ASTM D7091-2005 923 Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic Nonconductive Coatings .pdf

1、Designation: D 7091 05Standard 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 D 7091; the number immediately followi

2、ng 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice desc

3、ribes the nondestructive measurementof the dry film thickness of nonmagnetic coatings applied to thesurface of ferrous metals using magnetic gages and thenondestructive measurement of the dry film thickness ofelectrically nonconductive, nonmagnetic coatings applied tothe surface of nonferrous metals

4、 using eddy current gages. Thispractice is intended to supplement the manufacturers instruc-tions for the manual operation of the gages and is not intendedto replace them. It includes definitions of key terms, referencedocuments, the significance and use of the practice, theadvantages and limitation

5、s of coating thickness gages, and adescription of test specimens. It describes the methods andrecommended frequency for verifying the accuracy of gagesand for adjusting (optimizing) the equipment, describes afrequency for measuring the thickness of the coating(s) andlists the reporting recommendatio

6、ns.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 measuringon soft or tacky coatings are described in 5.6.1.3 Use of fil

7、m thickness measuring gages on metal-filledcoatings may produce erroneous results, depending on the typeand amount of metal in the coating film. The user shouldconsult the manufacturers instructions regarding the use ofcoating thickness gages on these types of coatings.1.4 Coating thickness can be m

8、easured 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 distance is displayed as coating thickness by thegages. Accordingly, these gages can

9、not distinguish the thick-ness of individual layers after they have all been applied. Thethickness of each layer must be measured after it is applied.Even then, the thickness of the measured layer is the cumula-tive thickness of that layer and all layers beneath it, down to thebase metal.1.5 Gages w

10、hich measure coating thickness using an ultra-sonic principle may also be able to measure the thickness ofcoatings applied to metal surfaces. This practice does notaddress the use of ultrasonic coating thickness gages. TestMethod D 6132 should be referenced for this application.1.6 Coating thickness

11、 can vary widely across a surface. Asa result, obtaining single-point measurements may not accu-rately represent the actual coating system thickness. Thispractice provides guidance for the frequency of coating thick-ness measurements, based on large areas of coated surface, ontest panels and on smal

12、l parts/components. The governingspecification is responsible for providing the user with theminimum and the maximum coating thickness for each layer,and for the total coating system.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is there

13、sponsibility 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:2D 609 Practice for Preparation of Cold-Rolled Steel Panelsfor Testing Paint, Varnish, Con

14、version Coatings, andRelated Coating ProductsD 823 Practices for Producing Films of Uniform Thicknessof Paint, Varnish, and Related Products on Test PanelsD 1730 Practices for Preparation of Aluminum andAluminum-Alloy Surfaces for PaintingD 6132 Test Method for Nondestructive Measurement ofDry Film

15、Thickness ofApplied Organic Coatings Using anUltrasonic Gage2.2 SSPC Standards:1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials and Applications and is the direct responsibility ofSubcommittee D01.23 on Physical Properties of Applied Paint Films.

16、Current edition approved Aug. 1, 2005. Published September 2005.2For 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 websi

17、te.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Copyright by ASTM Intl (all rights reserved); Sun Sep 28 02:18:05 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.SSP

18、C-PA2 Paint Application Standard No. 2 Measurementof Dry Coating Thickness with Magnetic Gauges33. 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.

19、3.1.1.1 DiscussionAn accuracy statement 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 afix

20、ed portion that remains constant across the measurementrange, plus a variable portion that is related to the measurementresult for a particular thickness.3.1.2 adjustment, nthe physical act of aligning a gagesthickness readings to match those of a known thickness sample(removal of bias), in order to

21、 improve the accuracy of the gageon a specific surface or within a specific portion of itsmeasurement range.3.1.2.1 DiscussionAn adjustment will affect the outcomeof subsequent readings. Also known as “optimization.”3.1.3 area measurement, nthe average of several spotmeasurements obtained over the c

22、oated surface.3.1.3.1 DiscussionFor large surfaces, an area measure-ment is commonly the average of at least five spot measure-ments obtained in approximately 9 m2(100 ft2) of surfacearea. For small test panels, it is commonly the average of threespot measurements on each test face (one from the top

23、 third,one from the middle third and one from the bottom third).3.1.4 base metal reading (BMR), na measurement ob-tained on the uncoated substrate using a coating thicknessgage.3.1.4.1 DiscussionThe BMR is the measured effect ofsubstrate roughness on a coating thickness gage that is causedby the man

24、ufacturing process (for example, castings) orsurface profile (roughness)-producing operations (for example,power tool cleaning, abrasive blast cleaning, etc.). Non-compensation for the base metal effect can result in anoverstatement of the true thickness of the coating. The basemetal reading is meas

25、ured, recorded and deducted from thethickness of each coat, in order to correctly state the thicknessof the coating over the surface roughness.3.1.5 calibration, nthe high-level, controlled and docu-mented process of obtaining measurements on traceable cali-bration standards over the full operating

26、range of the gage, thenmaking the necessary gage adjustments (as required) to correctany out-of-tolerance conditions.3.1.5.1 DiscussionCalibration of coating thickness gagesis performed by the equipment manufacturer, an authorizedagent, or by an authorized, trained calibration laboratory in acontrol

27、led environment using a documented process. Theoutcome of the calibration process is to restore/realign the gageto meet/exceed the manufacturers stated accuracy.3.1.6 certification, ndocumentation of the state of condi-tion of the gage, which can (but not required by definition) beaccompanied by cor

28、rective action (such as adjustment orcalibration, or both, or the replacement of components) neces-sary to correct any out-of-tolerance conditions.3.1.7 coating thickness standard (test block), na smooth,metal substrate with a coating of known thickness that istraceable to a national standard.3.1.8

29、compensation value, ngenerating a verifiable value,which is deducted from a measured value read from the gage,to correct for any surface conditions (that is, base metal effect).3.1.9 dry film thickness, nthe thickness of a coating (orcoating layers) as measured from the surface of the substrate.3.1.

30、9.1 DiscussionIf the surface is roughened, the dryfilm thickness is considered the thickness of the coating orcoating layers above the peaks of a surface profile.3.1.10 ferrous, na magnetic material such as carbon steel.3.1.10.1 DiscussionAlso known as ferro-magnetic.3.1.11 gage, nan instrument for

31、measuring quantity, or aninstrument for testing.3.1.11.1 DiscussionIn this practice, the term “gage” refersto an instrument for quantifying coating thickness.3.1.12 manufacturers specifications, na statement or setof statements that describes the performance characteristics ofthe gage under a given

32、set of conditions.3.1.12.1 DiscussionManufacturers specifications typi-cally includes the range of measurement, accuracy statement,operating temperature range, power source, dimensions andweight, and conformance to industry standards.3.1.13 measurement, nthe value obtained when placingthe probe of a

33、 thickness gage in contact with a surface.3.1.14 micrometer (micron), none one-thousands of amillimeter (0.001 mm); 25.4 microns = 1 mil.3.1.15 mil, nan imperial unit of measure; one one-thousands of an inch (0.001 in.); 1 mil = 25.4 microns.3.1.16 non-conductive, n a material that is unable tocondu

34、ct electricity.3.1.17 non-ferrous metal, na non-magnetic metal such asaluminum.3.1.18 reference standard, na specimen of known thick-ness used to verify the accuracy of a coating thicknessmeasuring gage.3.1.18.1 DiscussionA reference standard may or may notbe traceable to a National or International

35、 registry. Referencesshould include notations stating the accuracy of the standard.Reference Standards may be coated or plated metal plates, ormay be shims (with samples of substrate material). Subject toagreement between the buyer and the seller, a piece of coatedsubstrate may also be used as a pro

36、ject-specific referencestandard. Traceability may not be required for referencestandards used on a day-to-day basis. However, the referencestandard should contain the stated value and the degree ofaccuracy.3.1.19 shims, nstrips of flat, non-metallic sheet (typicallypolyester, with the thickness stat

37、ed or referenced in some form)used to adjust (optimize) a coating thickness gage in theintended range of use, over the surface of the representativesubstrate material.3Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor,Pittsburgh, PA 15222-4656. (see www.sspc.org)D7091052C

38、opyright by ASTM Intl (all rights reserved); Sun Sep 28 02:18:05 EDT 2008Downloaded/printed byGuo Dehua (CNIS) pursuant to License Agreement. No further reproductions authorized.3.1.19.1 DiscussionOther uses include: placement oversoft coatings to obtain thickness measurements without thegage probe

39、depressing the coating film, and verification of gageoperation. Also known as “foils.”3.1.20 spot measurement, nthe average of at least threemeasurements made within a 12 mm (12 in.) diameter circle.3.1.21 substrate, nthe base material, the type of surface,or the component that is being coated.NOTE

40、1This practice addresses only metal substrates.3.1.22 surface profile, nsurface roughness generated dur-ing the manufacturing process (for example, casting), or theaverage peak-to-valley depth generated by some power toolsand by abrasive blast cleaning operations.3.1.23 Type 1 gage, na magnetic pull

41、-off instrument thatmeasures the dry film thickness of non-magnetic coatings overa ferrous metal base.3.1.23.1 DiscussionFor Type 1 gages, a permanent mag-net is brought into direct contact with the coated surface. Theforce necessary to pull the magnet from the surface is measuredand interpreted as

42、the coating thickness value on a scale ordisplay on the gage. Less force is required to remove themagnet from a thick coating. The scale is nonlinear. Alsoknown as “pull-off gage.”3.1.24 Type 2 gage, nan electronic instrument that useselectronic circuitry and (but not limited to) the magneticinducti

43、on, Hall-effect or the eddy current principles, or both, toconvert a reference signal into a coating thickness reading.3.1.24.1 DiscussionThe probe of a Type 2 gage remainson the surface during the measurement process. Also known as“constant pressure probe” or “electronic” gages.3.1.25 verification

44、of accuracy, nobtaining measurementson a reference standard prior to gage use for the purpose ofdetermining the ability of the coating thickness gage to producereliable values, compared to the combined gage manufacturersstated accuracy and the stated accuracy of the referencestandard.4. Significance

45、 and Use4.1 Most 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 coatings will warrantycoating systems based upon, in part, achieving the propert

46、hickness 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 manufacturersproduce non-destructive coating thickness testing gages thatare

47、 used to measure the cumulative thickness of the coatinglayers, after they are dry. The manufacturers provide informa-tion for the adjustment and use of these gages, normally in theform of operating instructions. The user of this equipment mustbe knowledgeable in the proper operation of these device

48、s,including methods for verifying the accuracy of the equipmentprior to, during and after use as well as measurement proce-dures.4.2 This practice was prepared to describe the propermethods for verifying the accuracy of coating thickness mea-suring gages, as well as the proper methods for obtainingc

49、oating thickness measurements on both ferrous and non-ferrous metal substrates.5. Principles, Advantages, and Limitations of Gages5.1 Type 1 Magnetic Pull-Off gages are mechanical instru-ments that measure the force required to pull a permanentmagnet from a coated ferrous metal substrate. The magneticforce of attraction to the steel substrate beneath the coating isopposed by a spring or coil. 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 surface