Viscosity ASTM chart

Viscosity—Temperature. Oil viscosity decreases with increa sing temperature in the general pattern shown in Eigure 8, an example of ASTM charts which are available in pad form (ASTM D341). A straight line drawn through viscosities of an oil at any two temperatures permits estimation of viscosity at any other temperature, down to just above the cloud point. Such a straight line relates kinematic viscosity V in mm /s(= cSt) to absolute temperature T (K) by the Walther equation. 

Although the viscosity index is useful for characterizing petroleum oils, other viscosity—temperature parameters are employed periodically. Viscosity temperature coefficients (VTCs) give the fractional drop in viscosity as temperature increases from 40 to 100°C and is useful in characterizing behavior of siHcones and some other synthetics. With petroleum base stocks, VTC tends to remain constant as increasing amounts of VI improvers are added. Constant B in equation 9, the slope of the line on the ASTM viscosity—temperature chart, also describes viscosity variation with temperature. 

You can interpolate linearly for any API oil value between these equations and with extrapolation outside to 90°API. Temperature coverage is good from 50 to 300°F. If outside of this range, use the American Society for Testing and Materials (ASTM) Standard Viscosity-Temperature Charts for Liquid Petroleum Products (ASTM D-341 [6]). The values derived by Eqs. (1.1) to (1.4) are found to be within a small percentage of error by the ASTM D-341 method. 

It is good practice to always obtain at least one lab viscosity reading. With this reading, draw a relative parallel curve to the curve family in ASTM D-341. The popular Crane Technical Paper No. 410 reproduces this ASTM chart as Fig. B-6. If two viscosity points with associated temperature are known, then use the Crane log plot figure, also an API given method (ASTM D-341), to determine most any liquid hydrocarbon viscosity. 

Correlative methods are also available for application to aviation fuels. Such methods include the use of viscosity-temperature charts (ASTM D-341), calculation of the cetane index (ASTM D-976, ASTM D-4737), calculation of the viscosity index (ASTM D-2270), calculation of the viscosity gravity constant (ASTM D-2501), calculation of the true vapor pressure (ASTM D-2889), and estimation of the heat of combustion (ASTM D-3338). 

Anomalous viscosity in residual fuel oils is best shown by plotting the kinematic viscosity determined at the normal test temperature and at two or three higher temperatures on viscosity-temperature charts (ASTM D-341). These charts are constructed so that, for a Newtonian fuel oil, the temperature-viscosity relationship is linear. Nonlinearity at the lower end of the applicable temperature range is normally considered evidence of non-Newtonian behavior. The charts are also useful for the estimation of the viscosity of a fuel oil blend from knowledge of the component viscosities and for calculation of the preheat temperature necessary to obtain the required viscosity for efficient atomization of the fuel oil in the burner. 

The standard viscosity temperature charts (ASTM D-341) are useful for estimating viscosity at the various temperatures that are likely to be encountered in service. 

The Walther Equation and ASTM Viscosity-Temperature Charts... 

Figure 4-16 shows plots of the viscosity-temperature behavior on the high-range ASTM chart for three different oils, the viscosities of which were measured at 37.8, 60.0 and 98.9 C. Within the range of the experimental values the linearity of the plots is excellent. It should be noted that the log-log relationship compresses the scale for high values of the viscosity hence in this region an error of only 0.1% in drawing the line could mean an error of 2 to 20 centistokes. 

It can be seen in Fig. 4-16 that the viscosity of oil C is more sensitive to temperature than are the viscosities of the other two oils. The importance of such behavior in hydrodynamic lubrication is obvious. If the values of viscosity in the temperature range required by the hydrodynamic problem cannot be taken from the ASTM chart with precision, then analytical expressions such as Eqns 4-35b or 4-35c should be used. 

We must perforce devote some time and attention to the concept known as the vlscoilty Index, which has become embedded in the terminology of technological lubrication with some unfortunate connotations. Whereas the Walther equation and the ASTM viscosity-temperature charts are frankly empirical devices used to linearize the viscosity-temperature relations for convenience and utility, the viscosity index is an attempt to impart the mystique of quality by assigning an evaluative aspect to the... 

ASTM Method D 341, Standard Viscosity-Temperature Charts for Liquid Petroleum Products, ASTM Standards Book, Part 17—Petroleum Products, American Society for Testing and Materials, Philadelphia. 

Viscosity-Temperature Charts for Liquid Petroleum Products". D38l. ASTM... 

The Viscosity-Temperature Charts are available from ASTM, 1916 Race St., Philadelphia, PA 19103. Charts V and VI are intended for use with viscometric data bas on Fahrenheit temperature. It is anticipated that these two charts will be deleted when the current stock is deleted. When ordering, refer to Publication Code Number (PCN). 

X2.2.1 A plotting technique on ASTM viscosity temperature charts. X2.3. 

Percentage of tow viscosity component Fig. 4-44. ASTM-type viscosity-blending chart showing one set of experimental blends. 

Change of Viscosity with Temperature and Pressure. The engineei frequently must estimate the viscosity of an oil at other than the customary testing temperatures. This may be done by Fig. 443, but greater accuracy is possible by use of ASTM viscosity-temperature charts (see Fig. 4-45). However, in order to use these charts it is necessary to know the viscosity at two temperatures, or to know one viscosity and the Viscosity Index. Kinematic viscosity (or centipoises) can be obtained,by the use of Eqs. (3-2), (3-3), and (3-4) on page 25. 

With virtually any crude oil the viscosity change with temperatures can be an excellent guide to minimum crude processing temperatures. An ASTM chart of the viscosity versus temperature is useful to detect the paraffin formation or cloud point of the crude as shown in Figure 1.33. This normally establishes a minimum temperature for the treating process. There are examples of 30 API crude and higher that have pour-points of 80-90 °F (27-32 °C). Crude oils of this type are common in the Uinta and Green River Basins of the United States as well as in Southeast Asia. 

The viscosity of a hydrocarbon mixture, as with all liquids, decreases when the temperature increases. The way in which lubricant viscosities vary with temperature is quite complex and, in fact, charts proposed by ASTM D 341 or by Groff (1961) (Figure 6.1) are used that provide a method to find the viscosity index for any lubricant system. Remember that a high viscosity index corresponds to small variation of viscosity between the low and high... 

Suitable conversion tables are available (ASTM D341), and each table or chart is constructed such that for any given petroleum or petroleum product, the viscosity-temperature points result in a straight line over the applicable temperature range. Thus, only two viscosity measurements need be made at temperatures far enough apart to determine a line on the appropriate chart from which the approximate viscosity at any other temperature can be read. 

Petroleum Products and Lubricants, D341, ASTM, 1916 Race St., Philadelphia, Pa. Four large charts, low and high range, for Universal and for Kinematic viscosity may be purchased. The 0-100 F part of the temperature scale is used as 0-KX) per cent of blending agent. 

The Wright method, as illustrated in Fig. 4-45, utilizes the standard ASTM viscosity chart but in a way different from the method recom-... 

Four charts, low and high range, for Universal and for kinematic viscosity are available from the ASTM, 1916 Race St., Philadelphia, Pa. 

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