Fatigue Performance of Mooring Chains in Seawater
Status: Completed
Date Announced: May, 2012
Project reference: 22116
Mooring chains are used consistently for deep water oil and gas developments including mooring FPSO vessels, buoys and spars. Designs utilising larger links and higher strength materials (such as R5 grade) are being considered. However, the fatigue performance of higher grade chain lacks industrial understanding, meaning that possibilities such as increased static strength not resulting in a higher fatigue performance in seawater become a rising concern. Industry has therefore expressed the need to obtain fatigue test data under true operating conditions in order to gain a detailed understanding of the factors affecting fatigue performance.
Fatigue design recommendations provided by API and DNV are based mainly on fatigue data obtained in the 1990s. The maximum diameter tested was 76mm for studless and 100mm for studlink chain in steel grades R3 and R4. This means that data is extremely limited, especially for longer lives of the order of 1 million cycles.
This Joint Industry Project (JIP) has critically reviewed existing knowledge, provided full-scale fatigue data in seawater for high strength steel (grade R5) and large link diameter, and established the primary material properties affecting fatigue performance in seawater.
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