Alert
  • Published: 2 Nov 2011
  • Incident ID: 3395

Defective Clutch Results in Dropped Top Drive

Cause & Consequence

  • Other
Incident Consequence
Other

Incident Location

Drilling unit

Incident Activity

Drilling, workover

Lessons Identified

WHAT CAUSED IT:

 The operation was stopped during the process of breaking off the stand, rather than waiting until the Driller had the block at the floor for the start of the cycle; The rig operator did not notice that the clutch had not dumped its air when the clutch control was released to neutral;

 The clutch control had debris in the control mechanism, thus preventing the air’s release and signaling to the dump valves to dump the air to the clutch;

 The Driller noticed the brakes were not acting normal about two stands before the incident took place, but thought that the brakes had merely gotten water on them;

 The brake flange was leaking water and the driller thought the sluggishness of the brakes was due to water on the flanges.

Incident Recommendations

CORRECTIVE ACTIONS:

To address this incident, this company did the following:

 Instructed Drillers not to hand over control of the rig in the middle of breaking out a stand—set it back and bring the blocks to the floor in order to begin a new cycle in the procedure.

 Instructed Drillers to listen for changes; investigate smells; investigate the feel of controls or any changes in vibration.

o Things have a “normal” sound, appearance, smell and feel. The Driller should have investigated the cause when the brake felt sluggish for the two prior stands.

o A change in the sound of the brake or the sound of the air in the clutch dumping a few seconds late are indicators that something is wrong.

o If the brakes become wet the sound changes as they are applied.

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