GB/T 8926-2012 Determination of Insolubles in Used Lubricating Oils

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Card type: Test method

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

• Standard number: GB/T 8926—2012
• Chinese name: Determination of Insolubles in Used Lubricating Oils
• English name: Standard test method for insolubles in used lubricating oils
• Replacement relationship: replaces GB/T 8926—1988 "Determination of Insolubles in Used Lubricating Oils"
• Adoption relationship: modified adoption by redrafting method of ASTM D893:2005 (2010) "Determination of Insolubles in Used Lubricating Oils"
• Method number: Method A (without coagulant), Method B (with coagulant)
• Publication/implementation: published on 2012-11-05, implemented on 2013-03-01
• Custodianship: Subcommittee on Lubricating Oil Drain Criteria of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC 6)
• Drafting organization: Sinopec Research Institute of Petroleum Processing
• Main drafters: Chen Jie, Yang Tingting, Guo Tao

2. Scope of application and non-applicability

• 1.1 This standard specifies two methods for determining n-pentane insolubles and toluene insolubles in used lubricating oils.
• 1.2 Method A is applicable to the determination of n-pentane insolubles and toluene insolubles in used lubricating oils without coagulant; centrifugation is used to separate the insolubles from the oil-solvent mixture.
• 1.3 Method B is applicable to used lubricating oils containing detergent-dispersant additives, for determining coagulated n-pentane insolubles and coagulated toluene insolubles after adding coagulant; in addition to the substances separated by Method A, this method can also separate some fine substances that may be suspended in the oil.
• Note (after 1.3): Since Method A and Method B often give different values, the results obtained by Method A and Method B are not suitable for mutual comparison. When comparing periodic determination results for one sample, or comparing determination results from two or more laboratories, use the same method.
• Non-applicability: no explicit exclusionary non-applicability clause is provided in the available source.

3. Method principle

• 4.1 Method A: Mix a representative used lubricating oil test portion with n-pentane; after centrifugal separation, decant the upper oil solution, wash the precipitate twice with n-pentane, dry, and then weigh to obtain n-pentane insolubles. For determining toluene insolubles, mix another test portion with n-pentane and centrifuge; wash the precipitate twice with n-pentane, once with toluene-ethanol solution, and once with toluene, then dry the insoluble material and weigh to obtain toluene insolubles.
• 4.2 Method B: Mix a representative used lubricating oil test portion with n-pentane-coagulant solution; after centrifugal separation, wash the precipitate twice with n-pentane, dry, and then weigh to obtain coagulated n-pentane insolubles. For determining coagulated toluene insolubles, mix another test portion with n-pentane-coagulant solution and centrifuge; wash the precipitate twice with n-pentane, once with toluene-ethanol solution, and once with toluene, then dry the insoluble material and weigh to obtain coagulated toluene insolubles.

4. Reagents and materials (purity / preparation)

• 6.1 Purity of reagents: unless otherwise specified, the reagents used in this standard are of analytical reagent grade.
• 6.2 Water: shall meet the requirements for grade three water in GB/T 6682—2008.
• 6.3 n-Butyldiethanolamine: used as secondary coagulant. Warning: harmful if inhaled or swallowed.
• 6.4 95% Ethanol. Warning: flammable.
• 6.5 n-Pentane. Warning: extremely flammable, vapors can cause fire.
• 6.6 Isopropanol. Warning: flammable.
• 6.7 Toluene. Warning: flammable, vapors are harmful.
• 6.8 Toluene-ethanol solution: washing solution, prepared by mixing 1 volumes of toluene with 1 volumes of 95% ethanol solvent. Warning: flammable.
• 6.9 n-Pentane-coagulant solution: prepared by adding 50 mL n-butyldiethanolamine and 50 mL isopropanol to 1 L n-pentane solvent and mixing.
• Warning after 6.9: Because used oil may undergo significant changes during storage, the sample should be tested as soon as possible after being taken from the lubrication system, and the sampling time and test date should be noted.

5. Apparatus and equipment

• 5.1 Centrifuge tube: conical, dimensions shall meet the requirements of Figure 1, made of heat-resistant glass. Graduation requirements are shown in Figure 1; the graduations shall be clear, and the constricted tip shall be able to be tightly stoppered with a cork. The graduation error and the minimum graduations for various calibration marks are shown in Table 1; the centrifuge tube shall be calibrated using 20 ℃ distilled water.
  • Note: For routine analysis, ordinary graduated centrifuge tubes made of heat-resistant glass with a capacity of 100 mL may also be used.
• 5.2 Centrifuge: explosion-proof, shall meet all safety requirements for normal use. It shall be able to rotate two or more centrifuge tubes containing test portions at a certain speed, and this speed shall be controllable to give a relative centrifugal force of 600~700 (rcf) at the end of the centrifuge tube. The rotating head, trunnion rings, and trunnion cups (including rubber pads) shall have good construction to withstand the maximum centrifugal force of the centrifuge. During centrifugation, the trunnion cups and rubber pads shall firmly support the centrifuge tubes. The centrifuge shall be enclosed by a sturdy metal shield or casing to avoid danger. The rotational speed of the centrifuge rotating head n (r/min) is calculated according to formula (1):
  • n = 1337√(rcf/d) ... (1)
  • Where: rcf—— relative centrifugal force 600~700; d—— rotation diameter, the distance between the ends of two opposing centrifuge tubes during rotation, in millimeters (mm).
  • Table 2 gives the correspondence between centrifuge rotation diameter and rotation speed.
• 5.3 Oven: explosion-proof, capable of maintaining temperature at 105 ℃±3 ℃.
• 5.4 Balance: when weighing 100 mL beakers and centrifuge tubes, the balance sensitivity is 0.5 mg. When weighing test portions, the balance sensitivity is 0.1 g.
• 5.5 Graduated cylinder: graduated, capacity 100 mL.

Table 1 Calibration errors for conical centrifuge tubes

Table 2 Rotation speeds applicable to centrifuges with different rotation diameters

• indicates rotation diameter, the distance between the ends of two opposing centrifuge tubes (mm).

Figure 1 Conical centrifuge tube (the source text contains dimension annotations: inner diameter φ17±1, outer diameter φ36~37.75, frosted area (for marking), maximum radius 4, and graduation annotations such as 100/75/50/25/20/15; specific dimensions are subject to the figure in the source text, requires confirmation against the source standard (source-text extraction))

6. Recommended operating conditions

• Centrifugal relative centrifugal force: 600~700 rcf (see 5.2, 8.1.2, 8.1.3, 8.2.2).
• Centrifuge rotation speed: calculated according to formula (1), or selected according to the corresponding rotation diameter in Table 2.
• Centrifugation time: n-pentane insolubles are centrifuged for 20 min±1 min (see 8.1.2, 8.1.3); toluene insolubles are centrifuged for 10 min~20 min, until no visible suspended matter floats in the solution (see 8.2.2).
• Drying temperature: 105 ℃±3 ℃ (see 5.3, 8.1.1, 8.1.5, 8.2.4, 9.1.2).
• Drying time: centrifuge tube pre-drying 30 min (see 8.1.1); n-pentane insolubles drying 30 min (see 8.1.5); toluene insolubles drying 1 h (see 8.2.4).
• Test portion amount: 10.0 g±0.1 g (see 8.1.1).
• Restriction after mixing: do not let the mixture stand for more than 3 h (see 8.1.1).
• Safety note (note after 8.1.2): when handling flammable substances, for safety reasons, a refrigerated centrifuge should be used or centrifuge tubes with screw caps and seals should be used.

7. Sampling and test portion preparation

• 7.1 Unless otherwise specified, sampling shall be carried out in accordance with GB/T 4756 or SY/T 5317.
• 7.2 Heat the in-use oil in its original container to 60 ℃±5 ℃, and shake until all sediment is uniformly suspended in the oil. If the original container is made of opaque material, or if the sample amount exceeds three-quarters of the container volume, transfer the entire sample to a transparent glass bottle at least one-third larger than the sample volume, shake the sample in the original container vigorously, and transfer all traces of sediment from the original container to the transparent glass bottle. After all sediment is completely suspended, filter the entire sample or an appropriate test portion through a 150 μm screen to remove large contaminant particles.
• 7.2 Note: If the sample is clear and transparent and obviously free of sediment, the above filtration step may be omitted.
• 9.1.2 If it is known that the test portion contains water, or that the gum sediment contains water, before testing the test portion should first be placed in an open beaker, dried in an oven at 105 ℃±3 ℃, and then the test portion should be tested.

8. Analysis Steps

8 Method A: n-Pentane and Toluene Insolubles Without Coagulant

8.1 n-Pentane Insolubles

• 8.1.1 Place a clean centrifuge tube in an oven at 105 ℃±3 ℃ and dry it for 30 min, cool it in a desiccator, and weigh it to the nearest 1 mg. Add the prepared 10.0 g±0.1 g test portion to the centrifuge tube, and add n-pentane to the centrifuge tube until it is filled to the 100 mL mark; stopper the centrifuge tube tightly and shake until the mixture is uniformly mixed. Do not let the mixture stand for more than 3 h.
• 8.1.2 Open the stopper, and using a wash bottle with a nozzle, wash the insolubles on the stopper into the centrifuge tube with the minimum amount of n-pentane. Balance the mass of each pair of centrifuge tubes filled with test portion and solvent, place the centrifuge tubes into two symmetrical rotating heads of the centrifuge, and centrifuge for 20 min±1 min at the rotational speed of the corresponding centrifuge rotor when the relative centrifugal force calculated according to formula (1) is 600~700 (see Table 2). Without disturbing or dispersing the sediment, decant the supernatant liquid so that the liquid remaining in the centrifuge tube does not exceed 3 mL.
  • Note: When handling flammable substances, for safety reasons a refrigerated centrifuge should be used or centrifuge tubes with screw caps and seals should be used.
• 8.1.3 Add 10 mL±1 mL n-pentane to the centrifuge tube. Use a clean metal wire to break up and loosen all insolubles at the bottom of the centrifuge tube, rinse the insolubles adhering to the metal wire into the centrifuge tube with an appropriate amount of n-pentane until the centrifuge tube is filled to the 50 mL mark. Stopper the centrifuge tube tightly and shake until the mixture is uniformly mixed. Open the stopper and wash the insolubles on the stopper into the centrifuge tube with the minimum amount of n-pentane. Balance the mass of each pair of centrifuge tubes, place the centrifuge tubes into two symmetrical rotating heads of the centrifuge, and centrifuge for 20 min±1 min at the rotational speed of the corresponding centrifuge rotor when the relative centrifugal force calculated according to formula (1) is 600~700 (see Table 2). Carefully decant the supernatant liquid, avoiding disturbing the insolubles at the bottom of the centrifuge tube.
• 8.1.4 Repeat the test procedure specified in 8.1.3.
• 8.1.5 Place the centrifuge tube containing the washed sediment in an oven at 105 ℃±3 ℃ and dry it for 30 min, cool it in a desiccator, and weigh it to the nearest 1 mg.
• 8.1.6 When the sediment is heavy, if the centrifuge tube is placed directly into the oven, splashing may occur. In this case, before placing the centrifuge tube into the oven, the sediment may be allowed to dry locally naturally at room temperature or slightly elevated temperature.

8.2 Toluene Insolubles

• 8.2.1 Take a fresh test portion, repeat the test procedure of 8.1.1~8.1.4, precipitate and centrifuge the n-pentane insolubles, but do not dry the n-pentane insolubles in the centrifuge tube.
• 8.2.2 Add 10 mL±1 mL toluene-ethanol solution to the centrifuge tube, use a clean metal wire to break up and loosen all insolubles at the bottom of the centrifuge tube, rinse the insolubles adhering to the metal wire into the centrifuge tube with an appropriate amount of toluene-ethanol solution until the centrifuge tube is filled to the 50 mL mark. Stopper the centrifuge tube tightly and shake until the mixture is uniformly mixed. Open the stopper and wash the insolubles on the stopper into the centrifuge tube with the minimum amount of toluene. Balance the mass of each pair of centrifuge tubes, place the centrifuge tubes into two symmetrical rotating heads of the centrifuge, and centrifuge for 10 min–20 min at the rotational speed of the corresponding centrifuge rotor when the relative centrifugal force calculated according to formula (1) is 600–700 (see Table 2), until no visible suspended matter floats in the solution. Carefully decant the supernatant liquid from the centrifuge tube, taking care not to disturb the sediment.
• 8.2.3 Repeat the test procedure of 8.2.2 using toluene instead of toluene-ethanol solution.
• 8.2.4 Place the centrifuge tube in an oven at 105 ℃±3 ℃ and dry it for 1 h, cool it in a desiccator, and weigh it to the nearest 1 mg.

9 Method B: Coagulated n-Pentane Insolubles and Coagulated Toluene Insolubles with Coagulant

9.1 Coagulated n-Pentane Insolubles

• 9.1.1 Carry out the test according to the test procedures of 8.1.1 and 8.1.2, except that in the test procedure of 8.1.1, n-pentane-coagulant solution is used instead of n-pentane. Wash the sediment twice with n-pentane according to 8.1.3 and 8.1.4, dry and weigh the centrifuge tube according to 8.1.5.
• 9.1.2 If it is known that the test portion contains water, or that the gum sediment contains water, before testing the test portion should first be placed in an open beaker, dried in an oven at 105 ℃±3 ℃, and then the test portion should be tested.

9.2 Coagulated Toluene Insolubles

• Carry out the test according to the test procedures of 8.1.1 and 8.1.2, except that in the test procedure of 8.1.1, n-pentane-coagulant solution is used instead of n-pentane. Wash the sediment twice with n-pentane according to 8.1.3 and 8.1.4, wash the sediment with toluene-ethanol solution and toluene according to 8.2.2 and 8.2.3, dry and weigh the centrifuge tube according to 8.2.4.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 10.1 The insolubles in the in-use oil (mass fraction) w (%), calculated according to formula (2):
  • w = 100(B − A) / m … (2)
  • Where: A—— mass of the clean, dry empty centrifuge tube, in grams (g); B—— mass of the dried insolubles and centrifuge tube, in grams (g).
  • Note: In the original formula (2), the symbol for the test portion mass is missing in the source-text extraction text (only two symbol explanations A and B are seen); the denominator symbol requires confirmation against the source standard (source-text extraction).
• 11.1 If Method A is used (see Chapter 8), report the n-pentane insolubles and toluene insolubles of the test portion, expressed as mass fraction (%).
• 11.2 If Method B is used (see Chapter 9), report the coagulated n-pentane insolubles and coagulated toluene insolubles of the test portion, expressed as mass fraction (%).
• 11.3 Insoluble gum or coagulated insoluble gum may be reported according to Method A or Method B, i.e., expressed as n-pentane insolubles minus toluene insolubles.

10. Precision

• 12.1 Precision: Judge the reliability of test results according to the following provisions (95% confidence level).
• 12.1.1 Repeatability, r: In the same laboratory, by the same operator using the same apparatus, according to the same method, the difference between two test results obtained from continuous determination of the same test portion shall not exceed the following values:
  • 12.1.1.1 Method A n-Pentane Insolubles and Method B Coagulated n-Pentane Insolubles (see Table 3).

Table 3

• 12.1.1.2 Method A Toluene Insolubles and Method B Coagulated Toluene Insolubles (see Table 4).

Table 4

• Note: The repeatability data for toluene insolubles and coagulated toluene insolubles are calculated by formula (3): r = 0.216√I … (3)
• Where: I—— mean of toluene insolubles or mean of coagulated toluene insolubles.
• 12.1.2 Reproducibility, R: In different laboratories, by different operators using different apparatus, according to the same method, the difference between two single, independent results obtained from determination of the same test portion shall not exceed the following values:
  • 12.1.2.1 Method A n-Pentane Insolubles and Method B Coagulated n-Pentane Insolubles (see Table 5).

Table 5

• 12.1.2.2 Method A Toluene Insolubles (see Table 6).

Table 6

• Note: The repeatability data for toluene insolubles are calculated by formula (4): R₁ = 0.441√I_A … (4)
• Where: I_A—— is the average value of toluene insolubles.
• 12.1.2.3 Method B toluene insolubles after coagulation (see Table 7).

Table 7

• Note 1: The repeatability data for toluene insolubles after coagulation are calculated by formula (5): R₂ = 0.957√I_B … (5)
• Where: I_B—— is the average value of toluene insolubles after coagulation.
• Note 2: Because the interlaboratory precision (repeatability R₂) of this part of the standard is poor, the results of method B for toluene insolubles after coagulation are not suitable for comparison of results between laboratories.
• 12.2 Bias: Because the mass fraction of insolubles is defined only in this standard, the test procedure of this method has no bias.

11. Report

• 11.1 If method A is used (see Chapter 8), report the n-pentane insolubles and toluene insolubles of the sample, expressed as mass fraction (%).
• 11.2 If method B is used (see Chapter 9), report the n-pentane insolubles after coagulation and toluene insolubles after coagulation of the sample, expressed as mass fraction (%).
• 11.3 Insoluble gums or insoluble gums after coagulation may be reported according to method A or method B, that is, expressed as n-pentane insolubles minus toluene insolubles.
• 6.9 Post-warning: The sample should be tested as soon as possible after being taken from the lubrication system, and the sampling time and test date should be noted.
• Other report format requirements: not provided in the available source.

12. Normative references

• GB/T 4756 Petroleum liquids — Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6682—2008 Specifications and test methods for water for analytical laboratory use (ISO 3696:1987, MOD)
• SY/T 5317 Petroleum liquids — Automatic pipeline sampling (SY/T 5317—2006, ISO 3171:1988, IDT)
• Reference principle (Chapter 2): For dated references, only the dated version applies to this document; for undated references, the latest version (including all amendments) applies to this document.

13. Source and verification

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