HDGASA V2E4.pdf

2005 Volume 2 Issue 4HOT DIP GALVANIZERS ASSOCIATION Southern Africa25Featuring:Duplex coatings – “Save the surface... and you save all”“World of hot dip galvanizing around us”Eskom Hot Dip Galvanizing Awards Evening3 Duplex coating case histories

HOT DIP GALVANIZERS ASSOCIATION Southern AfricaFeaturing:Duplex coatings – “Save the surface... and you save all”“World of hot dip galvanizing around us”Eskom Hot Dip Galvanizing Awards Evening3 Duplex coating case histories2005 Volume 2 Issue 425HOT DIPGALVANIZINGOfficial journal of the Hot Dip Galvanizers Association Southern Africa • 2005 Volume 2 Issue 4CONTENTSISSN 1023/781XTODAY25The Association is a technicalinformation centre established forthe benefit of specifiers,consultants, end users and itsmembersPUBLISHED BY:Hot Dip Galvanizers AssociationSouthern AfricaQuality House, Unit U4,St. Christopher Road,St.Andrews, BedfordviewP.O. Box 2212 Edenvale 1610Tel: (011) 456-7960Fax: (011) 454-6304Email: hdgasa@icon.co.zaWebsite: www.hdgasa.org.zaSaskia Salvatori:Office ManagerEmail: hdgasa@icon.co.zaHeather Geere:Marketing Co-ordinatorEmail: heather@hdgasa.org.zaBob Wilmot:Executive DirectorCell: 082 325 8840Email: bob@hdgasa.org.zaTerry Smith:Editor & Technical MarketingDirectorCell: 082 893 3911Email: terry@hdgasa.org.zaWalter Barnett:Executive ConsultantCell: 082 891 5357Email: hdgasa@icon.co.zaSUB-EDITOR, ADVERTISING &SALES:Anne van VlietTel: (011) 462-5073Cell: 082 775 0711Email: mwvliet@mweb.co.zaDESIGN AND LAYOUT:Sandra AddinallTel: (011) 868-3408Fax: (011) 900-1922Email: graphicset@iafrica.comREPRODUCTION ANDPRINTING:Camera PressTel: (011) 334-3815Fax: (011) 334-3912Email: cpress@iafrica.comAdvertisers’ Index.................................................................................................................................................... 49RegularsExecutive Director’s Comment........................................................................................................................................ 2Note from the Editor ........................................................................................................................................................ 2Miss Conceptions ................................................................................................................................................................ 44Personality Profile ................................................................................................................................................................ 45Guest Writer ........................................................................................................................................................................ 46Walter’s Corner .................................................................................................................................................................. 47Member’s News.................................................................................................................................................................... 48Case History N°5................................................................................................................................................................ 55Case History N°6................................................................................................................................................................ 56Case History N°7................................................................................................................................................................ 57Feature – Duplex Coatings“Save the surface... and you save all” .............................................................................................................................. 6Duplex systems – a view from the HDGASA .............................................................................................................. 7Summary of testing the benefits of a duplex system (hot dip galvanizing plus paint) vs an allpaint system .......................................................................................................................................................................... 14Planning the duplex system for Goedehoop Colliery ................................................................................................ 16A paint applicator’s view on duplex coating systems.................................................................................................. 17Surface preparation for duplex coating systems – chemical pretreatment .......................................................... 22Surface preparation for duplex coating systems – mechanical pretreatment ...................................................... 23Duplex protection for a transmission line erected in an agressive environment ................................................ 24How to avoid premature failure of paint coatings applied to hot dip galvanized steel incorrosive coastal environments........................................................................................................................................ 25Some miscellaneous duplex coating applications ........................................................................................................ 27Zinc primers – an overview.............................................................................................................................................. 28Duplex coatings using powder paints ............................................................................................................................ 31Re-establishment of the Duplex Committee ................................................................................................................ 33Another yard stone, another day – O-line duplex is definitely the way ................................................................ 35Feature – “The world of hot dip galvanizing around us”Federation Square – Australia .......................................................................................................................................... 36Grand Arbour – Australia .................................................................................................................................................. 38Isabel II Park, Palencia – Spain .......................................................................................................................................... 40A snapshot of what is going on in North America...................................................................................................... 42GeneralEskom Hot Dip Galvanizing Awards Evening 2005...................................................................................................... 4Reader’s Comments ............................................................................................................................................................ 34HDGASA Information Disk .............................................................................................................................................. 49IZASA supports southern Africa architect’s competition .......................................................................................... 50“Road Shows” on the benefits of using hot dip galvanized rebar planned for 2006 .......................................... 52Adding value to steel for 40 years .................................................................................................................................. 53The “honest coating” stands up to its name ................................................................................................................ 54Front Cover: A kaleidoscope of various duplex coating photographsHot Dip Galvanizing – Adding value to Steel

PROUDLY SUPPLYING SOUTH AFRICA’SSTRUCTURAL STEEL REQUIREMENTS FOR AVARIETY OF PROJECTSHEAD OFFICE: STEELWORKSP.O. Box 111 Witbank 1035, Mpumalanga, South AfricaTel.: National (013) 690 9911 International +27 13 690 9911Fax: National (013) 690 9033 International +27 13 690 9033DOMESTIC SALESP.O. Box 994 Bedfordview 2008, Gauteng, South AfricaPellmeadow Office Park, Block B – 1st Floor,60 Civin Drive, BedfordviewTel.: National (011) 454 1583 International +27 11 454 1583Fax: National (011) 454 0705 International +27 11 454 0705(011) 454 0576 +27 11 454 0576EXPORT SALES & ORDER SERVICES,STEELWORKSP.O. Box 111 Witbank 1035, Mpumalanga, South AfricaTel.: National (013) 690 9016 International +27 13 690 9016Fax: National (013) 690 9063 International +27 13 690 9063

Eskom Hot Dip Galvanizing Awards Evening 20054 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Duplex systems – a viewfrom the Hot DipGalvanizers AssociationSouthern Africaby Bob Wilmot, HDGASAFeature – Duplex CoatingsThe leadersin duplexcoatingsystemsSIGMACOATINGSIntroductionIt has been estimated that corrosion ofsteel components and structures costSouth Africa approximately R4.5 to R5billion per year. This figure representssome 5.2% of our annual GDP. It istherefore clear that corrosionprotection systems, no matter in whatform they come, have the potential ofsaving the country substantial amountsof money. It also follows that thedesign and selection of suitablesystems will likewise lead to costsavings. It is unwise to develop andbase projects on initial costs withouttaking into account the long-termmaintenance requirements andassociated costs. It is likewise alsonecessary to match corrosion designsto service life, or in other words avoidboth under and over designing in termsof the corrosion protection. There aremany and varied corrosion protectionsystems available to the engineer orproject developer. It requiresexperience and a basic understandingof corrosion science in order to ensurethe selection of the most cost effectivesystem to suit the project. This shouldinclude "value analysis" and life timecosts involved in the protection of onesinvestment.Duplex coatingsThis paper sets out to consider aspecific type of corrosion protectionsystem, which is referred to as aDuplex system. The dictionarydescribes a duplex system asconsisting of two elements or a"twofold" composition. The duplexsystem described in this paper is sucha two-part corrosion protectioncoating, viz, hot dip galvanizing as thefirm base or primer, followed by aselection of (1 to 3 or 4) top paintcoatings to suit environmentalconditions. In principle, the duplexsystem is designed as a cost effectiveand balanced, designed coating,considering environmental conditionsand service life requirements.Fundamentals of the duplexsystemBriefly reviewing fundamentals thatconstitute the individual coatings, i.e.hot dip galvanizing and paint, of aduplex system, we will highlight thebenefits that such component partsplay within the corrosion protectioncoating.Fundamentals of a paint coatingPreparation paramount to successIn order to achieve a quality corrosionprotection system, the surfacepreparation of the steel to beprotected, no matter which system isto be used, is of paramountimportance to the success and longtermperformance of the coating. Agood protective paint system is asdependent on this requirement as thatof any other system. Too often thisaspect is overlooked resulting in lessthan adequate results. Generally theaccepted cleaning method for a goodpaint system is the use of "abrasiveblasting" to a specification of SA2 1 /2.The cleaning process is required toremove mill scale and products ofcorrosion such as ferrous oxide orDoesyour zincseem nakedin corrosiveenvironments?SIGMA COATINGS DESIGNSPECIFICATIONS FOR:Chloride attackCoal dust corrosionAggressive chemicalsAcid rainCoastal conditionsWet areasAlrode: (011) 389 4800Durban: (031) 205 3586PE: (041) 368 8066CT: (021) 511 2220www.sigmacoatings.co.za/.comCBT (011) 868-3408 SC1020/10/05

Feature – Duplex Coatingswhat is referred to as red rust. Failureto carry out this vital cleaningoperation will result in an inadequatepaint coating and hence less thanspecification requirements.Eta η layerMechanical bondingPaint relies on "mechanical bonding"or a process of the paint being "keyed"to the surface roughness of the steelbeing coated. Abrasive blasting aidsthis aspect in that the steel surface isroughened by the mechanicalcleaning action of the shot impactingthe steel. In addition, an etchingprimer is likewise employed, again inorder to key the paint coating to thesteel. Should the cleaning operationbe inadequate, loose particles and/orcontaminants remain, affecting themechanical bonding.Barrier protectionCorrosion protection of a paintsystem relies on a "neutral barrier"being introduced between the steelthat is to be protected, and thecorrosive environment. Thick coatings,coupled with permeability, uniformityand continuity of the paint system,i.e. "barrier protection" achieve greatercorrosion protection. Paint coatingsare generally reliant on "barrierprotection" as the first and only "Lineof Defence" against a corrosiveenvironment. Once this barrierprotection is breached (throughcoating damage or porosity),corrosion of the underlying steel cancommence resulting in corrosioncreep, blistering and ultimatelyspoiling off of the paint.Limited Cathodic Protection (CP)Limited cathodic protectionwithin a paint system is dependent onthe mixing in of an "electro-negativeto steel" metallic powder, such asaluminium or zinc, to form part of thepaint matrix. Specifications call for upto 90% metallic particles in the dryfilm thickness (DFT) of a paint coatingin order to claim any form of cathodicprotection. CP in paint remainsquestionable, due in the main to themake-up of the final composition ofthe coating.60 to 80μmbarrierprotectionBarrier protection – 1st line of defenceNo Type of paint (vehicle basis) a b c d1 Acrylic resin dispersions (1) F–G F–G G G2 Acrylic/styrene resin dispersions (2) G G G VG3 Acrylic/di-isocyanate (2-component) compositions G F G VG4 Vinyl resin copolymer F F G G5 Polyvinyl/acrylic resin combinations G G G VG6 Polyvinyl resin dispersions (3) F F–G G F–G7 Epoxy resin (2-component) (4) G G G VG8 Epoxy ester (5) P F G G9 Epoxy resin/coal tar combinations P F F G10 Polyurethane resin (2-component) (6) P F F–G GP = poor adhesion; F = fair (moderate) adhesion; G = good adhesion; VG = very good adhesion.a = freshly hot-dip galvanized steel, within approximately 4 hours of galvanizing.b = hot dip galvanized steel weathered for 1–3 months in a non-aggressive atmosphere.c = hot dip galvanized steel, cold-etched or hot-phosphated.d = hot dip galvanized steel sweep-blasted.(1)Aqueous dispersion of acrylic resin.(4)Epoxy resin with polyamide hardener.(2)Aqueous dispersion of acrylic/styrene resin.(5)Epoxy resin, esterified with dehydrated castor oil.(3)Aqueous dispersion of polyvinyl resin.(6)With an encapsulated di-isocyanate hardener.Table 2: Adhesion of air-drying paints to hot dip galvanized steel surfaces.Zeta ζ layerDelta δ layerGamma τ layerSteelFigure 1: Micrograph (x 200 mag.) of a hot dip galvanized coating, illustrating the various zinc/ironlayers and the metallurgical bonding that is formed between the coating and the steel.Reference: Duplex Systems, JFH van Eijnsbergen, Elsevier –1994.8 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsGALVANIC SERIES OF METALSELECTROPOSITIVEMore noble metalsELECTRONEGATIVELess noble metals• Gold• Silver• Stainless Steel (18/8)• Nickel• Monel (2/3Ni, 1/3Cu)• Aluminium Bronze (95%Cu, 5%Al• Copper• Brass• Tin• Lead• Cast Iron, unalloyed• Steel, low-alloyed• Carbon Steel, rolled• Cadmium• Aluminium• Zinc• MagnesiumTable 3. Galvanic series of metals which showszinc being electro-negative to steel and hencethe zinc is the anode with steel being thecathode in a typical corrosion cell.Typical paint systemsZn will protect steelZn is electro-negative to carbon steelThere is a large range and variety ofpaints, which start with single coatsystems and move up in quality andcost to very effective and sophisticatedsystems. This paper reviews a "top paintsystem", comprising Inorganic Zinc +Epoxy + Polyurethane in comparison tothe Duplex System.Chemical bonding (followsmetallurgical laws)Hot dip galvanized coatings are formedas a result of metallurgical laws, i.e. thebond formed between the steel and thehot dip galvanized coating is describedas a "chemical" bond, which is superiorto that of mechanical bonds. A furtherbenefit resulting from the metallurgicalprocess is the formation of abrasionresistant iron zinc alloys. In addition,the zinc iron alloy layers provide anestimated 30% improvement in theatmospheric corrosion protectionproperties of the coating. (ReferencePorter "Corrosion Resistance of Zincand Zinc Alloys" page 62, ref No.2).Figure 1 is a micrograph illustrating theformation of the zinc/iron alloy layersthat provide the bonding of the coatingto the steel substrate.Barrier protection (1st line of defence)Similar to a paint system, hot dipgalvanizing utilizes "barrierprotection" as its first line of defence,i.e. it forms a barrier between thesteel and the corrosive environment.However, unlike a typical paintsystem, barrier protection is the 1stline of defence, followed by a 2nd lineof defence, viz, Cathodic Protection(CP). It is important to understandand appreciate that the thicker thebarrier protection the greater thecorrosion protection that is provided.Cathodic protection (2nd line ofdefence)Two dissimilar metals in electricalcontact with each other, within anelectrolyte, an electrical current flowsbetween them, referred to as a Bimetalliccouple. Current passes fromthe anode (zinc), which "sacrificesitself" to protect the cathode (steel)(see figure 2). This is known ascathodic protection of the cathode bythe anode. In other words, we usephysics of the corrosion cell (bimetalliccouple), as a weapon to combat theonset of corrosion of the material thatwe use in our steel structures.The corroding anode is electro-negative(zinc) to the cathode (steel). Thisphenomenon of physical laws allowsFundamentals of a hot dip galvanized coatingPreparation paramount to successAgain preparation is paramount to thesuccess of the final corrosion protectioncoating. Preparation of steel, to be hotdip galvanized, is carried out in a factorycontrolled environment in whichchemicals are the principal cleaningagents employed to ensure allsurfaces are prepared for galvanizing. Itis fundamental for the hot dipgalvanizing, if the steel is notadequately cleaned it will not galvanize.We refer to hot dip galvanizing as an"honest coating" in that the cleaningoperation, i.e. the pre-treatmentpreparation, if not carried out to aquality standard, the steel will not hotdip galvanize and uncoated areas willimmediately be evident at the end ofthe process.Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 9

Feature – Duplex Coatingsfor the confident prediction as to whichmetals will be cathodic or anodic whenplaced in a corrosion cell or a "bimetalliccell". Table 3 lists a selectednumber of these metals and is used toexplain why zinc will "sacrifice" itself inorder to protect carbon steel.Self healing characteristics of zincZinc corrodes forming three products ofcorrosion, viz, zinc oxide, zinchydroxide, these being unstable andthe third stable "barrier protection" ofzinc carbonate. Should the hot dipgalvanized coating be damaged so asto expose the underlying steel,cathodic protection of the zinc willsacrifice itself so protecting theexposed steel. In addition, the zincproducts of corrosion tend to seal theexposed surface and so re-establish thebarrier protection. This characteristic isused very effectively when we considera duplex system, using paint incombination with hot dip galvanizing.What is a duplex coating?Having individually considered thefundamentals and characteristics ofpaint and hot dip galvanizing ascorrosion protection systems, we cannow evaluate the two systems acting incombination. We refer to such a systemas a Duplex coating, i.e. hot dipgalvanizing as the primer or firm baseon which a suitable top paint coatingor coatings can be added. The result, interms of corrosion protection, is a"synergistic" effect. Synergistic isdefined as the interaction orcooperation of two or more products,acting in unison to produce a new orenhanced effect compared to theirseparate effects.How does a duplex systemwork?When hot dip galvanizing (zinc andzinc/iron alloys) is used as the primeror "firm base" on which to apply thetop paint coating/s, we use theadhesion characteristics of hot dipgalvanizing and its metallurgicalbonding to steel. In addition, shouldthe top paint coating/s be damaged or,with time, become porous, the zincDamage sealed byproducts of corrosionFigure 2: Protection of steel by zinc in the case of hot dip galvanizing – cathodic protection 2nd lineof defence.1 2 3 4 5 6 7MAINTENANCE FREE LIFE OF THE COATINGCorrosion Description of Corrosion rate Corrosion rate Continuously hot Hot dip DUPLEXcategory environment (av. loss of (ave. loss of dip galvanized galvanized COATING SYSTEMsteel in µm/yr.) zinc in µm/yr.) sheeting coating (85µm) Hot dipCoating class – Steel thickness galvanizing +Z275 ≥ 6mm an appropriate(±20µm)paint systemNot required forC1 Interior: dry ≤ 1.3 ≤ 0.1 >50 >50 #1 corrosionprotection #2Interior:occasionalNot requiredC2 condensation > 1.3 to 25 0.1 to 0.7 >40 >50 #1 for corrosionExterior: exposed protection #2rural inlandC3Products of corrosionZnO.ZnCO3Steel (Fe)CathodeZinc (Zn)AnodeInterior:high humidity,Not requiredsome air pollution > 25 to 50 0.7 to 2.1 10 to 40 >40 for corrosionExterior: protection #2urban inland ormild coastalInterior:Coating life inswimming pools,columns 5 & 6, plusC4 chemical plant, etc. >50 to 80 21 to 4.2 5 to 10 20 to 40 the paint lifeExterior:multiplied by aindustrial inlandfactor of at leastor urban coastal 50%Exterior:Coating life inC5-I industrial with columns 5 & 6, plusor high humidity or >80 to 200 4,2 to 8,4 2 to 5 10 to 20 the paint lifeC5-M high salinity multiplied by acoastalfactor of atleast 50%#1 Although mathematically incorrect (coating thickness divided by the corrosion rate), the maintenance free life indicated in column 6 has for practical purposesbeen curtailed to a maximum of 50 years.General hot dip galvanizing specifications state the local (minimum) and the mean coating thicknesses. The coating thickness actually achieved, varies withthe steel composition and this can range from the minimum to at least 50% greater.As life expectancy predictions are normally based on the minimum coating thickness, they are usually conservative.#2 A duplex system may also be specified in order to provide a colour for aesthetic reasons.Note 1: The specification does not stipulate a maximum upper coating thickness limitation, however, excessively thick coatings on threaded articles are undesirable.In order to ensure effective tensioning, the coating thickness on the bolt should not exceed a maximum of 65µm, this applies particularly to high strengthbolts. See note 2.Note 2: The coating thickness referred to in the Association’s booklet, "Steel Protection by Hot Dip Galvanizing and Duplex Systems" in chapter 10 page 33 statesthis maximum to be 90µm. This is incorrect and should be amended to read 65µm.Where the service life of the coating is based on the coating thickness on the structure, all hot dip galvanized fasteners should be over coated with anappropriate paint system (duplex coating) in order to derive a similar life to that of the structure.Note 3: The loss values used for the corrosivity categories are identical to those of ISO 12944 part 2 and SANS 14713 (ISO 14713).Note 4: In coastal areas in hot humid zones, the coating thickness loss can exceed the limits of category C5-M. Special precautions must therefore be taken whenselecting a protective coating system for steel structures in such areas.Table 4: Atmospheric corrosivity categories and examples of typical environments taken from ISO 9223.products of corrosion will tend to sealsuch porosity in the top paint coatingand thereby re-establish the barrierprotection. In effect this provides thecorrosion protection system with a 3rdline of defence against the corrosiveenvironment.Where paint is applied direct onto thesteel and the barrier protection (1st10 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsDamage or porosity is sealed byZn products of corrosionBarrier protection re-establishedZn products of corrosion (ZnO.ZnCO3)Top paint coatingSteel (Fe)CathodeZinc (Zn)AnodeFigure 3: Protection of steel by a duplex system – hot dip galvanizing plus an appropriate paint system.line of defence) is breached allowingcorrosion of the underlying steel, thesteel products of corrosion, being farmore voluminous than the steel fromwhich they are formed, the paintcoating is subjected to stresses leadingto blistering and spalling off of thepaint (corrosion protection barrier).This process does not take place whenhot dip galvanizing is used as theprotective coating due to the fact thezinc products of corrosion are far lessvoluminous and hence does not resultin blistering or spalling off of thegalvanized coating. In addition,cathodic protection, characteristic ofzinc, prevents corrosion creep.When we use these characteristics ofhot dip galvanizing and anappropriate paint system employed incombination, we achieve thesynergistic effect, which is illustratedin figure 3.In order to further establish ameasure of the service life of a duplexsystem, we can use the followingsimple formula to calculate the neteffect:Duplex Service Life= Factor x (HDG Life + Paint Life)= 1.5 x (9years + 5 years)= 21 years to 5% red rustFactors used for differentEnvironments are listed below:◆ Industrial + marine 1.8 to 2.0◆ Sea water (immersion) 1.5 to 1.6◆ Non-aggressive climate 2.0 to 2.7Paint is not there to protect the hotdip galvanizing (zinc), but rather thehot dip galvanizing is there to supportthe paint when it starts to fail!Again preparation is paramountto successAs is the case of all types of coatings,the surface preparation is paramountto the success of the coating.Preparation of the steel, for galvanizing,is carried out in a plant environmentand this together with the fact that hotdip galvanizing is "an honest coating",ie. if the steel is not clean, it will notgalvanize, we are assured of the zinccoating to the steel. Preparation for theGALVATECH HOT DIP GALVANISERSduplex system concerns thepreparation of the hot dip galvanizedsurface suitable to accept the top paintcoating/s.Two forms of the zinc surfacepreparation are recommended, being:1. SWEEP blasting and NOT normalabrasive blasting2. Chemical cleaning.In the case of both methods thecleaning objective is the removal of allsurface contaminants, ie. passivatingsolution, products of corrosion and oilor grease, etc. The principal of; "if it isnot clean, it will not coat". Unlike thehot dip galvanized coating, paintrequires a surface into which it can bekeyed, ie. to be mechanical bonded tothe surface, in this instance, zinc.Once the zinc surface has beenprepared, by one of the two methodsindicated, the paint primer, beingGALVATECHHot dip galvanizingShotblastingIndustrial spray-paintingBest service andquality guaranteedTechnical assistanceby qualified engineersMembers of the Hot DipGalvanizers AssociationGalvanizing to SABSISO 1461 (SABS 763)HOT DIPGALVATECHGALVANISERSGALVATECH (Pty) Ltd Hot Dip GalvanisersSacks Circle, BelvilleTel: 021-951-1211CFax: 021-951-3400Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 11

Feature – Duplex Coatingscompatible with zinc, must followshortly in order to avoid the renewal ofcontaminants. This requirement is toooften overlooked resulting in prematurecoating failure and the consequentimpression that a duplex system isflawed. As with any paint system,preparation and correct application iscritical to the long-term performance ofthe system. This requirement applies inequal proportion to the application ofthe paint coating/s in the duplexsystem.One might illustrate a duplex system interms of a military battle, with corrosionbeing the enemy and our forces beingconstituted in terms of defence indepth, as well as an all-round defence.Duplex Coating Service LifeAs is the case with all types of corrosionprotection coating systems, the servicelife of the product is dependent on twobasic considerations, viz, the type ofcoating and, as important, theenvironment in which the coating isdesigned to operate.The question of the service life of aduplex coating system is illustrated interms of ISO 9223, which is similar tothe ISO 12944 specification. Thesespecifications set out to broadly definethe environment in terms of C1 (abenign environment) through to a C5Ior C5M (being severe corrosiveconditions). Using this specification,table 4 has been developed.In all of the foregoing discussion, wehave simply considered PAINT, withoutspecific reference to the number or typeof paint coating/s. This approach hasbeen adopted due to the fact that thereare many types and combinations ofpaint coating/s. We briefly referred toInorganic zinc + epoxy + polyurethaneas a very good paint system. Asuggested duplex system, that is anequivalent to such a paint system,would be to replace the paint primerwith that of hot dip galvanizing,followed by a compatible epoxy primerand a final top coating of polyurethaneto achieve an aesthetical appeal and toprotect against UV attack. In this systemwe would have the adhesion of hot dipgalvanizing to the steel followed by thepossibility of a number of differentPaint (film) CharacteristicsReference: Duplex Systems, JFH van Eijnsbergen, Elsevier –1994.Table 5: Adhesion of air-drying paints to hot dip galvanized steel surfaces.paint coatings selected to suit specificenvironmental conditions.ConclusionA Duplex system uses the strengths ofboth hot dip galvanizing and selectedpaint coatings to compile an enhanced"synergistic new performance" coating,which is cost effective where "valueanalysis", long term maintenance costsare taken into consideration, and asystem that will perform in severecorrosive environments.Types of paint mentioned in Fig. VI-11 2 3 4 5 6 7 8 9 10Application (a) B/S B/S S S S S/B S S S SDrying (b 1 ) Av Av Av Sh Sh Av Av Av Av AvHardening (b 2 ) Lo Lo Av Av Av Lo Av Av Lo AvHardness F F/G G/VG G G F G F/G F G/VGFlexibility G G G G G G F/G F/G G GImpact resistance G G/VG VG G VG G G G G VGGloss (retention) (c) F F VG P F F P F P VGColour fastness (d) VG VG VG P F F F F – VGPot stability (e) G G P VG VG G P G P PThermal resistance (f) F F G P F F F F P GWeather resistance (g)Rural climate VG VG VG VG VG VG VG VG P VGMarine climate F VG VG VG VG G VG G G VGIndustrial climate F F G G VG G VG F VG GChemical resistance (h)Acid solutions P F G G G F VG F VG GAlkaline solutions P P F G G P G P VG VGAdhesion see comparative values in table 2(a) B = mainly by brush; S = mainly by spraying or by continuous rolling.(b 1 ) Sh = short (less than I hour); Av = average (between 1 – 4 hours); Lo = long (4 – 12 hours);(drying depends on film thickness, temperature and humidity of surrounding air).(b 2 ) Sh = short (through-hardening within 3 hours); Av average (through-hardening within 1 – 7 days);Lo = long (through-hardening in 7 days or more).(c) Indications F and P mainly refer to chalking.(d) Indications F and P mainly refer to yellowing.(e) VG = 6 months and more at room temperature; G = 6 – 9 weeks at room temperature;F = approximately 4 weeks at room temperature; P = less than 36 hours (after addition of hardener).(f) VG = permanent at 50 – 150°C; G = permanent at 50 – 75°C; F = for short periods at 50 – 75°C only;P = up to 50°C only.(g) Loss of gloss and/or colour not counted.(h) Dependent on duration of immersion, concentration and temperature of aqueous solution.Surface preparation is a criticalfactor to the success of the coating’sperformance and as such, must notbe overlooked in terms of thespecification, as well as at the timeof the application.Although the paint coating systemsthat have been referred to and testedin this feature are excellent, it isalways wise when selecting a paintsystem, to discuss the relevant systemwith the applicable paintmanufacturer.12 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsSummary of testing the benefits ofa duplex system (hot dip galvanizingplus paint) vs an all paint systemA number of different coating systems were compared during a recent 4 000 hour accelerated weathering test,the article addresses only the conclusion and recommendations.For purposes of discussion and comparison we haveselected four specific coatings as indicated below. Inthese comparisons we wish to highlight the benefit ofusing hot dip galvanizing, with it’s metallurgical bondingto steel, as a superior form of primer for the subsequentpaint coatings.The discussion that follows will examine coatings 2 and11 and 3 and 8. These specific coatings have been chosenon the basis that they will be used in corrosiveconditions, classified in terms of ISO 9223, for class C4and C5 type environments.Evaluating the "top range" of coatings thatwould be employed in a C5 environment.Comparison No.1 (Sample Nos. 2 and 11)2. Hot dip galvanized + epoxy primer + epoxy MIO +polyurethane acrylic enamelcompared to11. Abrasive blast + inorganic zinc primer + modifiedaluminum epoxy mastic + cross-linked epoxy +aliphatic acrylic polyurethaneWhere the two samples have been cross scribed andexposed for 4 000 hours in a salt environment, one can seethe effect of corrosion. In the case of the hot dip galvanizedprimer (sample 2, on the left), the exposed steel is beingprotected by the cathodic protective properties of zinc, ie.zinc is electro-negative to steel, and where the zincproducts of corrosion have the tendency to seal the crossscribing with no red rust in evidence. With sample 11, onthe right, where an inorganic zinc rich primer has beenused as the base coat, little or no cathodic protection is inevidence and the exposed steel has developed red rust.Comparison No.2 (Sample Nos. 3 and 8)3. Hot dip galvanized + epoxy primer + polyurethanecompared to8. Abrasive blast + inorganic zinc + epoxy primer +polyurethaneAgain where the two samples have been cross scribedand exposed for 4 000 hours in a salt environment, onecan see the effect of corrosion.In the case of the hot dip galvanized primer (sample 3, onthe left), the exposed steel is being protected by theSample No. 2Sample No. 11Sample No. 3 Sample No. 8Comparison No. 1: Cross scribing after 4 000 hours salt sprayexposureComparison No. 2: Cross scribing after 4 000 hours salt sprayexposure14 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex Coatingscathodic protective properties of zinc. The zinc productsof corrosion have the tendency to seal the cross scribingand hence no red rust is in evidence.With sample 8, on the right, where inorganic zinc hasbeen used as the primer, little or no cathodic protectionis in evidence and the exposed steel has developed redrust. In addition there is significant indications of the toppaint coating becoming porous and developing cracking.The conclusions reached as a result of this study are notintended to detract from the undoubted durableperformance of the paint system incorporating aninorganic zinc rich primer. The results obtained dohowever highlight the significant benefits that can bederived by applying a hot dip galvanized coating beneatha similar heavy-duty organic paint system. Use is made ofthe metallurgical bonding of galvanizing to the steel, thebarrier and cathodic protection of zinc and the barrierprotection of paint. In terms of a C4 and C5 environment,hot dip galvanizing has a limited service life potential, asdoes a paint system when used separately. The twosystems used together as a Duplex system interactresulting in a Synergistic Effect.Estimated Cost Comparison(Based on 8mm steel at 31.85m 2 /ton)2. Hot dip galvanized + epoxy primer + epoxy MIO + polyurethaneacrylic enamelHot dip Epoxy Epoxy Polyurethane Totalsgalvanized primer MIO acrylic enamelR1 900/ton R640/ton R800/ton R960/ton R4 300/tonR59.65/m 2 R20.09/m 2 R25.12/m 2 R30.14/m 2 R135.00/m 211. Abrasive blast + inorganic zinc primer + modified aluminum epoxymastic + cross-linked epoxy + aliphatic acrylic polyurethaneAbrasive Inorganic Modified Cross-linked Aliphaticblast zinc aluminum epoxy acrylic Totalsepoxy masticpolyurethaneR960/ton R960/ton R960/ton R640/ton R960/ton R4 480/tonR30.14/m 2 R30.14/m 2 R30.14/m 2 R20.09/m 2 R30.14/m 2 R140.66/m 2Estimated Cost Comparison(Based on 8mm steel at 31.85m 2 /ton)3. Hot dip galvanized + epoxy primer + polyurethaneWhat we learnt from these tests!◆Zinc rich paints do not provide long-term cathodicprotection on exposed edges.Hot dip galvanized Epoxy primer Polyurethane TotalsR1900/ton R640/ton R960/ton R3500/tonR59.65/m 2 R20.09/m 2 R30.14/m 2 R109.88/m 2◆◆◆◆◆Zinc and Aluminium metal spraying and hot dipgalvanizing do provide long- term cathodic protectionon exposed edges.Hot dip galvanizing on its own is insufficient for longtermprotection, in extremely aggressiveenvironments.The paint coating of a duplex coating for aggressiveenvironments should be at least 150µm DFT.Make use of the HDGASA Codes of Practice whenpreparing for and evaluating duplex coatings.Make use of HDGASA for advice on duplexcoatings.8. Abrasive blast + inorganic zinc + epoxy primer + polyurethaneAbrasive blast Inorganic zinc Epoxy primer Polyurethane TotalsR960/ton R960/ton R640/ton R960/ton R3 520/tonR30.14/m 2 R30.14/m 2 R20.09/m 2 R30.14/m 2 R110.51/m 2Total coating thickness readings before and after4 000 hour testTotal coating thickness readings (μm)Min Mean MaxSample 2 Before test 190 212 224After test 205 246 292Sample 11 Before test 376 399 435After test 292 347 423It again goes to prove the saying that was firstenunciated by a certain knowledgeable expertfrom the paint industry: Hot Dip Galvanizingrepresents the best form of primer fora paint system!Sample 3 Before test 156 163 170After test 128 145 155Sample 8 Before test 180 195 213After test 254 267 278Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 15

Feature – Duplex CoatingsPlanning the duplex system forGoedehoop CollierySome ten years ago, the authorities atGrooteluk Colliery requested BraamBosman, a corrosion consultant, toundertake a survey in order to identifythe level of general corrosion thatcould be expected throughout themine as well as specific sites wheresevere corrosion could be anticipated.This assignment included the need toprovide a detailed specification forcorrosion control.The study included chemical analysisof process waters as well as anassessment of the calorific values ofthe grades of coal to be processed.Based on the results of this survey, acost effective specification wasproposed which was somewhatunique in that a single heavy dutyorganic paint coating (no primer) wasrecommended for application ontoPAINTED STEEL VS HOT DIP GALVANIZED STEELPAINTED STEELAfter some time, rust is formedunderneath the paint film, which onlybecome visible after a longer period ofdiffusion of oxygen and water throughthe paint film.Under-rusting proceeds, followed by lossof adhesion of the paint film because ofthe increased volume of rust products(approximately twice to three times thevolume of the steel from which they havebeen formed)Spread of rust and further loss ofadhesion of the paint film; rapiddestruction of the coating system.Protection by paint coating is almostcompletely gone. Complete derustingbecomes necessary before applying anew paint coating.When loss of adhesion is partial, theoverall protective value of the new paintcoating is very limited.Reference: Duplex Systems, JFH van Eijnsbergen, Elsevier, p. 22 Table 1.Table 6.HOT DIP GALVANIZED STEELFormation of insoluble zinc salts (zincpatina) at the interface by reactionswith oxygen and water. No rust isformed. Pores in the zinc film areblocked by solid volume zinc corrosionproducts.No loss of adhesion of zinc coating.Further blockade of pores by solidvolume zinc corrosion products. Partialcorrosion of the of the eta layer. Alloylayers still remain intact.Corrosion proceeds very slowly. Norust at the interface. Partial corrosionof the zinc layer proceeds. Alloy layersstill remain intact.Zinc coating system is weathered on apart of the steel surface. Still no rust;slow weathering of the alloy layers.Very few pinpoints of rust.Reconditioning is possible and easy.Upon further weathering of the alloylayers, more pinpoints of rust appear,slowly extending into rusty areas.Reconditioning is necessary at thispoint of weatheringsweep blasted hot dip galvanizedsurfaces using an ultra fine garnet“microblast” cleaning abrasive forsurface preparation.The contract for applying this duplexprotective system was awarded toBarloworld Galvanizers and ReefIndustrial Painters who wereresponsible for applying the paintcoating immediately after hot dipgalvanizing at the galvanizerspremises.Braam Bosman and his inspectorswere appointed to undertake routineinspections and surveillance in orderto ensure that the required qualitystandards were adhered to withspecial attention given to loading,offloading and stacking procedures.These control measures were alsoimplemented during site erection.As a result of these comprehensivecontrol procedures, a total coatingdamage factor of less than 2% wasrealised up to completion of theproject.A key to the success of this projectwas the positive teamwork betweenBarloworld Galvanizers, ReefIndustrial Painters and BraamBosman’s inspectorate. The conceptof applying the paint coatimmediately after hot dip galvanizingon the galvanizers premises proved tobe singularly successful.Technical support was provided byWalter Barnett of the Hot DipGalvanizers Association frominception through to completion ofthis successful project.Editors noteThe duplex coating applied at GoedehoopColliery is about ten years old and is featuredas one of the case histories.16 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsA paint applicator’s view on duplexcoating systemsby Mike Book proprietor of Duplex Coatings ccSurface preparation for duplex systemsIn order to apply duplex systems correctly, it is necessary toknow the general characteristics of the hot dip galvanizingprocess, so that one can determine the best method ofsurface preparation. Effective protection by a duplexsystem is only possible if long-term inter-coat adhesion isobtained by means of a paint coating that will not reactchemically with the zinc substrate.Inadequate preparation of the zinc surface, prior to theapplication of a compatible paint system or powder coatingis the main cause of premature failure.Failure to inform the galvanizer that the items will beduplex coated will usually result in the galvanized itemsbeing passivated in a sodium dichromate solution and mayinfluence paint adhesion (see photo overleaf – Adhesionfailure – paint applied to insufficiently treated hot dipgalvanizing) see also #1. Likewise zinc protuberances andlumps which may be acceptable on hot dip galvanized onlysurfaces, will not necessarily be removed if the galvanizer isunaware of the requirements to paint.We have two general types of cleaning:◆◆Mechanical:Sweep blasting; scouring with abrasive paper.Chemical Cleaning:Cold etching and phosphating; hot phosphating;chromating; galvannealing and outdoor weathering.The preferred method of preparation for large contractsconsisting of items of various configurations is the SweepBlast method.CBT (011) 868-3408 DC1022/10/05Specialists in the preparation and painting of hotdip galvanized steel, sweep blasting, abrasiveblasting, tank linings and industrial paintingContact Mike BookTel.: (011) 827-4221 • Fax: (011) 827-4561Cell: 072 782 8853 • Email: bulldogproj@murrob.comP.O. Box 82741 Southdale 2135Genrec Office Park, Cnr Dekema & Nieman Rd,WadevilleSave the surface... and you save allVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 17

Feature – Duplex CoatingsCold etching (phosphating) or the use of “Galvanized IronCleaners” is unreliable for the following reasons:◆◆◆◆◆Labour intensiveTime consumingAreas not etched properlyAreas not rinsed properly resulting in painting overcontaminated surfacesCertain GIC cleaners are not user friendly ie. are noteasy to remove if left on too long and allowed to dry.Sweep BlastingIt is essential that only highly skilled operatives trained inthe aspects of sweep blasting of galvanized items be usedto ensure that the galvanized coating is only decreased toby 8 - 13µm (see figure 5). This reduction in the galvanizedcoating thickness hardly influences the corrosionresistance.N.B Do not sweep blast continuously galvanized sheeting as thegalvanizing thickness is too thin and sweep blasting will damage thegalvanized protection. Chemical clean sheeting to a water break freesurface.(To sweep blast structural steel the air pressure should be setat 1.5 - 2.5 bar using a 6mm nozzle and a fine inert abrasiveeg. garnet. Sweep blasting at between 30 - 45m 2 per hour(blasting mild steel to S.A 2 1 /2 is 8 - 12m 2 per hour at 7 barpressure) from a nozzle distance of 500 - 700mm from thegalvanized surface will provide an ideal key for coating).A detailed code of practice for surface preparation andapplication of duplex systems has been published by theSouth African Hot Dip Galvanizers Association and is freelyavailable.Paints and specifications for duplex systemsThe selection of a coating or coating systems on hot dipgalvanized steel surfaces which have been chemically ormechanical pre-treated or (in some cases) only degreased,depends on four main parameters:a) Increased weather resistance ie. maximum duration ofprotection of an object in the atmosphere versus theaesthetic effect (colour) or vice versa.b) Paint application method to be used on the project.c) Environmental laws and rules regarding compositionand application of paint products.d) Consideration regarding the transport/erection damagerepairs on site.A wide variety of paint products are available nowadays,including powder coatings, water-dispersed paint (aqueouspaint products) epoxys, polyurethanes, vinyls etc., andwhen selecting a coating system the asset owner wouldtake into consideration the following:Adhesion failure – paint applied to insufficiently treated hot dip galvanizing.◆ The type of plant to be constructed.◆ The geographic location of the plant.◆ The natural local atmospheric environment (macroenvironment).◆ The plant operating or process environment (microenvironment).◆ Subsequent maintenance requirements. Certain plantswould be too costly to shut down to carry out generalmaintenance, and therefore these inaccessible areasmust be designed to accommodate the harshenvironment that they are exposed to.◆ Construction program.◆ Economics.All the Project owners’ requirements should be considered,and discussed in the light of these factors, before anyserious attempt is made to make decisions relating to thespecification.Coating specifications in most instances ignore ordisregard specific problems associated with application inthe working area and tend to assume that laboratoryconditions can be achieved “ in situ” and it is thereforeimportant to involve all the “players” ie. the asset owner,the consultant, the paint manufacturer, the galvanizer andthe applicator in the beginning, so that all parties have aclear understanding of the specification requirements.It is also advisable that at the beginning of the contractprogram a sample batch be processed to identify problemsand clarify the standard of the specification.Once all parties have agreed to the standard of theworkmanship, a sample be kept as a reference panel, andused as a bench mark for the contract.Accurate costing is a large contributing factor to thesuccess of a coating system so that the contractor can fulfillall the necessary obligations without the need toeconomise or cut corners.Without a reasonable financial commitment to the coatingspecification all efforts to achieve its inherent high goalswill be worthless.18 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsA system that is designed to fail, will fail.Duplex coating systems offer numerous advantages overcon-ventional coating systems in most applications seetable 1.The durable life expectancy of a typical paint system for a C5M-I environment (Zinc Epoxy Polyurethane system with a DFTof 250µm) is approximately 8 years to RI 3 degree of rusting.The durable life expectancy of a duplex system can becalculated using the following formulae and theincremental factors set out below:= HDG Life (15 years + paint 8 years) x 1.8= 41 years year’s to a 5% surface red rust.Factor used for different environments:◆ Industrial and Marine = 1.8 - 2.0◆ Sea Water Immersion = 1.5 - 1.6◆ Non aggressive climates = 2.0 - 2.7Editors noteSee also table 4 for durable life expectancies of a duplex system.The durability range is not a “guarantee time”, but atechnical consideration that can help the asset owner setup a maintenance program.Maintenance is often required at more frequent intervalsbecause of fading, chalking, contamination, wear and tear,and aesthetic reasons.Cost comparisons of a standard duplex systemvs a typical zinc/epoxy/polyurethane system for aC5M or C5I environment.The choice of a corrosion protection system is often basedon the initial cost per m 2 /tonne with little regard to longterm considerations. Unlike paint, hot dip galvanizing ispriced per tonne of structural steel and painting is priced atm 2 and then converted to a rate per tonne (m 2 rate x m 2 pertonne).COST COMPARISON DUPLEX SYSTEM vs HEAVY DUTY PAINT SYSTEMDuplex SystemHeavy Duty Paint SystemSteel thickness 3mm 6mm 8-10mm 15mm 3mm 6mm 8-10mm 15mmArea per tonne 84m 2 42m 2 28m 2 17m 2 84m 2 42m 2 28 m 2 17 m 2H.Dip Galv. CostR1700/tSee #2R1700/tSee #2R1700/tSee #2R1700/tSee #2Blast & Inorganic Zinc R55m 2 R55m 2 R55m 2 R55m 2Prep Epoxy P/U R64m 2 R64m 2 R64m 2 R64m 2 R56m 2 R56m 2 R56m 2 R56m 2Price per tonne for complete system R7064/t R4388/t R3492/t R2788/t R8484/T R4242/t R2828/t R1717/tDurable life expect. 41 yrs 41 yrs 41 yrs 41 yrs 15 yrs 15 yrs 15 yrs 15 yrsDLE per tonne cost per year R172/t R107/t R85/t R68/t R565/t R283/t R188/t R114/tAdd maint. Cost + 50% inflation factor 0 0 0 0 R847/t R424/t R282/t R171/tTotal cost per ton/yr R172/t R107/t R85/t R68/t R1412/t R711/t R470/t R285/t% Variance 0 0 0 0 820% 664% 553% 419%Table 7.Table 8.LIFE CYCLE COST SUMMARY FOR 41 YEARSDurable Life Expectancy Costper Year per TonSteel Thickness Total m 2 per ton Duplex System Heavy Duty % Cost DiffPaint System3mm 84m 2 R 1 72.00/T R 1 412.00/T 820%6 mm 42m 2 R 1 07.00/T R 711.00/T 664%8-10 mm 28m 2 R 85.00/T R 470.00/T 553%15 mm 17m 2 R 68.00/T R 285.00/T 419%Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 19

Feature – Duplex CoatingsTECHNICAL ADVANTAGES OF DUPLEX SYSTEMSDuplex Coatings VS Heavy Duty Coating System1) Preparation Pickle in acid – part of the process Abrasive blast to SA 2 1 /22) Curing Painting of the HDG can start immediately the item is Inorganic zinc’s require 2 - 3 day curing in a relativegalvanized – the sooner the better humidity of 70%3) Tie Coat No tie coat required Due to the open matrix of inorganic zincs a tie coat isrequired to “seal” the surface4) Uniformity No stripe coating of edges. Hot dip galvanizing produces Paint coatings are thinner over corners and sharp edges.a similar or greater coating thickness to that on all surfaces, These edges are prone to corrosion attack whenat edgesexposed to the exterior environments wherecondensation is evident5) Adhesion The hot dip galvanized coating is metallurgically bonded Inorganic zinc primers are susceptible to much crackingto the steelif applied too thick, especially in corners6) Inaccessible Because the items are dipped in molten zinc inaccessible Coating behind the lip on cold rolled lip channels areAreas areas are coated i.e. behind the lip on cold rolled lip difficult to paint and requires 100% inspectionchannels7) Transport/ Hot dip galvanizing is resilient to transport/erection The thicker the coating the more susceptible it is toerection damage transport/erection damage. Uncured zinc primers splitdamageabove the blast profileTable 9.For a true cost analysis the following must also be taken intoaccount:◆◆Ongoing maintenance cost during the life of the corrosionprotection systemLife cycle costing per m 2 for the durable life of the coatingsystem.We have based our costing on the following types ofstructural steel:◆◆◆◆3mm thick cold rolled purlins @ 84m 2 per tonne6mm thick structural steel (light) @ 42m 2 per tonne8 - 10mm thick structural steel (medium) @ 28m 2 pertonne15mm thick structural steel (heavy) @ 17m 2 per tonneFor this costing exercise, we have compared a duplex system(HDG + epoxy + polyurethane) to a paint system (inorganiczinc / epoxy / polyurethane) carried out in a “shop”environment where the rates shown in table 10 were used.It is quite clear that heavy duty paint coating systems areinitially cheaper than a Duplex System at the beginning of theproject for medium to heavy steel (>32 m 2 per tonne),however, in the long term can work out between 400 - 800%more expensive without taking into account the losses theasset owner may suffer due to downtime and the high cost ofaccess scaffolding, etc.With Duplex Coatings the cost savings start from thebeginning of the project.Duplex SystemCase Histories of duplex coatings applied 10 - 12years agoCase History “A”Location : Alusaf, Richards BayContractor : ABB FeralinContract : Alumina Conveyor system fromthe Richards Bay Harbour tothe Alumina Silos at Alusaf(± 4 500 tonnes)Specification : Chemically clean; epoxy zincphosphate primer;polyurethane enamelPaint Supplier : SigmaHeavy Duty Paint SystemHDGBlast & Inorganic ZincR1 700/tonne R55m 2Prep/Epoxy andStripe coat epoxy andPolyurethanePolyurethaneR64m 2 R56m 2Durable life expectancy in a C5M or C5I environment41 years 15 yearsMaintenance cost for corrosion purposes0 x 1.5 original coating costevery 15 yearsTable 10.Environment : C5 Marine/Industrial (harsh)20 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex Coatingsreacts with the zinc surfaces to form soap which causes lossof adhesion of the paint layer.If a Duplex System is to be applied, Hot Dip Galvanizewithout passivation (see #1).On the Hghveld, the exclusion of the sodium dichromatepassivation after hot dip galvanizing is of paramountimportance. However, when painting is likely to be delayedfor several days or weeks, particularly in moist, marineatmospheres, passivation of the steel should beencouraged.This painted only bracing (no hot dip galvanizing) is showing signs ofpremature failure amongst the other duplex coated members.condition, however, minormaintenance will be required onthe galvanized grating which hasbeen exposed to fumes from anearby stack. (see photo below).Case History “B”Location : Goodehoop Colliery – WitbankContractor : PH ProjectsGalvanizer : Barloworld GalvanizersSpecification : Sweep blast and 1 coat highbuild epoxy DFT –125µmPaint Supplier : SigmaEnvironment : C5 Industrial Coal washingPlant±1 500 tonnesThis Duplex System was specified and inspected by BraamBosman during 1995/1996 and a recent inspection showsno deterioration whatsoever, whereas a conveyor structureerected at the same time and coated with a conventionalpaint system, has deteriorated and will require majormaintenance within the next 3 years.It appears that a bracing between two columns wasmanufactured, painted and installed on site (nogalvanizing) and underthe same harsh wetenvironment of a coalwashing plant, thecoating is beginning tofail (see photo above).Future maintenance will be requiredon the hot dip galvanized gratings dueto micro climatic conditions.Refer also to Case Historyon Goedehoop Colliery.Cautionary notesAlkyd enamels should notbe used directly onto hotdip galvanized surfaces asthe alkyd saponifies ie.ConclusionConventional paint systems can be as much as 400 - 800%more expensive than a Duplex System over a period of 41years. Growing demand will increase competition andlower selling prices for Duplex Systems making it evenmore attractive to asset owners. The Hot Dip GalvanizingIndustry together with the cooperation of owners andspecifiers must not permit erosion of work standards.Everyone has to guard against the “low bid” trap at thebeginning of a project which can bring with it poorworkmanship, delays and costly re-work. Every contractmust provide QA/QC procedures that can verify properapplication.It is the responsibility of all the participants to strive todeliver high quality Duplex Systems which result in aLOW LIFE CYCLE COST.Editors noteCase History “A” – The gratings referred to in the above case historyare taking strain with detrimental attack of the coating taking place.As stated, steel exposed to harsh industrial/marine environments (C5Ior C5M) should be appropriately coated. Hot dip galvanizing on itsown will not necessarily provide an acceptable service free life.Alternative action includes the application of a duplex system,replacement of the gratings for stripping and re-galvanizing every tenyears of life (when at least 5% of the galvanized surface has failed) oralternatively using a more durable material such as a higher gradestainless steel or glass reinforced polyester, in this environment.#1 – The exclusion of the passivation by the galvanizer is not alwaysmandatory. Should painting follow shortly after hot dipgalvanizing then exclusion of the passivation is necessary,however, should painting be delayed for more than 4 hours in amoist aggressive marine atmosphere, then passivation by thegalvanizer should be encouraged.#2 – For simplicity the author has used R1 700.00 / ton for the cost oflight, medium and heavy steel. The actual cost however, variesdepending on location, from R2.50/kg for 3mm steel (light);R1.75 to R2.00/kg for 4 - 8mm steel (medium) and R1.60 toR1.75/kg for 10mm steel and above (heavy). Hot dipgalvanizing prices are amongst other plant related things affectedmainly by the zinc price and the Rand/Dollar exchange rate.Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 21

Feature – Duplex CoatingsSurface preparation for duplex coatingsystems – chemical pretreatmentChemical cleaningFor optimum functioning of duplexsystems, it is imperative to remove allcontaminants and other compounds fromthe zinc surface. For chemical cleaning,generally an aqueous alkaline solutionwith a pH of 11 to 12, is used. Solutions of2 to 5% by weight of one or more of thefollowing chemicals are used: sodiumhydroxide, sodium metasilicate, sodiumorthosilicate, trisodium phosphate,sodium nitrate and / or sodium carbonate.Horizontalgrease oildegreasedgrease oilVerticaldegreasedFigure 4: Practical testfor judging ofgalvanized steelsurfaces. One dropletof a 1% solution ofFettrot BB (Bayer) inethyl alcohol on metalsurface. Wait 30 - 60seconds. Form andextension of red ringindicate presence of oilor grease, as well aseffective degreasing(dotted lines).Mixtures of these products areaccompanied by small percentages ofemulsifying and chelating agents,breaking down during the degreasingprocedure on the zinc surface. Often, airis pumped through the degreasing tank toaccelerate degreasing reactions on thezinc surface, as well as to promote (bymechanical action) the removal of fattysubstances.For mass production, degreasingsolutions are sprayed onto the zincsurface during the passage of the hot dipgalvanized parts through a tunnel unit.Care should be taken to adjust bothposition (angle) of the spraying nozzlesand the pressure of the degreasingsolution. The temperature of thedegreasing solution should bemaintained at 60 to 85°C.In order to assess the cleanliness of thezinc surface prior to painting, thefollowing simple method may be used.Place one droplet of a 1% solution ofFettrot BB or Ceresrot (Bayer) in ethylalcohol onto the surface. After 30 - 60seconds, a circular doted line forms,indicating cleanliness of that surface.When degreasing is insufficient, acontinuous red circular line is formed. Onvertical, sufficiently degreased surfaces,the droplet sags less and the red line isintermittent whereas this line iscontinuous and more inclined to sag onpoorly degreased surfaces (see figure 4).A more sophisticated way of detectingimpurities on zinc surfaces is thephoton electron emission PEE method,which is nowadays also applicablewithout a vacuum.When weathered hot dip galvanizedsurfaces are degreased, weak acidsolutions of phosphoric acid or inhibitedsulfamine acid compounds are used,taking care that the pH value of such aciddegreasing solutions remains above 4.Sweep BlastingRefer to “Surface preparation for duplexcoating systems - mechanicalpretreatment”. The diagram below showsa typical surface profile of a correctlysweep blasted hot dip galvanized coatingwhich, when measured before and aftersweep blasting will tend to grow incoating thickness. The reason for thisgrowth is the fluffing up of the soft zinclayer and the electro magnetic coatingthickness guage probe, measuring thepeaks of the profile (see photos right).20μm5LCoating thickness readings before sweep blasting:Left: Mean 111 Min 94 Max 141 No. of readings 15Right: Mean 85 Min 73 Max 98 No. of readings 16Coating thickness readings after sweep blasting:Left: Mean 121 Min 99 Max 148 No. of readings 15Right: Mean 100 Min 84 Max 125 No. of readings 16h 1h 2h 3h 4h 5Figure 5: Surface profile of a swept galvanized steel surface over a length 5L.Top to bottom: R zR z = H + h + h + h + h1 2 3 4 55 Reduction of zinc coating thickness 8 - 13µ22 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsSurface preparation for duplex coatingsystems – mechanical pretreatmentBy Bradley Storer – BlastriteWith the demand for duplex coating systems growing, itis necessary to have the correct surface preparationspecification in place to ensure coating adherence to thehot dip galvanized surface.Pre-treatment of hot dip galvanized surfaces is best carriedout immediately after hot dip galvanizing, before thesurface becomes contaminated by oil, grease and dirt.Surface preparation methods for the duplex systems havevaried over the years from using chemical pretreatments,light abrasive blasting and mechanical methods forsurface preparation. The method that has proved mostsuccessful is light abrasive blasting – termed "sweepblasting". However sweep blasting has had it’s problems,with the incorrect abrasive, wrong particle size and thewrong blast pressure being used (blast pressure – airpressure at the blast nozzle).Figure 6: Photo shows the needle valve (not operational) for monitoringcorrect blast pressure by the operator.The abrasive choice plays a crucial role. When choosingthe abrasive one must ensure the following:◆Product is inert◆◆Appropriate particle size is used to achieve thespecified profile – a particle size that is too large canresult in a surface profile of 50 micron plus. Whilecorrect profile is about 10 - 15 micron (see figure 5).No recycled or contaminated abrasive is to be used.It is imperative that the surface preparation method bedone in accordance with the correct specification –numerous tests and following world best practicemethods has resulted in the following specification:1. AbrasiveGarnet – Microblast abrasive, grading being 150 - 300micron.2. Blast PressureBlast pressure – pressure at the nozzle to be regulated notto exceed 2.5 bar (40 - 50psi). A blast pressure of morethan 2.5 bar will result in the abrasive having more kineticenergy and therefore a larger surface profile being createdand possible damage to the hot dip galvanized coating.3. Stand-off distanceRand Sandblasting & CoatingsIndustries answer to:● Abrasive blasting ● Industrial Painting● Ultra high pressure water jet blasting & cleaning● Bitumen Coatings ● Tank & Pipe Linings● Coating & Wrapping of underground piping● Hot & Cold Insulation ● Sheet Metal fabrication● Roof Sheeting & Sidewall cladding● Asbestos removal & Abatement ● Scaffolding● Duplex Coating SystemsOffering you a ONE STOP service!!We undertake contracts through outSouthern Africa & AfricaFor enquiries & professional service contact:Matthew Laing (082 44 579 52) matthew@corrosionafrica.co.zaHercules Viljoen (082 44 069 42) hercules@corrosionafrica.co.zaHead Office Tel: +27(11) 955 3505 Fax: +27(11) 664 7746Email: rsb.jhb.@corrosionafrica.co.zaCBT (011) 868-3408 RSC 1024/10/05Distance between the blast nozzle and the substrate,the "rule of thumb" is that a distance of 500mm mustSMALL ENOUGH TO CARE, BIG ENOUGH TO DELIVER!!Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 23

Feature – Duplex Coatingsbe maintained between the endof the blast nozzle and thesubstrate.4. Oil & moisture trapCompressor and Blast Pots to beequipped with oil and moisturefilters.Duplex protection for atransmission line erected inan aggressive environmentThe above to be done in a "sweepblast" action, moving the nozzleacross the surface area in a quickmotionLight abrasive blasting in accordanceto the above mentioned method willresult in the correct surfacecleanliness and profile beingachieved:◆All zinc oxides / chalking isremoved◆ Blast profile of about 10 - 15micron obtainedAchieving the correct profile willresult in:1. Good adhesion of thesubsequent coating.2. Correct coating spreading rates.Achieving the incorrect profile willresult in:1. Damage to the hot dip galvanizedcoating with peaks stickingthrough coating.2. Increasing the consumption ofpaint.Editorial note:The majority of the above guidelines areaddressed in the Association’s CODE OFPRACTICE FOR SURFACEPREPARATION AND APPLICATIONOF ORGANIC COATINGS.In order to ensure the all important correctblast pressure is maintained and controlledby the operator, a needle valve can beinserted through the blast hose at theoperators hand instrument. Thisinstrument allows him to monitor thecrucial air pressure and hence maintainabsolute control over the sweep blastingoperation (see figure 6).Hot dip galvanizing is the protectivecoating generally specified for theprotection of electrical transmissiontowers in southern Africa andelsewhere throughout the world.Thousands of these structures canbe seen wherever one travels inSouth Africa where electrical poweris required to be transmitted overlong distances.Many years ago, engineers atEskom based their initial costcalculations on a maintenance freecoating life of 50 years for steeltransmission towers, which werehot dip galvanized. This projectionhas proved to be correct and ifanything conservative in mostinland regions. Meanwhile, thesavings in maintenance paintingcosts have been immense when oneconsiders the need to gain accessto these structures, which arespread eagled over long distances,not to mention disruptions inpower transmissions in order toenable maintenance crews to gainaccess to these structures.Understandably, the maintenancefree protective life of hot dipgalvanizing is diminished inaggressive coastal regions where, insome cases, duplex protection isadvisable.Some years ago, we were requestedto recommend a cost effectiveprotective system for a transmissionline to be erected along theaggressively corrosive Namibiancoastline. This line extendsrelatively near the coast for 20km,from Swakopmund to a substation“Kuiseb” some 20 to 25km fromWalvis Bay and then inland toWindhoek.The protective duplex systemrecommended entailed hot dipgalvanizing followed by theapplication of an epoxy primerovercoated with a highbuild epoxycontaining MIO and a top coat ofpolyurethane.Erection of this transmission linewas completed about two and a halfyears ago. The coastal section tothe substation and the inland lineup to a distance of about 45kmfrom the coast have been providedwith duplex protection. A recentsurvey of the protective systemsapplied in this instance indicatesclearly that there is no evidence ofpremature failure.The performance of this duplexsystem in these aggressivelycorrosive conditions will bemonitored regularly in the future.24 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex Coatingsthe cleaner must then bethoroughly rinsed off, with paintingcommencing as soon as possible(see note1 overleaf). Once thecleaned surfaces have been dried(in moist atmospheres) or hadsufficient time to dry completely ontheir own (in dry atmospheres).This is a universally approvedprocedure and a fundamentalprerequisite for successful painting.The third and equally importantrequirement is appropriate paintselection. This will be determined bythe micro-climatic conditions, whichcan vary substantially from onecorrosive site to another. Prevailingwind direction, rainfall, land contoursand proximity to the spray zone in acoastal environment, are allsignificant factors.As a rule of thumb, all sites within adistance of 500m of the tidal zoneshould be regarded as aggressivelycorrosive. The selected paint coatingmust be capable of withstandingaggressive attack by chloridesfrequently deposited onto coatingsurfaces for extended periods. Longperiods of wetness with chloridecontaminated moisture willexacerbate the corrosion problemwhile in low rainfall areas; theabsence of the washing effect of rainwater increases the propensity forcoating failure.The selected paint system mustpossess the following attributes:minimal porosity, UV resistance, highsolids content to reduce permeabilityby corrosive moisture and anadequate dry film thickness of at least100 up to about 250 microns DFT,depending on proximity to the sprayzone.How does this impact on the man inthe street? He goes to his localhardware shop to buy paint. There hefinds acrylic water based primers andenamel oil based topcoats to applyonto hot dip galvanized steel. Thisseems to be an obvious choice as theyare single pack, non-toxic products,which provide good adhesion.Above and below: An example of a failed duplex coating as a result of insufficient DFT of the paintcoating being subjected to the corrosive conditions of Muizenberg. Note the voluminous white zinccorrosion products.The problem with these coatings is thatthey provide very thin coverage varyingfrom 20 to 40 microns. The hot dipgalvanized articles are then paintedwith a two coat decorative paintsystem, which would be ideal for useonly in moderately corrosiveapplications.The paint coating is soon breached dueto permeation by moisture and saltspray and the underlying zinc surface isconverted into soluble zinc hydroxide.As the paint coating becomes morepermeable, it is further breached andthe item becomes coated with whitezinc corrosion products. These coatingswhich can fail very quickly arefrequently observed. They lead to agreat deal of confusion anddissatisfaction on the part of the clientwho looks to blame the painter, thegalvanizer or the paint supplier, whilethe real cause is incorrect paintselection and inadequate paintcoverage.It is imperative, especially within 500mfrom the sea, that a heavy duty paintsystem is applied to prevent the hotdip galvanizing coming into contactwith salt spray and moisture. An idealsystem is an epoxy primer, an epoxyMIO intermediate coat and apolyurethane topcoat to a total paintDFT of about 150 - 200 microns. Thisduplex system has providedoutstanding results in corrosive marineapplications where the synergisticeffect produced by combining theprotective properties of an organicpaint system with hot dip galvanizing isinvariably most effective in providinglong term corrosion control.As the above systems are normally onlyapplied in a factory, the best solutionwould be to ensure a paint applicatorapplies this heavy duty coating. Failingthis Mr. Citizen must ensure that hebuilds up his own paint coating to anacceptable dry film thickness.The ideal solution would be for thepaint companies to develop a user andenvironmentally friendly heavy dutypaint coating that could be applied bythe man in the street and capable ofwithstanding the harsh environmentencountered close to the sea.26 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsSome miscellaneous duplex coatingapplicationsThe following duplex coating applications took place at Galvatech in Bellville, Cape Town.Duplex coated water treatment plant pipes were sweep blasted both externally and internally after hot dip galvanizing and then coated with an epoxyprimer followed by 3 coats of coal tar epoxy.Duplex coated syncro lift mechanisms at Kalk Bay Harbour were sweep blasted after hot dip galvanizing followed by an epoxy primer, two coats of highsolids abrasion resistant epoxy paint. A final polyurethane coating was applied on site.Duplex coated steel reinforcement strips on the underside of the Kalk Bay concrete railway bridge.The hot dip galvanized strips were sweep blastedafter hot dip galvanizing and then coated with a special epoxy type of paint before being fixed to the underside of the bridge by way of mechanicalpins and epoxy adhesive.Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 27

Feature – Duplex CoatingsZinc primers – an overviewby Dr Colin Alvey, Corrosion Advisory Technical Services (Randburg) ccMetallic zinc as a protectiveprimerIt is generally accepted that particles ofmetallic zinc applied to a steel surfacein a paint matrix in the form of a zincprimer provide protection to the steelby the process of cathodic protection.In the presence of moisture as theelectrolyte, the steel forms the cathodeand the zinc the anode in the resultantcorrosion cell. The steel, being thecathode, does not corrode whilst thezinc, being the anode, corrodespreferentially and protects the steel.This protection continues until the zincin the paint matrix is consumed ordepleted.Hot dip galvanizing vs zinc richpaintIt must be remembered that it ismetallic zinc that affords cathodicprotection to steel and the extent ofprotection offered is directlyproportional to the coating thickness interms of hot dip galvanizing and interms of a zinc rich paint, the mass ofzinc present in the dry film as well asthe coating thickness. A further factor isthe environment at hand.Care should therefore be taken whenselecting zinc based coating systemsfor chemical environments. Zinc, beingan amphoteric metal, is attacked byboth acids and alkalis. Zinc should onlybe used in the pH range 6 to 12.5.Zinc phosphate and zinc chromatecontaining paints do not providecathodic protection as they areinhibitive rather than sacrificialpigments and provide protection by atotally different mechanism.When considering zinc rich paints, onlythose that contain sufficient quantitiesof metallic zinc dust will providecathodic protection. There mustobviously be sufficient zinc particlespresent to ensure that they are inelectrical contact with each other inorder to provide a common anode.Individual isolated zinc particlesdispersed in the paint binder will notprovide protection as they wouldessentially be insulated from thesubstrate and each other. On the otherhand, if too much zinc dust is added tothe paint there may not be sufficientbinder available to glue these particlestogether, giving an unbound coatingwith poor adhesion and cohesion. Inaccordance with ISO 12944, all zinc richpaints should contain a minimum of80% zinc in the dry film in order tofunction as sacrificial primers.From the point of view of zinc content,hot dip galvanizing is the ultimatezinc rich primer.visibility, camouflage, or when apleasing aesthetic appearance isnecessary.Duplex coating systems providesynergy by virtue of the fact that thedurability of the combined hot dipgalvanized / organic coating system isgreater than the sum of the separatedurabilities of the hot dip galvanizingand a organic coating layer applieddirectly to the steel substrate.The reasons for this synergistic effectare as follows.When moisture, oxygen andpollutants diffuse through a paintcoating onto steel, rust soon forms atthe interface. Since rust (a mixture ofvarious hydrated iron oxides withvarying compositions) has a volumewhich is approximately twice to threetimes the volume of the steel fromwhich it has been formed, the paintcoating will lose contact with thesubstrate and, depending upon itsadhesion and cohesion, will start tocrack and/or flake off.Powder coated mild steel – 2 000 hours saltspray.A "Duplex Coating" is a term firstintroduced by Jan van Eijnsbergen ofthe Dutch Hot Dip Galvanizing Institutein the early fifties. It describes theprotection of steel by over coating hotdip galvanizing with an organic coatingsystem. The purpose is to provideadditional corrosion resistance, easyPowder coated continuous hot dip galvanizedsheeting – Z275 – 2 000 hours salt spray.28 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsWhen hot dip galvanized steel is thebase of a paint system, the occurrenceof moisture, oxygen and pollutants atthe zinc / paint interface causes thepure zinc (or eta layer) to corrodeslowly. However, these zinc corrosionproducts (mainly zinc oxide and zinchydroxide) have a volume which is only15 - 20% more than the volume of zincfrom which they have been formed.These zinc corrosion products willblock off small pores, craters or cracksin the paint coating, thus conserving itsprotective properties over an extendedperiod, provided that adequateadhesion of the paint coating wasinitially achieved.The benefit of a metallic zinc primersuch as hot dip galvanizing under anorganic coating system is illustratedby the comparative photographs onthe opposite page. The photograph onthe left shows a powder coated mildsteel panel that has been exposed in asalt spray cabinet for 2 000 hours. Therust staining weeping from the scribecuts shows that the underlying steel iscorroding where the salt spray hasgained access to the substrate. Thecoating adjacent to the scribes isbeing lifted by the voluminous ironcorrosion products. The photographon the right shows a powder coatedpanel made from continuous hot dipgalvanized sheeting – coating classZ275 (equates to about a 20µmcoating thickness). In this instance themetallic zinc primer has providedcathodic protection to the underlyingsteel at the scribe cuts. Thesurrounding zinc is sacrificing itself toprotect the steel, forming white zinccorrosion products. The solid volumeof the zinc corrosion products is smalland therefore the coating adjacent tothe scribes has suffered little damage.After the same 2 000 hours periodthere is still sufficient zinc to preventcorrosion of the underlying steel. Thesacrificial nature of zinc at the scribepoints will in time deplete thesurrounding zinc coating and as itrecedes, leaving uncoated steel at thescribe point, localised corrosion willcommence. Maintenance paintingrepairs would then be required beforethe steel substrate is damaged.In extenuating circumstances such as,possible design restrictions, size ofcomponent, geographical location ofthe fabricator in comparison to thegalvanizer, or where hot dip galvanizingis impractical or impossible etc., hotdip galvanizing may have to besubstituted by either inorganic zinc ororganic (epoxy) zinc.It is beyond the scope of this article tocover the detailed pros and cons of hotdip galvanizing versus zinc rich paintsbut one of the main factors forconsideration remains costs. A numberof articles comparing the relative costsof hot dip galvanizing versus paintinghave been published.The essential difference that must beappreciated is that hot dip galvanizingcosts are calculated by mass, of steelhot dip galvanized whilst paintingcosts are based on area painted.Tables are available for most steelsections giving surface area by mass.DESIGNERS ANDMANUFACTURERSOF ELECTRICALHEATINGELEMENTS ANDSYSTEMSAs a rule of thumb the following canbe used:Extra light steelLight steelMedium steelHeavy steelmore than40m 2 /ton30 to 40 m 2 /ton20 to 30 m2/tonless than 20 m 2 /tonIn hot dip galvanizing, steel issubjected to a routine cleaningprocess, including, degreasing, acidpickling and fluxing, with intermediatewater rinsing, thereby creating athoroughly clean surface, essential forhot dip galvanizing to take place. Theresultant coating thickness isdependent on several factorsincluding, chemical composition ofthe steel, steel thickness and surfaceroughness, as well as a number ofother less important factors. In steelof thickness equal and greater than3mm but less than 6mm, the meancoating thickness is required to be at●●●●●●ZINC BATH HEATINGZINC BATHS COMPLETETEMPERATURE SENSORSPRE-CLEANING BATHHEATINGCONTROL EQUIPMENTGAS - ELECTRICCONVERSIONSPO Box 53483 Troyeville 2139Tel: [011] 894 3937Fax: [011] 894 3954www.hi-techelements.co.zaEmail: andre@hi-techelements.co.zaVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 29

Feature – Duplex Coatingsleast 70µm and on steel thicknessgreater than 6mm, 85µm.The painter will abrasive blast clean thesteel and then spray apply a suitable 75micron thick (inorganic or organic) zincrich primer coat for a protective coatingsystem at a cost based on the totalarea of steel he has painted.Case histories have shown that forsteel sections up to some 35m 2 /ton itis more cost effective to blast clean andpaint whereas for steel sections withgreater than 35m 2 /ton, it is more costeffective to hot dip galvanize. Obviouslythis cut off point varies with rawmaterial and labour costs at any pointin time. It will also be argued that thehot dip galvanized coating containsmore zinc and will therefore last longerthan the 75 micron of paint (with 80%zinc in the dry film). On the other handthe hot dip galvanizing will requirethorough cleaning before the primer orintermediate coat can be applied.The point is, however, that bothmethods of providing the requiredmetallic zinc primer can be costeffective, depending uponcircumstances. It is for this reason thatin recent years both options have beengiven in protective coatingspecifications, leaving the finaldecision whether to hot dip galvanizeor paint, up to market forces.apply the top coats without incurringfurther transport costs. The concept ofapplying paint at the galvanizerspremises has already been successfullyimplemented at a number ofgalvanizers throughout the country.Clearly hot dip galvanized coatings andpaint coatings complement each otherin the protective coatings industry.However, there is still a perception inthe market place that the galvanizersand paint manufacturers are incompetition with each other.Editorial comment to the article onzinc primers◆◆◆Although zinc is amphoteric, i.e. willcorrode at pH less than 6 and above12.5, if sufficiently over coated with acomprehensive organic coating system,it will provide better protection than thesame paint coating system applied overplain carbon steel.Due to the nature of paint having zincdust in the coating matrix, onapplication the zinc will tend toimmediately start sacrificing itself,leading to a relatively shortened periodof sacrificial protection, andconsequently corrosion protection.All paint coatings in time becomeporous and this allows moisture topenetrate the coating.◆◆paint, in steels from ultra light (70 to120m 2 /ton) to heavy steel (25m 2 /ton).This comparison excludes the cost ofindependent substrate and coatinginspection for the painted steelwork andadditional transportation of the hot dipgalvanized steel.A hot dip galvanized coating comprisesa series of Fe/Zn alloy layers makingup between 50 and 85% of the coating.In most instances the Fe/Zn alloys willprovide at least 30% greater corrosionresistance than a pure zinc coating.(Frank Porter).In our opinion, the logistics ofadditional transport concerns not onlythe galvanizers but many steelfabricators, faced with stringentenvironmental regulations for applyingpaint, lack of skilled painting staff andgeneral downsizing of expertise, forcesmany fabricators to outsource thepainting stage. Furthermore, there aremany hot dip galvanizers who havegained the necessary expertise toprepare and apply at least the primercoat, if not the entire coating system.Additionally, where this expertise is notavailable, some galvanizers can provideindustrial painters with floor space, inwhich preparation and subsequentpainting may take place. Onegalvanizer on the reef is currentlyconsidering an in-house powder coatingline.Unfortunately galvanizing has notfaired well in these instances asconsideration has to be given to thelogistics of galvanizing rather thanpainting.Most fabricators have a painting facilityin their shops such that the fabricatedsteel moves through the wheelabratorand into the paint shop where itreceives the primer, intermediate andsometimes the finishing coat before itis transported to site. If the steel is tobe hot dip galvanized the fabricator hasto fabricate, transport the steel to thegalvanizer and return it before applyingthe subsequent paint coatings. In orderto make hot dip galvanizing costeffective in this instance the galvanizerneeds a painting facility in order to◆◆In comparison to a coating thickness ofabout 20µm, produced by class Z275,continuous hot dip galvanizing ofsheeting (SANS 3575), general hotdip galvanizing (SANS 121) producesa thicker coating. 45µm - meancoating thickness, for steel less than1.5mm thick to 85µm, mean coatingthickness, for steel equal to or greaterthan 6mm. The thicker the availablecoating, the longer the period ofsacrificial protection at damaged areassuch as the scribe points detailed in thearticle, before the onset of localisedcorrosion.Recent price comparisons indicate thathot dip galvanizing on its own iscompetitive when compared to anabrasive blast and a paint coating ofabout 75µm DFT of inorganic zinc rich◆◆While there is merit in using a duplexcoating where it is required, such as inthe instances referred to in the article atthe start of this feature, there will inmost instances be co-operation betweenthe paint and hot dip galvanizingindustries. However, when a singlecoating is specified that must beappropriate and cost effective, there willalways be competition between theplayers of both industries.In Colin’s article he discusses theperformance of hot dip galvanizing incomparison to a zinc rich primer andsays that the details are toocumbersome for the article at hand. Wewould like to challenge the zinc primermanufacturers using the services ofColin Alvey to a performance duel.Any takers?30 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsDuplex Coatingsusing powder paintsBy Graeme Stead of Coating ConsultantsMy first experimentation with duplex coatings was in the early1980s. We had used a powder primer (which had been developedfor Volkswagen) over hot dip galvanizing for coating turnstiles forrailway stations. These were over coated with liquid polyurethaneenamel. These items were reported to give outstandingresistance to wear. An offshoot of this technology was a farm signwhich has been hanging on a pole on a dusty dirt road for morethan 20 years and is still in great shape despite being the targetof school kids’ stones for two decades!In fact I gave a picture of this sign to Sir Jan van Eijnsbergen whorequested examples of early duplex powder coatings in SouthAfrica. Sir Jan, who coined the name ‘duplex coatings’, producedhis famous book on duplex coatings in 1994 1. He wrote “Powdercoatings are increasingly used in Duplex Systems for two important reasons.First, they do not contain any volatile matter (solvents, thinners), thusavoiding costly installations to remove them and are more acceptable toworldwide environmental laws. Second, they possess superior surface hardnessand wear resistance in comparison with organic duplex coatings”. He tabledthe advantages and disadvantages as follows:Advantages◆ No volatile matter present◆ No environmental problems with volatile compounds◆ High impact and scratch resistance◆ High surface hardness◆ Small chance of coating damage during transportation andassembly◆ Low powder losses during application◆ High to very high resistance against moisture◆ Excellent adhesion◆ Even coating thickness◆ Less fire hazard◆ Less floor occupancy in comparison to liquid paintapplication (no flash-off and inter-coat drying zones)Disadvantages◆ Application only by electrostatic spraying or fluidized bedcoating◆ Limitations as to form and volume◆ Stoving is necessary◆ High investment costs for (semi automatic coating linesPowder coatings and hot dip galvanizing in combination provideexcellent corrosion resistant coatings. Such a duplex systemprovides a high grade architectural finish. The powder coatingcomprises an epoxy / epoxy polyester or pure polyesterthermosetting resin that is applied to a clean hot dip galvanizedsurface and cured at temperatures near 180ºC.

Feature – Duplex CoatingsSurface preparationThe surface preparation required to promote good adhesionbetween the powder coating and the hot dip galvanizedsurface is similar to that of paints. A profiled galvanizedsurface will provide an excellent surface for applying powdercoatings.◆◆◆◆◆◆◆The components should not be quenched after hot dipgalvanizing.The surface of the steel should remain clean.When transporting the steel be sure to cover loads andkeep dry.If surface contamination has occurred, clean the steel witha proprietary solvent/detergent that is designed forcleaning prior to powder coating.Maximum adhesion is achieved by using a zinc phosphatetreatment before powder coating the steel. The surfacemust be entirely clean as this treatment has no cleansingaction.It is an advantage to preheat the steel prior to powdercoating.Use a ‘degassing’ grade of polyester powder only. Antiblisteringagents such as polyethylene oxide, can be addedto the powder to prevent pinholing and promote goodadhesion 2 .Hot dip galvanizing substitutes very adequately for a primerand has many advantages over a liquid primer e.g. high edgecover, formation of corrosion resistant layers, very strongadhesion to the substrate – to mention just a few. As Sir Jansays: “Save the surface…..and you save all.” After theconsiderable work involved in hot dip galvanizing, followed bythe highly technical process of powder coating and baking, onewould think that sufficient corrosion protection had beenachieved! But alas, as many have found out to their cost, moreis required to provide resistance to exterior, wet conditions!One must remember that the underlying zinc is a potentiallyreactive metal surface. Successful exterior corrosion protectionis a matter of building sufficient insulation over the hot dipgalvanizing to prevent ingress of moisture. In other words, anadditional coat (or two) is / are required. van Eijnsbergen says:”The superior combination of an epoxy powder primer followed by anpolyester powder topcoat, yielding a much improved water resistance over(compared with) a single polyester powder coat after twelve weeks of GMScab Corrosion Test, is shown …etc.”The specifier must design for the worst case i.e. the thinnestpossible thickness which will be achieved by the particularapplication. Testing and/or thorough consultation is necessaryto determine whether the coating will be resistant to theenvironment for which it is planned. Excellent primers such aszinc rich epoxy powder primers, and liquid paint stovingprimers are available to enhance the corrosion protection ofthe polyester powder topcoat. One of the problems of powdercoatings is also its most attractive feature – its good looks.The unwary can be quite taken with the outstandingappearance of architectural finishes, not realising that thecoating thickness may be well under par.As with all industrial processes, quality control is of vitalimportance. Powder coatings only develop their true propertieswhen they have completed their required ‘heat history’ viz.stoving schedule. Under-cured powder coatings can be as brittleas glass! When properly cured they become tough, highlyadherent and abrasion resistant. Thickness, especially in recessesand corners requires to be carefully checked to maintain overallcoating integrity.The market for duplex powder coatingsThis consists of any item that can be hot dip galvanized and fitinto a powder coating facility (spray booth, conveyor and oven)The following applications were picked up on the South AfricanWeb Sites:◆ Various cable ladder and tray systems. All steel to be hot dipgalvanized and epoxy powder coated on exposed surfacesonly.◆ Catering equipment.◆ Lighting equipment.◆ Water tank walls constructed from Zincalume ® steel panels.Powder coated panels are available as an option and come ina wide range of colours.◆ Lighting products.◆ Security fence poles.◆ Satellite dishes.◆ Air conditioning plant.◆ Conservatory structures.◆ Panel and Switchboard components.May this list continue! Powder coating duplex systems are here tostay!References1.Eijnsbergen JFH van , Duplex Systems, Elsevier 19942.American Galvanizers Association – Powder coating hot dipgalvanized steel www.galvanizeit.orgEditors note:It has been found that when powder coating takes place over the sometimesrough surface achieved by hot dip galvanizing, a structured powder coatinghelps hide the small blemishes of the metallic coating. However, as aprecaution it is important to note that when the component is to be subjectedto aggressive marine or polluted industrial environments, the use of astructured powder coating should be avoided particularly as the recorded finalDFT will be practically less than the specified coating thickness due to thepeaks and valleys achieved by this type of powder. For aggressive climates asingle epoxy / epoxy polyester powder coating layer of at least 120µm or thecombination of an epoxy plus a polyester exterior powder coating of a similarcoating thickness should be specified. Consult the powder coatingmanufacturer.Powder coating over hot dip galvanizing generally calls for “degassing”. Thisinvolves heating the hot dip galvanized components to about 180°C to driveoff any moisture from the chemical process liquids and eliminates thepossibility of blisters appearing through the powder layer when stoving takesplace. The term “degassing” is therefore a misnomer as no gas is trapped inthe hot dip galvanized coating.32 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsRe-establishment of the Duplex CommitteeDuring the mid 1980s the South African Hot DipGalvanizers Association realised that, whilst there was anincreasing requirement for duplex coatings in SouthAfrica, there was little co-ordinated information availableas to which particular coating systems in the marketplace were suitable for duplex systems. They were verysensitive to the fact that the use of the wrong coatingsystems would lead to failures which would discredit theconcept of duplex systems. In order to ensure that thisdid not happen they called together the major paintmanufacturers in the country at that time and formed aspecialised "Duplex Committee". This committee, whichmet regularly, sponsored the independent testing of anumber of proprietary organic coatings for use in duplexsystems. The test work, carried out by Eric Duligal &Associates, covered the following:(i)(ii)Investigation of current practice andrecommendations of paint manufacturers onapplication of paints to hot dip galvanized surfaces.Testing of manufacturer's products and systems.qualifies to be used in a duplex system. In addition tospecifying the test methods, it also specifies theminimum test criteria or results that the coating mustachieve. This specification covers the selection of duplexsystems for use in the following environments:Mild -(rural) conditions.Industrial - conditions (mildly polluted environments,not in immediate proximity to chemicalplant).Marine -Mining -(coastal) environments.applications underground.Immersion - For the lining and coating of pipes carryingraw potable or re-circulated water, gas or oil,but excluding very aggressive chemicals suchas acids, bleach solutions, ferric chloridesolutions and brine.(iii) Adhesion of coatings to sweep blasted surfaces.(iv)(v)Evaluation of adhesion testing methods.Evaluation of different surface preparationmethods.Whilst the results achieved from these tests wereinteresting and indicated that there was a definite futurefor duplex systems in South Africa, the control of systemselection was going to be difficult, if not impossible,considering the vast number of proprietary productsavailable and the lack of documented performance resultsand case histories.It soon became apparent that formal codes andspecifications for duplex coatings were required. TheDuplex Committee then channelled its efforts intoproducing a specification and code of practice for duplexsystems and these were published in 1990.SpecialistPOWDER COATERSfor quality & serviceWe specialise in powdercoating over hot dip galvanizingon palisade fencingSpecification for the performance requirementsof coating systems: No SAHDGA 1-1990This document covers coating systems applied to newunweathered hot dip galvanized steel (sheet and section)excluding in-line coil coating. It is a very usefuldocument in that it specifies all of the tests to which acandidate coating system must be subjected before it12 Donald Ensor Rd, Glen AnilP.O. Box 40022, Redhill 4071Tel.: (031) 569 2684Fax: (031) 569 2686CBT (011) 868-3408 LEC1025/10/05LITEEPOXY COATING ccVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 33

Feature – Duplex CoatingsThe onus was on the paint manufacturer to test hismaterials for conformance to this specification beforerecommending or specifying their use in duplex systems.If the Association was advised by the manufacturer of hiscompliant systems, the Association could in turnrecommend the use of the particular systems to endusersand specifiers. Correctly implemented, thisspecification is of obvious benefit to all parties.Code of practice for surface preparation andapplication of organic coatings: No SAHDGA01-1990This code of practice, as is the case for the specification,refers to duplex systems applied to new unweathered hotdip galvanized steel (sheet and section) excluding in-linecoil coating. The code has been prepared for specifiers,end users, inspection authorities and paintingcontractors to make them aware of the proceduresnecessary to ensure acceptable adhesion of paint to hotdip galvanized surfaces. It was obviously intended tocover the application of only those materials that complywith the requirements of the "Specification for thePerformance Requirements of Coating Systems"described above.The implementation of the code of practice and its sisterspecification virtually guarantees a successful duplexcoating system.The protective coatings industry has changedconsiderably since the early 1990s with a number of newoverseas based manufacturers entering the market place.It is time for the Duplex Committee to re-convene toupdate the Specification and Code of Practice for DuplexSystems and to address new duplex systems andgalvanized iron cleaners.In a number of European countries duplex coatings arebecoming the rule rather than the exception, particularlyon architectural structural steelwork. With closercooperation between the hot dip galvanizing and paintingindustries, there is no reason why this should notbecome the trend in South Africa to the benefit of thesteel construction industry.Reader’s CommentsSandie Thomas of Richard Egan & Associates, writes –In magazine number 23, Case History N o 3/2005, the nameMitchels Plain was spelt incorrectly. It should be “MitchelsPlain” and not Mitchelsplein, as we spelt it.Editor – Thanks for your correction and interest in ourmagazine, Sandie.Johannes Potgieter of the Department of Water Affairs,writes – that he would like to see a register of all theinteresting articles that have been published in pastmagazines, compiled for easy reference.Editor – Thanks for the response Johannes, we arepresently compiling such a register and will advise in thenext magazine, when it is available. We will most probablyplace it on our Web Site!Ray Wilsenbach, MD of Nemtech felt that the photoentitled, “A typical hot dip galvanized support of anelectrified fence”, in magazine number 24, used to enhancethe article provided by Nemtech was inappropriate.Editor – Thanks for pointing this out, Ray we apologise forthe inconvenience but innocently added the photo toenhance the effect of the article.First name: ____________________________________Surname:____________________________________Contact tel:____________________________________Fax No: ______________________________________Email address: ________________________________Organisation represented: ______________________The above article was compiled by Dr Colin Alvey in theinterests of Duplex Coatings, the Association wishes tothank Colin for his interest.Should you be interested in being part of the re-established duplexcoating committee for both solution and powder coatings, kindly fillin the details below and fax or email them for the attention of TerrySmith at (011) 456 6304 or hdgasa@icon.co.za orterry@hdgasa.org.za.Interest: ______________________________________Interests would include: Paint and powdermanufacturers; paint applicators and powder coaters;abrasive blast media suppliers; abrasive blastingcompanies; Corrosion Consultants; general interest, etc.34 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – Duplex CoatingsAnother yard stone, another day –O-line duplex is definitely the wayGraeme Smart, Sales & Marketing DirectorThe recent award of the Mufulira projectto O-line by Marpels Joint Venture for thesupply of cable ladders, has once againproved that together the combined inputand expertise of all major industry rollplayers, can create a synergistic operationwhich would provide clients nationallyand internationally with sound solutionsat cost effective prices.After many hours of discussions and thehelp of experts in all areas of discipline itwas decided that a Duplex coating was tobe specified. The coating of whichconsists of hot dip galvanizing overcoated with an epoxy powder under coatfor added corrosion protection and a purepolyester powder finish for the UV raysproduced by the Zambian sun, has beenaccepted by the client.The resultant effects of this decision hasgiven O-line the opportunity to onceagain prove the value and effectiveness ofthe DUPLEX Coating system which in thepast, due to some misconceptions bycertain parties, did not receive therecognition it deserved.The Duplex coating system has withstoodthe test of time. Classical examples beingthat of Phalaborwa (Cable Ladders);Mossgas (Cable Trays); Hong Kong (SunShields) and many others of which Iquote Walter Barnett “ are still fightingthe common enemy” “corrosion”.O-line prides itself in that its powdercoating plant has an impeccable trackrecord when it comes to success in termsof adhesion and bonding of the powdercoating to the hot dip galvanizing. This isobtained through careful preparation ofthe product, which undergoes a sevenstageprocess before entering the spraylines. O-line runs a Chemetall line, whichis monitored three times a week toensure the cycle remains stable andconsistent.Seven Stage cycleThe stages begin with a degreasingprocess, which is a soap blend commonlyO-line Support Systems (Pty) LtdLeaders in Cable Management andStructural Support SystemsBRANCH ADDRESSES:O-line Support Systems (Pty) LtdReg. No. 1982/000082/0714 - 16 Prop Street, Selby Ext 11, JohannesburgP.O. Box 6457, Johannesburg 2000Tel: +27 (0)11 378-3700 • Fax: +27 (0)11 493-0048/0334Website: www.o-line.comGraeme SmartO-line Support Systems Pretoria (Pty) LtdReg. No. 1987/01406/079 Eland Street, Koedoespoort, PretoriaP.O. Box 2039, Silverton 0127Tel: +27 (0)12 333-6604/8543 • Fax: +27 (0)12 333-4522O-line Coatings (Pty) Ltd – Specialist PowderCoating ApplicatorsReg. No. 1981/09556/071 Rossouw Road, Wadeville, Germiston, JohannesburgP.O. Box 6457, Johannesburg 2000Tel: +27 (0)11 827 5754/5 • Fax: +27 (0)11 827 5809Joe DeetlefsO-line Support Systems KwaZulu-NatalA division of O-line Support Systems111 Escom Road, New Germany 3610P.O. Box 2534, New Germany 3620Tel: +27 (0)31 705-6355 • Fax: +27 (0)31 705-6358Robert MerzCape Support Systems (Pty) LtdReg. No. 1985/000416/076 Thor Circle, Viking Place, Thornton 7460Tel: +27 (0)21 531-9071 • Fax: +27 (0)21 531-8092Gerhard Swarts / Rudi PaulsenCape Support Systems Port ElizabethA division of O-line Support Systems11 Burman Road, Deal Party, Port ElizabethP.O. Box 1352, Port Elizabeth 6000Tel: +27 (0)41 486-3506 • Fax: +27 (0)41 486-3375Kevin MurphyVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 35

Feature – “The world of hot dip galvanizing around us”known as formula 30 then into a waterrinse. From the rinse, in the event ofwhite rust, it enters the de-rusting bathwhich is a combination of phosphoricand sulfuric acids followed by a secondwater rinse. From the second rinse intothe pre-treatment bath or etchingprocess back into a third water rinseand finally into the passivation bathand into the dryers.Once the product has left theChemetall line the product` enters the“degassing” stage whereby the item isheated to appropriate temperatures.Spray lineWith regards to the Mufulira Projectthe product undergoes a double coatapplication via electrostatic adhesionspraying, the under coat is an “Interpon100” epoxy based powder and thesecond coat is an “Interpon 600”polyester based powder. The curingprocess is achieved by utilising infraredin the first cure, and the addition ofgas for the second cure.O-line is certain that the duplexcoating will exceed expectations andcreate further opportunities,specifically where expertise andproduct solutions are sought withinSouth Africa.It is imperative that more projects arehandled in this manner, wherebyexpertise and organisations are able tojoin together in providing a service,which meets global standards,resulting in competitiveness againstforeign intervention in the Africanmarket. Projects of this nature are thelifeblood of our sustainability.To conclude O-line would like toextend our appreciation for theopportunities afforded us and thecontributions made by the followingorganisations and individuals.- SNC-LAVALIN /Marples JointVenture - Donald Coupland;- CATS - Dr Colin E. Alvey;- Hot Dip Galvanizers Association -Walter Barnett and Terry Smith;- AKZO NOBEL - Technical staff.Federation Square –AustraliaVisionFederation Square is one of the mostambitious and complex projects everundertaken in Victoria, Australia.It is a complete new city block, thefirst ever to physically connect thecentral business district with theYarra River. Situated at the heart ofcentral Melbourne, FederationSquare will be a fusion of arts andevents, leisure, hospitality andpromenading.DesignFederation Square’s design is theproduct of an internationalarchitectural competition won in July1997 by Lab Architecture Studio ofLondon in association with BatesSmart Architecture of Melbourne.Atelier One were appointed ProjectStructural Engineers. The judgingpanel said of the winning design: “Itdraws its inspiration from the uniquecharacteristics of Melbourne’sarcades and laneways andtransforms these elements into anew form of organisation,celebrating the city. The design willinvite pedestrians to explore acomplex and urban linkage of openand closed spaces, a set of differentamenities brought together in thearchitectural equivalent ofFederation”.Federation Square has beendescribed as an area with extensiveflow, integrating activities across thesite and forming links within it aswell as with the Yarra River, ArtsCentre, Southgate and the CentralBusiness District.Federation Square’s architecturalintent is to generate visual harmonyfor the site while maintainingdifferences between its civic, culturaland commercial buildings. Theapproach creates distinctions througha high degree of surface and materialvariation. The creative use of the“pinwheel” triangular grid, in whichevery panel is exactly the same sizewith only the orientation changing, asthe molular basis for this systemallows both façade cladding andframe shapes to be treated in acontinually changing visually dynamicway. On the main buildings threecladding materials have been used,sandstone, zinc and glass.Interest in the appearance of hot dipgalvanizing is its appeal as anaturally occurring cast coating witha distinctive metal character. Greateruniformity within certain parameterscan be achieved by concertedattention to steel detailing andfabrication.A number of buildings form thecomplex with significant steelinvolvement in the principlebuildings. These are clad in stone,zinc and glass panels of “pinwheel”shapes fixed to hot dip galvanizedsteel frames usually exposed to viewfrom within the buildings but alsooccasionally visible from outsidethrough exposed unclad holes.36 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – “The world of hot dip galvanizing around us”South and north atriumbuildingsThese public interactive buildings areframed in an exposed web of raw hotdip galvanized steel, clad internallyand externally in “pinwheel” shapedglass. The south atrium provides anamphitheatre, while the north atriumprovides public access to the NationalGallery. Arguably this will become oneof the most unique buildings in theworld.The primary frames and members arefabricated from 200mm square hollowsections with the inner and outerwalls a “web” like structure, nonparallel and approximately 1 200mmto 1 500mm apart. The pinwheelshaped glass is fixed to lightsecondary hot dip galvanized framesof the same shape. The primary steelis similarly shaped with more than1 000 straight pieces different andindividually numbered.factory for checking and stock pilingready for despatch to site in therequired erection sequence. As ofOctober 2001 approximately 90% ofthe primary steel was erected intothe unique web without the need forany remedial work to a member. Inexcess of 1 000 tonnes of hot dipgalvanized steel have been used.The Association wishes to thank GalvanizersAssociation – Australia for thiscontribution.Editorial CommentIt is worthwhile noting that in spite of some1 000 tons of very difficult steel sectionconfigurations (see photo) that were hot dipgalvanized, only 10% of the steel neededsome form of remedial work, over theproject period.This could only be achieved by firstly, initialand subsequent regular communicationbetween all parties, including the galvanizerand secondly a mix of other important aspects,including:• Size of members vs available bath sizes,weld growth and dimensional stability.• The position and optimum size of fill anddrain holes.• Steel composition.• The colour variance between hollow, plateand structural sections.• Disciplined QA program, includingsample approval by all parties.We are of the opinion that instituting soundand regular communication opportunitiesbetween all parties and by implementing therequirements of the “Architectural Check List”,see magazine no 24, a far higher degree of hotdip galvanizing coating success can be achievedto the satisfaction of all parties.Pre-production andprototypingConsultations were held with allparties to discuss every aspect of thehot dip galvanizing process and itsimpact on the visual and structuralcriteria of the project. The hot dipgalvanized colour and sheen variancebetween hollow, plate and stripsections were considered. Detailing,such as drain hole frequency, size andlocation, weld growth anddimensional stability within productdesign tolerance, were addressed.Steel composition was critical to theappearance outcome and was closelymonitored. A disciplined qualityassurance program was a commoninterest and responsibility. As allframes were double dipped due totheir size, the galvanizer institutedspecial procedures at their plant toensure that all offered standards weremaintained under a strict productionquality system.Fabricator deliveryCAPE GATE(PTY) LTDTel: 016 980 2121 Web: www.capegate.co.za Fax: 016 988 3421Cape Gate is a fully integrated producer ofsteel, wire and wire products with our ownsource of raw materials.All our products meet recognisedinternational standards and are sold worldwide in a secured and well establishedgrowing customer base.We serve....● Mining● Agriculture● Industry● Commerce● Civil engineering and construction● Domestic and foreignmarketsAfter hot dip galvanizing, memberswere returned to the fabricator’sVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 37

Feature – “The world of hot dip galvanizing around us”Grand Arbour – AustraliaRedevelopment of World Expo88 SiteThe South Bank Corporation is a bodycorporate established by theQueensland Parliament as gazetted onMay 8th 1989, with more recentamendments reflecting the growingrole of the Corporation in the furthermanagement of this city area. Themission of the Corporation is tofacilitate the development andoperation of a successful world-classleisure, business and residentialprecinct, for the enjoyment of visitorsand the general benefit of the Brisbanecommunity.Master PlanDenton Corker MarshallThe master plan of the expo site andsome adjoining neighbourhood,comprises approximately 43 hectaresalong the Brisbane River, directlyopposite the central business district.In addition to the Brisbane Conventionand Exhibition Centre, South Bankfeatures an international hotel, highquality corporate office development,selected academic facilities, residentialapartments and a range of restaurants,retail outlets, a swimming lagoon withits own beach and a tropical arbourlinking the entire development.ParklandThe 17 hectare South Bank Parklandsstretches along one kilometre of theriver bank, where further developmentincludes placement of tropicalrainforest trees, surrounding opengreen spaces of ground vegetation; asoothing contrast to city activity.VisionThe success of the development hasarisen from the adage that enthusiasmis infectious. In this case, it has alsobeen innovative and inspired.A cooperative team of experts havecreated a city development equal toany in the region, with an admirablybalance of community consideration,appropriate function, environmentalconcern and aesthetic appeal.Even yet, the project is notconsidered closed, where clearlyopportunity is being provided forfurther development for the futuregrowth of the area.The Arbour Denton Corker Marshall’sproject report comments: “The GrandArbour is a 1km long architectural andsculptural installation, providing aphysical and visual link between themany facilities of the South Bankprecinct. A central aspect of themasterplan development, the Arbourmediates with the new open parklandto the west, while providing a shelterednorth-south route through the entiresite. Sinuous steel posts, up to 10mhigh, support a band of purplebougainvillea, either above, to the sideor entirely enveloping the curving path.The juxtaposition of the various postconfigurations creates a diversity ofspaces from tight and enclosed to wideand expansive. Overlapping steelpanels form a plated yellow ribboncanopy along half of the Arbour’slength. A total of 406 hot dipgalvanized steel posts are spaced at 4mnominal centres. A uniquearchitectural and urban gesture, theGrand Arbour is designed to offerBrisbane a new, distinctive andmemorable landmark.38 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – “The world of hot dip galvanizing around us”Modular ComponentsThe height of the posts (10m) meantthat they would have to be in parts forease of transportation and assembly. Akit of parts, made up of a small rangeof components was the solution. Theposts were divided into three unequallengths – base, neck and head. Threevariants were devised for each part(A,B,C) resulting in a total of only ninedifferent components. Any basecomponent could be connected to anyneck and any neck with any head. Theycould also be rotated 180°. Thisallowed for a possible 108 differentpermutations for the post profiles,varying from 10m high gentlyundulating to head height expressivelycurving.Computer ModelThe complexity and non-linear natureof the project meant that traditionaldocumentation techniques would beinsufficient.Advanced Computer Aided Designfor all stages including design,documentation and construction wasutilised. The entire Arbour wassimulated as a full scale 3Dcomputer model, from which allplans, elevations and sections wereextracted.Specially written computerprogrammes analysed the CADmodel and automatically generatedschedules for the Arbour setout andpost components.FinishesHot dip galvanizing was selected asthe finish for the posts. Corten steel(a pre-rusted finish) had beenconsidered in the early stages, butconcerns over run-off staining of thepath (and pedestrians) negated itsuse. Furthermore its rusty browncolour would give the impressionthat the posts were imitating trees.The Arbour, while being organic, wasclearly to be a man-made insertioninto the landscape, not an imitationof nature. “The grey metallic finishof the hot dip galvanizing providedthe desired artificiality and industrialruggedness, in addition to a lowlevel of maintenance.”The Association wishes to thank GalvanizersAssociation – Australia for thiscontribution.

Feature – “The world of hot dip galvanizing around us”Isabel II Park, Palencia – SpainIntegration of the livingpresent and historicaltraditionThe concept of the public garden orpark should be a place of tranquillityand aesthetic beauty, where peoplecan go to find peace and to rechargetheir “batteries” in the midstof a busy city life. A good park willblend living gardens withcomplementary architecturalstructures that are both pleasing tothe eye and have a certain practicaluse. The architecture of the Isabel IIPark in Palencia, Spain has sought todo this in a novel way, suitable for aprogressively improved city.The structures occupy an area ofapproximately 38 000m 2 , includingthe area of the Paseo del Salón, anold avenue open to pedestrian trafficwhich is integrated within thegeneral space of the park. Inside theold park two highly differentiatedareas may be clearly identified. One,to the southeast, is made up of whatis known as the Historical Garden ofIsabel II, and features theornamental gardens and the oldestand leafiest wooded area. The other,to the northeast, has more openspaces.The new scheme attempts to unifythe two old areas of the park, withthe idea of creating a common skyroof,with vegetation in the old areaand the symbolic canopy of thepergola of hot dip galvanized steel ofvariable height in the modern area.Furthermore, the new layout of thepark joins these two aforementionedold areas through three longitudinalroutes, brought together in threebroad avenues running east-west.The Main Avenue runs through theentire park, parallel to thepedestrianised Paseo del Salón.Situated in the Paseo is a long, lowpergola with a structure of hot dipgalvanized sections and a roof ofexpanded hot dip galvanized steelsheet, that will serve as a venue forfuture exhibitions, and beneathwhich there has also been installed aseries of permanent kiosks.The Central Avenue runs along thelongitudinal axis of the historicalornamental gardens and the RoseGarden. The large pergola, aspacious hot dip galvanized steelstructure, is located on this avenue,in the area of greatest remodelling ofthe park. With its height itconstitutes a metallic canopyequivalent to the existing treecanopy in the area of the HistoricalGarden. This pergola is similarlycovered with expanded hot dipgalvanized steel sheeting, withdifferent perforations that throw ashadow that changes throughout theday, and below which is located thegarden of aromatic and medicinalplants. At the far end of the pergolathere is a lake, over which theCentral Avenue extends by means ofa footbridge, which is also hot dipgalvanized.The Open-Air AuditoriumHot dip galvanized steel is theselected material for theconstruction of the open airauditorium, and equal importance40 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – “The world of hot dip galvanizing around us”has been given to it in thearchitecture of all the elements in thepark, as described above. Due to itsaerial lightness, its iridescent colour,its great corrosion resistance and itslow maintenance cost, it proves to bethe ideal material, on one hand forgenerating a very beautiful contrastbetween nature and artifice and onthe other, for ensuring its practicaluse in the open air.The structure of the auditorium hasutilised steel sections, which havebeen hot dip galvanized. The slendervertical pillars are made of twoclipped profiles. They support a boxbuilt with a framework of steeltrusses, wrapped in a translucent skinof expanded hot dip galvanized steelsheet and a light covering of twolayers, one of cellular polycarbonateand the other of expanded hot dipgalvanized steel sheet as in thefaçade. This raised aerial box concealsthe structure that will be the supportfor the stage infrastructure, thescenery and the lighting equipment.The metallic structure of theauditorium was modulated in piecesof the greatest possible size, withinthe constraints imposed by transportand the galvanizing process, with theaim of producing a work with thefewest possible joints, all of whichare bolted.The Auditorium of the Isabel II Parkwas awarded First Prize in theSpanish Galvanizers AssociationAwards, 2004.The Association wishes to thank theSpanish Galvanizers Association for thiscontribution.The structure of the enclosed stagearea is organised into three sections.Four principal trusses parallel to thefront of the stage, 5.5m high and 15mwide, support the distance of 12mbetween pillars and have a projectionof 1.5m on both sides, through whichpass the two longitudinalmaintenance walkways. Perpendicularto the front of the stage and as a tieinto the aforementioned structurethere are two second-order trusseswith chord and web members. Finally,a third section of trusses is located onthe main trusses in the form of“hairpins” and acts as a support forthe four transverse walkways, as wellas a support substructure for thelattice of the façade. The enclosedstage area therefore contains fourtransverse and two longitudinalwalkways, made up by grid panels andhot dip galvanized steel flats.The foundation consists of areinforced concrete slab, under whichis a space that houses some smalldressing rooms and toilets, taking upa third of the area.LEADERS IN SURFACE CHEMISTRYOperate in a clean fume-free environmentproducing high quality galvanized productswith our Hi-Tech range. We offer:● Hi-Performance acid and alkaline degreasers● Permanent protection passivators● Enhancing pickling inhibitors● Highly specialized low fume fluxes● System compatible rinse aids● Fume suppressants for pickling baths● Rust control and rust converters● Paints to stop zinc coating on steel● Galvanized wire drawing lubricants● Zinc reclaimers from ash● Galvanized bath de-oxidizers and cleaners● Chemical systems process control● Process management and design● Galvanic coat and zinc analysisGAUTENG HEAD OFFICE:Tel: +2711 760 6000 Fax: +2711 760 6070WESTERN CAPE REGION:Tel.: +2721 557 8646 Fax.: +2721 557 8781Cell: +2782 353 0544 E-mail: chemplus@mweb.co.zaVolume 2 Issue 4 2005 Hot Dip Galvanizing Today 41

Feature – “The world of hot dip galvanizing around us”A snapshot of what is going on inNorth AmericaThe Association wishes to thank the AGA for this contribution.Caltrans District 7HeadquartersCaltrans is responsible for design, construction,operation and maintenance of California’s statehighway system. Due to previous experience, hot dipgalvanizing has been the exclusive choice of Caltransfor corrosion protection.Caltrans demonstrated the partnership with hot dipgalvanizing in an aesthetic fashion by integrating ahot dip galvanized fascia into the design of its newheadquarters, located in the historic civic centre areaof Los Angeles. Included in this visual image of whatCaltrans does on a daily basis – ie., design with hotdip galvanizing – is the structural steel and handrailfor the unique face of the building.Architect – MorphosisContractor – Clark Construction GroupLiberty Pedestrian Bridge overthe Reedy RiverThe Liberty Bridge is both a curved and cantileveredstructure, the only one of its kind in the USA,creating an aerial amphitheatre for pedestrians toenjoy the spectacular views of the Reedy River Fallsin Greenville, South Carolina. With a 90 foot (27.5m)high suspension towers that lean 15° away from thewalking deck, the bridge’s 330 foot (100m) long by200 foot (61m) clear span appears to float above thelandscape.Both the reinforcing steel and bridge cables were hotdip galvanized, as the architect stated, “I want thisbridge to stand for as long as possible withoutmaintenance to the concrete deck.”Architect – Miguel Rosales of Rosales, Gottemoeller &AssociatesEngineer – Schliach Bergermann42 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Feature – “The world of hot dip galvanizing around us”Harrisburg Airport MultimodalTransportation FacilityThe Harrisburg Airport Director, who had apreviously very positive experience using hot dipgalvanizing, together with the designers selectedthe coating again to protect most of the structuralelements of the building. “The designers liked thestrong contextual relationship between the hot dipgalvanized multimodal facility and the airport’snew terminal.”Architect & Engineer – HNTB ArchitectureWe recently received thefollowing letter from a reader:CK No 2005/009611/23P.O. Box 82741Southdale2135Re: Product “X”Tel.: 827-4221Fax: 827-4561Email: bulldogproj@murrob.comSpecialists in the preparation and painting of hot dip galvanized steel:sweep blasting, abrasive blasting, tank linings and industrial paintingI recently received a brochure from a paint manufacturer inKZN which contains extravagant claims concerning theprotective properties of a zinc rich paint that has beendeveloped. The brochure also contains statements of asomewhat questionable technical nature in comparing hot dipgalvanizing with this organic zinc rich product.I would value your comments.Underground Mining PersonnelCarriers & Transport VehiclesFor harsh underground coal-mining operations,other than the hood, fenders, bed and rails, hotdip galvanizing was selected to protect the entirevehicle. The ability of the coating to withstandabrasion, rough treatment and regular washdowns,necessary to remove dust build-up, wasthe major consideration for the selection.The durability of the hot dip galvanized coating onthese vehicles has saved the mining industrythousands of dollars and continues to attract endusersin a variety of other underground applications.Architect & Engineer – Terra ProYours sincerelyMike BookDuplex Coatings ccEditors comment:Walter had already pre-empted the concerns expressed by Mike Book incorrespondence addressed to the author of this brochure. Readers may findthese comments interesting. To avoid embarrassment, the name of the paintmanufacturer and that of his product have been withheld.I have read with interest your notice concerning the merits of “X” zinc richpaint. With respect, it is necessary to comment on some of the statementscontained in this notice.• You refer to the propensity for distortion in the case of hot dip galvanizing.Meanwhile, some 350 000 tonnes of steel other than sheet and wire issuccessfully hot dip galvanized annually in SA. The fact is that providedthe correct design fabrication and galvanizing procedures areimplemented, the incidence of distortion is minimal. To say therefore that“there will be a distortion that could be costly in the manufacturing of theitems” is misleading since the truth is that in the vast majority of cases,the absence of any distortion of components which have been hot dipgalvanized can be guaranteed.• You make the claim that “X has been formulated as a paint to offer thesame protection as galvanising”. This ignores the fact that hot dipgalvanizing is metallurgically bonded to the steel substrate by a series ofcorrosion and abrasion resistant Fe/Zn alloys whereas any paint systemrelies entirely on adequate surface preparation to ensure a mechanicalbond.• You state that “As can be seen in the photograph, the steel would have tobe grit blasted and the correct quality procedures will need to be followedin order to make this product a successful one”. You do not make it clearwhich process you are referring to but presumably you mean “X” sincethe hot dip galvanizing process does not require grit blasting for surfacecontinued on page 49...Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 43

MisconceptionsMISCONCEPTIONSMiss Conception puts it “straight”“Miss Conception” rectifies incorrect impressions concerning hot dip galvanizing.Hot dip galvanizing combined with a good paint system provides limited added corrosionprotection while the adhesion properties of a paint system applied onto a hot dip galvanizedsurface will always be suspect.True or false?The simple response to this statementis that it is based on misinformationand ignorance of technicallysubstantiated facts.While this subject has been discussedpreviously in this column it warrantsrevisiting.The demand for duplex protection (hotdip galvanizing plus a heavy-dutyprotective paint system) continues toincrease for applications whereaggressive corrosive conditions pertain.This trend is due to the numeroussuccessful results obtained bymonitoring the performance of duplexcoatings exposed to aggressiveconditions throughout the country andelsewhere. To illustrate, a slipway forfishing boats at Saldanha Bay wasoriginally protected by a good epoxypaint system. A similar structure at StHelena was subsequently protected bya duplex system where an epoxy paintsystem was applied over the hot dipgalvanized coating. After several yearsin service, the Saldanha Bay structurewas condemned as unsafe, due tocorrosion. Meanwhile, the consultingengineers involved with both theseprojects were monitoring theperformance of the duplex protectedstructure at St Helena.The performance of the duplex coatingat St Helena has been entirelysatisfactory with the result that theconsultants decided to recommendduplex protection for all replacementslipway steel at Saldanha Bay. This isan interesting project in that thecontractor was able to salvage some25% of the original steel components,which were subsequently hot dipgalvanized and painted with the sameduplex system as applied onto allreplacement steel. This is only one ofmany examples of success that can besited.Contrary to the commonmisconception, hot dip galvanizing isindeed an ideal surface on which toapply a paint coating. The best resultsare achieved if paint is applied ontofreshly hot dip galvanized surfaces afterappropriate surface preparation and assoon as possible after hot dipgalvanizing. Delayed painting to enablethe zinc surface to weather isunnecessary and can be undesirableparticularly in corrosive environmentswhere the coating may be subjected tosurface contamination. The selection ofa compatible paint is important. Mostpaints are compatible with zinc butalkyd enamels should not be applieddirectly onto a hot dip galvanizedsurface. This is because the alkydproducts react with zinc at the interfaceto form zinc soaps, which over a periodof time will result in de-adhesion. Thischemical reaction is technicallydescribed as saponification.As with any other material to bepainted, adequate surface preparationand surface cleanliness are importantprerequisites for acceptable paintadhesion. Some of the reputablegalvanized iron cleaning (GIC)chemicals, supplied by paintmanufacturers are quite effective forsubstrate preparation, provided thatthey are applied in accordance with themanufacturer’s instructions.Light sweep blasting of the hot dipgalvanized surface with the correctabrasive which is readily available, willprovide outstanding adhesion.Unfortunately this surface preparationmethod is abused by applicators whothrough ignorance and an absence oftechnical expertise combined with adegree of sheer stupidity, see the termsweep blasting as a method ofshattering the hot dip galvanizedcoating with an unsuitable abrasive atinordinately high blasting velocities.The motivation for such irresponsiblebehaviour, which is frequentlyencountered, is beyondcomprehension.If correctly done, sweep blasting willremove a negligible quantity of the zinccoating (at the most about 6 - 10microns) while at the same time it willprovide a surface profile of about 50microns.The concept of duplex protection isgaining in popularity with the resultthat many galvanizers in Europe areadopting the concept of a “one stopcorrosion protection shop” where bothhot dip galvanizing and subsequentpainting is undertaken at thegalvanizers’ premises. South Africangalvanizers are currently implementingthis concept to the extent that somehave already reached the mature stagewhere they can be acknowledged asboth galvanizers and competent paintapplicators.44 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Personality ProfilePersonalityProfileDarelle Tania Janse van RensburgI am an independent corrosion andcoating consultant and currently headthe Corrosion and Coating Section ofOrytech (Pty) Ltd. This company alsospecialises in industrial plant, projectmanagement services.I originally started out as a high schoolScience teacher, but later joined Eskom’sCorrosion Group, in 1990. Here, Ideveloped and obtained the necessaryskills as a corrosion protection specialistwith respect to power generation,distribution and transmission plants. Ilater headed the Corrosion Group atEskom and apart from having had aresource managerial function, alsoprovided technical advice and support inthe fields of industrial coatings, materialprotection and general corrosionproblems. During my period with Eskom,I have completed numerous research,inspections and failure investigationsprojects related to the corrosion andcorrosion protection of powergeneration, transmission anddistribution plants.Up to now, and even in my newcapacity as an independent consultant,I have been involved in the writing ofmany of Eskom’s corrosion protectionspecifications and have specified hotdip galvanizing on more occasions thanI can remember. My appreciation forhot dip galvanizing as an excellentlong-term corrosion protection systemhave come about, having first handwitnessed it’s high-quality performancein terms of corrosion protection ofstructural steelwork throughout SouthAfrica, that is with respect to Eskom’soverhead power line structures andsub-stations. Also, having personallytested numerous duplex-systems overthe years, I have come to recognise thathot dip galvanizing can be effectivelyused in high corrosive environments,especially when suitably overcoatedwith durable organic coating systems.My present goal is to expand andcontinue with the development of anindependent corrosion and corrosionprotection testing laboratories for heavydutyindustrial systems. I envisage thatin the years to come, many new systemswill be developed, tested and used incombination with hot dip galvanizing. Inaddition, it is certain that in many of thefuture material exposure programmesthat I may be involved with, hot dipgalvanizing will continue to be used as abench-mark corrosion protectionsystem, in terms of the performancetesting of many other materials.I presently hold the position of SecondVice President of the Corrosion Instituteof Southern Africa, and through thisfunction have come to greatly appreciatethe technical support and dedicationprovided to the industry, by the Hot DipGalvanizers Association of SouthernAfrica. Since only a few companiescontinue to invest in research anddevelopment programmes, it is good tosee that an industry, ie. hot dipgalvanizing industry, can still standtogether and jointly, support,investigate, share and research their owntechnology.

Guest WriterGuest WriterBob Andrew, our guest writer, is a consulting value engineer and Honorary Life Member of this Association.The reciprocal nature of languageI used to be intrigued andmystified by the origin oflanguages. Modern linguistics didnot help me much as mosttheories seemed to be solely interms of one language with littleattempt being made to give thema wider application. Our commonlinguistic ancestry seems to havea truly inaccessible past. I wasalarmed that according to someevolutionists, the distantcommon ancestor and the‘material cause’ of all modernlanguage might not even havebeen a language, but a form ofvertebrate evolution: of body,brain and behaviour, or whateverthis means.My understanding of languagetook a giant step forward when Irealised that all I needed to knowis that there is a relationshipbetween what is going on ‘in myhead’ and a bodily activity thatproduces sounds and gestureswhich are perceivable by othersand interpretable by them.Language seems to be mycapacity to try to alter the mentalorganisation of someone else.Sometimes, I succeed in this, butmore often I do not, especially, orso it seems, in relation to myteenage children. In this regard, Ifound it easier to change my ownmental state by talking to myself.Wild African parrots provided mewith an important key to theunderstanding of language. I readthat they coordinate their matingritual by producing a commonsong. While each bird appears tobe singing a full melody, it isactually a duet in which the twobirds progressively expand uponeach other's phrases. What isintriguing is that the level of theritual is determined not so muchby the 'meaning' of the soundsbut by the intensity and dynamicsof the melodic coupling. It seemsthat the mating ritual has'reciprocal altruism' (you scratchmy back, I'll scratch yours) boundup with it. The mutualcoordination of the matingbehaviour develops from a 'backand forth' kind of relationshipwhere each parrot benefits fromthe response of the other. Surely,this must be true about language.The last ten years of our newdemocracy in South Africa hastaught me a lot about language.We have eleven official languagestenindigenous ones and English.Previously, the differentlanguages were viewed as thecornerstones of the cultures theysupposedly represented and for avariety of reasons generally keptthe people apart from oneanother. Now, within a frameworkof democracy, they are bringingpeople together. South Africansare going out of their way to learnand speak as many of the otherlanguages as they can and evenwith just a smattering they arecommunicating. Personally, I havefound that it does not evenmatter if you can’t speak thelanguage properly but if you juststop and greet a person, usinggestures and a smile, one cancommunicate. I had aconversation the other day with acomplete stranger: we smiled, welaughed, we used one or twocommon words, we slappedhands, we touched and althoughwe did not know what the otherwas saying, both of us came awayknowing that we had bridged adivide and it was a very valuableexperience. Languages are also inthe process of blending. This mayhorrify the purists but it is a trendthat nobody can stop as it haspowerful tentacles driving into allaspects of our unique society,including music, writing and themedia.My firm view of language now isthat it is a powerful instrumentand constitutes one of theprincipal forces controlling andforming human behaviour.Language needs to be supportedby face-to-face contacts wheregestures, facial expressions andtone complement syntax andunderstanding. Unlike the Africanparrots, human beings need tosee one another to maximise theco-ordination of behaviourthrough language. As ishappening in South Africa,language can also help peopletruly ‘see’ one another.46 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Walter’s CornerWalter’s CornerCorrosion control by hot dip galvanizing plus paintZinc rates among the most intriguing metals provided by thecreator for the benefit of mankind. Apart from its nutritionalvalue and numerous other important metallurgic properties,millions of tons of zinc produced annually throughout theworld are used to provide protection from corrosion. This initself is an enigma since zinc is an unstable metal in its pureform, which is a polite way of saying that it is prone to corrode.Why then is it successfully used to reduce corrosion?The answer to this is fairly simple. When a zinc coatingapplied by the hot dip galvanizing process is exposed to theatmosphere, the zinc surface of the coating reacts with theoxygen and carbon oxide in the air to provide a stablecorrosion resistant surface film of zinc carbonate whichprotects the underlying reactive zinc.The prime objective of a hot dip galvanized coating and someof the other zinc coating processes is to provide animpermeable metal film, which precludes the contact ofmoisture and corrosion inducing substances with the steelsubstrate. The durability of this protective barrier isdetermined mostly by the corrosion resistant properties of zinccarbonate. This explains why added protection by way of anorganic paint coating enhances the durability of a hot dipgalvanized coating in aggressively corrosive applications, sincethe protective zinc carbonate layer on the surface of thegalvanized coating is enhanced by the added protection gainedfrom the paint coating. When moisture permeates through thepaint coating, any zinc corrosion products formed at the paint /zinc interface constitute a solid volume of about 20% greaterthan the zinc from which they have been produced. Were asimilar protective paint to be applied directly onto a steelsurface, the corrosion products produced at the interfacewould be some 2 to 3 times greater than the original steel.Clearly, the propensity for de-adhesion of the paint film andsubsequent coating failure is also far greater.When moisture permeates through the paint film to thesteel substrate, cathodic protection at the interface isprovided by the zinc particles present within the paint.Plainly, the presence of sufficient zinc particles is essential(80% of the dry film is generally recommended) in order toprovide electrical contact between the particles within thebinder as well as with the steel. Nevertheless, it followsthat once zinc particles have been consumed in providingsacrificial protection to the steel, the mechanism ofcathodic protection ceases and the barrier protectionprovided by the paint is reduced.This is not to say that zinc rich products are not what theyare “painted to be”. Products such as inorganic zinc silicatehave a proven successful track record as prime coats overwhich to apply a heavy-duty organic paint system. But Iventure to suggest that cost effective easy to apply duplexsystems (hot dip galvanizing plus paint) provide at leastequal if not enhanced long term corrosion protection to thatavailable from zinc containing paint systems.The second line of defence provided by zinc is cathodicprotection whereby zinc, which is electronegative in relation tosteel, constitutes the anode with steel as the cathode in acorrosion cell. This results in the zinc being preferentiallysacrificed to protect the steel.With a hot dip galvanized coating, cathodic protection will onlycome into effect and for that matter is only required once thecoating has been breached and underlying steel is exposed forwhatever reason. The benefit of this protective mechanism issignificant in that corrosion cannot creep under a galvanizedcoating, while small uncoated surfaces are provided withcathodic protection from the surrounding zinc film.In the case of paints, which contain zinc, the situation isdifferent in that zinc is added to the paint in order to augmentbarrier protection by the paint throughout its service life.Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 47

Member’s NewsBarloworld Galvanizersinstalls four metredeep kettleFor some time, the management ofBarloworld Galvanizers had givenserious consideration to installing adeeper kettle.This largely arose from a noticeabletrend towards more ‘long’ productsin excess of 2.3m requiring hot dipgalvanizing. Most products with a‘height’ in excess of this figure,particularly fabricated structures andbox frames, as well as fencing panelsand gates, required vertical doubledipping.Barloworld Galvanizers have for awhile now, had the ability togalvanize plate girders up to 18.5min length without distortion. Thishas resulted in extending the marketfor hot dip galvanizing, wherepreviously such products had to bepainted.The old Line 2 kettle neededreplacing, and rather than replacewith the same size kettle, thedecision was taken to extend thesize, so as to again be able to offermore to the market in terms of hotdip galvanizing as a corrosionprotection method.With the growing demand for hot dipgalvanizing for the architecturalsector, the need to overcome doubledipping, with the associatedaesthetic imperfections was alsotaken into consideration.It was then decided to install a 10mlong kettle, which is 2m wide and 4mdeep, thereby providing a totally newoffering to the market.A new heating system wasconfigured, so as to conserve energyusage, making this kettleexceptionally thermally efficient, akey environmental factor in this dayand age.The new kettle was commissioned inearly September, and considerablebenefits are already being realisednot least the speedier processingrate, which is impacting positivelyon turnaround times.The management and staff atBarloworld Galvanizers are extremelyproud to be able to bring thisoffering to the corrosion protectionmarket in southern Africa, as well asonce again, being at the forefront ofObituaryIt is with sadness that weannounce the death ofTony Franco onSaturday 5 November.Tony started his career in theearly sixties at RietfonteinGeneral Galvanizers and in thelatter years established severalgalvanizing plants, the first beingSouth Cape Galvanizers with hisson Marc. Bay Galvanizers inRichards Bay andPietermaritzburg were eventuallysold to other parties, when Tonymoved to the South Coast.We express our sincerecondolences to his wifeRonelle, son Marcand daughters Mia andKaylene and his family.introducing innovation to the hotdip galvanizing industry.Editors Note:We at the HDGASA congratulateBarloworld Galvanizers on this initiative,which will no doubt enhance our marketingefforts on hot dip galvanizing.Arrival of the 4 metre deep kettle.One of the first box frames to be hot dip galvanized in a single dip.48 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

GeneralHDGASAInformation DiscWe are extremely happy to report that the distribution ofthis magazine has grown from 3 000 contacts in April 2005to 5 093 contacts as at end September 2005. We are veryconfident that this number will be increased to at least 6000 by the end of February 2006. These contacts are madeup primarily of specifiers, consulting engineers, QS’sarchitects, fabricators, end users and members.In keeping with modern technologically, the HDGASA willbe compiling an Information Disk, which will be distributedearly in 2006.Our commitment to this CD will be to ensure that it ispowerful, professional, user friendly, informative and soexciting that everybody will want to browse and keep theCD handy. Obviously a project of this magnitude will incurcosts and we are therefore looking for sponsorship to assistwith funding this marketing project.Should you wish to take part in this project by way ofsponsorship, kindly contact the HDGASA as soon as possible.January/February:April/May:July/August:2006 FEATURESLighting, Lighting Masts, Electrical Pylons,Communication Masts.Conveyance Piping, Water & Grain Storage,Training & Education.Annual Awards Event, Agriculture.October/November: Gold, Platinum, Coal & Diamond Mining...continued from page 43preparation. But then you go on to say that “X can be paintedonto rusted surfaces”. This would seem to be a contradiction of theoriginal statement. In any case, during some 45 years experiencein the corrosion control industry, I have yet to come across a surfacetolerant organic coating that can be reliably applied onto a steelsurface that has not been adequately prepared.• You refer to the formation of white rust as beneficial. This is farfrom the truth. Zinc hydroxide (white rust) is an unstable andundesirable zinc corrosion product. When a hot dip galvanized zincsurface is exposed to the atmosphere, carbon dioxide and oxygenreact with the surface zinc to form stable corrosion resistant zinccarbonate which protects the underlying zinc. White rust is formedwhen carbon dioxide is depleted and moisture is present e.g. in thecase of closely packed pregalvanized sheets.• You do not indicate the actual zinc content of your zinc rich productwhich should contain 80% in the dry film to be effective. Thedurability of a zinc rich paint coating is to a large extent determinedby the zinc content.Finally, there are many excellent zinc rich paints available which providegood corrosion control and no doubt your product could be one of these,but to compare zinc rich paint with hot dip galvanizing is not comparingapples with apples.I respectfully suggest that to make claims that “X” is a superior productbased on suspect technical information is not conducive to the promotionof your product.Please accept these comments as constructive from someone who hasbeen involved in the corrosion control industry for almost half a century.The Association would like to acknowledge theadvertisers and thank them for their supportAkzo Nobel ..........................................................page 31Armco Galvanizers................................................page 39Barloworld Galvanizers............................Inside Front CoverCape Galvanizing ................................................page 25Cape Gate (Pty) Ltd ..............................................page 37Chem + Plus ..........................................................page 41CWI ......................................................................page 45Duplex Coatings cc................................................page 17Galvanizing Techniques ........................................page 51Galvatech ..............................................................page 11Highveld Steel & Vanadium Corp..........................page 3Hi-Tech Elements ....................................................page 29IZASA..................................................................Back CoverJotun Paints............................................................page 9Lite Epoxy Coating cc ............................................page 33O-line Support ......................................................page 35Plascon Barloworld................................................page 13Rand Sand & Blasting............................................page 23Sigma Coatings......................................................page 7Surface Treatment Technologies ............................page 47Zincor ....................................................................page 53Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 49

GeneralIZASA supports southern Africaarchitects’ competitionThe International Zinc Association ofSouthern Africa (IZASA), as part of itsmandate to support new initiativeswith zinc has recently co-sponsored theSouth African Institute of ArchitectsAward - Steel in the Fabric of the SouthAfrican house. The competition wassponsored to increase the awareness ofthe use of steel, primarily lightweightand galvanized, in residentialconstruction. Steel is used widely forresidential construction in NorthAmerica and Australia where framingsystems have been used for manyyears. Steel is perceived to have strongadvantages over other materials,principally durability, adaptability andspeed of construction.The International Zinc Association(IZA) has been an active supporterinternationally of such bodies suchas the Light Gauge Steel FramingAlliance and the Metal RoofingAssociation in the USA, the JapaneseIron and Steel light framinginitiative, and now the InternationalIron and Steel Institute (IISI)initiative Sustainable SteelConstruction. This focuses largelyupon the creating greater usage ofsteel in residential use. In terms ofthis, a number of interestingpointers for market developmenthave been obtained through aninitial market survey. For instance,although regional variances occur,2 Who decides which material to use: all elementsFigure 9. Pre-fabricated room systems beinginstalled in the UK (Materials World,Vol. 13,No. 7, July 2005)Beijing Delhi London New York RioFigure 7. Who decides the material in residential construction? (IISI).ArchitectClientContractorEngineerQSDesignerthe importance of the architect inthe initial materials selectionprocess for building has beenhighlighted (figure 7). Over 50% ofdecisions relating to materials aredetermined by the architect and endclient combined. When looking atthe statistics for materials use, it isclear that steel is nowhere nearbeing a dominant material (figure 8).Considering the ability of steel toprovide for longer spans and moreopen space, a clear message of moreawareness required requires actionrather than words.Principal materials for main structure in single family dwellingsConcreteMasonrySteelTimberOther metalsTilesGlassBeijing Delhi London New York RioFigure 8. Principal materials for main structure in single family housing (IISI).Although continuously hot dipgalvanized roof sheeting has beenused for many years in South Africait has not enjoyed great appealacross the whole residential marketplace.In Europe, the need todevelop more residential space isdriving a review of material choicesand construction techniques (figure9). In the South East of England forinstance, there is a plan to createover 250 000 homes over the nextfew years, with the urgency being50 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Generalsuch that it is being overseenthrough the office of the DeputyPrime Minister. Similar urgencies arerequired in South Africa.Off this base, the IZA internationally,and specifically IZASA locally, iscommitted to partnering thedevelopment of the steel basedresidential market. Some constraintsto development do exist such as theneed to review standards and drivebetter skills development but theseconstraints are in fact drivers foropportunities and have createdwhole new industries overseas.However, the architect still needs tobe at the forefront of specifying.To further the development of theuse of hot dip galvanized steel inresidential construction, the IZASAsponsored the Student’s prize in theArchitects competition to create anawareness and encourage wider useof light gauge steel framedstructures. Working in conjunctionwith the Southern African Institute ofSteel Construction, this industryFor hot dip galvanizing withservice excellence• 12 400 long x 1 400 wide x 2 600deep kettle• Shot blasting• Technical assistance• Collection and delivery service• Open Saturdays• SABS ISO 1461 accredited52 Burman Road, Deal Party, Port ElizabethTel.: 041-486-1432 Fax: 041-486-1439Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 51

Generalinitiative reached every tertiaryArchitecture Department in southernAfrica. Overall, some 28 submissionswere received and these will form thebasis of a travelling exhibition destinedfor every major building andconstruction event in the region overthe next couple of years. Using theinternationally regarded architect GlenMurcutt (who has practices in the US,Europe and Australia) as the draw card,the Architects competition was judgedat the Annual Regional ArchitectsCongress. The prize for the winningpracticing architect (provided by a localsteel producer) was an all expenses tripto attend a Glenn Murcutt Master-Class. The Students’ Prize was a cashprize to the winning student and a cashprize to the student’s ArchitectureDepartment. IZASA believes that onlythrough ongoing exposure to theArchitectural community will light steelframing be accepted in a traditionalbrick and tile community.As part of a Steel Initiative, IZASAsponsored the students’ prize at therecently held Annual Architectsmeeting in Bloemfontein. Submissionswere received from all the ArchitectureDepartments in South Africa. Thejudges commended the studentsubmissions and applauded their useof steel in creating space andchallenging conventional thinking onresidential dwellings.The winning entry came from MaritaMeyer, a 3rd year student from theArchitecture Department at theUniversity of the Free State. This entryfocused upon the creation of openspace and entry of natural light – easilyobtained with judicial use of steel. Hersubmission entitled, “A house withsteel for a South African Chinese familyin Johannesburg”, was based upon theidea of Shigeru Ban’s experimental“Naked House” adapted to a SouthAfrican setting. Bedrooms becomemovable steel-and-cardboard cubicles,and living areas are on platforms withcoasters too. All of these elementsmove around in a “shed” created withsteel portal frames and glass curtainwalls.Marita was thrilled to have wonthe prize and said it has certainly madeher think more about the use of openspace created so easily using hot dipgalvanized steel.Working with various partners, IZASA iscommitted to an ongoing programmeof education and development in thearea. It is hoped to hold Industryworkshops in the near future to plotthe road ahead and have stakeholder(including government) commitment toincrease the role of hot dip galvanizedsteel in residential development.For further information on the use ofhot dip galvanized steel in residentialconstruction kindly contact RobWhite at IZASA at izasa@icon.co.zaor the HDGASA.“Road Shows” on the benefits of using hotdip galvanized rebar planned for 2006The International Zinc Association Southern Africa isto partner the HDGASA in a series of countrywideseminars during early February 2006.Many instances of poor reinforced concrete structureperformance can be attributed to the corrosion ofrebar. This leads to early unsightly rust staining andeventual spalling of the concrete due to theexpansion forces created by corroding rebar. Despitethe often termed benign environment of the Highveld,local examples of such problems are giving increasingcause for concern. In addition, the range of climaticconditions experienced around the large coastalexpanse of the country has resulted in expensiverepair and reconstruction.The seminars will highlight the major causes ofdeterioration in concrete structures and the use ofhot dip galvanizing of rebar as a long term solution.The presentations will include local experiencetogether with that of international work, some ofwhich has been sponsored by the United Nations.Case history examples will be used to illustrate wherethe use of hot dip galvanized rebar has beensuccessful. The seminars will provide time to providefor a transparent open discussion amongst delegatesand speakers. Many concrete structures are built bygovernment and these seminars are targeted at thismarket as well as the building and constructionindustry in general. The seminars will last for twohours and refreshments will be provided.The seminar dates are:◆ Cape Town - Thursday 9th Feb 2006◆ Port Elizabeth – Friday 10th Feb 2006◆ Johannesburg – Monday 13th Feb 2006◆ Durban – Tuesday 14th Feb 2006For further information, please contact, Heather at theHDGASA on 011 456 7960 or email heather@hdgasa.org.za.52 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

GeneralADDING VALUE TO STEELFOR 40 YEARSThe Association held its annual prestigious awards evening in August whereamongst other things we celebrated the 40th anniversary of the Hot DipGalvanizers Association.To commemorate this momentous occasion, of “adding value to steel for 40years”, we decided to produce a historical DVD based on what we experienced onthe screen that night.For those that never attended the evening, the DVD takes one back with an insight into the historyof zinc, the players who for various reasons found themselves at the forefront of the discovery andlater development, the early smelters, etc. It also addresses its early uses and in particular its morerecent health benefit discoveries, including its aphrodisiac qualities.The history of hot dip galvanizing is also detailed from where it started in France and the UK and later on in South Africa,where it started with hot dip galvanizing of sheet imported from the UK and finally to when general hot dip galvanizingstarted and who the pioneers were.In order to defray costs the DVD is selling for the nominal cost of R80-00 per copy including VAT but excluding packaging andpostage, should anyone be interested in purchasing a copy, kindly contact Saskia Salvatori at the Associations offices.ZincorA Division of Kumba Base Metals LimitedSupplier of zinc metal....the answer to corrosion protection.Plover Street, Struisbult, Springs, 1559PO Box 218, Springs, 1560Tel: (011) 812-9500 Fax: (011) 363-3293Website: www.zincor.co.zaexcellence in zincISO14001ISO9001Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 53

GeneralThe “honestcoating”stands upto its nameHot dip galvanizing is known asthe “Honest Coating”.How did it get this name?A hot dip galvanized coating is formedby interaction between iron andmolten zinc and if the steel surface isnot clean it will not react with themolten zinc. Conversely, if the steel isclean it will react and produce acontinuous coating, so if coatingsappear sound and continuous, theyare sound and continuous.Marking of steel is essential foridentifying rolled sections and plateat the stockists yard. This is frequentlydone with adhesive labels which oftenare very difficult to remove, prior tothe process. These items are thenpurchased for fabrication and mustagain be identified prior to and afterfabrication.Temporary marking as in the use of oilbased paint and other non-waterbased products, play havoc in thedaily stress of the galvanizer whowhen it is detected tries with difficultyto remove these contaminants, sothat uncoated areas do not appearafter hot dip galvanizing.All water based paints, particularly ifmixed with 50% water work extremelywell as does the “Pental White 100WS”or “Pental White 100W” marking pen,available from your local stationer.The photos indicate marking labelsand oil based paint on black steel,mechanical removal of marking paintand finally the result after hot dipgalvanizing when inappropriatemarking paint has been used and notremoved before hot dip galvanizing.54 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Case HistoryNo. 05/2005Twistdraai CollieryCase HistoryThe applicationA perception exists that suggeststhat one cannot apply hot dipgalvanizing within a colliery. Hot dipgalvanizing has over the years beenextensively used for conveyors, bothoverland and even underground. Inthe most severe corrosive conditionssuch as a coal washing plant, hot dipgalvanizing plus a suitable top paintsystem has been applied withexcellent results.Environmental conditionsCorrosive conditions within theTwistdraai coal washing plant wouldbe classified as a C5 environment interms of ISO 9223. In other words,one of the more extreme corrosiveconditions listed in the ISOspecification.The photographs below can bestillustrate the corrosive conditionsencountered at the washing plant.The siteThis case study reviews theperformance of a duplex system atSasol’s Secunda Twistdraai coalwashing plant. Coal is delivered fromthe mine to the coal washing plant,where after processing it isdispatched to end users.Our findingsDuring the site inspection, some 53different overall coating thicknessreadings were taken with thefollowing results:Maximum 888µm,Mean coatingthickness 388µm, Minimum 277µm.This 378µm coating reading was typical of thatfound on the structural steel.In general terms the structural steeltogether with the duplex system wasfound to be in excellent condition. Itwas reported that the coating systemhas been in operation forapproximately 4 years. In addition anannual inspection is conductedaimed at monitoring the coatingperformance. A series ofphotographs were also taken andthese have been used to illustrateour findings as well as any specificcomments.ConclusionTwo examples of the extent and severity of the corrosion conditions on painted steel.A Duplex system uses the strengthsof both hot dip galvanizing andselected paint coatings to compileand enhance “synergistic newperformance” coating, which is costeffective where “value analysis” andlong-term maintenance costs aretaken into consideration. The systemis designed to provide extendedservice life in severe corrosiveenvironments.Surface preparation is a criticalfactor to the success of the coating’sperformance and as such, must notbe overlooked in terms of thespecification, as well as at the timeof the application.Further examples of the integrity of the duplex system.Hot dip galvanizing is simply the bestform of primer for a good paintsystem!Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 55

Case HistoryNo. 06/2005Case HistoryGoedehoop CollieryThe applicationGoedehoop Colliery has been inexistence since the early eighties. Inabout 1995 the mine embarked onseveral extensions, one of thembeing to the coal washout facility andconveyor material supply system. Itwas then suggested to minemanagement personnel that becauseof previous paint coating failures thata duplex coating system be used toprotect the steel.condition and had to be purposelydamaged, in order to assess andmeasure the hot dip galvanizedcoating thickness.In comparison the paint coating onthe carbon steel hand rails of thecoal washout facility had failed.The suggested system comprised asingle coat high build epoxy coatingapplied onto a sweep blasted hot dipgalvanized surface in accordance withthe Association’s Code of Practice forsurface preparation and applicationof organic coatings.General photo of the structure.Cross cutting proved that adhesion of thecoating was sound.The environmental conditionsCoal washing facilities are relativelyaggressive environments, due to thecombination of coal dust and water.See “Planning the Duplex System forGoedehoop Colliery”Our findingsAlthough in existence for a number ofyears the old wash out plant wasfound to have several coating failures.Coatings in these conditions areextremely difficult to maintain unlessthe entire operation is shut down.Hot dip galvanized coating thickness (paintremoved).Total duplex coating thickness.The duplex coating system on thesteelwork in the new area is inexceptional condition, so much sothat the organic coating had to bepurposely damaged in order toassess the adhesion of the organiccoating and overall condition of thehot dip galvanized coatingunderneath.ConclusionAfter 10 years of service the duplexcoating system is in exceptionalIn comparison the paint coating on the carbonsteel handrails has failed.General corrosion conditions of the coalwashout facility.56 Hot Dip Galvanizing Today Volume 2 Issue 4 2005

Case HistoryNo. 07/2005Phalaborwa Copper MineCase HistoryThe applicationLike most established organisations,Phalaborwa mining operation has itsown in-house corrosion preventionspecifications. In the mid eighties themine called for tenders for the supply ofcertain cable ladders for use on themine. Not being able to offer thespecified multi-coat, solution paintsystem, due to several technical reasons,O-line Support Systems offered tosupply the cable ladders coatedaccording to their own in-housedeveloped duplex powder coatingsystem. The mine was at first scepticalbut entertained the bid as long as thenew system was placed alongside theirtried and tested system for futureperformance evaluation. Theperformance of the new system in timeproved to be superior, which resulted inthe mine altering its specification toinclude the duplex coated cable ladders.original parallel installation could not belocated. However, we did find a cableladder system that was installed in themid eighties, using the proprietarypowder coated duplex system. The cableladders were reported to be the originalO-line system, which was hot dipgalvanized and then overcoated with anepoxy polyester powder. The cableladders are no longer in use due to thebuilding being declared redundant.In spite of the relatively non-corrosiveenvironment in this instance, thepowder paint is still adhering to thehot dip galvanized substrate and oncross-cutting the coating to ascertainpaint adhesion, the coating remainedintact despite trying to lift it at thecross-cut. There were however, severalother coatings on components locatedat the site that were in the process ofbreaking down.ConclusionAfter 20 odd years of service atPhalaborwa Copper Mine, the duplexcoated cable ladders are stillperforming well in that the powderpaint is still adhering well to the hotdip galvanized substrate.Editors commentSubsequent to our visit and discussions withMr Horn, we understand that there aremany kilometres of cable racking that areduplex coated, still performing adequatelyafter 18 to 20 years in many otheroperational parts of the mine.The investment made in powder coatingtechnology by O-line Support Systems sometwenty years ago, has proved to be well spent interms of the success the company has had inapplying duplex coating technology.The environmental conditionsPhalaborwa Copper Mine is situated inPhalaborwa, midway on the westernborder of the Kruger National GamePark. General atmospheric conditions athand are dry and dusty and appeared tobe a typical C1 to C2 environment.However it was confirmed thataggressive conditions exist in the acidand zinconia plant which produce anumber of corrosive chemicals, includingsulphuric acid and can be categorised asa C5I environment. Mr Koos Horn, arecently retired superintendent from themine, originally responsible forspecifying the duplex protective system,had this to say: “This method ofcorrosion control, since first specifyingthe duplex system, has outlasted allother coatings and materials usedpreviously in all conditions of the mineincluding the acid and zirconia plant”(See Corrosion Categories in terms ofISO 9223, table 4, page 10).Insitu cable ladders in the redundant TransferStation No. 1.Total coating thickness reading on the cleanedup side rail of the cable ladder.Our findingsDue to the age of the originalinstallation and subsequent staffretirements and changes, etc., theCable ladder cross rung.Exposed powder coating subjected to a crosscut adhesion test.Volume 2 Issue 4 2005 Hot Dip Galvanizing Today 57