<p>Polymeric materials are widely used in construction and industry, where long-term durability under sustained loads is critical. However, conventional methods for predicting service life and ranking material performance are often time-consuming. This study introduces a novel test method for evaluating the long-term strength of different polymer grades. By redesigning the traditional cylindrical internal pressure test specimen into a semi-spherical rupture dome, the method generates a uniform equal-biaxial stress state under internal pressure. Unlike standard pressure pipe tests, this configuration promotes brittle failure within shorter timeframes, while still allowing reliable performance ranking of polymer grades. The rupture stress is correlated with failure time, enabling lifetime prediction. The method was validated by testing two recycled polypropylene grades, Luxus 16005 and Luxus 16666, which showed clear differences in performance. Findings show that the rupture dome test effectively ranks materials by brittleness and predicts lifetime, making it a useful tool for informed material selection and design.</p>