The connecting thread of drill pipe is the weakest part of drill string. In order to overcome this shortcoming, it is usually necessary to thicken the end pipe wall of the drill pipe outward or inward to become an externally or internally thickened drill pipe. Traditional drill pipes are made of alloy seamless steel pipes with different compositions. The existing alloys are Mn, MnSi, MnB, MnMo, MnMoVB, etc. According to GB3423-82, harmful components such as phosphorus and sulfur are not limited to more than 0.04%. It is stipulated that the higher the steel grade of drill pipe, the greater the yield strength. However, in the process of thickening, the drill pipe will cause thermal damage, so the thick drill pipe must be standardized, quenched and tempered at high temperature.


Active drill pipe (also known as upper drill pipe) is located at the top of the drill pipe string, clamped by the vertical axis of the drill bit or chuck of the power bit, or rotated by a non-circular ring. The turntable is drilled into a hole connected to its lower end. Rod transfers rotational moment and axial force. The upper end of the active drill pipe is connected to the tap to transport the flushing liquid into the hole. The cross section size of the active drill pipe is large, so it is easy for chuck to rotate and not easy to bend. The cross-section shape has the shape of circle, square, square, hexagon and double keyway. The length of the active drill pipe should be slightly longer than the length of the drill pipe and the length of the through hole of the turret. Commonly used length is 4.5 meters or 6 meters.


Typically, trapezoidal threads are used for drill pipes with pitches of 4 to 8 mm and slopes of 5 degrees on each side. In order to prevent stress concentration, the root of the thread has a predetermined arc angle. The threaded part bears alternating stress, so it must have enough strength and wear resistance when tightening frequently. At the same time, the drill pipe is subjected to high pressure of flushing fluid flow, and special end face seal is required at the end of the drill pipe joint. In order to ensure the quality of drill pipe, the rolled steel pipe must be standardized, tempered or tempered. Because the drill string often rubs against the hole wall during the turning process, in order to enhance the wear resistance of the surface, the surface layer of the drill pipe must undergo high frequency quenching. However, in order not to affect the fatigue damage resistance of drill pipe, the surface depth of hardened and hardened surface must be controlled within 1 mm.