Torque may be expressed as tangential force (pounds) and lever arm (ft) or lb-ft. (It may also be expressed as pound inches). For any one revolution the torque-tangential force travels the circumference of a circle (whose radius is the torque arm) or 2 ft. Thus,
Torque (lb-ft) x 2 x rpm / 33,000 = Horsepower (totaling)
The upper limit of torque or rotating hp or “horsepower per rpm” is related to the torque capacity of the pipe or tool joints, especially with regard to breaking out tool joints after inevitable shock loads have been superimposed on the average operating torque involved.