Technical research commissioned by UK Water Industry Research (UKWIR) and conducted by the University of Sheffield has provided a breakthrough in understanding how and why cast iron pipes fail, according to the group.
The UK water industry faces a unique challenge due to a significant legacy of grey cast iron (GCI) infrastructure, much of which dates back to the interwar period. The newly released report, ‘Understanding how the deterioration of cast iron pipes evolves into leakage’, supports smarter, more proactive leakage management by validating a model for predicting the fatigue strength of GCI pipes.
Crucially, the project found that micro-cracks can naturally reseal when pressure is lowered, creating a temporary reprieve. Properly managed, this effect allows utilities to better prioritise their workloads and minimise service disruptions by buying valuable time for planned interventions.
Combined approach
The study employed a combined numerical and physical experimental approach, using high-speed cameras to record how leaking cracks developed in GCI pipes. Researchers used destructive laboratory tests to investigate the fatigue cracking process of GCI water pipes featuring artificial corrosion pits.
By focusing on the stress response of cast iron during pressure transients – high-speed waves caused by events on the network like pump operation or valve closure – the study identifies a previously misunderstood mechanism of leaks, bursts and pipe fatigue.
“A primary finding of the research is the observation of how corrosion pit shape and loading strongly influence the leakage failure mode,” explains Jeremy Heath, innovation manager at SES Water and programme lead for UKWIR’s Big Question 2 – How will we achieve zero leakage in a sustainable way by 2050?.
“The data revealed that under certain dynamic loads, micro-cracks in the pipe can reseal if the loading is reduced. This occurs because the residual strength of the cast iron pulls the crack shut, temporarily halting the leak.”
Implications for management
For network operators, this work provides a tool that can be used to compare the leakage failure risk of specific GCI water pipes at a resolution that was not previously possible.
The research also offers practical guidance on network monitoring. It concludes that reducing maximum stress through water pressure management is likely to allow larger leaking cracks to form, whereas occasional overloads from pressure transients and seasonal loads can cause stable cracks to become unstable prematurely.
Key technical takeaways include:
- Stress concentration: The fatigue strength of GCI pipes is significantly affected by the net stress concentration caused by different corrosion pit shape and load combinations
- Biaxial stress: 180° out-of-phase biaxial fatigue stresses can reduce the fatigue strength of GCI pipes featuring uniform corrosion by up to 28 per cent
- Targeted replacement: Implementing this tool will allow asset managers to more fully understand pipe deterioration and proactively replace pipes in a targeted way to reduce the occurrence of new leaks and reduce water loss
By accurately capturing pressure cycles in their networks, utilities can move towards proactive asset replacement, targeting pipes before the resealing phase ends and further leaks and bursts occur. The findings can help companies strengthen maintenance planning, target interventions more effectively and support progress towards UKWIR’s zero leakage ambition.
Mike Rose, chief executive, UKWIR, said, “Bringing together the best in academic research and our water service companies is at the heart of what UKWIR does. This collaborative project perfectly illustrates our mission to provide one voice for the shared issues facing water operators today.
“As well as addressing our big question on leakage, this important research tells us a lot more about water company assets and how we can prolong their life and manage them better.”
