How to Define Slurry Particle Size

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Accessing and describing the make of a deposit or a slurry is important in the selection of pumping equipment. Particle size along with particle distribution will affect pump wear, material selection, pipeline settling velocity, and how a deposit will or will not flow and therefore affect production rates. Deposits with oversized wood or trash particles will also create a problem known as “bird nesting”. Oversized rocks will create an issue known as “paving stoning”. Both subjects for another day

Although it is important to be able to accurately describe both particle size and distribution, today we will only address particle size.

To the right are examples of the types of terms used to describe rock in the sand and gravel industry.  Useful in obtaining a general feel for the makeup of a deposit but not very analytical. To be able to further clarify, and to easily describe the size of particles, some standards have been established.   Unfortunately, as with most things in our industry, there are multiple standards!!

The basis or method of the various standards is however common, and that is “ to define a particle in accordance with the size of the particle that will pass through a specific size mesh”.  Unfortunately, the sizes of mesh and the units of measure used to describe the mesh is not common. The four particle size standards  I have worked with are; “Tyler”,  “US Bureau of Standard Screens”, “British Standard Screens”, “I.M.M. Screens” and  Wentworth.

Diameter (mm) Diameter (phi) Wentworth Size Class
4096 256 -12 -8 Gravel Boulder
64 -6 Cobble
4 -2 Pebble
2 -1 Granule
1 0 Sand Very Coarse Sand
0.5 1 Coarse Sand
0.25 2 Medium Sand
0.125 3 Fine Sand
0.0625 4 Very Fine Sand
0.0313 5 Silt Coarse Silt
0.0156 6 Medium Silt
0.0078 7 Fine Silt
0.0039 8 Very Fine Silt
0.00006 14 Mud Clay

The Wentworth standard is rarely used but does contain a useful table that provides a clear cross-reference between common terms used to describe materials and the relative particle size in mm for that material.

U.S. Bureau of Standard Screens Tyler Screens British Standard Screens I.M.M. Screens
Mesh Aperture Mesh Aperture Mesh
Double
Tyler
Series
Mesh Aperture Mesh Aperture
Inches mm Inches mm Inches mm Inches mm
2.5 .321 7.925
3 .265 6.73 3 .263 6.680
3.5 .223 5.66 .221 5..613 3.5
4 .187 4.76 4 .185 4.699
5 .157 4.00 .156 3.962 5
6 .132 3.36 6 .131 3.327 5 .1320 3.34
7 .111 2.83 .110 2.794 7 6 .1107 2.81
8 .0937 2.38 8 .093 2.362 7 .0949 2.41 5 .100 2.51
10 .0787 2.00 .087 1.981 9 8 .0810 2.05
12 .0661 1.68 10 .065 1.651 10 .0660 1.67
8 .062 1.574
14 .0555 1.14 .055 1.397 12 12 .0553 1.40
10 .050 1.270
16 .0469 1.19 14 .046 1.168 14 .0474 1.20
12 .0416 1.056
18 .0394 1.00 .039 .991 16 16 .0395 1.00
20 .0331 .84 20 .0328 .883 18 .0336 .85
16 .0312 .792
25 .0280 .71 .0276 .701 24 22 .0275 .70
20 .025 .635
30 .0232 .59 28 .0232 .586 25 .0236 .60
35 .0197 .50 .0195 .495 32 30 .0197 .50 25 .020 .508
40 .0165 .42 35 .0164 .417 36 .0166 .421 30 .0166 .421
45 .0138 .35 .0138 .351 42 44 .0139 .353 35 .0142 .361
40 .0125 .317
50 .0117 .297 48 .0116 .295 52 .0166 .295
60 .008 .250 .0097 .246 60 60 .0099 .252 50 .01 .254
70 .008 .210 65 .0082 .208 72 .0083 .211 60 .0083 .211
80 .0070 .177 .0069 .175 80 85 .0070 .177 70 .0071 .180
100 .0059 .149 100 .0059 .147 100 .0060 .152 80 .0065 .157
90 .0055 .139
120 .0049 .125 .0049 .124 115 120 .0049 .125 100 .0050 .127
140 .0041 .105 150 .0041 .104 150 .0041 .105 120 .0042 .107
170 .0035 .088 .0035 .088 170 170 .0035 .088 150 .0033 .084
200 .0029 .074 200 .0029 .074 200 .0030 .076 170 .0029 .074
230 .0024 .062 .0024 .061 250 240 .0026 .065 200 .0025 .063
270 .0021 .053 270 .0021 .053 300 .0021 .053
325 .0017 .044 .0017 .043 325
400 .0015 .037

This was a very basic short discussion today but next time we will use the terminology and the information on particle size discussed today to delve into “Particle Distribution” and how it affects deposit flow and therefore production .

Cheers,

RJ