RR1093 - An assessment of proof load effect on the fatigue life of mooring chain for floating offshore installations. 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).
Long lengths of steel chain links are used in the mooring lines of offshore floating installations. As an installation moves under wave, wind and current conditions, the chains are subject to high loads that can promote metal fatigue and line failure through the nucleation and propagation of defects in the steel. This report assesses the impact on the fatigue life of chains of the proof loading carried out after manufacture. Proof loading involves testing chains at about 66% of the minimum breaking load specified in offshore standards. Proof loading has been found to be beneficial for the integrity of chain and enhances fatigue life under tensile loading. The report identifies other implications for chains with of out-of-plane bending and for twisted chains.
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