ASTM D2144-07(2013)

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 to 400 cm−1 (2.5 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Oct-2013
• ICS: 29.040.10 - Insulating oils
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.03 - Analytical Tests

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D2144 − 07 (Reapproved 2013)
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 2. Referenced Documents
1.1 These practices are to be used for the recording and
2.1 ASTM Standards:
interpretation of infrared absorption spectra of electrical insu-
D923Practices for Sampling Electrical Insulating Liquids
−1
lating oils from 4000 to 400 cm (2.5 to 25 µm).
E131Terminology Relating to Molecular Spectroscopy
E168Practices for General Techniques of Infrared Quanti-
NOTE 1—While these practices are specific to ratio recording or optical
null double-beam dispersive spectrophotometers, single-beam and HATR tative Analysis
(horizontal attenuated total reflectance), Fourier-transform rapid scan
E932PracticeforDescribingandMeasuringPerformanceof
infrared spectrophotometers may also be used. By computerized subtrac-
Dispersive Infrared Spectrometers
tion techniques, ratio methods can be used. Any of these types of
equipment may be suitable if they comply with the specifications
3. Terminology
described in Practice E932.
1.2 Two practices are covered, a Reference Standard Prac-
3.1 Definitions—For definitions of terms and symbols, refer
tice and a Differential Practice.
to Terminology E131.
1.3 These practices are designed primarily for use as rapid
4. Summary of Practices
continuitytestsforidentifyingashipmentofoilfromasupplier
by comparing its spectrum with that obtained from previous
4.1 The infrared absorption spectrum may be recorded on
shipments, or with the sample on which approval tests were
the spectrophotometer by either of the two practices outlined
made.They also may be used for the detection of certain types
below.Inbothpracticesdifferencesinwavelengthorfrequency
of contamination in oils, and for the identification of oils in
and intensity of the absorption bands are observed and mea-
storage or service, by comparison of the spectra of the
sured.
unknownandknownoils.Thepracticesarenotintendedforthe
4.1.1 Reference Standard Practice —An infrared cell filled
determination of the various constituents of an oil.
with the insulating oil test specimen is placed in the sample
1.4 Warning—Infrared absorption is a tool of high resolv-
beam of the spectrophotometer. With the shutter of the refer-
ing power. Conclusions as to continuity of oil quality should
ence beam open, the infrared absorption spectrum is recorded
not be drawn until sufficient data have been accumulated so
over the entire range of the instrument. The absorption spec-
that the shipment-to-shipment variation is clearly established,
trum of the test specimen is compared with a reference
for example.
spectrumobtainedwithoilfromaprevioustestspecimenorthe
1.5 The values stated in SI units are to be regarded as qualification oil.
standard. No other units of measurement are included in this
4.1.2 Differential Practice—Two cells having the same
standard.
sample path length are filled, one with the test specimen and
the other with the reference oil.The filled cells are then placed
1.6 This standard does not purport to address all of the
in the paths of the sample and reference beams, respectively,
safety concerns, if any, associated with its use. It is the
and the differential absorption spectrum recorded. This spec-
responsibility of the user of this standard to establish appro-
trum is then compared with the reference differential spectrum
priate safety and health practices and determine the applica-
obtainedinasimilarmannerwiththesamecellsfilledwiththe
bility of regulatory limitations prior to use.
reference oil.
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 Nov. 1, 2013. Published December 2013. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1963. Last previous edition approved in 2007 as D2144–07. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D2144-07R13. the ASTM website.
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D2144 − 07 (2013)
5. Significance and Use dissipated from the sample. For heavy cable oils, gently tilt or
invert the sample container and swirl the fluid several times
5.1 The infrared spectrum of an electrical insulating oil is a
and then permit it to stand undisturbed for 15 min.
record of the absorption of infrared energy over a range of
wavelengths. The spectrum indicates the general chemical
10. Cleaning, Storing, and Filling the Cell
composition of the test specimen.
10.1 After the cells have been used, thoroughly rinse them
NOTE 2—The infrared spectrum of a pure chemical compound is
withasuitablereagentgradeorfunctionallyequivalentorganic
probably the most characteristic property of that compound. However, in
solventsuchas2–propanol(isopropylalcohol)(careshouldbe
the case of oils, multicomponent systems are being examined whose
exercised to keep this solvent as dry as possible), followed by
spectra are the sum total of all the spectra of the individual components.
rinsing with a reagent grade or functionally equivalent hydro-
Because the absorption bands of the components may overlap, the
spectrumoftheoilisnotassharplydefinedasthatforasinglecompound. carbon solvent, such as petroleum naphtha and store in a
Forthesereasons,thesepracticesmaynotineverycasebesuitableforthe
desiccator until they are to be used.
quantitative estimation of the components of such a complex mixture as
10.2 Whenacellistobeused,cleanitagainasdescribedin
mineral oil.
10.1 followed by two rinsings with the sample obtained from
6. Apparatus
the middle portion of the fluid. Rinse the cell with a portion of
the sample using the hypodermic syringe, which shall also be
6.1 Infrared Spectrophotometer —An infrared spectropho-
−1
cleaned prior to use in accordance with 10.1.
tometer capable of operating within the 4000 to 400 cm (2.5
to 25-µm) range in accordance with Practice E932.
10.3 Whenfillingthecell,fillthecleanedandrinsedsyringe
with about 2 mL of the test specimen. With the cell in the
6.2 Absorption Cells—Threetypesofcellsmaybeusedfor
uprightpositionandtheTFE-fluorocarbonplugsremovedfrom
measuring the absorbance of electrical insulating oils, namely
the ports in the cell, insert the syringe in the lower port and
(1) the sealed or fixed liquid cell, (2) the variable space cell,
slowly fill the cell by exerting gradual pressure on the syringe
and ( 3) the demountable liquid cell. The use of the demount-
plunger.Whenoilisobservedflowingfromthetopport,laythe
able cell is not recommended for quantitative analysis. Use
cell flat, remove the syringe, plug the lower port tightly, and
sealed fixed liquid and demountable liquid cells that meet the
plugtheupperportloosely.(Warning—Apocketinsomecells
requirements of Practices E168. When measuring the absor-
may secrete minute quantities of a previous test specimen
bance of an oil by the Reference Standard Practice, a sealed or
which may contaminate the current test specimen and cause
fixed cell having a sample path length of 0.1 6 0.014 mm is
erroneousresults.Wherethisissuspected,drythecelloutafter
recommended. Cells having a fixed path length of 0.2 6 0.028
cleaning and rinsing with a reagent grade or functionally
mm have been found to be acceptable. When the Differential
equivalent hydrocarbon solvent, such as petroleum naphtha,
Practiceisused,two matched sealed or fixed cells eachhaving
and by sweeping it with dry nitrogen applied at a pressure not
a sample path length of 0.050 6 0.007 mm are recommended.
exceeding 2.5 kPa (20 mm Hg) above ambient.)
Where two matched cells are not available, a variable space
cell may be adjusted and used in place of one fixed cell. With
11. Procedure—Reference Standard Practice
−1
spectrophotometers having a range up to 16.7 µm (600 cm ),
11.1 Fill a clean sealed or fixed cell having a sample path
liquid cells may be provided with sodium chloride (NaCl)
lengthof0.10 60.014mm(or0.20 60.028mm)withthetest
windows. With instruments having a range up to 25 µm (400
−1
specimen as outlined in Section 10 and place the filled cell in
cm ),useliquidcellswithpotassiumbromide(KBr)windows.
thesamplebeam.Leavetheshutterinthereferencebeaminthe
6.3 Cell Filling Device—Use a glass hypodermic syringe of
open position. Adjust the scanning speed, gain, and other
2 to 5-mLcapacity or other suitable apparatus to fill the liquid
variable controls to the values established for the particular
cells.
spectrophotometertoprovidethedesiredresolution.Wherethe
instrumentisprovidedwithascalechanger,itisrecommended
7. Sampling
that it be used with the 2.5 to 1 ratio in preference to the linear
7.1 Obtain the sample in accordance with Practices D923.
mode in obtaining recordings of the spectra. Record the
infrared spectrum over the entire range of the instrument in
8. Calibration
accordance with Practices E168, using nonlinear absorbance
8.1 Adjust and calibrate the spectrophotometer and cells in
charts.
accordance with Practice E932.
11.2 Compare the infrared spectrum of the test specimen
withthereferencespectrumofatestspecimenfromaprevious
9. Conditioning
shipment, or the approved qualification oil, recorded by the
9.1 Store the sample in its original container and shield it
same procedure, using the same cell and with the same
from light. Allow the sealed container to stand undisturbed in
instrument settings. Comparison can be made by superimpos-
the room in which the test is to be made for a sufficient period
ing the two spectra over a viewing light or by testing both test
of time to permit the sample to attain room temperature before
specimens and recording the spectra on the same chart using
it is opened.
different colored inks. Software techniques may also be used
9.2 Prior to taking specimens of transformer oil or light for this comparison. Note and record any differences in the
cableoil,shakethesamplecontainerthoroughlyandallowitto wavelengths or frequencies of absorption bands and in appar-
stand undisturbed for 15 min in order for all air bubbles to be ent intensity of these bands. Differences between these spectra
D2144 − 07 (2013)
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-
12. Procedure—Differential Practice taining the reference oil in the instrument and scan the
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
having a path length of 0.050 6 0.007 mm; insert one cell in
and clean the cell. Fill the same cell with the test specimen of
the reference beam and the other in the sample beam. Adjust
oil and scan the spectrum at least three times. The resulting
thespectrophotometerasdescribedin11.1,setthepenposition
−1 spectrum will now be the differential spectrum of the test
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
that the cells are not matched or that the amplifier balance is
13.1 Convert measured absorbances and differences in ab-
not properly adjusted.
sorbance and report as absorbance per millimetre in order to
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 6 0.007 mm are not available, a variable cell
comparison of absorbance per millimetre measured with dif-
whose sample path length can be adjusted to equal the path
ferentpathlengthsonlywithcaution.Calculateabsorbanceper
length of the fixed cell may be used. The procedure for
millimetre using the equations given in this section for mea-
adjusting the sample path length of the variable cell is as
surements obtained by either the Reference Standard Practice
follows:
or the Differential Practice.
12.2.1 Set the variable path length cell to the nominal
thickness of the fixed path length liquid cell. 13.2 Reference Standard Practice —Differences in the ab-
sorbance per millimetre at specific absorption bands of spectra
12.2.2 Place the variable and fixed path length cells, both
filled with the reference oil, in the paths of the reference and obtained from two test specimens of oil shall be expressed as
the difference in absorbance, calculated as follows:
sample beams, respectively.
12.2.3 Close both beams of the spectrophotometer and
Differencebetweenabsorbancepermillimetre
adjust the electrical balance on the amp
...