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In the oil industry, polymers are used for sheathing dynamic risers. Polymersheaths keep the flexible waterproof and allow for the steel spirals displacements. Thepolymer has to be ductile at the working temperature (up to 90 °C), and this justifies theuse of polyamides and fluorinated polymers. Because they are exposed to a hightemperature in a fluid environment, the polymers progressively age. In the present study,we examine the evolution of mechanical properties of PA 11 between two states: asreceived and aged. Using precracked DENT specimens, we achieved to reproduce thebrittle slow crack growth which seems to be observed in field aged PA 11. Moreover, anappropriate numerical model is established. The computations are in good agreement withthe experimental results. The model is intended to help design of sheaths, and thus toprevent failures.