GB/T 25961-2010 Test method for corrosive sulfur in electrical insulating oils

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 25961-2010
• Chinese title: Test method for corrosive sulfur in electrical insulating oils
• English title: Standard test method for corrosive sulfur in electrical insulating oils
• Replacement relationship: not provided in the available source (the foreword only states modified adoption of ASTM D1275-06, and does not mention replacement of an old standard)
• Adoption relationship: modified adoption of ASTM D1275-06 Test method for corrosive sulfur in electrical insulating oils
• Issued / implemented: issued on 2011-01-10, implemented on 2011-05-01
• Main differences from ASTM D1275-06 (according to the foreword):
  • In clause 1, added “This standard applies to...”, and made ASTM 1.2 the introduction of this standard
  • Deleted ASTM 1.3 (all units are in the International System of Units)
  • Made the content of ASTM 1.4 the warning of this standard
  • In clause 2, added reference to GB/T 6682 (distilled water for cleaning test bottles)
  • Made clause 4 “Significance and use” of ASTM the introduction of this standard, with corresponding changes to clause numbering
  • Deleted ASTM 3.1 and the content of method A in clause 8 (method A has been transformed into a Chinese petrochemical industry standard)
  • In the reagents clause, added petroleum ether, anhydrous ethanol, and distilled water (for cleaning copper strips)
  • Deleted the keywords in clause 13 of ASTM
  • Deleted clauses 4, 8, and 13 of ASTM, and adjusted the numbering of other clauses according to the order after deletion

2. Applicable scope and non-applicability

• Applicable to: detection of corrosive sulfides (inorganic and organic sulfides) in new and in-service petroleum-based electrical insulating oils.
• Not applicable: no explicit non-applicable clause is provided in the available source.
• Note: the source does not provide the distinction of method A/B (the content of method A has been deleted).

3. Method principle

Place the prepared copper strip into a sealed thick-walled high-temperature-resistant test bottle containing 220 mL insulating oil, maintain at 150 ℃ for 48 h, and after the test observe the color change of the copper strip to determine the corrosion caused by sulfur and sulfides.

4. Reagents and materials (purity / preparation)

• 4.5 Abrasive: 240-grade silicon carbide sandpaper or abrasive cloth with particle size 63 μm; 63 μm silicon carbide powder, meeting the requirements of GB/T 2480.
• 5.1 Acetone: analytical reagent.
• 5.2 Petroleum ether: analytical reagent.
• 5.3 Anhydrous ethanol: analytical reagent.
• 5.4 Distilled water: meeting the grade-three water requirements in GB/T 6682.
• 5.5 Nitrogen: purity not lower than 99.9%.
• 4.4 Copper strip: purity 99.9%, thickness 0.127 mm~0.254 mm, uncontaminated.
• Others: sulfur-free laundry powder or other sulfur-free detergent; sulfur-free rubber tubing; quantitative filter paper; medical absorbent cotton; synthetic fiber gloves.

5. Instruments and equipment

• 4.1 Oven: temperature controlled at 150 ℃±2 ℃, preferably a forced-circulation constant-temperature blast oven.
• 4.2 Test bottle: 250 mL thick-walled high-temperature-resistant test bottle with a narrow neck and internal threads, made of chemically resistant glass; the neck is a threaded mouth, sealed with a PTFE (polytetrafluoroethylene) threaded stopper with a fluoroelastomer “O” ring to prevent air from entering (see Figure 1).
• 4.3 Tweezers: stainless steel, flat tip.
• 7.2 Glass tube or stainless steel tube: inner diameter 1.6 mm, connected to the pressure reducing valve or needle valve of the nitrogen cylinder.
• Figure 1 Schematic of the test bottle: 1— internally threaded mouth; 2—250 mL thick-walled high-temperature-resistant glass bottle with a narrow neck and internal threads; 3—PTFE threaded stopper; 4— fluoroelastomer O ring.

6. Recommended operating conditions

• Test temperature: 150 ℃±2 ℃.
• Holding time: 48 h±20 min.
• Nitrogen purge rate: 0.5 L/min, pass nitrogen for 5 min.
• Copper strip drying: dry in an oven at 80 ℃–100 ℃ for 3 min–5 min.
• After heating for about 15 min, loosen the bottle stopper to release pressure, then tighten it again.

7. Sampling and specimen preparation

• 7.1 The specimen should not be filtered.
• Specimen amount: 220 mL.
• Copper strip preparation (6.2): cut a 6 mm×25 mm copper strip, wipe off surface stains with 240-grade coarse silicon carbide sandpaper; after treatment, store in sulfur-free acetone for later use; before use, take it out of the acetone for final polishing: place quantitative filter paper underneath, wear synthetic fiber gloves and press the copper strip, use medical absorbent cotton moistened with acetone to pick up an appropriate amount of 63 μm silicon carbide powder from a glass plate and polish the copper strip surface; then use tweezers to hold fresh medical absorbent cotton and wipe forcefully along the long axis to remove all metal powder and abrasive until fresh cotton shows no marks; bend the polished copper strip into a V shape, with an angle of about 60°; successively clean with acetone, distilled water, and acetone, dry in an oven at 80 ℃–100 ℃ for 3 min–5 min, immediately remove and immerse in the specimen. The copper strip should not be dried with compressed air or inert gas.
• Note: It is also possible to polish a large piece of copper strip and then cut it into several copper strips of the correct size.

8. Analysis procedure

• 6.1 Cleaning of the test bottle: first rinse the test bottle and PTFE threaded stopper with chemical solvents (such as petroleum ether, anhydrous ethanol, etc.) to remove oil contamination, then wash with sulfur-free laundry powder or other sulfur-free detergent, then rinse with tap water, then rinse with distilled water, and finally dry in an oven.
• 7.2 Quickly place the prepared copper strip into a clean 250 mL test bottle containing 220 mL specimen, with the copper strip standing on its long edge at the bottom of the bottle, avoiding contact between the copper strip surface and the bottle bottom; connect a glass tube or stainless steel tube with inner diameter 1.6 mm to the pressure reducing valve or needle valve of the nitrogen cylinder (the rubber tubing must be sulfur-free), pass nitrogen into the specimen at a rate of 0.5 L/min for 5 min, then quickly install the PTFE bottle stopper with a fluoroelastomer “O” ring and tighten it.
• 7.3 Place the test bottle in an oven at 150 ℃, heat for about 15 min, then loosen the bottle stopper to release pressure, then tighten it again to prevent the test bottle from bursting; maintain at 150 ℃±2 ℃ for 48 h±20 min, then remove, cool to room temperature, carefully remove the copper strip with tweezers, clean the copper strip with acetone or another suitable solvent, and air-dry. The copper strip should not be dried with compressed air.
• 7.4 Observation: hold the tested copper strip and observe with light reflected from the copper strip at an angle of about 45°; if the copper strip surface has edge lines or is unclean, forcefully wipe its surface with a clean filter paper; as long as sediment falls off, report it as corrosion, and the sediment is the result of corrosion.

9. Qualitative and quantitative determination and calculation formula

• This method is a qualitative/semi-qualitative judgment, with no calculation formula.
• Result judgment (Table 1 Basis for judging copper strip corrosiveness):
  • Non-corrosive: the test strip is orange, red, light purple, with light purplish blue, or silver, or both, and multicolored respectively covering purplish red, silver, brass color or golden yellow, multicolored with magenta covering brass color, multicolored with red and green shown (peacock green), but without gray.
  • Corrosive: the test strip is obviously black, dark gray, or brown; graphite black or lusterless black; glossy black or jet-black shiny black, with any degree of peeling.
• Corrosiveness judgment may also use the copper strip corrosion standard color plate in GB/T 5096; Table 2 provides the corrosion standard color plate classification, for reference only:
  • Classification 1 Light discoloration: a. light orange, almost the same as freshly polished copper strip; b. dark orange
  • Classification 2 Moderate discoloration: a. purplish red; b. light purple; c. with light purplish blue or silver, or both, and multicolored respectively covering purplish red; d. silver; e. brass color or golden yellow; f. multicolored with magenta covering brass color; g. multicolored with red and green shown (peacock green), but without gray
  • Classification 3 Deep discoloration: a. obviously black, dark gray, or brown with only peacock green; b. graphite black or lusterless black; c. glossy black or jet-black shiny black
  • Classification 4 Corrosion: not provided in the available source (the content of this row in source-text extraction is missing / requires confirmation against the source standard)
  • Freshly polished copper strip: freshly polished copper strip cannot reproduce its appearance due to aging, so no description is given

10. Precision

This standard does not specify precision and bias, because the test result only indicates whether it matches the specified judgment basis, rather than being a quantitative analysis.

11. Report

Report the following:

• Sample name and number;
• Whether the specimen is corrosive or non-corrosive;
• Discoloration level, according to GB/T 5096.

12. Normative references

• GB/T 2480 Common abrasives—Silicon carbide
• GB/T 5096 Test method for copper strip corrosion of petroleum products
• GB/T 6682 Specifications and test methods for water used in analytical laboratories (GB/T 6682—2008, ISO 3696:1987, MOD)
• Note: In clause 2 of the source, GB/T 2480 and GB/T 5096 are not marked with a year; GB/T 6682 is marked as GB/T 6682—2008.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Q&A reference