FROM OFFSHORE FLEXIBLE FLOWLINES TO DYNAMICALLY INSTALLED ANCHORS – A CONCEPT STUDY

Decommissioned subsea flexible flowlines and umbilicals pose a particular waste management challenge as there is limited capacity to process these materials in Australia. Approximately 3200 km of flexible flowlines and umbilicals will be decommissioned in Australia over the next 3 decades. Research can play a significant role in developing and validating approaches to better recycle and repurpose these flowlines and umbilicals, and at a broader scale redefine how industrial waste is managed in Australia. This paper presents a concept study on designing new dynamically installed anchors using decommissioned flexible flowlines for supporting offshore floating facilities such as floating wind turbines, wave energy converters and floating aquaculture cages. For testing, a new model anchor was designed as if the anchor shaft was truncated from a decommissioned flexible flowline and ‘fish-scales’were serrated on the external plastic layer of the flowline to enhance anchor holding capacity after installation. The new model ‘fish-scale’ anchor and model conventional deep penetrating anchor were tested for hydrodynamic and geotechnical characteristics. Their performances during free-fall in water and during penetration in clay were compared. The preliminary test results provided confirmation on the concept that decommissioned flexible flowlines could be turned into dynamically installed anchors with potential better performance.