ASTM D2440-13(2021)

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: D2440 − 13 (Reapproved 2021)
Standard Test Method for
Oxidation Stability of Mineral Insulating Oil
This standard is issued under the fixed designation D2440; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope D664 Test Method for Acid Number of Petroleum Products
by Potentiometric Titration
1.1 This test method determines the resistance of mineral
D974 Test Method for Acid and Base Number by Color-
transformer oils to oxidation under prescribed accelerated
Indicator Titration
aging conditions. Oxidation stability is measured by the
D2112 Test Method for Oxidation Stability of Inhibited
propensity of oils to form sludge and acid products during
Mineral Insulating Oil by Pressure Vessel
oxidation. This test method is applicable to new oils, both
D2272 Test Method for Oxidation Stability of Steam Tur-
uninhibited and inhibited, but is not well defined for used or
bine Oils by Rotating Pressure Vessel
reclaimed oils.
D3487 Specification for Mineral Insulating Oil Used in
NOTE 1—A shorter duration oxidation test for evaluation of inhibited
Electrical Apparatus
oils is available in Test Method D2112.
2.2 IEC Publication:
NOTE 2—For those interested in the measurement of volatile acidity,
IEC 61125: 1992 Unused Hydrocarbon–Based Insulating
reference is made to IEC Method 61125.
Liquids—Test Methods for Evaluating the Oxidation Sta-
1.2 The values stated in SI units are to be regarded as
bility
standard. No other units of measurement are included in this
standard.
3. Summary of Test Method
1.3 This standard does not purport to address all of the
3.1 Atest specimen of mineral transformer oil is oxidized at
safety concerns, if any, associated with its use. It is the
a bath temperature of 110 °C, in the presence of a copper
responsibility of the user of this standard to establish appro-
catalyst coil, by bubbling oxygen through duplicate test speci-
priate safety, health, and environmental practices and deter-
mens for 72 and 164 h, respectively. The oil is evaluated at the
mine the applicability of regulatory limitations prior to use.
end of each aging period by measuring the amount of sludge
1.4 This international standard was developed in accor-
and acid formed. The test specimen is diluted with n-heptane
dance with internationally recognized principles on standard-
and the solution filtered to remove the sludge. The sludge is
ization established in the Decision on Principles for the
dried and weighed. The sludge-free solution is titrated at room
Development of International Standards, Guides and Recom-
temperature with standard alcoholic base to the end point
mendations issued by the World Trade Organization Technical
indicated by the color change (green-brown) of the added
Barriers to Trade (TBT) Committee.
p-naphthol-benzein solution.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
4.1 Theoxidationstabilitytestofmineraltransformeroilsis
B1 Specification for Hard-Drawn Copper Wire
a method for assessing the amount of sludge and acid products
formed in a transformer oil when the oil is tested under
prescribed conditions. Good oxidation stability is necessary in
This test method is under the jurisdiction of ASTM Committee D27 on
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom-
order to maximize the service life of the oil by minimizing the
mittee D27.06 on Chemical Test.
formation of sludge and acid. Oils that meet the requirements
Current edition approved Nov. 1, 2021. Published November 2021. Originally
specified for this test in Specification D3487 tend to minimize
approved in 1965 as D2440 – 65 T. Last previous edition approved in 2013 as
D2440 – 13. DOI: 10.1520/D2440-13R21. electrical conduction, ensure acceptable heat transfer, and
Supporting data have been filed at ASTM International Headquarters and may
preserve system life. There is no proven correlation between
beobtainedbyrequestingResearchReportRR:D27-1001.ContactASTMCustomer
performance in this test and performance in service, since the
Service at service@astm.org.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on International Electrotechnical Commission. Available from American National
the ASTM website. Standards Institute, 25 W. 43rd St., 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2440 − 13 (2021)
test does not model the whole insulation system (oil, paper,
enamel, wire). However, the test can be used as a control test
forevaluatingoxidationinhibitorsandtochecktheconsistency
of oxidation stability of production oils.
5. Apparatus
5.1 Aging (Oxidation) Bath—An oil bath, wax bath, or
aluminum block heater (see IEC Method 61125) of a suitable
type capable of controlling the temperature at 110 6 0.5 °C
with a temperature gradient of less than 1 °C in the body of the
liquid.When initially setting up the bath, a measurement of the
temperature gradient with the tubes immersed is to be con-
ducted to ensure that no temperature gradient exists as the
tubes may obstruct a uniform circulation. Use any nontoxic
liquid having low volatility at 110 °C and containing no
volatile additives and having a flash point above the test
temperature. Mineral oils, waxes and silicone oils have been
used satisfactorily. Circulation of the oil or wax heating
mediumbymeansofapumporstirrerisrequired.Seealso5.4,
relating to the depth of fluid in aging bath and position of oil
receptacles.
5.2 Drying Tower—A drying tower at least 25 cm in length
for conditioning of the oxygen supply.
FIG. 1 Oil Receptacle and Head
5.3 Oil Receptacle and Head—An oil receptacle consisting
of a heat-resistant glass test tube 25 mm in outside diameter,
1.25 mm in wall thickness, 210 mm in overall length including
a standard taper 24/40 outer joint, with a Dreschsel-type head
6.3 n-Heptane,fordilutionoftheoxidizedoil,precipitation,
consisting of a standard taper 24/40 inner joint with side outlet
and washing of the sludge shall conform to the following
tube 5.0 mm in outside diameter and an oxygen delivery tube
requirements:
5.0 mm in outside diameter and 3 mm, minimum, in inside
Relative Density at 20 °C 0.6836 to 0.6839
diameter which extends to within 2.5 6 0.5 mm of the bottom
Refractive index at 20 °C 1.3876 to 1.3879
of the oil receptacle and has its end ground at an angle of 30°
Solidification temperature, min, °C −90.72
Distillation 50 % shall distill between 98.38 and
to the axis of the tube. The design is shown in Fig. 1.
98.48 °C. Temperature rise between 20 and
5.4 Position the oil receptacle in the aging bath in accor- 80 % recovery shall be 0.20 °C maximum
dance with the drawing shown in Fig. 2.
6.4 p-Naphtholbenzein Indicator Solution—The specifica-
tions for p-naphtholbenzein are prescribed in Test Method
NOTE 3—The oil receptacle and position in the aging bath are
D974. Prepare a solution containing 10 g p-naphtholbenzein
essentially the same as specified in IEC Method 61125, “Test Method for
Oxidation Stability of Inhibited Mineral Insulating Oils,” Glassware
per litre of titration solvent (see 6.7).
dimensionshavebeenalteredslightlytoconformtosizesreadilyavailable
6.5 Oxygen—Minimum purity 99.4 %.
in the United States. Both types of tubes can be used.
6.6 Potassium Hydroxide Solution, Standard Alcoholic (0.1
5.5 Glass or Porcelain Crucibles—50 mL size.
N)—Prepare alcoholic potassium hydroxide solution and stan-
5.6 Filtering Membranes—Cellulose ester type membrane
dardize as described in Test Method D974. Commercially
filters of 5-µm porosity, 47 mm.
preparedAlcoholic Potassium Hydroxide Solution is available.
6. Reagents and Materials
6.7 Titration Solvent—Mix 3 parts by volume of toluene
with 2 parts by volume of isopropyl alcohol.
6.1 Purity of Reagents—Use reagent grade chemicals in all
tests.Unlessotherwiseindicated,allreagentsaretoconformto
6.8 Silicon Carbide Abrasive Cloth, 100-grit with cloth
the specifications of the Committee on Analytical Reagents of
backing.
the American Chemical Society, where such specifications are
6.9 Wire Catalyst—AWG No. 18 (0.0403-in. (1.01-mm)
available.
diameter) 99.9 % purity conforming to Specification B1. Soft-
6.2 Chloroform, cp, or acetone, cp.
drawn copper wire of equivalent grade may also be used.
6.10 Hydrochloric Acid, 10 Volume %.
“Reagent Chemicals,American Chemical Society Specifications,”Am. Chemi-
cal Soc., Washington, DC. For suggestions on the testing of reagents not listed by 7. Hazards
theAmerican Chemical Society, see “Reagent Chemicals and Standards,” by Joseph
7.1 Consult Material Safety Data Sheets for all materials
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the “United States
Pharmacopeia.” used in this test method.
D2440 − 13 (2021)
FIG. 2 Position of Oil Receptacle in Aging Bath
8. Preparation of Oxygen Supply and adjust the flow rate to deliver the conditioned oxygen at a
rate of 1.0 6 0.1 L/h to each tube of oil being tested.
8.1 Oxidize the oil by contact with oxygen of 99.4 %
minimum purity conditioned as follows:
9. Preparation of Oil Receptacle
8.1.1 Use metal or glass tubing to deliver the oxygen to the
9.1 Wash each oil receptacle thoroughly, first with acetone
oxygen delivery tube. Eliminate tubing connections when
and then with soap and water, and rinse in acid solution. The
possible. If used, the tubing should be at room temperature.
following reagents have been found suitable: chromic acid,
Limit the length of tubing exposed to the oxygen flow to 40
aqua regia, and ammonium persulfate. Wash each receptacle
mm. Do not use tubing connections in contact with the liquid
free of acid, using tap water, and finally rinse with distilled
of the heating bath or under conditions where the temperature
water. Dry in an oven at 105 to 110 °C for at least 3 h; cool to
of the tubing will be above room temperature. Where it is
room temperature before use.
necessary to use tubing connections, only sulfur-free tubing is
permissible. FOA/USP Nalgene tubing and certain types of
10. Preparation of Copper Catalyst
PVC tubing have been found satisfactory in this application.
10.1 Immediately before use, polish the copper wire with
8.1.2 Dry the oxygen by forcing it through a solid desiccant
silicon carbide abrasive cloth and wipe free of abrasive with a
of high moisture-absorbing capacity. Arrange the desiccant in
clean dry cloth. Clean the copper wire with acetone or
the drying tower to a depth of 205 to 254 mm. Change the
chloroform before it is wound to r
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