STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Rotary Equipment 621
Table 4-37
Drill-Stem Subs E131
1 2 3 4
Upper Connection Lower Connection
Type Class to Assemble wl to Assemble wl
A or B Kelly Sub Kelly
Tool Joint Sub
Tool Joint
Crossover Sub
Tool Joint
Drill Collar Sub
Drill Collar
Bit Sub
Drill Collar
C Swivel Sub Swivel Sub
Tool Joint
Tool Joint
Drill Collar
Drill Collar
Bit
Kelly
Kelly Cock
The kelly cock (Figure 4-92) is located between the kelly joint and the swivel.
The kelly cock will close the drill string if the swivel, drilling hose, or standpipe
develops a leak or rupture and threatens to blowout. It also closes in the event
that pressure within the hose exceeds the hose pressure rating. The specifications
for kelly cocks are provided in API Specification 7 [l].
Lower Kelly Valves
Some kellys (Figure 4-93) are equipped with a mud check-valve that is placed
immediately below the kelly. When mud pumps are shut off, this valve closes
to save mud that would otherwise be spilled out onto the rig floor. To avoid
loss of pressure across the tool, the kelly valve is either fully open or fully closed
while in operation. It opens and closes automatically and automatically allows
reverse flow.
Lower Kelly Cock
The lower kelly cock is often substituted for the lower kelly valve. It is operated
manually, as shown in Figure 4-92. The specifications for lower kelly cocks are
provided in API Specification 7 [l].
Kelly
The kelly (Figure 4-94) is a square-shaped or hexagonal-shaped pipe (drive
section) that transmits power from the rotary table to the drill bit. Also, drilling
mud is pumped downhole through the kelly. Kellys must conform to the
dimensions specified for the respective sizes in API Specification 7 [l].
The drive section of the hexagonal kelly is stronger than the drive section of
the square kelly when the appropriate kelly has been selected for a given casing
size. For a given bending load, the stress level is less in the hexagonal kelly;
thus the hexagonal kelly will operate for more cycles before failure.