Loss of Pressure Boundary through Buckling-Induced Fracture in the Ciudad Nezahualcóyotl Pipeline

A study is presented to investigate the fatigue and local buckling-induced fracture incident of a buried continuous pipeline during the 1985 Mexico City earthquake. Assuming pipeline wrinkling is caused by longitudinal wave propagation, peak ground strains are estimated from recorded velocity time histories near the site of the fractured pipeline and critical buckling strains are calculated from experimentally based empirical relationships. A physics-based model of the postbuckling deformation of the pipeline provides estimated deformation demands on the pipe, whereas a micromechanical fatigue-fracture model is used to determine the potential for fracture considering the estimated axial deformations from the recorded ground motion, plastic strain demands, and stress state at the critical fracture location. The ground motion at the Ciudad Nezahualcóyotl site in Mexico is assumed to have approximately seven cycles of ground deformation large enough to exceed the critical buckling strain of the member. From a postevent reconnaissance, photographs demonstrate that the pipeline did experience a circumferential fracture near a butt weld region; thus, fracture in the base metal along with the heat-affected zone (HAZ) is considered. Although there is no evidence as to the specific time of fracture during the earthquake, the results from the fatigue model are presented in a probabilistic manner to demonstrate the likelihood of failure in the base metal and HAZ. The model and general procedure developed herein is promising in the context of improvingseismic design criteria to prevent pressure boundary loss in buried steel pipelines.