Fault Phenomenon: Bauer BG40 rotary drilling rig relative slippage occurs between the rotary head and Kelly bar when transmitting high torque.

Troubleshooting Process:
– Checked Kelly bar square drive: square drive dimensions worn beyond tolerance.
– Checked rotary head drive keys: drive keys worn or broken.
– Checked lubrication: lack of grease on contact surfaces causing abnormal wear.
– Checked alignment: rotary head and Kelly bar misaligned.

Root Cause: The square drive of the top Kelly bar section is worn down in size due to long-term high torque operation, causing excessive clearance with the rotary head drive keys and resulting in slippage.

Required Parts: Repair or replace Kelly bar square drive (build-up weld and machine), replace drive keys.