ASTM D7091-2013 1304 Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic Nonconductive Coatings.pdf

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1、Designation: D7091 13Standard Practice forNondestructive Measurement of Dry Film Thickness ofNonmagnetic Coatings Applied to Ferrous Metals andNonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals1This standard is issued under the fixed designation D7091; the number immediately following

2、 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.This standard has been approved f

3、or use by agencies of the U.S. Department of Defense.1. Scope*1.1 This practice describes the use of magnetic and eddycurrent gages for dry film thickness measurement. This prac-tice is intended to supplement the manufacturers instructionsfor the manual operation of the gages and is not intended tor

4、eplace them. It includes definitions of key terms, referencedocuments, the significance and use of the practice, theadvantages and limitations of coating thickness gages, and adescription of test specimens. It describes the methods andrecommended frequency for verifying the accuracy of gagesand for

5、adjusting the equipment and lists the reporting recom-mendations.1.2 These procedures are not applicable to coatings that willbe readily deformed under the load of the measuring gages/probes, as the gage probe must be placed directly on thecoating surface to obtain a reading. Provisions for measurin

6、gon soft or tacky coatings are described in 5.7.1.3 Coating thickness can be measured using a variety ofgages. These gages are categorized as “magnetic pull-off” and“electronic.” They use a sensing probe or magnet to measurethe gap (distance) between the base metal and the probe. Thismeasured distan

7、ce is displayed as coating thickness by thegages.1.4 Coating thickness can vary widely across a surface. Asa result, obtaining single-point measurements may not accu-rately represent the actual coating system thickness. SSPC-PA2prescribes a frequency of coating thickness measurement basedon the size

8、 of the area coated. A frequency of measurement forcoated steel beams (girders) and coated test panels is alsoprovided in the appendices to SSPC-PA 2. The governingspecification is responsible for providing the user with theminimum and the maximum coating thickness for each layer,and for the total c

9、oating system.1.5 The values stated in inch-pound units are to be regardedas standard. No other units of measurement are included in thisstandard.1.6 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 stan

10、dard 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:2D609 Practice for Preparation of Cold-Rolled Steel Panelsfor Testing Paint, Varnish, Conversion Coatings, andRelated Coating P

11、roductsD823 Practices for Producing Films of Uniform Thicknessof Paint, Varnish, and Related Products on Test PanelsD1730 Practices for Preparation of Aluminum andAluminum-Alloy Surfaces for Painting2.2 SSPC Standard:3SSPC-PA 2 Procedure for Determining Conformance to DryCoating Thickness Requiremen

12、ts2.3 ISO Standard:4ISO 19840 Paints and varnishescorrosion protection ofsteel structures by protective paint systemsMeasurement of, and acceptance criteria for, the thicknessof dry films on rough surfaces1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Ma

13、terials, and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.Current edition approved Nov. 1, 2013. Published December 2013. Originallyapproved in 2005. Last previous edition approved in 2012 as D7091 12. DOI:10.1520/D7091-13.2For ref

14、erenced 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 Society for Protective Coatings (SSPC), 40 24th St.,

15、6th Floor,Pittsburgh, PA 15222-4656, http:/www.sspc.org.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive,

16、 PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 accuracy, nthe measure of the magnitude of errorbetween the result of a measurement and the true thickness ofthe item being measured.3.1.1.1 DiscussionAn accuracy stat

17、ement predicts theability of a coating thickness gage to measure the true thicknessof a coating to be measured. Accuracy statements provide theperformance capability across the full functional measurementrange of the gage. Accuracy statements frequently include afixed portion that remains constant a

18、cross the measurementrange, plus a variable portion that is related to the measurementresult for a particular thickness.3.1.2 adjustment (optimization), nthe physical act ofaligning a gages thickness readings to match those of a knownthickness sample (removal of bias), in order to improve theaccurac

19、y of the gage on a specific surface or within a specificportion of its measurement range.3.1.2.1 DiscussionAn adjustment will affect the outcomeof subsequent readings.3.1.3 base metal reading (BMR), na measurement ob-tained on the uncoated substrate using a coating thicknessgage.3.1.3.1 DiscussionTh

20、e BMR is the determined effect ofsubstrate roughness on a coating thickness gage that is causedby the manufacturing process (for example, castings) orsurface profile (roughness)-producing operations (for example,power tool cleaning, abrasive blast cleaning, etc.). Non-compensation for the base metal

21、 effect can result in anoverstatement of the true thickness of the coating.3.1.4 calibration, nthe high-level, controlled and docu-mented process of obtaining measurements on traceable cali-bration standards over the full operating range of the gage, thenmaking the necessary gage adjustments (as req

22、uired) to correctany out-of-tolerance conditions.3.1.4.1 DiscussionCalibration of coating thickness gagesis performed by the equipment manufacturer, their authorizedagent, or by an accredited calibration laboratory in a controlledenvironment using a documented process. The outcome of thecalibration

23、process is to restore/realign the gage to meet/exceedthe manufacturers stated accuracy.3.1.5 certification, ndocumentation of the state of condi-tion of the gage, which can (but not required by definition) beaccompanied by corrective action (such as adjustment orcalibration, or both, or the replacem

24、ent of components) neces-sary to correct any out-of-tolerance conditions.3.1.6 coating thickness standard, ncoated or plated metalplates, or uncoated shims of flat sheet, with assigned valuestraceable to a National Metrology Institution.3.1.6.1 DiscussionIn the case of the eddy currentprinciple, the

25、 coating and shim material must be non-metallic,whereas in the case of the magnetic induction and the Hall-effect methods the material must be nonmagnetic.3.1.7 compensation value, ngenerating a verifiable value,which is deducted from a measured value read from the gage,to correct for any surface co

26、nditions (that is, base metal effect).3.1.8 dry film thickness, nthe thickness of a coating (orcoating layers) as measured from the surface of the substrate.3.1.8.1 DiscussionIf the surface of the substrate isroughened, the dry film thickness is considered the thickness ofthe coating or coating laye

27、rs above the peaks of the surfaceprofile.3.1.9 ferrous, ncontaining iron.3.1.9.1 DiscussionDescribes a magnetic material such ascarbon steel. That material may also be known as ferromag-netic.3.1.10 gage (gauge), nan instrument for measuringquantity, or an instrument for testing.3.1.10.1 DiscussionI

28、n this practice, the term “gage” refersto an instrument for quantifying coating thickness.3.1.11 manufacturers specifications, na statement or setof statements that describes the performance characteristics ofthe gage under a given set of conditions.3.1.11.1 DiscussionManufacturers specifications ty

29、pi-cally include the range of measurement, accuracy statement,operating temperature range, power source, dimensions andweight, and conformance to industry standards.3.1.12 measurement (reading), nthe value obtained whenplacing the probe of a thickness gage in contact with a surface.3.1.13 micrometer

30、 (micron), none one-thousandth of amillimeter 0.001 mm; 25.4 microns = 1 mil.3.1.14 mil, na U.S. term referring to the imperial unit ofmeasure of one one-thousandth of an inch 0.001 in. referredto elsewhere in the world as “one thou;” 1 mil = 25.4 microns.3.1.15 nonconductive, na material that is un

31、able to con-duct electricity.3.1.16 non-ferrous metal, na nonmagnetic metal or metalalloy (for example, copper, aluminum or brass).3.1.17 reference sample, na coated or uncoated metalspecimen of the same material and geometry as the specificmeasuring application used to adjust and/or verify the accu

32、racyof a coating thickness measuring gage for a specific project.3.1.17.1 DiscussionA coated reference sample may ormay not have thickness values traceable to a National Metrol-ogy Institution. However, the reference sample should bemarked with the stated value and the degree of accuracy. Thecoating

33、 thickness of the sample should be close to the userscoating thickness measurement requirement.3.1.18 shims (foils), nstrips of flat sheet, with the thick-ness stated or referenced in some form, which can be used toadjust a Type 2 coating thickness gage in the intended range ofuse over the surface o

34、f the representative substrate material.3.1.18.1 DiscussionOther uses with Type 2 gages include:placement over soft coatings to obtain thickness measurementswithout the gage probe depressing the coating film, andverification of gage operation.3.1.19 substrate, nthe base material, the type of surface

35、,or the component that is being coated.NOTE 1This practice addresses only metal substrates.3.1.20 surface profile, nsurface texture generated duringthe manufacturing process (for example, casting), or theD7091 132peak-to-valley depth generated by some power tools and byabrasive blast cleaning operat

36、ions.3.1.21 Type 1 (pull-off) gage, na magnetic pull-off instru-ment that measures the dry film thickness of nonmagneticcoatings over a ferrous metal base.3.1.21.1 DiscussionFor Type 1 gages, a probe containinga permanent magnet is brought into direct contact with thecoated surface. The force necess

37、ary to pull the magnet from thesurface is measured and interpreted as the coating thicknessvalue on a scale or display on the gage. Less force is requiredto remove the magnet from a thick coating. The scale isnonlinear.3.1.22 Type 2 (electronic) gage, nan electronic instrumentthat uses electronic ci

38、rcuitry and (but not limited to) themagnetic induction, Hall-effect or eddy current principles, or acombination of a magnetic and eddy current principles, toconvert a reference signal into a coating thickness reading.3.1.22.1 DiscussionThe probe of a Type 2 gage remainson the surface during the meas

39、urement process.3.1.23 verification of accuracy, nobtaining measurementson coating thickness standards, comprising of at least onethickness value close to the expected coating thickness, prior togage use for the purpose of determining the ability of thecoating thickness gage to produce thickness res

40、ults within thegage manufacturers stated accuracy.4. Significance and Use4.1 This practice describes three operational steps necessaryto ensure accurate coating thickness measurement: calibration,verification and adjustment of coating thickness measuringgages, as well as proper methods for obtaining

41、 coating thick-ness measurements on both ferrous and non-ferrous metalsubstrates.4.2 Many specifications for commercial and industrial coat-ings projects stipulate a minimum and a maximum dry filmthickness for each layer in a coating system.Additionally, mostmanufacturers of high performance coating

42、s will warrantycoating systems based upon, in part, achieving the properthickness of each layer and the total coating system. Even if aproject specification is not provided, the coating manufactur-ers recommendations published on product data sheets canbecome the governing document(s). Equipment man

43、ufacturersproduce nondestructive coating thickness testing gages that areused to measure the cumulative or individual thickness of thecoating layers, after they are dry. The manufacturers provideinformation for the adjustment and use of these gages, nor-mally in the form of operating instructions. T

44、he user of thisequipment must be knowledgeable in the proper operation ofthese devices, including methods for verifying the accuracy ofthe equipment prior to, during and after use as well asmeasurement procedures.5. Principles, Advantages, and Limitations of Gages5.1 Type 1 magnetic pull-off gages e

45、mploy an attractionprinciple and a static (non-time varying) magnetic field. Thesemechanical instruments measure the force required to pull apermanent magnet from a coated ferrous metal substrate. Themagnetic force of attraction to the steel substrate beneath thecoating is opposed by a spring or coi

46、l. Tension is applied to thespring/coil until the magnetic attraction to the steel is over-come. The gage must be placed directly on the coated surfaceto obtain a measurement. The force holding the permanentmagnet to the ferrous base is inversely proportional to thethickness of the coating layer(s)

47、between the magnet and theferrous substrate. For example, a thin coating applied to aferrous substrate will require greater spring tension to pull themagnet off than will a thicker coating, since the magnet iscloser to the ferrous substrate with the thinner coating. Thisinverse relationship is refle

48、cted on the nonlinear gage scale.Most Type 1 magnetic pull-off gages do not require a powersource (for example, batteries). The manufacturers statedaccuracy is typically 5 to 10 % of the reading.5.2 Type 1 magnetic pull-off gages are susceptible tovibrations, which may cause the magnet to release fr

49、om thecoated substrate prematurely, yielding a false high value. Themanually operated gages may be susceptible to human errorcaused by inadvertently turning the dial wheel past the point atwhich the magnet pulls from the surface, yielding a false lowmeasurement. Type 1 gages should not be used on soft or tackycoatings, as the magnet may adhere to the coating causing falselow measurements, or coating materials may dry on the magnetcausing false high measurements. The exposed magnet mayattract metal filings, which can contaminate t