Effect of load flank angle modifications on the structural integrity of buttress threaded connections

Abstract

One of the main requirements of threaded & coupled connections used in oil-producing wells is the ability to resist high tensile loads. In order to ensure integrity under ever-increasing loads, the geometric parameters of the connection can be modified. In this paper, an FEA study of a 4.5 inch casing connection is reported to examine the effects of a modified load angle in combination with high tensile forces. The focus is on two failure mechanisms: jump-out and plastically deformed zones. Furthermore, a relative motion of pin and box at the contact regions is observed. It is concluded that using a negative load flank might be beneficial in order to prevent jump-out. At the same time, the deformations at the roots of the last engaged threads of the pin appear to be larger and relative sliding increases. Despite an optimization against one failure mechanism, the connection might fail as a result of an inevitable reduction of resistance against another.