E.J.W. van der Stok, K. Jacobson, S.O. Jansma, D. Lukes
Papers # 2018 Las-Vegas
The lack of a fast, universally-accepted test method for chlorine-dioxide-disinfected water is hindering the development of improved plastic piping materials. A literature survey was performed to define the degradation process in which chlorine dioxide affects the ageing of polypropylene, and to describe and reflect on the different test methods stipulated by standards and developed by research institutes.
Chlorine dioxide (ClO2) is increasingly used in drinking water applications, due to its high efficiency as a disinfectant. However, it also attacks polyolefins more aggressively than hypochlorite (ClO- ). This has led to premature failure of water pipes, especially at higher service temperatures.
To make polyolefins in general, and polypropylene specifically, more resistant to ClO2, it is imperative that the degradation mechanism is understood. Furthermore, these materials need to be tested in a rapid but functional manner to verify their resistance to the relevant failure mechanism as found in service. A literature survey was therefore carried out to define the degradation process and to describe and reflect on the different test methods stipulated by standards and developed by research institutes. It was concluded that it is imperative to ensure that the failure mode is not altered by accelerated ageing. Test methods should therefore use realistic concentrations and temperature conditions, which should be as close as possible to service conditions. This makes acceleration difficult. Flow, pH and oxidation reduction potential (ORP) must be monitored and controlled. Finally, the presence of an (applied) stress is crucial for the test to be representative of real service failures.
If pipe failure is the parameter used to characterize pipe performance, it is not realistic to expect results within a reasonable time. This means that another ranking criterion is required. A better understanding of the degradation mechanism of PP in ClO2 and the influence of stress is necessary to find the best parameters to identify an early warning signal that can predict final pipe failure.
