Contact stress analysis and calculation of stress concentration factors at the tool joint of a drill pipe

In this article threaded tool joint of a drill pipe, which is exposed to failure in vertical drilling more than other members, is analyzed using 3D finite element modeling through the use of ABAQUS 6.6 standard code. For modeling contact between mating surfaces of the threads nonlinear contact elements are used. Different types of loading composed of tension and compression, pure preload and a combination of them are applied to the model. According to API standard, a preload is also applied to the tool joint to improve the fatigue behavior. Some conclusive results have been drawn from the analysis including the location and the value of maximum stress concentration factor (SCF) in the pin and the box, the effect of preload on the SCF and as a result on the fatigue life of the tool joint and the contact stress distribution on the screw threads. Finally, convergence of the contact pressure on the contact surfaces is investigated.