ASTM_A_385_-_A_385M_-_15.pdf

Designation:A385/A385M15Standard 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.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 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 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 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 Safeguarding 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 basisthe metallurgical reaction between the steel and the moltenzinc,resulting in the formation of several iron-zinc compoundlayers,forexample,gamma(notalwaysvisiblemicroscopically),delta,and zeta in Fig.1.In addition,a layerof the molten zinc adheres to the surface of the compoundlayers as the steel is withdrawn from the galvanizing bath.Upon solidification,this adherent zinc forms the eta layer.3.2 It is known that the exact structural nature of thegalvanized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.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 0.04%,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%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 elements 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 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 coatings 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,phosphorus,carbon,and manganese can be galvanized1This 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 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 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 Document Summary page onthe ASTM website.3Available from American Institute of Steel Construction(AISC),One E.Wacker 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 States1 successfully.When the steel chemistry is known beforehand,experienced galvanizers can in some,but not all,instancesexerci