The viscosity of crude oils can be measured using a standard method (ASTM D2983). However, different reference temperatures, such as 40☌ (104 ☏), 50 ☌ (122 ☏), and 60 ☌(140 ☏), are also used to report kinematic viscosities of petroleum fractions. At Wearcheck, every sample gets four basic tests: ICP spectroscopy, particle quantification, viscosity at 40☌ and water screening. Values of kinematic viscosity for pure liquid hydrocarbons are usually measured and reported at two reference temperatures, 38☌ (100☏) and 99☌ (210☏) in cSt. Kinematic viscosity is expressed in units of centistokes (cSt), Saybolt Universal seconds (SUS), and Saybolt Furol seconds (SFS).
Viscosity of liquids is usually measured in terms of kinematic viscosity, which is defined as the ratio of absolute (dynamic) viscosity to absolute density (ν = μ/ρ). Among petroleum products, viscosity constitutes a critically important characteristic of lubricating engine oils. The Plastic Viscosity depends mainly on the friction between solids and the liquid. Plastic Viscosity is defined as the 600 RPM shear stress reading minus the 300 RPM shear stress reading. (Check also: Viscometer Test Procedure) Plastic Viscosity. Interestingly, the viscosity of liquid decreases with increasing temperature, while viscosity of gases increases with increasing temperature. Measurements are normally made at shear rates of 600 and 300 RPMs. Power requirement to transport (e.g., to pump) a fluid depends strongly on the fluid’s viscosity. Newton’s Law of Viscosity provides a physical definition of viscosity.
A high-viscosity fluid has a low tendency to flow, whereas low-viscosity fluids flow easily. Viscosity, commonly depicted by the symbol μ, is a physical property of a fluid that describes its tendency/resistance to flow.
