GB/T 12581-2006 Determination of oxidation characteristics of inhibited mineral oils

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Card type: Test method

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

• Standard number: GB/T 12581—2006
• Chinese name: Determination of oxidation characteristics of inhibited mineral oils
• English name: Standard test method for oxidation characteristics of inhibited mineral oils
• Replacement relationship: replaces GB/T 12581—1990
• Adoption relationship: modified adoption of ASTM D943-04a "Determination of oxidation characteristics of inhibited mineral oils"
• Publication/implementation: published on 2006-01-01, implemented on 2007-01-01
• Proposal/administration/drafting: proposed by China Petrochemical Corporation; administered by the Petrochemical Research Institute of China Petroleum & Chemical Corporation; drafting organization is the Lubricant Research and Development Center of PetroChina Company Limited; main drafters are Yu Bing, Su Jiang, Li Jianxin
• Previous versions: GB/T 12581—1990

2. Scope of application and non-applicability

• 1.1 specifies a method for evaluating the oxidation stability of inhibited turbine oils at high temperature and in the presence of oxygen, water, and metallic copper and iron. This method limits the maximum test time to 10000 h. This method is also applicable to other oils, such as hydraulic oils and other circulating oils with a relative density less than that of water and containing rust inhibitors and antioxidants.
• 1.2 uses International System of Units [SI] units.
• 1.3 involves certain hazardous materials, operations, and equipment, but it is not intended to address all safety issues associated with them; users should establish appropriate safety and protective measures and determine applicable management systems before use.
• Not applicable: no explicit non-applicable clauses are listed in the source text (except that Appendix A itself states it is not applicable to monitoring in-service oils, the main text does not list non-applicable scope).

3. Method principle

• Method summary (Chapter 3): The sample reacts with oxygen in the presence of water and an iron-copper catalyst at 95 °C, and the test is continued until the acid value of the sample reaches or exceeds 2.0 mgKOH/g. The test time required for the acid value of the sample to reach 2.0 mgKOH/g is the "oxidation life".
• Significance and use (Chapter 4): widely used in product specifications and for evaluating the oxidation stability of lubricants, especially lubricants easily contaminated by water; the correlation between its results and the oxidation stability of lubricants used in the field varies significantly with different service conditions and lubricants; the precision statement is based on measurements obtained from turbine oils.
• Note (Chapter 4): When using this method for testing, other deterioration phenomena may occur in the oil, such as sludge formation or corrosion of the catalyst coil, which are not reflected in the "oxidation life"; alternative methods for evaluating lubricants using this apparatus are under study; a test method for determining sludge tendency is already available, SH/T 0565.

4. Reagents and materials (purity / preparation)

• 6.1 Water purity: unless otherwise specified, water used in this method shall meet the requirements for grade two water according to GB/T 6682 specifications.
• 6.2 Reagent purity: generally analytical reagent grade; other grades are also permitted as long as the reagent purity can ensure that measurement precision is not affected.
• 6.3 Acetone: analytical reagent grade. Warning: harmful to health, flammable.
• 6.4 Catalyst coil
  • 6.4.1 Iron wire: high-quality carbon structural steel, diameter 1.6 mm (GB/T 699 specification 08 grade).
  • 6.4.2 Copper wire: cathode copper, diameter 1.6 mm (GB/T 5231 specification T2 grade), purity not less than 99.9%; soft copper wire of equivalent grade may also be used.
  • Note: commercially available catalyst coils may be purchased.
• 6.5 Detergent: water-soluble.
• 6.6 n-Heptane: analytical reagent grade. Warning: harmful if inhaled, flammable.
• 6.7 Concentrated hydrochloric acid: concentration (mass fraction) 36%, relative density 1.19. Warning: toxic and corrosive.
• 6.8 Isopropanol: analytical reagent grade. Warning: flammable.
• 6.9 Oxygen: purity not less than 99.5%, with suitable pressure regulation so that the oxygen flow rate through the apparatus remains constant; it is recommended to use a two-stage pressure regulator on the oxygen cylinder. Warning: vigorously accelerates combustion.
• 6.10 Cleaning agent: chromic acid cleaning solution. At room temperature, soak the items to be cleaned in chromic acid cleaning solution for 24 h for cleaning. Warning: corrosive, harmful to health.
• Appendix A Reagents (A.6):
  • A.6.1 Reagent purity: all tests shall use analytical reagent grade reagents; other grades are also permitted as long as the purity can ensure that measurement precision is not affected.
  • A.6.2 Acid value reference solution: any stable, oil-soluble acid that can produce an acid value of about 0.5 mgKOH/g may be used; this solution shall be standardized with GB/T 4945 or GB/T 7304; it has been demonstrated that a HVI 250 base oil containing 0.20% (mass fraction) dodecenylsuccinic anhydride can meet the requirements.
  • A.6.3 0.1 M Alcoholic potassium hydroxide solution: dissolve potassium hydroxide in isopropanol to prepare an approximately 0.1 M solution, standardize with pure potassium hydrogen phthalate dissolved in 100 mL water, and detect the endpoint using phenolphthalein as indicator (commercially available reagents may be used). Warning: corrosive, toxic if inhaled, alkaline, can cause irritation leading to dermatitis.
  • A.6.4 Dodecenylsuccinic anhydride. Warning: irritating to skin and eyes.
  • A.6.5 p-Naphtholbenzein indicator solution: p-naphtholbenzein must meet the specification requirements of GB/T 4945—2002 Appendix A; prepare a solution containing p-naphtholbenzein 10 g/L in 50:50 toluene:isopropanol mixed solvent. Warning: flammable, vapors harmful. Note: companies such as Fisher can supply p-naphtholbenzein indicator solution.
  • A.6.6 Isopropanol. Warning: flammable; reports indicate that if not inhibited, when containers storing isopropanol or reagent preparation bottles become empty and nearly dry, peroxides can be produced and explosive mixtures can form.
  • A.6.7 Titration solution: in a plastic bottle with a volume of 1 L, mix 350 mL toluene, 350 mL isopropanol, and 7 mL p-naphtholbenzein solution, add 15 mL 0.1 M potassium hydroxide isopropanol solution and mix well. Warning: flammable, vapors harmful, corrosive. Note: the concentration of the titration solution decreases over time, so it needs to be replaced periodically; replacing once a month can meet the requirements.
  • A.6.8 Toluene. Warning: flammable, vapors harmful.
• Appendix B Materials (B.1):
  • B.1.1 Test tube: made of borosilicate glass, length 250 mm, outer diameter 25 mm, inner diameter approximately 22 mm.
  • B.1.2 Cap: for test tubes, made of polyethylene, designed as a cylinder that can fit tightly over the outer surface of the test tube.
  • B.1.3 Desiccant packet: silica gel particles.
  • B.1.4 Flushing tube: made of stainless steel or glass, outer diameter approximately 5 mm, length 305 mm, used to deliver nitrogen to the bottom of the test tube.
  • B.1.5 Nitrogen: minimum purity 99.7%. Warning: compressed gas under high pressure. This gas can reduce the oxygen available for breathing.

5. Apparatus and equipment

• 5.1 Oxidation tube: includes test tube, condenser, and oxygen delivery tube, made of borosilicate glass, as shown in Figure 1; the test tube is marked with a 300 mL line at 20 °C (maximum error 1 mL).
• 5.2 Heating bath: capable of maintaining the sample temperature in the oxidation tube at 95 °C±0.2 °C, equipped with suitable stirring device to maintain uniform temperature throughout the heating bath, with dimensions sufficient to accommodate the required number of oxidation tubes, and ensuring that the insertion depth of the oxidation tubes in the heating bath is 390 mm±10 mm, and the immersion depth in the heating medium is 355 mm±10 mm. Note: a metal heating bath meeting the test method requirements may also be used; the type of heating bath used when the precision of this standard was determined has not been clearly established.
  • 5.2.1 Research has shown that direct sunlight or light can adversely affect the results of this test; to reduce the effect of light exposure on the sample, one or more of the following methods can be used to prevent the sample from being exposed to light.
  • 5.2.1.1 It is recommended to use a heating bath made of metal or metal and other opaque materials to prevent light from entering the test tube from the side; if an observation window is designed on the heating bath, an opaque cover should be installed on the observation window and kept closed when not observing.
  • 5.2.1.2 If a glass heating bath is used, the heating bath should be wrapped with aluminum foil or other opaque material.
  • 5.2.1.3 Using an opaque shield can prevent bright light from entering the test tube from the top.
• 5.3 Flowmeter: flow rate at least 3 L/h, accuracy 0.1 L/h.
• 5.4 Heating bath thermometer: oxidation characteristics thermometer No. 2, measurement range 72 °C~126 °C, meeting the requirements for thermometer GB-58 in GB/T 514; temperature measuring devices of equivalent or higher accuracy may also be used.
• 5.5 Oxidation tube thermometer: oxidation characteristics thermometer No. 1, measurement range 80 °C–100 °C, graduation value 0.1 °C, total length 250 mm, stem outer diameter 6.0 mm–7.0 mm, immersion depth 76 mm; meeting the requirements for thermometer GB-57 in GB/T 514; temperature measuring devices of equivalent or higher accuracy may also be used.
• 5.6 Thermometer holder: material is 1Cr18Ni9Ti stainless steel, used to fix the oxidation tube thermometer, dimensions as shown in Figure 2; the thermometer is fixed on the holder by two fluoroelastomer "O" type rings with an inner diameter of approximately 5.5 mm; thin stainless steel wire may also be used.
• 5.7 Catalyst coil winding rod: as shown in Figure 3.
• 5.8 Abrasive cloth: grain size 100 (basic particle size range 150 μm~125 μm), silicon carbide abrasive cloth.
• 5.9 Syringe: made of glass, with a volume of 10 mL and 50 mL, used respectively for sampling and replenishing water.
• 5.10 Injection sampling tube: 1Cr18Ni9Ti stainless steel tube, outer diameter 2.11 mm, inner diameter 1.60 mm, length 559 mm±2 mm, one end is machined to an angle of 90°, and the other end is equipped with a well-sealed connector that can be connected to the syringe; the connector is preferably made of an elastic material, such as polyfluorochloroethylene.
• 5.11 Stopper: used for sealing the connector of the injection sampling tube, made of polytetrafluoroethylene or polyfluorochloroethylene.
• 5.12 Sampling tube holder: used to support the injection sampling tube, material is methacrylate resin; dimensions are shown in Figure 4.
• 5.13 Sampling tube sleeve: placed above the sampling tube holder, used to fix the position of the end of the sampling tube; made of plastic tube, with an inner diameter of about 3 mm, a length of about 51 mm±1 mm, and material is polyvinyl chloride, polyethylene, polypropylene, or polytetrafluoroethylene.
• 5.14 Hose: inner diameter about 6.4 mm, wall thickness 2.4 mm, material polyvinyl chloride, used to introduce oxygen into the oxidation tube.
• Appendix A Apparatus (A.5):
  • A.5.1 10 mL glass beaker or glass bottle.
  • A.5.2 2 mL~5 mL glass syringe, a 5 mL syringe with a 20 gauge, 12 cm needle can meet the requirements.
  • A.5.3 Glass dropper with rubber bulb, capable of dispensing 35 to 40 drops of oil.

6. Recommended operating conditions

• Reaction temperature: 95 °C±0.2 °C (Chapter 3, 5.2, 9.5.1).
• Oxygen flow rate: 3 L±0.1 L, continuous aeration 30 min (9.3).
• Water addition: add 60 mL distilled water to the test tube (9.4); during the test, at least once every two weeks add distilled water to the oxidation tube to restore the water level to the shoulder of the oxygen delivery tube (9.6).
• Condenser outlet water temperature: during the test, it should not exceed 32 °C (9.2).
• Oxidation tube immersion depth: 355 mm±10 mm (5.2, 9.2).
• Maximum test time: 10000 h (1.1, 9.8.1).
• Sampling interval: test 500 h and thereafter every 168 h (one week) sample 3 mL (9.7.1); after the test time reaches 3000 h, sample and test every 500 h±25 h (9.7.2); when the oil is near the end of its test life, additional sampling is performed at the operator's discretion (9.7.3).
• Thermometer reading correction: because the thermometer's 76 mm immersion line is located at the oil surface, considering the heating of the thermometer stem above the immersion line, in order to obtain the true temperature, subtract 0.1 °C from the thermometer reading (9.5 Note 2).
• Bath temperature setting: the oil bath temperature can only be set using a new, unaltered sample under the conditions of water and oxygen flow as described in 9.2, or a dedicated simulated oxidation tube can be used for temperature measurement; the simulated oxidation tube must also contain an unaltered sample and be supplied with water and oxygen as described in 9.2 (9.5).

7. Sampling and sample preparation

• 7.1 The sample for this test can be taken from tanks, drums, small containers, or even equipment in operation; sampling is carried out in accordance with GB/T 4756.
• 7.2 The minimum sample amount required for a single test is 300 mL.
• 9.2 Add the sample to an empty oxidation tube up to the 300 mL mark.
• Appendix A Sampling (A.7.1): according to the steps specified in the oxidation test method, withdraw the minimum amount of test oil from the oxidation tube. Note: because oxidized oil undergoes significant changes during storage, the oil sample taken from the oxidation test apparatus should be tested as soon as possible.

8. Analytical procedure

• 8 Preparation of apparatus
  • 8.1 Cleaning the catalyst: before winding the catalyst coil, use absorbent cotton dipped in n-heptane to clean one each of iron wire and copper wire of length 3.00 m±0.01 m, then rub with emery cloth until a fresh metal surface is exposed; wipe off all metal and emery cloth debris with dry absorbent cotton; in subsequent operations, wear clean gloves (cotton, rubber, or plastic) when handling the catalyst coil to avoid contact with skin.
  • 8.2 Preparation of the catalyst coil: twist one end of the prepared iron wire and copper wire tightly together for three turns, then wind the two metal wires side by side simultaneously onto a threaded catalyst coil winding rod (see Figure 3), with the iron wire placed in the deeper thread; remove the coil from the winding rod, twist the free ends of the iron wire and copper wire together for three turns, then bend the two twisted ends into a shape that meets the requirements of the spiral coil; the total length of the wound coil is 225 mm±5 mm; if necessary, the coil can be stretched to the required length. Note: the finished catalyst coil is a double helix of copper wire and iron wire, with a total length of 225 mm±5 mm, inner diameter 15.9 mm–16.5 mm; the spacing between coils is uniform, and the center-to-center distance between adjacent turns of the same metal wire is 3.96 mm–4.22 mm; the winding rod shown in Figure 3 is designed to make such a coil; when using this winding rod, the iron wire is wound on a thread of diameter 14.98 mm, and the copper wire is wound on a thread of diameter 15.9 mm; the smaller diameter is to allow for springback of the iron wire after winding, so as to obtain a coil with a uniform inner diameter of 15.9 mm; if very soft annealed steel wire is used, both metal wires can be wound using the same thread diameter; other schemes that can produce a coil structure meeting the above requirements may also be used.
  • 8.3 Catalyst storage: before use, the catalyst coil may be stored in a dry inert gas; Appendix B gives a suitable procedure for storing the catalyst; before use, check to ensure that no corrosion products or contaminants are present on the catalyst coil; for overnight storage (less than 24 h), the coil may be stored in n-heptane; the n-heptane used for storing the catalyst must not contain traces of water and corrosive substances; n-heptane that meets the requirements of 6.6, redistilled and stored in a sealed bottle, may be used.
  • 8.4 Cleaning of new glassware: clean new oxygen delivery tubes, condensers, and test tubes with hot detergent solution, then rinse with tap water; clean the inside of the test tube, the outside of the condenser, and the inside and outside of the oxygen delivery tube with cleaning agent; thoroughly wash off the cleaning agent solution with tap water; then rinse all parts with distilled water and allow them to dry at room temperature or in an oven; after rinsing with distilled water, they may also be rinsed with isopropanol or acetone, or blown with dry air to accelerate drying at room temperature.
  • 8.5 Cleaning of used glassware: immediately after a test is completed, pour out all the oil in the test tube; rinse the glassware with n-heptane to remove oil stains, pour in hot detergent solution, clean with a long-handled brush, then rinse with tap water; if deposits still adhere to the glassware, fill the test tube with detergent solution, insert the oxygen delivery tube and condenser, and place the test tube in a heating bath controlled at the test temperature; soaking in this way for several hours will dissolve all adhering substances except iron oxide; then clean with hot (50 °C) hydrochloric acid to remove iron oxide; after removing all deposits, rinse all glassware with cleaning agent; rinse thoroughly with tap water until all acid is removed; then rinse all parts with distilled water and dry at room temperature or in an oven; after rinsing with distilled water, they may also be rinsed with isopropanol or acetone, or blown with dry air to accelerate drying at room temperature; before preparation for use, glassware should be stored in a dry, dust-free place.
  • 8.6 Cleaning of used sampling tube: immediately after a test is completed, drain all the oil from the sampling tube; rinse the sampling tube with n-heptane to remove oil stains and all adhering organic residues; repeatedly rinse with n-heptane and blow dry with air or nitrogen.
• 9 Test procedure
  • 9.1 Before conducting the test, adjust the temperature of the heating bath to about 95 °C; for final temperature adjustment, see 9.5.
  • 9.2 Add the sample to an empty oxidation tube up to the 300 mL mark; slide the catalyst coil down from above the oxygen delivery tube inlet; if the wires at one end of the coil are uneven, place that end downward; place the oxygen delivery tube together with the catalyst coil into the test tube; place the condenser on top of the oxygen delivery tube and test tube; place the sampling tube holder on top of the oxygen delivery tube; as shown in Figure 5, insert the injection sampling tube through the sampling tube sleeve and into the sampling tube holder; place the bottom end of the sampling tube inside the catalyst coil; insert a stopper into the connector of the sampling tube; immerse the test tube in the heating bath; adjust the liquid level of the heating bath so that the depth of the test tube immersed in the liquid is 355 mm±10 mm; connect the condenser to cooling water; during the test, the outlet water temperature of the condenser should not exceed 32 °C. Note: an alternative method to the sampling tube holder and sampling tube sleeve is to fix the sampling tube to the oxygen delivery tube with tape or a clamp; the sampling tube is fixed to the oxygen delivery tube at a position about 25 mm from the top of the condenser, and the bottom of the sampling tube is located at a distance of 152 mm±6 mm from the bottom of the bent end of the oxygen delivery tube.
  • 9.3 Use a new polyvinyl chloride hose with a length not exceeding 600 mm to connect the oxygen delivery tube to the oxygen source through a flow meter; before use, the new polyvinyl chloride hose should be cleaned on the inner wall with n-heptane and blown dry with air; adjust the flow rate to 3 L±0.1 L and aerate continuously for 30 min.
  • 9.4 Lift the condenser from the oxidation tube, add 60 mL distilled water to the test tube, and begin recording the oxidation time.
  • 9.5 Only new, un-degraded samples may be used to set the oil bath temperature under the conditions of water and oxygen flow as described in 9.2, or a dedicated simulated oxidation tube may be used for temperature measurement; the simulated oxidation tube must also be filled with un-degraded sample and have water and oxygen flow as described in 9.2. Note 1: When the oil sample in the simulated oxidation tube degrades significantly, it must be replaced periodically. Note 2: The installation is as shown in Figure 6. Since the 76 mm immersion line of the thermometer is located at the oil surface, considering the heating of the thermometer stem above the immersion line, in order to obtain the true temperature, 0.1 °C should be subtracted from the thermometer reading.
  • 9.5.1 Set the bath temperature so that it ensures the temperature of the un-degraded oil sample or simulated oxidation tube is controlled at 95 °C±0.2 °C. Use a thermometer or other temperature measuring device for temperature measurement; the thermometer or temperature measuring device is positioned in the oxidation tube by a thermometer holder, as shown in Figure 2; when using a simulated oxidation tube, it must be removed immediately after the temperature is set; when using an actual sample, the temperature measuring device must be removed immediately after the bath temperature is set; the bath temperature must always be higher than the sample temperature due to the cooling effect of the oxygen flow, and is related to the heating bath medium, capacity, circulation rate, and the number of oxidation tubes in the bath.
  • 9.5.2 Verify the uniformity of the bath temperature by measuring the temperature of simulated oxidation tubes or new, un-degraded test samples at different positions in the heating bath.
  • 9.5.3 During the oxidation test, periodically check and adjust the bath temperature according to the instructions in 9.5 and 9.5.1, using new, un-degraded oil samples or simulated oxidation tubes.
  • 9.6 During the test, add distilled water to the oxidation tube at least once every two weeks to restore the water level to the shoulder of the oxygen delivery tube; use a sampling tube and a 50 mL syringe to add water. Note: In some cases, the water level cannot be observed due to the formation of sediment and emulsion; mark the upper oil level in the filled oxidation tube by a suitable method, and periodically add water to maintain this level, thereby ensuring the appropriate amount of water in the oxidation tube; if necessary, a removable metal strip (Figure 7) can be used to indicate the corrected water level for water addition; for example, use an adjustable ring hook clamp to clamp the metal strip to the outside of the oxidation tube; when using this indicator, at the start of the test, adjust the lower end of the metal strip to the upper oil level; as the test proceeds and water evaporation causes the oil level to drop, especially before sampling, sufficient make-up water must be added to return the oil level to the position marked by the metal strip; after each sample is taken and before the test continues, move the indicator to the new oil level.
  • 9.7 Periodically sample and determine the acid value to monitor the oxidation of the oil sample.
  • 9.7.1 At test 500 h and thereafter every 168 h (weekly), take a 3 mL sample from the oxidation tube; sampling is carried out as follows: without interrupting the oxygen flow and without changing the position of the sampling tube, remove the stopper of the sampling tube, withdraw and return the sample twice, each time about 3 mL, to rinse the sampling tube; then withdraw a 6 mL sample into the syringe, hold the syringe barrel vertically at 15 s~20 s, allow the water to settle to the bottom of the syringe barrel, and while keeping the syringe barrel vertical, adjust the sample amount to 3 mL; this method allows most of the water withdrawn with the sample to return to the oxidation tube; re-stopper the sampling tube, transfer the 3 mL sample into a sample bottle for acid value analysis; the acid value determination may be based on SH/T 0163 or Appendix A; before sampling from the sample bottle for titration, shake the sample thoroughly. Note 1: The test results of this method are greatly affected by differences in the sampling procedure; therefore, the sampling procedure and schedule for acid value determination must be strictly followed; however, when the oil is known to have an oxidation life of less than 500 h, sampling may be carried out at any time according to the operator's judgment. Note 2: When the acid value is not greater than 0.5 mgKOH/g, Appendix A is the preferred method, but SH/T 0163 is also permitted; when the acid value exceeds 0.5 mgKOH/g, use SH/T 0163; SH/T 0163 and Appendix A both use a color change to indicate the titration endpoint; for dark-colored oils, potentiometric titration (such as GB/T 7304) may be better for endpoint detection.
  • 9.7.2 After the test time reaches 3000 h, sample and test every 500 h±25 h.
  • 9.7.3 When observation shows that the oil is approaching the end of its test life, additional sampling should be carried out according to the operator's judgment.
  • 9.8 Stop the test when the measured acid value is equal to or greater than 2.0 mgKOH/g. Note: When using this method to test turbine oils, the value 2.0 mgKOH/g serves as the limit; when oxidation proceeds rapidly in such oils, it is often encountered that this value is far greater than 2.0 mgKOH/g; at this time, the severe oxidation state of the oil, like the high acid value, often also exhibits other degradation phenomena: such as unpleasant odor, sediment formation, catalyst coil corrosion, severe darkening of the oil, and oil-water emulsion formation; if these oxidation phenomena are found before the scheduled sampling for acid value determination, sampling for acid value determination should be carried out immediately, and if the measured acid value is equal to or greater than 2.0 mgKOH/g, stop the test.
  • 9.8.1 If after 10000 h the acid value is still less than 2.0 mgKOH/g, the test should be terminated. Note: After exceeding 10000 h, continuous sampling causes the metal catalyst coil to be exposed to air; the effect of this exposure on the oxidation life of the oil has not been determined, and the precision of the method has not been specified.
• Appendix A Test Procedure (A.7):
  • A.7.1 Sampling: According to the procedure specified in the oxidation test method, withdraw the minimum amount of test oil from the oxidation tube. Note: Because oxidized oil undergoes significant changes during storage, the oil sample taken from the oxidation test apparatus should be tested as soon as possible.
  • A.7.2 Use a syringe to transfer 2.0 mL of titration solution into a beaker or bottle.
  • A.7.3 Use a dropper to add the sample dropwise to the titration solution, one drop at a time, while shaking continuously.
  • A.7.4 Count the number of drops of oil sample required when the titration solution changes from blue-green to orange-yellow; the titration is considered complete when the orange-yellow color is stable for at least 10 s.
  • A.7.5 Repeat steps 7.2~7.4 using an acid value reference solution instead of the sample as the titrant for the 2.0 mL titration solution; the endpoint colors of the two beakers should be consistent.
• Appendix B Procedure (B.2): Use a purge tube to pass nitrogen into a new test tube to blow out loose dust; the test tube must be clean and dry in appearance; tilt the test tube at a certain angle and gently slide the catalyst coil into the test tube; add a desiccant packet folded longitudinally to fit the test tube; insert the nitrogen purge tube into the middle of the test tube, then to the bottom, and purge the test tube with nitrogen for a few seconds; immediately after withdrawing the purge tube, seal the test tube with a polyethylene cap.

9. Qualitative and Quantitative and Calculation Formulas

• 10 Calculation: Calculate according to formula (1) the time (oxidation life) H when the acid value reaches 2.0 mgKOH/g, h:
  • H = A + [(2.0 − C)/(D − C)] × (B − A) ……(1)
  • Where: A— the time when the last measured acid value is lower than 2.0 mgKOH/g, h; B— the time when the measured acid value is higher than 2.0 mgKOH/g, h; C— the acid value at A hours, mgKOH/g; D— the acid value at B hours, mgKOH/g.
• Appendix A Calculation and Reporting (A.8):
  • A.8.1 Calculate the acid value An of the oil sample according to formula (A.1), mgKOH/g: An = A×B/C ……(A.1)
  • Where: A— the number of drops of acid value reference solution in 7.5; B— the acid value of the reference solution; C— the number of drops of oil sample in 7.4.
  • A.8.2 Report the result in the form of formula (A.2), mgKOH/g (the original formula A.2 content requires confirmation against the source standard (source-text extraction)).
• Appendix A Terminology (A.2): Acid value acid number—— the amount of base required to titrate a sample dissolved in a specified solvent to a specified endpoint, expressed as milligrams of potassium hydroxide per gram of sample. Note: In this test method, the acid value is calculated by comparing the number of drops of sample added when the color of the titration solution changes from blue-green to orange-yellow by dropping the sample into the titration solution, with the number of drops of reference sample added when the same color change occurs in the titration solution using a reference sample; because this is a direct comparison method, the resulting acid value can be reported as milligrams of potassium hydroxide per gram of sample.
• Appendix A Method Summary (A.3): A.3.1 Use a dropper to add the sample dropwise into a portion of 2.0 mL titration solution, and record the number of sample drops required to change the titration solution from blue-green to a stable orange-yellow; A.3.2 Titrate a second portion of 2.0 mL titration solution with a reference sample of known acid value, and record the number of reference sample drops required to change the titration solution from blue-green to a stable orange-yellow; A.3.3 Estimate the acid value of the sample using the acid value of the reference sample and the ratio of the number of reference sample drops required to change the color of the titration solution to the number of sample drops required to produce the same change.

10. Precision

• 12 Precision: Within the range of 700 h~3900 h, judge the reliability of the results according to the following provisions (95% confidence level).
  • 12.1 Repeatability r: The difference between two consecutive test results obtained by the same operator, using the same apparatus, according to the same test method, on the same test sample shall not exceed the value of formula (2): r = 0.192X ……(2); where: X— the arithmetic mean of the two replicate test results.
  • 12.2 Reproducibility R: The difference between two single, independent test results obtained by different operators, in different laboratories, using different apparatus, using the same method, on the same test sample shall not exceed the value of formula (3): R = 0.332X ……(3); where: X— the arithmetic mean of the two test results.
  • Note: The reproducibility of the results of two sets of duplicate tests R′. If in 12.2 each laboratory obtains two consecutive test results, then the difference between the averages of the two sets of consecutive test results obtained by the two laboratories shall not exceed the value of formula (4): R′ = 0.302X …… (4); where: X— the average of the arithmetic means of the test results of the two laboratories.
  • For more than two test results obtained from one or two laboratories, the reproducibility of their average can be calculated according to GB/T 17039.
• Appendix A Precision and bias (A.9): Judge the reliability of test results according to the following provisions (95% confidence level).
  • A.9.1 Precision: The precision of this test method was determined through interlaboratory statistical testing of test results from 8 laboratories on 9 samples with acid values (calculated as KOH) ranging from 0.06 mg/g~1.1 mg/g.
  • A.9.1.1 Repeatability rA: The difference between two consecutive test results obtained by the same operator, using the same instrument, according to the same test method, on the same test sample shall not exceed the value of formula (A.3): rA = 0.2XA …… (A.3); where: XA— the arithmetic mean of the two determination results.
  • A.9.1.2 Reproducibility RA: The difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, with the same method, on the same test sample shall not exceed the value of formula (A.4): RA = 0.7XA …… (A.4); where: XA— the arithmetic mean of the two determination results.
  • A.9.2 Bias: Because the acid value is determined solely according to the test method, there is no bias in this test method.

11. Report

• 11.1 Report the number of hours calculated when the sample oxidizes to an acid value reaching 2.0 mgKOH/g (oxidation life), h.
• 11.2 If after 10000 h the acid value is still less than 2.0 mgKOH/g, the test should be terminated; because the maximum oil oxidation life is limited to 10000 h, the test life and acid value should be reported in the form of greater than 10000 h (acid value z.zz) (the original text "z.zz" requires confirmation against the source standard (source-text extraction)).
• Appendix A Report (A.8.2): Report the results in the form of formula (A.2), mgKOH/g (the content of the original formula A.2 requires confirmation against the source standard (source-text extraction)).

12. Normative References

• GB/T 514 Liquid-in-glass thermometers for petroleum product testing — Technical specifications
• GB/T 699 Quality carbon structural steel
• GB/T 4756 Manual sampling of petroleum liquids (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 4945—2002 Determination of acid value and base value of petroleum products and lubricants (color indicator method)
• GB/T 5231 Wrought copper and copper alloys — Chemical composition and product forms
• GB/T 6682 Water for analytical laboratory use — Specifications and test methods (GB/T 6682—1992, neq ISO 3696:1987)
• GB/T 7304 Determination of acid value of petroleum products and lubricants (potentiometric titration method)
• GB/T 17039 Standard practice for utilization of test data to determine conformance with specifications
• SH/T 0163 Determination of total acid value of petroleum products (semi-micro color indicator method)
• SH/T 0565 Determination of sludge tendency of inhibited mineral oils
• Adopted document: ASTM D943-04a "Determination of oxidation characteristics of inhibited mineral oils"
• Appendix A References: GB/T 4945—2002 Appendix A (specification requirements for p-naphtholbenzein); GB/T 4945 or GB/T 7304 (calibration of acid value reference solution)

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