The ASTM D445 procedure can be applied to both transparent and opaque liquids :
- Transparent liquids need to be homogenized and degassed in an ultrasonic bath. If the sample fluid contains fibers or particles, an additional filtration step is required.
- Residual fuel oils and opaque liquids are homogenized by various heating and stirring steps, and particles must be removed with the help of a preheated filter. For opaque liquids, two reverse-flow capillaries are required to determine the kinematic viscosity.
Particles are one of the most common error sources. Filtering is required if the sample contains fibers or solid particles. The pore size of the required filtering screen is 75 µm, so particles larger than 75 µm need to be filtered. Apart from particles in the sample, dust particles inside the capillary can be the cause of faulty measurements. Consequently, correct storage and careful cleaning of the capillaries are essential.
By default, petroleum samples can be measured with manual or automated glass capillary viscometers. Defined Oswald-type, suspended-level type, and reverse-flow capillaries which are specified in the ASTM D445 standard can be used for different samples and viscosity ranges. These viscometers include glass capillaries, capillary holders, a temperature control unit, a temperature-controlled bath, a thermometer, a bath liquid suitable for the measuring temperature, and a time-measuring device that meets the standard’s required specifications.