Reliability based optimization ofinspection and maintenance schedules for offshore jacket structures subject to marine corrosion

Offshore structures are subject to different types of marine corrosion leading to fatiguewhich may ultimately result in a collapse of the entire structure. In reality, these catastrophicfailures rarely occur due to the application of protective coatings and regular inspection andmaintenance. However, these inspections are time intensive and costly, which is why an optimizedschedule is desired. This work proposes a reliability based optimization of the inspection intervalsusing the survival signature. The survival signature is a novel tool for the reliability analysis ofsystems and networks. Jacket structures are built from three basic components: legs, bracings,and chords. This allows for an easy translation of the physical structure into a system basedmodel as required by the survival signature. Components are grouped in types by corrosionzones (submerged, splash, atmospheric). Using the survival signature, the reliability of thejacket structure is computed by Monte Carlo simulation. Based on the system reliability theinspection and (if required) maintenance schedules are optimized, significantly reducing effortand cost. The main advantage of the proposed technique over traditional methods stems fromthe separation of structural and probabilistic information in the survival signature. This allowsto efficiently analyze the same structure in varying locations where different strengths of marinecorrosion can occur.