Production offshore units have a relative long operational life (about 20 years), during which are submitted to the ocean adverse environment loading produced by the combination of wind, waves and currents. This complex loading history can promote the nucleation and propagation of cracks in mooring line components. The presence of defects establishes a critical situation that can lead to catastrophic failures. In spite of residual stress plays a preponderant part in the structural integrity of a mechanical component, the presence of residual stress is not considered in traditional design of these mechanical components. Therefore, is fundamental to develop new and more precise methodologies for assessing the structural integrity of mooring components. The present contribution regards on modeling and simulation of the residual stress distributions in studless chain links using a tri-dimensional elastoplastic finite element model with large displacements. In the analysis three material conditions, associated with different mechanical properties, were considered. The results indicate that the presence of residual stresses modify significantly the stress distribution in the component. Also, residual stress distribution depends on the mechanical properties of the chain link material. The structural integrity of the mechanical component was studied using the concept of critical volume associated to the material volume susceptible to a certain critical crack size. This methodology permits the evaluation of the critical crack length distribution related to brittle fracture of the component.
Mooring lines of offshore oil exploitation platforms consist of long lengths of steel chain links, wire ropes and other accessories. Usually, these lines are designed for an operational life of about 20 years and periodic inspections are mandatory for monitoring the structural integrity of these components. The failure of a single element in a mooring line can cause incalculable environmental damage and severe economic losses. The ocean adverse environment loading produced by the combination of the wind, waves and currents leads to a complex alternate loading that can promote fatigue and crack propagation. Residual stress plays a preponderant part in the structural integrity of a mechanical component subjected to such loading. Offshore mooring line components as chain links enter in operation with a residual stress field created by the proof test dictated by offshore standards. However, the traditional design of such mechanical components does not consider the presence of residual stress. This study concerns about predict the residual stress field present in stud and studless chain links prior to operation to compare the fatigue life predicted by the traditional design methodology with the one predicted considering the residual stresses states present before operation. Numeric simulations with an elastoplastic finite element model are used to estimate the residual stress along the chain link that are present after the proof test and before operation. The results indicate that the presence of residual stresses modify significantly the fatigue life of the component.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.