Damage accumulation model for cracked pipes subjected to water hammer

Abstract

During service, oil and gas pipelines may be exposed to cyclical loads during service, which may lead to a structural failure. Failure is due in most cases to cracks in the structure. Mechanics of the propagation of surface cracks pose a serious challenge and, therefore, models are required to help analyze it. In this study, a nonlinear model is proposed to estimate the accumulation of fatigue damage in the case of defected pipes subjected to a water hammer. The studied pipes are in the presence of a semi-elliptical longitudinal surface crack. This numerical model allows the load sequence to be considered when the structure is under variable amplitude loading. The validated model is used in a parametric analysis, the purpose of which is to determine the influence of the fluid transported and the defect parameters on the evolution of the accumulated damage. The results allow the conclusion of the parameters that have the most impact on the harmfulness of the crack defect as well as the most dangerous cracks in the case of a pipe subjected to water hammer.