Fatigue of Drillstring: State of the Art

Failure due to fatigue is a very costly problem in oil and gas industry. Many investigators have previously addressed this problem, but its frequency of occurrence is still excessive. Torque and tension can be correctly predicted but computations of fatigue duration are still approximate. Regarding the fatigue failure of drillstring, this paper summarizes the state of the art. Prediction and calculation of fatigue duration are stated, including both history of the simplified approach based on Miner's rule and a few elements of the fracture mechanics theory. Existing inspection methods, their limitations and further recommendations are provided. Moreover, the fatigue tests are performed when human life and environment may be at risk. The loading conditions, the test frequency, the number and the size of test specimens are given. Environmental effects such as corrosion are recalled. Prevention and inhibitors are mentioned. Last chapter focuses on enhancement of drillstring. Drillpipes geometry improvement, connections re-design, steel properties such as toughness, tool-joints hardfacing and inspection of drillpipes are discussed