Drill pipe connection thread

Keywords:drill pipe, thread
The drill pipe connection thread is the weakest part of the drill string. In order to overcome this weakness, it is often necessary to thicken the end pipe wall of the drill pipe outward or inward to become an outer thickened or internally thickened drill pipe. The conventional drill pipe is made of alloy seamless steel pipe with different compositions. The existing alloy components are Mn, MnSi, MnB, MnMo, MnMoVB, etc., and the harmful components such as phosphorus and sulfur are not limited to more than 0.04%, according to GB3423-82. It is stipulated that the higher the steel grade of the 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 normalized, quenched and tempered at high temperature.

The active drill pipe (also called the upper drill pipe) is located at the uppermost part of the drill pipe column, and is clamped by the chuck of the drill vertical shaft or the power head, or is rotated by a non-circular ferrule in the turntable, and drilled into the hole connected to the lower end thereof. The rod transmits the turning moment and the axial force. The upper end of the active drill pipe is connected to the faucet to deliver the flushing liquid to the hole. The cross-sectional size of the active drill pipe is large, which is convenient for the chuck to be rotated and is not easy to bend. The cross-sectional shape has a circular shape, a square shape, a square shape, a hexagonal shape and a double key groove shape. The length of the active drill pipe should be slightly longer than the length of the drill pipe and the length of the turret through hole. The commonly used length is 4.5m or 6m.

Generally, the drill pipe adopts a trapezoidal thread with a pitch of 4 to 8 mm and a inclination of 5°on each side. In order to prevent stress concentration, the root of the thread has a predetermined arc angle. The threaded portion is subjected to alternating stress, so it must have sufficient strength and wear resistance during frequent screwing. At the same time, the drill pipe is subjected to the high pressure of the flushing liquid flow, and a special end face seal is required at the end of the drill pipe joint. In order to ensure the quality of the drill pipe, the rolled steel pipe must be normalized, tempered or tempered. Since the drill string often rubs against the wall of the hole during the turning process, in order to strengthen the surface anti-wear ability, the surface layer of the drill pipe must be subjected to high-frequency quenching. However, in order not to affect the performance of the drill rod against fatigue damage, the surface depth of the hardened and hardened surface must be controlled within 1 mm.
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