Guidelines For Welding - PCI
Guidelines for WeldingGalvanized SteelGregory LivelliFormerly, Techn ica l CoordinatorAmerican Galvanizers AssociationAurora, ColoradoHot dip ga lvanizing of steel components after fabrication is wellknown as an inexpensive method of corrosion protection. Thecoating is metallurgically formed in a bath of molten zinc. Thestructure of the coating, formed by the interdiffusion of zinc and iron,provides good adhesion to the steel and, because the intermetallicla yers are very hard, it also provides good abrasion resistance. Manystructures are ga lvanized after they have been welded in order toachieve optimum corrosion protection from the galvanized coating.Howeve'"' most products in the precast/prestressed industry can easilyand satisfactorily be welded after fabrication by practicing thetechniques outlined in this article. The following guidelines andinformation are intended to assist in employing the correcttechniques to ensure a high quality product or job.he strength of a weld dependson reliable workmanship andthe compatibility of weldingmaterials with the metals to be joined(see Fig. 1). In the precast/prestressedconcrete industry , zinc coated steelcan be joined using the same methodsemployed for uncoated steel. Themanual processes described in this article provide considerable flexibilityin joining galvanized reinforcingsteel.Welding galvanized steel specifications are derived from the AmericanWelding Society's (A WS) Specification D-19 .0 , Weldin g Zinc CoatedSteel. (Note that this specification is nolonger availab le from A WS .) Thisspecification calls for welds to be madeTThomas Langill, Ph.D.Techni ca l DirectorAmerican Galvanizers AssociationAurora, Colorado40on steel that is free of zinc, although already galvanized . The zinc coatingshould be removed for at least 2 to 4 in.(50 to 102 mm) from either side of theintended weld zone and on both sidesof the workpiece, if possible.Grinding with si licon abrasivediscs is the most effective means ofremoving the galvanized coating. Thezinc can also be removed by burningwith a carbon arc or an acetylenetorch while using an oxidizing flame,or by s hot bla s ting with portableequipment. If common practice requires removal of the zinc coating,welding procedures for uncoated steelshould be followed.Removal of zinc where a weld is tobe placed is the most conservative apPCI JOURNAL
proach in welding galvanized steel.Welding procedures will then be thesame as for uncoated steel.When the galvanized coating isnot removed , the weld should bemade using the galvanized basemetal with the thickest coating anticipated and qualified by test in accordance with A WS D 1.1 or A WSD 1.4 . These Welding ProcedureSpecifications (WPS) will permitwelding over surfaces with coatingsequal to or less than the coating usedin qualification testing . In general, toavoid zinc penetration of the welds ,the procedure should involve greaterroot openings in joints, electrodeswith low silicon content and slowerwelding speeds.MANUAL WELDING OFZINC COATED STEELSThe manual and semi-automaticwelding processes described belowprovide significant flexibility.When manually welding zinc coatedsteels, it is beneficial , but not necessary, to remove the zinc coating onand around the weld areas. The weldmetal may contain small quantities ofzinc but this does not influence themechanical properties.The tensile, bend and impact properties of welds in galvanized steel arepractically unchanged when comparedto welds in uncoated steels, but galvanized coatings on steel surfaces mayrequire different welding parameters.Different welding data calculationsand different methods of fabricationare sometimes required for galvanizedsteel.In general, manual metal arc welding procedures for galvanized steelare similar to welding uncoated steel.However , welding of galvanizedsteel generally requires that thewelder receive specialized training.In addition , qualifications of thewelder and welding procedure usingthe thickest coating anticipated isstrongly recommended.Uncertainty about fabrication differences and how problems connectedwith them can be solved has led to areluctance to specify welding of zinccoated structures. Without more detailed knowledge, welders are oftenunwilling to weld zinc coated steel.May-June1998Fig. 1. Welding of ga lvanized steel.Cas Metal Arc WeldingGas metal arc (GMA) welding, alsoknown as C0 2 or Metal-Inert Gas(MIG) welding, is a versatile semiautomatic welding process that is convenient and easy to use. Fig. 2 showsan illustration of C0 2 welding. GMAwelding is particu larly suited to thewelding of thinner materials.In GMA welding of galvanizedsteel, the presence of the zinc coatinghas no effect on weld mechanicalproperties , although it may producesome appearance changes due to weldspatter. Arc stability is excellent andgenerally unaffected by the galvanizedcoating. Some reduction in weldingspeed is required .Suitable conditions for C0 2 weldingof butt joints using 1/4 in. (6.4 mm)galvanized plate and for welding teejoints using 1/z in. (12.7 mm) plate aregiven in Tables 1 and 2.The weld takes place underneath aprotective gas shield. A small diameter [ 1h2 to 1!1 6 in. (0.8 to 1.6 mm)] consumable wire electrode is fed automatically to the weld torch. The highcurrent density resulting from thesmall diameter of the wire is in the region of 200 amperes per sq mm.The cheapest and most widely usedshielding gas for welding uncoatedsteel is carbon dioxide. Suitable conditions have been determined for GMAC0 2 welding galvanized steel with ashort circuit arc. For welding uncoatedmild steel, a more expensive shieldinggas, comprising 75 percent argon and25 percent C0 2 , is sometimes preferred because of its superior surfaceappearance, weld bead shape and re-.fl Direction\J of welding- --Nozzle ofwelding gunr;;%Consumoble "H- V. 1' fl/t:-'--- C02 Shielding gar- .::.; . - - .::: a rr :ffff'k V 130:ZFig. 2. Diagrammatic il lustration of C0 2 welding (Courtesy AWS).41
Table 1. Typica l weld ing conditions fo r C0 2 weld ing butt joints WelderpositionNumberof passesPassnumberFl at2IVoltage cal upI3Hori zontalin . ga lvanized steel.Current (A)2Overhead1/423W ire feedspeed(in./minute)Travel 01i9 hi 9 1hJ91f2Travel speed(uncoated)(in./minute)10II674 1h91716Taken from "Welding Zi nc Coated Steel" - AWS 0 19.0-72.Note: I in. 25.4 mm.Tab le 2. Typ ica l welding conditions fo r C0 2 welding tee jointsga lvani zed stee l.-WelderpositionI-- ---Hori zontalIVertical downVertical 02020f:Wire feedspeed(i!!./minute)j1451451451.J-45j1/2 in.T ravelspeed(in./minute)Travel speed(uncoated)(in./minute)510581058--I5 1h --Taken from "Welding Zinc Coated Steel" - AWS 0 19.0· 72.Note: I in. 25.4 mm .du ced spatter. These advantages donot apply to galvanized steel and lessexpensive C0 2 may be used satisfactoril y. Ho wever, mos t weldin g shopsnormally use an argon-C0 2 mi xturefor galvanized material.GMA we ldin g s peed s sho uld beslower to all ow ti me fo r the ga lvanized coating to bum off at the fro ntof th e we ld poo l. Th e redu cti o n inspeed relates to the thickness of thezinc coatin g, the joint type and thewelding position. Fillet welds in steelwith thicker galvanized coatings maybe welded more readily by increasingthe current I 0 amps. The in creasedheat input helps bum away the extrazinc at the front of the weld pool.Pene tr at io n of th e we ld in zi nccoated steels is less than for uncoatedsteels. Therefore, slightl y wider gapsmu st be provi ded fo r butt we lds. Asli ght side-to-si de move ment of thewelding torch helps achieve consistentpenetration when making butt welds inthe flat position.Spatte r in c reases w he n we ldin ggalvanized steel usi ng both C0 2 andan argon-C0 2 mixture shielding gas.Spatter particles adhere to the work42the particles trapped by the weldingnozzle.Spatter formati on increases with thethickness of the zin c coatin g and istherefore greater on batch-galvani zedmaterials than on continuously coatedsheet materi als. W he n tee join ts inbatch galvanized steel are welded inthe fl at position, spatter particles tendto ro ll into the co rn er of th e joint,causing difficulty in welding. Spatterfo rm ati on is also trou bl eso me whenwelding in the overhead position, resulting in spatter falling into the nozzle of the welding gun .The major differe nce between weldin g zi nc coated stee l and un coatedsteel using the gas metal arc weldingprocess arises from the need for higherheat input to remove the zinc from theweld pool and slower welding speedsto burn off as much as possible of thezinc coating. The presence of the zinccoating should have no adverse affectpi ece a nd ca n ca use an un s ig htl yappearance. Thi s can be avoided bya ppl y in g a s ili co n, pe tro le um o rgraphite-based spatter release co mpound to the workpi ece before welding. Spatter particles can then easilybe bru shed off; however, prob le msmay b e e nco unt ere d du e to th ebuildup of spatter in the nozzle of thewelding gun . The applicati on of ana nti- spatte r co mp ound w ill redu ceTab le 3. Typ ica l shielded meta l arc we lding conditio n fo r th e root pass in butt we ldsin 1/4 and 1/2 in. thi ck ga lva ni zed steel w ith rutil e electrodes.Electrodesize (in.)Welderposition'h'Flat132Vertical up1lt63Hori zontal3Hori zontal1lt613211s3l!z33132l!zRootopening (in.)132132Overhead311s11sFlat3Vertical up' 132Vertical up11sHori zontal3132Overhead132132'h''h'1lt63132Weldingcur rent (ac)(A)73 to 8973 to 8970 to 831098995 to 10983 to 95101 to 11 711 789Taken from "Welding Zinc Coated Steel" - AWS 019.0-72.Note: I in. 25.4 mm .PCI JOURNAL
on the weld properties. Using a shielding gas of argon and carbon dioxidecan give a more stable arc and producesmoother weld deposits with minimum spatter and zinc loss.1'1 Oir ction of wfidingShielded Metal Arc Weld ingShielded metal arc welding (SMA W)is a manual welding process in whichflux covered electrodes of 10 to 18 in.(254 to 457 mm) in length and 1116 to1h in. (1.6 to 12.7 mm) in diameter areused. This is the most common of allarc welding processes. The SMA Wprocess is shown in Fig. 3.Suitable welding conditions formaking the root pass of butt joints in11/4 and h in. (6.4 to 12.7 mm) galvanized steels are given in Tables 3 and4. The rutile electrodes for Table 3 areAWS E7013. The basic electrodes forTable 4 are AWS E7016. These conditions are similar to those used on uncoated steel. Normal welding procedure involves gouging out the jointfrom the rear side after a root pass onthe front side. It is possible to obtainfull penetration in the flat position ongalvanized steel with the 1116 in. (1.6mm) root opening normally used onuncoated steel if the following conditions exist: (1) the angle of the electrode to the plate is reduced from theusual 70 to 30 degrees; (2) the electrode is moved backward and forwardin a whipping motion in line with thejoint. This method of manipulation results in a decreased travel speed of 40percent from the travel speed on uncoated steel.Fig. 3. Diagrammatic illustration of shielded metal arc welding (Courtesy AWS).In the case of vertical and overheadbutt joints in galvanized steel, a rootopening of 3h z in . (2 mm) is necessary to obtain full penetration. A rootopening of 1116 in. (1.6 mm) is sufficient to give full penetration in thehorizontal position but the root passtends to have a peaky or bulbousshape, resulting in slag entrapment atthe edges of the weld. This slag canonly be removed by grinding . Increasing the root opening from 1116 to3/ 32 in. (1.6 to 2 mm) can prevent slagentrapment.A reduction of I 0 to 20 percenttravel speed is necessary when makingthe root pass in flat or vertical buttjoints in galvanized steel. Welds madein the horizontal or overhead positionsTable 4 . Typical shielded meta l arc welding condition for the root pass in butt w eldsin 1/4 and 1/2 in. thick galvanized steel with basic electrodes.Platethickness (in.)'I 'I 'I 'I 'I 'h'h'h'h'hElectrodesize (in.)3Welderposition1(A)132FlatVertical up31323132Hori l3109Overhead373 to 89Flat3100Vertical up3100Horizontal33'h'Overhead116Weldingcurrent (ac)3132Taken from "Weldmg Zmc Coated Steel" - AWS 019.0-72.Note: I in . 25 .4 mm.May-June 1998Rootopening (in.)11 6132132132132132132313285 to 90859583 to 95can be made at similar speeds to weldson uncoated steel.When the root pass has been made,subsequent weld passes can be madewith similar techniques to those usedfor uncoated steel because the weldbeads are deposited largely on previously uncoated weld metal and onlypartially on the galvanized bevelededges. There is usually insufficientzinc present to affect the welding operation. If excessively thick zinc coatings are present, an oscillating motionof the electrode should be used toslightly reduce travel speed.The SMA W process uses a fluxcovered electrode to stabilize the arc.The amount of spatter formed withSMA W galvanized steel is slightlygreater than compared with weldinguncoated steel. Generally, it is not sufficiently extensive to warrant the useof anti- spatter compounds . Weldingcurrents for SMA W galvanized steelare usually the same as those used foruncoated steel. The major differencesare that the root opening must be increased to give full weld penetrationand that the electrode must travelslower to remove the zinc.Manual Metal Arc WeldingManual metal arc welding is recommend for galvanized steels of 1/z in.(12 .7 mm) or greater thickness .GMA W is recommended for steelslighter than 1/z in. (12.7 mm). In general, manual metal arc welders can use43
current. The major difference betweenmanual arc welding galvanized steeland uncoated steel arises from the needfor higher heat input to remove the zincfrom the weld pool and slower weldingspeed to bum off as much as possibleof the zinc coating in front of the weldpool. This is achieved by giving theelectrode a whipping motion. A moredisturbed weld pool results, as well as agreater fluidity of the slag and an increase in spatter.the same procedures for galvanizedsteel as for uncoated steel, althoughthe following should be noted: The welding electrode, EXX10 andEXXll, should be applied slowerthan normal, with a whipping actionthat moves the electrode forward 1/sto 5h 6 in. (3.2 to 7.9 mm) along theseam in the direction of weld andthen back into the molten pool. Allvolatilization of the galvanized coating should be complete before beadprogress. This will prevent zinc entrapment in the weld metal. Aftervolatilization, welding is the sameas for uncoated steel. Weaving and multiple weld beadsshould be avoided. Heat input intothe joint should be kept to a minimum to avoid undue damage to theadjacent coating. A short arc length is recommendedfor welding in all positions to givebetter control of the weld pool andto prevent either intermittent excessive penetration or undercutting. Slightly wider gaps up to 3/ 32 in.(2 mm) are required in butt jointsor a 15-degree angle on the edgeof a standing plate in order to ensure complete penetration. The gapalso allows for the zinc and itsgases to escape and reduces cracking caused by restraint as the platethickness increases. Grinding off edges prior to weldingreduces fuming from the galvanizedcoating. Welding procedures will thenbe the same as for uncoated steel. After welding is complete , applyzinc touch-up material to the weldbead and the adjacent area to complete the corrosion protection.Electrodes similar to those used forarc welding uncoated steel can be used,along with the same electrode size andTable 5. Arc stud welding conditions forWelding Gun).Studdiameter (in.)STUD WELDINGArc stud welding is a rapid methodfor attaching a stud or other suitablyshaped part to a metal surface. An arcis initiated between the end of the studand the surface . The stud is heldagainst the surface in a hand operatedstud welding gun. After a length oftime, depending on the area of the studor attachment at the point of welding,the current is automatically switchedoff and the stud is forced, under springpressure, into the molten pool on thesurface to which it is to be attached.The full cross-sectional area of thestud is welded to the surface and theresultant tensile strength of the weldshould be equivalent to that of the studmaterial.Conditions for welding 1/4 and 1h in.(6.4 and 12.7 mm) uncoated and galvanized steel are given in Table 5. Ifgalvanized studs are used, it is essential to remove the zinc from the end ofthe face of the stud before weldingand from the surface of the plate inthe area where the stud is to bewelded. If the end face is still zinccoated, the weld metal may be violently expelled from the joint becauseof volatilization of the zinc from thefaying surface./21in. thick galvanized steel plate (PhillipsZinc coatingweight(oz. per sq ft)SpringcoarseTensionsfineCurrent (A)551010300350750750I'I 'I Nil22'h2' IsNil3' Is2' h2ITaken from "Weldmg Zmc Coated Steel" - A WS D 19.0-72.Note: I in. 25.4 mm .44WELDING GALVANIZEDREINFORCING BARSWelding of galvanized reinforcingbars without removal of the coatingcan be carried out using either shieldedmetal arc welding or carbon dioxidegas metal arc welding performed in accordance with AWS D1.4.Welding of galvanized metal mayal so be done after removing all thecoating from within 2 in. (50.8 mm) ofthe weld joint.The bar ends may be prepared to therequired profile by sawing, grinding oroxygen cutting. Cold shearing is notrecommended and bars prepared inthis way should be carefully inspectedto ensure that the ends have not beendamaged by the shearing process. Ifany damage is found, the ends must becut back beyond the area deformed byshearing.Fusion faces should be free from irregularities that would interfere withthe deposition of the specified size ofweld, or cause defects.If the ends of the reinforcing barsare prepared at the site, the preparededges will be free from zinc and welding will be the same as for uncoatedbars. The presence of zinc on the endof the bars to be welded has no significant effect on the welding procedureor the time required to make the joints.The only difference occurs in the formation of fumes when the preparededges are coated with zinc. Table 6gives typical welding procedures foreither uncoated or galvanized bars.The cold bending of reinforcing barsthat are very high in strength cancause an embrittlement condition inthe area of the bend. Galvanizing andwelding can act as some stress relieffor this area, but in many cases thefurther bending or handling of thesebars can cause cracking or completefailure. Extremely high strength barsshould be stress relieved after bendingand before galvanizing or they shouldbe bent in a heated condition.QUALITY OFWELDED JOINTSWelding procedures are described inthis paper for obtaining sound joints inzinc coated steels. It is necessary toconsider the mechanical properties ofPCI JOURNAL
sound welds on zinc coated steel andalso the mechanical properties ofwelded joints containing typical defects that can be caused by the presence of the zinc coating.It is not uncommon to find smallcracks in a fillet weld on galvanizedsteel, extending from the root toward theface of the bead. Whether cracking willoccur depends on many factors such asthe silicon content of the weld metal, thedegree of penetration of the weld, thethickness of the base metal that influences restraint of the joint, and the coating weight of the zinc and the microstructure of the zinc coating, whichare both influenced by the compositionof the base plate, particularly with respect to silicon content. Low-silicon orrutile (non-low-hydrogen) base electrodes with low silicon content (0.2Si orlower) generally reduce cracking.Undercut is the most prevalent defect found in fillet welds deposited inthe horizontal and vertical positionswith either rutile or basic coveredelectrodes. This defect can occur at either side in vertical welds, but in thehorizontal position, it generally is restricted to the vertical plate.Undercut is more likely to occurwith rutile electrodes when the slag isallowed to solidify slowly or when theweld produced has a concave profile.A weld with a more convex profilethat is frozen faster has a lower tendency to produce this defect. Rutileelectrodes that have less fluid slagproduce a weld profile that is convexand can be manipulated more readilyto avoid any undercut.An extra thick zinc coating maycause trouble in the vertical positionbecause when it is molten, it tends torun down into the weld pool andmakes the slag difficult to control.This can be prevented by maintainingas short an arc length as possible.Also , when welding galvanizedsteel, hydrogen induced cracking ofthe heat-affected zone may occur inthe base plate adjacent to the weld.The precaution s nece ssa ry for theavoidance of cracking include suchmeasures as reduction in cooling rateof the joint by the use of preheat or theuse of large diameter electrodes athigh currents. The hydrogen contentof a weld can be increased when it isdeposi ted on galvanized or zinc-richprimed steel.This extra hydrogen originates fromthe pickling process in galvanizing, orfrom the decomposition products ofprimers. It may be necessary to eitherremove primers from the vicinity ofthe joint before welding or u se ahigher preheating temperature thanwould be used on uncoated steel.Zinc-rich paints are available thathave been specially formulated suchthat it is not necessary to remove thecoating from the weld path prior towelding. A letter should be obtainedfrom the paint manufacturer stating itto be "weldable."A fairly extensive amount of research has been carried out over manyyears on the mechanical properties ofwelds in zinc coated steels. Researchperformed by the International LeadZinc Re searc h Organization ha sshown that the tensile, bend and impact properties of welds on galvanizedTable 6. Typical shielded metal arc welding conditions for un coated or ga lvanized reinforcing bars (Courtesy AWS).IDetailI'I 600I\/jBar size (in.)I1/s'is1/s3/s'I Rooting opening1h 6 in .--1--60 c : cJRooting openingI5/ 32I(A)Numberof passes1001201271273698-'I 12711 3'is5/ 32I1h 6 in.- 1'/"'Copper moldroot opening 3/s in.-'I mI60 double-Veevertical weldsBRoo 60o opening1h 6 in.BeadWeaveWeaveWeave33 1h4588WeaveWeave2Weave'hWeave'I IWeave3-III3'hI5/ 32II2'h3I-135Sf3 2TechniqueTime tocomplete(minutes)·---II2100/s-III1/s-r-Root opening5/s in.1100/s3---I--Root opening3/s in.Root open ing5/s in.ICurrent (ac)Electrodesize (in.)1I136Weave3-'--·I/sWeave695I -4-4-I3/sI14109595/s/s1IIWeaveWeave2 'h9INote: I in . 25.4 mm.May-June 199845
joints. In the case of tee or butt joints,a V -groove preparation or squaregroove with a gap will facilitate theescape of gases, minimizing porosity,more than a close square-groove joint.Pore formation is also influenced bythe thickness of the galvanized coatingrelative to the base steel.Close attention to welding conditions will reduce the extent of porositybut complete elimination is not alwayspossible. It is important to consider theeffect of porosity on static strengthand cracking of the weld joint.steels are equivalent to the propertiesof welds on uncoated steels.Fracture ToughnessCritical crack opening displacementmeasurements and drop weight testshave established that the fracture toughness properties of welds are unaffectedby the presence of galvanized coatings.Fatigue StrengthThe fatigue strength of arc welds ingalvanized steel is equivalent to weldsin uncoated steel made by C0 2 welding, as shown in Fig. 4. This showsthat the fatigue strength of the defectfree joint made with low silicon fillermetal is equivalent to that of a jointmade in uncoated steel.Effect of Porosity onFatigue StrengthWhen joints are subject to fatigueloading, welds in galvanized steelshould be made oversized to reducethe influence of any porosity in theweld metal. In evaluating the effect ofporosity on the fatigue strength of afillet weld, it is necessary to considerboth the function of the joint and thesize of the weld.When a fillet weld in galvanizedsteel is large enough relative to platethickness to fail by fatigue from the toeof the weld in the same manner as inuncoated steel, the presence of porosityin the weld does not reduce the fatiguestrength of the joint. Where the dimensions of a weld are just large enough tocause fatigue failure from the toe in asound weld, a weld containing porosityProperties ofWeld Containing PorosityPorosity will occur in certain weldjoint designs in galvanized steel depending on the coating thickness,volatilization of the zinc coating andthe entrapment of gas in the weld.Whatever welding process is used, theextent of porosity will depend on thesolidification rate of the weld metal,which is governed by heat input. Theheat input is dependent on the current,voltage and welding speed.Joint type will affect porosity formation because gases can escape morereadily from butt joints than from tee109139· 1"' 123 ·58"' 108·17 .;ee.s'. 92·6 77·261 ·8 I Uncaoted plat. GaW Wzed plate23 4 I70526 Cl) :5' \ \13457()6tI2345CrackingIntergranular cracking of filletwelds containing porosity, sometimesreferred to as zinc penetrator cracking,may also affect the strength of weldedjoints. As a precaution, it is advisableto carry out procedural and weldertests on materials and samples.Reconditioning Welded JointsWhen galvanized steel is welded,some of the zinc coating is volatilizedon each side of the weld and, while athin layer of zinc-iron alloy remains,there is a loss in corrosion resistance.In the case of zinc-rich painted steel,welding causes decomposition of thepaint film which is burnt off for somedistance on each side of the weld. Thewidth of the damaged zone will depend on the heat input and preheat.Damage to the zinc coating or baresteel areas after welding should be repaired with a coat of zinc-rich paint (95percent zinc) or epoxy paint immediately after welding and chipping of slagto replace the removed galvanizing.Hardware should be properly cleanedprior to application of a protectivetreatment. Restorations should be carried out in accordance with ASTMA780, Standard Practice for Repair ofDamaged and Uncoated Areas of HotDip Galvanized Coatings.The conditioned or repaired area ofthe zinc coating will have no effect onthe overall lifetime of the part. Repairmaterials and their coating thicknesshave been chosen to give comparablelifetimes to the coating minimums require(\ in ASTM A123, Standard Specification of Zinc (Hot-Dip Galvanized)Coating on Iron and Steel Products.There may be some visual differences between the original hot-dip galvanized coating and the repair areas,but the corrosion lifetime should beunaffected. Over a period of time, thevisual differences will become less obvious as the zinc coating weathers.4Endurance,cyclesFig. 4. SN curves showing fatigue tests on cruciform joints. C0 2 short-circuiting arcwelds on uncoated and ga lvan ized 1/2 in . (12.7 mm) Lloyds Grade A steel; AWSE60S-3 fi ller wire (Courtesy AWS).46at the root may fail preferentiallythrough the throat of the weld.WELDING GALVANIZEDSTEEL WITH OTHER METALSGalvanized steel can be welded toother metals, including stainless steel,when the welding techniques disPCI JOURNAL
cussed in this article are utilized. Forbest results with dissimilar metalwelding, the zinc coating should always be removed from around thearea of the weld.If the zinc metal penetrates thestainless steel, for instance, there canbe an embrittlement problem understress. After the welding has been accomplished with the dissimilar metals,the weld area should be coated with azinc touch-up product in order to prevent the onset of corrosion.SAFETY ANDHEALTH EFFECTSAll welding processes producefumes and gas to a greater or lesserextent. Fumes from cutting and welding are a controversial topic in today'senvironmentally conscious cultureand should be a concern of all weldersand fabricators. Manufacturers andwelders must identify the hazards associated with welding coated and uncoated steels, and workers must betrained to maintain work practicescomplying with the OccupationalSafety and Health Administration(OSHA) regulations.Fumes from welding galvanizedsteel primarily contain zinc, iron andlead. The fume composition andamount typically depend on the composition of material as well as the current, voltage and welding process type.Studies on the effects of human exposure to cutting and welding fumeshave presented contradictory and inconclusive evidence. Quantifying theeffects is difficult for several reasons.Working conditions vary widely, evenfor the same process.For example, helmets that cover thefront of the neck allow less fume infiltration than an open neck helmet. Posture also can greatly affect exposures.A welder working with his head in thefume plume is exposed to much higherconcentrations than a welder with hishead back away from the plume. Goodventilation minimizes the amount ofthe fume the worker breathes . PoorMay-June 1998ventilation can result in overexposure.Welding of galvanized steel shouldalways be done in well ventilated locations to prevent the inhalation offumes. If adequate ventilation cannotbe provided, personnel who may beexposed to fumes must be equippedwith hose masks or air respirators.Workers in confined areas should beprovided with a positive air supply. Inenclosed areas, each worker should berequired to wear an approved airsupplied respirator.The potential hazards associatedwith welding and cutting of galvanized steel are similar to those associated with welding most uncoatedsteels.Welding of zinc coated steel alsoproduces fumes and gases. The mostdramatic effect of welding fume ismetal fume fever, which is more commonly known as zinc chills , zincshakes or galvanize p
Fig. 1. Welding of ga lvanized steel. Cas Metal Arc W elding Gas metal arc (GMA) welding, also known as C02 or Metal-Inert Gas (MIG) welding, is a versatile semi automatic welding process that is con venient and easy to use. Fig. 2 shows an illustration of C02 welding. GMA welding is particularly sui
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