ASTM D7091-12
(Practice)Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
SIGNIFICANCE AND USE
This practice describes three operational steps necessary to ensure accurate coating thickness measurement calibration, verification and adjustment of coating thickness measuring gages, as well as proper methods for obtaining coating thickness measurements on both ferrous and non-ferrous metal substrates.
Many specifications for commercial and industrial coatings projects stipulate a minimum and a maximum dry film thickness for each layer in a coating system. Additionally, most manufacturers of high performance coatings will warranty coating systems based upon, in part, achieving the proper thickness of each layer and the total coating system. Even if a project specification is not provided, the coating manufacturer’s recommendations published on product data sheets can become the governing document(s). Equipment manufacturers produce nondestructive coating thickness testing gages that are used to measure the cumulative or individual thickness of the coating layers, after they are dry. The manufacturers provide information for the adjustment and use of these gages, normally in the form of operating instructions. The user of this 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 procedures.
SCOPE
1.1 This practice describes the use of magnetic and eddy current gages for dry film thickness measurement. This practice is intended to supplement the manufacturers' instructions for the manual operation of the gages and is not intended to replace them. It includes definitions of key terms, reference documents, the significance and use of the practice, the advantages and limitations of 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 and lists the reporting recommendations.
1.2 These 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 in 5.7.
1.3 Coating thickness can be measured using 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.
1.4 Coating thickness can vary widely across a surface. As a result, obtaining single-point measurements may not accurately represent the actual coating system thickness. SSPC-PA2 prescribes a frequency of coating thickness measurement based on the size of the area coated. A frequency of measurement for coated steel beams (girders) and coated test panels is also provided in the appendices to SSPC-PA2. The governing specification is responsible for providing the user with the minimum and the maximum coating thickness for each layer, and for the total coating system.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D7091 − 12
StandardPractice for
Nondestructive Measurement of Dry Film Thickness of
Nonmagnetic Coatings Applied to Ferrous Metals and
Nonmagnetic, Nonconductive Coatings Applied to Non-
1
Ferrous Metals
This standard is issued under the fixed designation D7091; the number immediately 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* minimum and the maximum coating thickness for each layer,
and for the total coating system.
1.1 This practice describes the use of magnetic and eddy
current gages for dry film thickness measurement. This prac- 1.5 The values stated in SI units are to be regarded as the
tice is intended to supplement the manufacturers’ instructions standard. The values given in parentheses are for information
for the manual operation of the gages and is not intended to only.
replace them. It includes definitions of key terms, reference
1.6 This standard does not purport to address all of the
documents, the significance and use of the practice, the
safety concerns, if any, associated with its use. It is the
advantages and limitations of coating thickness gages, and a
responsibility of the user of this standard to establish appro-
description of test specimens. It describes the methods and
priate safety and health practices and determine the applica-
recommended frequency for verifying the accuracy of gages
bility of regulatory limitations prior to use.
and for adjusting (optimizing) the equipment and lists the
2. Referenced Documents
reporting recommendations.
2
2.1 ASTM Standards:
1.2 These procedures are not applicable to coatings that will
D609 Practice for Preparation of Cold-Rolled Steel Panels
be readily deformed under the load of the measuring gages/
for Testing Paint, Varnish, Conversion Coatings, and
probes, as the gage probe must be placed directly on the
Related Coating Products
coating surface to obtain a reading. Provisions for measuring
D823 Practices for Producing Films of Uniform Thickness
on soft or tacky coatings are described in 5.7.
of Paint, Varnish, and Related Products on Test Panels
1.3 Coating thickness can be measured using a variety of
D1730 Practices for Preparation of Aluminum and
gages. These gages are categorized as “magnetic pull-off” and
Aluminum-Alloy Surfaces for Painting
“electronic.” They use a sensing probe or magnet to measure
2.2 SSPC Standard:
the gap (distance) between the base metal and the probe. This
SSPC-PA2 Procedure for Determining Conformance to Dry
measured distance is displayed as coating thickness by the
3
Coating Thickness Requirements
gages.
2.3 ISO Standard:
1.4 Coating thickness can vary widely across a surface. As
ISO 19840 Paints and varnishes—corrosion protection of
a result, obtaining single-point measurements may not accu-
steel structures by protective paint systems—
ratelyrepresenttheactualcoatingsystemthickness.SSPC-PA2
Measurement of, and acceptance criteria for, the thickness
4
prescribesafrequencyofcoatingthicknessmeasurementbased
of dry films on rough surfaces
on the size of the area coated.Afrequency of measurement for
3. Terminology
coated steel beams (girders) and coated test panels is also
3.1 Definitions of Terms Specific to This Standard:
provided in the appendices to SSPC-PA2. The governing
specification is responsible for providing the user with the
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
1
This practice is under the jurisdiction of ASTM Committee D01 on Paint and Standards volume information, refer to the standard’s Document Summary page on
Related Coatings, Materials, and Applications and is the direct responsibility of the ASTM website.
3
Subcommittee D01.23 on Physical Properties of Applied Paint Films. Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor,
Current edition approved April 1, 2012. Published April 2012. Originally Pittsburgh, PA 15222-4656. (see www.sspc.org)
4
approved in 2005. Last previous edition approved in 2005 as D7091 – 05. DOI: Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/D7091-12. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7091 − 12
3.1.1 accuracy, n—the measure of the magnitude of error thic
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This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D7091–05 Designation:D7091–12
Standard Practice for
Nondestructive Measurement of Dry Film Thickness of
Nonmagnetic Coatings Applied to Ferrous Metals and
Nonmagnetic, Nonconductive Coatings Applied to Non-
1
Ferrous Metals
This standard is issued under the fixed designation D7091; the number immediately 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1This practice describes the nondestructive measurement of the dry film thickness of nonmagnetic coatings applied to the
surface of ferrous metals using magnetic gages and the nondestructive measurement of the dry film thickness of electrically
nonconductive, nonmagnetic coatings applied to the surface of nonferrous metals using eddy current gages. This practice is
intended to supplement the manufacturers’ instructions for the manual operation of the gages and is not intended to replace them.
It includes definitions of key terms, reference documents, the significance and use of the practice, the advantages and limitations
of 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. *
1.1 This practice describes the use of magnetic and eddy current gages for dry film thickness measurement. This practice is
intended to supplement the manufacturers’ instructions for the manual operation of the gages and is not intended to replace them.
It includes definitions of key terms, reference documents, the significance and use of the practice, the advantages and limitations
of 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 and lists the reporting recommendations.
1.2 These 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 in 5.65.7.
1.3Use of film thickness measuring gages on metal-filled coatings may produce erroneous results, depending on the type and
amount of metal in the coating film. 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 using 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 distinguish the thickness 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 cumulative thickness of that layer and all layers beneath it, down to the base metal.
1.5Gages which measure coating thickness using an ultrasonic 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 D6132 should
be referenced for this application.
1.6Coating thickness can vary widely across a surface. As a result, obtaining single-point measurements may not accurately
represent the actual coating system thickness. This practice provides guidance for the frequency of coating thickness
measurements, based on large areas of coated surface, on test panels and on small parts/components. The governing specification
isresponsibleforprovidingtheuserwiththeminimumandthemaximumcoatingthicknessforeachlayer,andforthetotalcoating
system.
1.7
1.3 Coating thickness can be measured using 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.
1
This practice is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, an
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