Three-Dimensional Finite Element Formulation for Elastic-Plastic Nonlinear Analysis of Piping Systems

A three-dimensional pipe element, with eight degrees-of-freedom per node, is developed to consider the stresses arising from the pipe internal pressurization as well as the stresses arising from the three-dimensional flexural motion of the piping system. The scheme is developed for coupling with piping hydrodynamics so that a realistic safety assessment of a reactor’s piping system can be achieved. Using rigid co-rotational coordinates, the finite element formulation is suited for large displacement but small strain situations. Both geometric and material nonlinearities are considered. The equations of motion are integrated by an explicit procedure. Sample results are presented to demonstrate the performance of the element in its individual as well as coupled modes of deformation.