TECHNICAL

Corrosion protection& the environment:Galvanizing and Zinc Paint comparison, UPDATE 2009

BY NICK KARAKASCHCopyright Reserved © 2009

Keywords: Hot Dip Galvanizing, Inorganic Zinc Silicate Paint, Greenhouse Gas Emissions, Waste Management,Environmental Impact, Industrial Toxicity, Occupational Health & Safety, Lead, Potable Mains Water

The issues of environment sustainability andindustrial toxicity are now very significant at alllevels of society, no more so than with the Design/ Engineering Construction industry. Corrosionand protection, like all industries, comes at a costto the environment. The considerations of globalwarming, greenhouse gas emissions, acid rain, wastemanagement, manufacturing or application impacts,and long term environmental sustainability are justsome of the key issues used in the selection processfor Protective Systems.

ENVIRONMENTAL ISSUES FOR MATERIALSELECTION:

- What resources are necessary to provide theservice?-Is the application process environmentallyacceptable?- Are there any toxic fumes or waste produced?- Is the system environmentally acceptable - whatdoes it contain?- What airborne emissions and particles, if any, aregenerated?- Are there any OH&S issues associated with theprocess?

In the Protective Corrosion Industry, zinc metal in itsvarious forms is the most common material used tocombat steel corrosion. There have been numerousarticles written over many years comparing the meritsof Hot Dip Galvanizing (HDG) and Paint Systemsin terms of either environmental sustainability orimpact.

One comparison which seems to appear on a regularbasis is between HDG and three coat paint systems.Unfortunately this type of comparison appearsselective and is somewhat unbalanced as it distortsthe conclusions in favour of one system over theother. (Ref 2)

From a corrosion aspect, the only materials with a60-year proven performance record have either beenHDG or Inorganic Zinc Silicate (IZS) paint. Both are"one off systems" equal in performance in normalatmospheric environments. Whilst there are ThreeCoat Paint systems available, these are for severeconditions or for architectural reasons; they are not atrue reflection in comparison to either HDG or IZS inperformance or environmental impact with regard toone off systems.

The application and make up process of bothmaterials is vastly different and should be viewedin economic terms in the overall context of nettpresent value v nett future value. Considerationneeds to be given to such matters as energy andwater consumption, greenhouse gas emissions,industrial toxicity, environmental ecological impactsand the mineral resources necessary to provide theprotection.

There are three levels of environmental impactassociated with the protective coating industry. Itstarts at the mining level. Zinc is a naturally occurringmineral, the ore body needs to be mined, milled,smelted then refined to produce metallic zinc.From this point some of the zinc will end up in theapplication process for corrosion protection, either aszinc slabs for HDG or fine zinc particles for IZS. Fromthere the impact falls to the application industry asdiscussed herein. Finally, the long term environmentalimpact connected to the steel construction industry.

Both HDG and IZS have similar recorded casehistories listing in normal atmospheric conditions,however the volume of metallic zinc necessary toprovide the service is quite different, it favours IZSon average by 50% (Refer Table1). The reason for thedifference is in the physical make up of how the zincis bound into the system and its subsequent sacrificialcorrosion rate.

With HOGthe galvanizer has virtually no controlover thickness. The thickness or zinc mass achievedlargely depends on molten zinc temperature,immersion time and steel thickness. As the steelsection increases in thickness so does the final zincthickness. For this reason HOGstandards around theworld nominate minimum thicknesses for varyingsteel sections (Ref Table1).

For example, sections of 6mm and above are listedas 85 microns minimum; however in reality lt isconsiderably higher due to the nature of the process.Film thickness will range between 99-200 microns,well above the nominated minimum. The metallic zinccontent at 85 microns is a minimum of 600gramsjm2, (Ref 5). As consumption (thickness) increases, 50

does the level of environmental impact.

The volume of metallic zinc in water based IZSis constant and controlled by the manufacturingprocess. Respective international standards nominate85% by volume which calculates to 300grams persquare metre at 75 microns dry film thickness (Ref 6& Table 3).

The reason for the same level of protection with lowermetallic zinc is twofold. 1) Unlike HOG metallic zincparticles are encapsulated within an inert inorganicsilicate matrix thus protected. 2) Together with amicrocrystalline layer which forms on the steelsurface during application. This gives rise to a muchslower sacrificial consumption rate of metallic zinc.

METALLICZINCCOMPARISION

HDGEXAMPLE 1. 10 tonne 200UB30 steel beams

2. Surface area 30.9 me/tonne = 309 m2

3. Minimum Dry Film Thickness 85microns/me

Actual Dry Film Thickness 140 microns =1000 grams metallic ztnc/ms (Ref Table2)

FORMULA:309m' x 1000grams/m' - 309000grams - 309 kilos metallic zinc

IZS EXAMPLE 1. 10 tonne 200UB30 steel beams

2. Surface area 30.9 me/tonne = 309 m2

3. Recommended Dry Film Thickness75 mtcrons/ma

4. Actual Dry Film Thickness say 125microns/me at 500grams metallic zlnc/rns(Ref Table3)

FORMULA:309m2 x 500grams/m2 = 154500grams = 154.5 kilos metallic zinc

SUMMARYZINCESTIMATE HDG - 309 kilosIZS - 154.5 kilosDifference: 154.5 kilo (50%)

IZS Paint on average requires 50% less metallic zinc for equivalent performance

TABLE 1: ~Environmental

impact resourcescomparison

Environmental impact is proportional to Volume Consumption

ESTIMATEDWATERRESOURCEINDUSTRYCONSUMPTION

HDGEXAMPLE 1. Small/medium facility estimated 1.5 - 2 millionlitres pia

2. Estimate facilities 35

3.70-90 million litres pja Total industry estimate

IZS EXAMPLE 1.AppJication clean up (spray equipment) <40 litres/ day / 5 days / 50 weeks ~ 10000 litres x by m'volume x 5 = 50000L

2. Total material estimated volume 150000 litrescoating pia x 1 litre water

150000 Jitresfor manufacture & cleanup50000 litres application cleanup

Total ~ 200000LSay 225000 litres Total industry estimate

SUMMARYWATERESTIMATE HDG 70 - 90 million/ L for 85% market shareIZS 225000/ L for 15% market share

THE HDG PROCESS

The best way to describe the HDGprocess, it is basically one ofmechanical handling of steel througha cleaning process, then dipping intoa bath of molten zinc metal and finallyfollowed by quenching.

DegreasingThe process starts with degreaslng.This generally involves dipping into ahot alkali caustic solution usually atapprox, 85°C immersion time rangesfrom 1-20minutes depending on thedegree of contamination.

Environmental Impact:> Requires the use of vast quantitiesof potable mains water and heatingenergy on a continual basis> Environmental surroundings are hot,damp and caustic> Creates degreaslng sludge waste

HOG - ENISO1461/ASjNZS 4680

STEEL MINIMUM ACTUALAVERAGE METALLICTHICKNESS STANDARD DRY FILM ZINC CONTENT

THICKNESS THICKNESS (gm/m')(microns) (microns)

3mm plate> 70 99 707

4mm plate 70 110 785

5mm angle 70 110 785

6mm plate> 85 130 1000

12mm plate 85 150 1070

200 UB 85 140 1000

310-410 UB 85 150 1071

Heavy Structural 85 180-200 1285-1428Steel

180-200 PFC 85 120 857

125-150 PFC 85 110 785

RHS/SHS (light) 85 85-95 600-678

To convert thickness to metallic zinc weight x specific gravity (7.14) E.g. 140microns x 7.14 = 1000grams / m2

.••TABLE2: Metallic zinc comparison, HOG& zinc paints

RinsingImmediately after degreasing, rinsing takes place inhot mains water and in some cases may receive afinal cold rinse.

Environmental Impact:> Requires large quantities of reticulated mains waterand heating energy on a continual basis> Creates waste scum and sludge which settles to thetank bottom> Waste material requires removal on a continualbasis with special disposal requirements.

PicklingFurther cleaning takes place by pickling in eithersulphuric or hydrochloric acid.

Environmental Impact:> Requires vast quantities of mains water and heatenergy in the case of sulphuric acid use.> Environmental work conditions are hot, damp andextremely corrosive. Atmospheric acid levels are aslow as PHi. It is one of the most severe corrosiveenvironments to be encountered.> Creates toxic pickling waste and sludge

RinsingAfter pickling, the work is rinsed in reticulated mainswater

Environmental Impact:large use of recirculating potable mains water

FluxingFollowing rinsing, items are immersed in a fluxsolution generally containing approximately 30% zinc

ammonium chloride, together with wetting agents at65°C.

Environmental Impact:> Requires high water and energy usage, chemicalsand wetting agents>Work area hot, damp, requires use ofenvironmentally acceptable dust/fume extractionequipment> Atmospheric conditions are corrosive

Dipping into Molten ZincAssuming the item has been properly prepared,dipping and removal takes place at a controlled rate.

Environmental Impact:> Requires very high energy usage 365 days x24hours j day> Contains up to 1% lead (bound within the moltenzinc)>Traditionally there is a lead layer (average 100mm),at the bottom of the bath, its primary function is toinsulate the bottom from excessive heat and aidin the removal of zinc dross. Dross is a by-productlargely consisting of ash and flux skimmings whichare classified as hazardous waste (Basil Convention),and are restricted for export. Most of the dross isreprocessed into metallic zinc particles and zinc oxideused in a variety of other industries.> lead can adhere to HOG surfaces if the immersiondepth is not carefully controlled and penetrates intothe lead layer. Due to colour, it is very difficult tovisually distinguish between the dross and the HOG.The accumulation of dross (ash, flux, skimmings)invariably acts as a barrier between lead and zinc.However dross is removed on a regular basis, thereby

exposing lead to zinc and therefore diffusion of leadduring this exposure period into zinc takes place. Thesolubility of lead into zinc is temperature dependent,at normal HDG temperature of 450°C the solubility isup to 1.4%.> Considering the serious environmental and O.H&Sissues associated with lead, it is somewhat surprisingthat there is no acknowledgement (Ref 1&5) ofthe material being involved within the processeither by the HDG industry or in any of the relevantinternational standards.

QuenchingQuenching completes the process. Following dipping,quenching takes place in a solution containingsodium dichromate. This is necessary to inhibit earlyor flash white rusting.

Environmental Impact:> Requires the use of large volumes of potable mainswater> Chromate solutions are toxic and environmentalpollutants. Quenching materials which containHexavalent Chrome 6 are classified by the WorldHealth Authority as carcinogenic. (Ref 8) The solutionis changed regularly due to contamination of fluxresidues, zinc salts and oxides. Waste disposal isstrictly controlled by authorized agencies and licensedoperators. Disposal is a major problem and can onlybe carried out after certified neutralizing treatment.

The use of chrome quenching is now increasinglybeing banned by authorities throughout the worldfor environmental and O.H&S reasons. Neverthelesschrome quenching is still widely used, no rinsingfollows therefore no toxic effluent waste is producedat this point. However the quenching processinevitably steams, due to the hot HDG steel passingthrough. The chrome solution splashes, mists, anddrips in the work area as jibs carrying steel go in andout of the quench; this can lead to unacceptableconcentrations of airborne chromates. HexavalentChrome 6 has a short life (yet to be determined), thenconverts to trivalent chrome when the HDG surfaces

TTable3:

are exposed to air.

Whilst it is often stated that the amount ofHexavalent Chrome on HDG is virtually unmeasurable,one only needs to be reminded of the new scienceof Nanotechnology, matter that cannot be seen ordifficult to measure. It is now widely acknowledgedby the scientific community as a delivery vehicleresponsible for human health problems andenvironmental pollution.

HOG SUMMARY

HDG is an outstanding corrosion protection material,however the process necessary to provide that levelof performance is extremely corrosive to its own andsurrounding environment. HDG facilities have wet anddry areas of operation, with the wet pre-treatmentsection being without doubt one of the most severecorrosive environments to be encountered. Airborneacid levels are as low as PHi, largely due to eitherhydrochloric or sulphuric acid mist. Furthermore,hot caustic and pre flux tank areas contribute to acontinual damp, humid and moist atmosphere.

The severity of corrosion is such that on average atypical HDG facility requires structural restorationapproximately every 5-7 years. Whilst HDG and paintare competitors, the irony is that the HDG industryhas to call on its competitor paint, to provide thecorrosion protection necessary for its applicationfacilities. The overall process produces a streamof secondary waste and toxic materials, which aresubject to further processing for safe environmentaldisposal or recycling for use in other industries.

Environmentally the industry accounts for thefollowing:- Vast volumes of potable mains water are necessaryfor the process. A small to medium galvanizer wouldconsume approximately 1.5 to 2million Iitres of waterper annum.- High energy usage is required for pre-treatment andmolten zinc baths, 365days x 24hours ~ 8544

ZINC SILICATEPAINTSYSTEM - AS/NZS 3750.15

STEELTHICKNESS:Coating thickness for all steel sections is constant. Metallic zinc isdata from governmental analysis.

AS/ NZS Standard Thickness Metallic ZincZinc Content Content gm / m2

Inorganic (Water) 85% of Dry Film 75 microns 300(metallic zinc)

100 microns 400

125 microns 500

150 microns 600

hours/pa- Requires the use of extraction fans which contributeto acid rain- Generates large volumes of greenhouse gasemissions and toxic waste- The use of acid chemical compounds, some of whichare classified toxic pollutants and carcinogens.- Contains up to 1% lead with the possibility of afurther increase if the proper dipping procedures arenot adhered to, or when the lead layer is exposed tomolten zinc.- Requires the use of protective clothing equipment- When a facility ceases operation, invariably thesite has very little resale value due to industrial toxiccontamination caused by the process. Remedial andcleanup expenditure is in the extreme.

INORGANIC ZINC SILICATE (IZS) - COATINGPROCESS

The application of water based IZS is basically aconventional spray painting operation which involvestwo basic steps:1. Surface preparation of abrasive blasting cleaning2. Followed by the spray application of water basedIZS coating

Surface PreparationThere are two main methods used, to propelthe abrasive against the surface to be cleaned:1) Electrically driven centrifugal wheels or, 2)compressed air. Both methods are in enclosedchambers or booths, with the abrasive being

predominantly steel shot or grit. Insitu abrasiveblasting also occurs, however this is generally formaintenance purposes to existing structures. Theabrasive is mostly garnet which is non toxic orharmful. Under these circumstances, some dust isgenerated although most requirements these daysstipulate some form of encapsulation to contain anyfallout.

Environmental Impact:> Requires the intermittent use of either electrical ordiesel power for compressed air. On average 5hrs/dayx 5days x 52weeks ~ 1300hours/pa> Abrasive is recycled within the system. Dust iscontained within the booth and extracted via adust collector; approximate volume is 200litresevery 3 months. Dust collected is non toxic and ispredominantly steel mill scale and or iron oxide (rust)> No toxic waste or fume emissions are generated bythe process> Work environment is totally dry and benign> Protective clothing (hood) needs to be worn duringthe operation

IZS Application ProcedureIZS coatings are proprietary manufactured materialsand consist of two components: a) Metallic zincparticles and b) Water based liquid silicate. Thesecoatings are component applied by the conventionalspray painting method. The lead level of <0.1% is partof the trace elements bound within the zinc particles.No further lead or other heavy metals are used in themanufacturing process.

Environmental Impact:> Application environment is totally dry, non corrosiveand benign> No toxic fumes or waste is generated by theprocess> Lead component is <0.1%, one tenth of HOG levelswith no further possibility of increase> Empty paint containers are benign andrecycled> Mains water usage to clean spray equipment isminimal, <40litresjdayjoperation - 14000litres pja> Does not require the use of extraction equipment> No special requirements for safety equipment orclothing during application

IZSSUMMARY

The recorded performance is also outstanding. Thereis virtually no environmental impact apart from thesmall levels of greenhouse gas emissions associatedwith the intermittent use each day, of either electricalor diesel generated power,necessary to provide compressed air for surfacepreparation and painting activities. The waterresources required are insignificant as are the O.H&Srequirements.

There are always spray losses associated with spraypainting, the level with IZS is low and generally endsup as over thickness on the steel surface or on thefactory floor as overspray. It is periodically swept upand sold for recycling.

Annual volumes for an average operation are in theorder of 2 cubic metres (2m3). Material collected is amixture of IZS and normal everyday dirt and grime.

CONCLUSION

Zinc is almost exclusively used for the protectionof steel from corrosion. Like all processes, it isunder constant scrutiny to ensure environmentalsustainability.

It does come at a cost, be it financial or inenvironmental terms. Financially, the cost of providingcorrosion protection may only represent 1-2% of thetotal project cost; however the level of environmentalimpact will be proportional to the method used.

The Corrosion Industry internationally is awareof the challenges and is actively developing newtechnologies to eliminate or reduce the environmentalimpact of their particular materials or process toacceptable levels, where necessary.

The paint industry in particular has been subjected toclose scrutiny and has had the flexibility to introducenew technologies, for example, environmentallyfriendly non polluting water based or solvent freepaint materials.

Unfortunately the HDG industry, due to its inherentnature, has limited flexibility, being a one off processit has not fundamentally changed since conception.

It may just be that the HDG industry cannot change REFERENCESand has reached a state of equilibrium? Therefore

as a process it needs to be recognised for what it is, 1. EN 1501461 j ASjNZS 4680 After fabrication Hotalong with the environmental consequences of its use. Dip Galvanizing

Environmentally there is a marked difference between 2. OCCAS.A. - Q3. 2008the two established methods. IZS displays a muchlower environmental impact for the same level of 3. General Galvanizing Practice - Galvanizers, U.K.service under normal atmospheric conditions.

Although the recorded performance is similar, IZSconsumes infinitely less water and metallic zincresources, produces no industrial emissions ortoxic waste, and has minor emission pollution incomparison to HDG.

4. A & A Szokolick Consultants Pty Ltd

5. Hot Dip Galvanizing After Fabrication - GalvanizersAssociation Australia.

6. Dimetcote 5 Technical Literature

7. ASjNZS3750.15 - Inorganic Zinc Silicate PaintABOUTTHE AUTHOR

Nick Karakasch is the principal Consultant to TOcta~I _Corrosion Consultants Australia together withAustralian / International Galvanizing Zinc CoatiInstitute®.

8. World Health Authority (Research on cancer)

Nick's experience spans 40 years specializing ir,services to the protective coating, corrosion andfire protection industries. specializing in the are.of galvanizing, inorganic/organic zinc coatingsand structurei fire protection.

He spent many years in a management andtechnical capacity with the Dimet Coatingorganisation, the company which marketed theinvention of inorganic zinc silicate coatings,invented by one of the directors, Victor Nigl1ting,

He has also been the principal consultant to theGalvanizers Association of Australia. Whilst livirin South Africa in mid 1970's he was employeda Contracts Manager for R.J. Southey Pty Ltd.

INTERNATIONAl· AUSlRAUAN GALVANIZINGZINC COAnNG INSmUTE

. QUAUIT * R<\llNG

lftlC TOTAL CORROSION\! CONSULTANTSIiC (TRIDENT CRAFT PTY. LTD.)\! A.B.N. 87007204631

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GALVANIZERSASSOC\Al\ON

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Response by HDGASAto.- ·-"Galvani-zingand Zinc Paint comparison,'UPDATE'2009"*

* Published in Colour Coating and Corrosion SA, Quarter 1 2009 ..._.- ~.... -,_.- .._. ..,.-

Dear Edito~r; ...__.....- .- -~,-.~ -bofh --flone"olf-systems"--equailn performance in- - - - -- ',-'-- - -. normal. atmospheric. environments. -Apart from being

In his article entitled Galvanizing and Zinc Paint misleading, the statement is simply not true. It would,com pa rison, uPDATE--"2009;-author Nick Karakasch - "howeve r;'b€i"lilte'reshng to have the -aut hor' s defill itionreferred to-an article (ref 2) published-in Quarter 3 of.a "normal atmospheric environment"?2008 of CCC.This reference was to an article entitled'Corrosion - Protection "Systems: Aj,E~~iro;:;mental- "IvI-ostirlforme'd'authorities agree-Uiat a service lifeComparison". ..... --- -, - - . of -a carbon -steel- structure-Is determined by two"

fundamental factors, being (1) the coating systemWi'th respect to both-tt,; author a;d th;'~agazi;;~;'-'-iised -.ind(2f the environment in which thesystem

.... we-would request that the following comments' be ..·-is··to·operate.··l)efining·~~atmespheric -environments"pubtlshed In the!orthcoming,?ditiot1_Qf'y()_ur!1l~.ga~il]e. _t~..?._sp'~~!ficatio~.~(~S~ 12~44.~ ~_O 9223) are usedin order to provide a more balanced and objective view to classify a range of atmospheres. A benign, "verywith regards tocertalnaspects of the subjectartlcler' =-low" corrosion-condltions are categorlsed-as- a Cl

environment, ranging up through C2, C3, C4 and finally-Corrosh)-ri' Prote"Ction-Systems: An-Environmental a C5 or CS(lndustr'ia'l) ;'mdCSM (Marine)." ,.

Comparison (ref2)-·_·_-··-·,,· ..·_·· '" _._- ..... - .. - ' ....• _. _ NumerousprojectcasestudieshaveshownthatHDG on

This specific article was originally published in a~'-Tts'own~w'ill'provrcje'~itotaWy-adequate service life~eil.. - -.- -tnternatlonal journal and was the result'of'-a' study' in excess-of-30-te 60 years in G-1to-e3 environments. In

underta ken by t!1.~Environmental Technology Syst~m.~_ 04 and CS environments, HDG on its own has a serviceDepartment of the Institute for Environmental life ranging" from 30-years (C4fto-approximately 10Protection - Technology- at ..the Technical :University"'· years minimumin·severeCS·conditions .....0f.Berlin-'.- The stu..Qyiffi'oJy~g!u;.ompgri'§911 ...betW~.!:m .. _...._.__ .__ ..._. .._ .__ __paint coatings, in terms of EN ISO 12944 and hot When encountering C4 and CS environmentsdip' 'galvanizing according to"'"EN ISO 1461-'and Wl:Is--and'-an-extended service life is-required, normal

__ . bC!se(L<~t:l_.a.JifEL~y<;l.~a!?~e~~mentj_LCA)m~td~L.mthin.. recommen~ations are that a Duplex System bethe European Community. The article was a jolnt considered. ADuplex System consists-oTa HDG base

... publlcatlonbythe galvanizing'a's"sociatiohSc5f-Germany;'--'" coating, metallurgically' bonded-to the steel, followed"(he Netherlands and .Great Britain ...aod ..licensedjo . ~y a.t~().ort.~r~.e top p~LnL~y~t~m..Qve~the galvanizing ..associations in Spain. depending on the service life required. It is usually in

-- - .• '" -- ------- "- --'--- -thecontent-ot-a-ea-or CS"environment1:h-at'a Duplex__.Jl:t~_sarne ..•:ifticle was.flrst published in.South Africa ._Sys.!.em.Is C!.ons!~!e!L~n.sL cornparlsonato pG.lil)tare

in the Hot Dip Galvanizers Association's quarterly logically undertaken. Such comparisons are made- -- -'j ourna I" Hot "Dip-Galvanizing-Today' (2008 Volulife-S--- in terms-of 'service -llfe-expectetions, including' initial"___._. .L!?~.Y..~.l)JjllqlJy,_aI),dctUlle req uest, of C.olo.ur_C_oating_~D9 .Iif~.cygl~.co!?!~..s.it~.c.on,~ItioDs,Iocatl 9.ns.,pla IJn ed

& Corrosion SA, it was re-published in the Quarter 3 maintenance requirements and environmental..---.- ..- "2008 issu-e-with-permTssi-c5i1oflhEfl'lofDip Galvaliizers-"'--conditions at the ttme-ot-coatlng applications.

___ ._~s.,!?o.Giation._ _.....__.__...._ ..._._. __.._ ..... . _... "__ __ _ _Forthearticle under review, beingoneof"Environmental

-- .. Corrosion- Protect for Servi·ce-·-tife-of -Ste'el-Impact-Resources Comparison"-;-- the+following-few_ .. ._.._St~y.c.tures. _ _ _ _ _ __ ._cQrn!l1el"!tsa!e_IH.2.J!.Qsec:l:._ .

..........-..•-.-.. Coati ngs-are--generally' appl ie-enDsteel-structureS-for ·-·1..TlTe·artlclewotrld appea rto-suggesrthat a tlTickzl nc --.._.. reasona.ot.aesthencs, ...cotour. coding, w.ear_resistant.. .._~Q...a~i.l1g,_fQ.und~hen.hot .Q.ip_galyani~ingonly certain __

characteristics or for corrosion control requirements. types of steels, represents a significant negative- Cb'mparative articles tIlat"'cohtinue-fo Be wr'itten--impact-on-th·e-environment.--- ,..__ ._.-.- ... - - ---

.. _ comparing.hot.dip galvanlzlng (HDG)_to_tbaLoLvarious .. _. _. ._"."" ~_ _ _ _ _.__ .. _." _ _._paint systems usually relate to corrosion control Zinc is a wasting material and therefore the more zinc

..- ..- _······characferistics 6fone system 'versus tlie -ollier:- ..--..- ...--'-··rn·the"coatingthe longer'tlreservlce-trte of a structure:'_.__ -. ._.- .._ .._. ..... _.. _ ___._._ "'_' .__ .__ lh.!u!rot~~.!io.n aJld_~xteD~Q.nQLc;;.C!.tILQ.n~teel'sservice _

In the article under review, the author states that life has a far greater positive impact on the conservation5bth-HDG"ahCl iiiorganicziiicsilicate-(IZSfpaintare--ofi:he-environment tnarratew kgsor extra zinc. One

._ - --..--- .- ----------------_._-_ .._-,---- ._--,-_._ ....._ .._ ..__ .... _._------ . - ....

'- ---- ---_._-- .-~~-.----- -~ .._ _... ._ ..- --_ ...•._ ..•...- _ --..._._-_.... -_. - -- .- ----- - _._-

o needs to consider the environmental impact incurredin the production otonty one tonne of steel. The longersuch a tonne of steel remains in useful service thegreater the-reduction of environmental impact and theconservation and further demand of valuable naturalresources.

2. A large proportion of reprocessed zinc wasteproducts (dross and ash) from hot dip galvanizers areused in the paint industry.

3. Energy and materials usage within the HDG industryvary according to the type of materials being processed.Approximately 85% of the energy content in the steelis galvanized, with about 15% in the actual galvanizingprocess. This is not significantly different should onedecide to paint the steel structure.

4. The. apparent claim that Inorganic Zinc Silicate

O (IZS) paint will have a service life of 60 years, withoutmaintenance, and is equal to that of HOG, shouldbe supported by some- actual case studies. Recordsare available that clearly illustrate; HDG in !<:l to C3environments are capable of providing a service life of60 years maintenance free.

ConclusionAny conclusions to the distorted information containedin the article under review are best answered in termsof the original study conducted by EnvironmentalTechnology Systems Department of the Institute forEnvironmental Protection Technology at the TechnicalUniversity of Berlin. It is suggested that this particulararticle be re-published in your magazine with referenceto Nick Karakasch's article "Corrosion Protection & theEnvironment" .

In addition, I would propose that the technical papero "Zinc Rich Paint & Epoxies versus Hot Dip Galvanizing"should be published as further background supportinginformation to the above.

Further comments regarding this debate would bemost welcome.

Bob Wilmot. President, Hot Dip Galvanisers Association

We thank Bob for his incdepth_comments andJ!l response on the above-mentioned article, and urge~ readers to read the technical paper entitled "Zinc'";;!j - Rich Paint & Epoxies versus Hot Dip Galvanizing" on13 _. _0 page 29. Any turther comments to this debate are'-' most welcome. Please direct these to the Editor at

jodie@leafmedia.co.za

Dear Ms Davies-Coleman,

I read with interest the letter from Mr Bob Wilmot, President - HotDip Galvanizing Association (Gee SA, Quarter 2 2009), in responseto an article of mine titled Corrosion Protection and the Environment.Whilst I accept the principle of open debate and constructive criticism,his reference to misleading, untrue and distorting facts are not a truereflection of the article.

The article was specific to environmental issues associated with the"application process" for hot dip galvanizing and inorganic.zinc silicatecoatings, something Mr Wilmot failed to address in his critique. Apartfrom any health and safety issues, the galvanizing process producesa range of toxic waste materials, uses questionable chemicals one ofwhich is a known carcinogen and has lead involved in the process.It requires infinitely more resources to facilitate the process than itsopposite number. I make no apology for drawing attention to the useof lead and toxic materials associated with the process. Those at risk,through a duty of care, should be made aware of the dangers andthe associated liabilities. The conclusions of my article were quiteclear and undeniable; nevertheless he remained mute to the factspresented.

by either the Galvanizer or the Paint Industry. HOG and Inorganic zincsilicate coatings are standalone systems in the protective coatingindustry; case history listings simply cannot be denied or dismissedfor either. I have no doubt that if Mr Wilmot contacted any of the majorpaint companies, they would be more than happy to provide him withappropriate case history listings.

With regard to inorganic zinc, I would refer readers to an articfepublished in CCC Quarter 2, 2009, Inorganic Zinc Silicate Coatings- 70 Years On.

There are three points to be made regarding inorganic zinc1. The current water based Inorganic zinc silicates have been one off orstand alone materials for over 45 years. This status has been reflectedin previous and the current internationally recognised Australian/NewZealand Standard AS/NZS 2312. Guide to protection of structuralsteel against atmospheric corrosion, the origins of which date back tothe mid 1960's (Refer Fig 1).

2. The Morgan/Whyalla Pipeline in Australia is 70 years old. Thepredicted service life of the original inorganic based on the remainingthickness is expected to exceed 100years. The exposure environment

ranges from C1 through to C5M.Mr Wilmot states in his letter thatthe service life for HOG on its ownranges:• From 30years for C4 (high)environment,AS/NZS 2312 shows 15-25+years,depending on thickness.• C5M (very high marine) isapproximately 10 years-minimumAS/NZS 2312 nominates 5-25years, depending on thickness(Refer Fig. 1).

----- ~.---.----------The corrosion debate is a long standing

one. Inevitably it highlights thecompetitive nature of the competingindustries; unfortunately all too often

perceptions are created to gain marketacceptance or advantage.

I would refer Mr Wilmot to thepublished (HOGASA Code ofEthics) one of which states: "Actin the interest of the public byactively contributing to publichealth and safety and to theprotection of the environment"

I did make reference to anHOGASA article titled CorrosionProtection Systems 'AnEnvironmental Comparison'.Whilst there was environmentalcontent it compared HOG to an unnamed three coat paint system andused assumptions to conclude its findings. In not naming the paintsystem and using assumptions makes it difficult for a reader to makea valued judgement if all the facts are not given, regardless of whoconducted the study, commissioned it, or used it for a joint publication.Conclusions under these circumstances can at best be described assubjective. Corrosion science is a discussion based on evidence.

The study assumed that the steel structure was a multi storey car parkexternally exposed and on-site maintenance was required for the paintsystem after 20 and 40 years. My experience with multi-storey carparks is that they are either fully enclosed, particularly in the northernhemisphere or semi exposed under cover.

With paint systems, regardless of the generic type, it is the rate atwhich a coating deteriorates that determines its service life. Whenthe outer surface has excessively chalked and discoloured as a resultof UV attack and air borne pollutants, it may require top coating toprotect the underlying system, depending on the original system used.UV attack in enclosed situations does not occur at the same rate aswhen the coating is fully exposed. As for semi exposed conditions; thelikelihood of any attack would only be to the outer perimeter steel ifphysically exposed to atmosphere.

With HOG, thickness loss is by way of zinc corrosion when exposedto an electrolyte (water, oxygen and soluble salts). With paint, filmloss is primarlly through chalking from UV attack. The one exceptionbeing inorganic zinc silicate coatings; the binders used are inorganicsometimes referred to as water glass and therefore immune to UVattack. They are unaffected by radiation or radioactivity and have beenwidely used to protect steel in the containment shells of nuclear powerplants.

Mr Wilmot's letter raised the issue of service life and performance inan unrelated manner to environmental issues. Inevitably, comparisonsare made between anti-corrosive systems; no individual system has amonopoly to satisfy all needs regardless of any promotional activity

3. The offshore oil and shippingindustry which are not covered by the above standard is anotherenvironment where inorganic zinc is well suited. Galvanizing isvirtually excluded from this application as the service life is 3-5 yearsmaximum and is primarily confined to stair treads and gratings, thereason being they are impractical to paint due to their geometricalshape. The service life for the current formulations for inorganic zincis now approaching 30years. Onshore environments of C1. C2 and C3are listed as 25years+, however in practice case history listings hasexceeded 45years. To balance the statement, it also applies to HOGand Hot Thermal Zinc Metal Spray (Refer Fig 1).

My reference to normal atmospheric conditions was made on thebasis that they are largely considered benign; those described in theISO Standards as Cl, C2 and C3. The reason for the use of the wordnormal was that zinc is an amphoteric metal in that it will react withboth acids and alkalis. It performs best in benign or what I considernormal environments where the PH is in the neutral range of PH7.

Mr Wilmot directs readers to an article titled Zinc Rich Paint andEpoxy verses Hot Dip Galvanizing, CCC Quarter 2,2009, as supportinginformation to his letter. I am a little perplexed to see the relevance;there is no mention or reference to environmental matters. The articledescribes the process of how zinc protects steel and the meritsbetween zinc rich paint and epoxy coatings to hot dip galvanizing. Thereference to epoxy coatings is confusing as a comparison to HOG:the two materials are generically different, not used in the samecircumstance and therefore any comparison is irrelevant. The articleconcludes by stating that zinc rich paint or epoxy is not equivalent to hotdip galvanizing in terms of corrosion control and cathodic protection.J agree they are not, and never have been, something well recognisedwithin the industry therefore - why promote the comparison. There isno need -a product as widely used as HOG which has been in existencefor 170 years speaks for itself.

I understand and appreciate the frustrations felt by the Galvanizingindustry when claims are made, for example, that zinc rich paints areequivalent. Nevertheless this is also an issue with the paint industry

A B C D EI EM FVery low Low Medium High Very high Very high Inland

industrial marine

HDG 85 25+ 25+ 25+ 15-25 2-5 5-15 25+125 * 25+ 25+ 25+ 2-10 10-25 25+

IZS 75 25+ 25+ 25+ 15-25 2-5 10-15 25+Water based 125 25+ 25+ 25+ 25+ 5-10 15-25 25+TZS Hot Zinc 100 25+ 25+ 25+ 15-25 NR 5-15 25+Metal Spray 150 * * 25+ 25+ NR 10-15 25+

* While this system would have very high dllrability in this atmospheric category, it is unlikely to be economicNR Not recommended

where promotional activity has tended to be general suggesting thatall zinc coatings are equal in performance when experience and casehistory listings have clearly shown this notto be the case.

HDG as a standalone system should only be compared to either waterbased Inorganic Zinc Silicate or Hot Thermal Zinc Metal Spray, (ReferFig 1).

I am unaware of the HDGASA knowledge of zinc based coatings,however for the benefit of the readers, they are divided into two broadclasses and distinguished by the type of resin or binder used i.e.inorganic or organic resins such as epoxy or polyurethane etc. Theyare known in the industry as Inorganic zinc siticates and Zinc richprimers.

The best performing materials are the inorganics, particularly thewater based type. Zinc rich primers are rarely if ever used in their ownright and do not provide the same level of protection for a whole rangeof technical reasons. They are extensively used in systems rather thanone off standalone products. The irony is that whilst they do not haveanywhere near the same level of performance, they are neverthelesshighly recommended and widely used by the galvanizing industryas a repair material, something I have always found a little odd andparadoxical considering that the volume of zinc dictates performance.The metallic zinc content for the average zinc rich primer at 100microns is only 245 grammes. compared to 714 grammes for HDG,although in reality for structural steel the average is 1000 gramsplus.

Inorganic zinc silicates on average contain 30% more metallic zincthan zinc rich primers, their protecting mechanism is also somewhatdifferent. Freshly applied inorganic is porous; this allows the penetrationof the electrolyte (water, oxygen and soluble salts) to promote initialsacrificial corrosion of zinc, providing cathodic protection to theunderlying steel. The corrosion product produced is retained in thefilm, filling the voids between the zinc and isolating them electricallyfrom the environment. At this stage only a small percentage of theavailable zinc has been consumed. During this time a microcrystallinedeposit is also formed on the steel surface which has a stifling effect,thereby minimizing the current demand on the zinc. This extends theeffective life of the coating by holding in reserve un reacted zinc whichbecomes operative if the coating is damaged or zinc is exposed at alater date. Like HDG there is a self healing effect, should the surfacebe scored back to steel, the scored area becomes sealed with zinccorrosion product at which time the galvanic action ceases, in effectproviding a self regulating repair mechanism.

Both materials have barriers as the first line of defence. HDG has acarbonate film, usually only a few microns in thickness, when thisbarrier film is consumed either by abrasion or erosion; it activates thecorrosion of the underlying zinc. Performance time is then reflectedby the rate of zinc consumption when exposed to an electrolytewhich in turn is determined by the environmental conditions. Thecorrosion product produced accumulates loosely on the surface andis generally removed by rain, exposing fresh metallic zinc for thecycle to recommence. Performance time is entirely controlled by thezinc/alloy thickness, in other words the amount of zinc available for

page 4 I ccc SA auarter 3 2009

consumption.

Whi 1stinorgan ics have considerably lowervolumes of zi nc, performa neeis not reliant on volume alone. SCientific investigations over the past70 years have demonstrated that a combination of zinc and a complexlockout barrier is the corrosion mechanism for performance. Thecorrosion product produced is retained within the film making it muchmore difficult to dislodge and expose unused zinc particles for theprocess to continue.

For zinc to function as a protective medium, it must be periodically dryotherwise the consumption rate of zinc continues unabated, hencethe reason for lower performance in immersed or wet conditions. Thearticle states that a "continuous" electrolyte is self defeating for zinccoatings; however this principle applies equally to HDG. For galvanicaction to occur, the electrolyte does not need to be continuous. Whenmetallic zinc coupled to steel per se is exposed to an electrolyte, thegalvanic action is activated regardless of how the zinc is fixed into thesystem. Removing one of the electrolyte components, water, oxygen,or soluble salts terminates the process. lnorganics have a controlledconductivity. Measurements have shown that current flow or amperagebetween pure metallic zinc as in HDG is much greater than the currentflow between zinc held within an inorganic zinc silicate coatingillustrating that pure zinc goes into solution much faster than zinc heldwithin an inorganic coatings silicate binder.

Both systems provide barrier and cathodic protection. Whilst thereare differences in physical make up, case history listings in Australiaand throughout the world together with internationally recognisedstandards show performance to be similar in C1 to C3 environments;however performance varies in other environments where one orthe other will clearly outperform and be more suited for a particularapplication. No individual system can satisfy all needs regardlessof any industry promotional activity. Each system has a set of enduse requirements where, application conditions, and economicconsiderations will dictate where its special inherent properties willmake it the first choice.

The corrosion debate is a long standing one. Inevitably it highlightsthe competitive nature of the competing industries; unfortunatelyall too often perceptions are created to gain market acceptance oradvantage. Evaluating authorities rely on well informed sources fortechnical advice. The advice given in my view should be unbiased,technically correct, non-contradictory and above all based on provenperformance. Listed above is the durability - years to first maintenancefor the systems in question, as illustrated in Australian Standard AS/NZS 2312 2002 Guide to the protection of structural steel againstatmospheric corrosion. The figures quoted are guidelines basedon past performance, in practice they will fluctuate due to micro-environmental factors which may either increase or decrease thecorrosion stress.

Yours Sincerely

Nick KarakaschManaging Director, Total Corrosion Consultants, AUS.