Miller numbers

G 75 Test Method for Determination of Slurry Abrasivity (Miller Number) and Slurry Abrasion Response of... 

Positive displacement slurry pumps are used in a number of industries (Table 9-1). Solid piston pumps are reserved for the pumping of slurries of a low to medium abrasiveness (Miller Number <50) such as chalk slurry, fine coal, flotation material, and driUlng mud sludge. 

The American Society for Testing of Materials (Miller, 1987) has adopted the concept of the MUler number as a measure of the abrasivity of slurries. Standard G-75 describes the relative abrasivity based on the mass loss of a standard 27% chrome white iron block when rubbed in slurry for a particular period of time. To conduct the test and to measure the slurry abrasion response (SAR) number, also called Miller number, a special machine (Figure 10-5) is used. It consists of a wear block driven at 48 strokes per minute with a stroke length of 200 mm (8 in). A dead weight of 2.27 kg [5 lb] is applied to the wear block. At the bottom of the tray, a piece of Neoprene is installed to act as a lap. The tray takes the form of a flat bottom between V-shaped walls that confine the slurry around the block. The tray is filled with sand. The mounted blocks are lowered in the trays. Four, 4-hour tests are conduced and the weight of the block is... 

The Miller number is directly related to the abrasivity of the slurry. In other words, slurry... 

FIGURE 10-5 Machine for measuring the Miller number. (From Miller, 1987. Reproduced by permission of ASTM.)... 

The ASTM has developed a new standard (G75-01) to determine the slurry abrasivity (Miller) number and the slurry response of materials (SAR number). 

A variety of materials are available for the lining and manufacture of slurry handling equipment and piping. Various selections are available based on the degree of abrasiveness, corrosion, temperature, and presence of oils or solvents. In terms of measurement of wear, the American Society for Testing of Materials has developed a slurry abrasion response (SAR) number, also called Miller number. It is extremely useful for determining the need to line pipelines and pumps. 

ASTM. 1999. ASTM A532/A532M. Standard Specification for Abrasion-Resistant Cast Irons. ASTM. 2001. Test Method G75-01. Standard Test Method for Determination of Slurry Abrasivily (Miller Number) and Slurry Response of Materials (SAR Number). 

The Miller number of phosphate ore is smaller than 50 (Abulnaga, 2000). This means that phosphate is suitable for pumping with piston reciprocating pumps. 

Erosion and corrosion data are very important at an early stage of the design. There are a number of recommended tests. One method is the ASTM G75 Slurry Abrasivity Determination by the MiUer number system. The Miller number is established as the relative rate of mass or volume loss in 2 hours. Slurries with Miller numbers smaller than 50 are considered relatively nonabrasive and can be pumped with piston reciprocating pumps. Slurries with Miller numbers above 80 are considered relatively abrasive and require flushed plunger or membrane pumps (see Section 10-6). 

A final discussion deals with application of eqn (2.29) [or its equivalent (2.32)] or (2.27) (including the term T within the parentheses) when extrapolation is carried out. The classical equation given by Miller [numbered here as eqn (2.27)] corresponds formally to an interpolation although it is generally used in... 

Figure 12. Schematic of the ASTM G 75 slurry erosion tester to measure Miller Number.

Table 7 lists typical Miller numbers for selected slurry materials. The wide variation in Miller numbers for some materials is due to the inclusion of varying amounts of tramp materials that usually occur with the basic mineral. Information about the factors that contribute to Miller number abrasivity can be found in the ASTM G 75 standard. 

Table 7 Typical Miller numbers for selected slurry materials...

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