Lifetime Extension of Mooring Anchors

The mooring systems for floating offshore installations are typically designed for a life of 25 years. Life extension of the installations beyond original design life require either replacement of components or life extension of the existing, where keeping components in the systems as is require assessments knowing the condition of the components. Some of the components are difficult or impossible to inspect in operation, such as chain in the seabed and the anchors. On the NCS typically suction anchors have been used, where all the load bearing parts, including connection to mooring lines, are buried in the soil. Assumptions with respect of degradation were established in design of the anchors. However, actual degradation of the parts buried in the soil has been uncertain, and in situ inspection of the anchors has been impossible. Equinor has retrieved several anchors to shore which has enabled degradation investigation. Two suction anchors have been retrieved as mooring lines were taken out of service, while a third anchor has been retrieved and substituted from a mooring system in operation. By bringing the anchors to shore, thorough inspection followed by life extension evaluation for remaining anchors has been possible. This paper presents the work done on retrieving used mooring anchors, including description of condition and degradation mechanisms. The paper presents our conclusions for life extension of mooring anchors on the NCS.