Polybutene-1 pipes exposed to pressurized chlorinated water: Lifetime and antioxidant consumption

Pipes of isotactic polybutene-1 were pressure-tested in chlorinated water at a controlled pH (6.5 ± 0.1), and the lifetime was assessed as a function of temperature (95-115 °C) and chlorine content (≤3 ppm). These data were compared with data from pressure testing in hot water (0 ppm chlorine). The lifetime shortening in chlorinated water was significant even at relatively low chlorine contents, 0.5 ppm. A further increase in chlorine content led only to a moderate shortening of the lifetime. The temperature dependence of the lifetime data obeyed the Arrhenius law. The activation energy obtained for failure data in chlorinated water was ∼140 kJ mol⁻¹, which was greater than the value of 108 kJ mol⁻¹ earlier reported for failure data from hot-water pressure testing. A 0.5-mm thick layer of material at the inner wall in the fractured pipes showed depletion of the antioxidant system and the inner wall displayed a large number of surface cracks, confirming that there was a pronounced chemical degradation of the inner wall material. The decrease in the antioxidant concentration was independent of the chlorine concentration in the range 0.5-1.5 ppm. The time to reach depletion of the antioxidant system could be predicted by linear extrapolation in an oxidation induction time (log scale)-exposure time (linear scale) diagram.