The sustainable management of ageing cast iron trunk mains requires balancing maintenance needs with their long-term effects on corrosion behaviour. This study investigates how localised maintenance actions, activities which involve repairing leaks, condition assessments and installing fittings, together with the application of barrier mitigation techniques and corrosion inhibitors, influence the graphitic corrosion of cast iron using aqueous and soil corrosion cells. Electrochemical monitoring: open-circuit potential (OCP), electrochemical noise (ECN), and linear polarisation resistance (LPR), enabled comparative analysis of corrosion activity across varying surface conditions and mitigation approaches.

Aqueous corrosion cell tests were used to establish reference corrosion behaviour, and evaluating the impact of alkaline environments, corrosion inhibitors, and double-cell configurations. The results confirmed that initial surface condition can affect mitigation performance and that interventions applied on one surface of a cast iron section do not interact with or influence corrosion processes on the opposite side.

Soil corrosion cell experiments simulated buried conditions in London Clay with uncoated, partially coated, poorly coated, and fully coated samples. Partial and defective coatings did not exacerbate localised corrosion at coating interfaces. Fully coated samples showed the lowest electrochemical activity, while coatings and inhibitors provided surface-condition-dependent suppression. Microscopy validated these findings, showing no boundary-induced corrosion but confirmed the persistence of pre-existing graphitic corrosion beneath coatings.

OCP and ECN data indicated reduced corrosion activity when mitigation had been applied, though LPR measurements showed minimal change in corrosion current, suggesting the persistence of corrosion under pseudo-passive conditions. From an asset management perspective, the simulated maintenance interventions investigated were found not to accelerate deterioration from a corrosion perspective but may have limited effect on on-going graphitic corrosion, which continues at rates typically observed in cast iron pipes in service (0.05–0.2 mmpy).