Analysis of Friction Coefficient and Torque Curve of Tubing and Casing Threaded Connection

The deficiencies of the API TR 5C3 standard method for determining thread compound friction coefficient are analyzed. Based on the influence of friction coefficient of the tubing and casing connection under contact pressure on the make-up torque curve,as well as the friction mechanism and causes for thread galling,calculation is made to reveal that the surface contact pressure of small-OD tubing is generally higher than that of larger-OD casing,which explains why the tubing is more sensitive to different types of thread compounds. The make-up torque curves are calculated via batch finite element analysis,and the result is compared with actual torque curves. Then the real average friction coefficient of a certain type of thread compound is inversely deduced to be in the range of 0.06～0.08. Meanwhile,it is shown that the finite element calculation results are in good agreement with the actual make-up curves.