Clay: A tough choice

Clay is a preferred material for pipes where strength, longevity or environmental considerations are important. Its strength, durability and century-plus lifespan mean it is widely used in public-sector work such as schools and hospitals.

Plastic pipes, in contrast, have much less inherent strength and a high dependency on good bedding and site practice. Plastic progressively weakens in service and can lose up to 80% of its initial strength after 50 years. Nor is clay subject to the day-to-day vulnerabilities of plastic, which is susceptible to deformation, rodent attack and needs maintenance procedures such as rodding and high-pressure water jetting.

When it comes to corrosion and chemical resistance below ground, clay is a preferred material too. The increasing development of brownfield sites often leads to a design requirement for pipes with greater chemical resistance. Clay’s inert nature makes it an obvious choice for contaminated ground. And the use of special seals and connectors as required by specific ground conditions can enhance this inherent advantage of clay drainage systems.

Civils contractor Jackson Civil Engineering recently used Naylor clay drainage pipes on a high-profile development in Cornwall. The Beach is a scheme worth more than £100M, comprising luxury apartments and hotels at Carlyon Bay near St Austell. Sandy ground conditions on the site were a particular design consideration, as seawater posed a risk of corrosion to any plastic materials. Clay has excellent abrasion resistance, however, making it the obvious material choice.

Where ground is badly contaminated, trenchless installation methods are preferred because they minimise risks to installers. While jacking pipes are usually made out of materials such as concrete and GRP, clay readily lends itself to trenchless installation. Naylor’s Denlok range of jacking pipes has been developed as the natural choice because of its strength, ability to withstand abrasion and above all durability.

Denlok’s principal use has been in sewerage applications, in a challenging environment. The product has been installed under major motorways and highways, enabling traffic flow to be maintained.

Naylor’s development of a larger diameter jacking pipe was undertaken in conjunction with a Barhale Construction project for Thames Water at the Hoddesdon Transfer scheme near Waltham Cross in Hertfordshire,where Barhale installed Denlok using microtunnelling. This project, a major sewage transfer scheme close to the A10 trunk road, included 13 crossings beneath roads, rivers and railways.

How Naylor developed Denchem

Denchem is a high-performance chemical- and thermal-shock-resistant pipe, which was specially developed by Naylor Industries for trenchless installation.

The initial development of this product was in conjunction with a project at the Natref Oil Refinery in Sasolburg, South Africa. Denchem combined Naylor’s expertise in making jacking pipes for trenchless installation (Denlok) with its high-performance Hathernware High Temperature (HT) pipes, widely used in process and food manufacturing applications because they can handle very hot effluent discharges.

Specialist ceramic products such as Hathernware HT are suited to aggressive operating environments where effluents are corrosive, sudden temperature changes arise or chemical spillages or attacks occur.

The project at the Natref refinery in Sasolburg, South Africa, involved the replacement of a 200mm diameter, 190m long pipeline, which had severe structural defects. This pipeline was a key conduit for the removal of water and process effluent from the main process area. Investigations by project engineering consultancy GMKS identified various issues, including considerable depth (up to 6m), a high temperature variation (up to 120ÚC) and highly alkaline effluent (pH 11.5). There were also numerous existing parallel and crossing pipelines impeding a trenched solution and the surrounding ground had high hydrocarbon content. As if contaminated ground complicated by other pipelines were not enough, there were high instances of stray electric currents, effectively preventing the installation of a steel pipe, given the immense problems associated with the installation of effective cathodic protection.

To address these issues, Naylor combined its microtunnelling expertise with its knowledge of high-performance ceramics: and developed a jacking pipe for installation in aggressive and corrosive operating environments, which incorporated Viton seals and stainless-steel couplings. South African contractors Insitu-Pipelines installed the pipe, using a BM 400 Pilot/Auger system supplied by Bohrtec of Germany. The trenchless installation minimised operational disruption at the refinery and by late 2005, the Natref Oil Refinery had a pipeline with a thermal operating range of up to 120ÚC and an ability to withstand highly alkaline and acid flows.

Subsequently, Denchem has also been used domestically: its heat and chemical resistance led to the product being selected as replacement drainage by a UK brewery whose plastic pipes had melted during a sterilisation process. Using Denchem trenchless technology has enabled clients to undertake drainage replacement works with minimal operational disruption. The development of Denchem won Naylor two innovation awards in 2005.