Aging of unfilled polyethylene (PE) films in concentrated (80–100 ppm) chlorine dioxide (DOC) solutions at 20°C and 40 has been studied by IR spectrophotometry, melt rheometry, chlorine titration, and tensile testing to establish the mechanisms of PE degradation induced by DOC, to determine some important kinetic parameters, to identify the embrittlement mechanism, and to examine the possibility to predict nonempirically embrittlement from a kinetic model. Experimental results reveal that DOC initiates PE oxidation. This latter is responsible for hydroperoxide build‐up, and chain scissions occur when hydroperoxides reach a critical concentration above which they decompose bimolecularly. The weight average molar mass Mw decreases and embrittlement occurs when Mw approaches a value of 70 kg mol−1 as previously found in thermooxidation studies. A mechanistic scheme involving all the elementary steps of PE autooxidation plus one initiation and one termination step involving DOC has been elaborated. The kinetic scheme derived from this mechanistic scheme has been solved numerically and the results of simulations have been compared with experimental results. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

This article deals with the failure of polyethylene pipes transporting chlorine dioxide (DOC) disinfected water under pressures of few bars. Accelerated aging tries made at 20 or 408C show that the antioxidant is rapidly consumed in a superficial layer until a depth of about 1.2 mm. Carbonyl groups appear in a sharper layer of few hundreds micrometers. Natural aging results at various places, for various times up to about 30 years, reveal also a superficial attack with a depth of the order of 1.2 mm. An antioxidant loss by migration, in the whole sample thickness, is also observable. The shape of antioxidant concentration profiles indicates that the crossing of interfaces controls partially the whole migration kinetics. Failures, with brittle cracking, were observed in natural aging, after exposure times of the order of 5-15 years, i.e., far before the expected lifetime (50 years). A kinetic model has been elaborated to predict the time to failure. It is based on a chemical unit, which models the radical processes induced by DOC, and a mechanical unit based on an empirical creep law and a failure criterion depending of the molar mass calculated by the chemical unit.

Polyethylene connection pipes of wall thickness ranging from 3.0 to 4.5 mm, used for 0, 5, 9, 12, and 18 years in the French network of drinking water disinfected by bleach, have been analyzed. The stabilizer thickness profiles reveal that bleach destroys the stabilizer in a superficial layer of about 0.5 mm depth at the water-polymer interface. In the rest of the wall, stabilizer is lost by physical processes, i.e., transport by diffusion into the bulk, extraction at the water-polymer interface, and evaporation at the polymer-air interface. The whole loss kinetics is governed by extraction and evaporation. The classical scheme for evaporation-diffusion process has been used to model physical loss processes, but with boundary conditions different from the literature ones. Concerning chemical aspects, some mechanisms proposed in the literature are criticized. The identification of the bleach reactive species remains an open question. POLYM. ENG. SCI., 51:1541-

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The internal corrosion of cast iron and steel pipes is one of the main issues that drinking water distribution operators are facing. This study evaluated the relevance of 10 known corrosion indices according to their estimate of corrosion rate and iron particle release for 20 different water qualities. Pilot-scale contact trials were run over 45 days using cast iron and steel coupons. Corrosion rate was measured by coupon weight-loss and by an online linear polarization rate probe. Particle release was monitored by an online turbidimeter. The results showed that none of the indices properly predicted the level of risk associated with each water and that corrosion and particle release were not correlated. Two novel indices were developed to predict the corrosion and particle release risks independently of each other. The corrosion index showed a strong linear correlation with the corrosion rate of cast iron and slightly less reliable results for steel. The Particle Emission Index presented good correlation with turbidity in waters following contact with cast iron. These two indices thus showed interesting potential as tools to limit internal corrosion risks for metal pipes in water distribution networks.