ASTM B530-09(2021)

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: B530 − 09 (Reapproved 2021)
Standard Test Method for
Measurement of Coating Thicknesses by the Magnetic
Method: Electrodeposited Nickel Coatings on Magnetic and
Nonmagnetic Substrates
This standard is issued under the fixed designation B530; 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 priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This test method covers the use of magnetic instruments
1.8 This international standard was developed in accor-
for the nondestructive measurement of the thickness of an
dance with internationally recognized principles on standard-
electrodeposited nickel coating on either a magnetic or non-
ization established in the Decision on Principles for the
magneticsubstrate.Itisintendedtosupplementmanufacturers’
Development of International Standards, Guides and Recom-
instructions for the operation of the instruments and is not
mendations issued by the World Trade Organization Technical
intended to replace them.
Barriers to Trade (TBT) Committee.
1.2 These instruments measure either the magnetic attrac-
tion between a magnet and the coating-substrate combination
2. Referenced Documents
(categorized as “magnetic pull-off”), or the change in magnetic
2.1 ASTM Standards:
flux density within the probe (categorized as “electronic”).
B487 Test Method for Measurement of Metal and Oxide
1.3 For this test method, there are two types of coating-
Coating Thickness by Microscopical Examination of
substrate combinations that can be encountered:TypeA, nickel
Cross Section
coatings on a magnetic substrate, and Type B, nickel coatings
B499 Test Method for Measurement of Coating Thicknesses
on a nonmagnetic substrate.
by the Magnetic Method: Nonmagnetic Coatings on
1.4 The effective measuring ranges of instruments using the Magnetic Basis Metals
B504 Test Method for Measurement of Thickness of Metal-
principle of magnetic attraction are up to 50 µm (2 mils) for
TypeAcoatings, and up to 25 µm (1 mil) for Type B coatings. lic Coatings by the Coulometric Method
For gages based on change in magnetic flux density principles, B748 Test Method for Measurement of Thickness of Metal-
the effective ranges are much greater, and measurements up to lic Coatings by Measurement of Cross Section with a
1 mm (40 mils) or more, can be made on both types of Scanning Electron Microscope
coatings.
2.2 ISO International Standard:
1.5 Measurementsmadeinaccordancewiththistestmethod ISO 2361 Electrodeposited Nickel Coatings on Magnetic
and Nonmagnetic Substrates—Measurement of Coating
will be in compliance with the requirements of ISO Stan-
Thickness—Magnetic Method
dard 2361 as printed in 1982.
1.6 The values stated in SI units are to be regarded as the
3. Terminology
standard. The values given in parentheses are for information
3.1 Definitions of Terms Specific to This Standard:
only.
3.1.1 accuracy, n—the measure of the magnitude of error
1.7 This standard does not purport to address all of the
between the result of a measurement and the true thickness of
safety concerns, if any, associated with its use. It is the
the item being measured.
responsibility of the user of this standard to establish appro-
1 2
This test method is under the jurisdiction ofASTM Committee B08 on Metallic For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Test Methods. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved April 1, 2021. Published May 2021. Originally the ASTM website.
approvedin1970.Lastpreviouseditionapprovedin2014asB530 – 09(2014).DOI: Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
10.1520/B0530-09R21. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B530 − 09 (2021)
3.1.2 adjustment, n—the physical act of aligning an instru- 5.3 This method should not be used to determine the
ment’s thickness readings to match those of a known thickness thickness of autocatalytically deposited nickel-phosphorus al-
sample (removal of bias), in order to improve the accuracy of loys containing more than 8 % phosphorus on steel. Those
the instrument on a specific surface or within a specific portion coatings are sufficiently nonmagnetic for Test Method B499 to
of its measurement range. An adjustment will affect the be suitable for that determination, as long as the measurement
outcome of subsequent readings. is made prior to any heat treatment.
3.1.3 calibration, n—the high-level, controlled and docu-
6. Apparatus
mented process of obtaining measurements on traceable cali-
6.1 Coating Thickness Instrument, based on magnetic
bration standards over the full operating range of the
principles, commercially available, suitable to measure coating
instrument, then making the necessary instrument adjustments
thickness accurately.
(as required) to correct any out-of-tolerance conditions.
3.1.3.1 Discussion—Calibration of coating thickness instru-
6.2 Coating Thickness Standards, with assigned values
ments is performed by the equipment manufacturer, an autho-
traceable to a National Metrology Institution. They may be
rized agent, or by an authorized, trained calibration laboratory
coated or plated steel plates, or may be foils or shims of flat,
in a controlled environment using a documented process. The
non-metallic sheet (typically polyester).
outcome of the calibration process is to restore/realign the
7. Calibration and Standardization
instrument to meet/exceed the manufacturer’s stated accuracy.
3.1.4 reference standard, n—aspecimenofknownthickness
7.1 Calibration of coating thickness instruments is per-
used to verify the accuracy of a coating thickness measuring formed by the equipment manufacturer, an authorized agent, or
instrument.
by an authorized, trained calibration laboratory in a controlled
environment using a documented process. A Certificate of
3.1.5 verification of accuracy, n—obtaining measurements
Calibration showing traceability to a National Metrology
on a reference standard prior to instrument use for the purpose
Institution can be issued. There is no standard time interval for
ofdeterminingtheabilityofthecoatingthicknessinstrumentto
re-calibration, nor is one absolutely required, but a calibration
produce reliable values, compared to the combined instrument
interval can be established based on experience and the work
manufacturer’s stated accuracy and the stated accuracy of the
environment. A one-year calibration interval is a typical
reference standard.
frequency suggested by many instrument manufacturers.
4. Summary of Test Method
7.2 Before use, each instrument’s calibration accuracy shall
4.1 Magnetic pull-off instruments are mechanical instru-
be verified in accordance with the instructions of the
ments that measure the force required to pull a permanent
manufacturer, employing suitable thickness standards and, if
magnet from magnetic material. The magnetic force of attrac-
necessary, any deficiencies found shall be corrected.
tion to the magnetic coating or coating-substrate combination
7.3 During use, calibration accuracy shall be verified at
is opposed by a spring or coil. Tension is applied to the
frequent intervals, at least once a day.Attention shall be given
spring/coil until the magnetic attraction to the material is
to the factors listed in Section 8 and to the procedures
overcome. The instrument must be placed directly on the
described in Section 9.
coated surface to obtain a measurement. The force holding the
permanent magnet to the magnetic material is inversely pro- 7.4 Reference standards shall be coated standards obtained
portional to the thickness of the coating layer(s) between the
by electroplating nickel adherently onto a substrate. The
magnet and the magnetic material. For example, a thin nickel coating thickness of the reference standards shall bracket the
layer applied to a nonmagnetic substrate will require less
user’s highest and lowest coating thickness measurement
spring tension to pull the magnet off than will a thicker nickel requirement.
layer, since the thinner coating has weaker magnetic strength.
7.5 The substrate and the coating of the standard shall have
4.2 Electronic instruments measure a change in magnetic
the same magnetic properties as those of the test specimen (see
flux density within the probe to produce a coating thickness
8.2, 8.3, 8.11 and 8.12).
measurement.Theinstrumentprobemustbeplaceddirectly(in
7.5.1 To assure the similarity of the magnetic properties of
a perpendicular position) on the coated surface to obtain a
the nickel deposit and for Type A coatings on steel substrate,
measurement. These instruments determine the effect on the
referencestandardsshallbeproducedandmeasuredbyanother
magnetic field generated by the probe due to the proximity to
suitable test method, such as cross sectioning or the coulomet-
the substrate.
ric test method from a specimen produced under identical
conditions as the test specimen to be measured. To confirm the
5. Significance and Use
similarityofthemagneticpropertiesofthesubstratetothoseof
5.1 The thickness of a coating is often critical to its
the standards, a comparison of the readings obtained with the
performance. This magnetic method is suitable for measuring
bare basis metal of the standard to that of the test specimen is
nondestructively the thickness of some nickel coatings and for
recommended.
specification acceptance.
7.5.2 In the same manner, the similarity of the magnetic
5.2 This method requires that the magnetic properties of the properties of the coating of the test specimen to that of the
coating and its substrate be the same as those of the reference standard can be established by verifying with the cross
standards used for the calibration adjustment of the instrument. sectioning (Test Methods B487 or B748) or coulometric (Test
B530 − 09 (2021)
Method B504) methods that the thickness reading obtained on surface. A similar effect can occur with a single-pole probe, if
the test specimen by means of the properly adjusted instrument the tip is unevenly worn. Measurements made on curved test
corresponds to the actual thickness determined by one or both specimens may not, therefore, be valid unless the instrument is
of the above methods. specifically adjusted for such measurements.
7.6 Where indicated, the accuracy of the instrument should
8.6 Surface Roughness:
be checked by rotating the probe in increments of 90° (see 8.7 8.6.1 Measurements are influenced by the surface topogra-
and 8.8).
phy of the substrate and the coating, and a rough or scratched
surface will give individual instrument readings that all vary
7.7 For Type A coatings, the basis metal thickness for the
from point to point. In this case, it is necessary to make many
test and the calibration adjustment shall be the same if the
readings at different positions to obtain an average value that is
critical thickness, defined in 8.3, is not exceeded. When
representative of the mean coating thickness.
possible, back up the basis metal of the standard, or the test
8.6.2 Ifthebasismetalismagneticandrough,itmayalsobe
specimen, with a sufficient thickness of similar material to
necessary to check, and adjust if necessary, the zero of the
make the readings independent of the basis metal thickness.
instrument at several positions on a sample of the uncoated
7.8 If the curvature of the coating to be measured is such as
rough substrate.
to preclude calibration adjustment on a flat surface, the
8.6.3 If the roughness of the substrate surface is small,
curvature of the coated standard shall be the same as that of the
relative to the coating thickness, its effect will probably be
test specimen.
negligible.
8. Factors Affecting the Measuring Accuracy
8.7 Direction of Mechanical Working o
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