A study of the cyclic damage to buried pipelines during the passage of seismic waves

THE SEISMIC STRENGTH of underground pipelines is assessed based on the axial stresses on the pipeline from the so-called particular combination of loads and impacts. When calculating the stresses from seismic impact, several standard coefficients are introduced, which assume some damage to the pipeline while ensuring the safety of people and the integrity of equipment. These coefficients also take into account anchoring, which depends on the  backfill soil and the degree of pipeline criticality. Permissible stresses are accepted in accordance with regulatory documents for design (SNiP 2.05.06-85). The seismic strength of the pipeline in operation is assessed taking into account the seismic impact intensity which is actually reached during an earthquake, and the loads and impacts which affect a pipeline in an earthquake, as well as any defects present in the pipeline wall.   When a seismic wave passes through an underground pipeline, the girth welds are exposed to an alternating cyclic impact. Here, it is relevant to estimate the fatigue damages accumulated over the course of the earthquake. The magnitude of this damage depends on the intensity of the earthquake, the seismograph of the earthquake, the speed with which the longitudinal seismic wave travels along the longitudinal axis of the pipeline, the degree to which the pipeline is anchored by the soil, and the stress concentration coefficient in any defects.   This article studies the accumulation of cycle-induced damage caused by a longitudinal seismic wave. The results may be applied for evaluations of the cyclic longevity of girth welds with defects in pipelines operating in seismic zones.