Standard Active Last Updated: Apr 27, 2020
ASTM D971-20

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.


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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Book of Standards Volume: 10.03
Developed by Subcommittee: D27.07
Pages: 4
DOI: 10.1520/D0971-20
ICS Code: 75.100