The types of drill rods can be divided into three kinds according to their different threads, that is, the ordinary drill rods, the square kelly and the heavy weight drill pipe.
The ordinary drill rod is the main part of the drill stem. Its upper part is connected to the square kelly and the lower part is connected to the drill collar. Its function is to transmit torque, make the drill bit go down and deepen the borehole.
The square kelly is located at the uppermost end of the drill string. Its main function is to transmit torque and make sure to bear the weight of the drill string. The square kelly is composed of the driving part (square or hexagon), the upper joint (left-hand thread), and the lower joint (right-hand thread). The most commonly used one is the kelly with square shape.
Heavy weight drill pipe is the transition drill string section between ordinary drill rod and the drill collar. It can effectively alleviate the concentration of the stress in the transition section of drill collar and drill pipe in combination, providing bit pressure and effectively reducing the connection area and outer diameter wear rate between drill string and wall of a well.
With the popularization and application of drilling technologies such as cone drilling, air down-the-hole hammer drilling, and air-lift reverse circulation drilling, the API series of internal drill string components and downhole tools have also been widely used.
Drill pipe joint threads can be divided into number style connection threads (NC), internal flush style connection threads (IF), full-hole style connection threads (FH) and regular style connection threads (RGE) according to the types of tested oil drill pipe connection thread.
Number style connection (NC) threads is a kind of thread represented by the numerical value of inches and tenths of the pitch diameter of the thread base. It is applicated in drilling tools such as square tooth drill rod, drill rod, drill collars, and drilling tool stabilizer.
The internal flush style (IF) connection threads connect the outer thickened or inner and outer thickened drill pipe to form the inner diameter of the drill pipe joint, and the equal or similar diameter of the thickened inner diameter or the inner diameter of the pipe body. The drilling fluid flow resistance is small. But the outer diameter is large and easy is to wear.
Full-hole style (FH) connection threads connect the inner and outer thickened drill rod, forming the inner diameter of the drill pipe joint and the diameter that is equal with the inner diameter of the drill pipe joint and the thickened end, and both are smaller than the inner diameter of the pipe body. It has been widely used in faucets, square kelly, drill rod, drill collars and drill bits, etc.
The regular style (RGE) drill pipe joint thread is used to connect the inner thickened drill pipe. 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 that of the pipe.The aim is to apply it to bit connections.
The above is the brief introduction of types of drill rods and the thread classification. I hope it will be helpful to you. If you have other problems, you can leave a message on it.