Written by Kerryn Caulfield, Executive Director for Composites Australia Inc.
Sewer networks that collect and safely transport waste away from population centres are among the most important infrastructure assets in modern cities. For Melbourne, Victoria more than 320,000 million litres of sewage enters its sewerage system each year. This labyrinth of huge brick-lined sewers that snake underground relieving the city of its waste was mostly constructed in the late 1890s after the 1888 Royal Commission into Melbourne’s public health and sanitation crisis.
Now managed by Melbourne Water, the North Yarra Main Sewer, which is 2.8 metres in diameter and located 13-15 metres below the ground, has recently been diverted to make way for the West Gate Tunnel Project. This vital piece of infrastructure carries 20% of Melbourne’s sewage. Diverting the sewer will protect it from tunnelling and prevent disruptions to sewerage services across Melbourne’s north and west during the tunnel project.
The diversion of 600 metres of the North Yarra Main sewer pipe featured filament wound composite maintenance shafts designed, engineered and made by Victorian based firm, Corrosion Technology Australia Group (CTA). The company has been an authority on corrosion technology for over 25 years, and specialises in filament wound piping, ventilation and storage systems such as dual laminate tanks and vessels for petrochemical plants, water and sewage treatment and energy plants as well as the food processing industry.
Alex Brown, CEO of CTA says: “Under certain conditions hydrogen sulphide, which occurs particularly in sewage, is converted into sulfuric acid by the action of sulphur bacteria. The presence of hydrogen sulphide gas (H2S) in sewers can result in an accelerated corrosion of assets, particularly concrete which has a limited lifespan under such circumstances. The old brick-lined sewer has done a sterling job for 100 years. Nowadays, composites are a preferred solution when longevity and corrosion resistance is a key requirement.”
Corrosion resistant fibreglass reinforced composites have had a long and impressive history in infrastructure projects. Although well established in Europe and North America and the Middle East, where they are routinely used for applications with a design life of 100+ years, the uptake in Australia has been modest. More recently there has been a gradual increasing interest in Australia in exploring composite applications where concrete has been the traditional material of choice. Alex Brown says: “These applications cannot be fully realised without sound engineering design, material selection and high quality fabrication which is key to providing the longevity required by the infrastructure sector.”
There are no specific Australian Standards for these types of projects and very few standards relate specifically to composites. CTA’s Alex Brown says: “A lot of the details are refined through close collaboration with the client and using tools such as Finite Element Analysis and 3D modelling to ensure the final product meets not just the service loads, but also meets the particular requirements of the contractor working underground, installing this type of equipment in arduous conditions.”
While our sewer systems are a less than glamorous theme, their role and significance in keeping our communities healthy is undeniable. Alex maintains that “Composite pipes often have a higher premium upfront, but the advantages are bespoke complex shaping coupled with lighter weight that reduces field installation costs, and corrosion resistance properties all of which equates to minimal maintenance and a long service life – an all-round cost effective solution”.
This article first appeared in: Connection Magazine Issue 50: July, 2019