Abstract
Threaded and coupled connections generally present a non-uniform stress distribution, which is related to the higher stiffness of the box when compared to the pin. The non-uniform stress distribution can contribute to fatigue cracks and other failure modes in high pressure oil wells. An API 5CT P110 steel obtained from a seamless pipe was mechanically characterized. FEA models were carried out to investigate and compare two API casing connections under make-up torque and tensile efforts. A parametric study was performed using numerical models to determine the influence of some geometric features on the behavior of the API Buttress threaded connection. The API Buttress connection supported higher tensile loads than the API Short Round, however both standard connections showed high stress concentration in the last engaged thread and a non-uniform stress distribution. The manufacturing of grooves at the first and the last engaged threads proved to be an efficient way to reduce the stress concentration of Buttress casing connection and could be an alternative to the development of new products.
Highlights
Casing strings for oil and gas exploration and production are generally formed by threads
The use of threaded connection instead of welding is justified by the major productivity and the reversibility of the threaded connections[1]
Proprietary connections have been developed by companies to ensure the integrity of the strings in applications as highdeep oil wells or to improve some character of the basic API standard
Summary
Casing strings for oil and gas exploration and production are generally formed by threads. Dynamic loading is common in connection service conditions Aiming to maintain their integrity they are generally preloaded, for example, by the use of tapered threads. Finite Element Analysis was used to simulate the problem in the software Ansys® Workbench® version 14.5 Both connections were submitted to tensile stresses and the jump-out (which is the separation tendency between pin and box) was evaluated, as well as the stress concentration factor. A parametric study was applied to the base connection API Buttress to evaluate how some geometric modifications can influence the connection integrity and the stress concentration factor. This parametric study was based in a patent review[6,7,8,9,10]. Evaluation of Standard API Casing Connections and Parametric API Buttress Improvement by Finite Element
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