DuplexSystems

PaintingOverHot-DipGalvanizedSteel

American Galvanizers Association6881 South Holly Circle, Suite 108Centennial, CO 80112 USA1-800-HOT-SPECwww.galvanizeit.org

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DUPLEX SYSTEMS: Painting Over Hot-dip Galvanized Steel

TABLE OF CONTENTS:

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3How a Duplex System Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Cathodic Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Barrier Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Coating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Hot-dip Galvanizing After Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Paint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Synergistic Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5

Why Use a Duplex System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Extended Corrosion Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Synergistic Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Economic Benefit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Ease of Repainting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Aesthetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Safety Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Color Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Extend the Life of Previously Galvanized Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6Repair of Hot-Dip Galvanized Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6

How to Specify Hot-dip Galvanized Steel for Painting/Powder Coating . . . . . . . . . . . . . . . . . . . . . .7Surface Characteristics of Galvanized Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Post-treatments for Galvanized Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7Paint Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Duplex Systems in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9Related Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

2005 American Galvanizers Association. The material in this publication has been developed to provide accurate and authoritative information about painting over hot-dip galvanized steel after fabrication. Thismaterial provides general information only and is not intended as a substitute for competent professionalexamination and verification as to suitability and applicability. The publication of the material herein is notintended as a representation or warranty on the part of the American Galvanizers Association, Inc. Anyonemaking use of this information assumes all liability arising from such use.

INTRODUCTIONFor 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 corrosionprotection in what is commonly referred to as aduplex system. A duplex system is simplypainting or powder coating steel that has beenhot-dip galvanized after fabrication. When paintand hot-dip galvanizing are used together, thecorrosion protection is superior to eitherprotection system used alone.

Painting galvanized steel requires carefulpreparation and a good understanding of bothpainting and galvanizing. Many products havebeen galvanized and painted successfully fordecades; two examples are automobiles and radiotowers. Past experience provides excellenthistorical data for how best to achieve good paintadhesion. Studying past adhesion failures andsuccesses led galvanizers, paint companies,researchers, paint contractors, and other sources tocreate ASTM specification D 6386, Preparation ofZinc (Hot-Dip Galvanized) Coated Iron and SteelProduct and Hardware Surfaces for Painting.When the galvanized surface is prepared correctly,paint adhesion is excellent and the duplex systembecomes a highly successful method of corrosionprotection.

HOW A DUPLEX SYSTEM WORKS

Before deciding how to protect steel fromcorrosion, it is important to understand how steelcorrodes. Corrosion takes place because ofdifferences in electrical potential between smallareas on the steel surface that become anodic andcathodic. When an electrolyte connects the anodesto the cathodes, a corrosion cell is created.Moisture in the air forming condensation on thesteel surface is the most common electrolyte. Inthe electrolyte, a small electrical current begins toflow. The iron ions produced at the anodecombine with the environment to form the loose,flaky iron oxide known as rust.

In order to protect steel from corrosion,something must interfere with the corrosion cell,either by blocking the electrolyte or by becomingthe anode. Two common methods of corrosionprotection are cathodic protection (the formationof another anode) and barrier protection (blockingthe electrolyte from the steel surface). Hot-dipgalvanizing alone affords both types of protection,and painting over hot-dip galvanizing adds anadditional barrier layer on top of the zinc coating.

Cathodic ProtectionCathodic protection, also referred to as sacrificial

protection, is based on the knowledge that anodicmetals have a greater tendency to lose electronsthan more noble metals. Metals are ranked inorder of their susceptibility to corrosion, with theless noble, anodic metals, listed higher in thegalvanic series than the more noble, cathodicmetals (see Figure 1, next page). For example,zinc is more anodic than iron. When zinc and steelare connected in the presence of an electrolyte, thezinc becomes the anode in the corrosion cell and isslowly consumed, while the steel acts as thecathode and is protected. By providing cathodicprotection, a galvanized coating is able to offerprotection where small areas of steel are exposed,such as at scratches, drill holes, or cut edges. Thezinc provides cathodic protection through decadesof exposure until all the zinc is sacrificed.

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Barrier ProtectionBarrier protection prevents

corrosion simply byisolating the steel from theenvironment and potentialelectrolytes. The thicker,more dense a barrier coatingis, the better protection thatis provided. Withoutcathodic protection, abarrier system only lasts aslong as the coating staysintact and impenetrable. Anincomplete or compromisedbarrier coating allows steelto rust in the exposed area.The rust will undercut thebarrier coating near theexposed area and eventuallycause failure of the barrierprotection.

COATINGCHARACTERISTICS

The corrosion protection characteristics of hot-dip galvanizing and paint largely affect how thetwo coatings will perform as a duplex system.Understanding the nature of both coatings helpsensure the success of a duplex system.

Hot-dip Galvanizing After Fabrication

The two major types of hot-dip galvanizing areafter-fabrication and continuous sheet.Continuous sheet galvanizing involves sheet steelthat is galvanized in coils and then fabricated intoproducts. After-fabrication galvanizing involvessteel that has been fabricated into parts and thengalvanized. These two types of galvanizing havevery different characteristics and should not beconsidered interchangeable. All the informationin this publication pertains to materials that arehot-dip galvanized after-fabrication, according toASTM A 123, Zinc (Hot-Dip Galvanized) Coatingon Iron and Steel Products, and A 153, ZincCoating (Hot-Dip) on Iron and Steel Hardware.

After-fabrication hot-dip galvanizing is thefactory-controlled process of dipping properly

cleaned steel into a bath of molten zinc.Prior to immersion in the zinc, the steel isthoroughly cleaned in both alkaline and acidbaths. Zinc will not adhere to dirty steel, sothe integrity of the coating is immediatelyapparent as the steel is removed from thegalvanizing bath.

The galvanized coating is metallurgicallybonded to the steel through a series of zinc-iron alloy layers capped by a free zinc layer.A galvanized coating is more than just abarrier coating; it actually becomes part ofthe steel surface and is anodic to the steelsubstrate.

Because zinc readily reacts with theatmosphere, the galvanized coating isconstantly changing. Zinc reacts with theenvironment to form zinc oxide, zinchydroxide, and zinc carbonate. These zinc

reaction products are known as the zinc patina.The zinc patina actually helps protect thegalvanized coating, by providing additionalcorrosion protection. These changes and reactionon the surface of the coating affect how paint willadhere to the galvanized surface.

PaintPainting steel provides a barrier film between the

steel and the environment. A paint systeminvolves the use of several layers of coating, and

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When barrier protection is used alone, rust begins forming assoon as the barrier is breached. This painted handrail atCoors Field in Denver, CO. began rusting just a few yearsafter its installation.

Arrangement of Metalsin the Galvanic Series

Corroded EndAnodic or less noble

MagnesiumZinc

AluminumCadium

SteelStainless Steels (active)

TinNickelBrass

BronzesCopper

Nickel-Copper AlloysStainless Steels (passive)

SilverGold

PlatinumProtected End

Cathodic or more nobleFigure 1

sometimes, differentformulations of paint,depending on the typeof environment in whichthe structure will beexposed.

The most importantfactor for the success ofpaint systems areadhesion and continuity.If paint does not adhereto the steel, it cannot

protect it from the corrosive effects of theenvironment. Surface preparation is extremelyimportant because the degree of paint adhesionmay not be apparent immediately afterapplication. Only after a few months in the fieldmay poor surfacepreparation manifest itselfin paint failure. Having aclean, properly preparedsurface helps ensure that thefull potential of the paintsystem is realized. This isespecially true about duplexsystems.

Continuity of the paint systems is extremelyimportant for carbon steel, since pinholes andother imperfections quickly become rust pits.However, continuity is not as important in aduplex system because the zinc coating will notallow the steel to rust at these sites.

Synergistic EffectWhen hot-dip galvanized steel is painted, the

duplex system provides a more sophisticatedmanner of corrosion protection known as thesynergistic effect. The galvanized coating protectsthe base steel, supplying cathodic and barrierprotection. Paint, in turn, grants barrier protectionto the galvanized coating. The paint slows downthe rate at which the zinc is consumed, greatlyextending the life of the galvanized steel. Inreturn, once the paint has been weathered down ordamaged, the zinc is still available to providecathodic and barrier protection. Whenungalvanized, painted steel corrodes, voluminous

rust grows under the paint and eventually causesthe paint to peel (see Figure 2,below). However,if the steel is galvanized, the zinc corrosion isminimal and the paint peeling is reduced, therebygreatly increasing the life of the structure.

One of the most frequent reasons for paint failureis discontinuity (pinholes) in the paint coating. Agalvanized coating will eliminate early rusting atpinholes, and thus, the life of the steel product isgreatly increased.

The synergistic effect is particularly important atedges and corners, where galvanized coatings areoften thicker due to the diffusion reaction betweenzinc and the base steel (see figure 3, below).

A duplex system affords greater corrosionprotection than paint or hot-dip galvanized canprovide alone. In fact, many tests have shown that

a duplex system lastsfrom 1.5 to 2.5 times thenormal combined life ofboth zinc and the paintsystems. A periodicmaintenance schedulecan extend thissynergistic lifetime evenlonger.

WHY USE A DUPLEX SYSTEM

Each individual project raises unique reasons asto why a duplex system should be utilized, and theadvantages for choosing to do so are many.

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As this tubing is removedfrom the galvanizing bath,the integrity of the coating isreadily apparent.

Figure 2

Figure 3: Photomicrograph of the HDG coating

Extended Corrosion ResistanceThe most obvious and most important reason for

using a duplex system is the added corrosionprotection it provides. Other corrosion protectionsystem cannot match the corrosion resistanceprovided by painting over hot-dip galvanizedsteel.

Synergistic EffectIt’s typical for a duplex system to provide

corrosion protection 1.5 to 2.5 times longer thanthe sum of the lifetime of zinc or paint usedindividually. For example, if a galvanized coatingis expected to be maintenance-free for 40 yearsand a paint system is expected to last ten years,galvanizing and paint combined should protect thesubstrate steel for at least 75 years, or 1.5 times thesum of both systems.

Economic BenefitBecause duplex systems greatly extend the

service life of a product, maintenance costs aresignificantly decreased. Additionally, a productlasts longer before it must be replaced, thusdecreasing the life-cycle cost. The cost of aproduct that has been protected by galvanizing andpainting is lower over the entire life of the productthan most single system methods of corrosionprotection.

Ease of RepaintingAs the paint film weathers, the zinc in the

galvanized coating is present to provide bothcathodic and barrier protection until the structureis repainted. The exposed zinc surface then can be

repainted with minimal surface preparation.

AestheticsGalvanizing has an attractive metallic-gray

appearance suitable for a myriad of applications,but painting can offer aesthetic advantages. Onemight choose to paint over a galvanized coating sothat a project matches its specific environment—such as a stadium, theme park, or natural habitat.

Safety MarkingA duplex system of galvanized

steel and paint may be used toconform to safety regulations.For example, the FederalAviation Administration (FAA)requires structures over 200 feettall to be painted in thealternating pattern of white andinternational orange.

Color CodingPainting over galvanized steel also increases

safety in many environments by color-coding gas,steam, or chemical pipes, identifying hazardouswork areas and walkways, and marking high-voltage electrical lines and equipment.

Extend Life of PreviouslyGalvanized Steel

Paint is a logical choice to extend the life ofgalvanized structures once the zinc coating hassubstantially and naturally weathered away.Instead of being completely replaced, thegalvanized structure can easily be painted,extending its useful life. Organic zinc-rich paintsare specifically suited to this application.

Repair of Hot-dip Galvanized SteelZinc-rich paints can also be used to touch-up and

repair damaged areas on a galvanized coating inorder to comply with ASTM A 780, Repair ofDamaged and Uncoated Areas of Hot-DipGalvanized Coatings. Repairing a galvanizedcoating will significantly extend the useful life ofa product.

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Painting provides barrier protection to the base steel. Theintegrity of a duplex system relies on a uniform paintcoating to the hot-dip galvanized steel.

HOW TO SPECIFYHOT-DIP GALVANIZEDSTEEL FOR PAINTING/POWDER COATINGSurface Characteristics ofGalvanized Steel

The surface chemistry of galvanized steel differsdepending on the age of the coating, whichdictates the surface preparation required. ASTMD 6386 provides detailed surface preparationtechniques for all ages of galvanized steel.

As a galvanized coating begins to age, itsappearance changes. Gradually,the zinc reacts with theatmosphere to form the patinaof zinc oxide, zinc hydroxide,and zinc carbonate. As thepatina forms, the coating slowlybegins to take on a matte grayfinish. Although the zinc beginsreacting with the environmentimmediately upon removalfrom the galvanizing bath, thezinc patina can take up to twoyears to completely form,depending on the characteristicsof its environment, (humidity,moisture, chlorides, etc).

The zinc patina has differentcharacteristics at each stage ofits formation, and thus must be treated differentlywhen preparing hot-dip galvanized steel forpainting. After galvanizing, the top layer of zinccombines with oxygen and moisture to formparticulates of zinc oxide and zinc hydroxide.These particulates are loosely attached to the zincmetal and can be dissolved in water. If paint isapplied to the galvanized coating when theseparticles are on the surface, the paint mayexperience adhesion problems over time, as theparticles detach from the zinc surface.

When the full zinc patina has formed—afterabout one to two years of exposure to theatmosphere—the surface becomes a thin, solidfilm. This film is a mixture of zinc oxide, zinc

hydroxide, and zinc carbonate, which cannot bedissolved in water and adheres very tightly to thezinc metal. Paint can be applied directly onto thisclean surface and exhibit excellent adhesion.

Most people paint galvanized steel during themost difficult time period to do so—between 48hours and one year after galvanizing. During thistime frame, zinc is very reactive with theatmosphere and proper surface preparation iscritical. Successful surface preparation—including the removal of loose zinc oxide or zinchydroxide particles—will prevent adhesionproblems from occurring.

Post-Treatments for Galvanized Steel

After a piece of steel has beengalvanized, it is sometimes quenchedor treated by the galvanizer in orderto halt the reaction between the ironand zinc (and to facilitate immediateshipment of the galvanized steel).The most common post-treatmentsare water-quenching, chromate-quenching, and phosphating. Bothquenching methods (water andchromate) can adversely affect thebond between the galvanized steeland the paint; communicating withthe galvanizer prior to galvanizinghelps avoid post-treatments that canbe detrimental to paint adhesion.

Paint SelectionA partial listing of available paint, paint systems,

and powder coatings that are compatible withgalvanizing are listed in the following table (seetable 1, next page). The paint manufacturer canprovide more thorough information about thecompatibility of specific systems with galvanizedsteel. Always consult the paint manufacturerprior to painting galvanized steel. Differentphysical and chemical characteristics for the sametypes of paint may have varied reactions with agalvanized surface. The paint manufacturer andgalvanizer can assist in the creation of a successfulduplex system.

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Use of post-treatments, such aswater-quenching, can undermine thesuccess of a duplex system bycausing adhesion failure.

CONCLUSIONDuplex systems generally perform extremely

well when care is taken with surface preparationand paint selection. Be sure to take the followingsimple, logical steps to ensure a successful duplexsystem:

Let your galvanizer knowyour steel is to be painted.This will facilitate propersurface preparation—suchas making sure the steel isnot quenched aftergalvanizing and any coatingimperfections are remedied.

Take the time to correctlydetermine the age andcharacteristics of thegalvanized coating. Duplexsystems require propersurface preparation, and newly galvanized, partiallyweathered, and fullyweathered galvanized steeleach require differentmethods and amounts ofsurface preparation.

Proper cleaning andprofiling is key prior topainting. Be sure to choosethe cleaning and profiling

methods appropriate to your situation, closelyfollowing the recommended guidelines.

Select a paint system that is compatible with thegalvanized coating on the steel.

Discuss coating characteristics with thegalvanizer, and always consult the paintmanufacturer prior to painting galvanized steel.

As with any paintsystem, proper surfacepreparation of the hot-dip galvanized coatingto be painted is critical.The combination of thezinc of the galvanizedcoating and paintsynergistically providesan excellent corrosionprevention system thathas been utilized forover 40 years.

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Newly galvanized steel (above) typically exhibits a bright,shiny appearance. Weathered galvanized steel (below)usually possesses a dull, mottled gray appearance.

Type Compatibility CommentsAcrylicsAliphatic PolyurethanesAlkydsAsphaltsBituminousChlorinated RubbersCoal Tar EpoxiesEpoxiesEpoxy-Polyamide CuredLatex-AcrylicsLatex-Water-basedOil BasePortland Cement in OilSiliconesVinylsPowder Coating

SometimesYesNoNoYesYes

SometimesSometimes

YesYes

SometimesSometimes

YesNoYesYes

If the pH of the paint is high, problems may occur due to ammonia reacting with zincIf used as a top coat for a polyamide epoxy primer, it is considered a superior duplex systemThe alkaline zinc surface causes the alkyds to saponify, causing premature peelingPetroleum base is usually not recommended for use on galvanized steelUsed for parts that are to be buried in soilHigh VOC content has severely limited their availabilityRarely used, only if parts are to be buried in soilIf paint is specifically manufactured for use with galvanized steelHas superior adherence to galvanized steelHas the added benefit of being environmentally friendlyConsult paint manufacturerConsult paint manufacturerHas superior adherence to galvanized steelNot for use directly over galvanized steel, can be beneficial in high temperature systems w/ base coatUsually requires profiling, high VOC’s have severely limited their availabilityLow temperature curing powder coatings work exceptionally well over galvanized steel

Table 1: Compatibility of Hot-dip Galvanizing with Paint

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DUPLEX SYSTEMS IN ACTIONGrantville Station San Diego, CA

Grantville Station is a highly visible and heavilytrafficked trolley station in the Mission Valley area of SanDiego. The station is located in an urban area and amarine environment, so it is exposed to many corrosiveelements such as exhaust from vehicles and the salt airfrom the proximity to the ocean. The engineer selected aduplex system of hot-dip galvanizing and paint to protectthe spiral stairs, shade canopies, and pedestrian restraintsfrom corrosion. The combination of galvanizing andpaint will provide steel corrosion protection up to 2.5times longer than the sum of a galvanized or paintedstructure alone.

The structural systems are constructed of pipe and tube brace frames and wide-flange moment frames.Galvanized in 2004, the structure required special venting and care during the HDG process becauseof the complexity and size of the very large prefabricated sections. Furthermore, because the steelwas specified for a duplex system, a smooth finish was required for the paint coating.

With the long-term corrosion protection the zinc coating provides to the duplex system, GrantvilleStation will be able to withstand the corrosive elements of the city and marine environment. This willallow the station to remain an attractive showpiece for the city of San Diego and the hot-dipgalvanizing industry for many years to come.

Germantown Avenue Bridge Philadelphia, PAThe Germantown Avenue Bridge located in Philadelphiawas built in 2003. Although the bridge contains over 40tons of hot-dip galvanized open floor deck grating,covered by cedar planking, the focus of the bridge is the25 tons of duplex coated railing. The powder coatingduplex system was specified partially because of thepositive results of a nearby duplex coated bridge.However, the duplex system was ultimately chosenbecause the city of Philadelphia and the surroundingChestnut Hill community desired a long-lasting andaesthetically appealing bridge and they had high expectation that a duplex system would provide acorrosion-free structure.

Because of the extreme public visibility of the bridge and the desire for an aesthetically pleasingstructure, it was important that the bridge and the railing be flawless. The galvanizer and fabricatorworked diligently to ensure the fabricated handrail was best suited for galvanizing, because anyimperfections in the handrail welds, bends, etc. would be magnified by the zinc coating of hot-dipgalvanizing, and further highlighted by the powder coating applied over the zinc.

The quality control and inspection of this project were superior, and the Germantown Avenue Bridgeis now in place for all of the residents of Philadelphia to admire.

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Skaneateles Community Center Skaneateles, NYThe Skaneateles Community Center is located in anaffluent community along Skaneateles Lake inSkaneateles, New York. The community center wasdesigned to give the residents a place for winter activitiesand keep “cabin fever” to a minimum. The center containsan ice skating rink, pool, meeting rooms, game rooms,basketball courts, and a cafeteria. The architect wanted auniform appearance that flowed from the humid indoorpool area to the cool ice rink, while the owner wanted along-lasting center that could withstand the constant trafficof excited children. The architect specified a duplex

system of hot-dip galvanized steel for its corrosion performance in the humid, acidic (chlorine) poolarea and in the low temperature of the ice rink, and paint to maintain a uniform appearance throughoutthe center.

All of the railings were galvanized and then painted, and other structural components were galvanizedas well. Because of the high visibility and heavy traffic of the railings, all the galvanized materialrequired a very smooth finish to prepare for the paint coating.

The durability the duplex coating provides will give the Skaneateles community a long-lasting,corrosion-free center to cherish for many years into the future.

Kanawha RTA Trolley Bus Charleston, WVThe Kanawha Regional Transit Authority (KRTA) hadbeen experiencing severe corroding of the frame andsuperstructure of their trolley buses. The frames andsuperstructures of the buses had been painted, and theharsh winters and road salts used in the area were causingserious, unsightly corrosion. However, the wheel wells,which had been galvanized and arguably had the mostexposure to the salt spray, had only minimal deterioration.Taking this into account, the KRTA decided toindependently research the performance of hot-dipgalvanized steel and found it to be the best solution to thecorrosion problem on its trolley buses.

The decorative skin, windows, rails, steps, landings, and wood accessories were removed from thebuses, and a new frame and superstructure were fabricated. Then the pieces were hot-dip galvanizedfor corrosion protection, and painted for aesthetic appeal. The frames and superstructure requiredspecial care to avoid any warping and distortion so the doors, windows, steps, landings, exterior woodpanels, and other accessories could be reused and reinstalled on the buses.

Although very little of the duplex system area is visible, the duplex coating will make the trolley busesmore durable, providing low-maintenance costs for the KRTA, and give the public a unique, visuallyappealing mode of transportation for generations to come.

DUPLEX SYSTEMS IN ACTION

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American Society for Testing and Materials (ASTM)100 Barr Harbor Drive, PO Box C700 — West Conshohocken, PA 19428-2959 USAPhone: 610-832-9585, Fax: 610-832-9555Web: www.astm.org, Email: service@astm.orgA 123 Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel ProductsA 153 Specification for Zinc Coating (Hot-Dip) on Iron and Steel HardwareA 780 Specification for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized CoatingsB 201 Practice for Testing Chromate Coatings on Zinc and Cadmium SurfacesD 6386 Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and

Hardware Surfaces for PaintingE 376 Practice for Measuring Coating Thickness by Magnetic-Field or Eddy-Current

(Electromagnetic) Test Methods

Canadian Standards Association (CSA)5060 Spectrum Way — Mississauga, Ontario L4W 5N6 CANADA1-800-463-6727/416-747-4000, Fax: 416-747-2473Web: www.csa.ca, Email: info@csagroup.orgG 164-M Hot Dip Galvanizing of Irregularly Shaped Articles

The Society for Protective Coatings (SSPC)40 24th Street 6th Floor — Pittsburgh, PA 15222-4656 USAPhone: 1-877-281-7772/412-281-2331. Fax: 412-281-9992Web: www.sspc.org, Email: sroka@sspc.orgSurface Preparation Specification No. 1 Solvent CleaningSurface Preparation Specification No. 2 Hand Tool CleaningSurface Preparation Specification No. 3 Power Tool CleaningSurface Preparation Specification No. 7 Brush-Off Blast CleaningPaint Specification No. 27 Basic Zinc Chromate-Vinyl Butyrol Wash Primer

Related Materials

Corrosion and Electrochemistry of Zinc, Zhang, Greg, New York, 1996.

Duplex Systems, Van Eijnsbergen, JFH, Elsevier Science, New York, 1994.

Suggested Specification for Painting over Hot Dip Galvanized Steel, American Galvanizers Association, Centennial, Colorado, 1998

Wet Storage Stain,American Galvanizers Association, Centennial, Colorado, 1997

Zinc Handbook, Porter, F., Marcel Dekker, Inc., New York, 1991.

RELATED SPECIFICATIONS

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American Galvanizers Association6881 South Holly Circle, Suite 108Centennial, CO 80112Phone: 720-554-0900Fax: 720-554-0909Email: aga@galvanizeit.orgWeb: www.galvanizeit.org