A Limit Pressure Criterion for Cracked Cylinders and Piping Branch Junctions

The concepts of limit loads and plastic loads for piping components are outlined. The difficulty associated with specifying reliable definitions for these quantities is addressed. These difficulties include the selection of a deformation parameter, the selection of a location within the structure where this deformation is to be calculated or measured and the criterion to be used to assess if the deformation is sufficient for the structure to be considered to have reached its limit or plastic load. An alternative method based upon plastic work has recently been advocated [1]. This definition is based upon the plastic work that may be calculated during a routine finite element computation. Having plotted the cumulative plastic work against a load parameter, it was shown possible to identify levels at which collapse mechanisms form and where gross plastic deformation becomes evident. The present work attempts to add some precision to this definition. This has been done by determining the important geometric parameters and forming non-dimensional quantities to allow new plots in which the limit or plastic loads can be extracted directly and without any ambiguity. The technique is shown to be reliable for cracked and uncracked plain cylinders and cracked and uncracked piping branch junctions.