Recovery of marine energy is progressing from the prototype stage to arrays, and all of the systems currently being developed include critical elements manufactured from polymers and composites. Structural MRE (Marine Renewable Energy) components range from composite turbine blades, for floating wind and tidal turbines, to polymer fiber ropes for wave, tidal and floating wind mooring systems. Elastomeric components are also widely used for sealing and protection. In all cases it is essential to understand how seawater diffuses into these polymers and how it affects mechanical properties; this allows appropriate safety factors to be applied without excessive over-conservative design, and can result in significant cost reduction. This paper will present a methodology for evaluating the long term behavior of such components based on accelerated testing. Three examples will be shown to illustrate the approach; tidal turbine blade composites, synthetic fiber rope moorings, and rubber components. In each case the seawater diffusion kinetics will be described first, then the influence of water on mechanical behavior will be quantified for the particular loadings of interest, and finally results from fully coupled fatigue tests in seawater will be discussed.

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