Did the Victorians get it right when it came to materials selection, or can we put our faith in high specification 21st century materials to build a sustainable infrastructure? When it comes to specifying pipes for sewer applications and land drainage, whether to opt for ultra-modern plastics or traditional clay is a very hotly- debated topic. B&E explores which material pipe specifiers should plumb for.

We have a lot  to thank the Victorians for. Great advances in engineering have given us a legacy to be proud of. The Victorians built like their heady age would never pass, and our towns and cities stand testament to their success.  Municipal buildings, bridges, transport networks and even our sewage systems are still very much in use in the 21st Century.

Great Victorian legacy
If you look at how their infrastructure copes with the vastly increased weight of modern traffic, you could justly accuse Victorian engineers of over-specifying materials. One such example is how the London sewage network can handle modern jetting machinery. Despite massive upgrades to the infrastructure to cope with a huge rise in the capital’s population over the last 150 years, the materials themselves selected for the job perform well under modern use. For many people, a traditional clay pipe is a much more reliable option than uPVC, polyethylene and polypropylene alternatives developed within the last 50 years.

Banned in the UK
This situation came to a head over the last 10 years when water authorities in the UK banned their contractors from using plastic pipes in sewers, and opted for clay, ductile iron and concrete instead.

The plastics lobby has been keen to use innovation to convince clients that it does have the strong, durable, lightweight, material for the 21st Century. Dwr Cymru Welsh Water suspended the use of plastic, amid concerns about the performance of the material under modern jetting pressures. The British Plastics Federation Pipes Group managed to have the ban lifted in 2002 after it set up a group of accredited manufacturers and developed a training programme for installation and site handling practices.

A long-standing ban by three remaining water companies looked to have been lifted, albeit partly and on paper, when one manufacturer developed a pipe it said could meet their standards. Thames Water, Anglian Water and Southern Water maintained a steadfast ban. They said they wanted pipes to withstand higher jetting pressures than the Water Industry Standard, which sets a maximum of 2,610psi. After it suspended plastic pipes around 10 years ago,Thames gave a figure of 4,000psi as an acceptable maximum jetting pressure.

The Miracle Pipe
However, manufacturer Uponor last year claimed to have developed a pipe to meet this standard, and has moved production to the UK to grab what it thinks is a large part of the market. The company is reticent when it comes to talking about the structure of its pipe, or even to name all the materials used. It does claim to have a structured solid wall sewer pipe, manufactured from polypropylene.

Uponor has pressed the usual advantages of specifying a plastic pipe – it is more than eight times lighter than clay, which makes it a lot easier to move around onsite. It also claims the material’s flexibility makes its impact resistance 50 times greater than clay. The plastic pipe can withstand a brick falling from 3m, whereas a 150mm clay pipe will crack when a brick hits it from 6cm, the company claims.

With the benefits of strength and lightness on its side, surely plastic is the material of choice. So, why does the material attract such strong criticism? If it can out-perform traditional materials like clay, surely plastic deserves to be the material of the 21st Century. Does the future, as was famously said to Dustin Hoffman’s character Benjamin Braddock in The Graduate, really lie in plastic?

Traditional is Best
One very vocal opponent to the use of plastics in sewers comes, surprisingly, from a manufacturer who is keen to develop the material. Naylor Industries has, over the last six years, developed plastics manufacturing facilities to the point when they equal the company’s traditional clay pipes business. However, chief executive Edward Naylor says that the UK isn’t replacing its sewer infrastructure at a fast enough rate to justify putting plastics into the ground.

Plastics might be flexible and light, says Naylor, but it lacks the durability to make it a suitable material for sewers. The flexibility that makes it withstand a shock impact, also leads to structural degradation and a loss of shape that causes problems with the flow of the sewer, he says.

“Over 50 years, plastic loses 50% to 80% of its strength,” says Naylor. “If you have it in heavily trafficked areas, particularly for sewerage applications, from day one it is getting weaker. There becomes a point when it has lost its roundness enough to become obsolete.”

He says the loss of shape is something that particularly concerns clients. This is a problem that can begin with practices onsite. “The water companies are latching onto measuring the roundness of the pipes before they have been put into the ground,” he says. “If it is not round, you’ve usually not compacted the soil around the pipe.”

Increasing the thickness of a plastic pipe to improve its durability would price the product out of the market, says Naylor.“The whole point of twin wall piping is to get the strongest pipe with the least amount of raw material,” he says. “The inner wall will be as thick as a credit card. If you want to make it stronger, then you will make a thicker wall. If you’ve got so much raw material in the pipe, why would you want to buy plastic.”

UK Can’t Build Fast Enough
With concerns over the life expectancy of plastic pipes, Naylor says the UK isn’t replacing its infrastructure fast enough to have a sustainable sewer network.  “On average, at the current rate of investment a sewer will have to last 350 years,” he says. “How can they justify the material is the right kind, if the sewer has to last longer and longer?”

Naylor says the choice of material is down to cheapness, not longevity. “In a sewerage scheme, the raw material accounts for 10% of the costs,” he says. “The contractors are allowed to use what they want. They are encouraged to use the cheapest material they can, which could be plastic. The result is that the job will have to be done again much sooner than if they had used clay pipe in the first place.”

1960s Legacy Spells Success for Plastics?
British Plastics Federation Pipes and Fittings Group director Frank Jones tells B&E the organisation has studied plastic pipes in situ, and is confident they do not lose much structural integrity while in the ground. “We’ve been pulling pipes out of the ground, which were put there in the 1960s and they are more or less at their original specification,” he says. “In principle you’ve got no deterioration over 50 years and we’re saying this could go on up to 100 years.” 

If contractors get it right onsite, says Jones, their clients should not have cause to worry over the longevity of their pipes. “If the pipe’s been designed for sewers,” he says, “and provided it’s installed correctly, my approach is: If they’ve got the right rate of effluent, there’s no reason the pipes won’t go for 100 years.”

However, Naylor is adamant that the 21st Century choice of materials for sewage infrastructure lacks the robustness of the products used by Victorian engineers. He warns that using more expensive materials today, might save disaster for future generations. “The Victorians had the view to do the job once and do it right,” he says. “We’re squandering their heritage for the sake of a few pounds.

“To me, water isn’t something, which can generate earnings per share each year. This attitude is completely out of kilter on something that might have to last 100 years. The next generation will have to pick up the cost of this."

---