Resonant test rig for the rotating fatigue testing of drill pipes

Drill strings are key components for oil and gas extraction, and also in scientific explorations, such as to reach deep sub-seafloor sediments. Drill strings are mainly composed of drill pipes, whose failure is usually triggered by fatigue. Because of this, a dedicated test rig to investigate the fatigue strength of drill pipes gives the opportunity to find design stress parameters and crack initiation sites. The University of Pisa (Italy), in collaboration with ACTA Srl (Italy), developed a resonant test rig which allows fatigue tests to be performed on drill pipe specimens, saving time and energy costs with respect to an alternative fatigue facility, such as a four-point bending testing equipment. In this resonant test rig, an eccentric mass on one side rotates at an angular speed near, but lower than the first natural frequency of the structure, thus providing a rotating bending moment on the drill pipe specimen. Several aspects of the test rig, such as the strain gauge calibration and the correct set-up of the control system, are fundamental to perform proper tests. A description of the test rig and of its various components is given in this presentation. A fatigue test series example is also presented in collaboration with JAMSTEC (Japan) who are interested in explorative drilling, especially at deep sub-seafloor locations.