ASTM D7006-03
(Practice)Standard Practice for Ultrasonic Testing of Geomembranes
Standard Practice for Ultrasonic Testing of Geomembranes
SIGNIFICANCE AND USE
This practice covers test arrangements, measurement techniques, sampling methods, and calculations to be used for nondestructive evaluation of geomembranes using ultrasonic testing.
Wave velocity may be established for particular geomembranes (for specific polymer type, specific formulation, specific density). Relationships may be established between velocity and both density and tensile properties of geomembranes. An example of the use of ultrasound for determining density of polyethylene is presented in Test Method D 4883. Velocity measurements may be used to determine thickness of geomembranes (1, 2).2 Travel time and amplitude of transmitted waves may be used to assess the condition of geomembranes and to identify defects in geomembranes including surface defects (for example, scratches, cuts), inner defects (for example, discontinuities within geomembranes), and defects that penetrate the entire thickness of geomembranes (for example, pinholes) (3, 4). Bonding between geomembrane sheets can be evaluated using travel time, velocity, or impedance measurements for seam assessment (5-10). Examples of the use of ultrasonic testing for determining the integrity of field and factory seams through travel time and velocity measurements (resulting in thickness measurements) are presented in Practices D 4437 and D 4545, respectively. An ultrasonic testing device is routinely used for evaluating seams in prefabricated bituminous geomembranes in the field (11). Integrity of geomembranes may be monitored in time using ultrasonic measurements.
Note 1—Differences may exist between ultrasonic measurements and measurements made using other methods due to differences in test conditions such as pressure applied and probe dimensions. An example is ultrasonic and mechanical thickness measurements.
The method is applicable to testing both in the laboratory and in the field for parent material and seams. The test durations are very short as wave transmission through geomembrane...
SCOPE
1.1 This practice provides a summary of equipment and procedures for ultrasonic testing of geomembranes using the pulse echo method.
1.2 Ultrasonic wave propagation in solid materials is correlated to physical and mechanical properties and condition of the materials. In ultrasonic testing, two wave propagation characteristics are commonly determined: velocity (based on wave travel time measurements) and attenuation (based on wave amplitude measurements). Velocity of wave propagation is used to determine thickness, density, and elastic properties of materials. Attenuation of waves in solid materials is used to determine microstructural properties of the materials. In addition, frequency characteristics of waves are analyzed to investigate the properties of a test material. Travel time, amplitude, and frequency distribution measurements are used to assess the condition of materials to identify damage and defects in solid materials. Ultrasonic measurements are used to determine the nature of materials/media in contact with a test specimen as well. Measurements are conducted in the time-domain (time versus amplitude) or frequency-domain (frequency versus amplitude).
1.3 Measurements of one or more ultrasonic wave transmission characteristics are made based on the requirements of the specific testing program.
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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Designation: D 7006 – 03
Standard Practice for
Ultrasonic Testing of Geomembranes
This standard is issued under the fixed designation D 7006; 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.
1. Scope Ultrasound Technique
E 1316 Terminology for Nondestructive Examinations
1.1 This practice provides a summary of equipment and
procedures for ultrasonic testing of geomembranes using the
3. Terminology
pulse echo method.
3.1 Definitions:
1.2 Ultrasonic wave propagation in solid materials is corre-
3.1.1 geomembrane, n—an essentially impermeable geo-
lated to physical and mechanical properties and condition of
synthetic composed of one or more synthetic sheets.
the materials. In ultrasonic testing, two wave propagation
3.1.2 atmosphere for testing geomembranes, n—air main-
characteristics are commonly determined: velocity (based on
tained at a relative humidity of 50 to 70 % and a temperature
wave travel time measurements) and attenuation (based on
of 21 6 1°C.
wave amplitude measurements). Velocity of wave propagation
3.1.3 For definitions of terms related to ultrasonic testing,
isusedtodeterminethickness,density,andelasticpropertiesof
refer to Terminology E 1316.
materials. Attenuation of waves in solid materials is used to
determine microstructural properties of the materials. In addi-
4. Summary of Practice
tion, frequency characteristics of waves are analyzed to inves-
4.1 Mechanical waves are introduced to a geomembrane
tigate the properties of a test material. Travel time, amplitude,
from a surface of the material using an ultrasonic transducer.
and frequency distribution measurements are used to assess the
Transmission characteristics of the waves in the geomembrane
condition of materials to identify damage and defects in solid
are determined. The measured characteristics are used to
materials. Ultrasonic measurements are used to determine the
evaluate certain properties and condition of geomembranes.
nature of materials/media in contact with a test specimen as
well. Measurements are conducted in the time-domain (time
5. Significance and Use
versus amplitude) or frequency-domain (frequency versus
5.1 This practice covers test arrangements, measurement
amplitude).
techniques, sampling methods, and calculations to be used for
1.3 Measurements of one or more ultrasonic wave transmis-
nondestructive evaluation of geomembranes using ultrasonic
sion characteristics are made based on the requirements of the
testing.
specific testing program.
5.2 Wave velocity may be established for particular
1.4 This standard does not purport to address all of the
geomembranes (for specific polymer type, specific formula-
safety concerns, if any, associated with its use. It is the
tion, specific density). Relationships may be established be-
responsibility of the user of this standard to establish appro-
tween velocity and both density and tensile properties of
priate safety and health practices and determine the applica-
geomembranes. An example of the use of ultrasound for
bility of regulatory limitations prior to use.
determining density of polyethylene is presented in Test
Method D 4883. Velocity measurements may be used to
2. Referenced Documents
determine thickness of geomembranes (1, 2). Travel time and
2.1 ASTM Standards:
amplitude of transmitted waves may be used to assess the
D 4437 Practice for Determining the Integrity of Field
conditionofgeomembranesandtoidentifydefectsingeomem-
Seams Used in Joining Flexible Polymeric Sheet
branes including surface defects (for example, scratches, cuts),
Geomembranes
inner defects (for example, discontinuities within geomem-
D 4545 Practice for Determining the Integrity of Factory
branes), and defects that penetrate the entire thickness of
Seams Used in Joining Manufactured Flexible Sheet
geomembranes (for example, pinholes) (3, 4). Bonding be-
Geomembranes
tween geomembrane sheets can be evaluated using travel time,
D 4883 Test Method for Density of Polyethylene by the
velocity, or impedance measurements for seam assessment
This practice is under the jurisdiction of ASTM Committee D35 on Geosyn-
thetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes. The boldface numbers in parentheses refer to the list of references at the end of
Current edition approved Dec. 1, 2003. Published January 2004. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7006–03
(5-10). Examples of the use of ultrasonic testing for determin- shall be used to obtain good near surface resolution and to
ing the integrity of field and factory seams through travel time eliminate near field effects for accurate measurement of ultra-
and velocity measurements (resulting in thickness measure- sonic wave propagation characteristics in geomembranes. A
ments) are presented in Practices D 4437 and D 4545, respec- plastic spacer has been found to be effective for geomem-
tively. An ultrasonic testing device is routinely used for branes. The thickness of the spacer shall be at least twice the
evaluating seams in prefabricated bituminous geomembranes thicknessofthetestspecimen.Thethicknessofthespacershall
in the field (11). Integrity of geomembranes may be monitored be less than 5 to 10 times the thickness of the test geomem-
in time using ultrasonic measurements. brane. For testing geomembranes with various thicknesses, use
the material with the largest thickness for selection of the
NOTE 1—Differences may exist between ultrasonic measurements and
thickness of the spacer. The spacer shall be sufficiently large to
measurements made using other methods due to differences in test
covertheactivesurfaceareaofthetransducertoensurethatthe
conditions such as pressure applied and probe dimensions.An example is
ultrasonic and mechanical thickness measurements. waveform generated is fully transmitted to the test specimen
throughthespacer.Thecenterfrequencyofthetransducershall
5.3 The method is applicable to testing both in the labora-
be between 1 and 20 MHz (a 10 MHz transducer has been
tory and in the field for parent material and seams. The test
found to be effective). Focused transducers shall be used for
durations are very short as wave transmission through
texturedgeomembranestoensuremeasurementsaremadeover
geomembranes occurs within microseconds.
essentiallya“point”onthetestmaterial.Othermeansmayalso
be used if high frequency mechanical waves can be generated
6. Apparatus
with these devices.
6.1 The test equipment consists of a single transducer (both
6.3 Pulsegeneratorshallgeneratepulsesofelectricalenergy
transmitter and receiver); a pulse generator; a pulse receiver
that activate the transducer. Pulsers that generate spike or
(includes amplifier and filters for noise reduction); electronic
square wave type voltage pulses have been found to be
circuits to measure and record waveforms, to measure wave
effective for testing geomembranes.
travel time, to measure wave amplitudes, and to display
6.4 The receiver shall amplify and filter the signal received
received signals; electronic circuitry to time and synchronize
by the transducer after the waves have been transmitted
all instrument functions; and connecting cables. The test
through a test sample.
apparatus is shown in Fig. 1.
6.2 Piezoelectric transducers are effective for wave trans- 6.5 Electronic circuitry shall be used to measure travel time
mission. Compressional waves (P-waves, longitudinal waves) of waves in a test sample. The circuitry shall allow for
determination of travel times with a precision equal to or better
shall be used for ultrasonic testing of geomembranes.Aspacer
FIG. 1 Test Apparatus
D7006–03
NOTE 4—Correctionfactorsshallbeusedifcomparisonsaretobemade
than 0.1 µs. If attenuation and amplitude measurements are
between standard and nonstandard testing conditions. Correction factors
desired, instrumentation shall be used to record the waveforms
are determined by taking measurements at nonstandard conditions and
received from a test material. The circuitry shall allow for
normalizing these by the measurements conducted at standard conditions.
determination of amplitudes with a precision equal to or better
than 1 mV. Electronic circuitry may also be used to display 10.3 Surface Preparation—The surface of the test geomem-
received signals. Analog to digital converters and computer- brane shall be free of excessive dust, particles, and any other
ized signal acquisition and analysis setups have been found to materials that may interfere with wave transmission. The
be effective for testing geomembranes. surface of geomembranes may be cleaned with a damp cloth to
6.6 Electronic circuitry shall be used to time and synchro- ensure a clean measurement surface prior to testing.
nize all instrument functions to eliminate uncertainty in the
determination of wave transit times.
11. Procedure
11.1 Ultrasonic measurements in geomembranes shall be
NOTE 2—The apparatus listed here has been found to be effective for
testinggeomembranes.Ultrasonictestingofmaterialsisawellestablished conducted using the pulse echo test method. In this method,
field and other types of devices may also be used for testing geomem-
ultrasonic waves are sent and received from one surface of a
branes. Details for various test arrangements and examples of devices
testspecimenusingoneortwotransducers.Asingletransducer
produced by various manufacturers are available in (12). Effectiveness of
shall be used in the measurements of geomembranes.
alternative devices shall be demonstrated prior to their routine use for
11.2 Ultrasonic measurements on geomembranes may be
geomembranes.
taken using two test arrangements. In both arrangements, the
7. Materials
transducer shall be orthogonal to the test geomembrane.
7.1 A coupling agent shall be used to ensure good contact
11.2.1 Arrangement A—In this arrangement the transducer
between the transducer and test specimen. Coupling agents assembly is placed over the test geomembrane. The transducer
include water, commercial ultrasonic couplants, oil, petroleum
assembly consists of the ultrasonic transducer and the spacer.
jelly,grease,glycerin,propyleneglycol,orotherviscousfluids. Apply a small amount of couplant between the transducer and
Water has been used effectively on flat surfaces. More viscous the spacer to ensure that the two units are in good contact with
materials may be used on inclined surfaces. no air gaps. Then, apply a small amount of couplant on the
surface of the geomembrane at the measurement location.
8. Sampling and Test Specimens
Place the transducer assembly on the geomembrane leaving a
8.1 Test specimens shall be cut such that a distance greater
thin film of couplant between the assembly and the geomem-
than 10 times the thickness of the specimen shall be left
brane. Ensure that the transducer assembly is in good contact
between the transducer and the edges of the specimen in every
(i.e., no air gaps) with the geomembrane.Asmall load may be
direction.
permanently attached on top of the transducer to provide good
8.2 In field testing, measurements shall be taken at locations
contactwiththegeomembraneandensurethatthetransduceris
that are at a distance greater than 10 times the thickness of the
perfectly orthogonal to the test specimen. This arrangement is
specimen from the edges of the geomembrane sheet in any
presented in Fig. 2a.
direction.
11.2.2 Arrangement B—In this arrangement the transducer
assembly is placed below the test geomembrane.Apply a small
NOTE 3—Seam inspection tests may be conducted at locations closer to
the edge of geomembranes than specified in 8.2. Effectiveness of the near
amount of couplant between the transducer and the spacer to
edge measurements shall be demonstrated prior to their routine use to
ensure that the two units are in good contact with no air gaps.
ensure that potential edge reflections do not interfere with measurements
Then, apply a small amount of couplant on the top surface of
through the thickness of geomembranes.
the spacer. Place the geomembrane over the spacer leaving a
thinfilmofcouplantbetweenthespacerandthegeomembrane.
9. Calibration
Ensure that the geomembrane is in good contact (i.e., no air
9.1 The electronic equipment shall be calibrated to ensure
gaps) with the transducer assembly. This arrangement is
accurate determination of the transit time. Calibration bars or
presentedinFig.2b.Inthisarrangement,nopressureisapplied
blocks with known thicknesses and wave transmission veloci-
to the geomembrane. Pressure can affect the thickness of the
ties shall be used for calibration procedures.
geomembrane, which can affect the travel time in the geomem-
10. Conditioning brane. This arrangement is applicable when the underside of a
geomembrane is accessible.
10.1 For baseline measurements (i.e., measurements used to
establish baseline ultrasonic properties for a particular
NOTE 5—Commercially available “delay line” transducers can be used
geomembrane), specimens shall be exposed to the standard
in TestArrangementA. These transducers have plastic spacers attached to
atmosphere for testing geomembranes for a period sufficient to theultrasonicunits.Useofthesetypesoftransducershasbeenfoundtobe
effective for testing geomembranes. Commercially available immersion
reach moisture and temperature equilibrium. Exposure for 24 h
transducer setups can be used in Test Arrangement B. In these setups a
has been found to be effective for reaching equilibrium.
water resistant transducer is placed at a certain depth in a water bath. The
10.2 Tests can be conducted at conditions outside the range
specimen is placed directly on the surface of water at a fixed distance
for standard atmosphere conditions for various applications
away from the transducer. The water between the specimen and the
such as field measurements. For these measurements, speci-
transducer acts as the spacer. These systems are particularly effective for
mens shall be in moisture and temperature equilibrium with
focused transducers. Care must be taken not to leave the test specimen in
their surrounding environment. contact with water for extended periods of time when using these setups.
D7006–03
FIG. 2 Test Arrangements
Test specimens shall not be exposed to water for more than 30 min during
directly or record the received signal for further processing to
a test.
determine the trave
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