ABSTRACT
Proof load testing for mooring equipment is usually required to confirm the safety of mooring components, and each length of mooring chain should be proof load tested in accordance with relevant offshore standards. High residual stresses at mooring chain links would be generated due to proof load testing and its effects on the fatigue life of mooring chain links are usually ignored in the mooring fatigue design. This paper is to investigate the influence of residual stresses induced by proof load testing on fatigue lives of mooring chain links. A frequency-domain analysis for a semi-submersible operating at Offshore Western Africa (OWA) is performed for predicting the tensile loading acting on the mooring system, in which environment effects including waves, swells and winds are taken into account. A Fracture Mechanics (FM) based fatigue analysis for the mooring chain links accounting for the effects of proof load testing is then conducted based on the estimated tensile loads. The stress intensity factor ranges used in the FM based fatigue analysis are determined by a non-linear elastoplastic finite element (FE) analysis. The procedure of proof load testing is simulated in the FE analysis.
