Net-section-collapse analysis of circumferentially cracked cylinders - part I: arbitrary-shaped cracks and generalized equations

This is the first in a series of two papers generated from a study on net-section-collapse (NSC) analysis of circumferentially cracked pipes. In this paper (part I), a generalized NSC method is presented to predict the maximum moment of a circumferentially cracked pipe with a variable-depth internal surface crack subject to combined bending and tension (pressure-induced) loads. Two sets of equations were derived. The first set involves the case where the entire crack is subjected to tension, while the second set involves the case where part of the crack is subjected to compression. For the second set, separate equations were derived for both tight (closed) and blunt (open) cracks. In both cases, these equations are based on the static equilibrium of the cracked pipe subject to externally applied bending moment and pipe internal pressure. The generalized method is capable of predicting NSC moment of a pipe with any arbitrary-shaped crack that has symmetry with respect to the bending plane of the pipe. Using this method, the maximum moments of cracked pipes with constant-depth, elliptical, and parabolic cracks were calculated to study the influence of crack shape on a pipe's load-carrying capacity. Later, the method was applied to analyze two full-scale pipe fracture experiments. The results show that the generalized NSC method can accurately predict experimental moments when the failure mechanism is governed by the limit-load criterion. (C) 1998 Elsevier Science Ltd. All rights reserved.