ASTM G12-07
(Test Method)Standard Test Method for Nondestructive Measurement of Film Thickness of Pipeline Coatings on Steel
Standard Test Method for Nondestructive Measurement of Film Thickness of Pipeline Coatings on Steel
SIGNIFICANCE AND USE
Measurements of film thickness are an essential part of most ASTM test methods related to coatings on steel pipe. Adequate thickness is important for a coating to fulfill its function of preventing or mitigating corrosion of steel pipelines.
The accuracy of the thickness measurements may be influenced by the deformability of the coating. This test method is not applicable to coatings that would be readily deformable under the force exerted by the probe of the measuring instrument.
SCOPE
1.1 This test method describes the nondestructive measurement of the thickness of a dry, nonmagnetic coating applied to the external surface of steel pipe. The method is recommended for coating thicknesses up to 6 mm (0.240 in.) and for any diameter pipe, but not smaller than 10 mm (0.5 in.). It does not apply to excessively soft films.
1.2 The values stated in SI units to three significant decimals are to be regarded as the standard. The values given in parentheses are for information only.
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: G12 − 07
StandardTest Method for
Nondestructive Measurement of Film Thickness of Pipeline
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Coatings on Steel
This standard is issued under the fixed designation G12; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Apparatus
1.1 This test method describes the nondestructive measure- 4.1 The apparatus shall be a nondestructive-type thickness
ment of the thickness of a dry, nonmagnetic coating applied to gage capable of being standardized over its range of intended
the external surface of steel pipe. The method is recommended use. It shall be designed so that variations in magnetic flux or
for coating thicknesses up to 6 mm (0.240 in.) and for any magneticattractionbetweenitsdetectionunitandthesteelbase
diameter pipe, but not smaller than 10 mm (0.5 in.). It does not can be calibrated to indicate the thickness of the coating
apply to excessively soft films. material.
1.2 The values stated in SI units to three significant deci- 4.2 It shall be suitable for measuring thicknesses of dry,
mals are to be regarded as the standard. The values given in nonmagnetic coatings on either a flat or a circular base.
parentheses are for information only.
5. Standardization of Instruments
1.3 This standard does not purport to address all of the
5.1 The instrument shall be standardized in accordance with
safety concerns, if any, associated with its use. It is the
the manufacturer’s instructions before use by employing suit-
responsibility of the user of this standard to establish appro-
able thickness standards. The standardization shall be checked
priate safety and health practices and determine the applica-
at frequent intervals during use.
bility of regulatory limitations prior to use.
5.2 Nonmagnetic standards of uniform thickness are avail-
2. Summary of Test Method
able in either of two types, foil or coated substrate, as supplied
or recommended by the manufacturer of the instrument.
2.1 The coating thickness is determined by an instrument
5.2.1 Foils (Shims)—The thickness of the foil should be as
thatmeasuresthicknessbynondestructivetechniques,basedon
close as possible to the expected thickness of the coating to be
variations in magnetic flux or magnetic attraction between its
measured. The foil should be placed on a smooth, clean,
detection unit and the magnetic base material.
low-carbon, steel plate, making certain that there is intimate
contact between the foil and the substrate. It is recommended
3. Significance and Use
that single foils of proper thickness be used and that foils be
3.1 Measurements of film thickness are an essential part of
replaced frequently, since they are subject to indentation. Foils
most ASTM test methods related to coatings on steel pipe.
are advantageous for standardizing on curved surfaces and are
Adequate thickness is important for a coating to fulfill its
often more readily available than coated standards.
function of preventing or mitigating corrosion of steel pipe-
NOTE1—Forsomeinstrumentsthereisaneffectivedepthofpenetration
lines.
of the field created by the instrument probe. This is the critical depth of
3.2 The accuracy of the thickness measurements may be
thickness at which the instrument will no longer be affected by increases
influenced by the deformability of the coating. This test
of substrate thickness. Since it depends on the instrument and substrate, it
should be determined experimentally.
method is not applicable to coatings that would be readily
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deformable under the force exerted by the probe of the
5.2.2 Coated Substrate Standards —These standards con-
measuring instrument.
sist of nonmagnetic coatings of known thickness permanently
bonded to a low-carbon steel (1010 grade) substrate, 8 mm
(0.30 in.) thick. The thickness standard should be as close as
1 possible to the expected thickness of the coating to be
This test method is under the jurisdiction of ASTM Committee D01 on Paint
and Related Coatings, Materials, andApplications and is the direct responsibility of
measured.
Subcommittee D01.48 on Durability of Pipeline Coating and Linings.
Current edition approved July 1, 2007. Published July 2007. Originally approved
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in 1969. Last previous edition approved in 1998 as published G12 – 83 (1998) Coated substrate standards may be obtained from the U. S. Department of
which was withdrawn March 2007 and reinstated in July 2007. DOI: 10.1520/ Commerce, National Bureau of Standards, Standard Materials Unit, Washington,
G0012-07. DC 20234.
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