1、Designation: A385/A385M 15Standard Practice forProviding High-Quality Zinc Coatings (Hot-Dip)1This standard is issued under the fixed designation A385/A385M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revision
2、. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the precautions that should be takento obtain high-quality hot-dip galvanized coatings.1.2 Where experience on
3、 a specific product indicates arelaxing of any provision, the mutually acceptable change shallbe a matter for agreement between the manufacturer andpurchaser.1.3 This specification is applicable to orders in eitherinch-pound units (as A385) or in SI units (as A385M).Inch-pound units and SI units are
4、 not necessarily exactequivalents. Within the text of this specification and whereappropriate, SI units are shown in brackets. Each system shallbe used independently of the other without combining values inany way.2. Referenced Documents2.1 ASTM Standards:2A123/A123M Specification for Zinc (Hot-Dip
5、Galvanized)Coatings on Iron and Steel ProductsA143/A143M Practice for Safeguarding Against Embrittle-ment of Hot-Dip Galvanized Structural Steel Products andProcedure for Detecting EmbrittlementA153/A153M Specification for Zinc Coating (Hot-Dip) onIron and Steel HardwareA384/A384M Practice for Safeg
6、uarding Against Warpageand Distortion During Hot-Dip Galvanizing of SteelAssembliesA563 Specification for Carbon and Alloy Steel Nuts2.2 American Institute of Steel Construction (AISC) Docu-ments:3Steel Construction Manual3. Steel Selection3.1 The production of a galvanized coating has as its basist
7、he metallurgical reaction between the steel and the moltenzinc, resulting in the formation of several iron-zinc compoundlayers, for example, gamma (not always visiblemicroscopically), delta, and zeta in Fig. 1. In addition, a layerof the molten zinc adheres to the surface of the compoundlayers as th
8、e steel is withdrawn from the galvanizing bath.Upon solidification, this adherent zinc forms the eta layer.3.2 It is known that the exact structural nature of thegalvanized coating, as typified by Fig. 1, may be modified inaccordance with the exact chemical nature of the steel beinggalvanized. Certa
9、in elements found in steels are known to havean influence on the coating structure. The elements carbon inexcess of about 0.25 %, phosphorus in excess of 0.04 %, ormanganese in excess of about 1.3 % will cause the productionof coatings different from the coating typified by Fig. 1. Steelswith silico
10、n in the range 0.04 % to 0.15 % or above 0.22 % canproduce galvanized coating growth rates much higher thanthose for steels with silicon levels below 0.04 % and between0.15 % and 0.22 %. Recent studies have shown that even incases where the silicon and phosphorous are individually heldto desirable l
11、imits, a combined effect between them canproduce a coating as shown in Fig. 2, which typically wouldhave a mottled or dull gray appearance.3.3 These elements manifest their structural effect as anaccelerated growth of the compound layers, particularly thezeta layer, and the virtual elimination of th
12、e eta layer. Cosmeti-cally this accelerated growth is seen as a gray matte finishedcoating as opposed to the usual bright and smooth appearanceof galvanized coatings. Sometimes, a large surface may haveadjacent areas of matte finish and bright finish leading to amottled appearance.3.4 There is some
13、evidence that the coatings resulting fromthis accelerated growth are more brittle and less adherent thannormal coatings. There is also evidence that these coatings aresubject to a premature red staining in atmospheric exposure;however, this staining has been found not to be associated withcorrosion
14、of the substrate steel.3.5 A problem with steel chemistry is not usually apparentuntil after an item has been galvanized. Not all combinations ofsilicon, phosphorus, carbon, and manganese can be galvanized1This practice is under the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Stee
15、l Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved Oct. 1, 2015. Published October 2015. Originallyapproved in 1955. Last previous edition approved in 2011 as A385 111. DOI:10.1520/A0385_A0385M-15.2For reference
16、d ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Institute of Steel Construction (AISC), One E.Wack
17、er Dr., Suite 700, Chicago, IL 60601-2001, http:/www.aisc.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1successfully. When the steel chemistry is known beforehand,experienced galvanizers can in some, but not all, instancesexerci
18、se limited control over the coatings as shown in Fig. 2.Also, the combination of two different steel types or thick-nesses in one item may result in a nonuniform galvanizingfinish. The experience of the steel supplier, designer,manufacturer, and galvanizer should determine the steel selec-tion.3.6 I
19、n general, galvanized coatings are specified because oftheir corrosion resistance, not because of their appearance. Therelative corrosion resistance of the normal and abnormalcoatings is, for all practical purposes, equal.3.7 Steels with very low levels of silicon (less than 0.02%)and aluminum-kille
20、d steels regularly present a challenge indeveloping a galvanized coating that meets the thicknessrequirements of Specifications A123/A123M or A153/A153M.Phosphorus (less than 0.020%) can also exhibit low coatingthicknesses. For these steels, it may be difficult to meet thecoating thickness requireme
21、nts of Specifications A123/A123Mor A153/A153M. In these cases the galvanizer and the pur-chaser should agree on a plan of action. Some choices are toaccept the lower coating thickness, apply a paint coating overthe galvanized coating (Duplex System), blast clean the steelbefore hot-dip galvanizing t
22、o increase the coating thickness,over-pickle the steel in sulfuric acid to roughen the surface andincrease the coating thickness, or other possible solutions.4. Assemblies of Different Materials or Different Surfacesor Both4.1 Whenever possible, assemblies should consist of ele-ments of similar stee
23、l chemistry and surface condition.4.2 Whenever different analyses of steel or different sur-faces of steel are united in an assembly the galvanized finish isnot generally uniform in appearance. These differences in-clude:4.2.1 Excessively rusted surfaces.4.2.2 Pitted surfaces.4.2.3 Machined surfaces
24、.4.2.4 Cast iron (especially with sand inclusion).4.2.5 Cast steel.4.2.6 Malleable iron.4.2.7 Hot-rolled steel.4.2.8 Cold-rolled steel.4.2.9 Steel containing chemical elements in excess of thoserecommended in 3.2.FIG. 1 Photomicrograph of Normal Galvanized Coating (X 400)FIG. 2 Photomicrograph of Du
25、ll Gray, Thick-Galvanized Coating (X 200)A385/A385M 1524.3 Where combinations are unavoidable, thorough abrasiveblasting of the entire assembly will normally improve galva-nizing quality.5. Overlapping or Contacting Surfaces5.1 Overlapping or contacting surfaces that have not had alledges seal welde
26、d are undesirable.5.2 When the distance between the overlapping surfaces isless than332 in. 2.38 mm, these surfaces will not normally bewet by molten zinc. Furthermore, cleaning solution compoundsthat remain on these surfaces volatilize during the galvanizingprocess and may interfere with zinc wetti
27、ng in adjacent areas.Such uncoated surfaces cause a rust staining after exposure tothe environment. Traditionally however, steel grating has beenmanufactured without seal welding and when properlyexecuted, this manufacturing means has permitted the galva-nized coating to satisfy the quality requirem
28、ents of the appli-cable ASTM specifications.5.3 When the overlap surface area is large and the edgeshave been seal welded, air or moisture or both entrappedtherein can develop destructive pressures when the assembly isheated to the galvanizing temperature, which is nominally850F 454C. Vent holes or
29、unwelded area around theadjoining surfaces should be provided through one or bothsides into the lapped area in accordance with the followingtables.6. Sheet Steel Rolled Over a Wire or Rod Stiffener6.1 All oil or grease should be removed from both the sheetsteel and wire or rod before rolling (see Fi
30、g. 3). Grease or oilbecomes volatile at the galvanizing temperature and willgenerate gas which will prevent zinc from sealing the contactedges. All steel should be degreased before pickling and in thecase of folded assemblies, before folding and assembling (seeFig. 4).7. Weld Flux Removal and Weldin
31、g Rods7.1 Welding flux residues are chemically inert in normalpickling solutions. Thus, they will not be removed by standardgalvanizing cleaning techniques and are best removed at thetime of fabrication by grit or sand-blasting or by a wire needlegun.7.2 It is desirable to choose a welding rod with
32、a chemicalcomposition as close as possible to the parent metal.7.3 Welding rods high in silicon may cause excessivelythick or darkened coatings or both to form in the welded area.8. Flame Cut Cope Edges Preparation8.1 Flame cut copes on beams can be extremely sensitive toresidual stresses in the ste
33、el beam and, with the rough surfacefrom the flame cutting operation, can be sources of crackingduring the thermal cycling of the hot-dip galvanizing process.The steel beams start near ambient temperature then areimmersed in the molten zinc and heated to above 800F forusually 5 to 10 minutes. The ste
34、el beams are then cooled backto ambient temperature so the thermal cycling can createthermal stresses in the area of the cope.8.2 One method that has had fairly good success at mini-mizing the cracking at the edges of the flame cut cope is toweld a bead along the sides of the cope in the area where
35、theflame cutting was done before hot-dip galvanizing. Thiswelding operation will reheat the area and may relieve some ofthe residual stress near the cope edges. The weld bead will noteliminate all incidents of cracking but will greatly reduce thelikelihood of cracking.8.3 The weld rod material shoul
36、d be chosen as described inSection 7.9. Cold Forming Before Galvanizing9.1 Refer to the latest revision of Practice A143/A143M.10. Shearing, Cutting and Punching Before Galvanizing10.1 Refer to the latest revision of Practice A143/A143M.TABLE 1 Vent Holes for Overlapped Areas for Steels12 in. 12.75m
37、m or Less in ThicknessOverlapped Area in.2cm2 Vent Holes Unwelded Areaunder 16 103 None None16 103 to under 64 413 One38 in. 1 cm 1 in. 2.5 cm64 413 to under 400 2580 One12 in. 1.25 cm 2 in. 5.1 cm400 2580 and greater,each 400 2580One34 in. 1.91 cm 4 in. 10.2 cmTABLE 2 Vent Holes for Overlapped Area
38、s for Steels Greater than12 in. 12.75 mm in ThicknessOverlapped Area in.2cm2 Vent Holes Unwelded Areaunder 16 103 None None16 103 to under 64 413 None None64 413 to under 400 2580 One12 in. 1.25 cm 2 in. 5.1 cm400 2580 and greater,each 400 2580One34 in. 1.91 cm 4 in. 10.2 cmFIG. 3 Rolled SurfacesFIG
39、. 4 Folded SurfacesA385/A385M 15311. Warpage and Distortion11.1 Refer to the latest revision of Practice A384/A384M.12. Design Recommendations for Providing for the FreeFlow of Cleaning Solutions, Fluxes, Air, and Zinc12.1 All fabricated assemblies shall be so designed withvent and drain holes such
40、that no air is trapped during theimmersion of the assemblies into cleaning solutions or moltenzinc. Similarly these holes shall allow all solutions and moltenzinc to drain freely from the assemblies. Failure to follow thispractice will result in areas that will not galvanize properly, orthat may ret
41、ain entrapped flux or excessive amounts of zinc.12.2 Free flow of cleaning solutions and molten zinc shallalso be provided for in assemblies of hot-rolled shapes. This isaccomplished by cropping the corner to provide an openingwith a minimum area of 0.3 in.21.9 cm2 at the corners of allstiffeners (s
42、ee Fig. 5), gussets, or bracing (see Fig. 6).12.3 Air or moisture, or both, entrapped within closedfabricated pipework, such as handrail, can develop destructivepressures when heated to the galvanizing temperature. Pipehandrail shall preferably be vented full open internally, asshown in Fig. 7. In a
43、ddition, there shall be one38-in. 9.5-mmminimum diameter external hole at each intersection to preventany possible explosions in the event that the fabricator neglectsto provide internal venting. This hole shall be located as closeas possible to the weld bead joining the two steel pieces and theedge
44、 of the hole shall be not more than 0.5 in. 12 mm fromthe edge of the weld bead. Where internal venting is notpossible, external vents shall be provided with one vent hole ineach side of each intersection. The vent openings shall be aminimum of38 in. 1 cm in diameter or 25 % of the diameterof the pi
45、pe that is used, whichever is larger (see Fig. 8) andshall be located as described above.12.4 Figs. 9-12 show most of the conditions encounteredwith tubular product assemblies. The venting shall openwherever possible. This is the most desirable situation. Aminimum vent opening of 25 to 30 % of the c
46、ross-sectionalarea of tubular structure shall be specified where full-openventing is not possible. For small cross sections, larger percentvent openings are recommended. See attached drawings forspecific recommendations. In box sections (see Fig. 9) wheregusset plates are used, the gusset plates sha
47、ll be clipped at thefour corners. In addition, a center hole shall be provided so thatthe cumulative area of the vent holes meets the recommendedminimum. Gusset plates shall not be spaced closer than 36 in.914 mm apart. In the case of columns with end plates (seeFig. 10) where the end plate must be
48、closed, the shaft of thecolumn shall be vented. The vent opening shall be a half circlewith its diameter at the base plate (D, Fig. 10). This is muchsuperior to putting a hole with the circumference of the holetangential to the base plate. On trusses (see Fig. 11 and Fig. 12)where tubular members in
49、tersect, vent holes are recommendedat both sides of the intersection.13. Moving Parts13.1 When a galvanized assembly incorporates movingparts (such as drop handles, shackles, and shafts) a radialclearance of not less than116 in. 1.59 mm must be allowed toensure full freedom of movement following galvanizing.13.2 Moving parts such as handles or hinges should begalvanized separately and assembled after galvanizing. It maybe necessary to post heat these parts in order to have themfunction freely. T
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