ASTM D2440-99
(Test Method)Standard Test Method for Oxidation Stability of Mineral Insulating Oil
Standard Test Method for Oxidation Stability of Mineral Insulating Oil
SCOPE
1.1 This test method determines the resistance of mineral transformer oils to oxidation under prescribed accelerated aging conditions. Oxidation stability is measured by the propensity of oils to form sludge and acid products during oxidation. This test method is applicable to new oils, both uninhibited and inhibited, but is not well defined for used or reclaimed oils. Note 1-A shorter duration oxidation test for evaluation of inhibited oils is available in Test Method D2112. Note 2-For research purposes only for those interested in the measurement of volatile acidity, reference is made to the work of IEC Subcommittee 10A.
1.2 The values stated in acceptable metric units are to be regarded as the standard.
1.3 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 2440–99
Standard Test Method for
Oxidation Stability of Mineral Insulating Oil
This standard is issued under the fixed designation D 2440; 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.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope 2.2 IEC Publication:
CEI/IFC 61125: 1992 Unused Hydrocarbon–Based Insulat-
1.1 This test method determines the resistance of mineral
ing Liquids—Test Methods for Evaluating the Oxidation
transformer oils to oxidation under prescribed accelerated
Stability
aging conditions. Oxidation stability is measured by the
propensity of oils to form sludge and acid products during
3. Summary of Test Method
oxidation. This test method is applicable to new oils, both
3.1 Atest specimen of mineral transformer oil is oxidized at
uninhibited and inhibited, but is not well defined for used or
a bath temperature of 110°C, in the presence of a copper
reclaimed oils.
catalyst coil, by bubbling oxygen through duplicate test speci-
NOTE 1—A shorter duration oxidation test for evaluation of inhibited
mens for 72 and 164 h, respectively. The oil is evaluated at the
oils is available in Test Method D 2112.
end of each aging period by measuring the amount of sludge
NOTE 2—For those interested in the measurement of volatile acidity,
and acid formed. The test specimen is diluted with n-heptane
reference is made to the work of IEC Subcommittee 10A.
and the solution filtered to remove the sludge. The sludge is
1.2 The values stated in metric units are to be regarded as
dried and weighed. The sludge-free solution is titrated at room
the standard.
temperature with standard alcoholic base to the end point
1.3 This standard does not purport to address all of the
indicated by the color change (green-brown) of the added
safety concerns, if any, associated with its use. It is the
p-naphthol-benzein solution.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Significance and Use
bility of regulatory limitations prior to use.
4.1 Theoxidationstabilitytestofmineraltransformeroilsis
a method for assessing the amount of sludge and acid products
2. Referenced Documents
formed in a transformer oil when the oil is tested under
2.1 ASTM Standards:
prescribed conditions. Good oxidation stability is necessary in
B 1 Specification for Hard-Drawn Copper Wire
order to maximize the service life of the oil by minimizing the
D 664 Test Method forAcid Number of Petroleum Products
formation of sludge and acid. Oils that meet the requirements
by Potentiometric Titration
specified for this test in Specification D 3487 tend to minimize
D 974 Test Method for Acid and Base Number by Col-
electrical conduction, ensure acceptable heat transfer, and
orIndicator Titration
preserve system life. There is no proven correlation between
D 2112 Test Method for Oxidation Stability of Inhibited
performance in this test and performance in service, since the
Mineral Insulating Oil by Rotating Bomb
test does not model the whole insulation system (oil, paper,
D 2272 Test Method for Oxidation Stability of Steam Tur-
enamel, wire). However, the test can be used as a control test
bine Oils by Rotating Pressure Vessel
forevaluatingoxidationinhibitorsandtochecktheconsistency
D 3487 Specification for Mineral Insulating Oil Used in
of oxidation stability of production oils.
Electrical Apparatus
5. Apparatus
5.1 Aging (Oxidation) Bath—An oil bath, wax bath, or
This test method is under the jurisdiction of ASTM Committee D-27 on
aluminum block heater (see IEC Standard 61125) of a suitable
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
type capable of controlling the temperature at 110 6 0.5°C
mittee D27.06 on Chemical Test.
Current edition approved May 10, 1999. Published August 1999. Originally with a temperature gradient of less than 1°C in the body of the
e1
published as D 2440 – 65 T. Last previous edition D 2440 – 97 .
liquid. Use any nontoxic liquid having low volatility at 110°C
ASTM Research Report No. RR: D-27-1001, available fromASTM Headquar-
ters, 100 Barr Harbor Drive, West Conshohocken, PA 19428.
Annual Book of ASTM Standards, Vol 02.03.
4 6
Annual Book of ASTM Standards, Vol 05.01. International Electrotechnical Commission. Available from American National
Annual Book of ASTM Standards, Vol 10.03. Standards Institute, 1430 Broadway, New York, NY 10018.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 2440
and containing no volatile additives and having a flash point 6. Reagents and Materials
above the test temperature. Mineral oils, waxes and silicone
6.1 Purity of Reagents—Use reagent grade chemicals in all
oils have been used satisfactorily. Circulation of the oil or wax
tests.Unlessotherwiseindicated,allreagentsaretoconformto
heating medium by means of a pump or stirrer is recom-
the specifications of the Committee on Analytical Reagents of
mended. See also 5.4, relating to the depth of fluid in aging
the American Chemical Society, where such specifications are
bath and position of oil receptacles.
available.
5.2 Drying Tower—A drying tower 25 to 30 cm in height, 6.2 Chloroform, cp, or acetone, cp.
fitted with a ground-glass stopper and side tubes for condition- 6.3 n-Heptane, for dilution of the oxidized oil, precipita-
tion, and washing of the sludge shall conform to the following
ing of the oxygen supply.
requirements:
5.3 Oil Receptacle and Head—An oil receptacle consisting
Relative Density at 20°C 0.6836 to 0.6839
of a heat-resistant glass test tube 25 mm in outside diameter,
Refractive index at 20°C 1.3876 to 1.3879
1.25 mm in wall thickness, 210 mm in overall length including
Solidification temperature, min, °C −90.72
a standard taper 24/40 outer joint, with a Dreschsel-type head Distillation 50 % shall distill between 98.38 and
98.48°C. Temperature rise between 20 and
consisting of a standard taper 24/40 inner joint with side outlet
80 % recovery shall be 0.20°C maximum
tube 5.0 mm in outside diameter and an oxygen delivery tube
6.4 p-Naphtholbenzein Indicator Solution—The specifica-
5.0 mm in outside diameter and 3 mm, minimum, in inside
tions for p-naphtholbenzein are prescribed in Test Method
diameter which extends to within 2.5 6 0.5 mm of the bottom
D 974. Prepare a solution containing 10 g p-naphtholbenzein
of the oil receptacle and has its end ground at an angle of 30°
per litre of titration solvent (see 6.7).
to the axis of the tube. The design is shown in Fig. 1.
6.5 Oxygen—Obtained from liquid oxygen, minimum pu-
5.4 Position the oil receptacle in the aging bath in accor-
rity 99.4 %.
dance with the drawing shown in Fig. 2.
6.6 Potassium Hydroxide Solution, Standard Alcoholic (0.1
N)—Prepare alcoholic potassium hydroxide solution and stan-
NOTE 3—The oil receptacle and position in the aging bath are essen-
dardize as described in Test Method D 974. Commercially
tially the same as specified in IEC Standard 61125, “Test Method for
preparedAlcoholic Potassium Hydroxide Solution is available.
Oxidation Stability of Inhibited Mineral Insulating Oils,” Glassware
6.7 Titration Solvent—Mix 3 parts by volume of toluene
dimensionshavebeenalteredslightlytoconformtosizesreadilyavailable
in the United States.
with 2 parts by volume of isopropyl alcohol.
6.8 Silicon Carbide Abrasive Cloth, 100-grit with cloth
5.5 Filtering Crucibles—A glass filter crucible having a
backing.
maximum diameter of the pores between 5 and 15 µm as
6.9 Wire Catalyst—AWG No. 18 (0.0403-in. (1.01-mm)
determined in accordance with the method described in the
diameter) 99.9 % purity conforming to Specification B 1.
Appendix. Cellulose ester type membrane filters of 5-µm
Soft-drawn copper wire of equivalent grade may also be used.
porosity have been used successfully also.
6.10 Hydrochloric Acid, 10 Volume %.
7. Hazards
7.1 Consult Material Safety Data Sheets for all materials
used in this test method.
8. Preparation of Oxygen Supply
8.1 Oxidize the oil by contact with oxygen of 99.4 %
minimum purity conditioned as follows:
8.1.1 Use metal or glass tubing to deliver the oxygen to the
oxygendeliverytube.Eliminaterubberconnectionsifpossible.
If used, the rubber should be at room temperature. Limit the
length of rubber tubing exposed to the oxygen flow to 13 mm.
Do not use rubber connections in contact with the liquid of the
heating bath or under conditions where the temperature of the
rubber will be above room temperature. Where it is necessary
“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-
cal Soc., Washington, DC. For suggestions on the testing of reagents not listed by
theAmerican Chemical Society, see “Reagent Chemicals and Standards,” by Joseph
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
Pharmacopeia.”
A suitable material is ASTM n-Heptane Knock Test Reference Fuel, marketed
by the Phillips Petroleum Co., Bartlesville, OK.
Solid p-naphtholbenzein conforming to the specifications indicated is available
from Distillation Products Industries, Eastman Organic Chemicals Dept., Rochester
FIG. 1 Oil Receptacle and Head 3, NY.
D 2440
FIG. 2 Position of Oil Receptacle in Aging Bath
to use rubber connections, only sulfur-free rubber is permis- aqua regia, and ammonium persulfate. Wash each receptacle
sible. FOA/USPNalgene tubing has been found satisfactory in free of acid, using tap water, and finally rinse with distilled
this application. water. Dry in an oven at 105 to 110°C for at least 3 h, cool to
8.1.2 Dry the oxygen by forcing it through a solid desiccant roomtemperatureinadesiccator,andkeepthereceptacleinthe
ofhighmoisture-absorbingcapacity. Arrangethedesiccantin desiccator until ready for use.
the drying tower to a depth of 205 to 254 mm. Change the
10. Preparation of Copper Catalyst
desiccant when the indicator begins to change colors from
10.1 Immediately before use, polish the copper wire with
moisture absorption. If an indicator is not used, change the
desiccant at least weekly. silicon carbide abrasive cloth and wipe free of abrasive with a
clean dry cloth.
8.1.3 After passing oxygen through the drying tower, admit
it directly to the receptacle containing the oil to be tested. Do 10.2 Wind a 300-mm length of the polished wire into a
helical coil approximately 16 mm in outside diameter and 50
not preheat the oxygen.
8.1.4 Determine the rate of oxygen supply with an elec- mm in height. Clean the coil thoroughly with chloroform or
acetone, air dry, and insert immediately into the oil receptacle.
tronic flow meter, calibrated rotameter, or soap bubble buret,
and adjust the flow rate to deliver the conditioned oxygen at a Handle the clean copper coil only with clean tongs to avoid
contamination.
rate of 1.0 6 0.1 L/h to each tube of oil being tested.
10.3 Commercially available, prepackaged, preformed coils
9. Preparation of Oil Receptacle
thatmeettherequirementsdescribedinthistestmethodmaybe
9.1 Wash each oil receptacle thoroughly, first with acetone usedasanalternativemethodofcatalystpreparation.Cleanthe
and then with soap and water, and rinse in acid solution. The coil in a 10 % HCl solution for 30 s, rinse three times with tap
following reagents have been found suitable: chromic acid, water and with distilled water, chloroform or acetone and air
10 11
Anhydrous magnesium perchlorate (Anhydrone or Dehydrite) is a suitable Ammonium Persulfate is available as Nochromix from Interex Corporation, 3
desiccant for this purpose. Strathmore Road, Natick, MA 01760.
D 2440
dry immediately before use. Preformed coils were used in a of n-Heptane into three equal aliquots to be used for the
1997 Round Robin Study and found suitable for this applica- sequential washing of the oxygen delivery tube copper catalyst
tion.
coil and the test receptacle to recover the adhering oil. Into the
same flask, thoroughly rinse the catalyst coil, delivery tube,
11. Preparation of Glass Filtering Crucible
and test receptacle to recover adhering oil, using a total of 300
11.1 Clean the glass filtering crucible and dry in an air oven
mL of n-Heptane.
at 105 to 110°C until it has reached constant mass. Cool and
15.2 Weighing Sludge—Allow the mixture to stand in the
store in a desiccator and, when needed, weigh to the nearest
dark for 24 h, at a temperature of 20 6 2°C, before filtering
0.0001 g.
throughaglassfilterorpolymermembrane,previouslydriedto
constant weight. To prevent sludge from passing through the
12. Conditioning of Test Specimen
filter, use a small pressure drop at the start of filtering. Pass
12.1 Filter the oil test specimen by gravity at ambient
cloudy filtrates through a second time. Remove all traces of oil
pressureoratreducedpressure,throughacid-freefilterpaperto
fromthesludgebyrepeatedwashingwithn-Heptane.Washthe
remove traces of sediment, fiber, and excess water. Alterna-
500-mL Erlenmeyer flask with n-heptane to remove adherent
tively, filter the test specimen under vacuum through a 0.45 µm
oil, and empty each rinse into the filter. Use a total volume of
mixed ester or cellulose filter. Discard the first 25 mLof the oil
150 mLof n-heptane, divided into three aliquots for sequential
filtrate.Carefullyprotectthefiltrateduringthefiltrationagainst
washes, for washing the sludge. Dry the filter containing the
dust and other contaminations.
sludge at 110°C to constant mass and weigh to the nearest
0.0001 g. Transfer sludge adhering to the catalyst, test recep-
13. Procedure
tacle, oxygen delivery tube, and the 500-mL Erlenmeyer flask
13.1 Prepare two copper catalysts as described in Section
by dissolving the sludge in small quantities of chloroform or
10.Insertoneineachoftwoclean,dryoilreceptaclesprepared
acetone (a total of 30 mL) into a tared porcelain vessel. Dry at
as described in Section 9.
110°C after the evaporation of the chloroform or acetone to
13.2 Transfer 25 6 0.01 g of the conditioned oil test
constant mass. Add the weight of the residue to that of the
specimen into each of the two prepared oil receptacles by
sludge obtained by precipitation with n-heptane. Express the
means of a clean dry pipet. Immediately place the head on the
total sludge as a percentage of the initial weight of the oil as
oil receptacle to protect the oil from contamination during the
follows:
interval between placing the
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