Fatigue life improvement of threaded connections by cold rolling

Failures in drillstring threaded connections continue to afflict the oil industry at a cost of millions of dollars per year. In an attempt to reduce these failures the industry has generally adopted the fatigue-life-enhancing technique of cold rolling the threaded connections which act as stress concentrations. However, this beneficial process is only specified as optional in the industry standards, and where it is performed there is very little detail provided about this important process. This paper describes full-scale fatigue tests that investigate the cold-rolling process. From the development of cold-rolling equipment and the gathering of fatigue experimental data, several key factors have been identified that influence the operational lifetime of drillstring threaded connections.