Torsional Strength And Make Up Torque
Drill Pipe Tool Joint Torsional Strength
- Most standard API tool joints are weaker in torsion than the Drill Pipe tubes to which they are welded.
- API sets tool joint torsional strength arbitrarily at 80 percent of tube torsional strength. This tool joint torsional strength ratio (TSR) of 0.8 is the basis for establishing tool joint ID and OD.
- As the drill pipe tool joint OD wears the torsional strength decreases. Tool joints with TSR's less then 0.8 are used successfully in low torsion drilling, and some high for torsion drilling applications require tool joint torsional ratings higher than the standard TSR of 0.8.
Drill Pipe Make Up Torque
- Tool joints are made up by applying sufficient makeup torque to force the pin and box shoulder tightly together and make a seal. This is accomplished when makeup stretches the pin and compresses the box shoulder.
- Makeup torque is determined by the tool joint OD and ID and not by the properties and dimensions of the drill pipe tube. For a given pin ID the makeup torque increases as the tool joint OD increases. Similarly, for a given tool joint OD the makeup torque decreases as the pin ID increases.
- The standard makeup torque is the torque that would stress the weaker pin or box to 60% of its minimum yield strength of 72,000 psi. (Minimum yield strength of all tool joints is 120,000 psi regardless of the grade of the drill pipe).
such that the makeup torque exceeds the maximum torsional load anticipated during drilling operations.