Digester Tank Renovation

Introduction

A digester tank serving a major UK water supplier had suffered severe corrosion, causing water ingress and significant loss of wall thickness. Replacement was not feasible due to the tank's complex location, requiring a full structural refurbishment to restore operational integrity.

Our Solution

Following initial preparation, shot blasting to SA 2.5 revealed extensive substrate pitting, necessitating installation of a secondary internal steel skin. To address the risk of water ingress and corrosion within the interstitial void, a specialist expanding polyurethane foam system was proposed. The foam was heated to 40°C and injected through pre-drilled holes, expanding to fill the cavity completely. Thermal imaging monitored coverage in real-time, ensuring no voids remained. Injection holes were re-welded, re-blasted, and pressure jetted to remove contamination. EonCoat was then spray-applied internally to 500 microns DFT, followed by two additional coats of glass flake epoxy, delivering a combined protective system rated for the aggressive service environment.

Key Benefits

• Secondary steel skin restored full structural integrity where wall thickness was critically compromised
• Expanding polyurethane foam eliminated void space, preventing concealed corrosion and water ingress behind the secondary skin
• Thermal imaging ensured 100% cavity fill with no undetected voids
• EonCoat plus glass flake epoxy combined system extends design life by more than 30 years
• Tank retained in service, avoiding costly and logistically impractical full replacement

Conclusion

The digester tank was successfully returned to full operational service with a significantly extended design life. This project demonstrates UCL's capability to engineer bespoke structural and coating solutions where conventional approaches are not viable.