Australia has over 187,000 kms of in-ground water mains and nearly 142,000 kms of sewer mains infrastructure.
Much of this was installed more than five decades ago during post second world war boom years and is now operating well beyond its anticipated 50-year life. The Water Services Association of Australia and other similar bodies throughout the world have identified internal corrosion as a key cause of pipe failure.
Ageing water and sewer infrastructure in Australia is a threat to economic growth, public health and the environment, and its upgrading and renovation is a very significant cost burden for water utilities and governments. From a monitoring and maintenance point of view, it is difficult to predict pipeline failure, particularly from internal wall corrosion, which may reduce the anticipated service life of a pipe.
In rural and regional Australia, the matter is further compounded, with remote installation locations presenting a challenge to pipeline monitoring functions. In these situations, the cost of repair can be significantly higher than in cities. And there is another significant factor to consider, namely climate.
The increasing frequency of drought and a warmer climate, combined with a burgeoning population and consumer lifestyle expectations, which rely on safe potable water, is placing pressure on Australia’s traditional water sources. As water reserves shrink, the quality from available sources is frequently sub-optimal requiring more disinfection to achieve the standards prescribed by the Australian Drinking Water Guidelines, as published by the National Health and Medical Research Council.
In Australia, disinfection of potable drinking water is achieved primarily by chlorination with sodium hypochlorite or chlorine gas. The amount of chlorine required to achieve disinfection varies depending on several factors; these include water pH, temperature, transit time to the consumer and the quality of the raw water. For health reasons and to inhibit the regrowth of undesirable microorganisms from point of treatment to the consumer’s tap, it is necessary to ensure a residual concentration persists in the water as it travels through the pipeline system.
However, since chlorine is a strong oxidising agent, its presence in potable water can be a cause of internal wall degradation in some common pipe materials that leads to accelerated pipe degradation. The detrimental effect of chlorine on these pipe materials is further exacerbated in hot climates where the average water temperature may be higher than 21 degrees, and where pipes are installed at shallow depth and/or beneath impervious surfaces.
As a consequence, some industry experts have questioned whether the 50-year life expectancy of pipe networks can be relied upon in those potable water networks in hot climatic regions, which for health reasons are aggressively chlorinated.
Fortunately, premature oxidation induced failures have not been observed in PVC pipes, as PVC is not subject to oxidative degradation when exposed to chlorine-based disinfectants, even at higher temperatures.
This is possibly due to the polymer’s relatively low diffusion rates, glass transition temperature and, it has been hypothesised, an increase in the strength (molecular weight) of PVC as a result of the presence of chlorine disinfectants.
Also, unlike metal pipes, PVC pipes won’t rust or corrode over time because PVC does not react with air and water in the manner metallic materials do. The inner surface of PVC water pipe remains smooth, and virtually unaltered over its lifecycle. This has been confirmed by measurements of the pressure (friction) losses in PVC pipelines, which do not deteriorate with time.
In hot climatic regions – such as northern Australia – PVC pipe is the ideal infrastructure pipe material for water mains and provides a predictable service life. It is well documented in overseas studies that PVC pipe features a remarkably low failure rate in comparison to other pipe materials.
For water network owners facing increasing rates of breaks and failures and the associated costs of renovating or replacing aging assets, decisions need to be based on good information and data. On its performance in highly oxidative disinfected water applications, PVC remains an obvious material of choice.