Risk Based Inspection and Repair Optimization of Ship Structures Considering Corrosion Effects

A theoretical framework of risk based optimal inspection and repair planning is proposed for the ship structures subjected to corrosion deterioration. The planning problem is formulated as an optimization problem where the expected lifetime costs were minimized with a constraint on the minimum acceptable reliability index. The safety margins are established for the inspection events, the repair events and the failure events for ship structures. Moreover, the formulae are derived to calculate failure probabilities and repair probabilities. Based on them, a component subjected to pitting corrosion is investigated to illustrate the process of selecting the optimal inspection and repair strategy. Furthermore, some sensitivity studies were provided. The results show that the optimal inspection instants should take place before the reliability index reaches the minimum acceptable reliability index. The optimal target failure probability is 10⁻³. In addition, a balance can be achieved between the risk cost and total expected inspection and repair costs by using the risk based optimal inspection and repair method, which is very effective in selecting the optimal inspection and repair strategy.