Nonlinear Finite Element Analysis of Pressure Vessel Welds

The computer resources needed to perform nonlinear finite element analyses on the shell-flange fillet weld of a pressure vessel are extensive. To facilitate this process a reduced fea model was developed. The vessel that was analyzed had an 1828.8 mm (72 in.) inside diameter and was 12.7 mm (.5 in.) thick. The vessel was assumed to have no nozzles or access openings. It is demonstrated using linear analysis that only 711.2 mm (28 in.) of the shell were needed to capture most of the effects of the flange on the shell. It is also shown that with the correct restraints the head of the vessel need not be modeled. A macroscopic plastic deformation study illustrates that the first signs of macroscopic plastic deformation occur at the base or toe of the shell-flange weld. A method to approximate the fatigue life of such a pressure vessel is discussed. The plastic enclave grows, as the monotonic pressure increases, down the shell and through the thickness thereby predicting a longitudinal rupture. Thus, two of the more significant modes of failure of pressure vessels are indicated by the nonlinear analysis