ASTM D6132-13(2017)
(Test Method)Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gage
Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gage
SIGNIFICANCE AND USE
5.1 Many coating properties are markedly affected by the film thickness of the dry film such as adhesion, flexibility, wear, durability, chemical resistance, and hardness. To be able to compare results obtained by different operators, it is essential to measure film thickness carefully.
5.2 Most protective and high performance coatings are applied to meet a requirement or a specification for the dry-film thickness of each coat, or for the complete system, or both. Coatings must be applied within certain minimum and maximum thickness tolerances in order that they can fulfill their intended function. In addition to potential performance deficiencies, it is uneconomical to apply more material than necessary when coating large areas such as floors and walls.
5.3 Low readings may occur occasionally on coatings with rough surfaces. The instrument may allow a user adjustment to prevent this.
5.4 This test method may not be applicable to measure organic coating thickness on all substrates. The instrument's ability to detect a distinct interface between the coating and the substrate may be impeded if the coating and the substrate are of similar composition, density or attenuation or if the coating is non-homogeneous. Verify operation on a known thickness of the coating/substrate combination if these circumstances are thought to exist.
5.5 Multilayered coatings have many interfaces and the instrument will measure to the interface separating the two most acoustically different materials. Some instruments have the ability to detect and measure the individual layer thicknesses in a multi-layer system.
5.6 The use of this test method is not necessarily limited by the type of substrate material.
SCOPE
1.1 This test method describes the use of ultrasonic film thickness gages to measure accurately and nondestructively the dry film thickness of organic coatings applied over a substrate of dissimilar material. Measurements may be made on field structures, on commercially manufactured products, or on laboratory test specimens. These types of gages can accurately measure the dry film thickness of organic coatings on a variety of substrates such as concrete, wood, wallboard, plastic, fiber composites and metal.
1.2 This test method is not applicable to coatings that will be readily deformable under load of the measuring instrument as the instrument probe is placed directly on the coating surface to take a reading.
1.3 The effective range of instruments using the principle of ultrasonics is limited by gage design. A thickness range of 8 μm to 7.60 mm (0.3 to 300 mils) has been demonstrated.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address 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.
1.6 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.
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Designation: D6132 − 13 (Reapproved 2017)
Standard Test Method for
Nondestructive Measurement of Dry Film Thickness of
Applied Organic Coatings Using an Ultrasonic Coating
Thickness Gage
This standard is issued under the fixed designation D6132; 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.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method describes the use of ultrasonic film
D823 Practices for Producing Films of Uniform Thickness
thicknessgagestomeasureaccuratelyandnondestructivelythe
of Paint, Varnish, and Related Products on Test Panels
dry film thickness of organic coatings applied over a substrate
D1005 Test Method for Measurement of Dry-Film Thick-
of dissimilar material. Measurements may be made on field
ness of Organic Coatings Using Micrometers
structures, on commercially manufactured products, or on
D4138 Practices for Measurement of Dry Film Thickness of
laboratory test specimens. These types of gages can accurately
Protective Coating Systems by Destructive, Cross-
measure the dry film thickness of organic coatings on a variety
Sectioning Means
of substrates such as concrete, wood, wallboard, plastic, fiber
E177 Practice for Use of the Terms Precision and Bias in
composites and metal.
ASTM Test Methods
1.2 This test method is not applicable to coatings that will
E691 Practice for Conducting an Interlaboratory Study to
be readily deformable under load of the measuring instrument
Determine the Precision of a Test Method
astheinstrumentprobeisplaceddirectlyonthecoatingsurface
2.2 SSPC—The Society for Protective Coatings Standards:
to take a reading.
PA 2 Procedure for Determining Conformance to Dry Coat-
ing Thickness Requirements
1.3 The effective range of instruments using the principle of
PA 9 Measurement of Dry Organic Coating Thickness on
ultrasonicsislimitedbygagedesign.Athicknessrangeof8µm
Cementitious Substrates Using Ultrasonic Gages
to 7.60 mm (0.3 to 300 mils) has been demonstrated.
2.3 ASME—The American Society of Mechanical Engi-
1.4 The values stated in SI units are to be regarded as
neers:
standard. No other units of measurement are included in this
B46.1 Surface Texture (Surface Roughness, Waviness, and
standard.
Lay)
1.5 This standard does not purport to address the safety
3. Terminology
concerns, if any, associated with its use. It is the responsibility
3.1 Definitions of Terms Specific to This Standard:
of the user of this standard to establish appropriate safety and
3.1.1 accuracy, n—the measure of the magnitude of error
health practices and determine the applicability of regulatory
between the result of a measurement and the true thickness of
limitations prior to use.
the item being measured.
1.6 This international standard was developed in accor-
3.1.1.1 Discussion—An accuracy statement predicts the
dance with internationally recognized principles on standard-
abilityofacoatingthicknessgagetomeasurethetruethickness
ization established in the Decision on Principles for the
of a coating to be measured. Accuracy statements provide the
Development of International Standards, Guides and Recom-
performance capability across the full functional measurement
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This test method is under the jurisdiction of ASTM Committee D01 on Paint the ASTM website.
and Related Coatings, Materials, andApplications and is the direct responsibility of Available from Society for Protective Coatings (SSPC), 800 Trumbull Dr.,
Subcommittee D01.23 on Physical Properties of Applied Paint Films. Pittsburgh, PA 15205, http://www.sspc.org.
Current edition approved June 15, 2017. Published July 2017. Originally Available from American Society of Mechanical Engineers (ASME), ASME
approved in 1997. Last previously edition approved in 2013 as D6132 – 13. DOI: International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
10.1520/D6132-13R17. www.asme.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6132 − 13 (2017)
range of the gage. Accuracy statements frequently include a intended application, used to adjust and/or verify the accuracy
fixed portion that remains constant across the measurement ofanultrasoniccoatingthicknessmeasuringgageforaspecific
range,plusavariableportionthatisrelatedtothemeasurement project.
result for a particular thickness. 3.1.13.1 Discussion—A coated reference sample may or
may not have thickness values traceable to a National Metrol-
3.1.2 adjustment, n—the physical act of aligning a gage’s
ogy Institution. However, the reference sample should be
thickness readings to match those of a known thickness sample
marked with the stated value and the degree of accuracy. The
(removal of bias), in order to improve the accuracy of the gage
coating thickness of the sample should be equal to or slightly
on a specific coating.
greater than the user’s coating thickness measurement require-
3.1.2.1 Discussion—An adjustment will affect the outcome
ment and the coating material must have the same acoustic
of subsequent readings.
velocity and attenuation as the coating to be measured.
3.1.3 calibration, n—the high-level, controlled and docu-
3.1.14 substrate, n—the base material, the type of surface,
mented process of obtaining measurements on traceable cali-
or the component that is being coated.
brationstandardsoverthefulloperatingrangeofthegage,then
3.1.15 verification of accuracy, n—obtaining measurements
makingthenecessarygagemodification(asrequired)tocorrect
any out-of-tolerance conditions. on coating thickness standards, comprising of at least one
thicknessvalueclosetotheexpectedcoatingthickness,priorto
3.1.3.1 Discussion—Calibration of coating thickness gages
gage use for the purpose of determining the ability of the
is typically performed by the equipment manufacturer, their
coating thickness gage to produce thickness results within the
authorized agent, or by an accredited calibration laboratory in
gage manufacturer’s stated accuracy.
a controlled environment using a documented process. The
outcomeofthecalibrationprocessistorestore/realignthegage
4. Summary of Test Method
to meet/exceed the manufacturer’s stated accuracy.
3.1.4 certification, n—documentation of the state of condi- 4.1 Instruments complying with this test method measure
tion of the gage, which can (but not required by definition) be thickness by emitting an ultrasonic pulse into the coating that
accompanied by corrective action (such as adjustment or is reflected back from the substrate to the probe. The travel
calibration, or both, or the replacement of components) neces- time is converted into a thickness reading. The instrument’s
sary to correct any out-of-tolerance conditions. probe must be placed directly on the coating surface to take a
reading.
3.1.5 coating thickness standard, n—coated metal plates, or
uncoated shims of flat sheet, with assigned values traceable to
4.2 After verifying accuracy on a known coated part of the
a National Metrology Institution.
object or material of the same kind, the instrument probe is
coupled with the coated specimen, after proper cure and
3.1.6 couplant, n—a substance such as water, oil, grease, or
conditioning according to the coating manufacturer’s instruc-
paste used to avoid the retarding of sound transmission by air
tions.
between the transducer and the test piece during ultrasonic
examination.
4.3 It should be recognized that the accuracy of the mea-
surements can be influenced when:
3.1.7 dry film thickness, n—the thickness of a coating (or
4.3.1 The coated object to be measured is not planar with
coating layers) as measured from the surface of the substrate.
respect to the transducer face at the point of measurement,
3.1.8 gage (gauge), n—an instrument for measuring
4.3.2 Coating density is not uniform, and
quantity, or an instrument for testing.
4.3.3 The substrate peak-to-valley surface profile of the
3.1.8.1 Discussion—In this test method, the term “gage”
coated specimen exceeds the coating thickness.
refers to an instrument for quantifying coating thickness.
NOTE 1—The height of surface profile can be determined in accordance
3.1.9 manufacturer’s specifications, n—a statement or set of
with ASME B46.1.
statements that describes the performance characteristics of the
gage under a given set of conditions.
5. Significance and Use
3.1.9.1 Discussion—Manufacturer’s specifications typically
5.1 Many coating properties are markedly affected by the
include the range of measurement, accuracy statement, oper-
film thickness of the dry film such as adhesion, flexibility,
atingtemperaturerange,powersource,dimensionsandweight,
wear, durability, chemical resistance, and hardness. To be able
and conformance to industry standards.
to compare results obtained by different operators, it is essen-
3.1.10 measurement (reading), n—the value obtained when
tial to measure film thickness carefully.
placing the probe of a thickness gage in contact with a surface.
5.2 Most protective and high performance coatings are
3.1.11 micrometer (micron), n—one one-thousandth of a
appliedtomeetarequirementoraspecificationforthedry-film
milimetre (0.001 mm); 25.4 microns =1 mil.
thickness of each coat, or for the complete system, or both.
3.1.12 mil, n—a U.S. term referring to the imperial unit of
Coatings must be applied within certain minimum and maxi-
measure of one one-thousandth of an inch (0.001 in.) referred
mum thickness tolerances in order that they can fulfill their
to elsewhere in the world as “one thou;” 1 mil = 25.4 microns.
intended function. In addition to potential performance
3.1.13 reference sample, n—a specimen, coated with a deficiencies, it is uneconomical to apply more material than
material that is as close as possible in composition to the necessary when coating large areas such as floors and walls.
D6132 − 13 (2017)
5.3 Low readings may occur occasionally on coatings with coating thickness standards and, if necessary, any deficiencies
rough surfaces.The instrument may allow a user adjustment to found shall be corrected. The probe should also be examined
prevent this. for cleanliness and excessive wear before verifying the accu-
racy and before obtaining coating thickness measurements.
5.4 This test method may not be applicable to measure
8.2.1 If gage readings obtained during verification are
organic coating thickness on all substrates. The instrument’s
outside the combined accuracy of the coating thickness stan-
ability to detect a distinct interface between the coating and the
dard and the manufacturer’s stated gage accuracy, the gage
substrate may be impeded if the coating and the substrate are
should be returned to the manufacturer or their authorized
of similar composition, density or attenuation or if the coating
agent for calibration.
is non-homogeneous.Verify operation on a known thickness of
the coating/substrate combination if these circumstances are 8.3 Adjustment—Measurement accuracy directly corre-
thought to exist. sponds to the sound velocity of the coating being measured.
Because ultrasonic instruments measure the transit time of an
5.5 Multilayered coatings have many interfaces and the
ultrasonicpulse,theymayrequireanadjustmentbytheuserfor
instrument will measure to the interface separating the two
each coating material. To determine if an adjustment is
most acoustically different materials. Some instruments have
necessary, the user should measure a known thickness of the
the ability to detect and measure the individual layer thick-
coating (reference standard) as determined by:
nesses in a multi-layer system.
8.3.1 Using a destructive, cross-sectioning method such as
5.6 The use of this test method is not necessarily limited by
described in Practice D4138,or
the type of substrate material.
8.3.2 Nondestructively (that is, not destroying film integ-
rity) removing and measuring the coating with a micrometer in
6. Apparatus
accordance with Test Method D1005,or
6.1 Gage Body—an electronic instrument that utilizes trans-
8.3.3 Cross sectioning the product and measuring the coat-
ducer probes.
ing thickness by imaging the coating cross-section under a
microscope or by using computerized image analysis. In the
6.2 Transducer Probe—a measurement probe (sensor) using
case of variable coating thickness or coatings applied to rough
an ultrasonic principle and numerical techniques, attached to
substrate surfaces the average coating thickness should be
the gage body. The appropriate transducer probe is selected
calculated by computer image analysis.
based on the anticipated organic coating dry film thickness.
The gage manufacturer may be contacted for a recommenda-
8.4 Best adjustment results are achieved on coatings with a
tion.
thicknessequaltoorgreaterthanthecoatingthicknessrangeto
be measured and on coating material having the same acoustic
7. Test Specimen
velocity and attenuation as the coating to be measured. Follow
7.1 When this test method is used in the field, the specimen
the manufacturer’s instructions.
isthecoatedstructureorarticleonwhichthedryfilmthickness
NOTE 3—It has been reported that the physical properties of some
is to be evaluated.
coatings such as acrylic-melamine can vary over the time of the cure.
7.2 For laboratory use, apply the materials to be tested to
9. Procedure
panels of the same composition, structure or article on which
the dry film thickness is to be evaluated. Cure the organic
9.1 Use the instrument only after calibration has been
coating in accordance with the coating manufacturer’s instruc-
verified in accordance with Section 8.
tion.
9.2 Ensure that the coating is properly cured prior to use of
NOTE 2—Coatings should be applied in accordance with Practices
the instrument.
D823, or as agreed upon between the purchaser and the seller.
9.3 A couplant is often required to transmit the ultrasonic
8. Calibration, Verification and Adjustment of Apparatus pulse from the gage’s probe into the coating. Water is ideal for
coatings with a smooth surface. For coatings with a rough
8.1 Calibration of coating thickness gages is performed by
surface, a propylene glycol gel couplant is best, providing it is
the equipment manufacturer, their aut
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D6132 − 13 D6132 − 13 (Reapproved 2017)
Standard Test Method for
Nondestructive Measurement of Dry Film Thickness of
Applied Organic Coatings Using an Ultrasonic Coating
Thickness Gage
This standard is issued under the fixed designation D6132; 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.
1. Scope*Scope
1.1 This test method describes the use of ultrasonic film thickness gages to measure accurately and nondestructively the dry film
thickness of organic coatings applied over a substrate of dissimilar material. Measurements may be made on field structures, on
commercially manufactured products, or on laboratory test specimens. These types of gages can accurately measure the dry film
thickness of organic coatings on a variety of substrates such as concrete, wood, wallboard, plastic, fiber composites and metal.
1.2 This test method is not applicable to coatings that will be readily deformable under load of the measuring instrument as the
instrument probe is placed directly on the coating surface to take a reading.
1.3 The effective range of instruments using the principle of ultrasonics is limited by gage design. A thickness range of 8 μm
to 7.60 mm (0.3 to 300 mils) has been demonstrated.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address 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.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D823 Practices for Producing Films of Uniform Thickness of Paint, Varnish, and Related Products on Test Panels
D1005 Test Method for Measurement of Dry-Film Thickness of Organic Coatings Using Micrometers
D4138 Practices for Measurement of Dry Film Thickness of Protective Coating Systems by Destructive, Cross-Sectioning
Means
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 SSPC—The Society for Protective Coatings Standards:
PA 2 Procedure for Determining Conformance to Dry Coating Thickness Requirements
PA 9 Measurement of Dry Organic Coating Thickness on Cementitious Substrates Using Ultrasonic Gages
2.3 ASME—The American Society of Mechanical Engineers:
B46.1 Surface Texture (Surface Roughness, Waviness, and Lay)
This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.23 on Physical Properties of Applied Paint Films.
Current edition approved Nov. 1, 2013June 15, 2017. Published December 2013July 2017. Originally approved in 1997. Last previously edition approved in 20082013
as D6132 – 08.D6132 – 13. DOI: 10.1520/D6132-13.10.1520/D6132-13R17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Available from Society for Protective Coatings (SSPC), 40 24th St., 6th Floor, 800 Trumbull Dr., Pittsburgh, PA 15222-4656,15205, http://www.sspc.org.
Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, ThreeTwo Park Ave., New York, NY 10016-5990,
http://www.asme.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6132 − 13 (2017)
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 accuracy, n—the measure of the magnitude of error between the result of a measurement and the true thickness of the item
being measured.
3.1.1.1 Discussion—
An accuracy statement predicts the ability of a coating thickness gage to measure the true thickness of a coating to be measured.
Accuracy statements provide the performance capability across the full functional measurement range of the gage. Accuracy
statements frequently include a fixed portion that remains constant across the measurement range, plus a variable portion that is
related to the measurement result for a particular thickness.
3.1.2 adjustment, n—the physical act of aligning a gage’s thickness readings to match those of a known thickness sample
(removal of bias), in order to improve the accuracy of the gage on a specific coating.
3.1.2.1 Discussion—
An adjustment will affect the outcome of subsequent readings.
3.1.3 calibration, n—the high-level, controlled and documented process of obtaining measurements on traceable calibration
standards over the full operating range of the gage, then making the necessary gage modification (as required) to correct any
out-of-tolerance conditions.
3.1.3.1 Discussion—
Calibration of coating thickness gages is typically performed by the equipment manufacturer, their authorized agent, or by an
accredited calibration laboratory in a controlled environment using a documented process. The outcome of the calibration process
is to restore/realign the gage to meet/exceed the manufacturer’s stated accuracy.
3.1.4 certification, n—documentation of the state of condition of the gage, which can (but not required by definition) be
accompanied by corrective action (such as adjustment or calibration, or both, or the replacement of components) necessary to
correct any out-of-tolerance conditions.
3.1.5 coating thickness standard, n—coated metal plates, or uncoated shims of flat sheet, with assigned values traceable to a
National Metrology Institution.
3.1.6 couplant, n—a substance such as water, oil, grease, or paste used to avoid the retarding of sound transmission by air
between the transducer and the test piece during ultrasonic examination.
3.1.7 dry film thickness, n—the thickness of a coating (or coating layers) as measured from the surface of the substrate.
3.1.8 gage (gauge), n—an instrument for measuring quantity, or an instrument for testing.
3.1.8.1 Discussion—
In this test method, the term “gage” refers to an instrument for quantifying coating thickness.
3.1.9 manufacturer’s specifications, n—a statement or set of statements that describes the performance characteristics of the
gage under a given set of conditions.
3.1.9.1 Discussion—
Manufacturer’s specifications typically include the range of measurement, accuracy statement, operating temperature range, power
source, dimensions and weight, and conformance to industry standards.
3.1.10 measurement (reading), n—the value obtained when placing the probe of a thickness gage in contact with a surface.
3.1.11 micrometer (micron), n—one one-thousandth of a milimetre (0.001 mm); 25.4 microns =1 mil.
3.1.12 mil, n—a U.S. term referring to the imperial unit of measure of one one-thousandth of an inch (0.001 in.) referred to
elsewhere in the world as “one thou;” 1 mil = 25.4 microns.
3.1.13 reference sample, n—a specimen, coated with a material that is as close as possible in composition to the intended
application, used to adjust and/or verify the accuracy of an ultrasonic coating thickness measuring gage for a specific project.
D6132 − 13 (2017)
3.1.13.1 Discussion—
A coated reference sample may or may not have thickness values traceable to a National Metrology Institution. However, the
reference sample should be marked with the stated value and the degree of accuracy. The coating thickness of the sample should
be equal to or slightly greater than the user’s coating thickness measurement requirement and the coating material must have the
same acoustic velocity and attenuation as the coating to be measured.
3.1.14 substrate, n—the base material, the type of surface, or the component that is being coated.
3.1.15 verification of accuracy, n—obtaining measurements on coating thickness standards, comprising of at least one thickness
value close to the expected coating thickness, prior to gage use for the purpose of determining the ability of the coating thickness
gage to produce thickness results within the gage manufacturer’s stated accuracy.
4. Summary of Test Method
4.1 Instruments complying with this test method measure thickness by emitting an ultrasonic pulse into the coating that is
reflected back from the substrate to the probe. The travel time is converted into a thickness reading. The instrument’s probe must
be placed directly on the coating surface to take a reading.
4.2 After verifying accuracy on a known coated part of the object or material of the same kind, the instrument probe is coupled
with the coated specimen, after proper cure and conditioning according to the coating manufacturer’s instructions.
4.3 It should be recognized that the accuracy of the measurements can be influenced when:
4.3.1 The coated object to be measured is not planar with respect to the transducer face at the point of measurement,
4.3.2 Coating density is not uniform, and
4.3.3 The substrate peak-to-valley surface profile of the coated specimen exceeds the coating thickness.
NOTE 1—The height of surface profile can be determined in accordance with ASME B46.1.
5. Significance and Use
5.1 Many coating properties are markedly affected by the film thickness of the dry film such as adhesion, flexibility, wear,
durability, chemical resistance, and hardness. To be able to compare results obtained by different operators, it is essential to
measure film thickness carefully.
5.2 Most protective and high performance coatings are applied to meet a requirement or a specification for the dry-film thickness
of each coat, or for the complete system, or both. Coatings must be applied within certain minimum and maximum thickness
tolerances in order that they can fulfill their intended function. In addition to potential performance deficiencies, it is uneconomical
to apply more material than necessary when coating large areas such as floors and walls.
5.3 Low readings may occur occasionally on coatings with rough surfaces. The instrument may allow a user adjustment to
prevent this.
5.4 This test method may not be applicable to measure organic coating thickness on all substrates. The instrument’s ability to
detect a distinct interface between the coating and the substrate may be impeded if the coating and the substrate are of similar
composition, density or attenuation or if the coating is non-homogeneous. Verify operation on a known thickness of the
coating/substrate combination if these circumstances are thought to exist.
5.5 Multilayered coatings have many interfaces and the instrument will measure to the interface separating the two most
acoustically different materials. Some instruments have the ability to detect and measure the individual layer thicknesses in a
multi-layer system.
5.6 The use of this test method is not necessarily limited by the type of substrate material.
6. Apparatus
6.1 Gage Body—an electronic instrument that utilizes transducer probes.
6.2 Transducer Probe—a measurement probe (sensor) using an ultrasonic principle and numerical techniques, attached to the
gage body. The appropriate transducer probe is selected based on the anticipated organic coating dry film thickness. The gage
manufacturer may be contacted for a recommendation.
7. Test Specimen
7.1 When this test method is used in the field, the specimen is the coated structure or article on which the dry film thickness
is to be evaluated.
7.2 For laboratory use, apply the materials to be tested to panels of the same composition, structure or article on which the dry
film thickness is to be evaluated. Cure the organic coating in accordance with the coating manufacturer’s instruction.
NOTE 2—Coatings should be applied in accordance with Practices D823, or as agreed upon between the purchaser and the seller.
D6132 − 13 (2017)
8. Calibration, Verification and Adjustment of Apparatus
8.1 Calibration of coating thickness gages is performed by the equipment manufacturer, their authorized agent, or by an
accredited calibration laboratory in a controlled environment using a documented process. A certificate of calibration showing
traceability to a National Metrology Institute can be issued. There is no standard time interval for re-calibration, nor is one
absolutely required, but a calibration interval can be established based on experience and the work environment. A one-year
calibration interval is a typical frequency suggested by many gage manufacturers.
8.2 Verification of Accuracy—Before use, each instrument’s calibration accuracy shall be verified by the user in accordance with
the instructions of the manufacturer, employing suitable coating thickness standards and, if necessary, any deficiencies found shall
be corrected. The probe should also be examined for cleanliness and excessive wear before verifying the accuracy and before
obtaining coating thickness measurements.
8.2.1 If gage readings obtained during verification are outside the combined accuracy of the coating thickness standard and the
manufacturer’s stated gage accuracy, the gage should be returned to the manufacturer or their authorized agent for calibration.
8.3 Adjustment—Measurement accuracy directly corresponds to the sound velocity of the coating being measured. Because
ultrasonic instruments measure the transit time of an ultrasonic pulse, they may require an adjustment by the user for each coating
material. To determine if an adjustment is necessary, the user should measure a known thickness of the coating (reference standard)
as determined by:
8.3.1 Using a destructive, cross-sectioning method such as described in Practice D4138, or
8.3.2 Nondestructively (that is,
...
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