The use of High Density Polyethylene (HDPE) lining in seepage prevention in dams was identified to reduce the cost of water storage. To make it acceptable to end users, it is necessary to determine its lifespan when exposed to tropical climates using viscoelastic models. The Findley Power Law was used to build a model for prediction of the material behaviour at elevated temperature in both short term and long term applications. Time-Temperature Superposition (TTSP) was also used to develop master curves for prediction of long term properties. Micrographs were presented to track the changes during the aging process under different conditions. A simple model was developed for estimation of the service life of the HDPE lining that only requires determination of maximum strain at a given temperature. It was further concluded that the welded joint was the most serious factor undermining the service life of the lining material under tensile creep and that alternating temperature had a more damaging effect on the lining material than elevated temperature hence the lining is likely to suffer more damage in the tropics than in other climates.