ASTM D3339-95e2
(Test Method)Standard Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
Standard Test Method for Acid Number of Petroleum Products by Semi-Micro Color Indicator Titration
SCOPE
1.1 This test method covers the determination of acidic constituents in new or used petroleum products and lubricants soluble or nearly soluble in mixtures of toluene, and isopropyl alcohol. The test method is especially intended for cases in which the amount of sample available to be analyzed is too small to allow accurate analysis by Test Methods D974 or D664. It is applicable for the determination of acids having dissociation constants in water larger than 10-9. Extremely weak acids having dissociation constants smaller than 10-9 do not interfere. Salts titrate if their hydrolysis constants are larger than 10-9.
1.2 This test method can be used to indicate relative changes in acid number that occur in an oil during use under oxidizing conditions. Although the titration is made under definite equilibrium conditions, the method does not measure an absolute acidic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid number is known.
1.3 Since this test method requires substantially less sample than Test Methods D974 or D664, it provides an advantageous means of monitoring an oxidation test by changes in acid number by (a) minimizing test sample depletion for acid number analyses and thus minimizing the disturbance of the test or (b) allowing additional acid number analyses to be made while maintaining the same test sample depletion and thus providing additional data.
Note 1--Some oils, such as many cutting oils, rust-proofing oils, and similar compounded oils, or excessively dark-colored oils, may be more difficult to analyze by this test method due to obscurity of the color-indicator end point. These oils can be analyzed by Test Method D664 provided sufficient sample is available. However, this situation is much less likely using Test Method D3339 than using Test Method D974 due to the use of a more highly dilute sample during the titration and due to the greater stability of the end point color change. The acid numbers obtained by Test Method D3339 may or may not be numerically the same as those obtained by Test Method D664 but they should be of the same order of magnitude.
Note 2--The results obtained using this method have been found to be numerically the same as those obtained using Test Method D974, within the precision of the two methods, for new or oxidized lubricants of the type primarily intended for hydraulic or steam turbine type service. The oxidized lubricants were obtained using the Test Method D943 oxidation test. This correlation is shown by the correlation coefficient r = 0.989 with slope s = + 1.017 and intercept y = + 0.029, calculated using the acid numbers obtained using both titration methods for the samples used for the precision statement (12.2).
1.4 The values stated in acceptable SI units are to be regarded as the standard. Values in inch-pound units are for information only.
1.5 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. For specific hazard statements, see Sections 7 and 9 and A1.14 and A2.3.1.
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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.
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Designation: D 3339 – 95 An American National Standard
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Acid Number of Petroleum Products by Semi-Micro Color
1
Indicator Titration
This standard is issued under the fixed designation D 3339; 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.
2
e NOTE—Figure 1 was corrected editorially in October 1998.
NOTE 2—The results obtained using this method have been found to be
1. Scope
numerically the same as those obtained using Test Method D 974, within
1.1 This test method covers the determination of acidic
the precision of the two methods, for new or oxidized lubricants of the
constituents in new or used petroleum products and lubricants
type primarily intended for hydraulic or steam turbine type service. The
soluble or nearly soluble in mixtures of toluene, and isopropyl
oxidized lubricants were obtained using the Test Method D 943 oxidation
alcohol. The test method is especially intended for cases in test. This correlation is shown by the correlation coefficient r 5 0.989
with slope s 5 + 1.017 and intercept y 5 + 0.029, calculated using the
which the amount of sample available to be analyzed is too
acid numbers obtained using both titration methods for the samples used
small to allow accurate analysis by Test Methods D 974 or
2
for the precision statement (12.2).
D 664. It is applicable for the determination of acids having
−9
1.4 The values stated in acceptable SI units are to be
dissociation constants in water larger than 10 . Extremely
−9
regarded as the standard. Values in inch-pound units are for
weak acids having dissociation constants smaller than 10 do
information only.
not interfere. Salts titrate if their hydrolysis constants are larger
−9
1.5 This standard does not purport to address all of the
than 10 .
safety concerns, if any, associated with its use. It is the
1.2 This test method can be used to indicate relative changes
responsibility of the user of this standard to establish appro-
in acid number that occur in an oil during use under oxidizing
priate safety and health practices and determine the applica-
conditions. Although the titration is made under definite
bility of regulatory limitations prior to use. For specific hazard
equilibrium conditions, the method does not measure an
statements, see Note 3, Note 4, Note 5, Note 6, and Note 12.
absolute acidic property that can be used to predict perfor-
mance of an oil under service conditions. No general relation-
2. Referenced Documents
ship between bearing corrosion and acid number is known.
2.1 ASTM Standards:
1.3 Since this test method requires substantially less sample
D 664 Test Method for Acid Number of Petroleum Products
than Test Methods D 974 or D 664, it provides an advanta-
3
by Potentiometric Titration
geous means of monitoring an oxidation test by changes in acid
D 943 Test Method for Oxidation Characteristics of Inhib-
number by (a) minimizing test sample depletion for acid
3
ited Mineral Oils
number analyses and thus minimizing the disturbance of the
D 974 Test Method for Acid and Base Number by Color-
test or (b) allowing additional acid number analyses to be made
3
Indicator Titration
while maintaining the same test sample depletion and thus
4
D 1193 Specification for Reagent Water
providing additional data.
D 4175 Terminology Relating to Petroleum, Petroleum
NOTE 1—Some oils, such as many cutting oils, rust-proofing oils, and
5
Products, and Lubricants
similar compounded oils, or excessively dark-colored oils, may be more
difficult to analyze by this test method due to obscurity of the color-
3. Terminology
indicator end point. These oils can be analyzed by Test Method D 664
3.1 Definitions:
provided sufficient sample is available. However, this situation is much
less likely using Test Method D 3339 than using Test Method D 974 due 3.1.1 acid number, n—the quantity of base, expressed in
to the use of a more highly dilute sample during the titration and due to
milligrams of potassium hydroxide per gram of sample, that is
the greater stability of the end point color change. The acid numbers
required to titrate a sample to a specified end point.
obtained by Test Method D 3339 may or may not be numerically the same
3.1.1.1 Discussion—In this test method, acids or salts with
as those obtained by Test Method D 664 but they should be of the same
order of magnitude.
2
Use of the correlation coefficient is given in Mack, C., Essentials of Statistics
1
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