, and is also recyclable; thus making it anenvironmentally 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 whencompared to painted steel. The entire structure (with the exception of the outer skin of thebuilding) is hot-dip galvanized for corrosion protection - a necessary requirement towithstand the damaging effects of an industrial environment.

ConclusionAny exterior environment is prime for the use of hot-dip galvanized steel. Commonapplications include theme park rides, stadiums, utility towers, bridge girders and decks,ornamental fences, docks, boat trailers, anchoring rods, bolts and nuts, handrail, gratingwalkways, and stairs.

In addition to the long-term corrosion protection it offers, hot-dip galvanizing is chosenbecause it provides maintenance-free performance for decades.

Website: www.galvanizeit.orgToll-free phone: 1-800-468-7732Email: [email protected]

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