The Effect of the Aging Process of Polyamide 11 Used in Flexible Pipelines and Its Influence on the Permeability of Carbon Dioxide

This study investigates how long‐term natural aging affects the CO 2 permeability of polyamide 11 (PA11) pressure sheaths recovered from decommissioned flexible risers. PA11 samples were extracted from two 18‐year‐old risers—a gas‐lift line and an oil‐production line—and characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and corrected inherent viscosity (CIV) to assess crystallinity, plasticizer content, thermal stability, and molecular degradation. CO 2 permeation tests were then conducted under controlled conditions and compared with predictions obtained using the CheFEM 3 physics‐based permeation model. The results indicate limited plasticizer loss and modest increases in crystallinity after long‐term service, while CIV decreased more markedly in the production riser due to harsher operating conditions. Permeability trends show that service exposure influences CO 2 transport, with minor degradation leading to increased permeability and more advanced degradation resulting in permeability reduction, consistent with chemi‐crystallization effects. Experimental permeation values were generally close to those predicted by numerical simulations, particularly when minor degradation effects were accounted for. Overall, the findings demonstrate that naturally aged PA11 pressure sheaths retain effective barrier performance after long service life, providing experimental support for integrity assessments, permeability modeling, and the potential reuse or repurposing of decommissioned flexible pipes.