Resonant Fatigue Tests on Drill Pipe Connections with Different Geometries and Sizes

In this study, a resonant bending fatigue test rig, designed and implemented by the University of Pisa, is presented, providing a detailed description of the set-up of the machine, the strain gauges calibrations, and the control system used with the main electronic devices. Several geometries of drill pipe connections and pipe samples made of different materials were tested, and all the obtained experimental fatigue results are presented in the paper and compared to previous experimental data. Fractographic images are provided to clearly show that, in two kinds of drill pipe connections, the crack initiation was found at the connection zone, whereas for another connection geometry, it was found at the pipe body. In order to interpret these latter results, a discussion about the section modulus of bending of the various sections of the drill pipes was provided, along with an FE model of a specific zone of one of these connections.