Force analysis and tightening optimization of gas sealing drill pipe joints

• The force carried by gas sealing joints differs from API ones.
• The axis and radial equilibrium equations of gas sealing joints are put forward.
• The equilibrium equations are verified through FEM.
• Showing the stress distribution of gas sealing joints
• We introduce the concept of “sealing strength” to evaluate sealing performance of tool joints.

In this article threaded tool joints of gas sealing drill pipes, which are exposed to different tightening turns and tension load, are analyzed using an elaborate finite element modeling through the use of MSC.Marc13.0. The corresponding mechanics model is also established and the reliability of the model is verified by finite element simulation and full scale test. Some conclusive results have been drawn from the analysis including that the force distribution of the gas sealing joints is quite different from the API standard one, and the metal seal structure can greatly improve the seal performance of the joint under tension load. Research also shows that reasonable tightening turns can effectively reduce the thread axial load growth amplitude under the tensile load as a result improving the fatigue life of the tool joints.