Viscosity - D445-97

Significance and Use

Many petroleum products, and some non-petroleum materials, are used as lubricants, and the correct operation of the equipment depends upon the appropriate viscosity of the liquid being used. In addition, the viscosity of many petroleum fuels is important for the estimation of optimum storage, handling an operational conditions. Thus, the accurate determination of viscosity is essential to many product specifications.

Summary of Test Method

The time is measured for a fixed volume of liquid to flow under gravity through the capillary of a calibrated viscometer under a reproducible driving head and a closely controlled and known temperature. The Kinematic viscosity is the product of the measured flow time and the calibration constant of the viscometer.


Very closely allied to this test method is: ASTM D446-97: Standard Specifications and Operating Instructions for Glass Capillary Kinematic Viscometers. In actual practice, the first does not exist without the other.

When we are told the kind of oil we are testing, we can use this test to determine whether it is on specification, whether it is thickening and whether it is thinning out; there are limits to how much thinning or thickening can be tolerated.

Notwithstanding the fact that we are bound to signal an “off-specification” viscosity result, there are times when, whether the viscosity is off or not, we are required to do some “extra” testing so that we may better interpret (analyze) the test result obtained. In the case of oil thickening this may be Infra-red Spectrometry or “Fuel Soot Actual Determination” In the case of oil thinning we would do a Flash Point Test or a Simulated Distillation. NOTE: These tests are covered later.

One way or another, other routine tests or extra tests or both are often needed to interpret the test result obtained.

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