Mechanism-Based Degradation and Structural Integrity of Marine Renewable Energy Systems: Multiscale Modelling, Materials Challenges, and Future Qualification Frameworks

Marine renewable energy systems, including offshore wind, tidal, and wave technologies, are central to global net-zero strategies but remain constrained by reliability-driven costs and uncertainty in structural performance. In harsh offshore environments, interacting degradation mechanisms (such as corrosion–fatigue, hydrogen embrittlement, variable-amplitude loading, wear, and manufacturing-induced variability) govern failure, yet are not adequately captured by existing empirical design frameworks. This review presents a comprehensive, mechanism-based perspective on structural integrity in marine renewable energy systems, explicitly linking microstructure-sensitive deformation and damage processes to engineering-scale performance and reliability. The materials landscape, including structural steels, titanium alloys, fibre-reinforced composites, and additively manufactured materials, is critically examined with emphasis on process–structure–property–performance relationships. Multiscale modelling approaches are synthesised, spanning crystal plasticity finite element modelling, mesoscale damage formulations, fracture mechanics, structural reliability methods, and emerging digital twin and data-driven frameworks. A key contribution of this work is the integration of microstructure-resolved modelling with system-level reliability and qualification, addressing a critical gap between materials physics and engineering design standards. The review identifies critical limitations in current practices, including the lack of explicit treatment of coupled degradation mechanisms, insufficient representation of manufacturing variability, and the absence of consistent uncertainty propagation across scales. Building on these insights, an integrated, mechanism-resolved framework is proposed that combines multiscale modelling, manufacturing-aware qualification, inspection-informed updating, and hybrid physics–data approaches. This framework supports a transition from static, empirical design towards predictive, lifecycle-based structural integrity assessment, enabling improved reliability, reduced uncertainty, and more cost-effective deployment of next-generation marine renewable energy systems.