Characterisation and Durability of Recovered Subsea Flowline Polymers

Polymers employed in subsea flowlines are designed to withstand harsh offshore environments and mechanical loading throughout operational lifespans exceeding 10 years. However, exposure to ultraviolet radiation, ocean currents, salinity, microorganisms and mechanical stresses can initiate and accelerate material degradation, thereby compromising performance. Currently, there are no established methodologies for identifying and characterising unknown polymers retrieved from decommissioned environments or for the assessment of their degradation. This study characterises both uncommissioned and decommissioned flowlines using spectroscopy, thermal analysis and microscopy, with experimental parameters optimised for each technique to ensure accurate identification of polymer types and evaluation of material integrity. The primary polymers identified were high‐density polyethylene (HDPE) and polyamide 12 (PA12), containing 33% BBSA plasticiser and trace levels of inorganic fillers (26% Ca, 31% Ti and 19% Fe). Despite prolonged subsea exposure, decommissioned polymers demonstrated physicochemical properties and morphologies comparable to those of uncommissioned flowlines, including high thermal stabilities (454°C–471°C and 457°C–494°C) and distinct crystallinity (57%–61% and 29%–34%), respectively. Infrared (IR), Raman and pyrolysis–gas chromatography–mass spectrometry (Py‐GC/MS) analyses produced consistent spectra and chromatograms, with no significant peak shifts or intensity variations, confirming strong durability. Morphological analysis revealed minor surface scratches, attributed primarily to sample pretreatment. Furthermore, the primary elements are C (63%–86%), O (13%–19%) and N (15%), mainly originating from the polymer backbone. The observed material stability indicates potential for reuse, recycling or upcycling, thereby advancing circular economy approaches in offshore infrastructure management and mitigating environmental impact.