Failure of a threaded pressurized vessel

A fracture mechanics analysis of a threaded pressure vessel, which has been welded to a plug of similar material is presented. Owing to the presence of threads (circumferential notches) in a pressure vessel, premature fracture may occur due to the propagation of a crack nucleating from the thread root. In order to determine the internal pressure, which induces this fast fracture, a semi-analytical approach is used which combines both linear elastic fracture mechanics and finite element analysis. An estimation of the axial stress required to propagate the crack is obtained from the fracture mechanics approach, using the far-field axial stress in the threaded region recovered from a finite element analysis. Moreover, experimental evidence substantiates the validity of this type of composite analytical approach, by confirming both the rupture pressure and the residual hoop strain after fracture.