What is the purpose of a Kelly saver sub?

• A. It seals the borehole.
• B. It lubricates the Kelly.
• C. A Kelly saver sub protects the Kelly from excessive wear by absorbing the torque and stress during drilling operations.
• D. It increases drilling speed.

Answer: (C)

The main idea here is that a Kelly saver sub acts as a protective buffer at the top of the drill string. It’s placed between the Kelly and the rest of the drill pipe to take the brunt of torsional loads and shock during drilling. By absorbing torque and stress, it shields the Kelly’s connections and square drive from excessive wear, extending the life of the Kelly and reducing maintenance or replacement costs. It isn’t meant to seal the borehole, lubricate the Kelly, or directly speed up drilling.