STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Hoisting System 599
spooling condition, this dimension can vary according to the type of
operation.
b. The curvature radius of the groove profile should be equal to the radii
listed in Table 4-32.
c. The groove depth should be approximately 30% of the nominal diameter
of the wire rope. The crests between grooves should be rounded off to
provide the recommended groove depth.
Diameter of Sheaves. When bending conditions over sheaves predominate in
controlling rope life, sheaves should be as large as possible after consideration
has been given to economy of design, portability, etc. When conditions other
than bending over sheaves predominate as in the case of hoisting service for
rotary drilling, the size of the sheaves may be reduced without seriously affecting
rope life. The following recommendations are offered as a guide to designers
and users in selecting the proper sheave size.
D,=dxF (4-25)
where DT = tread diameter of sheave in in. (mm) (see Figure 4-76),
d = nominal rope diameter in in. (mm), and
F = sheave-diameter factor, selected from Table 4-35.
It should be stressed that if sheave design is based on condition C, fatigue due
to severe bending can occur rapidly. If other operation conditions are not
present to cause the rope to be removed from service, this type of fatigue is
apt to result in wires breaking where they are not readily visible to external
examination. Any condition resulting in rope deterioration of a type that is
difficult to judge by examination during service should certainly be avoided.
DRILLING LINE &
CASING LINE WEAVES
DETAfL A
SAhIDLfflE SHEAVE
DETAIL B
Figure 4-76. Sheave grooves [ll].