ASTM B530-96

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: B 530 – 96
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
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 B 530; 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 and Nonmagnetic Substrates—Measurement of Coating
Thickness—Magnetic Method
1.1 This test method covers the use of magnetic instruments
for the nondestructive measurement of the thickness of an
3. Significance and Use
electrodeposited nickel coating on either a magnetic or non-
3.1 The thickness of a coating is often critical to its
magnetic substrate. For autocatalytic nickel coating, see Sec-
performance. This magnetic method is suitable for measuring
tion 7.
nondestructively the thickness of some nickel coatings and for
1.2 These instruments measure either the magnetic attrac-
specification acceptance.
tion between a magnet and the coating-substrate combination,
3.2 This method requires that the magnetic properties of the
or the reluctance of a magnetic flux path passing through the
coating and its substrate be the same as those of the calibration
coating and the basis metal.
standards.
1.3 For this test method, there are two types of coating-
substrate combinations that can be encountered: Type A, nickel
4. Factors Affecting the Measuring Accuracy
coatings on a magnetic substrate, and Type B, nickel coatings
4.1 Coating Thickness—Inherent in the method is a mea-
on a nonmagnetic substrate.
suring uncertainty that, for thin coatings, is constant and
1.4 The effective measuring ranges of instruments using the
independent of the coating thickness; for thicknesses greater
principle of magnetic attraction are up to 50 μm for Type A
than about 50 μm, this uncertainty is proportional to the coating
coatings, and up to 25 μm for Type B coatings. For reluctance
thickness.
gages, the effective ranges are much greater, and measurements
4.2 Magnetic Properties of the Basis Metal (Type A coat-
up to 1 mm or more, can be made on both types of coatings.
ings only)—Magnetic thickness measurements are affected by
1.5 Measurements made in accordance with this test method
variations in the magnetic properties of the basis metal. For
will be in compliance with the requirements of ISO Stan-
practical purposes, magnetic variations in low-carbon steel can
dard 2361 as printed in 1982.
often be considered to be insignificant. To avoid the influences
1.6 This standard does not purport to address all of the
of severe or localized heat treatments and cold working, the
safety concerns, if any, associated with its use. It is the
instrument should be calibrated using a calibration standard
responsibility of the user of this standard to establish appro-
having a basis metal with the same magnetic properties as that
priate safety and health practices and determine the applica-
of the test specimen or, preferably and if available, with a
bility of regulatory limitations prior to use.
sample of the part to be tested before application of the coating.
4.3 Basis Metal Thickness (Type A coatings only)—For
2. Referenced Documents
each instrument, there is a critical thickness of the basis metal
2.1 ASTM Standards:
above which the measurements will not be affected by an
B 499 Test Method for Measurement of Coating Thick-
increase in that thickness. Since it depends on the instrument
nesses by the Magnetic Method: Nonmagnetic Coatings on
2 probe (Note 1) and the nature of the basis metal, its value
Magnetic Basis Metals
should be determined experimentally, if it is not supplied by
2.2 ISO International Standard:
the manufacturer.
ISO 2361 Electrodeposited Nickel Coatings on Magnetic
NOTE 1—The term “instrument probe” also includes the term “magnet.”
4.4 Edge Effect—The method is sensitive to abrupt changes
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on
General Test Methods.
Current edition approved April 10, 1996. Published June 1996. Originally
published as B 530 – 70. Last previous edition B 530 – 88. Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 02.05. Floor, New York, NY 10036.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 530
in the surface contour of the test specimen. Therefore, mea- the relative thickness of each of the layers.
surements made too near an edge or inside corner will not be 4.11.1 A heat treatment at 400°C for 30 min will equalize
valid, unless the instrument is specially calibrated for such a the magnetic permeability of dull (Watts) nickel coatings of the
measurement. This also applies to measurements made on same composition. Bright nickel deposits may or may not have
geometrically limited areas, such as narrow conductors on the same magnetic properties after heat treatment.
printed circuit boards. 4.12 Nickel Coatings on the Back of the Substrate (Type B
coatings only)—Nickel coatings on the back of the substrate
4.5 Curvature—Measurements are affected by the curvature
can affect the measurements, depending on the thickness of the
of the test specimen. The influence of curvature varies consid-
substrate.
erably with the make and type of instrument, but always
4.13 Pressure—Instrument readings are sensitive to the
becomes more pronounced as the radius of curvature de-
pressure with which the probe is applied to the test specimen.
creases. Instruments with two-pole probes may also produce
No deformation of the coating or probe should be allowed.
different readings, depending on whether the poles are aligned
Errors that sometimes are encountered with the use of manual
in planes parallel or perpendicular to the axis of a cylindrical
probes can be avoided by employing spring-loaded probes that
surface. A similar effect can occur with a single-pole probe, if
exert a relatively constant pressure.
the tip is unevenly worn. Measurements made on curved test
specimens may not, therefore, be valid unless the instrument is 4.14 Probe Orientation—Instrument readings may be sen-
sitive to the orientation of the magnet in relation to the field of
specifically calibrated for such measurements.
gravity of the earth. Thus, the operation of an instrument in a
4.6 Surface Roughness:
horizontal or upside-down position may require a different
4.6.1 Measurements are influenced by the surface topogra-
calibration, or may be impossible.
phy of the substrate and the coating, and a rough or scratched
surface will give individual instrument readings that all vary
5. Calibration of Instruments
from point to point. In this case, it is necessary to make many
5.1 Before use, each instrument shall be calibrated in
readings at different positions to obtain an average value that is
accordance with the instructions of the manufacturer, employ-
representative of the mean coating thickness.
ing suitable thickness standards. During use, the calibration
4.6.2 If the basis metal is magnetic and rough, it may also be
shall be checked at regular intervals, at least once a day.
necessary to check the zero of the instrument at several
Attention shall be given to the factors listed in Section 4 and to
positions on a sample of the uncoated rough substrate.
the procedures in Section 6.
4.6.3 If the roughness of the substrate surface is small,
5.2 The calibration standards shall be coated standards
relative to the coating thickness, its effect will probably be
obtained by electroplating nickel adherently onto a substrate.
negligible.
The coating thickness of the calibration standards shall bracket
4.7 Direction of Mechanical Working of the Basis Metal
the user’s highest and lowest coating thickness measurement
(Type A coatings only)—Measurements made by an instrument
requirement.
having a two-pole probe or an unevenly worn single-pole probe
5.3 The substrate and the coating of the standard shall have
may be influenced by the direction in which the magnetic basis
the same magnetic properties as those of the test specimen (see
metal has been subjected to mechanical working, such as
4.2, 4.3, 4.12 and section 4.12.1).
rolling. The reading may change with the orientation of the
5.3.1 To assure the similarity of the magnetic properties of
probe on the surface.
the nickel deposit and for Type A coatings the steel substrate,
4.8 Residual Magnetism (Type A coatings only)—Residual
calibration standards shall be produced by another suitable test
magnetism in the basis metal affects the measurements made
method, such as cross sectioning or the Coulometric test
by instruments that employ a stationary magnetic field. Its
method from a specimen produced under identical conditions
influence on measurements made by reluctance instruments
as the test specimen to be measured. To confirm the similarity
employing an alternating magnetic field is much smaller.
of the magnetic properties of the substrate to those of the
4.9 Stray Magnetic Field—Strong stray magnetic fields,
standards, a comparison of the readings obtained with the bare
such as those produced by various types of electrical equip-
basis metal of the standard to that of the test specimen is
ment, can seriously int
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