ASTM D1275-24

Standard Test Method for Corrosive Sulfur in Electrical Insulating Liquids

SIGNIFICANCE AND USE
3.1 In most of their uses, insulating liquids are continually in contact with metals that are subject to corrosion. The presence of elemental sulfur or corrosive sulfur compounds will result in deterioration of these metals and cause conductive or high resistive films to form. The extent of deterioration is dependent upon the quantity and type of corrosive agent and time and temperature factors. Detection of these undesirable impurities, even though not in terms of quantitative values, is a means for recognizing the hazard involved.  
3.2 Two methods are provided, one for copper corrosion and one for silver corrosion. Copper is slightly less sensitive to sulfur corrosion than silver but the results are easier to interpret and less prone to error. The silver corrosion procedure is provided especially for those users who have applications where the insulating liquid is in contact with a silver surface.
SCOPE
1.1 This test method describes the detection of corrosive sulfur compounds (both inorganic and organic) in electrical insulating liquids.  
1.2 New and in-service insulating liquids may contain elemental sulfur or sulfur compounds, or both, that cause corrosion under certain conditions of use. This test method is designed to detect the presence of, or the propensity to form, free (elemental) sulfur and corrosive sulfur compounds by subjecting copper or silver to contact with an insulating liquid under prescribed conditions.  
1.3 The values stated in SI units are to be regarded as the standard. Inch-pound units are included for informational purposes.  
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

• Status: Published
• Publication Date: 14-Jan-2024
• ICS: 29.040.10 - Insulating oils
• Technical Committee: D27 - Electrical Insulating Liquids and Gases
• Drafting Committee: D27.06 - Chemical Test

Relations

• Replaces: ASTM D1275-15 - Standard Test Method for Corrosive Sulfur in Electrical Insulating Liquids
• Effective Date: 15-Jan-2024
• Referred By: ASTM D117-22 - Standard Guide for Sampling, Test Methods, and Specifications for Electrical Insulating Liquids
• Effective Date: 15-Jan-2024
• Referred By: ASTM D6871-17 - Standard Specification for Natural (Vegetable Oil) Ester Fluids Used in Electrical Apparatus
• Effective Date: 15-Jan-2024
• Referred By: ASTM D5222-23 - Standard Specification for Less Flammable High Molecular Weight Hydrocarbon Mineral Electrical Insulating Liquids
• Effective Date: 15-Jan-2024
• Referred By: ASTM D8240-22e1 - Standard Specification for Less-Flammable Synthetic Ester Liquids Used in Electrical Apparatus
• Effective Date: 15-Jan-2024
• Referred By: ASTM D3487-16e1 - Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus
• Effective Date: 15-Jan-2024
• Referred By: ASTM D8180-23 - Standard Specification for Rerefined Mineral Insulating Liquid Used in Electrical Apparatus
• Effective Date: 15-Jan-2024

Overview

ASTM D1275-24 is the internationally recognized standard test method for detecting corrosive sulfur in electrical insulating liquids. Electrical insulating liquids, commonly used in transformers and other electrical equipment, are in frequent contact with metal components such as copper and silver. The presence of elemental sulfur or sulfur compounds in these insulating liquids can result in severe corrosion, leading to equipment deterioration and the formation of conductive or resistive films that compromise performance.

This standard outlines procedures for detecting corrosive sulfur using copper and silver corrosion tests, helping organizations identify and manage risks associated with corrosive impurities in both new and in-service insulating liquids.

Key Topics

• Corrosive Sulfur Detection: Describes test methods for detecting both inorganic and organic corrosive sulfur compounds in electrical insulating liquids.
• Test Methods: Provides two approaches:
  • Copper Corrosion Procedure: Involves aging a copper strip with the insulating liquid under controlled conditions and visually inspecting for corrosion.
  • Silver Corrosion Procedure: Similar to copper, but designed for cases where insulating liquid is in contact with silver surfaces.
• Test Conditions: Both procedures expose metal strips to the insulating liquid at 150 °C for 48 hours in sealed, nitrogen-purged bottles to simulate operational conditions.
• Interpretation: Samples are classified as corrosive or noncorrosive based on visual inspection, with copper and silver strip color changes indicating the presence of corrosive sulfur.
• Controls and Reporting: Ensures accuracy through use of positive and negative control samples, and requires comprehensive reporting of test findings, including classification and tarnish levels.

Applications

ASTM D1275-24 is crucial in industries reliant on electrical insulating liquids for equipment performance and longevity. Key applications include:

• Transformer Oil Monitoring: Regular testing of transformer oils prevents costly failures due to metal corrosion.
• Quality Assurance for Manufacturers: Insulating liquid producers use the standard to verify product safety before distribution.
• Utility and Industrial Maintenance: Power and industrial facilities routinely test in-service liquids to assess risk and plan maintenance.
• Research and Product Development: Laboratories and R&D teams use the test methods for evaluating new insulating liquids or additives.
• Regulatory Compliance: Meets requirements for government and industry safety standards related to electrical equipment.

By reliably identifying corrosive sulfur, the standard supports equipment reliability, reduces unplanned outages, and extends asset life.

Related Standards

ASTM D1275-24 is part of a broader framework of standards for electrical insulating oils and corrosion testing. Related standards include:

• ASTM D130 - Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test
• ASTM D923 - Practices for Sampling Electrical Insulating Liquids
• DIN 51 353 - Testing of Insulating Oils; Detection of Corrosive Sulfur, Silver Strip Test
• ANSI B74.10 - Grading of Abrasive Microgrits
• ASTM E11 - Specification for Woven Wire Test Sieve Cloth and Test Sieves

Keywords: corrosive sulfur, electrical insulating liquids, copper corrosion, silver corrosion, transformer oil, ASTM D1275-24, equipment reliability, sulfur compounds, corrosion testing, insulating oil standards.

By following ASTM D1275-24, users ensure that their electrical insulating liquids are noncorrosive and maintain the integrity and performance of critical electrical infrastructure.

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: D1275 − 24
315/98
Standard Test Method for
Corrosive Sulfur in Electrical Insulating Liquids
This standard is issued under the fixed designation D1275; 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 adopted for use by government agencies to replace Method 5328-2 of Federal Test Method Standard No. 791b.
This standard was adopted as an ASTM-IP Standard.
This standard has been approved for use by agencies of the U.S. Department of Defense.
INTRODUCTION
Prior to 2006, this test method existed as a singular method in which the main aging parameters of
the test specimen were 19 h at 140 °C. In 2006, it was determined that those parameters were
inadequate (not sensitive enough to detect all levels of corrosive sulfur) and Method B was instituted
in which the main aging parameters were 48 h at 150 °C. The old parameters were kept as Method A
to avoid any confusion. The 2015 edition of this test method for the copper corrosion procedure reverts
back to a singular method in which the main aging parameters are the same as the previous Method
B (2006-2014). Results from the current test method cannot be compared or correlated to the method
prior to 2006 and only to Method B from 2006 to 2014.
1. Scope 1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This test method describes the detection of corrosive
ization established in the Decision on Principles for the
sulfur compounds (both inorganic and organic) in electrical
Development of International Standards, Guides and Recom-
insulating liquids.
mendations issued by the World Trade Organization Technical
1.2 New and in-service insulating liquids may contain
Barriers to Trade (TBT) Committee.
elemental sulfur or sulfur compounds, or both, that cause
corrosion under certain conditions of use. This test method is
2. Referenced Documents
designed to detect the presence of, or the propensity to form,
2.1 ASTM Standards:
free (elemental) sulfur and corrosive sulfur compounds by
D130 Test Method for Corrosiveness to Copper from Petro-
subjecting copper or silver to contact with an insulating liquid
leum Products by Copper Strip Test
under prescribed conditions.
D923 Practices for Sampling Electrical Insulating Liquids
1.3 The values stated in SI units are to be regarded as the E11 Specification for Woven Wire Test Sieve Cloth and Test
standard. Inch-pound units are included for informational Sieves
purposes.
2.2 Other Document:
ANSI B74.10 Grading of Abrasive Microgrits
1.4 This standard does not purport to address all of the
DIN 51 353 Testing of Insulating Oils; detection of corrosive
safety concerns, if any, associated with its use. It is the
sulfur, silver strip test
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This test method is under the jurisdiction of ASTM Committee D27 on the ASTM website.
Electrical Insulating Liquids and Gases and is the direct responsibility of Subcom- Available from American National Standards Institute, 25 W. 43rd St., 4th
mittee D27.06 on Chemical Test. Floor, New York, NY 10036, USA.
Current edition approved Jan. 15, 2024. Published February 2024. Originally Available from Deutsches Institut für Normung e.V.(DIN), Am DIN-Platz,
approved in 1953. Last previous edition approved in 2015 as D1275 – 15. DOI: Burggrafenstrasse 6, 10787 Berlin, Germany, http://www.din.de or http://
10.1520/D1275-24. www.bleuth.de
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1275 − 24
3. Significance and Use 5.4 Suitable Solvent—Technical grade acetone, heptane,
hexane and pentane.
3.1 In most of their uses, insulating liquids are continually
in contact with metals that are subject to corrosion. The 5.5 Water, distilled.
presence of elemental sulfur or corrosive sulfur compounds
6. Summary of Test Methods
will result in deterioration of these metals and cause conductive
or high resistive films to form. The extent of deterioration is
6.1 Copper Corrosion—220 mL of insulating liquid is aged
dependent upon the quantity and type of corrosive agent and
in a sealed heavy-walled bottle for 48 h at 150 °C in the
time and temperature factors. Detection of these undesirable
presence of a copper strip.
impurities, even though not in terms of quantitative values, is
6.2 Silver Corrosion—220 mL of insulating liquid is aged in
a means for recognizing the hazard involved.
a sealed heavy-walled bottle for 48 h at 150 °C in the presence
3.2 Two methods are provided, one for copper corrosion and
of a silver strip.
one for silver corrosion. Copper is slightly less sensitive to
7. Preparation of Apparatus
sulfur corrosion than silver but the results are easier to interpret
and less prone to error. The silver corrosion procedure is
7.1 Chemically clean bottles and PTFE screw plugs with
provided especially for those users who have applications
solvents to remove insulating liquid residue, then wash the
where the insulating liquid is in contact with a silver surface.
bottles with a suitable solvent such as heptane or hexane, or use
a phosphate-type cleaning powder or liquid. Rinse with tap
4. Apparatus
water, then with distilled water, and dry in an oven. Replace the
fluoro-elastomer O-ring before each test to avoid cross con-
4.1 Bath—A hot-air oven or liquid bath provided with
tamination or a compromised seal.
suitable means of heating to, and controlling at 150 °C 6 2 °C.
A circulating hot-air oven is preferred.
7.2 Polish a larger piece of copper or silver foil from which,
after the final polishing, several strips of the proper size may be
4.2 Bottles —Heavy-walled, 250 mL, bottles of chemically
cut. Remove blemishes from both surfaces of the copper or
resistant glass constructed with necks to receive a polytet-
silver foils with the 240-grit silicon carbide paper or sanding
rafluoroethylene (PTFE) threaded plug equipped with a fluoro-
pads. Cut a strip(s) of copper or silver foil 6 mm by 25 mm
elastomer O-ring. Bottles of such capacity and design are
( ⁄4 in. by 1 in.). Strips may be stored in sulfur-free acetone at
required in order to allow sufficient space for expansion of the
this point for future use. Do the final polishing of the strip by
insulating liquid and to eliminate intrusion from atmospheric
removing it from the acetone, holding it in the fingers protected
gases. Flat bottomed bottles are preferred.
with ashless filter paper or nitrile gloves, and rubbing with
4.3 Copper Foil, 99.9+ % pure, 0.127 mm to 0.254 mm
230-mesh silicon carbide grains picked up from a glass plate
(0.005 in. to 0.010 in.) in thickness.
with a pad of absorbent cotton moistened with a drop of
4.4 Silver Foil, 99.99+ % pure, 0.5 mm thick.
acetone. Wipe the strip with fresh pads of cotton and subse-
quently handle only with stainless steel forceps (do not touch
4.5 Polishing Material, consisting of 240-grit silicon car-
with fingers). Rub in the direction of the long axis of the strip.
bide paper or cloth (refer to Specification E11), and also
Clean all metal dust and abrasive from the strip, using
230-mesh silicon carbide grains and pharmaceutical absorbent
successive clean cotton pads until a fresh pad remains unsoiled.
cotton. Aluminum oxide or silicon carbide sanding pads can be
Bend the clean strip in a V-shape at approximately a 60° angle
substituted but the surface finish of the foil piece must closely
and wash successively in acetone, distilled water, and acetone.
mirror that of using silicon paper or cloth.
Dry in an oven for 3 min to 5 min at 80 °C to 100 °C and
NOTE 1—It should be noted that 240-grit silicon carbide paper and
immediately immerse the copper or silver strip in the prepared
230-mesh silicon carbide grains have particle sizes of about the same size
test specimen of insulating liquid (Note 2). Do not use
(63 μm). In the United States, abrasive papers are classified in accordance
with ANSI B74.10. Abrasive powders are classified by ASTM mesh size. compressed air or an inert gas to dry the metal strip.
NOTE 2—This method of cleaning has been adapted from Test Method
5. Reagents
D130.
5.1 Acetone, ACS reagent grade.
8. Copper Corrosion Procedure
5.2 Hydrochloric Acid—ACS reagent grade, 36.5 % to
8.1 Retrieve a sample for testing in accordance with Prac-
38.0 % assay.
tices D923. Use the insulating liquid to be tested as received.
5.3 Nitrogen Gas—Commercial cylinders of nitrogen gas
Do not filter the insulating liquid.
are satisfactory for this purpose.
8.2 Promptly place the prepared copper strip in a clean
250 mL bottle to which has been added 220 mL of the
5 insulating liquid to be tested. Place the bent copper strip
The sole source of supply of the Bottles and PTF screw plugs known to the
standing on its long edge so that no flat surface lies along the
committee at this time is Prism Research Glass, P.O. Box 14187, Research Triangle
Park, NC 27709, part number DOB-B-250. If you are aware of alternative suppliers,
glass bottom of the vessel. Bubble nitrogen through the
please provide this information to ASTM International Headquarters. Your com-
insulating liquid in the bottle by means of a 1.5 mm inner
ments will receive careful consideration at a meeting of the responsible technical
diameter (approximately ⁄16 in. inner diameter) glass or
committee, which you may attend. Laboratories already using bottles from Ace
Glass can continue. stainless steel tube connected to the reduction or needle valve
D1275 − 24
TABLE 1 Copper Strip Classifications
of the cylinder (connections must be sulfur-free) for 5 min at a
rate of 0.5 L/min. Quickly screw in the PTFE plug equipped
...

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: D1275 − 15 D1275 − 24
315/98
Standard Test Method for
Corrosive Sulfur in Electrical Insulating Liquids
This standard is issued under the fixed designation D1275; 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 adopted for use by government agencies to replace Method 5328-2 of Federal Test Method Standard No. 791b.
This standard was adopted as an ASTM-IP Standard.
This standard has been approved for use by agencies of the U.S. Department of Defense.
INTRODUCTION
Prior to 2006, this test method existed as a singular method in which the main aging parameters of
the test specimen were 19 h at 140°C.140 °C. In 2006, it was determined that those parameters were
inadequate (not sensitive enough to detect all levels of corrosive sulfur) and Method B was instituted
in which the main aging parameters were 48 h at 150°C.150 °C. The old parameters were kept as
Method A to avoid any confusion. The current2015 edition of this test method for the copper corrosion
procedure reverts back to a singular method in which the main aging parameters are the same as the
previous Method B (2006-2014). Results from the current test method cannot be compared or
correlated to the method prior to 2006 and only to Method B from 2006 to 2014.
1. Scope
1.1 This test method describes the detection of corrosive sulfur compounds (both inorganic and organic) in electrical insulating
liquids.
1.2 New and in-service insulating liquids may contain elemental sulfur or sulfur compounds, or both, that cause corrosion under
certain conditions of use. This test method is designed to detect the presence of, or the propensity to form, free (elemental) sulfur
and corrosive sulfur compounds by subjecting copper or silver to contact with an insulating liquid under prescribed conditions.
1.3 The values stated in SI units are to be regarded as the standard. Inch-pound units are included for informational purposes.
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.
This test method is under the jurisdiction of ASTM Committee D27 on Electrical Insulating Liquids and Gases and is the direct responsibility of Subcommittee D27.06
on Chemical Test.
Current edition approved Nov. 15, 2015Jan. 15, 2024. Published January 2016February 2024. Originally approved in 1953. Last previous edition approved in 20062015
as D1275 – 06D1275 – 15. which was withdrawn January 2015 and reinstated in December 2015. DOI: 10.1520/D1275-15.DOI: 10.1520/D1275-24.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D1275 − 24
2. Referenced Documents
2.1 ASTM Standards:
D130 Test Method for Corrosiveness to Copper from Petroleum Products by Copper Strip Test
D923 Practices for Sampling Electrical Insulating Liquids
E11 Specification for Woven Wire Test Sieve Cloth and Test Sieves
2.2 Other Document:
ANSI B74.10 Grading of Abrasive Microgrits
DIN 51 353 Testing of Insulating Oils; detection of corrosive sulfur, silver strip test
3. Significance and Use
3.1 In most of their uses, insulating liquids are continually in contact with metals that are subject to corrosion. The presence of
elemental sulfur or corrosive sulfur compounds will result in deterioration of these metals and cause conductive or high resistive
films to form. The extent of deterioration is dependent upon the quantity and type of corrosive agent and time and temperature
factors. Detection of these undesirable impurities, even though not in terms of quantitative values, is a means for recognizing the
hazard involved.
3.2 Two methods are provided, one for copper corrosion and one for silver corrosion. Copper is slightly less sensitive to sulfur
corrosion than silver but the results are easier to interpret and less prone to error. The silver corrosion procedure is provided
especially for those users who have applications where the insulating liquid is in contact with a silver surface.
4. Apparatus
4.1 Bath—A hot-air oven or liquid bath provided with suitable means of heating to, and controlling at 140 or 150 6 2°C.150 °C
6 2 °C. A circulating hot-air oven is preferred.
4.2 Bottles —Heavy-walled, 250-mL,250 mL, bottles of chemically resistant glass constructed with necks to receive a
polytetrafluoroethylene (PTFE) threaded plug equipped with a fluoro-elastomer O-ring. Bottles of such capacity and design are
required in order to allow sufficient space for expansion of the insulating liquid and to eliminate intrusion from atmospheric gases.
Flat bottomed bottles are preferred.
4.3 Copper Foil, 99.9+ % pure, 0.1270.127 mm to 0.254 mm (0.005(0.005 in. to 0.010 in.) in thickness.
4.4 Silver Foil, 99.99+ % pure, 0.5 mm thick.
4.5 Polishing Material, consisting of 240-grit silicon carbide paper or cloth (refer to Specification E11), and also 230-mesh silicon
carbide grains and pharmaceutical absorbent cotton. Aluminum oxide or silicon carbide sanding pads can be substituted but the
surface finish of the foil piece must closely mirror that of using silicon paper or cloth.
NOTE 1—It should be noted that 240-grit silicon carbide paper and 230-mesh silicon carbide grains have particle sizes of about the same size (63 μm).
In the United States, abrasive papers are classified in accordance with ANSI B74.10. Abrasive powders are classified by ASTM mesh size.
5. Reagents
5.1 Acetone, ACS reagent grade.
5.2 Hydrochloric Acid—ACS reagent grade, 36.5 to 38.0 % 36.5 % to 38.0 % assay.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American National Standards Institute, 25 W. 43rd St., 4th Floor, New York, NY 10036, USA.
Available from Deutsches Institut für Normung e.V.(DIN), Am DIN-Platz, Burggrafenstrasse 6, 10787 Berlin, Germany, http://www.din.de or http://www.bleuth.de
The sole source of supply of the Bottles and PTF screw plugs known to the committee at this time is Prism Research Glass, P.O. Box 14187, Research Triangle Park,
NC 27709, part number DOB-B-250. If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will
receive careful consideration at a meeting of the responsible technical committee, which you may attend. Laboratories already using bottles from Ace Glass can continue.
D1275 − 24
5.3 Nitrogen Gas—Commercial cylinders of nitrogen gas are satisfactory for this purpose.
5.4 Suitable Solvent—technicalTechnical grade acetone, heptane, hexane and pentane.
5.5 Water, distilled.
6. Summary of Test Methods
6.1 Copper Corrosion—220 mL of insulating liquid is aged in a sealed heavy-walled bottle for 48 h at 150°C150 °C in the
presence of a copper strip.
6.2 Silver Corrosion—220 mL of insulating liquid is aged in a sealed heavy-walled bottle for 48 h at 150°C150 °C in the presence
of a silver strip.
7. Preparation of Apparatus
7.1 Chemically clean bottles and PTFE screw plugs with solvents to remove insulating liquid residue, then wash the bottles with
a suitable solvent such as heptane or hexane, or ususe a phosphate-type cleaning powder or liquid. Rinse with tap water, then with
distilled water, and dry in an oven. Replace the fluoro-elastomer O-ring before each test to avoid cross contamination.contami-
nation or a compromised seal.
7.2 Polish a larger piece of copper or silver foil from which, after the final polishing, several strips of the proper size may be cut.
Remove blemishes from both surfaces of the copper or silver foils with the 240-grit silicon carbide paper. paper or sanding pads.
Cut a strip(s) of copper or silver foil 66 mm by 25 mm ( ⁄4 in. by 1 in.). Strips may be stored in sulfur-free acetone at this point
for future use. Do the final polishing of the strip by removing it from the acetone, holding it in the fingers protected with ashless
filter paper or nitrile gloves, and rubbing with 230-mesh silicon carbide grains picked up from a glass plate with a pad of absorbent
cotton moistened with a drop of acetone. Wipe the strip with fresh pads of cotton and subsequently handle only with stainless steel
forceps (do not touch with fingers). Rub in the direction of the long axis of the strip. Clean all metal dust and abrasive from the
strip, using successive clean cotton pads until a fresh pad remains unsoiled. Bend the clean strip in a V-shape at approximately
a 60° angle and wash successively in acetone, distilled water, and acetone. Dry in an oven for 33 min to 5 min at 80 to 100°C80 °C
to 100 °C and immediately immerse the copper or silver strip in the prepared test specimen of insulating liquid (Note 2). Do not
use compressed air or an inert gas to dry the metal strip.
NOTE 2—This method of cleaning has been adapted from Test Method D130.
8. Copper Corrosion Procedure
8.1 Retrieve a sample for testing in accordance with Practices D923. Use the insulating liquid to be tested as received. Do not filter
the insulating liquid.
8.2 Promptly place the prepared copper strip in a clean 250-mL250 mL bottle to which has been added 220 mL of the insulating
liquid to be tested. Place the bent copper strip standing on its long edge so that no flat surface lies along the glass bottom of the
vessel. Bubble nitrogen through the insulating liquid in the bottle by means of a 1.5 mm inner diameter (approximately ⁄16 in. inner
diameter) glass or stainless steel tube connected to the reduction or needle valve of the cylinder (connections must be sulfur-free)
for 5 min at a rate of 0.5 L/m
...