Time Intervals for Maintenance of Offshore Structures Based on Multiobjective Optimization

Abstract

With the aim of establishing adequate time intervals for maintenance of offshore structures, an approach based on multiobjective optimization for making decisions is proposed. The formulation takes into account the degradation of the mechanical properties of the structures and its influence over time on both the structural capacity and the structural demand, given a maximum wave height. The set of time intervals for maintenance corresponds to a balance between three objectives: (a) structural reliability, (b) damage index, and (c) expected cumulative total cost. Structural reliability is expressed in terms of confidence factors as functions of time by means of closed-form mathematical expressions which consider structural deterioration. The multiobjective optimization is solved using an evolutionary genetic algorithm. The approach is applied to an offshore platform located at Campeche Bay in the Gulf of Mexico. The optimization criterion includes the reconstruction of the platform. Results indicate that if the first maintenance action is made in 5 years after installing the structure, the second repair action should be made in the following 7 to 10 years; however, if the first maintenance action is made in 6 years after installing the structure, then the second should be made in the following 5 to 8 years.

Cost–Benefit Assessment of Offshore Structures Considering Structural Deterioration

“…where a 0 is the initial crack condition and a f represents the final crack condition after N cycles. The failure cost, C F m |DI,∆t , involves the structural damage that is expressed in this study in terms of a normalized damage index, DI, as follows [21]:…”

“…The parameters k and r at h max = 23 m are equal to 5.8 × 10 3 and 5.2. The epistemic uncertainties related to demand and capacity are equal to 0.15 [21]. Figure 9 shows the expected number of failures over time indicating an increase up to a value of 0.0093 at ∆t = 20 years.…”

“…Deferred production cost is estimated as follows [60]: 20) where DL is equal to 30 years [28]; C C is the price of crude oil, equal to 92 USD/barrel; U C represents the economic benefit of selling, equal to 12%; T RP is the time to recover the product, with a value of four years. The annual discount rate, γ m , is equal to 6% [21].…”

“…Ref. [21] propose an approach for establishing maintenance programs of offshore structures based on multiobjetive optimization that considers structural reliability, damage index, and cost. Ref.…”

Risk-Cost Optimization of Buried Pipelines Using Subset Simulation

“…Reliability-based maintenance optimization approaches have been applied in different engineering projects, such as bridges, buildings, pipelines, offshore structures, mechanical components, etc. (Saydam and Frangopol 2015;Beaurepaire et al 2012;Chen et al 2013;Tolentino and Ruiz 2013;Tee et al 2014a). Development of reliability-based management of inspection, monitoring, maintenance, and repair of various types of offshore structures has been described, with a focus on management of hull damage due to crack growth and corrosion (Moan 2005).…”