Fatigue Performance of Thermal Spray Aluminium Coated Mooring Chains

Abstract

Corrosion-fatigue is the main damage mechanism of chains in permanent mooring systems. Fatigue loading is unavoidable, but corrosion can be mitigated or prevented; so, the impact of its reduction in the corrosion-fatigue damage mechanism is of great interest. TSA (Thermal Spray Aluminium) coating has been applied for corrosion mitigation in mooring chains, typically at the splash zone, where higher corrosion rates are expected compared to those in submerged condition. TSA coating was first applied in mooring chains in 2001 at the Gulf of Mexico. This early experience of TSA demonstrated its effectiveness in preventing corrosion of top chains and led to several projects applying TSA in the same location. However, TSA’s effect on the fatigue performance of mooring chains had not been investigated so far. The paper presents full scale fatigue test results of TSA coated mooring chains. Six fatigue tests have been carried out on 76 mm chain, which results show increased fatigue endurance relative to comparable fatigue test data of freely corroding chains in seawater. The results are statistically analysed and compared with all available test data of uncoated chains from Joint Industry Projects, in order to assess the effect of the coating in the fatigue strength of mooring chains.