What Does Pull-Back Force Mean?
Pull-back force is a measurement of the tensile load, or force, applied to a drill string during pull-back. Drilling rigs and guided boring rigs are "rated" according to the maximum pull-back force that can be applied to the rig's drill string. Excessive loads, or force, can lead to tensile failure.
Trenchlesspedia Explains Pull-Back Force
The loads placed on a drill string when it's pushed to create a bore during trenchless construction can lead to tensile failure.
Tensile failure is the point at which the forces on the string can cause it to (a) stretch to the point where it thins out and can no longer stand the load placed upon it, or (b) weaken over successive uses until it becomes brittle and shatters.
Pull-back force is one potential cause of tensile failure. As pipe is pulled back through a bore, the drill string is sometimes stretched to the point where it can no longer support the load placed upon it, or the drill string has suffered such loads for extended periods and fails because it has lost all elasticity and shatters when the load is placed upon it.
Because of this failure potential, drilling rigs and guided boring rigs used in trenchless construction have a rating based on the pull-back force that leads to this type of failure in the drill string.