1、Designation: A 385/A 385M 09Standard Practice forProviding High-Quality Zinc Coatings (Hot-Dip)1This standard is issued under the fixed designation A 385/A 385M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This practice covers the precautions that sho
3、uld be takento obtain high-quality hot-dip galvanized coatings.1.2 Where experience on 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 either
4、inch-pound units (as A 385) or in SI units (as A 385M).Inch-pound units and SI units are 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 wa
5、y.2. Referenced Documents2.1 ASTM Standards:2A 143/A 143M Practice for Safeguarding Against Em-brittlement of Hot-Dip Galvanized Structural Steel Prod-ucts and Procedure for Detecting EmbrittlementA 384/A 384M Practice for Safeguarding Against Warpageand Distortion During Hot-Dip Galvanizing of Stee
6、l As-sembliesA 563 Specification for Carbon and Alloy Steel Nuts3. Steel Selection3.1 The production of a galvanized coating has as its basisthe metallurgical reaction between the steel and the moltenzinc, resulting in the formation of several iron-zinc compoundlayers, for example, gamma (not always
7、 visible microscopi-cally), delta, and zeta in Fig. 1. In addition, a layer of themolten zinc adheres to the surface of the compound layers asthe steel is withdrawn from the galvanizing bath. Uponsolidification, this adherent zinc forms the eta layer.3.2 It is known that the exact structural nature
8、of thegalvanized coating, as typified by Fig. 1, may be modified inaccordance with the exact chemical nature of the steel beinggalvanized. Certain 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.
9、04 %, ormanganese in excess of about 1.3 % will cause the productionof coatings different from the coating typified by Fig. 1. Steelswith silicon 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 %
10、 and between0.15 % and 0.22 %. Recent studies have shown that even incases where the silicon and phosphorous are individually heldto desirable limits, 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 element
11、s manifest their structural effect as anaccelerated growth of the compound layers, particularly thezeta layer, and the virtual elimination of the eta layer. Cosmeti-cally this accelerated growth is seen as a gray matte finishedcoating as opposed to the usual bright and smooth appearanceof galvanized
12、 coatings. Sometimes, a large surface may haveadjacent areas of matte finish and bright finish leading to amottled appearance.3.4 There is some evidence that the coatings resulting fromthis accelerated growth are more brittle and less adherent thannormal coatings. There is also evidence that these c
13、oatings aresubject to a premature red staining in atmospheric exposure;however, this staining has been found not to be associated withcorrosion 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, ph
14、osphorus, carbon, and manganese can be galvanizedsuccessfully. When the steel chemistry is known beforehand,experienced galvanizers can in some, but not all, instancesexercise limited control over the coatings as shown in Fig. 2.Also, the combination of two different steel types or thick-nesses in o
15、ne item may result in a nonuniform galvanizing1This practice is under the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Steel Products and is the direct responsibility of SubcommitteeA05.13 on Structural Shapes and Hardware Specifications.Current edition approved May 1, 2009. Publis
16、hed June 2009. Originallyapproved in 1955. Last previous edition approved in 2008 as A 385 08a.2For referenced 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 Documen
17、t Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.finish. The experience of the steel supplier, designer, manufac-turer, and galvanizer
18、 should determine the steel selection.3.6 In 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.4. Assemblies of Different Material
19、s or Different Surfacesor Both4.1 Whenever possible, assemblies should consist of ele-ments of similar steel 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.
20、 These differences in-clude:4.2.1 Excessively rusted surfaces.4.2.2 Pitted surfaces.4.2.3 Machined surfaces.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 thos
21、erecommended in 3.2.4.3 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 welded are undesirable.5.2 When the dist
22、ance 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 wetting in adjacent areas.Such uncoated
23、surfaces cause a rust staining after exposure tothe environment. Traditionally however, steel grating has beenmanufactured without seal welding and when properly ex-ecuted, this manufacturing means has permitted the galvanizedcoating to satisfy the quality requirements of the applicableASTM specific
24、ations.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 isFIG. 1 Photomicrograph of Normal Galvanized Coating (X 400)FIG. 2 Photomicrograph of Dull Gray, Thick-Galvanized Coatin
25、g (X 200)A 385/A 385M 092heated to the galvanizing temperature, which is nominally850F 454C. Vent holes or unwelded area around theadjoining surfaces should be provided through one or bothsides into the lapped area per the following tables.6. Sheet Steel Rolled Over a Wire or Rod Stiffener6.1 All oi
26、l or grease should be removed from both the sheetsteel and wire or rod before rolling (see Fig. 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
27、 folded assemblies, before folding and assembling (seeFig. 4).7. Weld Flux Removal and Welding 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 g
28、rit or sand-blasting or by a wire needlegun.7.2 It is desirable to choose a welding rod with 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 Prep
29、aration8.1 Flame cut copes on beams can be extremely sensitive toresidual stresses in the steel 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 the
30、n areimmersed in the molten zinc and heated to above 800F forusually 5 to 10 minutes. The steel 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 th
31、e edges of the flame cut cope is toweld a bead along the sides of the cope in the area where 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
32、of cracking but will greatly reduce thelikelihood of cracking.8.3 The weld rod material should be chosen as described inSection 7.9. Cold Forming Before Galvanizing9.1 Refer to the latest revision of Practice A 143/A 143M.10. Shearing, Cutting and Punching Before Galvanizing10.1 Refer to the latest
33、revision of Practice A 143/A 143M.11. Warpage and Distortion11.1 Refer to the latest revision of Practice A 384.12. 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 that
34、 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 retain
35、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 (see F
36、ig. 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 addit
37、ion, 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 of
38、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 inTABLE 1 Vent Holes for Overlapped Areas for Steels12 in. 12.75mm or Less in ThicknessOverlapped Area in.2cm2 Vent Holes Unwelded A
39、reaunder 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 Areas for Steels Greaterthan12 in. 12.75 mm in ThicknessOverlapped Area
40、 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. 4 Folded SurfacesA 385/A 385M 093each side of each intersection. T
41、he vent openings shall be aminimum of38 in. 1 cm in diameter or 25 % of the diameterof the pipe 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
42、 possible. This is the most desirable situation. Aminimum vent opening of 25 to 30 % of the cross-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 rec
43、ommendations. In box sections (see Fig. 9) wheregusset plates are used, the gusset plates shall 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.9
44、14 mm apart. In the case of columns with end plates (seeFig. 10) where the end plate must be 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 h
45、oletangential to the base plate. On trusses (see Fig. 11 and Fig. 12)where tubular members intersect, 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
46、 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. This hea
47、ting may cause discoloration of thegalvanized coating near the heated area.14. Marking for Identification14.1 Paint is not removed by pickling and must not be usedwhen marking for identification material to be galvanized.14.2 Satisfactory identification may be provided by weldingthe identifying mark
48、s on the material, by embossing theidentifying marks on a steel tag of no less than No. 12 gage(0.105 in. 2.69 mm) and securing to the material with a heavywire such as No. 9 gage (0.148 in. 3.76 mm), or by diestamping the identifying marks into the material with charac-ters12 in. 12.7 mm high and a
49、 minimum of132 in. 0.79 mmdeep.14.3 All markings shall remain legible after galvanizing.15. Galvanized Steel in Concrete15.1 Galvanized steel can be placed in direct contact withconcrete as the galvanized coating forms an excellent bondwith the concrete materials. When embedding steel parts inconcrete, the highest quality system is produced when all of thesteel parts are coated with the same corrosion protectionsystem. If there are galvanized parts in concrete near steel partswith no co
