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1、ASTM D7091-05Designation:D709105Standard Practice forNondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic,Nonconductive Coatings Applied to Non-Ferrous Metals1This standard is issued under the?xed designation D7091;the number immediately
2、following the designation indicates the year of 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(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1This practice des
3、cribes the nondestructive measurement of the dry?lm thickness of nonmagnetic coatings applied to the surface of ferrous metals using magnetic gages and the nondestructive measurement of the dry?lm thickness of electrically nonconductive,nonmagnetic coatings applied to the surface of nonferrous metal
4、s using eddy current gages.This practice is intended to supplement the manufacturersinstruc-tions for the manual operation of the gages and is not intended to replace them.It includes de?nitions of key terms,reference documents,the signi?cance and use of the practice,the advantages and limitations o
5、f coating thickness gages,and a description of test specimens.It describes the methods and recommended frequency for verifying the accuracy of gages and for adjusting(optimizing)the equipment,describes a frequency for measuring the thickness of the coating(s)and lists the reporting recommendations.1
6、.2These procedures are not applicable to coatings that will be readily deformed under the load of the measuring gages/ probes,as the gage probe must be placed directly on the coating surface to obtain a reading.Provisions for measuring on soft or tacky coatings are described in5.6.1.3Use of?lm thick
7、ness measuring gages on metal-?lled coatings may produce erroneous results,depending on the type and amount of metal in the coating?lm.The user should consult the manufacturers instructions regarding the use of coating thickness gages on these types of coatings.1.4Coating thickness can be measured u
8、sing a variety of gages.These gages are categorized as“magnetic pull-off”and “electronic.”They use a sensing probe or magnet to measure the gap(distance)between the base metal and the probe.This measured distance is displayed as coating thickness by the gages.Accordingly,these gages cannot distingui
9、sh the thick-ness of individual layers after they have all been applied.The thickness 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 the base metal.1.5Gages which measure co
10、ating thickness using an ultra-sonic principle may also be able to measure the thickness of coatings applied to metal surfaces.This practice does not address the use of ultrasonic coating thickness gages.Test Method D6132should be referenced for this application.1.6Coating thickness can vary widely
11、across a surface.Asa result,obtaining single-point measurements may not accu-rately represent the actual coating system thickness.This practice provides guidance for the frequency of coating thick-ness measurements,based on large areas of coated surface,on test panels and on small parts/components.T
12、he governing speci?cation is responsible for providing the user with the minimum and the maximum coating thickness for each layer, and for the total coating system.1.7This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility of the u
13、ser of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1ASTM Standards:2D609Practice for Preparation of Cold-Rolled Steel Panels for Testing Paint,Varnish,Conversion Coatings,and Relat
14、ed Coating ProductsD823Practices for Producing Films of Uniform Thickness of Paint,Varnish,and Related Products on Test PanelsD1730Practices for Preparation of Aluminum and Aluminum-Alloy Surfaces for PaintingD6132Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Co
15、atings Using an Ultrasonic Gage2.2SSPC Standards:1This practice is under the jurisdiction of ASTM Committee D01on Paint and Related Coatings,Materials and Applications and is the direct responsibility of Subcommittee D01.23on Physical Properties of Applied Paint Films.Current edition approved Aug.1,
16、2005.Published September2005.2For referenced ASTM standards,visit the ASTM website,http:/ contact ASTM Customer Service at servicehttp:/ Annual Book of ASTM Standards volume information,refer to the standards Document Summary page on the ASTM website.1Copyright?ASTM International,100Barr Harbor Driv
17、e,PO Box C700,West Conshohocken,PA19428-2959,United States.SSPC-PA2Paint Application Standard No.2Measurement of Dry Coating Thickness with Magnetic Gauges 33.Terminology3.1De?nitions of Terms Speci?c to This Standard:3.1.1accuracy ,n the measure of the magnitude of error between the result of a mea
18、surement and the true thickness of the item being measured.3.1.1.1Discussion An accuracy statement predicts the ability of a coating thickness gage to measure the true thickness of a coating to be measured.Accuracy statements provide the performance capability across the full functional measurement
19、range of the gage.Accuracy statements frequently include a ?xed portion that remains constant across the measurement range,plus a variable portion that is related to the measurement result for a particular thickness.3.1.2adjustment ,n the physical act of aligning a gages thickness readings to match
20、those of a known thickness sample (removal of bias),in order to improve the accuracy of the gage on a speci?c surface or within a speci?c portion of its measurement range.3.1.2.1Discussion An adjustment will affect the outcome of subsequent readings.Also known as “optimization.”3.1.3area measurement
21、 ,n the average of several spot measurements obtained over the coated surface.3.1.3.1Discussion For large surfaces,an area measure-ment is commonly the average of at least ?ve spot measure-ments obtained in approximately 9m 2(100ft 2)of surface area.For small test panels,it is commonly the average o
22、f three spot measurements on each test face (one from the top third,one from the middle third and one from the bottom third).3.1.4base metal reading (BMR),n a measurement ob-tained on the uncoated substrate using a coating thickness gage.3.1.4.1Discussion The BMR is the measured effect of substrate
23、roughness on a coating thickness gage that is caused by the manufacturing process (for example,castings)or surface pro?le (roughness)-producing operations (for example,power tool cleaning,abrasive blast cleaning,etc.).Non-compensation for the base metal effect can result in an overstatement of the t
24、rue thickness of the coating.The base metal reading is measured,recorded and deducted from the thickness of each coat,in order to correctly state the thickness of the coating over the surface roughness.3.1.5calibration ,n the high-level,controlled and docu-mented process of obtaining measurements on
25、 traceable cali-bration standards over the full operating range of the gage,then making the necessary gage adjustments (as required)to correct any out-of-tolerance conditions.3.1.5.1Discussion Calibration of coating thickness gages is performed by the equipment manufacturer,an authorized agent,or by
26、 an authorized,trained calibration laboratory in a controlled environment using a documented process.The outcome of the calibration process is to restore/realign the gage to meet/exceed the manufacturers stated accuracy.3.1.6certi?cation ,n documentation of the state of condi-tion of the gage,which
27、can (but not required by de?nition)be accompanied by corrective action (such as adjustment or calibration,or both,or the replacement of components)neces-sary to correct any out-of-tolerance conditions.3.1.7coating thickness standard (test block),n a smooth,metal substrate with a coating of known thi
28、ckness that is traceable to a national standard.3.1.8compensation value ,n generating a veri?able value,which is deducted from a measured value read from the gage,to correct for any surface conditions (that is,base metal effect).3.1.9dry ?lm thickness ,n the thickness of a coating (or coating layers
29、)as measured from the surface of the substrate.3.1.9.1Discussion If the surface is roughened,the dry ?lm thickness is considered the thickness of the coating or coating layers above the peaks of a surface pro?le.3.1.10ferrous ,n a magnetic material such as carbon steel.3.1.10.1Discussion Also known
30、as ferro-magnetic.3.1.11gage ,n an instrument for measuring quantity,or an instrument for testing.3.1.11.1Discussion In this practice,the term “gage”refers to an instrument for quantifying coating thickness.3.1.12manufacturers speci?cations ,n a statement or set of statements that describes the perf
31、ormance characteristics of the gage under a given set of conditions.3.1.12.1Discussion Manufacturers speci?cations typi-cally includes the range of measurement,accuracy statement,operating temperature range,power source,dimensions and weight,and conformance to industry standards.3.1.13measurement ,n
32、 the value obtained when placing the probe of a thickness gage in contact with a surface.3.1.14micrometer (micron),n one one-thousands of a millimeter (0.001mm);25.4microns =1mil.3.1.15mil ,n an imperial unit of measure;one one-thousands of an inch (0.001in.);1mil =25.4microns.3.1.16non-conductive ,
33、n a material that is unable to conduct electricity.3.1.17non-ferrous metal ,n a non-magnetic metal such as aluminum.3.1.18reference standard ,n a specimen of known thick-ness used to verify the accuracy of a coating thickness measuring gage.3.1.18.1Discussion A reference standard may or may not be t
34、raceable to a National or International registry.References should include notations stating the accuracy of the standard.Reference Standards may be coated or plated metal plates,or may be shims (with samples of substrate material).Subject to agreement between the buyer and the seller,a piece of coa
35、ted substrate may also be used as a project-speci?c reference standard.Traceability may not be required for reference standards used on a day-to-day basis.However,the reference standard should contain the stated value and the degree of accuracy.3.1.19shims ,n strips of ?at,non-metallic sheet (typica
36、lly polyester,with the thickness stated or referenced in some form)used to adjust (optimize)a coating thickness gage in the intended range of use,over the surface of the representative substrate material.3Available from Society for Protective Coatings (SSPC),4024th St.,6th Floor,Pittsburgh,PA 15222-
37、4656.(seehttp:/ uses include:placement over soft coatings to obtain thickness measurements without the gage probe depressing the coating?lm,and veri?cation of gage operation.Also known as“foils.”3.1.20spot measurement,nthe average of at least three measurements made within a12mm(1?2in.)diameter circ
38、le.3.1.21substrate,nthe base material,the type of surface, or the component that is being coated.N OTE1This practice addresses only metal substrates.3.1.22surface pro?le,nsurface roughness generated dur-ing the manufacturing process(for example,casting),or the average peak-to-valley depth generated
39、by some power tools and by abrasive blast cleaning operations.3.1.23Type1gage,na magnetic pull-off instrument that measures the dry?lm thickness of non-magnetic coatings overa ferrous metal base.3.1.23.1DiscussionFor Type1gages,a permanent mag-net is brought into direct contact with the coated surfa
40、ce.The force necessary to pull the magnet from the surface is measured and interpreted as the coating thickness value on a scale or display on the gage.Less force is required to remove the magnet from a thick coating.The scale is nonlinear.Also known as“pull-off gage.”3.1.24Type2gage,nan electronic
41、instrument that uses electronic circuitry and(but not limited to)the magnetic induction,Hall-effect or the eddy current principles,or both,to convert a reference signal into a coating thickness reading.3.1.24.1DiscussionThe probe of a Type2gage remains on the surface during the measurement process.A
42、lso known as “constant pressure probe”or“electronic”gages.3.1.25veri?cation of accuracy,nobtaining measurements on a reference standard prior to gage use for the purpose of determining the ability of the coating thickness gage to produce reliable values,compared to the combined gage manufacturers st
43、ated accuracy and the stated accuracy of the reference standard.4.Signi?cance and Use4.1Most speci?cations for commercial and industrial coat-ings projects stipulate a minimum and a maximum dry?lm thickness for each layer in a coating system.Additionally,most manufacturers of high performance coatin
44、gs will warranty coating systems based upon,in part,achieving the proper thickness of each layer and the total coating system.Even if a project speci?cation is not provided,the coating manufactur-ers recommendations published on product data sheets can become the governing document(s).Equipment manu
45、facturers produce non-destructive coating thickness testing gages that are used to measure the cumulative thickness of the coating layers,after they are dry.The manufacturers provide informa-tion for the adjustment and use of these gages,normally in the form of operating instructions.The user of thi
46、s equipment must be knowledgeable in the proper operation of these devices, including methods for verifying the accuracy of the equipment prior to,during and after use as well as measurement proce-dures.4.2This practice was prepared to describe the proper methods for verifying the accuracy of coatin
47、g thickness mea-suring gages,as well as the proper methods for obtaining coating thickness measurements on both ferrous and non-ferrous metal substrates.5.Principles,Advantages,and Limitations of Gages5.1Type1Magnetic Pull-Off gages are mechanical instru-ments that measure the force required to pull
48、 a permanent magnet from a coated ferrous metal substrate.The magnetic force of attraction to the steel substrate beneath the coating is opposed by a spring or coil.Tension is applied to the spring/coil until the magnetic attraction to the steel is over-come.The gage must be placed directly on the coated surface to obtain a measurement.The force holding the permanent magnet to the ferrous base is inversely proportional to the thickness of the coating layer(s)between the magnet and the ferrous substrate.For exa