NB/SH/T 0870-2013 Determination of dynamic viscosity and density of petroleum products and calculation of kinematic viscosity — Stabinger viscometer method

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

• Standard number: NB/SH/T 0870-2013
• Chinese full title: Determination of dynamic viscosity and density of petroleum products and calculation of kinematic viscosity — Stabinger viscometer method
• English title: Standard test method for dynamic viscosity and density of liquids by stabinger viscometer (and the calculation of kinematic viscosity)
• Replacement relationship: not provided in the available source (no replacement of any standard is mentioned)
• Adoption relationship: modified adoption by redrafting method of ASTM D7042-10
• Technical differences from ASTM D7042-10:
  • The referenced standards in Chapter 2 of ASTM D7042-10 are modified to the corresponding Chinese national standards and industry standards
  • The keywords of Chapter 16 are deleted
  • References are added
• Drafting organizations: drafted under the responsibility of PetroChina Dalian Lubricant Research and Development Center, with participation of Daqing Oilfield Engineering Co., Ltd.
• Main drafters: Xie Pingping, Tan Xiao, Liu Honghui, Chen Jie, Li Jicheng, Ding Dongmei, Ma Xiaoyi, Gao Min
• Administrative organization: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC 1)
• Proposing organization: China Petrochemical Corporation
• Publication/implementation: published on 2013-06-08, implemented on 2013-10-01
• Publishing body: National Energy Administration

2. Scope of application and non-applicability

• Applicable to the determination of dynamic viscosity and density of petroleum products and the calculation of kinematic viscosity.
• Specifies a method for simultaneously determining the dynamic viscosity (ŋ) and density (ρ) of transparent and opaque liquid petroleum products and crude oil. Kinematic viscosity (υ) can be obtained by dividing dynamic viscosity (ŋ) by the density (ρ) at the same temperature.
• The test results depend on the properties of the sample and are applicable to liquids in which shear stress and shear rate are proportional (i.e., Newtonian fluids).
• Precision investigation range (base oils only): at 40˚C, dynamic viscosity 2.05 mPa•s～456 mPa•s; at 100˚C, dynamic viscosity 0.83 mPa•s～31.6 mPa•s; at 15˚C, density 0.82 g/mL～0.92 g/mL (see 15.4).
• It is also applicable to samples with wider viscosity, density and temperature ranges, but the precision and bias listed in this standard (see Chapter 15) may not apply to such samples.
• Not applicable: the available source does not explicitly list non-applicable objects (only Newtonian fluids are used as the premise for applicability).

3. Method principle

Inject the sample into a precisely temperature-controlled measuring cell, which consists of a pair of concentric rotating cylinders and a U-type vibrating tube. The dynamic viscosity is obtained by measuring the equilibrium rotational speed of the inner cylinder under shear stress and eddy-current braking (related to calibration data), and the density is obtained by measuring the vibration frequency of the U-type tube (related to calibration data). The kinematic viscosity is calculated from the ratio of dynamic viscosity to density.

4. Reagents and materials (purity / preparation)

• 7.1 Sample solvent: used to clean the measuring cell and capable of dissolving the sample.
  • 7.1.1 For most samples, volatile petroleum ether or naphtha may be used. If the solvent can evaporate quickly and leave no residue, a drying solvent is not required.
  • 7.1.2 For residual fuels, aromatic solvents such as toluene and xylene may be used for pre-cleaning to remove asphaltenes.
• 7.2 Drying solvent: a volatile reagent miscible with the sample solvent (see 7.1), high-purity ethanol (96% or higher purity).
• 7.3 Dry air or nitrogen: used to purge the measuring cell. If the temperature of the measuring cell is below or close to the dew point temperature of ambient air, a suitable desiccant should be used.
• 9.2 Certified viscosity and density reference standard materials: used for laboratory verification check procedures; they shall be certified by a laboratory meeting the requirements of GB/T 15481 or corresponding national standards; viscosity standard materials shall be traceable to the standard viscometer procedure specified in ASTM D2162; the uncertainty of density standard materials is 0.0001 g/mL; the standard values shall all be provided with corresponding uncertainties (k=2; 95% confidence level). See ISO 5725.
• 9.3 Thermometer: digital thermometer with probe (diameter 6.25 mm, length not exceeding 80 mm); uncertainty (k=2; 95% confidence level) shall not exceed ±0.01˚C; it shall be certified by a laboratory meeting the requirements of GB/T 15481 or corresponding national standards.
• 6.4 Filter membrane: pore size 75 µm.
• 6.5 Magnet: used to remove iron filings from the sample; a magnetic stir bar may be used.

5. Apparatus and equipment

• 6.1 Stabinger viscometer
  • 6.1.1 Viscosity test unit: a measuring system with concentric cylinder construction. The outer cylinder (sample tube) is driven by a motor maintaining a certain rotational speed; the low-density inner cylinder (rotor) is suspended in the rotating shaft under the centrifugal force of the higher-density sample, located at the longitudinal position of the magnet and soft iron ring, and the system has no bearing friction; the permanent magnet in the inner cylinder generates eddy currents in the copper lining, and the rotational speed of the inner cylinder is determined by the balance between the torque driving viscous force and the torque retarding the eddy currents, measured by an electronic system (Hall effect sensor) by calculating the frequency of the rotating magnetic field (see Figure 1 and item 2 of Figure 2).
  • 6.1.2 Density test unit: a digital density meter consisting of a U-type vibrating sample tube, an electronic excitation and frequency counting system (see item 3 of Figure 2).
  • 6.1.3 Temperature control unit: a copper block outside the viscosity measuring cell and density measuring cell ensures a constant temperature of the measuring cells; a thermoelectric heating and cooling system (see item 1 of Figure 2) ensures that the temperature of the copper block is stable within ±0.005˚C from the set temperature of the viscosity cell throughout the entire temperature range; the uncertainty of temperature calibration (k=2; 95% confidence level) shall not exceed ±0.03˚C in the range of 15˚C～100˚C, and shall not exceed ±0.05˚C outside this temperature range.
  • 6.1.4 Thermal equilibrium time: related to the heat capacity and conductivity of the liquid and the difference between the sample temperature and the test temperature; within 1min, when the continuously measured viscosity value remains at ±0.07% (relative deviation) and the density value remains at ±0.00003 g/mL (absolute deviation), the sample temperature is sufficiently equilibrated.
• 6.2 Syringe: commercially available, at least 5mL, with standard connector; the material shall not react with any liquid sample and cleaning liquid it contacts.
• 6.3 Overflow channel or pressure adapter: optional part, used to inject the sample into the measuring cell by pressure or suction to avoid bubbles in the sample; the material shall not react with any liquid sample and cleaning liquid it contacts.
• 6.4 Filter membrane: pore size 75 µm, used to remove particles from the sample.
• 6.5 Magnet: used to remove iron filings from the sample; a magnetic stir bar may be used.

6. Recommended operating conditions

• Temperature control: the temperature of the copper block is stable within ±0.005˚C (see 6.1.3).
• Temperature calibration uncertainty: not exceeding ±0.03˚C in the range of 15˚C～100˚C; not exceeding ±0.05˚C outside this range (k=2; 95% confidence level).
• Thermal equilibrium criterion: within 1min, the continuously measured viscosity value remains at ±0.07% (relative deviation) and the density value remains at ±0.00003 g/mL (absolute deviation).
• Recommended calibration interval: the calibration interval for viscosity and density is one month; the calibration interval for temperature control is one year (see 9.1).
• Test temperature: set by the operator (see 11.1.1, 11.2.1); the available source does not give a fixed recommended temperature value.

7. Sampling and sample preparation

• 8.1 Sampling: all steps of obtaining a portion of the sample from a pipe, tank or other system and transferring it to a laboratory test container; the laboratory test container shall be sufficient to hold enough sample and allow the sample to be mixed uniformly.
• 8.2 Particles: for samples that may contain particles (such as in-service oil or crude oil), a 75 µm filter membrane may be used to remove particles, and a magnet may be used to remove iron filings; for waxy tests, a preheated filter may be used, heating to melt wax crystals before filtration.
• 8.3 Sample: a portion or a certain volume taken from the laboratory sample and injected into the measuring cell.
  • 8.3.1 If required, mix the sample uniformly; mixing in an open container at room temperature will cause loss of volatile substances, so mixing in a sealed container or under low-temperature conditions is recommended.
  • 8.3.2 Use a suitable syringe to draw the test sample from a fully mixed laboratory sample, or use other suitable accessories and connecting tubes to inject the sample directly from the mixing container into the measuring cell; for samples containing wax or with a higher pour point, they should first be heated to a temperature sufficient to melt the wax crystals before drawing.

8. Analytical procedure

• 11.1 Standard procedure (cleaning and drying)
  • 11.1.1 Set the temperature to the test temperature.
  • 11.1.2 Ensure that the measuring cell is clean and dry as described in 12.1.
  • 11.1.3 Draw at least 3mL of sample with a syringe (if sufficient sample, filling the syringe is recommended), inject at least 2mL of sample into the measuring cell; leave the syringe in the injection port and start the test; when the instrument indicates that the test is valid, record the measurement result.
  • 11.1.4 Continue to inject 1mL of sample (do not pull out the syringe) and repeat the test.
  • 11.1.5 If the deviation between two consecutive measurement results exceeds the repeatability requirement of 15.1.1, repeat 11.1.4 until the deviation is within the range; discard all previous results and report the last measurement value as the final result.
    • 11.1.5.1 For products not listed in the precision in Chapter 15, the user is responsible for determining their repeatability requirement through a series of tests.
    • 11.1.5.2 If all the sample in the syringe is injected before a valid measurement result is obtained, clean and dry the measuring cell as described in 12.1 and repeat 11.1.3; if no valid result is still obtained after several repeated measurements, report the average value and standard deviation (k=2; 95% confidence level) and note that the repeatability exceeds the requirement of 15.1.1.
  • 11.1.6 Clean and dry the measuring cell as described in 12.1.
• 11.2 Alternative procedure (sample displacement): for two mutually soluble samples in sequence (such as various diesel fuels), the user is responsible for confirming the applicability of this procedure to each type of sample.
  • 11.2.1 Set the temperature to the test temperature.
  • 11.2.2 Ensure the measuring cell is clean and dry as described in clause 12.1.
  • 11.2.3 Draw at least 5mL of sample with a syringe (when sufficient sample is available, it is recommended to use a 10mL or larger syringe and fill it completely); slowly inject at least 3mL of sample into the measuring cell, ensuring that the new sample can displace the previous one without mixing the two; leave the syringe in the injection port and start the test; when the instrument indicates that the test is valid, record the measurement result.
  • 11.2.4 Continue slowly injecting 2mL of sample (do not remove the syringe) and repeat the test.
  • 11.2.5 If the deviation between two consecutive measurement results exceeds the repeatability requirement of 15.1.1, repeat 11.2.4 until the deviation is within range; discard all previous results and report the last measurement value as the final result.
    • 11.2.5.1 For products not listed in the precision section of chapter 15, it is the user's responsibility to determine their repeatability requirement through a series of tests.
    • 11.2.5.2 If all the sample in the syringe is injected before a valid measurement result is obtained, repeat 11.2.3; if after several repeated measurements a valid result is still not obtained, report the mean and standard deviation (k=2; 95% confidence level), and note that the repeatability exceeds the requirement of 15.1.1.
  • 11.2.6 Test the next sample and repeat 11.2.3 to 11.2.5.
  • 11.2.7 After completing the test of the last sample, perform the cleaning procedure in accordance with clause 12.1.
• 12 Clean the measuring cell
  • 12.1 Inject at least 3mL of sample solvent into the measuring cell (see 7.1); check whether the density measuring cell is completely filled by the displayed density value; start the motor for at least 10s, and for difficult-to-dissolve samples, extend the motor running time and repeat this step; then rinse the measuring cell with dry solvent (see 7.2) and purge with dry air or nitrogen; when the air density value is less than 0.0020 g/mL, it indicates that the measuring cell is clean and dry; if the density value is greater than 0.0020 g/mL, repeat this step.
  • 12.2 Special cleaning procedure: if necessary, manually wipe and brush the measuring rotor with a suitable sample solvent and clean the viscosity measuring cell, and clean the density vibrating tube with a suitable cleaning liquid; when repeated calibration check tests still cannot meet the tolerance described in clause 9.4, follow the instrument manufacturer's operating instructions to perform this procedure.
• 9 Calibration and verification
  • 9.1 Only the calibration equipment mentioned in clause 6.1 is allowed to be used, and periodic verification is carried out using the certified reference standard materials in clauses 9.2 and 9.3; the recommended calibration period for viscosity and density is one month, and for temperature control calibration is one year; the calibration procedure should follow the instrument manufacturer's operating instructions.
  • 9.4 Tolerance: when the calibration test result calculated according to Appendix A exceeds the tolerance range of the standard value, recheck each step of the calibration procedure, including the special cleaning procedure in clause 12.2, to identify the cause. Note: Results exceeding the tolerance range are usually due to residues in the measuring cell that cannot be removed by routine cleaning.
• 10 Adjustment
  • 10.1 When repeated calibration check tests do not meet the tolerance range described in clause 9.4 and the cause of the error cannot be found, the instrument needs to be adjusted; the adjustment steps follow the instrument manufacturer's operating instructions.
  • 10.2 Use certified viscosity and density reference standard materials that meet the requirements of clause 9.2, and within the viscosity, density, and temperature ranges specified by the instrument manufacturer.
  • 10.3 Perform a calibration check test after the adjustment procedure is completed.

9. Qualitative and quantitative and calculation formulas

• 13.1 The recorded value is the final result; dynamic viscosity is expressed in mPa•s, kinematic viscosity in mm²/s, and density in g/mL or kg/m³.
• 13.2 Viscosity index: given the kinematic viscosity of the same sample at 40˚C and 100˚C, the viscosity index (VI) can be calculated according to GB/T 1995.
• 13.3 Density extrapolation method: given the density of the same sample at 40˚C and 100˚C, the density at other temperatures can be calculated by linear extrapolation; the limit of the extrapolation temperature is determined by the phase transition point of the sample (such as cloud point or appearance of bubbles); it is the user's responsibility to confirm the applicability of this calculation method for each type of sample.
• Kinematic viscosity calculation relationship: kinematic viscosity (υ) = dynamic viscosity (ŋ) / density at the same temperature (ρ) (see chapter 1, chapter 4).
• Appendix A Tolerance range calculation (normative appendix):
  • A.1 According to the laboratory quality control procedure, determine the standard deviation σsite of the on-site uncertainty; if σsite is unknown, take 0.30% for viscosity and 0.0005 g/mL for density. Note: For uncertainty, see test method NB/SH/T 0843.
  • A.2 From the recognized reference value (ARV) of the certified reference material (CRM) provided by the supplier's label or document, determine the combined expanded uncertainty (CEU); if the uncertainty of density is unknown, take CEU=0.0005 g/mL.
  • A.3 The standard error (SEARV) of the recognized reference value is calculated by dividing CEU by the coverage factor k provided by the supplier's label or document; if the coverage factor k is unknown, take k=2.
  • A.4 Establish the tolerance range, calculated according to formula (A.1) (the formula content in the original text requires confirmation against the source standard (source-text extraction), the specific expression is not shown in the main text).
  • A.4.1 Example of viscosity tolerance range calculation, see formula (A.2) (the formula content in the original text requires confirmation against the source standard (source-text extraction)).
  • A.4.2 Example of density tolerance range calculation, see formula (A.3) (the formula content in the original text requires confirmation against the source standard (source-text extraction)).
  • Note: The tolerance range calculation is based on test method ASTM D6617.

10. Precision

• 15.1 Precision: determined through statistical analysis results among multiple laboratories, the reliability of test results is judged according to the following provisions (95% confidence level).
• 15.1.1 Repeatability: in the same laboratory, by the same operator using the same instrument, using the same method, the difference between two test results obtained from continuous measurements of the same sample shall not exceed the value in Table 1.

Table 1 Repeatability

Note: X is the average of two results

• 15.1.2 Reproducibility: in different laboratories, by different operators using different instruments, using the same method, the difference between two single, independent results obtained from measurements of the same sample shall not exceed the value in Table 2.

Table 2 Reproducibility

Note: X is the average of two results

• 15.2 Bias: because samples with recognized reference values cannot be obtained for testing, this standard cannot provide information on bias.
• 15.3 Relative bias: this standard has no bias for ASTM D445 and ASTM D4052 (see B.1 and B.2). Note: SH/T 0604 and ASTM D4052 are equivalent in technical content.
• 15.4 Interlaboratory study: the precision was determined through statistical analysis of test results from 12 laboratories on 10 mineral oils (additive-free base oils). The 10 mineral oils cover: at 40˚C, dynamic viscosity 2.05 mPa•s to 456 mPa•s; at 100˚C, dynamic viscosity 0.83 mPa•s to 31.6 mPa•s; at 15˚C, density 0.82 g/mL to 0.92 g/mL. The density at 15˚C can be calculated by linear extrapolation from the densities at 40˚C and 100˚C. According to the standard procedure in clause 11.1, the sample is measured in duplicate at the shortest possible time interval, generally within 10min. The interlaboratory study follows ASTM D6300 and ASTM D6708. To determine the bias, in the same laboratory, the viscosity of the sample was measured using a glass capillary kinematic viscometer according to ASTM D445, and the density of the sample was measured using a digital density meter according to ASTM D4052.
• Appendix B (informative appendix) Bias comparison:
  • B.1 Comparison of the bias between the kinematic viscosity of this standard 100℃ and ASTM D445
    • B.1.1 For the test results of base oil samples from multiple laboratories (see 15.4), the bias was calculated according to ASTM D6708. Comparative studies show that the bias correction for kinematic viscosity at 100˚C is Y=0.998%X, corresponding to a bias of 0.2% in the measured value. Comparing the precision data of this standard and the reference standard, the recommended bias correction is smaller than the repeatability requirement of the viscosity range of the interlaboratory study, and also smaller than the uncertainty of the certified viscosity reference standard material (see Table B.1). Therefore, the bias is not significant.
    • B.1.2 The bias of kinematic viscosity at 40˚C is 1.000X, equivalent to 0.0%.

Table B.1 Precision and bias of base oil kinematic viscosity (100˚C)

Note: X is the average of two results, in units of mm²/s.

• B.2 Comparison of the deviation between the density of this standard 40℃ and ASTM D4052
  • B.2.1 For the test results of base oil samples from multiple laboratories (see 15.4), the bias was calculated according to ASTM D6708. Comparative studies show that the bias correction for density at 40˚C is Y= (1.0053X-0.0046) g/mL, corresponding to a maximum measured density deviation value of 0.0003 g/mL. Comparing the precision data of this standard and the reference standard, the recommended bias correction is smaller than the repeatability requirement for the density range of the interlaboratory study, and also smaller than the uncertainty of the certified viscosity reference standard materials (see Table B.2). Therefore, the bias is not significant.
  • B.2.2 The density bias at 15˚C is 0.0000 g/mL.

Table B.2 Precision and bias of base oil density (40˚C)

Note: X is the average of two results, in units of g/mL.

11. Report

Report the following information:

• 14.1 Type and identification of the sample.
• 14.2 Reference to this standard.
• 14.3 Bias introduced by the test procedure as determined by agreement or other means.
• 14.4 Dynamic viscosity or kinematic viscosity results shall be retained to four significant figures; density results expressed in g/mL shall be retained to three decimal places, and when expressed in kg/m³ shall be reported as an integer (for example: 0.877 g/mL or 877 kg/m³); report the test temperature, with temperature retained to the second decimal place.
• 14.5 Test date and time.
• 14.6 Name and address of the laboratory.

12. Normative references

• GB/T 1995 Petroleum products — Calculation of viscosity index
• SH/T 0604 Crude petroleum and petroleum products — Determination of density (U-shaped oscillating tube method) (SH/T 0604-2000, eqv ISO 12185:1996)
• ASTM D445 Transparent and opaque liquids — Determination of kinematic viscosity and calculation of dynamic viscosity
• ASTM D2162 Basic calibration procedures for standard viscometers and viscosity standard oils
• ASTM D4052 Determination of density, relative density, and API gravity of liquids (digital density meter method)
• References:
  • [1] GB/T 15481 General requirements for the competence of testing and calibration laboratories (GB/T 15481-2000, ISO/IEC 17025:2005, IDT)
  • [2] NB/SH/T 0843 Statistical techniques for the evaluation of analytical testing systems in the petrochemical industry
  • [3] ISO 5725 Accuracy (trueness and precision) of measurement methods and results
  • [4] ASTM D6300 Standard practice for determination of precision and bias data for use in test methods for petroleum products and lubricants
  • [5] ASTM D6617 Detection of laboratory bias based on a single test result from a check sample
  • [6] ASTM D6708 Laboratory quality control techniques — Evaluation and improvement of the expected agreement between two test methods for the same property of a measurement material

13. Source and verification

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