According to the different thread, the drill pipe of oil drilling rig can be divided into ordinary drill pipe, square tooth drill pipe and weighted drill pipe. The common drill pipe is the main component of the drill string. The top is connected with the square drill pipe and the bottom is connected with the drill collar. Its function is to transmit torque, make the drill bit drill down and deepen the borehole. The square drill rod is located at the upper end of the drill string. Its main function is to transmit torque. Its work is to bear the weight of the drill string. It is composed of a driving part (square or hexagonal), an upper joint (left-handed thread), and a lower joint (right-handed thread). The square drill rod is commonly used. The heavy drill pipe is the transition drill string section between the ordinary drill pipe and the drill collar, which can effectively alleviate the stress concentration of the transition section in the combination of the drill collar and the drill pipe, provide the drill pressure and can effectively reduce the connection area of the drill string and the well wall and the outer diameter wear rate.

With the popularization and use of drilling techniques such as tooth wheel drilling, air down-the-hole hammer drilling and air lift reverse circulation drilling, API series of well drill string components and downhole tools have been more and more widely used. In particular, the API series drilling tool joint thread connecting the drill string components plays an indispensable role. Drill pipe joint thread can be divided into digital thread (NC), internal flat thread (IF), through eye thread (FH) and regular thread (RGE) according to the type of oil drill pipe joint thread to be tested.

Numeric (NC) Thread Thread in inches and tenths of an inch of the pitch diameter of the thread base. All sizes of threads use V-0.038R flat-top round-bottom triangular tooth type, which is characterized by a round tooth root radius of 0.038 inches (0.965mm). Digital thread is the preferred thread recommended by API. This type of thread can be divided into two types: 1:6 and 1:4 according to taper. It is applied to drilling tools such as square tooth drill pipe, drill pipe, drill collar, drill stabilizer, etc. NC50 thread is also used on drill bit in Daqing Oilfield.

The inner flat (IF) joint thread connects the outer thickened or inner and outer thickened drill pipe to form the inner diameter of the drill pipe joint, the thickened inner diameter of the pipe body and the inner diameter of the pipe body are equal or similar. The drilling fluid flow resistance is small, but the outer diameter is large, which is easy to wear. All thread sizes are V-0.065 flat-topped flat-bottomed triangular teeth with a flat bottom and a crest width of 0.065 inches (1.651mm). In addition to 5 1/2 IF, other specifications of the thread because the structure size and the corresponding digital thread is exactly the same, so it has interchangeability. However, this type of thread is prone to stress concentration due to its tooth shape structure, so API has eliminated it, including 4 1/2 IF and 4 IF, and replaced it with NC50 and NC46 digital threads.

Through-hole (FH) drill pipe joint thread connects the inner and outer thickened drill pipe to form the inner diameter of the drill pipe joint and the inner diameter of the thickened end are equal, but both are smaller than the inner diameter of the drill pipe body. Although the specifications of this type of thread are few, it uses V-0.065, V-0.050 (tooth bottom is circular arc, tooth top width is 0.050 inches, 1.27mm) and V-0.040 (tooth bottom is circular arc, tooth top width is 0.040 inches, 1.02mm). It has been widely used in faucets, square tooth drill pipes, drill pipes, drill collars and drill bits, etc. At present, except for 5 1/2 FH and 6 5/8 FH, which use V-0.050 profile and 1:6 taper, the rest are among the API eliminated threads. The 4 FH, which only uses the V-0.065 profile, is replaced by the digital thread NC40 as well as the internal flat thread.

The regular type (RGE) drill pipe joint thread has been used to connect the inner thickened drill pipe, forming the inner diameter of the drill pipe joint is smaller than the thickened inner diameter, and the inner diameter of the thickened end of the drill pipe is smaller than the inner diameter of the pipe body. The main purpose of API's design of regular threads is to apply them to drill connections. Since the drill bit is located at the end of the drill string, the existence of stress concentration at the bottom of the thread is irrelevant, so API retains all their specifications. This type uses V-0.050 and V-0.040 tooth types. In the 40th edition of API SPEC 7, 1REG and 1 1/2 REG threads with V-0.055 tooth types (flat tooth bottom, tooth top width of 0.055 inches, 1.397mm) are newly added.

Drill pipe in the market due to different manufacturers, classification is also very different. Taking the drill pipe produced by Qianjiang Machinery as an example, it is mainly divided into twist drill pipe, imitation British drill pipe, rib drill pipe, etc. The thread and length are customized according to customer needs. With the improvement of drill pipe research and development technology, the quality of drill pipe has been significantly improved, and the price of drill pipe is also falling. In the future, China's drill pipe market will develop towards a trend of technology, management and quality.