Oxidative Degradation of Corrugated HDPE Pipe in Water and Air

Session 7B
3:50 pm

Grace Hsuan, Drexel University

The oxidation resistance (OR) of a 900 mm (36-inch) diameter corrugated HDPE pipe was carried out in forced air ovens and water baths to simulate the dry and wet field conditions. Three temperatures (65, 75, and 85oC) were used to accelerate the oxidation reactions, and thus the oxidation behavior at site ambient temperature (23oC) can be predicted using the Arrhenius equation. The depletion of antioxidant (AO) was measured by the oxidative induction time (OIT) test, and changes of polymer properties were evaluated by melt index (MI) and tensile tests.

The AO depletion rate proceeded much faster in water than in air incubation, and the AO decreased exponentially with time. The percentage of MI retained decreased steadily with time, while the tensile break elongation showed a large variability throughout the incubation period. It seems that the MI retained value would be a more suitable property to define the different oxidation stages than the conventional tensile break elongation. For this particular corrugated HDPE pipe, a 90% MI retained value was identified to be the end of the AO lifetime, which corresponded to 3 minutes OIT value. As MI retained value decreased to 80%, the tensile break elongation started to drop consistently with time. At 60% MI retained value, the tensile break elongation decreased to more than 50% signifying the end of the service life for the pipe.

Based on the MI retained value, the service life of the 900 mm corrugated HDPE pipe was predicted to be approximately 500 years at 23oC water condition. For the air incubation, the service life is unable to be predicted, since the MI retained values at 75 and 65oC still maintains above 90%. On the other hand, the AO lifetime at 23oC was predicted to be approximately 450 years.

Y. Grace Hsuan
Professor

W-K (Connie) Wong
Ph.D. Candidate

Drexel University
Department of Civil, Architectural and Environmental Engineering