ASTM D974-06
(Test Method)Standard Test Method for Acid and Base Number by Color-Indicator Titration
Standard Test Method for Acid and Base Number by Color-Indicator Titration
SIGNIFICANCE AND USE
New and used petroleum products can contain basic or acidic constituents that are present as additives or as degradation products formed during service, such as oxidation products. The relative amount of these materials can be determined by titrating with acids or bases. This number, whether expressed as acid number or base number, is a measure of this amount of acidic or basic substances, respectively, in the oil—always under the conditions of the test. This number is used as a guide in the quality control of lubricating oil formulations. It is also sometimes used as a measure of lubricant degradation in service; however, any condemning limits must be empirically established.
Since a variety of oxidation products contribute to the acid number and the organic acids vary widely in corrosive properties, the test cannot be used to predict corrosiveness of an oil under service conditions. No general correlation is known between acid number and the corrosive tendency of oils toward metals. Compounded engine oils can and usually do have both acid and base numbers in this test method.
SCOPE
1.1 This test method covers the determination of acidic or basic constituents (Note 1) in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and isopropyl alcohol. It is applicable for the determination of acids or bases whose dissociation constants in water are larger than 109; extremely weak acids or bases whose dissociation constants are smaller than 109 do not interfere. Salts react if their hydrolysis constants are larger than 109.
Note 1—In new and used oils, the constituents considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, and addition agents such as inhibitors and detergents. Similarly, constituents considered to have basic properties include organic and inorganic bases, amino compounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts of heavy metals, and addition agents such as inhibitors and detergents.
Note 2—This test method is not suitable for measuring the basic constituents of many basic additive-type lubricating oils. Test Method D 4739 can be used for this purpose.
1.2 This test method can be used to indicate relative changes 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 or basic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid or base numbers is known.
Note 3—Oils, such as many cutting oils, rustproofing oils, and similar compounded oils, or excessively dark-colored oils, that cannot be analyzed for acid number by this test method due to obscurity of the color-indicator end point, can be analyzed by Test Method D 664. The acid numbers obtained by this color-indicator test method need not be numerically the same as those obtained by Test Method D 664, the base numbers obtained by this color indicator test method need not be numerically the same as those obtained by Test Method D 4739, but they are generally of the same order of magnitude.
1.3 The values stated in acceptable SI units are to be regarded as the standard.
1.4 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
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Standards Content (Sample)
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Contact ASTM International (www.astm.org) for the latest information
An American National Standard
Designation:D974–06
Designation: 139/98
Standard Test Method for
1
Acid and Base Number by Color-Indicator Titration
This standard is issued under the fixed designation D974; 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 (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.
numbers obtained by this color-indicator test method need not be
1. Scope*
numerically the same as those obtained by Test Method D664, the base
1.1 This test method covers the determination of acidic or
numbers obtained by this color indicator test method need not be
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basic constituents (Note 1) in petroleum products and lubri-
numerically the same as those obtained by Test Method D4739, but they
cants soluble or nearly soluble in mixtures of toluene and
are generally of the same order of magnitude.
isopropylalcohol.Itisapplicableforthedeterminationofacids
1.3 The values stated in SI units are to be regarded as
or bases whose dissociation constants in water are larger than
standard. No other units of measurement are included in this
−9
10 ; extremely weak acids or bases whose dissociation
standard.
−9
constants are smaller than 10 do not interfere. Salts react if
1.4 This standard does not purport to address all of the
−9
their hydrolysis constants are larger than 10 .
safety concerns, if any, associated with its use. It is the
NOTE 1—In new and used oils, the constituents considered to have responsibility of the user of this standard to establish appro-
acidic characteristics include organic and inorganic acids, esters, phenolic
priate safety and health practices and determine the applica-
compounds, lactones, resins, salts of heavy metals, and addition agents
bility of regulatory limitations prior to use.
such as inhibitors and detergents. Similarly, constituents considered to
have basic properties include organic and inorganic bases, amino com-
2. Referenced Documents
pounds, salts of weak acids (soaps), basic salts of polyacidic bases, salts
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2.1 ASTM Standards:
of heavy metals, and addition agents such as inhibitors and detergents.
D117 Guide for Sampling, Test Methods, and Specifica-
NOTE 2—This test method is not suitable for measuring the basic
constituents of many basic additive-type lubricating oils. Test Method tions for Electrical Insulating Oils of Petroleum Origin
D4739 can be used for this purpose.
D664 TestMethodforAcidNumberofPetroleumProducts
by Potentiometric Titration
1.2 Thistestmethodcanbeusedtoindicaterelativechanges
D1193 Specification for Reagent Water
that occur in an oil during use under oxidizing conditions.
D4175 Terminology Relating to Petroleum, Petroleum
Although the titration is made under definite equilibrium
Products, and Lubricants
conditions, the method does not measure an absolute acidic or
D4739 Test Method for Base Number Determination by
basicpropertythatcanbeusedtopredictperformanceofanoil
Potentiometric Titration
under service conditions. No general relationship between
bearing corrosion and acid or base numbers is known.
3. Terminology
NOTE 3—Oils, such as many cutting oils, rustproofing oils, and similar
3.1 Definitions:
compounded oils, or excessively dark-colored oils, that cannot be ana-
3.1.1 acid number, n—the quantity of base, expressed in
lyzed for acid number by this test method due to obscurity of the
milligrams of potassium hydroxide per gram of sample that is
color-indicatorendpoint,canbeanalyzedbyTestMethodD664.Theacid
required to titrate a sample to a specified end point.
3.1.1.1 Discussion—In this test method, the indicator is
1
This test method is under the jurisdiction of ASTM Committee D02 on
p-naphtholbenzeintitratedtoagreen/green-brownendpointin
PetroleumProductsandLubricantsandisthedirectresponsibilityofSubcommittee
a toluene-water-isopropanol solvent.
D02.06 on Analysis of Lubricants.
In the IP, this test method is under the jurisdiction of the Standardization
Committee. This test method was adopted as a joint ASTM-IP standard in 1965.
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Current edition approved Nov. 1, 2006. Published November 2006. Originally For referenced ASTM standards, visit the ASTM website, www.astm.org, or
approved in 1948. Last previous edition approved in 2004 as D974–04. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
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Statementsdefiningthistestmethod,itsmodification,anditssignificancewhen Standards volume information, refer to the standard’s Document Summary page on
applied to electrical insulating oils of mineral origin will be found in GuideD117. the ASTM website.
*A Summary of Changes section appears at t
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