4 Analytical Instrumentation
ASTM D7042: THE QUANTUM LEAP IN VISCOSITY TESTING TECHNOLOGY
Introduction
Viscosity is a critical quality-control parameter across many industries, particularly in petroleum, where it serves as a key indicator for products ranging from crude oil to refi ned outputs. Traditionally, the industry has relied on glass capillaries in line with the ASTM D4451
standard
to measure viscosity manually. This method, being gravity-dependent, primarily reports only kinematic viscosity rather than dynamic viscosity. In contrast, modern viscosity measurement techniques are independent of gravitational infl uence and measure dynamic viscosity directly. To facilitate comparisons to other methods, these modern methods also calculate kinematic viscosity by incorporating an additional density measurement, and dividing dynamic viscosity by the sample density.
ν = η/ρ
ν… kinematic viscosity η… dynamic viscosity ρ… density
the SVM test method, as an example, we’ll highlight the benefi ts of these innovations for both individual users and the industry as a whole.
A shift from tradition to innovation
The ASTM D445 standard, a traditional method for determining kinematic viscosity, was fi rst introduced in 1937, making it an over 80-year-old technique. Achieving accurate results with ASTM D445 typically requires a skilled operator who rigorously follows the detailed standard procedure, which has now over 15 pages. Among its many requirements, ASTM D445 mandates precise temperature control, allowing no more than a ±0.02 °C variation within the capillary bath, correct positioning of the capillary to within 1° (or even 0.3° for specifi c viscometers), establishing an appropriate equilibration time through trial, regular verifi cation of timer accuracy, and ensuring a minimum fl ow time of 200 seconds.
Over recent decades, efforts have been made to modernize ASTM D445 by integrating automated procedures into what has historically been a manual method. Automated D445 systems are defi ned as apparatuses with one or more mechanized steps that retain the fundamental technique and principles of the manual method. To enhance measurement speed and broaden the viscosity range, a complex “kinetic energy correction” calculation was introduced. However, as ASTM D445 expanded to include automation, only a limited range of samples – including FAME, base oils, and formulated oils – were tested at only select temperatures to verify consistency with the manual method. Currently, there is no comprehensive assessment confi rming that automated systems are unbiased for all sample types used in the petroleum industry, leaving this gap unaddressed.
SVM Series: Automatic ASTM D7042 Viscometers
In this article, we explore recent advancements in viscosity measurement techniques, which have evolved well beyond simply measuring multiple physical parameters simultaneously. We will also discuss why new viscosity testing methods have adopted measurement principles distinct from the traditional glass capillary technique. Using ASTM D7042,2
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Even with automation, several inherent limitations of the glass-capillary method persist. These include a restricted viscosity range for individual capillaries (typically 5 to 100- fold), the need for large volumes of volatile and potentially toxic bath liquids (typically 1 L to 5 L), extended temperature equilibration times (30 minutes recommended), signifi cant solvent (40 mL to 100 mL) and sample volume (12 mL to 13 mL), as well as considerable energy usage (1,000 W and more per bath). Moreover, despite the degree of automation, a D445 viscometer only measures a single parameter, kinematic viscosity, limiting its application in multiparametric analyses.
Due to these drawbacks - and to meet modern-day industry demands with respect to economic and environmental expectations, and safety requirements - instrument manufacturers have developed more contemporary automated techniques. Those methodologies, like ASTM D7042, follow
SVM 3001: Maximum Flexibility - Multiple Parameters and Widest Temperature Range
a novel measuring principle, capable of determining dynamic viscosity, density and thus kinematic viscosity, with up to a tenfold decrease in volumes of sample and solvent, rapid thermoelectric heating and cooling with a wide accessible temperature range, as well as a measuring cell that covers the entire viscosity range relevant to the petroleum industry.
Direct measurement of kinematic
viscosity: Only a myth As previously noted, modern techniques determine kinematic viscosity indirectly, deriving it from separate measurements of dynamic viscosity and density. However, no single technique exists that can directly measure kinematic viscosity. In traditional glass capillary methods, the primary parameter measured is the sample’s fl ow time, which must then be multiplied by a calibration constant, individually determined for every single capillary, to yield the kinematic viscosity:
ν=C*t
v = kinematic viscosity C = calibration constant t = time
Furthermore, the calibration constant itself is infl uenced by the local gravitational acceleration (g) at the site of calibration. If the gravitational acceleration at the measurement location differs from that at the calibration site by more than only 0.1 %, an adjustment to the calibration constant is required to ensure accuracy.
Multi-talent powerhouse
ASTM D7042, the SVM method, provides more than just a single parameter with the push of a button. In addition to the
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