SH/T 0790-2007 Determination of Oxidation Induction Time of Lubricating Greases (Pressure Differential Scanning Calorimetry)

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 name / English name / replacement relationship

• Standard number: SH/T 0790-2007
• Chinese name: Determination of Oxidation Induction Time of Lubricating Greases (Pressure Differential Scanning Calorimetry)
• English name: Standard test method for oxidation induction time of lubricating greases by pressure differential scanning calorimetry
• Replacement relationship: not provided in the available source (the foreword only states modified adoption of ASTM D5483-02, and does not mention replacement of an old version of the standard)
• Adoption relationship: modified adoption of ASTM D5483-02
• Publication/implementation: published on 2007-08-01, implemented on 2008-01-01
• Issuing body: National Development and Reform Commission of the People's Republic of China
• Custodian: Sinopec Research Institute of Petroleum Processing
• Drafting organization: Sinopec Lubricant Shanghai Branch
• Main drafters: Lu Meiyu, Fu Jiyu, Chen Ying

2. Scope of application and non-applicability

• 1.1 This standard specifies the determination of the oxidation induction time of lubricating greases by pressure differential scanning calorimetry (PDSC method), with an oxygen pressure of 3.5 MPa and a temperature between 155 ℃～210 ℃.
• 1.2 This standard uses the International System of Units [SI] units.
• 1.3 This standard involves certain hazardous materials, operations and equipment, but does not address all safety issues associated with them. Therefore, users must establish appropriate safety and protective measures and determine corresponding management rules before using this standard.
• Non-applicable scope: not provided in the available source.

3. Method principle

• 4.1 Weigh a small amount of lubricating grease into a sample pan and place it in the test cell. Heat the test cell to the specified temperature, then introduce oxygen at a certain pressure. Maintain the test cell at the specified temperature and oxygen pressure until an exothermic oxidation reaction occurs. Determine the extrapolated onset time as the oxidation induction time of the lubricating grease at the specified test temperature.
• 4.2 Combined with the kinetic equation of this test method, the oxidation induction time at other temperatures can be estimated.
• 5 Significance and use: The oxidation induction time measured by this method can be used to characterize the oxidation stability of lubricating greases. It can be used for product research and development, quality control and other specific purposes. However, the correlation between the results of this test method and service performance has not been established.

4. Reagents and materials (purity / preparation)

• 7.1 Oxygen: dry, purity not less than 99.5% (volume fraction). Note: oxidizer. Gas is used under pressure. In addition to other precautions, stainless steel or copper tubing is suitable for oxygen, and the pressure gauge is specified as an oxygen pressure gauge.
• 7.2 Indium: purity not less than 99.9% (mass fraction).
• 7.3 Balance: sensitivity 0.1 mg.
• 6.1 Aluminum sample pan: capable of withstanding 3.5 MPa pressure at 210 ℃, with a pressure gauge division value of 200 kPa or smaller. Aluminum SFI (Solid Fat Index) sample pans may also be used. Note: Better reproducibility can be obtained when preparing lubricating grease samples using SFI sample pans (see Figure 3), which have a more consistent surface area than flat-bottomed pans.

5. Apparatus and equipment

• 6 Pressure differential scanning calorimeter (PDSC instrument), equipped with the following units (see Figure 1): thermal analyzer, PDSC test cell, flowmeter, differential scanning calorimeter, oxygen cylinder.
• 6.1 Aluminum sample pan (see Section 4).
• 6.2 Thermal analyzer.
• 6.3 Oxidation stability software.
• 6.4 Calibration software.
• 6.5 Flowmeter: range at least 200 mL/min.
• 6.6 Sample sealing press.

6. Recommended operating conditions

• Oxygen pressure: 3.5 MPa ± 0.2 MPa (8.1.2, 8.2.1, 9.6)
• Oxygen flow rate: 100 mL/min ± 10 mL/min (8.1.2, 8.2.1, 9.7)
• Test temperature: 155 ℃, 180 ℃, 210 ℃ (1.1, 8.2.1, 9.1, 12.1)
• Heating rate (calibration): 10 ℃/min (8.1.3)
• Heating rate (test specimen): 100 ℃/min (9.4, as in the source text, suspected to be 10 ℃/min, requires confirmation against the source standard (source-text extraction))
• Test temperature equilibration time: 2 min (9.5)
• Maximum holding time after opening the oxygen valve: 120 min (9.8)

7. Sampling and specimen preparation

• 9.2 Weigh 2.0 mg ± 0.1 mg of lubricating grease into the sample pan so that the specimen is evenly spread over the flat surface. Do not allow the sample to splash into the groove of the sample pan. Note: An example of the sample spread in the sample pan is shown in Figure 3.
• 9.3 According to the PDSC instrument manufacturer's instructions for placing the sample pan, place the unsealed sample pan containing the specimen on the platform of the PDSC instrument test cell. According to the PDSC instrument manufacturer's instructions for placing the reference pan, place an empty sample pan of the same specification on the platform of the PDSC instrument test cell. Close the PDSC instrument test cell and the pressure release valve.

8. Analytical procedure

• 8 Calibration
  • 8.1 Sample temperature calibration
    • 8.1.1 Weigh about 10 mg of indium into a sample pan, add a lid and seal it with a sealing press. Place the sealed sample pan on the sample platform of the PDSC instrument test cell. Seal an empty pan in the same manner and place it on the reference platform. Cover the PDSC instrument test cell lid and close it.
    • 8.1.2 Gently open the oxygen cylinder valve, and use the pressure regulator to adjust the inlet pressure of the PDSC instrument test cell to 3.5 MPa ± 0.2 MPa. Open the inlet valve of the PDSC instrument test cell so that the pressure slowly fills the PDSC instrument test cell. After 2 min, adjust the outlet valve so that the oxygen flow rate through the flowmeter is 100 mL/min ± 10 mL/min. The open positions of these valves should be fixed during the test.
    • 8.1.3 Heat the thermal analyzer from room temperature (about 22 ℃) to 180 ℃ at a heating rate of 10 ℃/min. After the run is completed, measure the melting point temperature of indium. If the measured temperature deviates from 157.4 ℃ ± 0.2 ℃, calibrate according to the hardware or software calibration procedure described in the manufacturer's instrument manual. If a hardware calibration procedure is used, the temperature calibration shall be performed at an oxygen pressure of 3.5 MPa and a flow rate of 100 mL/min. A typical calibration curve is shown in Figure 2.
    • Note 1: For thermal analyzers whose PDSC instrument test cell has no gas outlet, sample temperature calibration should be performed according to the instrument manufacturer's recommendations.
    • Note 2: The melting point of indium at one atmosphere is 156.6 ℃, but under the oxygen pressure conditions of 3.5 MPa in this standard, its melting point rises to 157.4 ℃.
  • 8.2 Temperature controller calibration
    • 8.2.1 Remove the sample pan and reference pan from the PDSC instrument test cell, and close the PDSC instrument test cell. Slowly open the oxygen pressure to 3.5 MPa ± 0.2 MPa, and use the PDSC instrument test cell outlet valve to adjust the oxygen flow rate to 100 mL/min ± 10 mL/min. Select the required test temperature (e.g., 210 ℃, 180 ℃, 155 ℃).
    • 8.2.2 Program the temperature so that the PDSC instrument test cell is maintained at the selected test temperature. After 10 min, if the difference between the displayed temperature and the selected temperature exceeds ± 0.2 ℃, slowly adjust the temperature controller until they match. After adjustment, wait at least 5 min before continuing the next calibration step to check whether the temperature is stable.
    • Note: If the PDSC instrument does not have this temperature controller calibration function, the temperature controller calibration should be performed according to the instrument manufacturer's recommendations.
  • 8.3 Calibration of the reference pressure gauge of the PDSC instrument test cell
    • 8.3.1 Use a calibrated pressure transducer or a pre-calibrated gauge, and calibrate according to the PDSC instrument test cell operation manual.
• 9 Test procedure
  • 9.1 Before starting the test, the thermocouple shall be calibrated and controlled at the test temperature (e.g., 210 ℃, 180 ℃, 155 ℃) according to steps 8.2.1 and 8.2.2. If the test temperature is unknown, calibration shall be performed at 210 ℃.
  • 9.2 See Section 7.
  • 9.3 See Section 7.
  • 9.4 Starting from room temperature (about 22 ℃), heat the specimen to the test temperature at a rate of 100 ℃/min. (as in the source text, requires confirmation against the source standard (source-text extraction))
  • 9.5 Equilibrate the specimen at the test temperature for 2 min. Note: This step was not used in the statistical test for determining precision. The statistical test used the PDSC instrument manufacturer's software to determine the equilibration time to reach the test temperature; the step in 9.5 eliminates the method's dependence on the PDSC instrument manufacturer. Since this step is before applying oxygen pressure to the test cell, it does not have a significant effect on the measured oxidation induction time result.
  • 9.6 Open the oxygen valve and slowly pressurize to 3.5 MPa ± 0.2 MPa. This requires approximately 2 min of time to reach maximum pressure. The determination of the oxidation induction period starts counting from the moment the oxygen valve is opened.
  • 9.7 When the pressure is balanced, check the oxygen flow rate of the PDSC instrument test cell and adjust it with the outlet valve to 100 mL/min ± 10 mL/min. Note: For thermal analyzers of the PDSC instrument test cell that have no gas outlet, there is no need to adjust the gas outlet flow rate.
  • 9.8 After the oxygen valve has been open for 120 min, close the oxygen valve, open the test cell pressure release valve, and slowly release the test cell pressure. If the oxidation induction period is approximately known, the test may be stopped as soon as oxidation exotherm just occurs.
  • 9.9 Draw the thermal curve and measure the extrapolated onset time of the oxidation exotherm. Report this time, rounded to 0.1 min, as the oxidation induction period of the specimen. If multiple oxidation exothermic peaks are observed, report the oxidation induction period of the largest oxidation exothermic peak (a typical PDSC curve is shown in Figure 4).
  • 9.10 If the oxidation induction period is less than 10 min, start from clause 9.2 and retest at a slightly lower temperature. Before retesting, the test cell should be cooled to room temperature.
  • 9.11 When the oxidation induction period meets the requirements specified in clause 9.10, complete the repeatability test.
  • 9.12 If the difference between the two measured values exceeds the permissible difference for determination (Chapter 12), discard these two measured values, start from clause 9.2 and carry out two determinations again; if the difference between the two measured values meets the permissible difference requirement for determination, average the two measured values to obtain one test result.

9. Qualitative and Quantitative and Calculation Formulas

• 3.1 Extrapolated onset time (extrapolated onset time): the time measured on the thermal curve, which is the intersection point of the extrapolated baseline and the tangent at the point of maximum rate of the oxidation exothermic peak.
• 3.2 Oxidation induction period (oxidation induction time, OIT): the period of time from the beginning of contact with the oxidizing atmosphere to the extrapolated onset time.
• 3.3 Pressure differential scanning calorimeter (pressure differential scanning calorimeter, PDSC): a differential scanning calorimeter as described in the terminology of ASTM E473, capable of maintaining the specimen under a controlled high pressure.
• 3.4 Thermal curve (thermal curve): a graphical representation of specimen heat flow versus time.
• 10 Calculation of induction period at other temperatures
  • 10.1 After the oxidation induction period of a certain grease has been determined, equation (1) can be used to estimate the oxidation induction period at other temperatures:
    • t = A·exp (17500/T) … (1)
    • Where: t— estimated oxidation induction period, min; A— oxidation coefficient of the specimen; T— temperature, K (required test temperature).
  • The oxidation coefficient (A) is constant for a given grease. It is calculated using equation (2) from the oxidation induction period reported in clause 9.12.
    • A = oxidation induction period / exp (17500/T) … (2)
  • The estimated oxidation induction period can serve as a guide for selecting a suitable other test temperature. The estimated oxidation induction period is not part of the reported results of this test method.

10. Precision

• 12.1 Precision: This precision was determined by statistical testing in 5 laboratories on 11 samples at 3 different temperatures (155 ℃, 180 ℃ and 210 ℃), with oxidation induction periods ranging from 9.0 min to 45.3 min. The reliability of test results is judged according to the following provisions (95% confidence level).
  • 12.1.1 Permissible difference for determination: For two determinations on the same specimen, the difference between the two measured values shall not exceed the value specified in equation (3):
    • Permissible difference for determination = 0.59m … (3)
    • Where: m— average of the two measured values.
  • 12.1.2 Repeatability: The difference between two test results obtained by the same operator using the same instrument under the same operating conditions on the same specimen (each test result being the average of two measured values) shall not exceed the following value specified in equation (4):
    • Repeatability = 0.42m^1/2 … (4) (the exponent source-text extraction in the source text is “2”, requires confirmation against the source standard (source-text extraction))
    • Where: m— average of the two test results.
  • 12.1.3 Reproducibility: The difference between two independent test results obtained by different operators in different laboratories on the same specimen (each test result being the average of two measured values) shall not exceed the following value specified in equation (5):
    • Reproducibility = 0.71m^1/2 … (5) (the exponent source-text extraction in the source text is “2”, requires confirmation against the source standard (source-text extraction))
    • Where: m— average of the two test results.
• 12.2 Bias: Since the value of the oxidation induction period can only be defined by the test method, no bias has been established for this standard.
• Appendix A (informative appendix) PDSC Statistical test data are shown in Table A.1. In Table A.1, the oxidation induction period data are represented by “min”. Each pair of oxidation induction period results for a grease is represented by the results of two individual determinations. (For the data in Table A.1, see the source text; source-text extraction is misaligned, requires confirmation against the source standard (source-text extraction))

11. Report

• 11.1 Report the result to the nearest 0.1 min; the average calculated in clause 9.12 may be used as the oxidation induction period of the specimen.
• 11.2 Report the test temperature.

12. Referenced Documents

• ASTM E473 Terminology related to thermal analysis
• ASTM D5483-02 (modified adoption of the source standard)

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