Critical Cast Iron Wastewater Assets: Towards In-Service Assessment of Residual Mechanical Performance
Creators: name: Ugoh, Governor Arouriwo Gibson
Publisher: name: University of Surrey
Year: 2023

description: The removal of wastewater from urban areas is an unglamorous but essential activity for society. Each
description: day, the London wastewater networks convey over four billion litres of wastewater to treatment works.
description: The sewers of Bazalgette, built in the late 1850s and still in use today, are primarily brick, but cast iron
description: is used in situations where the wastewater needs to be conveyed across roads, railways, and rivers, or
description: if the flow needs to be pumped. As with cast iron used for clean water, wastewater pipes are
description: susceptible to both internal and external corrosion, and in both cases, local conditions can have a
description: significant effect on the rate of corrosion.<br>
description: <br>
description: The network has served London with great success for more than 150 years, but previous research
description: conducted to understand the deterioration of cast iron pipes in the clean water network has raised
description: concerns about the remaining longevity. Whilst it is not unnatural to recommend a widespread pipe
description: replacement as the easiest fix to prevent failure, the network is huge and mostly built as integral parts
description: of railway and road bridges or underneath buildings. Pipe replacement would be capital intensive and
description: result in a significant service disruption. Therefore, mechanical performance ranking asset
description: management strategies are needed, which focus on targeted replacement of deteriorated parts of the
description: network to help prioritise critical work. This necessitates proactive asset management strategies
description: capable of predicting the residual mechanical performance of individual sewers in the network.<br>
description: <br>
description: Prior art regarding graphitic corrosion of cast iron, as a leading cause of in-service deterioration, relates
description: almost exclusively to clean water networks. Hence, Thames Water, in collaboration with the University
description: of Surrey, has taken a proactive step through this EngD to transfer knowledge from clean to waste
description: network, to develop models toward predicting the residual mechanical performance of cast iron assets
description: found in wastewater network, and to conduct proof of concept studies to select cost-effective nondestructive
description: evaluation (NDE) techniques.<br>
description: <br>
description: This work has extracted mechanical data needed to accurately predict remaining mechanical
description: performance and has revised previously developed loss-of-section and fracture mechanics models to
description: provide a failure envelope for wastewater pipes under combined vertical loading and internal pressure.
description: This revision accounts for some important parameters such as the operating environment, loading
description: regimes, internal and external corrosion, which differ, not unexpectedly, from the clean water scenario.<br>
description: <br>
description: Finally, this work has conducted conceptual studies to adapt magnetostriction, a direct strain
description: measurement technique, and digital image correlation (DIC), an optical full-strain approach, as two
description: complementary NDE techniques for cast iron pipes application. These techniques have been validated
description: using samples instrumented with strain gauges. Detailed finite element models have also been
description: analysed. It has shown the magnetostriction and DIC could measure the operating loads in cast iron
description: pipes without significant surface preparation. These could be used as spot-detection and in situ
description: monitoring techniques for continuing use of Bazalgette’s sewer pipes.<br>