Time Variant Reliability of Mooring System Considering Corrosion Deterioration

Abstract

This paper deals with time variant overload reliability analysis of a mooring system due to corrosion deterioration. A probabilistic model for uniform corrosion is adopted to predict the strength degradation. A simplified method and nonlinear finite element analysis are used to calculate the breaking strength of the chain link and comparison is made. The strength of one mooring line is modeled by a weakest link system. The effect of correlation in corrosion models for different chain links in one mooring line and the effect of higher corrosion rate in the splash zone are discussed. The annual failure probability of the most loaded mooring line of a semi-submersible is calculated. The first and second order motions of the semi-submersible and the corresponding line tensions are found by a simplified analysis. The time variant reliability analysis is performed by approximating the degraded strength by a piece-wise constant model. The annual failure probability is obtained for different years. It is found that the annual failure probability increases significantly as the chain is corroded.

Reliability‐based resilience assessment method for mooring systems under mooring failure

“…Different corrosion models for mooring chains have been proposed 73‐75 . In this paper, we employ the uniform corrosion model recommended by DNVGL‐OS‐E301 15 .…”

“…Over time, corrosion reduces the breaking strength and axial stiffness of the mooring chain. We use the formula recommended by Leira et al 74 to calculate the reduced breaking strength and axial stiffness: $$${T}_{{\rm{b}}}(t)={T}_{{\rm{b}}0}{\left[\frac{D(t)}{{D}_{0}}\right]}^{2}$$$ $$$EA(t)=E{A}_{0}{\left[\frac{D(t)}{{D}_{0}}\right]}^{2}$$$where $$D(t)$$ is the diameter of the mooring chain after $$t$$ years of service; $${T}_{{\rm{b}}0}$$ and $$E{A}_{0}$$ is the initial breaking strength and axial stiffness of the mooring chain; $${T}_{{\rm{b}}}(t)$$ and $$EA(t)$$ is the breaking strength and axial stiffness of the mooring chain after $$t$$ years of service.…”

“…Different corrosion models for mooring chains have been proposed. [73][74][75] In this paper, we employ the uniform corrosion model recommended by DNVGL-OS-E301. 15 This model assumes a constant corrosion rate of 0.4 mm/year.…”

“…Over time, corrosion reduces the breaking strength and axial stiffness of the mooring chain. We use the formula recommended by Leira et al 74 to calculate the reduced breaking strength and axial stiffness:…”

Fatigue Analysis of Deepwater Hybrid Mooring Line Under Corrosion Effect

“…Gao et al [16] introduced the reliability calculation to the corrosion fatigue damage analysis. Lardier et al [17] applied the S-N curve and the fracture mechanics method to calculate the fatigue reliability of catenary mooring lines under corrosion effect.…”