Optimum inspection planning for minimizing fatigue damage detection delay of ship hull structures

Fatigue is one of the main factors which can produce cracks, and lead to failure of ships. For these structures, damage occurrence and propagation due to fatigue are affected by the action of sea water waves and the sea environment as well as operation, fabrication, and modeling of ship structures under uncertainties. In order to efficiently maintain the safety of ship structures, an optimum inspection plan should be made by considering these uncertainties using a probabilistic approach. In this paper, such an approach is presented and applied to ship hull structures subjected to fatigue. The resulting inspection plan is the solution of an optimization problem based on the minimization of expected fatigue damage detection delay. Damage detection delay will produce the maintenance delay which, in turn, is likely to endanger the serviceability and even the survival of the structure. The formulation of the expected damage detection delay includes uncertainties associated with damage occurrence, propagation, and detection. The effects of the quality and number of inspections on the optimum inspection planning are investigated. A well-balanced inspection planning is considered as a solution of an optimization problem with two conflicting criteria. This well-balanced inspection planning provides optimum inspection types and times. Furthermore, the cost-effective inspection plans are designed to provide the optimum strategy either by considering a single type or multiple types of inspections.