Raw materials in the chemical process industries (CPI) usually have a reported viscosity value on the data sheet that accompanies the product. Experiments have shown that the viscosity values obtained at 0.1 or 0.01 rpm can be several orders of magnitude higher than the one recorded at 20 rpm. When pumping asphalt, the startup torque required to get the pump going initially suggests that a second viscosity test at a much lower rotational speed makes sense. However, this straightforward single-point test does not provide the complete picture for asphalt flow behavior. Record the viscosity value, make sure that it falls within prescribed maximum and minimum limits, and then report whether the number passes or fails. The standard test method for pumpability, according to ASTM D4402, is to use a regular viscosity (RV) torque rotational viscometer at 20 rpm or a low viscosity (LV) instrument at 12 rpm. An important concept, sometimes forgotten, is that a material’s viscosity is not a single-point measurement, but often depends on a number of factors.

This article reacquaints the reader with the basic concepts and terminology for viscosity and addresses techniques to quantify it. The bottom line is to come up with ways to measure viscosity so that you can quantify whether a material will flow the way it needs to.

For handlers of all materials that flow, either while being processed or in an end-use, it is important to think about the materials’ flow characteristics. To be brief, viscosity is resistance to flow. Most engineers know what viscosity is, but may have trouble explaining it.

Dynamic viscosity units water standard