Aging and Lifetime Assessment of Polyethylene Liners for Heat Storages – Effect of Liner Thickness
Abstract
This paper deals with the global aging behavior and lifetime assessment of polyethylene liner materials for seasonal heat storages. Hot water aging experiments at elevated temperatures of 95, 105 and 115°C were carried out using specimens with various thicknesses of 100, 500 and 2000 µm. The aging indicator strain-at-break was monitored for up to 1500 days. The experimental hot water data were fitted by potential and Arrhenius equations referring to thickness and temperature dependency. By merging both equations a semi-empirical model was established and used for lifetime estimation of polyethylene liner materials. The low divergence of the lifetime values between experimental and calculated failure data indicates the high accuracy of the thickness/temperature-model. A lifetime value of 18 years was derived for 3 mm thick polyethylene based liner materials for solar district heating systems.