ASTM B499-96(2002)
(Test Method)Standard Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis Metals
Standard Test Method for Measurement of Coating Thicknesses by the Magnetic Method: Nonmagnetic Coatings on Magnetic Basis Metals
SIGNIFICANCE AND USE
The thickness of a coating is often critical to its performance. For most nonferrous coatings on steel, the magnetic method is reliable for measuring coating thickness nondestructively and is suitable for specification acceptance testing and SPC/SQC applications. The test method requires that the magnetic properties of the substrate used during the calibration be the same as that of the test specimen.
SCOPE
1.1 This test method covers the use of magnetic instruments for the nondestructive measurement of the thickness of nonmagnetic coatings over ferrous or other magnetic base metals.
Note 1—Autocatalytically deposited nickel-phosphorus alloys containing more than 8 % phosphorus are sufficiently nonmagnetic to be measured by this test method, as long as the measurement is made prior to any heat treatment.
1.2 These instruments measure either the magnetic attraction between a magnet and the basis metal, as influenced by the presence of the coating, or the reluctance of a magnetic-flux path passing through the coating and the basis metal.
1.3 Measurements made in accordance with this test method will be in compliance with the requirements of ISO International Standard 2178 as printed in 1982.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Endorsed by American
Designation:B499–96 (Reapproved 2002) Electroplaters’ Society
Endorsed by National
Association of Metal Finishers
Standard Test Method for
Measurement of Coating Thicknesses by the Magnetic
1
Method: Nonmagnetic Coatings on Magnetic Basis Metals
This standard is issued under the fixed designation B 499; 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 (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope testing and SPC/SQC applications. The test method requires
that the magnetic properties of the substrate used during the
1.1 This test method covers the use of magnetic instruments
calibration be the same as that of the test specimen.
for the nondestructive measurement of the thickness of non-
magnetic coatings over ferrous or other magnetic base metals.
4. Factors Affecting the Measuring Accuracy
NOTE 1—Autocatalyticallydepositednickel-phosphorusalloyscontain-
4.1 The following factors affect the accuracy of a coating
ing more than 8 % phosphorus are sufficiently nonmagnetic to be
thickness measurement:
measured by this test method, as long as the measurement is made prior
4.1.1 Coating Thickness—Inherent to the test method is a
to any heat treatment.
measurementuncertaintythat,forthincoatings,isconstantand
1.2 These instruments measure either the magnetic attrac-
independent of the coating thickness. The magnitude of this
tionbetweenamagnetandthebasismetal,asinfluencedbythe
measurement uncertainty is primarily a function of test piece
presence of the coating, or the reluctance of a magnetic-flux
surface finish (see 4.1.6 on surface roughness). For thicknesses
path passing through the coating and the basis metal.
greater than about 25µ m, this uncertainty is proportional to the
1.3 Measurementsmadeinaccordancewiththistestmethod
coating thickness.
will be in compliance with the requirements of ISO Interna-
4.1.2 Magnetic Properties of the Basis Metal—Magnetic
tional Standard 2178 as printed in 1982.
thickness measurements are affected by variations in the
1.4 This standard does not purport to address all of the
magnetic properties of the basis metal. (For practical purposes,
safety concerns, if any, associated with its use. It is the
magnetic variations in low-carbon steel can often be consid-
responsibility of the user of this standard to establish appro-
ered to be insignificant. To avoid the influences of severe or
priate safety and health practices and determine the applica-
localized heat treatments and cold working, the instrument
bility of regulatory limitations prior to use.
should be calibrated using a calibration standard having a basis
metal with the same magnetic properties as that of the test
2. Referenced Documents
specimen or, preferably and if available, with a sample of the
2.1 International Standard:
part to be tested before application of the coating.)
ISO 2178 Non-Magnetic Coatings on Magnetic Substrate—
4.1.3 Basis Metal Thickness—For each instrument, there is
2
Measurement of Coating Thickness—Magnetic Method
a critical thickness of the basis metal above which the
measurements will not be affected by an increase in the
3. Significance and Use
thickness of the basis metal. Since it depends on the instrument
3.1 The thickness of a coating is often critical to its
probe (Note 2) and the nature of the basis metal, its value
performance. For most nonferrous coatings on steel, the
should be determined experimentally if not supplied by the
magnetic method is reliable for measuring coating thickness
manufacturer.
nondestructively and is suitable for specification acceptance
NOTE 2—In this method “instrument probe” will also include the term
“magnet.”
1
This test method is under the jurisdiction ofASTM Committee B08 on Metallic
4.1.4 Edge Effects—The method is sensitive to abrupt
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
changes in the surface contour of the test specimen. Therefore,
General Test Methods.
Current edition approved April 10, 1996. Published June 1996. Originally
measurements made too near an edge or inside corner will not
published as B 499 – 69. Last previous edition B 499 – 88. Replaces portions of
bevalidunlesstheinstrumentisspecificallycalibratedforsuch
A 219.
2 a measurement. The effect may extend to about 20 mm from
Available from American National Standards Institute, 11 W. 42nd St., 13th
Floor, New York, NY 10036. the discontinuity, depending on the instrument.
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