Understanding Long-Term Photo-Oxidative Degradation and Service Life Prediction of Modified HDPE Marine Aquaculture Pipes: Experimental Insights and Model Predictive Performance

Marine environments and UV radiation severely degrade high-density polyethylene (HDPE) aquaculture pipes. This study introduces a novel empirical framework integrating physicochemical data with COMSOL Multiphysics to predict the long-term, heterogeneous degradation of modified HDPE over a 50-year service life. To enhance weatherability, HDPE was compounded with a UV absorber (UV531) and an antioxidant (AO1010). Simulation results show that the optimal formulation (1% UV531) retains a tensile strength of 26.3 MPa after 50 years—a 17% reduction versus 29% for additive-free control. This performance stems from UV531 absorbing 240–340 nm radiation, whereas AO1010’s long-term effect was negligible. Crucially, COMSOL captured a surface-to-core oxidation gradient and non-uniform degradation, providing more realistic structural predictions than conventional homogeneous models. Importantly, by coupling empirical kinetics (G0 and kd) from a 15-year equivalent accelerated exposure (5.0 GJ m−2) with seawater diffusion (1.77 × 10−13 m2/s) in COMSOL, a comprehensive 50-year time-dependent degradation prediction across the pipe wall was achieved. This simulation-driven strategy establishes a robust, highly efficient approach to optimizing material longevity for sustainable marine applications.