Fatigue behaviour of threaded couplings – experimental research

Abstract

In this article the fatigue behaviour of threaded connections is studied, as used in oil country tubular goods (OCTG). Some manufacturers have designed their own couplings (so called „premium connections‟) and they claim having an improved fatigue life or better sealability. This study will compare different coupling designs with the standard API connection. The methods used to compare the different designs are based on two-dimensional finite element analyses. Experimental research is conducted to validate the results of the FEA. The experimental research consists of a 4-point bending fatigue test, which will result in a SN-curve for the threaded connection. Based on numerical and experimental results a performance factor is deduced for the particular connection design. This factor will be used to find the best design of threaded couplings. As eventual goal of this study, with the insights gained, a threadedconnection with optimized fatigue life and sealability will be designed.