ASTM_D_4138_-_07a_2013.pdf

Designation:D413807a(Reapproved 2013)Standard Practices forMeasurement of Dry Film Thickness of Protective CoatingSystems by Destructive,Cross-Sectioning Means1This standard is issued under the fixed designation D4138;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope*1.1 This practice describes the measurement of dry filmthickness of coating films by microscopic observation ofprecision angular cuts in the coating film.Use of theseprocedures may require repair of the coating film.This practiceis intended to supplement the manufacturers instructions forthe manual operation of the gages and is not intended to replacethem.It includes definitions of key terms,referencedocuments,the significance and use of the practice,and theadvantages and limitations of the instruments.1.2 Three procedures are provided for measuring dry filmthickness of protective coating systems:1.2.1 Procedure AUsing groove cutting instruments.1.2.2 Procedure BUsing grinding instruments.1.2.3 Procedure CUsing drill bit instruments.1.3 These procedures are not applicable for soft or ductilesubstrates that may deform under the test gage cutting tip.Thesubstrate should be sufficiently rigid to prevent deformation ofthe coating during the cutting process.The surface may be flator moderately curved.Pipes as small as 25 mm(1 in.)indiameter may be measured in the axial direction.1.4 Individual coats in a multicoat system where there is adiscernible visual difference between coats or the overallthickness of a coating system can be measured by theseprocedures.1.5 The range of thickness measurement is typically 2 to2000 microns(0.1 to 80 mils)and depends upon the cuttingangle of the blade.1.6 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.7 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D823 Practices for Producing Films of Uniform Thicknessof Paint,Varnish,and Related Products on Test PanelsD1005 Test Method for Measurement of Dry-Film Thick-ness of Organic Coatings Using MicrometersD7091 Practice for Nondestructive Measurement of DryFilm Thickness of Nonmagnetic Coatings Applied toFerrous Metals and Nonmagnetic,Nonconductive Coat-ings Applied to Non-Ferrous Metals3.Terminology3.1 Definitions of Terms:3.1.1 accuracy,nthe measure of the magnitude of errorbetween the result of a measurement and the true thickness ofthe item being measured.3.1.2 dry film thickness,nthe thickness of a coating(orcoating layers)as measured from the surface of the substrate.3.1.3 micrometre(micron),none one-thousandths of amillimetre(0.001 mm);25.4 microns=1 mil.3.1.4 mil,nan imperial unit of measure;one one-thousandths of an inch(0.001 in.);1 mil=25.4 microns.3.1.5 reticle,na scale on transparent material fitted at thefocal plane of the eyepiece of the microscope for the purposeof measuring the width of a feature within the image.4.Summary of Practice4.1 The three procedures are based on measurement of dryfilm thickness by observation of the width of angular cuts in thecoating through a microscope having a built-in reticle with ascale.Each procedure employs different instruments to makethe cut in the coating.1These practices are under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings,Materials,and Applications and are the direct responsibilityof Subcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved July 1,2013.Published July 2013.Originally approvedin 1982.Last previous edition approved in 2007 as D4138 07a.DOI:10.1520/D4138-07AR13.2For 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.*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 4.2 Procedure AUses a carbide or carbide-tipped wedge tocut a groove in the coating.The groove is cut at a precise angleto the surface.Various wedge angles are available.Thisprocedure requires the manual cutting of the coating bydragging a cutting wedge through both the coating and thesurface of the substrate.In this operation,the cutter trailsmidway between the two guide studs.Continuous 3pointsurface contact should be maintained to assure precise verticalalignment of the groove.Excessive pressure on th