ASTM B244-09(2021)
(Test Method)Standard Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings on Nonmagnetic Basis Metals with Eddy-Current Instruments
Standard Test Method for Measurement of Thickness of Anodic Coatings on Aluminum and of Other Nonconductive Coatings on Nonmagnetic Basis Metals with Eddy-Current Instruments
SIGNIFICANCE AND USE
5.1 The thickness of a coating is often critical to its performance. This eddy-current method is nondestructive and is suitable for measuring the thickness of anodic coatings on aluminum, as well as the thickness of most nonconductive coatings on nonmagnetic basis metals.
5.2 This test method requires that the conductivity of the substrate be the same in the reference standard used for calibration adjustment and in the coated article to be measured.
SCOPE
1.1 This test method covers the use of eddy-current instruments for the nondestructive measurement of the thickness of a nonconductive coating on a nonmagnetic basis metal. It is intended to supplement manufacturers’ instructions for the operation of the instruments and is not intended to replace them.
1.2 This test method is particularly useful for measuring the thickness of an anodic coating on aluminum alloys. Chemical conversion coatings are too thin to be measured by this test method.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.4 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B244 − 09 (Reapproved 2021) Endorsed by American
Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Test Method for
Measurement of Thickness of Anodic Coatings on
Aluminum and of Other Nonconductive Coatings on
Nonmagnetic Basis Metals with Eddy-Current Instruments
This standard is issued under the fixed designation B244; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the use of eddy-current instru-
B499 Test Method for Measurement of Coating Thicknesses
ments for the nondestructive measurement of the thickness of
by the Magnetic Method: Nonmagnetic Coatings on
a nonconductive coating on a nonmagnetic basis metal. It is
Magnetic Basis Metals
intended to supplement manufacturers’ instructions for the
operation of the instruments and is not intended to replace
3. Terminology
them.
3.1 Definitions of Terms Specific to This Standard:
1.2 This test method is particularly useful for measuring the
3.1.1 accuracy, n—the measure of the magnitude of error
thickness of an anodic coating on aluminum alloys. Chemical
between the result of a measurement and the true thickness of
conversion coatings are too thin to be measured by this test
the item being measured.
method.
3.1.2 adjustment, n—the physical act of aligning a instru-
1.3 The values stated in SI units are to be regarded as the
ment’s thickness readings to match those of a known thickness
standard. The values given in parentheses are for information
sample (removal of bias), in order to improve the accuracy of
only.
the instrument on a specific surface or within a specific portion
of its measurement range. An adjustment will affect the
1.4 This standard does not purport to address all of the
outcome of subsequent readings.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.1.3 calibration, n—the high-level, controlled and docu-
priate safety, health, and environmental practices and deter- mented process of obtaining measurements on traceable cali-
mine the applicability of regulatory limitations prior to use.
bration standards over the full operating range of the
instrument, then making the necessary instrument adjustments
1.5 This international standard was developed in accor-
(as required) to correct any out-of-tolerance conditions.
dance with internationally recognized principles on standard-
3.1.3.1 Discussion—Calibration of coating thickness instru-
ization established in the Decision on Principles for the
ments is performed by the equipment manufacturer, an autho-
Development of International Standards, Guides and Recom-
rized agent, or by an authorized, trained calibration laboratory
mendations issued by the World Trade Organization Technical
in a controlled environment using a documented process. The
Barriers to Trade (TBT) Committee.
outcome of the calibration process is to restore/realign the
instrument to meet/exceed the manufacturer’s stated accuracy.
This test method is under the jurisdiction ofASTM Committee B08 on Metallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
Test Methods. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2021. Published May 2021. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approvedin1949.Lastpreviouseditionapprovedin2014asB244 – 09(2014).DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/B0244-09R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B244 − 09 (2021)
3.1.4 reference standard, n—aspecimenofknownthickness manufacturer, employing suitable thickness standards and, if
used to verify the accuracy of a coating thickness measuring necessary, any deficiencies found shall be corrected.
instrument.
7.3 During use, calibration accuracy shall be verified at
3.1.5 verification of accuracy, n—obtaining measurements
frequent intervals, at least once a day.Attention shall be given
on a reference standard prior to instrument use for the purpose
to the factors listed in Section 8 and to the procedures
ofdeterminingtheabilityofthecoatingthicknessinstrumentto
described in Section 9.
produce reliable values, compared to the combined instrument
7.4 Coating thickness standards of known thickness are
manufacturer’s stated accuracy and the stated accuracy of the
available either as shims or foils or as coated specimens.
reference standard.
7.4.1 Foils:
4. Summary of Test Method
7.4.1.1 Foils used for accuracy verification and adjustment
of eddy-current instruments are generally made of plastic.
4.1 Instruments complying with this test method measure
Theyareadvantageousforadjustmentsoncurvedsurfaces,and
coatingthicknessbytheuseofeddycurrents.Aprobeisplaced
are more readily available than coated standards.
directly on the coated surface in a perpendicular position and
electronic circuitry is used to convert a reference signal into a 7.4.1.2 To prevent measurement errors, it is necessary to
ensure that intimate contact is established between foil and
coating thickness measurement.
substrate. Resilient foils should be avoided if possible. Foils
4.2 The instrument probe coil is energized by alternating
are subject to indentation and should, therefore, be replaced
current that induces eddy currents in the metal substrate. The
frequently.
eddy currents in turn create a secondary magnetic field within
7.4.2 Coated Standards—These calibration standards con-
the substrate. The characteristics of this secondary field are
sist of nonconductive coatings of known, uniform thickness
dependent upon the distance between the probe and the basis
permanently bonded to the substrate material.
metal. This distance (gap) is measured by the instrument probe
7.4.3 The coating thickness of the standards used shall
and shown on the instrument display as the thickness (microns
bracket the user’s highest and lowest coating thickness mea-
or mils) of the intervening coating.
surement requirement. Standards suitable for many applica-
5. Significance and Use
tions of the test method are commercially available and may be
used provided the certified values are traceable to a National
5.1 The thickness of a coating is often critical to its
Metrology Institution.
performance. This eddy-current method is nondestructive and
is suitable for measuring the thickness of anodic coatings on
7.5 The basis metal thickness for the test and the calibration
aluminum, as well as the thickness of most nonconductive
adjustment shall be the same if the critical thickness, defined in
coatings on nonmagnetic basis metals.
8.3, is not exceeded.When possible, back up the basis metal of
the standard or of the test specimen with a sufficient thickness
5.2 This test method requires that the conductivity of the
of similar material to make the readings independent of the
substrate be the same in the reference standard used for
basis metal thickness. A way to determine if the basis metal
calibration adjustment and in the coated article to be measured.
thickness exceeds the critical thickness is to make measure-
6. Apparatus
ments before and after backing up the basis metal with similar
metal at least 3 mm (120 mils) thick. If there is no difference
6.1 Coating Thickness Instrument, based on eddy current
between the readings, the critical thickness is exceeded.
principles, commercially available, suitable to measure coating
thickness accurately.
7.6 If the test specimen is soft and thin, it is subject to
6.2 Coating Thickness Standards, with assigned values indentation by the probe. Because of this, and despite the use
of special probes or fixtures, measurements on such specimens
traceable to a National Metrology Institution. They may be
coated aluminum plates, or may be foils or shims of flat, are sometimes impossible to make.
non-metallic sheet (typically polyester).
7.7 If the curvature of the test specimen to be measured is
such as to preclude calibration adjustment on a flat surface, the
7. Calibration and Standardization
curvature of the coated standard or o
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