Digester Tank Renovation
THE CHALLENGE
A digester tank for a major water supplier was severely damaged, with corrosion leading to water ingress. Due to the extent of the damage, the client had initially wanted to replace the tank. However, due to its complex location, this was not possible. Instead, the decision was made to completely refurbish the steel structure, to renew its operational capabilities.
OUR SOLUTION
In preparation for the coating, the surface was shot blasted to a standard of SA 2.5. Unfortunately, this revealed extensive pitting in the steel substrate which was likely caused by the corrosive nature of the tanks’ typical contents. This resulted in a lack of wall thickness, so the engineers decided the best course of action would be to install a secondary steel skin to the inside of the tank.
Upon completion of the secondary skin installation, concerns grew that water pressure and possible water ingress behind the secondary skin may cause deflection and unseen corrosion in the void between the skins. To resolve this issue, we proposed an expanding polyurethane system that could be injected into the space between the skins, which would prevent water ingress and reinforce the overall tank structure.
The specially formulated polyurethane foam was heated to 40°C and injected into pre-drilled holes in the wall cavity, where it expanded and solidified. Due to the quick curing nature of this solution, it was essential that our operatives worked quickly and filled the spaces, leaving no gaps.
To achieve this, we used thermal imaging technology to monitor the process and identify any empty areas in real-time and fill them immediately. Once this process was complete, the holes were re-welded and re-blasted to remove any mill scale and contamination, then pressure jetted to remove embedded blast media.
We spray applied a layer of EonCoat to the full internals of the tank, to a DFT of 500 microns. The hole tank was then pressure washed again before applying to additional coats of a glass flake epoxy. This combined system provides exceptional protection for the tank, adding more than 30 years to its design life in this aggressive environment.
