ASTM D7946-19
(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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.5 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.
General Information
Relations
Buy Standard
Standards Content (Sample)
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: D7946 − 19
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* 2. Referenced Documents
2
2.1 ASTM Standards:
1.1 This test method covers procedures for the determina-
D1193Specification for Reagent Water
tion of initial pH (i-pH) in new and in-service lubricants.
D4057Practice for Manual Sampling of Petroleum and
NOTE 1—In new and used oils, the constituents that may be considered
Petroleum Products
to have characteristics influencing the i-pH value include organic and
inorganic acids, esters, phenolic compounds, lactones, resins, salts of D4177Practice for Automatic Sampling of Petroleum and
heavy metals, salts of ammonia and other weak bases, acid salts of
Petroleum Products
polybasic acids, and addition agents such as inhibitors and detergents.
“Initial” is used to differentiate from aqueous systems. The analysis is
3. Terminology
terminated after a defined time interval whenever equilibrium conditions,
3.1 Definitions:
as known for pH measurements in aqueous systems, are not reached (see
3.1.1.2)
3.1.1 initial pH (i-pH), n—the measure of the hydrogen ion
(H+) concentration when a fixed sample amount of lubrication
1.2 Thistestmethodisusedtoindicaterelativechangesthat
oil is dissolved into a fixed volume of solvent and using a
occur in oil during use under oxidizing conditions or due to
specified detection system.
contamination by blow-by gases of combustion processes of
3.1.1.1 Discussion—This test method expresses the amount
biogases regardless of the color or other properties of the
of dissociated acidic components as i-pH of a sample in a
in-service lubricants. Although the initial pH is made under
mixtureoftolueneandpropan-2-oltowhichasmallamountof
definite equilibrium conditions, the test method is not intended
water has been added.
to measure an absolute acidic property that can be used to
3.1.1.2 Discussion—The measured i-pH is called initial
predictperformanceofoilunderserviceconditions.Nogeneral
since the original definition of the pH-scale depends on
correlation between corrosion of non-ferrous bearing metals
aqueous solutions. Its application to organic solutions will not
and initial pH value is known.
give stable electrode potential for all types of samples. A
1.3 The values stated in SI units are to be regarded as potential reading after a defined time is used in those cases
standard. No other units of measurement are included in this
instead.
standard.
4. Summary of Test Method
1.4 This standard does not purport to address all of the
4.1 The oil sample is dissolved in solvent mixture and the
safety concerns, if any, associated with its use. It is the
i-pH value is measured using a glass indicating electrode and
responsibility of the user of this standard to establish appro-
a reference electrode or a combination electrode. The meter
priate safety, health, and environmental practices and deter-
readings are measured manually or automatically.
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor-
5. Significance and Use
dance with internationally recognized principles on standard-
5.1 New and used petroleum products may contain acidic
ization established in the Decision on Principles for the
constituents that are present as additives, degradation products
Development of International Standards, Guides and Recom-
formed during service, such as oxidation products or compo-
mendations issued by the World Trade Organization Technical
nents formed from combustion gases. The i-pH-value is a
Barriers to Trade (TBT) Committee.
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.
1
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
2
Subcommittee D02.06 on Analysis of Liquid Fuels and Lubricants. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2019. Published January 2020. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2014. Last previous edition approved in 2014 as D7946–14. DOI: Standards volume information, refer t
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7946 − 14 D7946 − 19
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. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 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.
2. Referenced Documents
2
2.1 ASTM Standards:
D1193 Specification for Reagent Water
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
3. Terminology
3.1 Definitions:
3.1.1 initial pH (i-pH), n—the measure of the hydrogen ion (H+) concentration when a fixed sample amount of lubrication oil
is dissolved into a fixed volume of solvent and using a specified detection system.
3.1.1.1 Discussion—
This test method expresses the amount of dissociated acidic components as i-pH of a sample in a mixture of toluene and
propan-2-ol to which a small amount of water has been added.
3.1.1.2 Discussion—
1
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.06 on Analysis of Liquid Fuels and Lubricants.
Current edition approved July 1, 2014Dec. 1, 2019. Published August 2014January 2020. Originally approved in 2014. Last previous edition approved in 2014 as
D7946 – 14. DOI: 10.1520/D7946-14.10.1520/D7946-19.
2
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 the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
---------------------- Page: 1 ----------------------
D7946 − 19
The measured i-pH is called initial since the original definition of the pH-scale depends on aqueous solutions. Its application to
organic solutions will not give stable electrode potential for all types of samples. A potential reading after a defined time is used
in those cases instead.
4. Summary of Test Method
4.1 The oil sample is dissolved in solvent mixture and the i-pH value is measured using a glass indicating elect
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.