The traveling block, crown block, and wire line
are the three components whose function is to
connect the supporting derrick or mast with the
load of pipe to be lowered into or withdrawn from
the hole. During drilling operations, load usually
consists of the drill pipe and drill collars, with
the bit attached to the bottom of the drill collars.
However, a string of special pipe called casing,
which is often a heavier load than the drill pipe
and collars, has to be lowered into the hole and
cemented. The wire line is reeved around sheaves
in the crown block of the top on the derrick or mast.
As is true of almost every part of many rotary
rigs, the blocks and wire-line assembly must have
great strength to be able
to bear heavy loads .Friction must also be eliminated
in the blocks insofar as possible while still
maintaining the desired strength. Thus, well made
bearings and proper lubrication of these bearings
by the crew are very important.
As wire-rope manufacturers like to emphasize,
a wire ripe,
or wire line, is in itself a machine in the sense
that it requires lubrication. This is because of
the constant movement of strands within the wire
line rubbing against one another as the rope flexes
over sheaves in the block assembly. Because wire
line is an expendable item, it can be an appreciable
expense on any drilling rig; this is particularly
true unless a planned program of purchase and use
of the wire line is in effect from the beginning.
To achieve the greatest economy from the use
of wire line on a drilling rig, the line selected
should be of the proper length and its diameter
should be in accord with both the load requirements
and the design of the sheaves in the traveling block
and crown block through which the line must travel.
The line should be frequently inspected to ensure
that it is in good condition. The drilling line should
be moved periodically-slipped is the field term-so that
it wears evenly as it is used. Cutoff
procedures should take into account the amount of
usage-that is, the ton-miles of service.
(If a wire line has moved a 1-ton load a distance of 1 mile,
then the lie has received 1 ton-mile of usage.)