Torque Testing

TETR is a TMT Laboratories acronym that stands for Tension versus Elongation, Torque, and Rotation. This test provides the mechanical characteristics of a rope, cable, or umbilical over the test tension range.

The TETR tests are conducted using specimens terminated with resin filled sockets. Resin filled sockets will produce the proper load distribution among the strength member elements and other cable elements without altering the stress balance and without inducing any external torque or rotation into the cable. All the cable components are captured in the resin to ensure their contribution to elongation, torque, and rotation.

The TETR test is conducted on a horizontal machine equipped with a hydraulic cylinder and strain-gauge load cell (See pictures at left). Cable elongation is measured using an extensometer attached directly to the specimen. Cable torque is measured using a torque reaction arm and load cell. Elongation and Torque are measured by load cycling from near zero to the desired test tension until the torque and elongation characteristics stabilize (usually 10 cycles). These cycles reveal the constructional stretch, stabilized elongation and torque.

The sample is attached to a friction-compensated swivel with a rotation sensor built into the swivel. Typically, ten more load cycles are conducted to record rotation versus tension. TMT Laboratories has three sizes of friction compensated swivels with a load range between 0 – 300,000-lbf to best fit a range of project requirements. These swivels use active compensation to minimize the effects of swivel bearing friction. Thus, the friction compensated swivel allows more accurate measurements of cable torque and rotation than possible using other types of swivels.

Diameters can be measured following the TETR at discrete tensions. These diameter measurements, along with the elongation, torque, and rotation data can be used with TMT Labs proprietary Cable Solver Software to fine tune the rope or cable design if desired.

Finally, the cable can be pulled to failure while recording elongation versus tension to measure the rope or cable’s breaking strength.

Please contact us to discuss your rope, cable or umbilical mechanical characterization needs further.