Mooring System Reliability Index (MSRI) Implementation Guide

The MSRI is grounded in reliability engineering principles adapted for the unique challenges of marine environments—including stochastic wave and current loads, seabed soil variability, corrosion, fatigue, and installation uncertainties. It employs a limit-state-based approach where system failure is defined as exceeding a critical threshold (e.g., anchor drag, line rupture, or excessive platform displacement) under combined environmental and operational loads. Probabilistic modeling—often using Monte Carlo simulation, first-order reliability methods (FORM), or surrogate-assisted reliability analysis—is applied to propagate uncertainties in input parameters (e.g., metocean data, material properties, and geometric tolerances) through a high-fidelity numerical model of the mooring system. The resulting failure probability is transformed into the MSRI via a monotonic, interpretable mapping (e.g., MSRI = 1 − P_f^α, where α ≥ 1 adjusts sensitivity near low-probability regimes). Crucially, MSRI is not a standalone safety factor but a performance-based metric designed to enable comparative assessment across alternative mooring configurations (e.g., catenary vs. taut vs. synthetic hybrid), facilitate regulatory alignment with ISO/IEC 17065 and IEC TS 62600-301 standards, and support digital twin–enabled condition monitoring by updating the index with real-time sensor data and inspection findings.