Through the analysis of the working environment and force situation of the drill pipe, it is found that the main forms of failure of the drill pipe are fracture, plastic deformation (such as bending) and severe wear of the fillet. Among these forms of failure, fracture damage is the most serious. The damage takes the form of fracture of the drill pipe when the shoulder of the head of the drill pipe is subjected to large torsional and impact effects. When fracture occurs, the three-tooth bit is left in the formation and cannot be removed because it is disconnected from the outside world, and the cost of the three-tooth bit is quite high, thus causing considerable damage to the user.
The reason for the occurrence of fracture is usually due to the high hardness, poor plasticity and toughness of the connection between the shoulder of the oil drill pipe head and the pipe body. According to the metallographic organisation analysis, the grain size class of this part of the tempered sowthite organisation (organisation after high temperature tempering treatment) is generally not within the required class range, and this happens in close connection with the quenching process.
In addition to fracture, there is also bending. This means that the rod portion of the drill pipe is plastically deformed. The greater the curvature of the bend in the body of the tube, the more it exceeds the elastic limit in the body of the tube, and the more plastic deformation occurs in the body of the tube. The plastic deformation that occurs in the drilling tool will have less impact on the user and will not cause serious damage. It is only necessary to correct the drilling tool, which will restore the tool to its original state, and then put it back into use. The reason why plastic deformation occurs is that it is also closely related to the quenching and tempering treatment of the drilling tool. If the hardness of the quenched and tempered drill pipe is low, the tempered soxhlet organization is less, or the soxhlet grains are coarse and the
layer spacing is too large, the plasticity and toughness of the drill pipe is poor, and bending is inevitable.
Post time: Mar-07-2022