Abstract: The thread joint of drill pipe is prone to fracture failure during longdistance horizontal directional drilling, which seriously affects its drilling performance. A twodimensional numerical simulation model of thread drill pipe joint of horizontal directional drilling rig is established to study the stress characteristics, tensile and compressive properties of drill pipe joint under the action of screwingup. Then, based on orthogonal experimental optimization method, the key structural parameters of thread drill pipe joint are optimized. The optimized parameters of drill pipe joint thread are: taper 1:16, pitch 6.25 mm, tooth height 3.195 mm, the bearing surface angle 28°, and the guide surface angle 32°. By comparing the tensile and compressive properties of the optimized drill pipe joint with those before optimization, it is found that the tensile property and compressive property of the optimized thread joint are improved by 9.8% and 15.2%, respectively.

Key words: horizontal directional drilling machine, drill pipe joint, numerical simulation, tensile performance, compressive performance; orthogonal test