ASTM D2144-07(2021)
(Practice)Standard Practices for Examination of Electrical Insulating Oils by Infrared Absorption
Standard Practices for Examination of Electrical Insulating Oils by Infrared Absorption
SIGNIFICANCE AND USE
5.1 The infrared spectrum of an electrical insulating oil is a record of the absorption of infrared energy over a range of wavelengths. The spectrum indicates the general chemical composition of the test specimen.
Note 2: The infrared spectrum of a pure chemical compound is probably the most characteristic property of that compound. However, in the case of oils, multicomponent systems are being examined whose spectra are the sum total of all the spectra of the individual components. Because the absorption bands of the components may overlap, the spectrum of the oil is not as sharply defined as that for a single compound. For these reasons, these practices may not in every case be suitable for the quantitative estimation of the components of such a complex mixture as mineral oil.
SCOPE
1.1 These practices are to be used for the recording and interpretation of infrared absorption spectra of electrical insulating oils from 4000 cm−1 to 400 cm−1 (2.5 μm to 25 μm).
Note 1: While these practices are specific to ratio recording or optical null double-beam dispersive spectrophotometers, single-beam and HATR (horizontal attenuated total reflectance), Fourier-transform rapid scan infrared spectrophotometers may also be used. By computerized subtraction techniques, ratio methods can be used. Any of these types of equipment may be suitable if they comply with the specifications described in Practice E932.
1.2 Two practices are covered, a Reference Standard Practice and a Differential Practice.
1.3 These practices are designed primarily for use as rapid continuity tests for identifying a shipment of oil from a supplier by comparing its spectrum with that obtained from previous shipments, or with the sample on which approval tests were made. They also may be used for the detection of certain types of contamination in oils, and for the identification of oils in storage or service, by comparison of the spectra of the unknown and known oils. The practices are not intended for the determination of the various constituents of an oil.
1.4 Warning—Infrared absorption is a tool of high resolving power. Conclusions as to continuity of oil quality should not be drawn until sufficient data have been accumulated so that the shipment-to-shipment variation is clearly established, for example.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.7 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.
General Information
Relations
Standards Content (Sample)
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: D2144 − 07 (Reapproved 2021)
Standard Practices for
Examination of Electrical Insulating Oils by Infrared
Absorption
This standard is issued under the fixed designation D2144; 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.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.7 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 These practices are to be used for the recording and
ization established in the Decision on Principles for the
interpretation of infrared absorption spectra of electrical insu-
−1 −1 Development of International Standards, Guides and Recom-
lating oils from 4000 cm to 400 cm (2.5 µm to 25 µm).
mendations issued by the World Trade Organization Technical
NOTE 1—While these practices are specific to ratio recording or optical
Barriers to Trade (TBT) Committee.
null double-beam dispersive spectrophotometers, single-beam and HATR
(horizontal attenuated total reflectance), Fourier-transform rapid scan
2. Referenced Documents
infrared spectrophotometers may also be used. By computerized subtrac-
tion techniques, ratio methods can be used. Any of these types of 2.1 ASTM Standards:
equipment may be suitable if they comply with the specifications
D923Practices for Sampling Electrical Insulating Liquids
described in Practice E932.
E131Terminology Relating to Molecular Spectroscopy
1.2 Two practices are covered, a Reference Standard Prac-
E168Practices for General Techniques of Infrared Quanti-
tice and a Differential Practice. tative Analysis
E932PracticeforDescribingandMeasuringPerformanceof
1.3 These practices are designed primarily for use as rapid
Dispersive Infrared Spectrometers
continuitytestsforidentifyingashipmentofoilfromasupplier
by comparing its spectrum with that obtained from previous
3. Terminology
shipments, or with the sample on which approval tests were
3.1 Definitions—For definitions of terms and symbols, refer
made.They also may be used for the detection of certain types
to Terminology E131.
of contamination in oils, and for the identification of oils in
storage or service, by comparison of the spectra of the
4. Summary of Practices
unknownandknownoils.Thepracticesarenotintendedforthe
4.1 The infrared absorption spectrum may be recorded on
determination of the various constituents of an oil.
the spectrophotometer by either of the two practices outlined
1.4 Warning—Infrared absorption is a tool of high resolv-
below.Inbothpracticesdifferencesinwavelengthorfrequency
ing power. Conclusions as to continuity of oil quality should
and intensity of the absorption bands are observed and mea-
not be drawn until sufficient data have been accumulated so
sured.
that the shipment-to-shipment variation is clearly established,
4.1.1 Reference Standard Practice —An infrared cell filled
for example.
with the insulating oil test specimen is placed in the sample
1.5 The values stated in SI units are to be regarded as
beam of the spectrophotometer. With the shutter of the refer-
standard. No other units of measurement are included in this
ence beam open, the infrared absorption spectrum is recorded
standard.
over the entire range of the instrument. The absorption spec-
trum of the test specimen is compared with a reference
1.6 This standard does not purport to address all of the
spectrumobtainedwithoilfromaprevioustestspecimenorthe
safety concerns, if any, associated with its use. It is the
qualification oil.
responsibility of the user of this standard to establish appro-
4.1.2 Differential Practice—Two cells having the same
priate safety, health, and environmental practices and deter-
sample path length are filled, one with the test specimen and
mine the applicability of regulatory limitations prior to use.
the other with the reference oil.The filled cells are then placed
in the paths of the sample and reference beams, respectively,
These practices are under the jurisdiction of ASTM Committee D27 on
Electrical Insulating Liquids and Gases and are the direct responsibility of
Subcommittee D27.03 on Analytical Tests. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2021. Published January 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1963. Last previous edition approved in 2013 as D2144–07 (2013). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D2144-07R21. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2144 − 07 (2021)
and the differential absorption spectrum recorded. This spec- the room in which the test is to be made for a sufficient period
trum is then compared with the reference differential spectrum of time to permit the sample to attain room temperature before
obtainedinasimilarmannerwiththesamecellsfilledwiththe it is opened.
reference oil.
9.2 Prior to taking specimens of transformer oil or light
cableoil,shakethesamplecontainerthoroughlyandallowitto
5. Significance and Use
stand undisturbed for 15 min in order for all air bubbles to be
5.1 The infrared spectrum of an electrical insulating oil is a
dissipated from the sample. For heavy cable oils, gently tilt or
record of the absorption of infrared energy over a range of
invert the sample container and swirl the fluid several times
wavelengths. The spectrum indicates the general chemical
and then permit it to stand undisturbed for 15 min.
composition of the test specimen.
10. Cleaning, Storing, and Filling the Cell
NOTE 2—The infrared spectrum of a pure chemical compound is
probably the most characteristic property of that compound. However, in
10.1 After the cells have been used, thoroughly rinse them
the case of oils, multicomponent systems are being examined whose
withasuitablereagentgradeorfunctionallyequivalentorganic
spectra are the sum total of all the spectra of the individual components.
solventsuchas2–propanol(isopropylalcohol)(careshouldbe
Because the absorption bands of the components may overlap, the
exercised to keep this solvent as dry as possible), followed by
spectrumoftheoilisnotassharplydefinedasthatforasinglecompound.
rinsing with a reagent grade or functionally equivalent hydro-
Forthesereasons,thesepracticesmaynotineverycasebesuitableforthe
quantitative estimation of the components of such a complex mixture as
carbon solvent, such as petroleum naphtha and store in a
mineral oil.
desiccator until they are to be used.
10.2 Whenacellistobeused,cleanitagainasdescribedin
6. Apparatus
10.1 followed by two rinsings with the sample obtained from
6.1 Infrared Spectrophotometer —An infrared spectropho-
the middle portion of the fluid. Rinse the cell with a portion of
−1 −1
tometercapableofoperatingwithinthe4000cm to400cm
the sample using the hypodermic syringe, which shall also be
(2.5 µm to 25 µm) range in accordance with Practice E932.
cleaned prior to use in accordance with 10.1.
6.2 Absorption Cells—Three types of cells may be used for
10.3 Whenfillingthecell,fillthecleanedandrinsedsyringe
measuring the absorbance of electrical insulating oils, namely
with about 2 mL of the test specimen. With the cell in the
(1) the sealed or fixed liquid cell, (2) the variable space cell,
uprightpositionandtheTFE-fluorocarbonplugsremovedfrom
and (3) the demountable liquid cell. The use of the demount-
the ports in the cell, insert the syringe in the lower port and
able cell is not recommended for quantitative analysis. Use
slowly fill the cell by exerting gradual pressure on the syringe
sealed fixed liquid and demountable liquid cells that meet the
plunger.Whenoilisobservedflowingfromthetopport,laythe
requirements of Practices E168. When measuring the absor-
cell flat, remove the syringe, plug the lower port tightly, and
bance of an oil by the Reference Standard Practice, a sealed or
plugtheupperportloosely.(Warning—Apocketinsomecells
fixed cell having a sample path length of 0.1 mm 6 0.014 mm
may secrete minute quantities of a previous test specimen
is recommended. Cells having a fixed path length of
which may contaminate the current test specimen and cause
0.2mm 60.028mm have been found to be acceptable. When
erroneousresults.Wherethisissuspected,drythecelloutafter
the Differential Practice is used, two matched sealed or fixed
cleaning and rinsing with a reagent grade or functionally
cells each having a sample path length of
equivalent hydrocarbon solvent, such as petroleum naphtha,
0.050 mm 6 0.007 mm are recommended. Where two
and by sweeping it with dry nitrogen applied at a pressure not
matched cells are not available, a variable space cell may be
exceeding 2.5 kPa (20 mm Hg) above ambient.)
adjusted and used in place of one fixed cell. With spectropho-
−1
tometers having a range up to 16.7 µm (600 cm ), liquid cells
11. Procedure—Reference Standard Practice
may be provided with sodium chloride (NaCl) windows. With
−1
11.1 Fill a clean sealed or fixed cell having a sample path
instrumentshavingarangeupto25µm(400cm ),useliquid
length of 0.10 mm 6 0.014 mm (or 0.20 mm 6 0.028 mm)
cells with potassium bromide (KBr) windows.
with the test specimen as outlined in Section 10 and place the
6.3 Cell Filling Device—Use a glass hypodermic syringe of
filled cell in the sample beam. Leave the shutter in the
2 to 5-mLcapacity or other suitable apparatus to fill the liquid
referencebeamintheopenposition.Adjustthescanningspeed,
cells.
gain, and other variable controls to the values established for
the particular spectrophotometer to provide the desired resolu-
7. Sampling
tion. Where the instrument is provided with a scale changer, it
7.1 Obtain the sample in accordance with Practices D923.
is recommended that it be used with the 2.5 to 1 ratio in
preference to the linear mode in obtaining recordings of the
8. Calibration
spectra. Record the infrared spectrum over the entire range of
the instrument in accordance with Practices E168, using
8.1 Adjust and calibrate the spectrophotometer and cells in
nonlinear absorbance charts.
accordance with Practice E932.
11.2 Compare the infrared spectrum of the test specimen
9. Conditioning
withthereferencespectrumofatestspecimenfromaprevious
9.1 Store the sample in its original container and shield it shipment, or the approved qualification oil, recorded by the
from light. Allow the sealed container to stand undisturbed in same procedure, using the same cell and with the same
D2144 − 07 (2021)
instrument settings. Comparison can be made by superimpos- with the reference oil and the other with the test specimen and
ing the two spectra over a viewing light or by testing both test insert them in the paths of the reference and sample beams,
specimens and recording the spectra on the same chart using respectively. Record the differential infrared spectrum over the
different colored inks. Software techniques may also be used entire range of the instrument in accordance with Practices
for this comparison. Note and record any differences in the E168, using a nonlinear absorbance chart. Compare the
wavelengths or frequencies of absorption bands and in appar- reference/reference differential infrared spectrum obtained in
ent intensity of these bands. Differences between these spectra accordance with either 12.1 or 12.2 with the sample/reference
can be amplified considerably by using an expanded ordinate differential infrared spectrum of this paragraph. Comparison
scale during the scanning. can be made by recording on the same chart with a different
coloredinkorbysuperimposingthetwospectraoveraviewing
11.3 Measurements of the absorbance at specific absorption
light. Note and record any differences in the wavelengths or
bands, if required, are made by the base-line method described
frequencies of absorption bands and in apparent intensity of
inPracticesE168andcorrectedforthicknessbyexpressingthe
these bands.
results as absorbance per millimetre.
NOTE 4—This procedure is recommended to ensure that the recording
11.4 When using an FT-IR instrument, scan the atmosphere
ofspuriousabsorptionsduetoamplifierdriftatzeroenergynullpointsare
atleastthreetimeswith no cell in the instrument andstorethis
not erroneously assumed to be absorptions induced by differences in
averagedspectrumasthebackground.Placethecellcontaining
composition.
thetestspecimenintheinstrumentandagainscanthespectrum
12.4 Measurements of the absorbance per millimetre, if
at least three times. The resulting spectrum will be that of the
required, shall be made as described in 11.3.
test specimen.
12.5 When using an FT-IR instrument, place the cell con-
taining the reference oil in the instrument and scan the
12. Procedure—Differential Practice
spectrum at least three times. Store the averaged spectrum as
12.1 Fill two matched cells with the reference oil, each
the background. Remove the cell from the instrument, empty
havingapathlengthof0.050mm 60.007mm;insertonecell
and clean the cell. Fill the same cell with the test specimen of
inthereferencebeamandtheotherinthesamplebeam.Adjust
oil and scan the spectrum at least three times. The resulting
thespectrophotometerasdescribedin11.1,setthepenposition
spectrum will now be the differential spectrum of the test
−1
at approximately 50% transmission at 4000 cm (2.5 µm),
specimen of oil minus that of the reference specimen of oil.
and record the differential infrared spectrum over the entire
range of the instrument, in accordance with Practices E168.
13. Calculation
Evidences of peaks (positive or negative) will be an indication
13.1 Convert measured absorbances and differences in ab-
that the cells are not matched or that the amplifier balance is
sorbance and report as absorbance per millimetre in order to
not properly adjusted.
correct for variations in the sample path length, within the
NOTE 3—Peaks that are below the base line are considered “positive”
tolerances prescribed for the cells. Absorbance may not be a
and those above the base line are “negative.”
linear function of sample path length over a wide range of cell
12.2 When two fixed matched cells having a sample path
lengths; therefore strictly adhere to the cell sizes and make
length of 0.050 mm 6 0.007 mm are not available, a variable
comparison of absorbance per millimetre measured with dif-
cellwhosesamplepathlengthcanbeadjustedt
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