The net-section stress associated with the extension of a part-through full-circumference crack in a pipe

Earlier workers have used a simple net-section stress approach, based on collapse-type analyses, to predict the size and shape of a part-through circumferential crack that will cause failure of a pipe fabricated from a ductile material: stainless steel. The equations of equilibrium are applied, assuming that the cracked section behaves like a plastic hinge, with a region of uniform tensile stress, σ*, acting above the neutral axis and a region of uniform compressive stress, — σ*, acting below the neutral axis; σ* is the average of the yield and ultimate stresses. Both experimental and fracture mechanics calculations have hither to shown that crack extension occurs at net-section stresses that are approximately the same as that used in the collapse analysis, when the crack is of the through-wall type, thus providing partial vindication of the net-section stress approach. The present paper extends this work and a fracture mechanics analysis shows that the net-section stress associated with the extension of a part-through full-circumference crack can be appreciably higher than that for a through-wall crack. The paper therefore provides further support for the usefulness of the simple net-section stress approach for predicting the failure of a stainless steel pipe containing a circumferential crack, since its predictions should be conservative in this situation.