ASTM D7946-14
(Test Method)Standard Test Method for Initial pH (i-pH)-Value of Petroleum Products
Standard Test Method for Initial pH (i-pH)-Value of Petroleum Products
SIGNIFICANCE AND USE
5.1 New and used petroleum products may contain acidic constituents that are present as additives, degradation products formed during service, such as oxidation products or components formed from combustion gases. The i-pH-value is a measure of the amount of acidic substances and their acidity defined under the conditions of test. The i-pH-value is used as a measure of lubricant degradation in service.
5.2 The corrosiveness of acidic components depends on their concentration and acidity. The i-pH-value is a measure of the amount of dissociated acidic components with the potential of corrosiveness towards metals.
5.3 Since a variety of oxidation and blow-by products contribute to the i-pH-value, this test method cannot be used to predict corrosiveness of oil or blends under service conditions against metallic components. No general correlation is known between i-pH-value and the corrosive tendency of blends or oils toward metals.
SCOPE
1.1 This test method covers procedures for the determination of initial pH (i-pH) in new and in-service lubricants.
Note 1: In new and used oils, the constituents that may be considered to have characteristics influencing the i-pH value include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents such as inhibitors and detergents. “Initial” is used to differentiate from aqueous systems. The analysis is terminated after a defined time interval whenever equilibrium conditions, as known for pH measurements in aqueous systems, are not reached (see 3.1.1.2)
1.2 This test method is used to indicate relative changes that occur in oil during use under oxidizing conditions or due to contamination by blow-by gases of combustion processes of biogases regardless of the color or other properties of the in-service lubricants. Although the initial pH is made under definite equilibrium conditions, the test method is not intended to measure an absolute acidic property that can be used to predict performance of oil under service conditions. No general correlation between corrosion of non-ferrous bearing metals and initial pH value is known.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this 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.
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Designation: D7946 − 14
Standard Test Method for
1
Initial pH (i-pH)-Value of Petroleum Products
This standard is issued under the fixed designation D7946; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope D4177Practice for Automatic Sampling of Petroleum and
Petroleum Products
1.1 This test method covers procedures for the determina-
tion of initial pH (i-pH) in new and in-service lubricants.
3. Terminology
NOTE 1—In new and used oils, the constituents that may be considered
3.1 Definitions:
to have characteristics influencing the i-pH value include organic and
inorganic acids, esters, phenolic compounds, lactones, resins, salts of 3.1.1 initial pH (i-pH), n—the measure of the hydrogen ion
heavy metals, salts of ammonia and other weak bases, acid salts of
(H+) concentration when a fixed sample amount of lubrication
polybasic acids, and addition agents such as inhibitors and detergents.
oil is dissolved into a fixed volume of solvent and using a
“Initial” is used to differentiate from aqueous systems. The analysis is
specified detection system.
terminated after a defined time interval whenever equilibrium conditions,
3.1.1.1 Discussion—This test method expresses the amount
as known for pH measurements in aqueous systems, are not reached (see
3.1.1.2) of dissociated acidic components as i-pH of a sample in a
mixtureoftolueneandpropan-2-oltowhichasmallamountof
1.2 Thistestmethodisusedtoindicaterelativechangesthat
water has been added.
occur in oil during use under oxidizing conditions or due to
3.1.1.2 Discussion—The measured i-pH is called initial
contamination by blow-by gases of combustion processes of
since the original definition of the pH-scale depends on
biogases regardless of the color or other properties of the
aqueous solutions. Its application to organic solutions will not
in-service lubricants. Although the initial pH is made under
give stable electrode potential for all types of samples. A
definite equilibrium conditions, the test method is not intended
potential reading after a defined time is used in those cases
to measure an absolute acidic property that can be used to
instead.
predictperformanceofoilunderserviceconditions.Nogeneral
correlation between corrosion of non-ferrous bearing metals
4. Summary of Test Method
and initial pH value is known.
4.1 The oil sample is dissolved in solvent mixture and the
1.3 The values stated in SI units are to be regarded as
i-pH value is measured using a glass indicating electrode and
standard. No other units of measurement are included in this
a reference electrode or a combination electrode. The meter
standard.
readings are measured manually or automatically.
1.4 This standard does not purport to address all of the
5. Significance and Use
safety concerns, if any, associated with its use. It is the
5.1 New and used petroleum products may contain acidic
responsibility of the user of this standard to establish appro-
constituents that are present as additives, degradation products
priate safety and health practices and determine the applica-
formed during service, such as oxidation products or compo-
bility of regulatory limitations prior to use.
nents formed from combustion gases. The i-pH-value is a
2. Referenced Documents
measure of the amount of acidic substances and their acidity
2
defined under the conditions of test. The i-pH-value is used as
2.1 ASTM Standards:
a measure of lubricant degradation in service.
D1193Specification for Reagent Water
D4057Practice for Manual Sampling of Petroleum and
5.2 The corrosiveness of acidic components depends on
Petroleum Products
their concentration and acidity.The i-pH-value is a measure of
theamountofdissociatedacidiccomponentswiththepotential
1
of corrosiveness towards metals.
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
5.3 Since a variety of oxidation and blow-by products
Subcommittee D02.06 on Analysis of Lubricants.
contributetothei-pH-value,thistestmethodcannotbeusedto
Current edition approved July 1, 2014. Published August 2014. DOI: 10.1520/
D7946-14.
predict corrosiveness of oil or blends under service conditions
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
against metallic components. No general correlation is known
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
between i-pH-value and the corrosive tendency of blends or
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. oils toward metals.
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