BAKER HUGHES - Drilling Fluids Reference Manual

MECHANICAL SOLIDS CONTROL
Test Sieve Opening, µm Test Sieve Opening,
No. No. µm
5 4000 60 250
6 3350 70 212
7 2800 80 180
8 2360 100 150
10 2000 120 125
12 1700 140 106
14 1400 170 90
16 1180 200 75
18 1000 230 63
20 850 270 53
25 710 325 45
30 600 400 38
35 500 450 32
40 425 500 25
45 355 635 20
50 300
Table 10 - 3 ASTM Sieve Designation 3
The number usually given in screen designations can be misleading. It can refer to micron opening
size, number of openings per inch, U.S. Test Sieve equivalent opening size, sum of wires in each
direction, or average cut point related to U.S. Test Sieve screens.
Two common screen cloths used for the manufacture of screens are market grade (MG) and tensil
bolting cloth (TBC). These terms refer to wire sizes used in the manufacturing of the screens,
market grade being a coarser wire than tensil bolting cloth. Some manufacturers use wire diameters
finer than tensil bolting cloth to achieve a greater open area on the screen while maintaining the
mesh count. This results in a weaker wire that will pass larger solid particles.
Solids Removal by Centrifugal Force
All mechanical devices for solids control, excluding vibrating screens, depend upon particle
separation by size and specific gravity of particles. Examination of the equation describing the
settling rate of particles indicates that the settling velocity of a particle depends upon particle size,
particle density, liquid density, liquid viscosity and the gravitational force induced. The
relationship of these factors is demonstrated by Stokes' equation for settling velocity.
where,
V
G d
=
2
( )( − )
D S
D M
μ
V = settling rate, cm/sec
3 ISO API RP 13C July 2004
BAKER HUGHES DRILLING FLUIDS
REVISION 2006 10-10
REFERENCE MANUAL