THE PROBLEM – Anglia Water Tank Lining Refurbishment
The sludge storage tanks at Anglian Waters sewage treatment works in Godmanchester had begun to suffer perforations and significant corrosion as a result of hydrogen sulphide/sulphuric acid attack. The client had considered replacing the tanks but due to the environmental impact it was chosen to repair and re-line the existing tanks selecting Corroless Eastern as the tank lining company to undertake the works.
THE SOLUTION – Anglia Water Tank Lining Refurbishment
The tanks internals were prepared by method of abrasive blasting to remove any corrosion and breakdown present and provide an ideal surface for tank re-lining. Upon entering the second and third tanks we found the tanks had been previously lined. This previous tank lining system although well adhered was found to be concealing sub film corrosion and perforations in the tanks structure, thus necessitating its complete removal. The three tanks internals were prepared to Swedish Standard SA2.5 and a minimum surface profile of 75 microns raised. Where the tank panels intersected and around the bolt/stud heads there was a significant quantity of polyurethane mastic that was preventing our seamless lining of the tanks structures. For this reason the mastic was removed in its entirety which revealed further areas of breakdown and laminate corrosion.
Tank Lining Epoxies
Once prepared the tanks were rinsed to remove any chloride salts and contaminants which would lead to premature coating failure with conventional tank lining epoxies and polyurethanes this would then necessitate re-blasting to Swedish Standard SA2.5 to prevent corrosion occurring hidden under the tank lining. However because we were going to prime the tanks using Corroless’ unique rust stabilising epoxy primer (Corroless EPF) this would not be necessary.
Any perforations or damage to the tanks structures were repaired using glass fibre chopped strand matting with Corroless EPF as the binding resin. Due to the large number of bolts/studs penetrating the tank and in line with recognised good coating practice at each stage of the coatings cycle a heavy stripe coat was applied all bolts and seams present to ensure full film build, where possible in a contrasting colour. The tanks were primed throughout using Corroless EPF rust stabilising epoxy primer to a dry film thickness of 200 microns by method of airless spray. Corroless EPF contains a unique mined pigment that means it stabilises any corrosion present to inert magnetite, such as the flash rusting which occurred as a result of rinsing down.
Once satisfied that the priming stage of the tank lining process was up to specification two coats in contrasting colours of Corroless Eastern EN (Epoxy Novalac) was applied throughout the tanks at a thickness of 200 microns per coat. Corroless Eastern EN is an extremely chemical resistant epoxy novalac which can resist up to 96% sulphuric acid and is reinforced with screened glass flake to give excellent abrasion resistance as well. Once cured a DC holiday spark test was conducted throughout the tanks to find possible defects and pin holes in the tanks linings. Where necessary these were rectified by touching in using the same protective coating material.