Lifetime Assessment of Polyolefinic Liners for Pit Thermal Energy Storages

This paper presents the lifetime assessment of polyolefinic liner materials for pit thermal energy storages (PTES). The study introduces a predictive approach based on accelerated aging of micro-specimens, enabling lifetime extrapolation to real-scale liners under service-relevant conditions. A novel high-temperature-resistant polypropylene (PP-HTR) was tested between 85°C and 135°C. Aging was evaluated by oxidation onset temperature and strain-at-break, determined through thermal analysis and tensile testing. Results were compared to commercial polypropylene random copolymer (PP-R) and high-density polyethylene (PE-RT) grades. For lifetime extrapolation, an Arrhenius relationship was established for temperature dependence and a power law model for the effect of thickness. Assuming cumulative damages, lifetime values were estimated for several upcoming PTES. The novel PP-HTR liner exhibited superior long-term durability, outperforming PP-R and PE-RT materials by a factor of 4 and 6, respectively. Endurance times of up to 50 years at 80°C were deduced.