CONCENTRIC DRILL STRING Russian patent published in 2003 - IPC

FIELD: well drilling, particularly, concentric drill strings for planetary-drill bit drilling. SUBSTANCE: concentric drill string consists of pipes of external and internal strings, threaded pipe joints for pipes of external string, slotted joints with sealing members for pipes of internal string and radial spherical bearings. In this case, bushing with external bearing spherical surface is press-fitted onto external surface of splined coupling half with internal splines, and spherical bearing is installed in body mounted into semi-joint with internal thread. EFFECT: increased serviceability and reliability of concentric drill string and reduced power consumption for its rotation. 2 dwg