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Viscosity is a physicochemical property that evaluates the resistance that fuel offers to flow, influencing the engine’s operation and combustion process. Its control is aimed at good fuel atomization and the preservation of lubricating characteristics. Changes in viscosity can lead to wear on various parts of the engine. Viscometers typically measure the viscosity of fuels in the oil and gas industry. These instruments can measure the time it takes for a fluid to move a given distance through a pipe or the time it takes for an object of a given size and density to pass through the liquid. The traditional test method, ASTM D445, differentiates the procedure for opaque liquids from transparent ones; that is, it requires a warm-up of the sample between 60 °C and 65 °C for 1 h. This additional step can overload laboratory routines, although it is not guaranteed to have a metrologically significant effect on the final result. Thus, this study evaluated the relevance of complying with this step in the test method for the kinematic viscosity of opaque liquids using a 32 factorial experimental design. Based on the F test, p-value, confidence intervals, and percentage contribution of the sum of squares approaches concerning the regression analysis, one concluded that the warm-up time was not a relevant factor in the kinematic viscosity, specifically of very low sulphur fuel oil, Brazilian fuel oil, and atmospheric residue diluted with diesel oil, which are fluids at room temperature.

Brazilian regulation requires the test methods for analysing the shrinkage factor, and the solubility ratio in crude oils must be estimated under the measurement conditions for appropriation. Since these physicochemical parameters depend upon the density, a Brazilian oil company proposed an adapted and more user-friendly methodology for adjusting the digital density meter under high pressure and temperature conditions. This study aimed to evaluate the metrological compatibility of this proposal by comparing it with the fit model presented by a manufacturer of a digital densimeter and with the tabulated reference values of fluid density. Since the density data behaviour presented non-normal distributions, the Wilcoxon signed-rank test showed metrological compatibility between the approaches studied in the pressure range from 0 psi to 1200 psi (8.273709 MPa) and the temperature range from 5 °C to 70 °C.