Numerical Investigation of 3D Scanned Mooring Chains - Effects of Stress Concentrations from Corrosion Pits
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This thesis aims to numerically evaluate severe corrosion pits on offshore mooring chain. Pitting corrosion is considered a significant degradation mechanism as cracks tend to nucleate and propagate in areas of high stress concentration. Hence, the idea has been to replicate the pits using a 3D scanner, and subsequently analyze the pits in a finite element software. The study is part of a collaborative research project between Statoil ASA and NTNU, where the motivation is the fatigue life of offshore mooring lines. It is believed that surface conditions, like pitting corrosion, are highly influential on the chain segments fatigue life. The final aim is to introduce clear criteria for deciding whether a chain is too damaged to continue service or not. A method for replicating and evaluating the effects of the corrosion pits has been devised in the following. However, before it can be used on an actual situation, the methods capabilities need to be proved for a simple scenario. Consequently, this thesis has focused on developing the method and testing it on artificially made corrosion pits.