Rotary shouldered thread connections: Working limits under combined staticloading

Rotary shouldered connections (RSC), used in the oil and gas industries, ar e probably the most stressed components of the drill string because they ar e subjected both to make-zip torque and to axial and bending loads. Since l oads can vary and can result in fatigue crack initiation and propagation, t here is often severe damage to the first threads engaged. Such damage leads to shoulder load reduction and discontinuity in the drill string. Once we know the geometric dimensions and the materials of the pin and box elements composing the RSCs, AN standards make it possible to evaluate the working limits of RSCs when they are subjected to make-up torque, torsion and tensi on. It is not, however, possible to establish the stress state of the conne ction for extreme working limits. The aim of this paper is to propose a num erical procedure, confirmed by full-scale experimental tests, which enables the evaluation both of the working limits, combined make-lip and axial ten sile loads, and of the stress state of RSCs for any load condition and, in particular, when RSCs are subjected to extreme combinations of make-up, tor sion and axial tensile loads.