How is the grade of oil drill pipe determined?

Based on the analysis of the working environment and stress of oil drill pipes, the main failure modes of drill pipes include fracture, plastic deformation (such as bending), and serious wear of the thread. Among them, fracture is the most serious form of failure. This failure form is manifested in that when the shoulder of the drill rod head bears a large torsion and impact force, the drill rod will break there. After the fracture occurs, the three-thread drill bit can only stay in the formation and cannot be taken out because it loses the connection with the outside world. The cost of the three-thread drill bit is quite expensive, which will cause considerable losses to the customer.

The reason for the fracture is often due to the high hardness of the joint between the shoulder of the drill pipe head and the pipe body, and the poor plasticity and toughness. Through the analysis of the metallographic structure, the grain size grade of this part of the tempered sorbite structure (the structure obtained by quenching high temperature tempering) is usually not within the required grade range. The occurrence of this situation is greatly related to the quenching process. Link.

In addition to fracture, there is also bending. That is, the rod body part of the drill rod is plastically deformed. When the curvature of the tube body is larger than the elastic limit of the tube body, the tube body undergoes plastic deformation. The plastic deformation of the drill pipe has little impact on the customer, and there is no serious impact caused by the fracture. It only needs to be straightened to restore the drill pipe and then put it back into use again. The reason for the plastic deformation is also the same as that of the drill pipe. The quenching and tempering treatment is closely related. If the hardness of the quenched and tempered drill pipe is low, the tempered sorbite structure is less or the sorbite grain is relatively coarse, and the interval between the layers is larger, the plasticity and toughness of the drill pipe will be poor, and the bending will occur. It is inevitable.

The wear phenomenon of the drill pipe thread is related to the