Faflei O. Increase of fatigue strength of double-shoulder threaded tool joints of drill string elements

The dissertation is devoted to increasing the fatigue strength of double-shoulder threaded tool joints of drill string elements by developing their new structures taking into account the stress-strain state and the influence of cyclic loading asymmetry on tensile stresses on the crack resistance of pipe material. The method of calculating the recommended and maximum screwing moments of the double-shoulder threaded tool joints of drill string elements has been improved, taking into account the influence of the additional support end of the nipple and the coupling and the change in the friction coefficient. The model for automated design of constructions of double-shoulder threaded tool joints of weighted drill pipes has been improved. The influence of structural elements of the developed threaded tool joints under the action of the screwing moment on their stress-strain state and crack resistance is investigated. The influence of cyclic loading asymmetry under tensile stresses on the rate of propagation of fatigue cracks in the pipe mate-rial is estimated.