Measurement and Testing

  • How is Oil Quality Tested?

How is Oil Quality Tested?

Apr 16 2021

Quality testing is an integral part of the crude oil industry. Not only does it help determine price, but it allows buyers to optimise their purchases and choose the right oil for their needs. Changes in crude oil quality are common, with factors such as blend ratios, well depletion, sediment contamination, corrosion and transport issues all affecting integrity. For this reason, it’s important for buyers to prioritise oil quality testing.

Sourcing samples

Depending on the scenario, oil samples can be obtained from a variety of sources. These can include cargo ships, pipelines, reservoirs, storage tanks, refineries and forecourts. Once a sample has been obtained, how is oil quality tested? Below we explore some of the key methods used to assess oil quality.

Laboratory testing

In-depth oil testing is conducted in purpose-built laboratories by highly skilled petroleum chemists with access to sophisticated equipment and instruments. Once samples have been collected, oil is sent to laboratories to undergo testing. This process is known as a crude oil assay and offers the buyer detailed insight into the characteristics of a sample.

The best laboratory tests will adhere to standards outlined by industry-leading organisations such as the American Society for Testing and Materials (ASTM), International Organisation for Standardisation (ISO) and the Institute of Petroleum (IP).

Testing for sulphur

Sulphur content is one of the most important variables and determines if an oil is classed as sweet or sour. Ultraviolet Fluorescence is a common test method used to determine sulphur content in light hydrocarbons, with the process outlined in detail by the ASTM. Wavelength Dispersive X-ray Fluorescence Spectrometry (WDXRF) is another popular test method used to measure the sulphur content of petroleum fuels, with scientists using a polychromatic x-ray beam to excite sulphur electrons.

Testing for density

Density is another important standard, with many oil assays using the Standard Test Method for Density, Relative Density, or API Gravity of Crude Petroleum and Liquid Petroleum Products by Hydrometer Method outlined by the ASTM. This involves pouring a sample into a tall container, then lowering the hydrometer into the liquid until it floats.

When testing the characteristics of lubricating oils, it’s important to have a clear and precise understanding of the additive elements contents. Not only does this guarantee optimal engine and machine performance, it extends the life of moving parts and minimises environmental impact. Frank Portala from Bruker AXS discusses the best-practice methods used to carry out elemental analysis in ‘ASTM D7751: Determination of Additive Elements in Lubricating Oils by EDXRF Analysis.’


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