Investigation of API 8 Round Casing Connection Performance—Part III: Sealability and Torque

The performance of the API LT&C 8 Round casing connection is investigated using 7-in.-29-lb/ft pipe size. Part I showed that the finite element method was applicable for analysis using both a threaded and an unthreaded model. Part II investigated the effects of various thread tapers and external loads on connection hoop stresses. It also evaluated maximum assembly interference based on an assumed criteria. Part III addresses connection sealability based on contact pressure. Geometric end effects are found to be significant in the unthreaded model. Sealability in the middle portion predicted by hand equations is shown to be reasonable. The threaded model shows that tension reduces sealability by disengaging thread stab flanks. Assembly forces are analyzed and, along with the test results, are used to find an equation for torque. The effects of thread taper variations, tension, and pressure on torque are shown.