Tool joints makeup torque

The magnitude of the makeup torque corresponding to the maximum load capacity of the tool Joint makeup torque. 

Caution No safety factor is included in this example calculation. Additional checkup must be done if the obtained value of the torque is not greater than the recommended makeup torque for tool joints. 

The tool Joint holds drill pipe together, and the shoulders (similar to drill collars) form a metal-to-metal seal to avoid leakage. The tool Joint threads are designed to be made up with drilling fluid containing solids. Clearance must be provided at the crest and root of threads in order to accommodate these solids. Therefore, the shoulder is the only seal. To keep the shoulders together, proper makeup torque is required. 

However, makeup torque applied to the tool Joint produces as axial preloading in the pin and the box as well as a torsional stress. 

In particular, makeup torque induces a tensile state of stress within the pin and compression stress in the box. Thus, when the tool Joint is exposed to the additional axial load due to the weight of the drill string suspended below the Joint, the load capacity of the tool Joint is determined by the tensile strength of the pin. 

Therefore, the actual torque applied to the drill string should not exceed the recommended makeup torque otherwise, the load capacity of the tool Joint is reduced. 

The API recommended makeup torque for different types of tool Joints and classes of drill pipe is given in Table 4-89. 

Normally, not more than two sections are designed but, if absolutely necessary, even three sections can be used. To calculate the tensile load capacity of drill pipe, it is suggested to apply Equation 4-58 and use the recommended makeup torque of the weakest tool joint for the rotary torque. 

Reduce the stress levels in the pin by utilizing makeup torque on tool joints at the low end of the recommended torque range. 

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