The effect of temperature on the stress–strain state of the tool joint threaded connection of drill pipes
DOI:
https://doi.org/10.31471/1993-9965-2025-2(59)-24-32Keywords:
drill string; tool joint threaded connection; stress–strain state; stresses; thread turns; temperature.Abstract
The article examines the design and operational features of tool joint threaded connections (TJTC) of the drill string, which are used to connect drill pipes, subs, bits, stabilizers, and other components. TJTCs must provide high strength, fatigue resistance under tensile, compressive, and bending loads, as well as under torque, while also ensuring tightness, wear resistance, and fast assembly. An important factor in the operation of TJTCs is the correct application of lubricant and adherence to the specified makeup torque, since violation of these conditions may lead to failure of the connection. The paper presents the causes of TJTC failures. When studying TJTC designs, researchers consider a broad range of factors; however, they usually do not take into account the influence of temperature acting on the connection during assembly and during drill string operation in the well. Due to the complexity and high cost of full-scale testing of large and complex equipment (including TJTCs), finite element method (FEM) modeling of their stress–strain state has become widely used. The paper presents a TJTC model constructed in accordance with API standards and determines the stress–strain state of the connection under makeup torque, axial loading, and temperature. Modeling was performed for three cases: when both the pin and box temperatures are 20 °C; when the pin temperature is 20 °C and the box temperature is 100 °C; and when both components are at 100 °C. The results show that as the temperature difference between the pin and box increases, the stresses in the thread roots of the box rise significantly, while the maximum stresses in the pin decrease. The most severe operating conditions occur when the pin temperature is 20 °C and the box temperature is 100 °C under tensile axial load and makeup torque, which is typical for drill string sections located closer to the wellhead. Further research includes modeling heat transfer between the drilling fluid and the TJTC, considering the material’s thermal conductivity, and adjusting makeup torque to improve the accuracy of assessing the stress–strain state of TJTCs.
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