The article deals with assessment of cracked oil pipelines and addresses the problem of defect initiation. When testing main pipelines for strength or when the pressure is increased during operation (in order to maintain pumping volumes when decommissioning intermediate stations), cracks sitting in the pipe body before the pressure increase may steadily propagate (initiate). When assessing a defect hazard in order to determine the safety factor of defective pipeline against fracturing pressure, it is necessary to take into account the possibility of crack initiation. The defect initiation also reduces the fatigue life in line with the stage of crack propagation. During the pipeline strength tests, it is necessary to take into account the possibility of crack initiation when determining the interval for re-testing in order to assess the size range of cracks that could initiate during tests and remain in the pipeline thereafter. The paper presents the results of assessing the steady propagation of longitudinal part-through cracks in pipes of main oil pipeline under increasing pressure and under cyclic loads with a constant pressure range using a subcritical fracture diagram. It also presents the results of assessing the influence of crack initiation on the safety factor of a cracked pipeline against fracturing pressure and cyclic durability.
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