Cause & Consequence
- Moving, flying or falling object
Incident Info Source
Specific Incident Equipment
Drilling line and draw works clamps
The rig had last slipped and cut drilling line approximately two weeks prior to this event and no
problems with the drilling line or clamp had been noted since the last cut.
The ton miles since last cut were within acceptable limits at the time of the event.
The drilling line clamp on this drawworks uses four hex bolts to retain the drilling line. Upon
examination of the drilling line clamp, it was noticed that the two of the four bolts on the clamp had
been tightened about two rounds of the nut less than the other two bolts.
Further examination revealed excessive wear of the clamp itself, as evidenced by a widening of the
grooved throat of the clamp body by approximately 7 to 8 mm (5/16”).
This led to a conclusion that the immediate cause of the event was that the clamp had been undertightened
at the time of the last slip and cut.
It is less clear to what extent the generally worn condition of clamp reduced the clamping force on
The written rig operations policy guidelines for slipping and cutting drilling line were amended to include:
Requirement for visual inspection of drilling line clamp;
An inspection guideline, with acceptance/rejection criteria, for visual inspection of the drilling line
clamp, bolts, U-bolts and nuts;
Proper clamp tightening procedures, including recommended nut torque;
Appropriate interval for dimensional and non-destructive testing (NDT) inspection of drilling line
Appropriate interval for replacement of bolts or U-bolts, nuts and lock washers.
A pre-job meeting must be conducted prior to slipping and cutting drilling line to review the procedures as
a reminder of the importance of proper inspection and tightening of clamps and fasteners.
Inspection of wire rope retainers and retaining clamps on all lifting equipment which utilizes wire rope for
lifting including but not limited to drawworks, floor winches, man-rider winches, utility winches, casing
stabbing boards, cranes, etc. to be performed on all rigs.
Lessons learned and corrective actions requirements to be distributed to all operations and maintenance
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