Influence of design features on the structural integrity of threaded pipe connections

Abstract

When drilling and completing High Pressure High Temperature (HPHT) wells, the applied casingand tubing have to be able to withstand extreme conditions. Very often, the threaded connections are themost critical components in the entire chain. The overall design of several threaded and coupled (T&C)connections (eg. VAM TOP, JFEBear and the newest PatriotTC) is very similar. However, even bymodifying one single feature of the geometry, an improved structural integrity (eg. fatigue resistance, leaktightness or collapse strength) can be obtained. This paper gives an overview of the most importantgeometrical features and discusses their alleged effects on the structural integrity of the coupling.Ghent University, Laboratory Soete, BelgiumAt first, different thread designs were compared with each other and the effects on maximum allowabletorque during make-up and tension during service conditions were evaluated. Secondly, literature showsthat the use of an adequate torque shoulder is favourable, especially during the make-up stage. Whendesigning connections for purposes involving gasses, a gastight seal is required. The third part of this paperdiscusses the influences on the sealability and performance limits when making changes to the sealingarea. At last, the effect of overall changes (such as stress relief grooves) in the design and theirconsequences during running is shortly discussed. Based on this review, design guidelines for ‘optimized’premium T&C couplings can be formulated.