White Oil Inspection

White oil testing mainly conducts scientific testing and analysis on the kinematic viscosity, flash point, pour point and solidification point, colour, aromatic hydrocarbon and sulfur contents, acid value and base value and other items, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for the production enterprise quality control and downstream user product acceptance.

Testing items

Kinematic viscosity: The kinematic viscosity is the key indicator for the measurement of the internal friction of the white oils when flowing under the gravity, usually determined at the different temperatures (such as 40 degrees Celsius and 100 degrees Celsius). This testing is directly related to the lubrication performance, heat transfer efficiencies and applicability in the specific applications of the white oils. For example, the high viscosity white oils are suitable for the heavy load gear lubrication, while the low viscosity white oils are commonly used in the textile and cosmetics industries.

Flash point (open/closed cup): The flash point is the core parameter for the evaluation of the white oil safety, referring to the lowest temperatures at which the oil vapour and air mixtures momentarily flash when meeting the open flames under the specified conditions. The open cup flash points are commonly used for the high flash point oils, while the closed cup flash points are applicable to the oils with the stronger volatilities. This indicator is crucial for the storage, transportation and use safety of the products.

Pour point and solidification point: The pour point refers to the lowest temperatures at which the oils can maintain the flow under the standard conditions, while the solidification point is the highest temperatures at which the oils stop flowing. These two indicators jointly characterise the low temperature fluidity of the white oils, determining their use performance in the cold environments, and are the important evaluation bases for the industrial white oils and refrigeration oils.

Colour (Saybolt/platinum-cobalt): The colour of the white oils is the important appearance indicator of their refining depths and purity. Usually determine with the Saybolt colour numbers or platinum-cobalt (Pt-Co) colour numbers. The excessively deep colours may mean that the oils contain the incompletely removed impurities such as the aromatic hydrocarbons and gums, affecting their applications in the high-end daily chemicals and pharmaceutical fields.

Aromatic hydrocarbon and sulfur contents: The aromatic hydrocarbon contents, especially the polycyclic aromatic (PCA) contents, are the keys for the measurement of the white oil toxicities and safety. The sulfur contents reflect the corrosiveness and environmental friendliness of the oils. Determined through the ultraviolet absorbances (UV absorbance) or chromatography methods, and the low aromatic hydrocarbon and low sulfur are the mandatory requirements of the food grade and cosmetic grade white oils.

Acid value and base value: The acid value represents the contents of the acidic substances in the oils (calculated as the KOH), while the base value represents the contents of the alkaline substances. The excessively high acid values of the new oils may originate from the refining process residues; the acid value increases during the use predict the oxidative deterioration. This indicator is used for the monitoring of the oil corrosiveness and chemical stability.

Water-soluble acids and bases and moisture: The water-soluble acids and bases test whether the inorganic acids or bases exist in the oils, and these substances will strongly corrode the equipment. The moisture content determination prevents the oil emulsification, additive failures or equipment rust caused by the presence of the moisture, ensuring the oil purity.

Testing scope

Industrial white oils: Mainly used as the processing aids, lubricants and heat transfer fluids in the industries such as the plastics, chemical fibres and rubber. The inspection reports need to emphatically focus on their basic physical indicators such as the viscosities, flash points and pour points, as well as the colours and oxidation stability, ensuring that they meet the temperature and stability requirements of the specific processes.

Cosmetic grade white oils: Applied in the personal care products such as the skin care, hair care and lipsticks. Their inspection scope is extremely strict, and in addition to the basic physical performance, must mandatorily test the ultraviolet absorbances (280-289 nm and 290-299 nm), polycyclic aromatic hydrocarbons (PCA), readily carbonisable substances, etc., to conform to the various pharmacopoeias (such as the USP and EP) and cosmetic raw material safety standards.

Food grade white oils: Used for the food processing machinery lubrication, food mould release, candy polishing, etc. Their testing scope needs to follow the regulations such as the FDA 21 CFR 178.3620 and China's GB 1886.215, and the core is the safety indicators, such as the heavy metals (lead and arsenic), carcinogens such as the benzopyrene, as well as the strict aromatic hydrocarbon and sulfur content limits.

Pharmaceutical grade white oils: As the pharmaceutical excipients, used for the ointment bases, capsule lubrication, etc. Their testing standards are the strictest, usually need to conform to the monograph provisions of the United States Pharmacopeia (USP), European Pharmacopoeia (EP) or Chinese Pharmacopoeia (ChP), including the full biological and chemical safety tests such as the sterility tests, bacterial endotoxins and solid paraffin inspections.

White oils for the special processes: Including the textile oil agents, refrigeration oils, transformer oils, etc. The inspection scope needs to be combined with the downstream special application scenarios, such as the textile white oils need to test their emulsifying properties and the effects on the dyeing fastness; the refrigeration oils need to test their compatibility with the refrigerants and flocculation points, etc.

Comparison testing of the new and used oils: For the white oils in service, the scope of the inspection reports not only includes the performance indicators, but also needs to cover the contamination degree analyses (particle counting), oxidation products (FTIR), additive consumption conditions, etc., to evaluate the remaining lives of the oils and the equipment wear states, guiding the oil change cycles.

Testing methods

Kinematic viscosity determination method (GB/T 265 / ASTM D445): Adopt the glass capillary viscometers, measure the times required for a certain volume of the oils to flow through the calibrated capillaries under the gravity in the constant temperature baths, and calculate the kinematic viscosity values. This is the most classic and accurate viscosity measurement method, widely applied to the oil quality control.

Flash point determination method (GB/T 3536 / ASTM D92): The Cleveland open cup method (COC) is the common method for the determination of the white oil flash points. Inject the samples into the open cups of the specific specifications, heat at the specified rates and regularly sweep above the liquid surfaces with the standard flames, and record the lowest temperatures at which the flash fires occur. The closed cup method uses the sealed containers, applicable to the samples with the higher volatilities.

Ultraviolet absorbance method (GB/T 11081 / IP 346): The core method for the precise determination of the aromatic hydrocarbons, especially the carcinogenic polycyclic aromatic (PCA) contents in the white oils. After the dilution of the samples with the n-hexane, measure the absorbances with the ultraviolet spectrophotometers at the specific wavelengths (such as 290-299 nm). The lower the absorbance values, the more thorough the aromatic hydrocarbon removal and the safer the products.

Colour determination method (GB/T 3555 / ASTM D156): The Saybolt colour determination method is to inject the samples into the glass tubes of the standard lengths, and carry out the visual comparisons with the standard colour plates under the specific light sources, determining their colour numbers. The platinum-cobalt colorimetric method compares the sample colours with the standard solutions of the different concentrations of the potassium chloroplatinate and cobalt chloride, expressed by the colour numbers, with the higher precisions.

Pour point and solidification point determination method (GB/T 3535 / ASTM D97): After the preheating of the samples in the specified test tubes, cool at the specific rates, and every 3 degrees Celsius take out the test tubes horizontally to observe the flow conditions. The temperatures at which the liquid surfaces no longer move when the test tubes are horizontally placed for 5 seconds plus 3 degrees Celsius are the pour points. The solidification point determination observes the highest temperatures at which the liquid surfaces stop flowing.

Sulfur content determination method (GB/T 17040 / ASTM D4294): The energy dispersive X-ray fluorescence spectrometry (EDXRF) is the common method. This method uses the X-rays to excite the sulfur atoms in the samples, and quantifies the sulfur contents through the measurement of the characteristic X-ray fluorescence intensities produced thereby, with the advantages of the fast speeds, non-destructiveness and high precisions.

Testing standards

Domestic standards:

1. GB/T 265-1988, Petroleum products — Determination of kinematic viscosity and calculation of dynamic viscosity

2. GB/T 3536-2008, Petroleum products — Determination of flash and fire points — Cleveland open cup method

3. GB/T 261-2008, Determination of flash point — Pensky-Martens closed cup method

4. GB/T 11081, White oils — Determination of ultraviolet absorbance

5. GB/T 3555, Petroleum products — Determination of Saybolt colour

6. GB/T 3535, Petroleum products — Determination of pour point

7. GB/T 17040, Petroleum products — Determination of sulfur content by energy-dispersive X-ray fluorescence spectrometry

8. GB 1886.215, National food safety standard — Food additive — White mineral oil

9. United States Pharmacopeia (USP), European Pharmacopoeia (EP) and Chinese Pharmacopoeia (ChP) — White mineral oil monographs

10. GB/T 602, Chemical reagent — Preparations of standard solutions for impurity determination

11. GB/T 603, Chemical reagent — Preparations of reagent solutions for use in test methods

International standards:

1. ASTM D445, Standard test method for kinematic viscosity of transparent and opaque liquids

2. ASTM D92, Standard test method for flash and fire points by Cleveland open cup tester

3. ASTM D156, Standard test method for Saybolt color of petroleum products

4. ASTM D97, Standard test method for pour point of petroleum products

5. ASTM D4294, Standard test method for sulfur in petroleum and petroleum products by energy dispersive X-ray fluorescence spectrometry

6. IP 346, Determination of polycyclic aromatics in unused lubricating base oils and asphaltene free petroleum fractions — Dimethyl sulphoxide extraction refractive index method

7. FDA 21 CFR 178.3620, Food additives permitted for direct addition to food for human consumption — White mineral oil

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Kinematic viscometers: The core equipment includes the high-precision constant temperature baths (temperature control accuracies of plus or minus 0.01 degrees Celsius), a set of the metrologically calibrated Ubbelohde or Cannon-Fenske capillary viscometers, as well as the high-precision timers. The constant temperature bath media are usually the transparent mineral oils or water, ensuring the constant temperatures of the samples during the testing and guaranteeing the data accuracies.

Open/closed cup flash point testers: The fully automatic flash point testers have been widely used. The instruments integrate the heating modules, flame ignition and scanning devices, temperature sensing and control systems. During the testing, the instruments strictly automatically heat up, ignite, detect the flash phenomena and record the temperatures according to the standard procedures, eliminating the human operation errors and improving the safety and repeatability.

Ultraviolet-visible spectrophotometers: The key instruments for the determination of the white oil ultraviolet absorbances. The instruments are required to have the high resolutions, low stray light and good wavelength accuracies. Usually equipped with the quartz cuvettes and special analysis software, can precisely scan the absorbance curves of the specific wavelength ranges and carry out the data processing.

Automatic pour point/solidification point testers: The modern instruments adopt the optical sensing technologies to replace the human observations. The instruments automatically cool the samples according to the programs, and monitor the sample fluidity in real time through the photoelectric sensors. When the sample flow stops, automatically record and report the pour point or solidification point temperatures, with the high testing efficiencies and objective results.

X-ray fluorescence spectrometers (XRF): Used for the rapid determination of the sulfur and trace metal elements, etc. The instruments generate the primary X-rays through the X-ray tubes to excite the samples, receive and analyse the secondary (fluorescence) X-ray spectra emitted by the samples with the detectors, and calculate the contents of the various elements through the built-in standard curves or fundamental parameter methods.

Gas chromatographs (GC): The gas chromatographs equipped with the flame ionisation detectors (FID) or mass spectrometric detectors (MS) can be used for the analysis of the light components and solvent residues in the white oils, or the qualitative and quantitative analysis of the complex aromatic compounds through the hyphenation with the mass spectrometry (GC-MS), providing the deeper composition information.

Karl Fischer moisture analyzers: Used for the precise determination of the trace moisture in the white oils. The coulometric Karl Fischer moisture analyzers are applicable to the samples with the extremely low moisture contents (ppm levels), and the principle is to electrolyse the iodide ions to generate the iodine, the iodine reacts with the water in the samples, and the moisture contents are precisely determined through the calculation of the electricity consumed by the electrolysis.