GB/T 6540-2025 Determination of color of petroleum products

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 title / English name / replacement relationship

• Standard number: GB/T 6540—2025
• Chinese full title: Determination of color of petroleum products
• English name: Determination for colour of petroleum products
• Replacement relationship: replaces GB/T 6540—1986 "Method for determination of color of petroleum products"; this document was first issued in 1986, and this is the first revision.
• Publication/implementation: published by 2025-10-05, implemented by 2026-05-01.
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280).
• Drafting organizations: Sinopec Research Institute of Petroleum Processing Co., Ltd., Sinopec Lubricant Co., Ltd., PetroChina Guangxi Petrochemical Company, Beijing Petroleum Product Quality Supervision and Inspection Center, Sinopec Sales Co., Ltd. Beijing Petroleum Branch.
• Main drafters: Mei Li, Zheng Yu, Xu Hualing, Li Heran, Tian Deying, Hu Enxiu, Shi Xia, Li Tao, Yang He, Zhao Jie, Wang Chao, Wang Shoucheng.

2. Scope of application and non-applicability

• This document describes a method for determining the color of petroleum products by visual inspection.
• Applicable to the determination of color of various petroleum products such as lubricating oils, kerosene, diesel, petroleum wax, etc.
• Not applicable: not provided in the available source.

3. Method principle

Pour the sample into a sample container, and under a standard light source, compare it with standard glass color comparison plates with color numbers ranging from 0.5 to 8.0, and take the equal color number as the color number of the sample. If no exact matching color is found for the sample color and it falls between two standard colors, report the darker color number of the two colors. (See Chapter 4 Method summary)

4. Reagents and materials (purity / preparation)

• 5.1 Diluent: kerosene or other diluent (such as white oil or 100 neutral solvent naphtha), used to dilute dark samples during testing; its color should be lighter than the +21 Saybolt color measured by GB/T 3555.
• 5.2 Qualitative filter paper: medium speed, diameter 9 cm~12.5 cm.
• 5.3 Distilled water: meets the requirements of GB/T 6682—2008 grade three water or above.
• Purity and specific preparation methods: not provided in the available source (apart from the above description).

5. Instruments and equipment

• 6.1 Colorimeter: composed of a light source, standard glass color comparison plates, a sample container with a cover, and an observation eyepiece, and shall meet the requirements of Annex A.
• 6.2 Sample container: a transparent colorless glass sample container, a transparent flat-bottomed glass test tube with an inner diameter of 30 mm–32.4 mm and a height of 115 mm–125 mm, with a wall thickness not greater than 1.6 mm, and specifications conforming to GB/T 6986.
• 6.3 Sample container cover: may be made of suitable material; the inner surface of the cover is dark black; all sample container covers can completely shield against external light.
• 6.4 Ultrasonic bath: its size should accommodate the container holding the sample and be able to eliminate foam or entrained air in samples with relatively high viscosity.
• 6.5 Oven: capable of maintaining temperature up to 85 ℃±2 ℃.

6. Recommended operating conditions

• Light source: artificial light source, composed of a light source lamp, daylight filter glass, and a flashing translucent opal glass; the spectral characteristics produced by the combined components are similar to northern daylight (color temperature 6700 K±300 K). (Annex A.2)
• Light source lamp: a color lamp with a color temperature of 2750 K or a quartz halogen lamp with a color temperature of 2900 K; provide a translucent background with an illuminance of 900 lx±100 lx. (A.2.1.1)
• Observation conditions (two fields of view): the two illuminated surfaces are symmetrically distributed on both sides of the vertical centerline; the distance between the nearest parts in the horizontal direction shall be not less than 2° and not greater than 3.6° in visual angle to the observer's eye; the diameter of each illuminated surface shall be at least 2.2° in circumference in visual angle. (A.1.2)
• Observation conditions (three fields of view): the illuminated surfaces are symmetrically distributed on both sides of the vertical centerline, so that when the illuminated surface and any color standard comparison plate are observed, the visual angle is not less than 0.3° or not greater than 0.6°. (A.1.3)
• For other operating temperature conditions, see Chapter 8 (liquid products are heated to above the cloud point by 6 ℃; petroleum wax 85 ℃±2 ℃ or above the melting point by 11 ℃~17 ℃).

7. Sampling and sample preparation

• 7.1 Sample according to the requirements of GB/T 4756 or GB/T 27867.
• 7.2 For relatively viscous lubricating oils, use an ultrasonic bath (6.4) for about 10 min without heating to eliminate foam or entrained air in the oil.
• 8.1 Liquid petroleum products: pour the sample into the sample container (6.2) to a height of 50 mm or above 50 mm, and observe the sample. If the sample is opaque, the sample may be heated to above the cloud point by 6 ℃ (according to GB/T 6986), and then its color is measured at that temperature. If the sample is turbid, the sample should be filtered through qualitative filter paper until transparent before measurement. If the color of the sample is darker than standard color No. 8.0, mix 15 parts by volume of sample with 85 parts of diluent, and determine the color of the mixture.
• 8.2 Petroleum wax products: break the sample into small pieces as much as possible, place it in an oven (6.5) at 85 ℃±2 ℃ or above the melting point of the petroleum wax by 11 ℃~17 ℃, heat to melt, with heating and constant-temperature time not exceeding 1.5 h, and determine its color at this temperature. If the sample is still turbid after melting, filter it at this temperature using qualitative filter paper to obtain a clear sample before measurement, and when reporting the sample color, note that the sample was filtered. If the sample color is darker than No. 8.0, at the same temperature mix 15 parts by volume of the molten sample with 85 parts of diluent, and determine the color of the mixture at this temperature.

8. Analysis procedure

• 9.1 Fill one or more sample containers with distilled water to a height of 50 mm or above 50 mm, place the sample container in a compartment of the colorimeter (6.1) through which the standard glass color comparison plates can be observed, then place another sample container containing the sample into another compartment. Cover with the sample container cover (6.3) to isolate all external light.
• 9.2 Turn on the light source and compare the color of the sample with the standard glass color comparison plates. When using a three-field colorimeter, the sample should be placed between the standard glass color comparison plate numbers of adjacent colors, or between the standard glass color comparison plate number that best matches its color and the standard glass color comparison plate number of the adjacent darker color. When using a two-field colorimeter, determine the standard glass color comparison plate number that is the same as the sample color; when they cannot be exactly the same, use the standard glass color comparison plate number of the adjacent darker color. Perform two consecutive determinations on a single sample and report the result of each determination.

9. Qualitative and quantitative determination and calculation formula

• 10.1 The standard glass color comparison plate number that is the same as the sample color is taken as the color number of the sample color, for example: No. 3.0, No. 7.5.
• 10.2 If the color of the sample lies between two standard glass color comparison plates, report the darker glass color comparison plate number and add "<" before the color number (for example, <No. 3.0, <No. 7.5); it should not be reported as a color darker than the given standard (for example, >No. 2.5, >No. 7.5). If the color of the sample is darker than No. 8.0, stop the determination and report >No. 8.0. If the color of the sample is lighter than glass color comparison plate No. 0.5, report <No. 0.5.
• 10.3 If the sample has been diluted according to Chapter 8, add the word "diluted" after the color number reported for the mixture color, for example, <No. 7.5 (diluted).
• 10.4 If the two determination results for the sample color are inconsistent, report the darker color number.
• 10.5 If the sample has been filtered before color determination, add the note "sample filtered" when reporting.
• Calculation formula: not provided in the available source (this method is a visual colorimetric method and has no calculation formula).

10. Precision

• 11.1 General: this document judges the reliability of test results in accordance with the provisions of 11.2 and 11.3 (95% confidence level).
• 11.2 Repeatability: for consecutive determinations by the same operator, in the same laboratory, using the same instrument, on the same sample, the difference between the two test result color numbers shall not be greater than No. 0.5.
• 11.3 Reproducibility: for determinations by different operators, in different laboratories, using different instruments, according to the same test method, on the same sample separately, the difference between the two single, independent result color numbers shall not be greater than No. 1.0.

11. Report

• For result reporting requirements, see Chapter 10 (10.1~10.5): report the color number, the rule for adding "<", dilution annotation, filtration annotation, and when the two results are inconsistent, report the darker color number.
• Other report formats: not provided in the available source.

12. Normative references

• GB/T 3555 Determination of Saybolt color of petroleum products - Saybolt colorimeter method
• GB/T 4756 Manual sampling of petroleum liquids
• GB/T 6682—2008 Specifications and test methods for water for analytical laboratory use
• GB/T 6986 Determination of cloud point of petroleum products
• GB/T 27867 Automatic pipeline sampling of petroleum liquids
• GB/T 1.1—2020 "Directives for standardization work - Part 1: Structure and drafting rules for standardization documents" (cited in the foreword)

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 Q&A