Out-of-Plane Bending (OPB) fatigue of mooring chains was first identified as a failure mechanism after the failure of several mooring chains of a deep water offloading buoy in 2002. The discovery of this failure mechanism resulted in a Joint Industry Project (JIP) that ran from 2007 to 2013 and provided valuable insights as well as a design methodology. Up until recently, a lack of class requirements and design guidance forced some providers of mooring systems to perform their own OPB investigations, including full-scale testing and finite element analysis (FEA). Some of these investigations have been performed by the authors. This good amount of knowledge collectively owned by the authors has been compiled to develop a guidance note that can be valuable for the industry. This paper presents an overview of the new requirements and recommendations for chain OPB fatigue. It also provides further background information on the key aspects of chain OPB fatigue analysis and design and uses quantitative and qualitative examples to highlight the importance of the main recommendations. Moreover, the paper discusses the various hardware designs that have been developed to minimize chain OPB fatigue as well as other possible means of mitigation.
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