NB/SH/T 0836-2010 Determination of acidity value of insulating oil Automatic potentiometric titration method

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Card type: Test method

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

• Standard number: NB/SH/T 0836—2010 (the original cover source-text extraction writes "NB/SII/T 0836—_201 0", the page header writes "NB/SH/T 0836—2010", the page header and main text shall prevail)
• Chinese name: Determination of acidity value of insulating oil Automatic potentiometric titration method
• English name: Determination of acidity of insulating liquids—Automatic potentiometric titration (the original cover source-text extraction writes "Determination of addity of insulating liqlli buckle Automatic potenliometric titration", requires confirmation against the source standard (source-text extraction))
• Adoption relationship: modified adoption of IEC 62021-1:2003 "Insulating liquids—Determination of acidity—Part 1:Automatic potentiometric titration" (MOD)
• Replacement relationship: not provided in the available source
• Publication/implementation: published on 2010-05-01, implemented on 2010-10-01; issued by the National Energy Administration
• Drafting organization: Lanzhou Lubricating Oil Research and Development Center of PetroChina Lubricant Company
• Drafters: Cheng Xingguo, Wei Xiaona
• Custodianship: Petroleum Fuels and Lubricants Subcommittee of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC1)
• Proposed by: China Petrochemical Corporation
• Appendix: Appendix A is an informative appendix (comparison list of clause numbers of this standard and IEC 62021-1:2003 clause numbers)

2. Scope of application and non-applicability

• 1.1 This standard specifies the method for determining the acidity value of unused and used electrical mineral insulating oils.
  • Note: In unused and used electrical mineral insulating oils, acidic components include organic acids, phenolic compounds, oxidation products, resins, metal-organic salts and additives.
• 1.2 This standard can be used to indicate the relative changes that occur when mineral insulating oil is used under oxidizing conditions, regardless of whether its color or other properties change.
• 1.3 The acidity value can be used for quality control of unused electrical mineral insulating oil.
• 1.4 In used electrical mineral insulating oil, various oxidation products affect the acidity value, and these oxidation products have different corrosiveness. This standard cannot be used to predict the corrosiveness of electrical mineral insulating oil in service.
  • Note: The acidity value results determined by this standard may be the same as or different from the results determined by GB/T 4945 and GB/T 7304, but they are usually of the same order of magnitude.

3. Method principle

Dissolve the sample in solvent, under nitrogen protection, use a glass indicating electrode and a reference electrode, perform potentiometric titration with potassium hydroxide isopropanol solution, automatically plot the potentiometer readings and the volume of titrant, and when the endpoint pH value is 11.5, read the corresponding volume as the titration endpoint. (Chapter 4)

4. Reagents and materials (purity / preparation)

Unless otherwise specified, all reagents used are analytical grade reagents. Water shall meet the requirements for Grade GB/T 6682 water.

• 5.1 Potassium hydroxide isopropanol solution (this clause source-text extraction in the original text is severely incomplete; only "take 3?g potassium hydroxide [incomplete]…" "stored solution…in ±10mL isopropanol…cool, then stopper the flask…" can be recognized; the specific concentration and preparation steps require confirmation against the source standard (source-text extraction))
• 5.2 Titration solvent (the original text source-text extraction is incomplete; only "5.2.1 (see 5.2)…" is visible; composition and preparation require confirmation against the source standard (source-text extraction))
• 5.3 Titration solvent (the original text source-text extraction is incomplete; only "5.3…" is visible; composition and preparation require confirmation against the source standard (source-text extraction))
• 5.4 Saturated potassium chloride isopropanol electrolyte (reference electrode electrolyte; changed from saturated potassium chloride aqueous solution to saturated potassium chloride isopropanol solution, see the foreword difference explanation)
• 5.5 Standard buffer solution for calibration (the original text source-text extraction is incomplete; only "5.5 calibration [garbled]…" is visible; the specific buffer type and pH value require confirmation against the source standard (source-text extraction))
• 5.6 Electrode (the original text source-text extraction is incomplete; it involves terms such as potassium hydrogen phthalate and potassium hydroxide isopropanol solution; the specific content requires confirmation against the source standard (source-text extraction))
• 5.7 Nitrogen: purity not less than 99.9%
• Warning: Ammonium persulfate is a strongly corrosive agent; handle with care (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))
• Others: commercial cleaning solution recommended by the electrode manufacturer; alkali asbestos (or soda lime) drying tube, replaced regularly (the original text source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction))

5. Instruments and equipment

(Chapter 6; the original text source-text extraction is severely incomplete; the following is the recognizable content, and the rest requires confirmation against the source standard (source-text extraction))

• 6.1 Automatic pH titrator: can change or fix the titration amount; the instrument must be grounded to avoid stray currents; requires a precision of at least... (value requires confirmation against the source standard (source-text extraction))
• 6.2 Titrant container: one titrant container, ... (the original text is incomplete, requires confirmation against the source standard (source-text extraction)); automatic burette
• 6.3 Glass indicating electrode: it is recommended to use a ... glass electrode; the electrode is connected to the potentiometer with a cable
• 6.4 Magnetic stirrer
• 6.5 ... (the original text is incomplete, requires confirmation against the source standard (source-text extraction))

6. Recommended operating conditions

• Titration endpoint pH value: 11.5 (Chapter 4, 10.2.3)
• Nitrogen protection: add nitrogen protection during titration to eliminate the influence of carbon dioxide in the air (foreword); during blank titration, introduce nitrogen into the beaker at a flow rate of 3.0 L/h～4.0 L/h 20 s to expel air, then adjust the nitrogen flow rate to 10 L/h±0.1 L/h, and adjust the stirring speed to prevent sample splashing (10.1.2 Note)
• Amount of titration solvent: 20 mL±0.1 mL (10.1.1, 10.2.1); when the titration solvent is 80 mL, the sample amount can be correspondingly increased to 20 g±2.0 g (foreword, 10.2.1 Note)
• Titrant: 0.05 mol/L potassium hydroxide isopropanol solution (10.2.3)
• It is recommended to use dynamic titrant addition to reduce analysis time (10.2.3 Note)
• Instrument calibration: measure the pH reading of the standard buffer solution every day, extrapolate the titration endpoint pH value as 11.5 and input it into the instrument program; for the potentiometric titrator pH, the linearity and slope outside 4～11 must meet the deviation required by the instrument manufacturer; the instrument requires temperature correction (Chapter 9)

7. Sampling and sample preparation

• Prepare the titration sample as described in Chapter 7 (10.2.1). The original text source-text extraction of Chapter 7 is severely incomplete; only terms such as "7.1", "7....", and an isolated, incomplete word are visible; the specific sampling requirements require confirmation against the source standard (source-text extraction).
• Foreword difference explanation: In this standard, according to China's actual situation, the sampling chapter gives separate sampling requirements for unused oil and used oil.
• Referenced sampling methods: GB/T 4756 Petroleum liquids manual sampling method; GB/T 7597 Sampling method for power oils (transformer oil, turbine oil) (Chapter 2).

8. Analysis steps

8.1 Blank titration (10.1)

• 10.1.1 After replacing with a batch of fresh titration solvent, perform blank titration twice a day according to clause 10.2 using 20 mL±0.1 mL titration solvent.
• 10.1.2 Under nitrogen protection, continuously perform blank titration with 20 mL titration solvent until the difference between two consecutive determinations is less than 0.005 mL, and take the average value as K (see Chapter 11).
  • Note: Introduce nitrogen into the beaker at a flow rate of 3.0 L/h～4.0 L/h 20 s to expel the air in the beaker, then adjust the nitrogen flow rate to 10 L/h±0.1 L/h, and adjust the stirring speed to prevent sample splashing.
• 10.1.3 Absorption of carbon dioxide by the titration solvent or the inherent acidity value in isopropanol will cause the blank titration measured value to increase. If the potassium hydroxide isopropanol solution titration exceeds 0.06 mL (based on 20 mL solvent), measures need to be taken to eliminate the occurrence of a higher measured value.
  • Note: When the blank titration is 80 mL titration solvent, until the difference between two consecutive determinations is less than 0.01 mL, take the average value as K. Absorption of carbon dioxide by the titration solvent or the inherent acidity value in isopropanol will cause the measured value to increase. If the potassium hydroxide isopropanol solution titration exceeds 0.10 mL, measures need to be taken to eliminate the occurrence of a higher measured value.

8.2 Sample titration (10.2)

• 10.2.1 Prepare the titration sample as described in Chapter 7, weigh 5 g±0.1 g sample in the titration cell, to the nearest 0.001 g. Add 20 mL±0.1 mL titration solvent (see 5.3).
  • Note: When the titration solvent is 80 mL, the sample amount can be correspondingly increased to 20 g±2.0 g, to the nearest 0.001 g.
• 10.2.2 Place the titration cell on the titration stand, and under nitrogen protection, stir the solution until the sample is completely dissolved and the pH reading is unchanged. Limit the stirring speed to prevent sample splashing or air entrainment into the solution.
• 10.2.3 Under nitrogen protection, according to the procedure recommended by the instrument manufacturer, titrate with 0.05 mol/L potassium hydroxide isopropanol to the endpoint where the pH value is 11.5. If the instrument cannot set the titration to stop immediately, the endpoint will be higher.
  • Note: It is best to use dynamic titrant addition to reduce analysis time.
• 10.2.4 When the pH value is 11.5, complete the titration, read the burette reading, and record it as V.
• 10.2.5 Rinse the electrode and burette tip with titration solvent (see 5.2). Immerse the glass bulb of the glass electrode in water to rehydrate it, and remove excess water. When analyzing used oil samples, first soak the electrode in water containing a few drops of hydrochloric acid, then rinse with water.
• 10.2.6 If there is still titration work that has not yet been carried out, store the electrode in water.

8.3 Electrode maintenance (8.2)

• 8.2.1 Clean the electrode weekly… (the original source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction)); for further cleaning, immerse the glass electrode… into…; once a month.
• 8.2.1.2 When not in use, immerse the… end of the electrode in 0.1 mol/L… (the original source-text extraction is incomplete, requires confirmation against the source standard (source-text extraction)), then rinse with water.
• 8.2.2.1 For the reference electrode, replace the saturated potassium chloride isopropanol electrolyte at least once a week (see 5.4). When using a sleeve-type electrode, carefully remove the upper ground-glass sleeve and thoroughly clean both surfaces of the glass sleeve. Gently put the sleeve back so that a few drops of electrolyte are expelled to rinse the glass joint and wet the ground-glass surface. Reset the glass sleeve and refill with saturated potassium chloride isopropanol electrolyte (see 5.4).
• 8.2.2.2 When the reference electrode is not in use, the electrode should be immersed in potassium chloride isopropanol electrolyte (see 5.4), and the electrolyte level in the electrode should be kept higher than the level of the fluid in which it is immersed. During storage, close the filling hole with a stopper.
• 8.2.2.3 If necessary, clean the electrode with water at least once a week. Refill with potassium chloride isopropanol electrolyte (see 5.4).

9. Qualitative and quantitative determination and calculation formula

The acid value of the sample is calculated according to formula (3), mgKOH/g:

Acid value = (V − K) × C × 56.1 / m

Where:

• V—— volume of potassium hydroxide isopropanol solution used for titrating the sample, mL;
• K—— volume of potassium hydroxide isopropanol solution used for blank titration, mL;
• C—— molar concentration of the potassium hydroxide isopropanol solution, mol/L;
• m—— mass of the sample, g;
• 56.1—— molar mass of potassium hydroxide, g/mol.

(The original formula source-text extraction reads “acid value: [garbled formula]…(3)”; the main body of the formula has been restored according to the symbol explanation in Chapter 11, requires confirmation against the source standard (source-text extraction))

Term definitions (Chapter 3):

• 3.1 Acid value acidity: the amount of alkali required per 1 g of sample when a sample undergoes potentiometric titration in a specific solvent and the pH value reaches 11.5, expressed as mgKOH/g.
• 3.2 Unused oil unused oil: electrical mineral insulating oil that has not been used or has not come into contact with electrical equipment.

10. Precision

The reliability of test results is judged according to the following provisions (95% confidence level). Note: For unused oil with an acid value less than or equal to 0.05 mgKOH/g, the establishment of precision refers to GB/T 5683 (thus in the original, requires confirmation against the source standard (source-text extraction), in the reference it is GB/T 6683).

12.1 Repeatability

In the same laboratory, by the same operator using the same instrument, according to the same method, the difference between two results obtained from continuous determination of the same sample shall not be greater than the value specified in Table 1:

Table 1 Repeatability

12.2 Reproducibility

By different operators, in different laboratories, using different instruments, according to the same method for determination of the same sample, the difference between two single, independent results obtained shall not be greater than the value specified in Table 2:

Table 2 Reproducibility

11. Report

Take the average of two measurement results. For unused oil with an acid value less than or equal to 0.05 mgKOH/g, the result shall be accurate to 0.001 mgKOH/g; other results shall be accurate to 0.01 mgKOH/g. (Chapter 13)

12. Normative references

Standards cited in Chapter 2:

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6682 Water for analytical laboratory use—Specification and test methods (GB/T 6682—2008, ISO 3696:1987, MOD)
• GB/T 7597 Sampling method for power oils (transformer oil, turbine oil)

References:

• [1] GB/T 4945 Determination of acid and base numbers of petroleum products and lubricants (color indicator method)
• [2] GB/T 6683 Determination of precision data for test methods of petroleum products
• [3] GB/T 7304 Determination of acid number of petroleum products and lubricants (potentiometric titration method)

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 reference Q&A