Gill, Knapp, W.Bradley, L.Bradley
PE-X & Other Pipes # 1998 Gothenburg
The objectives of this research are to better understand the degradation of cross-linked polyethylene (PEX) tubing subjected to pressurized, hot chlorinated water in flow-through systems (like home plumbing) and to estimate its service lifetime. PEX tubing was subjected to pressure testing with flowing hot, chlorinated water at elevated temperatures from 90 ' C to 120 O C . with chlorine levels between 0 and 5 ppm. The combined effects of free chlorine, pH, and metal ion content on the time-tofailure were found to better correlate with the oxidation-reduction potential (ORP) than with the free chlorine content directly. Consumption of the antioxidant was analyzed using the oxidation-induction time (OIT) as a function of fraction of the time-to-failure in the tests, with the antioxidant being fouild to be completely consumed in less than half of the time-to-failure at 115 O C . Fractographic observations made using a scanning electron microscope (SEM) indicated no degradation until the antioxidant was completely consumed. The mechanical integrity of the pipe at failure in the tests. which was always by leakage, was evaluated using burst tests. The nature of the damage at failure was investigated using highly polished cross-sections of pipe which failured by a pin hole leak.
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