In the energy sector, semi-crystalline polymersa are primarily used within structures located in aggressive environments, to form coatings (waterproofing, thermal or electric barriers). These materials possess an intrinsic flexibility exploited in some offshore applications, such as oil production pipelines, but they are also found in electric cables for the offshore wind energy sector.

Through these various applications, the polymers can be exposed to a variety of extreme stresses: pressure (>1,000 bar), swell, high voltage, temperatures (from -20°C to 150°C), liquid and gas diffusion. In the latter case, the penetration of chemical species within the polymers can affect their mechanical behavior via multiphysical mechanisms that can cause damage: from the creation of microcavities to the appearance of cracks potentially leading to fracture.

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Microstructure of a clay (a) and a polymer (b).

Towards a poro-chemical-mechanical model

In order to describe the integrity of semi-crystalline polymers in harsh environments, a model inspired by natural porous and non-permeable materials, such as clays, was developed by IFPEN. The model makes it possible to consider multi-physical couplings from both a theoretical and numerical point of view. The analogy with clays is based on the microstructural arrangement (figure) and viscoplastic mechanical behavior. But beyond this comparison, it is a phenomenological model capable of introducing couplings between deformation and diffusion of species that was introduced.

Hence, the parallel with natural porous media, combined with a rigorous theoretical framework, recently made it possible to treat complex phenomena, such as pressure-diffusion cavitation, hydrolytic weakening and competition between fracture mechanisms (brittle or with plasticity)(1). One potential avenue for enhancing this model is to describe damage by the diffusion of electric arcs,
within coatings for immersed electric cables.

a - Comprising a crystalline phase and an amorphous phase.

(1) S. Maiza, X. Lefebvre, N. Brusselle, M-H. Klopffer, L. Cangémi, S. Castagnet, J.C. Grandidier. Submitted to Journal of Applied Polymer Science.

Scientific contacts: nadege.brusselle@ifpen.fr - laurent.cangemi@ifpen.fr