Five things you may not know about plastic pipes

Here in the Intelligent Water Decisions research group we think, study and learn a lot about pipes. Here are five things about plastic pipes that you may not know.

1. The origin of plastic pipes

Although Polyvinyl Chloride (PVC) was first synthesised in the 19th Century, the commercial production of PVC pipes only began in the 1930s [1].

The first PVC tubes were manufactured in Germany. They were used to build drinking water and drainage facilities for the Berlin Olympic Games.

The process for manufacturing PVC pipes was similar to pasta production. A Belgian company converted twin-screw, Italian pasta machines to extruders. Those extruders were suitable for processing PVC tubes for electric conduits. Then, inspired by this method, a Dutch water utility in the 1950s founded a company (WAVIN) to mass produce PVC pressure pipes for potable water.

The production and use of Polyethylene (PE) pipes began at around the same time.

2. Plastic pipes are used more than you think they are

In the 1980s, Australia’s water reticulation market was already using PVC pipes about 60% of the time [1]. Large diameter plastic pipes have been widely used for water mains here since the 1990s. They have particularly been used on mining sites.

Nowadays, plastic pipes make up around 85% of the water-services related infrastructure in Australia’s cities. Plastic pipes have long been the standard for telecommunication, sewage, irrigation and gas transmission.

3. Plastic pipes are ‘pipe of choice’… but we don’t really understand them

Even though plastic pipes are the ‘pipe of choice’ for nearly all types of fluid transmission, our understanding of them is shallow. The mechanical and chemical properties of plastic materials are complex. There are also many variations of ‘plastic’ (e.g. PVC-O, PVC-M, PVC-U, LDPE, HDPE …).

This means that modelling the hydraulic behaviour of plastic pipes under unsteady flow conditions is hard. The current design and operation practices of plastic pipeline systems are guided more by experience than science.

Our knowledge of plastic pipes is like the parable of the blind men and the elephant.

4. Plastic pipes do fail – but it’s not because they’re old

Some people may have the impression that ‘plastic pipes will last forever’. It is true that plastic pipes have a long average life expectancy. It is also true that they do not corrode like ferrous pipes do. But they do have many shortcomings like low strength, tendency to crack under stress, and poor resistance to weathering.

The typical causes for premature failures in plastic pipes include:

• improper installation practices
• manufacturing defects
• rock impingement
• excessive bending at fittings.

Small cracks tend to grow and become leaks and bursts over a relatively short period of time in plastic, because of the nature of the material. A survey from the US showed that 70% of failures in PVC pipes occur in the first five years after installation [2].

5. We can’t effectively detect leaks in plastic pipes yet

Each year in Australia we experience 19,000 water main breaks and 265 gigalitres of real water loss. That is enough water for 1.5 million homes [3]! Conventional acoustic-based leak detection techniques rely on the noise generated by leaks. These techniques are reasonably effective in metallic pipes, but not in plastic pipes.

Leak acoustic signals are overwhelmed by noise after just several metres because of the high degree of damping in plastic pipes. The vast majority of plastic pipeline leaks go undetected. Undetected leaks contribute to continuous water loss.

More frustratingly, even if we can identify leaks in plastic pipes, we often can’t locate them before they develop into breaks: We often don’t see them until the water floods to the surface.

Do you want to know more about plastic pipes and leak detection? Get in touch with our Intelligent Water Decisions research group.

References:

[1] M. Heathcote, History of plastics pipe systems in Australia, Plastics Industry Pipe Association of Australia, Chatswood, NSW, 2009.
[2] S. Folkman, Water main break rates in the USA and Canada: a comprehensive study, Utah State University, Logan, Utah, 2012.
[3] Bureau of Meteorology, National Performance Report 2014-2015: Urban Water Utilities, Melbourne, VIC, Australia, 2016.