DRILL STRING WITH BEND RESISTANT COUPLING Russian patent published in 2018 - IPC E21B17/02 E21B17/42 F16L15/00 

FIELD: drilling of soil or rock.

SUBSTANCE: group of inventions relates to percussion-rotary drilling for making a deep wellbore. Rill string rod to form part of a drill string, wherein the rod comprises a hollow elongate main length section extending axially between a first end and a second end, male spigot portion provided at the second end having an externally threaded section and a non-threaded shank positioned axially intermediate the threaded section and a shoulder, threaded section comprising at least one helical ridge and trough extending axially from the shank, shoulder axially separating and projecting radially outward relative to the main length section and the spigot portion, the shank extending axially from an annular side surface of the shoulder. Wherein an axial length of the spigot portion is configured such that the annular surface is capable of abutting an annular end surface of a female end portion of a neighbouring rod of the drill string. Wherein an outside diameter or width of the shrank in a direction perpendicular to a longitudinal axis of the rod is equal to or more than the outside diameter of the main length section along a full axial length of the shank, and an external shape profile of the shank is curved to flare radially outwardly in contact with the transition region into the annular side surface.

EFFECT: minimization of stress concentration in the coupling.

14 cl, 3 dwg