ASTM D971-20
(Test Method)Standard Test Method for Interfacial Tension of Insulating Liquids Against Water by the Ring Method
Standard Test Method for Interfacial Tension of Insulating Liquids Against Water by the Ring Method
SIGNIFICANCE AND USE
4.1 Interfacial tension measurements on electrical insulating liquids provide a sensitive means of detecting small amounts of soluble polar contaminants and products of oxidation. A high value for new mineral insulating oil indicates the absence of most undesirable polar contaminants. The test is frequently applied to service-aged mineral oils as an indication of the degree of deterioration.
Note 1: Different liquid matrixes are reviewed in Appendix X1.
SCOPE
1.1 This test method covers the measurement of the interfacial tension between insulating liquid that has a relative density (specific gravity) less than water and water, under non-equilibrium conditions.
1.2 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. See 7.2 for a specific warning statement.
1.3 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.
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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: D971 − 20
Standard Test Method for
Interfacial Tension of Insulating Liquids Against Water by
1
the Ring Method
This standard is issued under the fixed designation D971; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope rigidly standardized nonequilibrium conditions in which the
measurement is completed within 60 s after formation of the
1.1 This test method covers the measurement of the inter-
interface.
facial tension between insulating liquid that has a relative
density (specific gravity) less than water and water, under
4. Significance and Use
non-equilibrium conditions.
4.1 Interfacialtensionmeasurementsonelectricalinsulating
1.2 This standard does not purport to address all of the
liquidsprovideasensitivemeansofdetectingsmallamountsof
safety concerns, if any, associated with its use. It is the
soluble polar contaminants and products of oxidation. A high
responsibility of the user of this standard to establish appro-
value for new mineral insulating oil indicates the absence of
priate safety, health, and environmental practices and deter-
most undesirable polar contaminants. The test is frequently
mine the applicability of regulatory limitations prior to use.
applied to service-aged mineral oils as an indication of the
See 7.2 for a specific warning statement.
degree of deterioration.
1.3 This international standard was developed in accor-
NOTE 1—Different liquid matrixes are reviewed in Appendix X1.
dance with internationally recognized principles on standard-
5. Apparatus (Figs. 1 and 2)
ization established in the Decision on Principles for the
3
Development of International Standards, Guides and Recom-
5.1 Tensiometer —Force measurement on the tensiometer
mendations issued by the World Trade Organization Technical
maybemadeusingatorsionwire,loadcell,oranyothermeans
Barriers to Trade (TBT) Committee.
of linearly determining tension in the range of 0 to 100 mN/m.
5.1.1 Horizontal platform to hold the sample container
2. Referenced Documents
should be capable of movement upward or downward using a
2
2.1 ASTM Standards:
mechanical screw, lever mechanism, electronic drive, or any
D923Practices for Sampling Electrical Insulating Liquids
other means of precisely changing vertical position of the
sample.
3. Summary of Test Method
5.2 Rings made of platinum or platinum-iridium alloy may
3.1 InterfacialTensionisdeterminedbymeasuringtheforce
beused.Theringshouldbeweldedintoacontinuouscircleand
necessary to detach a planar ring of platinum wire from the
attached to at least two parallel stirrups. Circumference of the
surface of the liquid of higher surface tension, that is, upward
ring should be minimum 40 mm and diameter of the ring wire
from the water insulating liquid interface. To calculate the
shouldbeabout0.3mm.Ratiooftheringmajorradius(R)and
interfacial tension, the force so measured is corrected by an
the wire radius (r) should be known (R/r) to at least three
empirically determined factor which depends upon the force
significant figures. Stirrups should be at least 25 mm long.
applied, the densities of both the insulating liquid and water,
5.2.1 The ring may be suspended from or rigidly fixed into
and the dimensions of the ring. Measurements are made under
the tensiometer force measuring system.
5.3 Sample Container—Glass beaker or clear cylindrical
1
This test method is under the jurisdiction of ASTM Committee D27 on container having a minimum diameter of 45 mm.
Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcom-
mittee D27.07 on Physical Test.
6. Reagents
Current edition approved April 1, 2020. Published May 2020. Originally
6.1 Purity of Reagents—Reagent grade chemicals shall be
approved in 1948 as D971–48 T. Last previous edition approved in 2012 as
D971–12. DOI: 10.1520/D0971-20.
used in the test.
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
3
Standards volume information, refer to the standard’s Document Summary page on Tensiometers that use the Du Nouy principle for measuring interfacial and
the ASTM website. surface tension should be used.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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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: D971 − 12 D971 − 20
Standard Test Method for
Interfacial Tension of Oil Insulating Liquids Against Water
1
by the Ring Method
This standard is issued under the fixed designation D971; 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
1.1 This test method covers the measurement of the interfacial tension between mineral oil insulating liquid that has a relative
density (specific gravity) less than water and water, under non-equilibrium conditions.
1.2 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. See 7.2 for a specific warning statement.
1.3 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:
D117 Guide for Sampling, Test Methods, and Specifications for Electrical Insulating Liquids
D923 Practices for Sampling Electrical Insulating Liquids
D2285 Test Method for Interfacial Tension of Electrical Insulating Oils of Petroleum Origin Against Water by the Drop-Weight
3
Method (Withdrawn 2008)
3. Summary of Test Method
3.1 Interfacial Tension is determined by measuring the force necessary to detach a planar ring of platinum wire from the surface
of the liquid of higher surface tension, that is, upward from the water-oil water insulating liquid interface. To calculate the
interfacial tension, the force so measured is corrected by an empirically determined factor which depends upon the force applied,
the densities of both oil the insulating liquid and water, and the dimensions of the ring. Measurements are made under rigidly
standardized nonequilibrium conditions in which the measurement is completed within 60 s after formation of the interface.
4. Significance and Use
4.1 Interfacial tension measurements on electrical insulating oilsliquids provide a sensitive means of detecting small amounts
of soluble polar contaminants and products of oxidation. A high value for new mineral insulating oil indicates the absence of most
undesirable polar contaminants. The test is frequently applied to service-aged mineral oils as an indication of the degree of
deterioration.
NOTE 1—Different liquid matrixes are reviewed in Appendix X1.
5. Apparatus (Figs. 1 and 2)
3
5.1 Tensiometer —Force measurement on the tensiometer may be made using a torsion wire, load cell, or any other means of
linearly determining tension in the range of 0 to 100 mN/m.
1
This test method is under the jurisdiction of ASTM Committee D27 on Electrical Insulating Liquids and Gasesand is the direct responsibility of Subcommittee D27.07
on Physical Test.
Current edition approved May 1, 2012April 1, 2020. Published May 2012May 2020. Originally approved in 1948 as D971 – 48 T. Last previous edition approved in
20042012 as D971 – 99aD971 – 12.(2004). DOI: 10.1520/D0971-12.10.1520/D0971-20.
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.
3
Tensiometers that use the Du Nouy principle for measuring interfacial and surface tension should be used.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1
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D971 − 20
FIG. 1 Manual Interfacial Tensiometer
FIG. 2 Top View of Manual Interfacial Tensiometer
5.1.1 Horizontal platform to hold the sample container should be capable of movement upward or downward using a mechanical
screw, lever mechanism, electronic drive, or any other means of precisely changing vertical position of the sample.
5.2 Rings made of platinum or platinum-iridium alloy may be used. The ring s
...
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