ASTM D3612-96

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Designation: D 3612 – 96
Standard Test Method for
Analysis of Gases Dissolved in Electrical Insulating Oil by
Gas Chromatography
This standard is issued under the fixed designation D 3612; 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 2.2 IEEE Standard:
C 57.104 Guide for the Interpretation of Gases Generated in
1.1 This test method covers two procedures for extraction
Oil-Immersed Transformers
and measurement of gases dissolved in electrical insulating oil
2.3 IEC Standard:
having a viscosity of 20 cSt (100 SUS) or less at 40°C (104°F),
Publication No. 567 Guide for the Sampling of Gases and
and the identification and determination of the individual
of Oil from Oil-Filled Electrical Equipment and for the
component gases extracted. Other methods have been used to
Analysis of Free and Dissolved Gases
perform this analysis.
1.2 The individual component gases that may be identified
3. Terminology
and determined include:
3.1 Definitions of Terms Specific to This Standard:
Hydrogen—H
3.1.1 gas content of oil by volume—in Method A, the total
Oxygen—O
Nitrogen—N
2 volume of gases, corrected to 760 torr (101.325 kPa) and 0°C,
Carbon monoxide—CO
contained in a given volume of oil, expressed as a percentage.
Carbon dioxide—CO
In Method B, the sum of the individual gas concentrations
Methane—CH
Ethane—C H
2 6 corrected to 760 torr (101.325 kPa) and 0°C, expressed in
Ethylene—C H
2 4
percent or parts per million.
Acetylene—C H
2 2
3.1.2 parts per million (ppm) by volume of (specific gas) in
Propane—C H
3 8
Propylene—C H
3 6 oil—the volume of that gas corrected to 760 torr (101.325 kPa)
and 0°C, contained in 10 volume of oil.
1.3 This standard does not purport to address all of the
3.1.3 sparging, v—agitating the liquid sample using a gas to
safety concerns, if any, associated with its use. It is the
strip other gases free.
responsibility of the user of this standard to establish appro-
3.1.4 volume concentration of (specific gas) in the gas
priate safety and health practices and determine the applica-
sample—the volume of the specific gas contained in a given
bility of regulatory limitations prior to use. For specific
volume of the gas sample at the same temperature and pressure
precautionary statements see 6.1.8.
(as the measured total volume), expressed either as a percent-
2. Referenced Documents
age or in parts per million.
2.1 ASTM Standards:
4. Summary of Test Method
D 2779 Test Method for Estimation of Solubility of Gases
4.1 Method A—Dissolved gases are extracted from a sample
in Petroleum Liquids
of oil by introduction of the oil sample into a pre-evacuated
D 2780 Test Method for Solubility of Fixed Gases in
known volume. The evolved gases are compressed to atmo-
Liquids
spheric pressure and the total volume measured.
D 3613 Test Methods of Sampling Electrical Insulating Oils
4.2 Method B—Dissolved gases are extracted from a sample
for Gas Analysis and Determination of Water Content
of oil by sparging the oil with the carrier gas on a stripper
D 4051 Practice for Preparation of Low-Pressure Gas
column containing a high surface area bead.
Blends
4.3 There may be some differences in limits of detection and
E 260 Practice for Packed Column Gas Chromatography
precision and bias between Methods A and B for the various
gases.
4.4 A portion of the extracted gases (Method A) or all of the
This test method is under the jurisdiction of ASTM Committee D-27 on
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
gases extracted (Method B) are introduced into a gas chro-
mittee D27.03 on Analytical Tests.
matograph equipped with suitable adsorption column(s). The
Current edition approved March 10, 1996. Published May 1996. Originally
published as D 3612 – 77. Last previous edition D 3612 – 95.
Annual Book of ASTM Standards, Vol 05.02.
3 5
Annual Book of ASTM Standards, Vol 10.03. Available from IEEE, 345 E. 47th St., New York, NY 10017.
4 6
Annual Book of ASTM Standards, Vol 14.02. Available from IEC.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 3612
composition of the sample is calculated from its chromatogram 6. Apparatus
by comparing the area of the peak of each component with the
6.1 Apparatus of the type shown in Fig. 1 or Fig. 2 is
area of the peak of the same component on a reference
suitable for use with up to 50-mL samples of oil and consists
chromatogram made on a standard mixture of known compo-
of the following components:
sition.
NOTE 2—This sample size has been found to be sufficient for most oils.
However, oil that has had only limited exposure to air may contain much
5. Significance and Use
smaller amounts of nitrogen and oxygen. For these oils it may be desirable
5.1 Oil and oil-immersed electrical insulation materials may
to increase the size of the sample and the extraction apparatus.
decompose under the influence of thermal and electrical
NOTE 3—Alternative apparatus designs including the use of a Toepler
pump have also been found successful.
stresses, and in doing so, generate gaseous decomposition
products of varying composition which dissolve in the oil. The
6.1.1 Polytetrafluoroethylene (PTFE) Tubing, narrow-bore,
nature and amount of the individual component gases that may
terminated with a Luer-Lock fitted glass syringe, and leading to
be recovered and analyzed may be indicative of the type and
a a solid plug, three-way, high-vacuum stopcock.
degree of the abnormality responsible for the gas generation.
6.1.2 Degassing Flask, with a glass inlet tube, of sufficient
The rate of gas generation and changes in concentration of
volume to contain up to 50 mL of oil below the inlet tube,
specific gases over time are also used to evaluate the condition
capable of being evacuated through a vacuum pump, contain-
of the electric apparatus.
ing a PTFE-coated magnetic spin bar, and mounted on a
magnetic stirrer.
NOTE 1—Guidelines for the interpretation of gas-in-oil data are given in
6.1.3 Means of Measuring Absolute Pressure within the
IEEE C57.104.
apparatus.
Ace Glass and Lurex Glass manufacture glass extractors. For Ace Glass, the
glass apparatus conforming to Fig. 1 is Part E-13099-99-99 and Fig. 2 is Part
E-1400-99. Available from P.O. Box 688, 1430 Northwest Blvd., Vineland, NJ
08360 or Lurex Glass, 1298 Northwest Blvd., Vineland, NJ 08360.
FIG. 1 Extraction of Gas from Insulating Oil
D 3612
FIG. 2 Extraction of Gas from Insulating Oil
6.1.4 Vacuum Pumping System, capable of evacuating the 6.1.8 Reservoir of Mercury, sufficient to fill the collection
−3
glassware to an absolute pressure of 1 3 10 torr (130 mPa) flask and collection tube.
or lower.
NOTE 4—Caution: Mercury vapor is extremely toxic. Appropriate
6.1.5 Vacuum Glassware, sufficiently large compared to the
precautions should be taken.
volume of the oil sample, so that virtually complete degassing
7. Sampling
is obtained and that the volumetric collection ratio is as large as
possible. A500-mL gas collecting flask has been found suit-
7.1 Obtain samples in accordance with the procedure de-
able.
scribed in Test Method D 3613 for sampling with syringetype
6.1.6 High-Vacuum Valves or Stopcocks, employing the
devices or rigid metal cylinders. The use of rigid metal
minimum necessary amounts of high-vacuum stopcock grease
cylinders is not recommended for use with Method B.
are used throughout the apparatus.
7.2 The procurement of representative samples without loss
6.1.7 Gas Collection Tube, calibrated in 0.01-mL divisions, of dissolved gases or exposure to air is very important. It is also
capable of containing up to 5 mL of gas, terminated with a
important that the quantity and composition of dissolved gases
silicone rubber retaining septum. A suitable arrangement is remain unchanged during transport to the laboratory. Avoid
shown in Fig. 3.
prolonged exposure to light by immediately placing drawn
samples into light-proof containers and retaining them there
until the start of testing.
7.2.1 To maintain the integrity of the sample, keep the time
between sampling and testing as short as possible. Evaluate
containers for maximum storage time. Samples have been
stored in syringes and metal cylinders for four weeks with no
appreciable change in gas content.
NOTE 5—Additional sampling procedures using flexible metal cans are
currently being studied for use with Method A.
METHOD A—VACUUM EXTRACTION
8. Method A—Vacuum Extraction
8.1 Method A employs vacuum extraction to separate the
gases from the oil. The evolved gases are compressed to
atmospheric pressure and the total volume measured. The
gases are then analyzed by gas chromatography.
9. Preparation of Apparatus
FIG. 3 Retaining Rubber Septum for Gas Collection Tube 9.1 Check the apparatus carefully for vacuum tightness of
D 3612
all joints and stopcocks. less. (In Fig. 1, the space above the mercury in the reservoir
9.2 Measure the total volume of the extraction apparatus, must also be evacuated.)
V , and the volume of the collection space, V , and calculate 10.3 Connect the oil sample syringe by the PTFE tubing to
T c
the ratio as the volumetric collection ratio: the three-way stopcock leading to the degassing flask.
10.4 Flush a small quantity of oil from the syringe through
V
c
(1)
the tubing and stopcock to waste, making sure that all the air in
V 2 V
T o
the connecting tubing is displaced by oil.
where V 5 the volume of oil to be added.
o
10.4.1 Any gas bubbles present in the syringe should be
9.3 Calculate the degassing efficiencies for each individual
retained during this flushing operation. This may be accom-
component gas as follows:
plished by inverting the syringe so that the bubble remains at
the plunger end of the syringe during the flushing operation.
E 5 (2)
i
K V
i o
10.5 Close the stopcocks to the vacuum pumps and then
1 1
V 2 V
T o
slowly open the three-way stopcock to allow oil and any gas
bubbles that may be present from the sample syringe to enter
where:
the degassing flask.
E 5 degassing efficiency of component i,
i
10.6 Allow the desired amount of oil to enter the degassing
V 5 volume of oil sample,
o
flask and operate the magnetic stirrer vigorously for approxi-
V 5 total internal volume of extraction apparatus before
T
mately 10 min. This is the volume, V used in the calculation
oil sample is introduced, and
o
K 5 Ostwald solubility coefficient of component i. in 15.4.
i
10.6.1 If a gas bubble is present in the syringe, either
9.4 Determine the Ostwald solubility coefficients of fixed
analyze the total content of the syringe including the bubble;
gases in accordance with Test Method D 2780.
or, if the gas bubble is large, and it is suspected that the
9.5 Ostwald solubility coefficients that have been deter-
concentration of dissolved gases is high, measure and analyze
mined for a number of gases in one specific electrical insulat-
the gas bubble separately, extract an aliquot of the oil sample,
ing oil at 25°C are shown as follows. Values for gases in other
and correct as applicable.
oils may be estimated by reference to Test Method D 2779.
10.7 Close the stopcock isolating the collection flask, and
Ostwald Solubility (Note 6)
Component Gas
Coefficient, K , 25°C, 760 mm Hg
i allow mercury to flow into the collection flask.
Hydrogen 0.0558
10.8 Open the stopcock to the reference column and by
Nitrogen 0.0968
means of the hand pump (Fig. 1) or leveling bottle (Fig. 2)
Carbon monoxide 0.133
Oxygen 0.179
bring the level of the mercury in the reference column even
Methane 0.438
with the level in the collection tube.
Carbon dioxide 1.17
10.9 Measure the volume of extracted gas in the collection
Acetylene 1.22
Ethylene 1.76
tube, and correct for collection efficiency by dividing it by the
Ethane 2.59
volumetric collection ratio calculated in 9.2. Correct to 760 torr
Propane 11.0
(101.325 kPa) and 0°C. Determine the volume of oil degassed
NOTE 6—The Ostwald coefficient values shown in this table are correct
in the degassing flask. Record the gas content as a percentage
only for the specific mineral oil having a density at 15.5°C of 0.855 g/cm
of the oil by volume.
3 used in the original determination. Ostwald coefficients for mineral oils
10.10 Because the total concentration of gas is not extract-
of different density may be calculated as follows:
able from the oil, a rinse step may be required when high
0.980 2 density
K ~corrected!5 K (3) quantities are present. The extractor can be rinsed with oil
i i
0.130
3 containing nondetectable quantities of gases, except for those
where, density 5 density of the oil of interest, g/cm at 15.5°C (60°F).
present in air. The amount of rinsing needed will be dependent
This equation is derived from the equation in Test Method D 2779. Note
especially that all of the Ostwald coefficients are changed by the same upon the gas concentration, type (solubility in oil), and
factor, meaning that though the absolute solubilities of each of the gases
efficiency of the extractor. To ensure that the combustible gases
will change if a different oil is used, the ratio of the solubility of one gas
have been sufficiently removed from the extractor, the rinse oil
to another gas will remain constant.
may be treated as a sample. General rinse procedures may be
9.6 A procedure to check the extraction efficiency requires
established. However, for samples with very high concentra-
the use of prepared gas-in-oil standards of known concentra-
tions of gases verify effectiveness of the rinse procedure.
tion. The methods of preparation are outlined in Annex A1 and
GAS ANALYSIS
Annex A2.
11. Apparatus
10. Procedure
11.1 Gas Chromatograph, consisting essentially of a carrier
10.1 Lower the mercury level from the collection flask.
gas source, a pressure regulator, a sample injection port and
10.2 Evacuate the system of collection flask and degassing
−3
chromatography column(s), flow meter(s), detector(s), and
flask to an absolute pressure of 1 3 10 torr (130 mPa) or
recorder(s) or recording integrator(s).
11.2 Provide means for measuring and controlling tempera-
tures of the adsorption column, the inlet port, and the detector
“Analysis of Gas Dissolved in Transformer Oils;” Daoust, R., Dind, J. E.,
Morgan, J., and Regis, J.; Doble Conference, 1971, Sections 6–110. to within 60.5°C.
D 3612
NOTE 7—Use Practice E 260 as a reference for
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