Validating numerically predicted make-up of threaded connections using digital image correlation and infrared monitoring

To ensure a reliable connection between two pipe sections, an initial make-up is applied to the threaded connections to induce a favorable stress state. Using finite element analysis techniques, it is possible to predict the internal strains and stresses of the connection when torque is applied. This article presents the outline of an experimental setup, which allows to directly validate the occurring strains together with the torque versus turn diagram and indirectly the contact pressures. The strains are measured by means of digital image correlation and strain gages. Both methods provide similar results and comply with the predicted finite element analysis strains when taper mismatch is taken into account. In an effort to qualitatively validate the simulated contact pressures, the temperature of the box is measured during make-up by means of infrared monitoring. The maximum temperature increase occurs near the vanishing threads where contact pressures are larger. Despite promising results, no decisive validation for the contact pressures could be obtained.