Paper. Hot-Dip Galvanizing for Corrosion - AGA

7/28/2019 Paper. Hot-Dip Galvanizing for Corrosion - AGA

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HOT-DIPGALVANIZING FORCORROSION PROTECTIONa specifier’s guide

american galvanizers association



American Galvanizers Association2

© 2012 American Galvanizers Association. The material provided herein has been developed to provide accurate and authoritative informationabout after-fabrication hot-dip galvanized steel. This material provides general information only and is not intended as a substitute for competentprofessional examination and verification as to suitability and applicability. The information provided herein is not intended as a representation orwarranty on the part of the AGA. Anyone making use of this information assumes all liability arising from such use.

HOT-DIPGALVANIZINGFOR CORROSIONPROTECTIONa specifier’s guide

Corrosion What & WhyCorrosion Process

Hot-Dip Galvanizing (HDG)HistoryProcess

Why Specifiers Choose HDGCorrosion Protection

Barrier, Cathodic, Zinc PatinaDurability

Abrasion ResistanceUniform ProtectionComplete Coverage

LongevityAtmosphereSoilWaterConcrete

Other EnvironmentsAvailability & Versatility

Abundant MaterialsEfficiencyFlexibility

AestheticsNatural/BlendingArchitectural ApplicationsDuplex Systems

SustainabilityEnvironmentalEconomic

Specifying HDGConclusion



American Galvanizers Association 3

Corrosion:what & whyCorrosion and repair of corrosion damage are multi-billion dollar problems – the latest estimates show metallic corrcosts the United States approximately $423 billion annually ($52 billion in Canada), or about 3% of each nation’s GHowever, the cost of corrosion is much greater than just nancial, it can also lead to waste of natural resources, hazarfailures, and many other indirect costs. Corrosion is a natural phenomenon which can never be completely eliminhowever, it is a misconception nothing can be done. Employing adequate corrosion protection systems at the startproject, such as hot-dip galvanizing, can signi cantly reduce these annual costs.For more than 100 years, hot-dip galvanizing after fabrication has been speci ed to combat steel corrosion in the harsenvironments throughout various markets. However, the speci cation and use of hot-dip galvanized steel evolves consas new markets emerge. Once considered only as a means of corrosion protection, hot-dip galvanizing is now specian array of reasons including lower initial cost, durability, longevity, availability, versatility, sustainability, and even aesUnderstanding the characteristics and performance of hot-dip galvanized steel will facilitate and increase the speci cati

the coating in applications where galvanizing will enhance the project.

corrosion processCorrosion, which can be simply de ned as rust, is more appropriately thetendency for metals to revert to their natural, lower energy state of ore. Metalliccorrosion is an electrochemical process meaning it involves both chemicalreactions and the ow of electrons. A basic electrochemical process that drivesthe corrosion of metals is galvanic action, where current is generated internally by physical and chemical reactions occurring among the components of the cell.

corrosion costs the US

$423 BILLIONannually




galvanic corrosionTere are two primary types of galvanic cells that causecorrosion: the bimetallic couple and the concentration cell. A bimetallic couple (Figure 1) is like a battery, consisting of two dissimilar metals immersed in an electrolyte solution. Anelectric current ( ow of electrons) is generated when the twoelectrodes are connected by an external continuous metallicpath. A concentration cell consists of an anode and cathodeof the same metal or alloy and a return current path. Teelectromotive force is provided by a di erence in concentrationof the solutions contacting the metal(s). In a galvanic cell, thereare four elements necessary for corrosion to occur:

• Anode - Electrode at which negative ions are dischargedand positive ions are formed, or other oxidizing reactionsoccur. Corrosion occurs at the anode.

• Cathode - Electrode at which positive ions are discharged,negative ions are formed, or other reducing reactionsoccur. Te cathode is protected from corrosion.

• Electrolyte - Conducting medium in which the ow of current is accompanied by movement of matter. Electrolytesinclude water solutions of acids, bases, and salts.

• Return Current Path - Te metallic pathway connecting the anode to the cathode. It is often the underlying substrate.

Removing any one of these elements will stop the current ow and corrosion will not occur. Substituting a di erent metal for theanode or cathode may cause the direction of the current to reverse,resulting in a change of the electrode experiencing corrosion.Te galvanic series lists metals and alloys in decreasing orderof electrical activity. Metals toward the top of the list are “lessnoble” and have a greater tendency to lose electrons than metalsfound lower on the list. Utilizing hot-dip galvanized steel exploitsthis phenomenon by sacri cing zinc (anode) to protect theunderlying steel (cathode).

corrosion of steelTe corrosion process that takes place on a piece of bare steel

is very complex due to variations in the composition/structureof the steel, presence of impurities due to the higher instanceof recycled steel, uneven internal stress, or exposure to a non-uniform environment.

It is easy for microscopic areas of the exposed metal to beco

relatively anodic or cathodic, and many of these areas cdevelop in a small section of the exposed metal. Terefore,is highly possible several di erent galvanic corrosion cellspresent in the same small area of the actively corroding piof steel.

+ -

ExternalCircuit

Electrolyte

CONVENTIONAL CURRENT

Electrons Electrons

AnodeCathode

Figure 1: Bimetallic Couple





Hot-DipGalvanizing (HDG)

As the corrosion process progresses, the electrolyte may change due to materials dissolving in or precipitating fromthe solution. Additionally, corrosion products might tend tobuild up on certain areas of the metal. As time goes by, theremay be a change in the location of cathodic and anodic areasand previously uncorroded areas of the metal are attacked andcorrode (Figure 2).Te corrosion rate of metals is controlled by factors such astemperature, humidity, pH of the electrolyte, and the electricalpotential and resistance of anodic and cathodic areas.

for corrosion protectionHot-dip galvanizing is the process of immersing fabricatedsteel or iron into a kettle or bath of molten zinc. Te process isinherently simple which provides a distinct advantage over othercorrosion protection methods. Originating more than 250 yearsago, here is a tour of the history and process in more detail.

history of galvanizingTe recorded history of galvanizing dates back to 1742 wheP.J. Malouin, a French chemist described a method of coatiniron by dipping it in molten zinc in a presentation to the FrenRoyal Academy. Tirty years later, Luigi Galvani, galvanizinnamesake, discovered more about the electrochemiprocess that takes place between metals. Galvani’s rese was furthered in 1829 when Michael Faraday discovered zinc’s sacri cial action, and in1836, French engineer Sorel obtaineda patent for the early galvanizing process. By 1850, the Britishgalvanizing industry wasusing 10,000 tons of zinca year for the protectionof steel, and in 1870, therst galvanizing plantopened in the UnitedStates. oday, galvanizing is found in almost every major application and

industry where iron or steelis used. Hot-dip galvanizedsteel has a proven and growing history of success in myriadapplications worldwide.

Figure 2: Changes in cathodic and anodic areas

C

A

C

C

A

A

A

C

A

A

C

C

C

A

C

C

A

A

Mosaic of anodes and cathodes,electrically connected by theunderlying steel.

Moisture in the air provides theelectrical path between anodes andcathodes. Due to differences inpotential, electric current begins to flowas the anodic areas are consumed.Iron ions produced at the anodecombine with the environment to formthe flaky iron oxide known as rust.

As anodic areas corrode, new materialof different composition and structureis exposed. This results in a change ofelectrical potentials and changes thelocation of anodic and cathodic sites.Over time, previously uncorroded areasare attacked and uniform surfacecorrosion results. This continues untilthe steel is entirely consumed.





Why SpecifiersChoose

inspectionTe inspection of hot-dip galvanized steel is simple andquick. Te two properties of the hot-dip galvanized coating closely scrutinized are coating thickness and coating appearance. A variety of simple physical and laboratory tests may be performed to determine thickness, uniformity,

adherence, and appearance.Products are galvanized according to long established,accepted, and approved standards of AS M, theInternational Standards Organization (ISO), the CanadianStandards Association (CSA), and the American Associationof State Highway and ransportation O cials (AASH O).Tese standards cover everything from the minimum coating thicknesses required for various categories of galvanized itemsto the composition of the zinc metal used in the process.esting methods and interpretation of results are coveredin the publication, T e Inspection of Products Hot-DipGalvanized after Fabrication, published by the AmericanGalvanizers Association (AGA). Tis publication, as well asall others referenced in this guide, can be found on the AGA website ( www.galvanizeit.org ).

hot-dip galvanizingraditionally, hot-dip galvanized steel is speci ed for its superiorcorrosion protection, especially in harsh environments. Toughcorrosion resistance is inherent any time galvanizing is utilized,more and more speci ers select hot-dip galvanized steel forother reasons, including lowest initial cost, durability, longevity,availability, versatility, aesthetics, and sustainability.

corrosion protectionSteel is an abundant, e cient building material that providesspeci ers design freedom. However, for projects exposed tothe atmosphere and other harsh environments, it is critical tocoat the steel for corrosion protection. Often large constructionprojects target a 50-100 year design life, highlighting the need for

durable, long lasting corrosion protection. Hot-dip galvaniz(HDG) provides three levels of corrosion resistance to stbarrier protection, cathodic protection, and the zinc patina.

barrier protection

Te rst line of corrosion defense is barrier protection. Likpaints, the hot-dip galvanized coating provides protection isolating the steel from the electrolytes in the environment.long as the barrier is intact, the steel is protected and corros will not occur. However, if the barrier is breached, corros will begin.Because a barrier must remain intact to provide corrosresistance, two important properties of barrier protectiare adhesion to the base metal and abrasion resistance. Ttightly-bonded, impervious nature of zinc metal makesa very good barrier coating. Coatings such as paint thhave pin holes are susceptible to penetration by element

causing under lm corrosion tospread rapidly.

i n s p e c t i o n




cathodic protectionIn addition to barrier protection, hot-dip galvanizing protects steel cathodically, which means zinc willpreferentially corrode to protect the underlying base steel.Te Galvanic Series of Metals (Figure 4) is a list of metalsarranged in order of electrochemical activity in seawater

(the electrolyte). Tis arrangement of metals determines what metal will be the anode and cathode when the two areput in an electrolytic cell. Metals higher on the list are anodicto the metals below them meaning they provide cathodic orsacri cial protection when the two are connected. Terefore,zinc protects steel. In fact, this cathodic protection ensureseven if the HDG coating is damaged to the point bare steelis exposed (up to ¼ inch in diameter), no corrosion willbegin until all the surrounding zinc is consumed.

zinc patina And the nal factor in HDG’s long-lasting corrosionprotection is the development of the zinc patina. Te zincpatina is the formation of zinc corrosion by-products onthe surface of the steel. Zinc, like all metals, begins tocorrode when exposed to the atmosphere. As galvanizedcoatings are exposed to both moisture and free owing air,corrosion by-products will naturally form on the coating surface. Te formation of these by-products (zinc oxide,zinc hydroxide, and zinc carbonate) occurs during natural wet and dry cycles in the environment. Te zinc patina,once fully developed, slows the corrosion rate of zinc toabout 1/30th the rate of steel in the same environmentand acts as an additional passive, impervious barrier forthe hot-dip galvanized coating.

durability Another aspect of hot-dip galvanizing is proven durability.Hot-dip galvanized steel has been speci ed extensively in petro-chemical, industrial, power/utility, and bridge/highway projects because of its unmatched durability inthese harsh environments. Hot-dip galvanizing remainsdurable thanks to its abrasion resistance, uniformprotection, and complete coverage.

abrasion resistance A unique characteristic of the hot-dip galvanized coatingthe development of tightly-bonded (~3,600 psi), abrasiresistant intermetallic layers.Figure 5 is a cross-section a galvanized steel coating showing the three intermetalayers (Gamma, Delta, and Zeta) and top layer pure zinc (Eta). During the galvanizing process, thelayers develop naturally during a metallurgical reactbetween the iron in the steel and zinc in the kettle. Athe photomicrograph also shows the hardness of eachthe layers as a Diamond Pyramid Number (DPN), yocan see the three intermetallic layers are harder than tbase steel, while the eta layer has ductility which madamaging the HDG coating very di cult.

CORRODED ENDAnodic or less noble

Magnesium

Zinc

Aluminum

Cadmium

Steel

Lead

Tin

Nickel

Brass

Bronzes

Copper

Nickel-Copper Alloys

Stainless Steels (passive)

Silver

Gold

Platinum

Cathodic or most noblePROTECTED END

Figure 4: Galvanic Series

Any one of thesemetals and alloyswill theoreticallycorrode while offering

protection to anyother which is lowerin the series, so longas both are electricallyconnected. In actualpractice, however, zincis by far the mosteffective inthis respect.

Figure 5: Photomicrograph of a galvanized coating

Eta(100% Zn)70 DPN Hardness

Zeta(94% Zn 6% Fe)179 DPN Hardness

Delta(90% Zn 10% Fe)244 DPN Hardness

Gamma(100% Zn 6% Fe)

250 DPN HardnessBase Steel(100% Zn)159 DPN Hardness




T i m e

t o f i r s t m a

i n t e n a n c e

* ( y e a r s )

. . .......

Rural

Suburban

T emperate Marine

T ropical M arine

Industria l

Key

Average Thickness of Zinc (mils)*Time to first maintenance is defined as the time to % rusting of the steel surface.

mil = . µm = . oz/ft

Figure 7: Time to First Maintenance Chart

longevityHot-dip galvanized steel is often utilized in some of the harshestenvironments imaginable, yet it provides maintenance-freelongevity for decades. Te corrosion resistance of hot-dipgalvanizing varies according to its surrounding environments,but generally corrodes at a rate of 1/30 of bare steel in the sameenvironment. Measurements of the actual consumption rate of the coating during the rst few years of service provide good data for projecting a conservative estimate for the remaining life torst maintenance, because as zinc corrosion products build onthe surface, which in most environments are adherent and fairly insoluble, the corrosion rate often slows as time progresses. Whether exposed in the atmosphere, subjected to blazing UV rays,snow, and/or other elements, submerged in water, or embeddedin soil or concrete, hot-dip galvanized steel can withstand thedi erent corrosive elements and ful ll the intended design life.More information about hot-dip galvanized steel’s longevity can be found in the AGA’s publicationPerform ance of Hot-DipGalvanized Steel Products.

in the atmosphereTe most common exposure environment for hot-dip galvanizedsteel is atmospheric. As hot-dip galvanized steel is exposed tothe atmosphere, the zinc interacts with free owing air and

moisture to develop the zinc patina. Te zinc patina is criticalto the longevity of galvanized steel in the atmosphere; and thus,accelerated, salt-spray tests that do not mimic real world exposureconditions are not an accurate predictor of HDG’s longevity.Te performance of atmospherically exposed hot-dip galvanizedsteel depends on ve main factors: temperature, humidity,rainfall, sulfur dioxide (pollution) concentration in the air,and air salinity. None of these factors can be singled out as themain contributor to zinc corrosion, but they all play a role in

determining the corrosion protection hot-dipgalvanized (zinc) coatings can provide in certainatmospheric conditions.For nearly a century, independent and industry testing of samples in ve environments (industrial, rural,suburban, tropical marine, and temperate marine)have yielded real-world performance data for hot-dipgalvanized steel. Using this real-world corrosion data,statistical methods, and neural network technology,Dr. Gregory Zhang of eck Metals Ltd. developedthe Zinc Coating Life Predictor (ZCLP) to estimatethe life of hot-dip galvanized coatings in atmosphericconditions. Using the ZCLP, you can input speci cparameters for any environment and get an estimatedtime to rst maintenance ( FM) for the galvanizedcoating (Figure 7).ime to rst maintenance is de ned as 5% rusting of the base steel surface, which means 95% of thezinc coating is still intact, and an initial maintenanceis recommended to extend the life of the structure. According to AS M A123, the governing speci cationfor hot-dip galvanizing, steel ¼ -inch thick or greatemust have at least 3.9 mils of zinc on the surface, butmore often than not, there will be greater than theminimum requirement. Terefore, using the FMchart, hot-dip galvanized structural steel (>1/4-inchthick) provides 72-73 years of life to rst maintenanceeven in the most corrosive atmosphere, industrial.




CHART

CHART

Zinc Coating Thickness (mils)

S e r v i c e L i f e *

( y

e a r s

)

Low pH (< . )

. . . . . .

pH

H

pH

H

pH= . H = . %

pH= . H = . %

pH= . H = . %



( y

e a r s

)

High pH (> . )

. . . . . .

pH

H

pH

H

pH= . H = . %

pH= . H = . %

pH= . H = . %

* Service life is defined as the time to necessary part replacement or underground maintenance. mil = . µm = . oz/ft

Hot-Dip Galvanized Steel’s Estimated Service Life in Soil

Low Moisture (< . %)



( y e a r s

)

. . . . . .

pH= . H = . %

pH= . H = . %

pH= . H = . %

pH

H

pH

H

CHART

High Moisture (> . %)



( y e a r s

)

. . . . . .

pH

H

pH

H

pH= . H = . %

pH= . H = . %

pH= . H = . %

CHART

H i g h C h l o

r i d

e s

>

P P M

H i g h C h l o

r i d

e s

>

P P M

Figure 8: Soil Charts

in soil

Another common exposure for hot-dip galvanized steelis partially or fully buried in soil. With more than 200di erent types of soil identi ed in North America, hot-dip galvanizing’s performance in soil is varied and hard topredict. Te main factors that dictate the corrosivity of thesoil are moisture content, pH level, and chlorides. Tesesoil conditions are a ected by additional characteristicssuch as aeration, temperature, resistivity, and textureor particle size. A general rule of thumb is galvanizing performs well in brown sandy soils, and not as well ingray, clay-like soils. Tis is because soil with larger particles

wick moisture away from the surface more quickly so the

galvanized piece has less exposure to moisture.Te rst step to estimating the performance of hot-dipgalvanized steel in soil is to classify it. And as the corrosionrate of steel in soil can range from less than 20 micronsper year in favorable conditions, to 200 microns per yearor more in very aggressive soils, misclassifying the soil canlead to unpredicted performance. Te AGA has developeda chart for estimating HDG’s performance in soil basedon real world corrosion data. In this case, service life isde ned as total consumption of the coating plus 25%, andis an indication of when the structure should be replaced.

Tere are four di erent charts based on the classi cation of thesoil (Figure 8 ). Using the chart, the rst classi cation is by chloridcontent — Charts 1 and 2 (top row) are used for soils with hichlorides (>20 PPM) and Charts 3 and 4 (bottom row) are usefor soils with low chlorides (<20 PPM).Once you have identi ed the chloride content, there is a seconclassi cation to determine the correct chart to use. For soils whigh chlorides, the second determination would be moistucontent. Soils with low moisture (<17.5%) fall on Chart while soils with high moisture (>17.5%) fall on Chart 2. For lchlorides, the second determination is the pH level. Soils whigh pH levels (>7.0) fall on Chart 3, while soils with low p

(<7.0) fall on Chart 4.Te blue line on all four charts represents the average for sosurveyed in that characteristic group. Te green line representhe best soil in the category sampled, and the red line represethe worst soil in the category from the study. Te shaded areashow how the changes in pH and moisture content a ecthe estimated service life. Assuming 3.5 mils as a minimthickness for HDG buried in soil, the chart shows the averalife in the harshest soils (uncommon) would be approximat50 years and in the best soils exceed 120 years.




in moisture-rich environments A less common environment for galvanizsteel is submerged in or exposed to watMoisture is highly corrosive to most metincluding steel and zinc. However, becauof the development of the passive, mosnon-soluble zinc patina, the corrosion raof galvanized steel is much slower than bsteel. Tere are many di erent types of water(pure water, natural fresh water, potable wat(treated drinking water), and seawater) aneach has di erent mechanisms that determinthe corrosion rate.Similar to soils, the varieties of water mapredicting corrosion rates difficult. hougpH level has the most profound effecmany parameters affect corrosion of metin a water environment including oxygcontent, water temperature, agitation, thpresence of inhibitors, and tide conditionDespite the difficulty of predictincorrosion, hot-dip galvanizing steel is oof the best methods of corrosion protectiofor submersed applications because of complete, uniform coverage. Water with high free oxygen or carbon dioxicontent is more corrosive than water containinless of these gases, and hard water is much lcorrosive than soft water. A natural scale insoluble salts tends to form on the galvanizsurface under conditions of moderate or hig water hardness. Te salts combine with zinc t

form a protective barrier of calcium carbonaand basic zinc carbonate.Similar to fresh water, galvanized coatinprovide considerable protection to steel whimmersed in sea water and exposed to salt sprIn uencing factors in the corrosion of zinc ifresh water also apply to sea water; however,dissolved salts (primarily sul des and chloridin sea water are the principal determinanof the corrosion behavior of zinc. Given thigh level of chloride in sea water, a very hcorrosion rate might be expected. However, t

presence of magnesium and calcium ions hastrong inhibiting e ect on zinc corrosion.

in concreteConcrete is an extremely complex material. Tuse of various types of concrete in constructihas made the chemical, physical, and mechaniproperties of concrete and its relationship metals a topic of ongoing studies. Reinforcisteel bars (rebar) are embedded in concrete provide strength, and are critical to the integri

Metrolina GreenhousesHuntersville, North Carolina

Established in 1971 with a 20,000-square-foot greenhouseon 3 acres in Charlotte, North Carolina, MetrolinaGreenhouses has grown to be the largest single sitegreenhouse in the United States. The first greenhousewas a one acre plastic covered galvanized structure. Hot-dip galvanizing, used from day one, has been integralto all new expansion and construction. Galvanized steelwas engineered into the first buildings and all futureconstruction will include it to protect the steel fromthe moist environment of the greenhouse.

Metrolina Greenhouses’ newest $50 million addition willbring the total size of the building to 5.8 millionsquare feet. They employ 550 people year round and use an

additional 300 temporary workers during the peak times ofthe year. Every year more than 75 million plants and over700 varieties are grown in this heated greenhouse.

Metrolina’s founder referenced the exceptionally longlife of galvanized steel in the hot, moist greenhouseenvironment as integral to their construction andproduction goals. After 41 years, hot-dip galvanizedsteel has protected the greenhouse structures fromcorrosion in a perenially wet environment, and willcontinue to do so maintenance-free for several moredecades of greenhouse activity and plant production.

Longevity




and performance of the structure throughout its life. Asconcrete is a porous material, corrosive elements such as water,chloride ions, oxygen, carbon dioxide, and other gases travelinto the concrete matrix, eventually reaching the rebar. Oncethe concentration of these corrosive elements surpasses steel’scorrosion threshold, the rebar starts to corrode. As the rebarcorrodes, pressure builds around the bar leading to cracking,staining, and eventually spalling of the concrete (Figure 9).

Because failure of the rebar leads to compromised or failing structural capacity, protecting against premature rebar failureis key. Similar to in the atmosphere, galvanized rebar extendsthe life of the steel in concrete. Te corrosion mechanisms inconcrete are quite di erent than atmospheric exposure, andone of the biggest factors is chloride concentration. Galvanizedrebar can withstand chloride concentration at least four to vetimes higher than black steel, and remains passivated at lowerpH levels, slowing the rate of corrosion.

In addition to the higher chloride tolerance, once zinccorrosion products are formed from the galvanized rebar, they are less voluminous than iron oxide and actually migrate away from the bar. Figure 10shows the white zinc particles particlesmigration away from the bar (galvanized coating) and intothe pores of the concrete matrix. Tis migration prevents thepressure buildup and spalling caused by iron oxide particles.

Te total life of galvanized steel in concrete is made up of thetime taken for the zinc to depassivate, plus the time taken forconsumption of the zinc coating, as it sacri cially protects

the underlying steel. Only after the coating has been fully consumed in a region of the bar will localized steel corrosionbegin. Additional studies and information on galvanizedrebar can be found at www.galvanizedrebar.com and inthe AGA publicationGalvanizing for C orrosion Protection:A Speci er’s Guide to Reinforcing Steel or on the AGA websiteat www.galvanizeit.org.

Figure 9: Spalling concrete

Figure 10: Zinc migration in rebar

r e b a r

s p a l l i n g




Talbot SubstationDayton, Washington

One of the great benefits of utilizinghot-dip galvanized steel for corrosionprotection is galvanized pieces can beeasily stored for future use. This meansowners can stockpile elements they know theywill need for replacement or expansion,buying when prices are low and creating astockpile of usable goods for the future.

This can be especially advantageousfor structures such as substations,distribution towers, cell phone towers,highway and transportation products(guardrail, sign poles, light poles,handrails) and more.

A substation, like the one above, caneasily stockpile and even store elementson site, exposed to the elements. Asthey lie in wait to be used, the durablezinc barrier and cathodic protection willkeep the pieces corrosion-free and readyfor use at a later date.

Forty-seven tons of steel weregalvanized for the Talbot substation,including all structural steel,fasteners, anchor bolts, concreteembeds, bollards, light fixture mountingbrackets, and all switch operatorgrounding platforms. Replacement partsfor these pieces and more could easilybe bought ahead of time and stored,waiting for use, with the protectionof galvanized steel.

Availability & Versatility

in other environmentsTere are a number of other environments where hot-dipgalvanized steel is commonly speci ed for its longevity. Soenvironments where hot-dip galvanized steel can perfo

well are in chemical solutions with neutral pH (4-13), contact with treated wood, and in extreme temperatures (-F to 392 F). Environments where HDG is not recommendeare chemical solutions with pH levels outside those listed, in contact with other metals. wo exceptions to the dissimimetals rule are aluminum and stainless steel unless they arthe presence of salt water or air with a high chloride conte

availability & versatilityHot-dip galvanized (HDG) steel is versatile and readily availa A wide variety of shapes and sizes ranging from small nbolts, and fasteners to larger structural pieces, to even the mintricately detailed artistic pieces, can be galvanized. Becausthe total immersion process, even complex fabrications cancoated entirely for corrosion protection.Many corrosion protection methods depend on proper temperatuand humidity conditions for correct application. Howevbecause hot-dip galvanizing is a factory controlled process, itbe accomplished 24/7/365 rain or shine. Zinc solidi es upo

withdrawal from the bath, so there are no delays for curing; agalvanized steel could realistically be galvanized, shipped to theand erected on the same day. On the other hand, if the galvanizmaterial does not need to be installed immediately, it is easily stooutside, as UV rays do not degrade the coating’s integrity.

abundant materials As North America continues to strive for sustainable developmthe same thinking should be applied to the materials used construction. Another characteristic of zinc, making it idea

suited for this job is its abundance. Te main materials used in thgalvanizing process, zinc and steel are common; in fact, zinc is27th most abundant material in the earth’s crust, and iron is th4th. Zinc and steel are also both 100% recyclable without the lof any chemical or physical properties – steel is the most recymaterial in the world.Zinc is a natural element found in air, soil, and water. Approximat5.8 million tons of zinc are cycled through the atmosphere annuathrough natural phenomena. Zinc is also common and essentto life. Zinc is found in a number of products we use daily suchcosmetics, tires, cold remedies, baby creams to prevent diaper rtreatments for sunburns, and sunscreens. In fact, zinc oxide blo

more UV rays than any other single ingredient used in sunscreFurthermore, we all require zinc to live as it helps with regufunctions such as vision, reproduction, digestion, and breathing.

efficiency With galvanized steel, you can do more with less. Because ofhigh strength-to-weight ratio, specifying projects with steel samaterials and energy. In fact, on average one ton of steel providessame strength as 8 tons of concrete, and according to the World St Association, the strength-to-weight ratio minimizes substructcosts and can also save money on transportation and handling.




Aesthetics

El Andaluz Commercial Offices & ResidencesSanta Barbara, California

El Andaluz takes galvanizing fromfunctional to fantastic, incorporatingstructural and artistic galvanizedelements strikingly juxtaposed with abold kaleidoscope of ornately coloredceramic tile floors, fountains, ledgesand stairs. The commercial offices ofEl Andaluz, coupled with residentialcondominiums, prominently display hot-dip galvanized steel elements in thearchitects adaptation of a similarpicturesque courtyard six blocks from thePacific Ocean in Santa Barbara.

With a reputation for favoring galvanizedsteel elements in his creations, thearchitect was depending on the zincpatina finish, which develops in themonths after galvanizing to enhance thelook of his artistic creation. As thepatina develops, the galvanized steelnot only takes on a uniform matte grayappearance, completing the architect’svision, but will also ensure long-lastingprotection for the project. The galvanizedsteel was incorporated to assure thestructural integrity of the architecturaldisplay for decades to come, as well as forthe aesthetic appeal.

In addition to the appealing metalliccolor, the steel was able to be formedand cut into artistic shapes. In otherprojects, galvanized steel beams have alsobeen bent and arched to create curvatures,or even wavy paneling. Galvanized steel

pairs aesthetics, visual flexibility, anddurability into successful structures thatlast for generations.

In addition to the abundance and quick turnaround time,galvanized steel also facilitates the expansion of existing structuresdue to its exibility and stockability. Galvanized steel membersare easy to retro t and expand by welding, bolting, and/orsplicing of existing vertical and horizontal structural elementsand adding reinforcement. Adding to existing structures allowsmaximum e ciency of available space. Steel members are lighterthan many other materials but still provide great strength, soexpansion within the same footprint is possible.Furthermore, because of hot-dip galvanized steel’s durable,maintenance-free nature, elements can be stockpiled outside foryears without compromising the zinc coating and its corrosionprotection. Te zinc coating of HDG is una ected by UV rays,extreme temperatures, rain, snow, or humidity, so with properstorage it is simple to keep an inventory on-hand for quick replacement in an emergency. Stocking frequently used partsuntil they are needed saves time, and if bought when prices arelow, saves money.

safetyStructural safety and stability are critically important to theintegrity of steel construction, and cannot be maintained if thestructure has been weakened by the ravages of corrosion. Hot-dip galvanized steel pieces which remain corrosion resistant fordecades preserve the structural integrity of steel constructionand protect against disaster.One area of safety where hot-dip galvanized steel providesadvantages is in areas of seismic activity. Steel elementsare more ductile and lighter, reducing the inertia e ectsof seismic loading. Able to bend within reason withoutbreaking, the tensile strength of hot-dip galvanized steel canprotect structures from damage or even total failure during seismic activity.

aesthetics Aesthetics are important to nearly every constructionproject. Whether an attractive, artfully designed sculpture orarchitecturally exposed steel element, or bridge, bus station,or other infrastructure element, galvanized steel o ers designexibility, and an attractive, natural gray nish – or if color isdesired it can be easily painted or powder coated.




natural blending with surroundingsFor some galvanized steel projects, such as electricsubstations, solar panels, or rail line infrastructure, thegoal is often to blend seamlessly with the surroundings. As galvanized steel weathers and the zinc patina forms, thecoating becomes a uniform matte gray. Whether in rural, wooded areas that are wildlife sensitive or in the city wherenon-re ectivity is important, the natural, non-intrusivenish of hot-dip galvanizing compliments and blends in

with any environment.

architecturally exposedIn addition to providing a natural, blendable appearance,utilizing hot-dip galvanizing on architecturally exposedstructural steel (AESS) provides visual peace of mind thesteel is in good condition. AESS elements are often designed

to be centerpieces and talking points of steel construction.Te high strength-to-weight ratio and ductility of steel allowsfor curves, arches, and intricate patterns and designs whenplanning AESS elements. However, when AESS elements areexposed to the atmosphere, it is important to ensure they remain beautiful design elements by protecting them againstcorrosion. Hot-dip galvanized AESS elements can ghtcorrosion for decades without sti ing your design freedom.

duplex systemsTe natural, matte gray nish does not suit every project of every speci er – as sometimes color is preferred or needed for

branding, safety marking, etc. However, by specifying a duplesystem – galvanizing your project and then painting or powdercoating over to the desired color ensures you don’t have to sacri cthe corrosion protection bene ts and extended maintenance of HDG steel.

Duplex systems provide more bene t than just aesthetic optionsTe combination of hot-dip galvanized steel and paint or powdercoating provide a synergistic e ect. Te paint/powder extendsthe life of the coating by providing an additional barrier coatinto the zinc layers, while the galvanized steel prolongs the life




the paint coating by preventing under lm corrosion andpeeling.Te result of the two coatings working in synergy is extendedcorrosion protection. Te service life of a duplex system is1.5 to 2.3 times the sum of the individual systems. Forexample, if the life of the galvanized coating in a particularenvironment is 70 years, and the expected life of the paint is10 years, the expected life of the duplex system would be atleast 120 years (1.5 x (70+10)).Tis extended service life assumes no maintenance willbe done to keep the paint or powder coating intact.Realistically, if someone invests the premium cost upfrontfor a duplex system, they likely plan to keep the color onthe structure. So, in practical terms, the synergistic e ect of utilizing a duplex system is the extended maintenance cycleit provides. With hot-dip galvanized steel as a “primer,” thetime to rst maintenance of the paint or powder coating isextended 1.5 to 2.0 times what it would be for bare steel.Te AGA’s publication Duplex System s: Painting O ver Hot-Dip Galvanized Steel and instructional DVD guidePreparing HDG Steel for Paint provide more information on specifying

duplex systems.

sustainabilitySustainable development is the social, economic, andenvironmental commitment to growth and development thatmeet the needs of the present without compromising the ability of future generations to meet their own needs. As the socialpressure continues to mount to construct the built environmentsustainably, speci ers are becoming more invested and analyticalin the materials they choose. Hot-dip galvanized steel’smaintenance-free longevity provides positive environmental andeconomic bene ts to future generations.

environmental advantages As previously stated, zinc exists naturally in the air, water, andsoil and is the 27th most abundant element in the Earth’s crust.More than 5.8 million tons of zinc is naturally cycled through theenvironment by plant and animal life, rainfall, and other naturalactivity. And zinc is essential for all life – from humans to the smallestmicroorganisms. Terefore, utilizing hot-dip galvanized steel is notharmful to the environment as the zinc is already naturally foundin the area.In addition to being natural, zinc, like steel, is in nitely recyclable without the loss of any physical or chemical properties.

Approximately 30% of the world’s zinc supply comes from recycledsources each year, and more would be recycled if it were available.Furthermore, steel is the most recycled material in the world withvirtually 100% of structural steel coming from recycled sources,making galvanized steel an in nitely renewable material. A life-cycle assessment (LCA) is an objective measurement of a product’s environmental impact. Often called a “cradle-to-grave”study, LCA quanti es the environmental impact of a process orproduct from raw material acquisition, energy inputs and emissionoutputs during production and use, and end-of-life management

s u s t a i n a b l e




Raw Material &Energy Inputs

Inputs forMaintenance † = 0

EnergyInputs

Production

• Steel• Zinc Metal

• Galvanizing Process

Use

• Bridges• Light Poles

• Parking Garages• Truck Frames• Sign Structures

End-of-Life

Steel & Zinc Recycle Loop (100%)

CO2SO2

etc.Zinc Corrosion

Products

Emissions ‡

†For all but the most aggressive, corrosive environmental conditions, there are no energy or raw material inputs during use (75+ years).

‡ For hot-dip galvanized steel, naturally occurring zinc oxide, zinc hydroxide, and zinc carbonate.

Figure 11: LCA of Galvanizing

With the original steel guardrail panels galvanized backin 1955, the rails on the MI/M-102 Bridge and Rail Projectwere due for corrosion repair. Fortunately, because ofthe protection provided by the galvanized coating onthe railing panels, highway traffic damaged only 15-20percent of the more than 300 tons of steel that wouldneed replacement in the repair. The specifier had learnedmany states have been taking old guardrail, stripping,regalvanizing, and returning it to service - so MDOT

decided to regalvanize the existing steel guardrail panels.

MDOT felt recycling the existing steel was an excellentopportunity to contribute to the “Keep It Green”initiative being supported by the department. The statesaved more than half of the budget earmarked for thisproject because they only had to replace 20 percent of theold material. This is a great example of the recyclabilityof steel - rather than downsampling at end-of-life, theproject continues on using the original steel. Hot-dipgalvanized steel provided this project with cradle-to-cradle sustainability, as well as durable, maintenance-free protection.

Sustainability

M-102 Bridge Rail ReconstructionDetroit, Michigan

(recycling/disposal). LCAs have begun togain favor in the speci cation community asa means of gauging a product’s sustainability.In 2008, the International Zinc Association (IZA) hired internationally renowned LCA experts Five WindsInternational and PE International toconduct a life-cycle inventory (LCI)and life-cycle assessment (LCA) forhot-dip galvanized steel. Utilizing data from worldwide sources regarding energy consumption and air/fluid/solid emissions measured during zincproduction and during the actualgalvanizing process, combined withanalogous survey data collected fromthe steel industry, an LCA for hot-dipgalvanized steel was compiled.Figure 11 shows an overview of the impact of hot-dip galvanized steel from production toend-of-life.Hot-dip galvanizing is unique in that all material and energy inputs and emission outputs are isolated to the productionphase, as there is no maintenance required for 70 years ormore in most environments, and it is 100% recyclable atthe end-of-life. Te AGA’s publicationHot-Dip Galvanizing

for Sustainable Designhas more information on galvanizedsteel’s sustainability, including the full LCA study.

economic advan tagesIn addition to building structures that are environmentally-friendly, for true sustainability these structures must also beeconomically responsible for future generations. Hot-dipgalvanized steel can provide economic savings both initially and throughout the life of a project, freeing up money fornew construction rather than costly maintenance.

Tere has long been a perception in the specifyincommunity that hot-dip galvanized steel is cost prohibiton an initial basis. However, due to regular proceimprovements, galvanized steel is not only competitive often less expensive than other corrosion protection systeinitially. Furthermore, because of quick turnaround anerection, utilizing hot-dip galvanized steel often provi wider-ranging cost savings during construction.Tough initial cost is important, analyzing the costthroughout the life of the project provide a mocomprehensive cost picture for future generations. Life-cycost (LCC) takes into account not only the initial cost, but thdirect maintenance costs throughout the life of the structuand the time value of money over the project life utilizing present value (NPV) and net future value (NFV) calculatio




Specifying

Because hot-dip galvanized steel provides decades of maintenance-free corrosion protection, often the initial cost is the nal,life-cycle cost. Evaluating LCC can be cumbersome, so to facilitatethe analysis, the AGA developed the Life-Cycle Cost Calculator atgalvanizeit.org/galvanizingcost/. Te online calculator allowsusers to input the parameters for a project and compare the initialand life-cycle costs of hot-dip galvanizing to more than 30 othercorrosion protection systems based on published cost data. Formore information, visit the online calculator or read the AGA’s

publicationHot-Dip Galvanizing Costs Less,Lasts Longer.

hot-dip galvanizingOnce the decision has been made to specify hot-dip galvanizedsteel, it is important to open the lines of communication betweenthe speci er, fabricator, and galvanizer. Communication early in the design process is key to producing optimum quality galvanized coatings, minimize cost, and improve turnaroundtimes. Corrosion protection begins at the drawing board, andincorporating appropriate design details and principles willensure success. Te AGA’s publicationT e Design of Products toBe Hot-Dip Galvanized after Fabricationprovides informationbased on well-established speci cations.Tere are three main speci cations that govern the coating thickness, adherence, and nish for hot-dip galvanizedcoatings – AS M A123, A153, and A767. A123 is the mainspeci cation, and covers all types of galvanized productsexcept fasteners and small parts which are covered by A153,and reinforcing steel bars, covered by A767. Tere are a handful of supporting speci cations referenced in thesespeci cations that cover design practices, repair and touch-up,and painting over galvanizing. In conjunction with AS M,the AGA publishes a compilation of these speci cations,

Selected Speci cations for Hot-Dip Galvanizing, which can bepurchased from the AGA.

Conclusion As the world continues to evolve, so too do the speci cationpractices and designs of construction. Developers of thebuilt environment shoulder the responsibility of creating a better world for future generations by constructing buildings,infrastructure and other elements that are sustainable. Hot-dip galvanized steel, which has been used successfully for more than 100 years, provides sustainability throughits superior corrosion protection, durability, longevity,availability, and versatility. Te natural, recyclable mattegray nish of hot-dip galvanized steel transcends time withlittle environmental and economic impact, improving thequality of life in the future.



American Galvanizers Association6881 South Holly Circle, Suite 108Centennial, Colorado 80112Phone: 720-554-0900Fax: [email protected]

Paper. Hot-Dip Galvanizing for Corrosion - AGA

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