RR1098 - Degradation of mooring chains of floating offshore installations: chain measurement, estimation of wear, corrosion rates, and their effect on break load. Mooring Integrity Joint Industry Project Phase 2

Mooring integrity for floating offshore installations is an important safety issue for the offshore oil and gas industry. This report is one outcome from Phase 2 of the Joint Industry Project on Mooring Integrity. This work ran from 2008 to 2012 and had 35 industry participants. It followed the Phase 1 work described in HSE Research Report RR444 (2006). The Phase 2 work compiled research on good practice and an overview is given in HSE Research Report RR1090 (2017).

Mooring chains inevitably degrade over time leading to loss of strength of individual mooring lines and the mooring system as a whole. This report describes how the reduced dimensions of the chain may be measured by various techniques, both underwater or when brought above the surface. It investigates typical wear and corrosion rates experienced in the field, and the change in the minimum break load of used mooring chains. The report provides: practical guidelines on likely wear and corrosion rates to inform decisions at the design stage on chain diameter allowance; indicative wear and corrosion rates to inform judgements on whether rates seen in use are typical or anomalous; and guidelines on how the minimum break load will change with degradation.

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Updated 2021-04-15