NB/SH/T 0905-2024 Determination of color of petroleum products — Automatic tristimulus method

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Card type: Test method

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

• Standard number: NB/SH/T 0905—2024
• Chinese full title: Determination of color of petroleum products — Automatic tristimulus method
• English title: Determination for color of petroleum products—Automatic tristimulus method
• Replacement relationship: replaces NB/SH/T 0905—2015 (this is the first revision; first published in 2015)
• Publication/implementation: published on 2024-12-25, implemented on 2025-06-25
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Proposed by: China Petrochemical Corporation

2. Scope of application and non-applicability

• Applicable: determination of the color of petroleum products by the tristimulus method, and conversion of the results according to calculation rules into the corresponding color numbers in GB/T 3555 and GB/T 6540.
• Applicable samples: petroleum products such as undyed gasoline, diesel, naphtha, kerosene, white oil, fuel oil, and lubricating oil; also applicable to the Saybolt color determination of petroleum wax products.
• Not applicable: solid samples without appropriate treatment; petroleum products containing dyes or having strong fluorescence.

3. Method principle

Inject the test sample into the sample cell, and place the sample cell in the optical path of the automatic instrument. The instrument obtains the CIE tristimulus values by measuring the transmittance of the test sample (under CIE light source C and CIE 1931 standard observer), and converts them into Saybolt color or color plate color through appropriate calculation rules. (See Chapter 4)

4. Reagents and materials (purity / preparation)

• 6.1 Unless otherwise specified, use analytical grade reagents.
• 6.2 Dilution solvent: kerosene or white oil or colorless solvent with a Saybolt color number greater than +21 as measured by this document or GB/T 3555; used for the determination of color plate color after dilution of dark oils.
• 6.3 Qualitative filter paper: medium speed, diameter 9cm to 12.5cm.
• Warning: kerosene is flammable and its vapor is harmful.
• Appendix A Reagents for preparation of colorimetric standard samples (informative):
  • Dyes: Sudan yellow (Solvent Yellow 16) CAS 4314-14-1; Sudan 1 (Solvent Yellow 14) CAS 842-07-9; Solvent Blue 35 CAS 17354-14-2; Sudan red 5B (Oil Red O) CAS 1320-06-5; Solvent Violet 14 CAS 8005-40-1; Transparent Violet B (Solvent Violet 13) CAS 81-48-1; Solvent Green 28 CAS 28198-05-2.
  • Alkyl diphenylethane: capacitor grade as described in IEC 867, 15℃ density 0.9865g/cm³～0.9877g/cm³.
  • Dodecane: composition and content are shown in Table A.1 (undecane ≤0.2%, dodecane ≥99.5%, tridecane ≤0.2%, volume fraction); tristimulus values are shown in Table A.2 (X ≥90.00, Y ≥92.00, Z ≥105.00).
  • The absorption range of dye solutions is shown in Table A.3; the preparation of Saybolt color mixed dye solutions is shown in Table A.4; the weighing amounts for Saybolt color mixed dye solutions are shown in Table A.5; the specified values for Saybolt color standard samples are shown in Table A.6; the preparation of color plate color mixed dye solutions is shown in Table A.7; the preparation of color plate color standard samples is shown in Table A.8; the specified values for color plate color standard samples are shown in Table A.9.

5. Instruments and equipment

• 5.1 Instruments meeting 5.1.1 or 5.1.2 may be used for this document.
• 5.1.1 Requirements for spectrophotometer:
  • a) Wavelength range: 380nm～780nm;
  • b) Effective wavelength width: the effective wavelength width of the slit beam should be at 10nm±2nm or 5nm±1nm;
  • c) Linearity: ±0.5% of full scale; reproducibility: ±0.2%;
  • d) Wavelength accuracy: ±1nm;
  • e) Geometric conditions: normal illumination and collection, the illumination beam does not include rays with an angle greater than or equal to 5° from the center line; the inclination angle of the illumination beam center line relative to the perpendicular to the sample surface is within the range of 0°±2°;
  • f) It should be able to calculate tristimulus values using CIE standard light source C and CIE 1931 standard observer (CIE XYZ);
  • g) If the measurement results of other types of spectrophotometers are equivalent to those of the instruments described in 5.1.1 from 1) to 6), they may also be used.
• 5.1.2 Tristimulus filter colorimeter: has high precision for measuring the color of transparent liquids; can convert the transmitted light of the sample into tristimulus values according to ASTM E308 using CIE standard light source C and CIE 1931 standard observer; can correlate the tristimulus values with GB/T 3555, GB/T 6540 color numbers and automatically calculate the Saybolt color number and/or color plate color number; when measuring petroleum wax samples, it needs to have a heating function, at least capable of heating to 85℃, and can maintain the sample cell at a constant temperature of 85℃ during measurement.
• 5.1.3 Sample cell: clean, colorless and transparent, not contaminated by the test sample; 33mm optical path is used for measuring color plate color, 100mm optical path is used for measuring Saybolt color; operate according to the instrument instructions.
• 5.2 Ultrasonic bath: non-heating type (optional), used to eliminate gas or bubbles in viscous samples.
• 5.3 Balance: accurate to 0.1g.
• 5.4 Oven: static (without fan-assisted circulation), capable of heating to 85℃±5℃, temperature control accuracy 2℃.
• Appendix A Instruments (informative): sample cell optical path lengths 10mm, 33mm, 100mm; balance precision 0.1mg or higher; pipette capacity 2mL; volumetric flasks 200mL and 250mL; stoppered ground-glass conical flasks 100mL; beakers 50mL.

6. Recommended operating conditions

• Liquid petroleum products: measure at room temperature (see 9.2.1).
• Petroleum wax products: the instrument and sample cell should be kept at a constant temperature of 85℃ for at least 30min; after the molten sample is injected into the preheated sample cell, stabilize for 5min～10min (see 9.2.2).
• Melting of petroleum wax: heat and melt in an oven at 85℃±5℃ or 11℃～17℃ above the melting point of the petroleum wax; the heating and constant temperature time should not exceed 1.5h (see 8.2).
• Opaque liquid samples: heat to 6℃ above the cloud point (see GB/T 6986), and observe the color at this temperature (see 8.1).
• The sample injection volume should exceed 70% of the sample cell volume (see 9.2.1, 9.2.2).
• For a single sampling, continuously measure 3 times; for liquid petroleum products, the difference between the results of 3 times shall not exceed 1 Saybolt color numbers or shall not exceed 0.5 color plate color numbers; for petroleum wax products, the difference between the results of 3 times shall not exceed 1 Saybolt color numbers; take the test result with the darkest color among the 3 times as the reported result (see 9.2.1, 9.2.2).

7. Sampling and sample preparation

• 7.1 Sampling shall be carried out in accordance with the requirements of GB/T 4756, GB/T 27867 or SH/T 0229.
• 7.2 Viscous samples (such as lubricating oil) tend to retain gas or bubbles when heated in an oil bath; an ultrasonic bath (do not turn on the heating function if present) may be used for 10min to remove gas or bubbles.
• 8.1 Liquid petroleum products: if the test sample is opaque, heat to 6℃ above the cloud point (see GB/T 6986), and observe the color at this temperature; if the color plate color of the test sample is greater than 8.0, mix 15 parts of sample with 85 parts of kerosene (volume ratio), and determine the color of the mixture.
• 8.2 Petroleum wax products: weigh about 100g of petroleum wax sample, break it into small pieces as much as possible, place it in an oven at 85℃±5℃ or 11℃～17℃ above the melting point of the petroleum wax, and heat to melt; the heating and constant temperature time shall not exceed 1.5h; if it is still not clear after melting, filter it using qualitative filter paper under 85℃±5℃ conditions to obtain a clear test sample before measurement, and indicate in the report of the sample color that the sample has been filtered.

8. Analysis steps

• 9.1 Calibration
  • 9.1.1 Prepare the spectrophotometer or tristimulus filter colorimeter according to the instrument instructions, and periodically determine standard samples for Saybolt color and/or color plate color according to GB/T 3555 and/or GB/T 6540 to check instrument performance. For the preparation method of colorimetric standard samples, see Appendix A.
  • 9.1.2 For basic calibration check procedures, see Appendix B; calibration checks may also be performed according to the instrument supplier's instructions.
• 9.2 Measurement
  • 9.2.1 Liquid petroleum products: at room temperature, pour the sample into the sample cell; the injection volume should exceed 70% of the sample cell volume; place the sample cell in the instrument optical path and perform color measurement according to the instrument instructions; for a single sampling, continuously measure 3 times, and the difference between the results of consecutive 3 tests shall not exceed 1 Saybolt color numbers or shall not exceed 0.5 color plate color numbers; take the test result with the darkest color among the 3 measurement results as the reported result.
  • 9.2.2 Petroleum wax products: the instrument and sample cell should be kept at a constant temperature of 85℃ for at least 30min; immediately inject the molten test sample into the preheated sample cell and stabilize for 5min～10min; the injection volume should exceed 70% of the sample cell volume; measure the color of the test sample according to the instrument operating instructions; for a single sampling, continuously measure 3 times, and the difference between the results of 3 tests shall not exceed 1 Saybolt color numbers; take the test result with the darkest color among the 3 measurement results as the reported result.
• Appendix B Basic calibration procedure (informative):
  • B.1 Saybolt color measurement: complete setting, calibration, and standardization according to the instrument manual; pour dodecane into the sample cell and measure the tristimulus values (100mm cell recommended); repeat the measurement for each Saybolt color standard sample; calculate the psychometric lightness L* and psychometric chromaticity a*, b* according to ASTM E308 (equations B.1 to B.3); use equation (B.4) to calculate the color difference ΔEab between dodecane and the standard samples, and plot the color difference against Saybolt color to obtain the calibration curve; equation (B.5) is used for a cell with path length 100mm (S = α + β/(log ΔEab − τ), typical value of α is 51.1, typical value of β is 44.5, typical value of τ is 2.55).
  • B.1.2 Sample measurement: sample according to GB/T 4756, GB/T 27867, or SH/T 0229; if the sample is opaque, filter with qualitative filter paper until transparent (replace the filter paper if necessary); obtain the tristimulus values of the sample and convert them to L*, a*, b*, use equation (B.4) to calculate the color difference ΔE*ab between dodecane and the sample; use the B.1.1 curve to determine the Saybolt color number of the sample, to one decimal place.
  • B.2 Color plate color measurement: complete setting, calibration, and standardization according to the instrument manual; pour the color plate color standard sample into the cell and measure the tristimulus values (33mm cell recommended); repeat the measurement for each standard sample; use equation (B.6) to calculate the sum of optical densities ΣD (DX=log10(X/Xn), DY=log10(Y/Yn), DZ=log10(Z/Zn), Xn=98.072, Yn=100.000, Zn=118.225); use equation (B.7) A = α + β×ΣD to prepare the calibration curve (typical value of α is 0.25, typical value of β is 0.8695); measure the sample according to B.2.3, to one decimal place; if the color plate color number exceeds 8.0, dilute with dilution solvent at sample:dilution solvent = 15:85 (volume ratio) and then measure the chromaticity of the mixed sample.

9. Qualitative and quantitative determination and calculation formulas

• Result conversion: the instrument obtains the CIE tristimulus values by measuring transmittance (CIE light source C and CIE 1931 standard observer), and converts them into Saybolt color or color plate color through appropriate algorithms (see Chapter 4).
• Appendix B Calculation formulas:
  • Equation (B.1) L* = 116×(Y/100)^(1/3) − 16
  • Equation (B.2) a* = 500×[(X/98.72)^(1/3) − (Y/100)^(1/3)]
  • Equation (B.3) b* = 200×[(Y/100)^(1/3) − (Z/118.225)^(1/3)]
  • Equation (B.4) ΔEab = [(L1−L0)² + (a1−a0)² + (b1−b*0)²]^(1/2)
  • Equation (B.5) S = α + β/(log ΔE*ab − τ) (for a cell with path length 100mm; typical value of α is 51.1, typical value of β is 44.5, typical value of τ is 2.55)
  • Equation (B.6) ΣD = DX + DY + DZ
  • Equation (B.7) A = α + β×ΣD (typical value of α is 0.25, typical value of β is 0.8695)
• Reporting rules (Chapter 10):
  • 10.1 Report the color plate color as “No. ×××”, or the Saybolt color as “Saybolt color No. ×××”.
  • 10.2 When the Saybolt color is darker than +30 Saybolt color number, round to an integer; when lighter than +30 Saybolt color number, report as greater than +30 Saybolt color number.
  • 10.3 Color plate color reporting: ×.1 to ×.4 add “less than” and change to ×.5 (e.g., 3.1 to 3.4 is reported as less than No. 3.5); ×.5 report that value (e.g., 3.5 is reported as No. 3.5); ×.6 to ×.9 add “less than” and round to the next integer value (e.g., 3.6 to 3.9 is reported as less than No. 4.0); ×.0 report that value (e.g., 4.0 is reported as No. 4.0); greater than 8.0 is reported as greater than No. 8.0.
  • 10.4 If the sample has been diluted according to Chapter 8, add the word “diluted” when reporting the color of the mixture (e.g., less than No. 7.5 (diluted)).
  • 10.5 Turbid samples cannot be tested directly; they should be filtered until transparent before measurement; if filtered, add the words “sample filtered” to the report.

10. Precision

• 11.1 General: The precision for liquid petroleum products was obtained through a precision study by 5 laboratories on 10 petroleum products; the precision for petroleum wax products was obtained according to the requirements of GB/T 6683.1 through a precision study by 6 laboratories on 11 petroleum wax samples; judged at the 95% confidence level.
• 11.1.1 Repeatability (r):
  • Liquid petroleum products: Saybolt color r1=0.14 Saybolt color number; color plate color r2=0.10 number.
  • Petroleum wax products: Saybolt color r3=0.60 Saybolt color number.
• 11.1.2 Reproducibility (R):
  • Liquid petroleum products: Saybolt color R1=1.24 Saybolt color number; color plate color R2=0.48 number.
  • Petroleum wax products: Saybolt color R3=2.22 Saybolt color number.
• 11.2 Bias:
  • 11.2.1 There is no bias between the test results of this document and the test results of GB/T 6540.
  • 11.2.2 There is no bias between the test results of this document and the test results of GB/T 3555 in the range of 0 to +30; results in the range of -16 to 0 have bias.

11. Report

• Report according to Chapter 10 (see the reporting rules in Section 9 of this card).
• Report contents: color plate color number or Saybolt color number; add “diluted” when diluted; add “sample filtered” when filtered.

12. Reference documents

• GB/T 3555 Standard test method for Saybolt color of petroleum products—Saybolt chromometer method
• GB/T 4756 Standard practice for manual sampling of petroleum liquids
• GB/T 6540 Standard test method for color of petroleum products
• GB/T 6986 Standard test method for cloud point of petroleum products
• GB/T 27867 Standard practice for automatic sampling of petroleum liquids by pipeline
• SH/T 0229 Standard practice for sampling of solid and semi-solid petroleum products
• References:
  • [1] IEC 867 Insulating Liquids—Specification for Unused Liquids Based on Synthetic Aromatic Hydrocarbons
  • [2] Japanese Industrial Standard: K0510 High Purity Dodecane
  • [3] IP 17 Color measurement—Lovibond colorimeter
  • [4] ASTM E308 Practice for computing the colors of objects by using the CIE system
  • [5] GB/T 6683.1 Petroleum and related products—Determination of precision data in relation to methods of test—Part 1: Determination of precision data of test methods

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick reference for questions and answers