April 28, 2021
DPM-FAQSeries Topic 8: What is Torsional Strength Ratio (TSR)?
Torsional Strength Ratio (TSR) is the ratio of tool joint torsional strength divided by the pipe body torsional strength. This is usually available in the Drill Pipe Performance Data Sheet.
Most tool joints are weaker in torsion than the drill pipe tubes to which they are welded. As the drill pipe tool joint OD wears, the torsional strength decreases. Tool joints with TSR less than 0.800 are used in low torsion drilling.
API sets TSR of 0.800 as the basis for premium tool joint OD for used pipes. As the drill pipe is used and downgraded to premium grade, the tool joint OD for premium grade is calculated by assuming a TSR of 0.800 when the drill pipe tube is worn to 80% of the nominal wall thickness.
For proprietary connections, DP-Master has removed the Premium column of the tool joint section and replaced it with the Minimum column. This is to ensure the maximum performance of the tool joint. Instead of stating the premium OD, the minimum OD is indicated. In addition, a connection wear curve is included in the Drill Pipe Performance Data Sheet so that the correct make-up torque (MUT) is used depending on the actual remaining tool joint OD.
It is important to ensure the correct MUT is used. If insufficient torque is applied, there are risks of downhole make-up and thread damages.