Investigation of the Influence of tapered Thread Pitch Deviation on the Drill-String Tool-Joint Fatigue Life

Pipes and drill string elements are connected by tapered threads on the pin and box. These connections are called string-grid tool-joint. Such connections are made by lathe. Therefore, their accuracy largely depends on the kinematics of the lathe, as well as the accuracy of the profile of the cutters and their geometric parameters. One of the basic parameters of thread accuracy is its pitch. An important indicator for a tapered threaded connection is the accuracy of the lead angle and pitch. There for these two parameters and their influence on strength are the objects in this research. Increasing the thread pitch in the direction of the larger diameter of the pin taper can lead to a decrease in the fatigue strength of the joint.