THE PROBLEM
The water authorities surge vessel had failed a recent insurance inspection as a result of both internal and external corrosion. The internal corrosion could also provide an ideal habitat for aquatic microorganisms.
SOLUTION
As requested by our client we allowed for the removal of all existing coatings, prior to the application of a regulation 31 approved tank lining internally and a suitable anti corrosion coating system externally.
Abrasive blasting to remove all existing coatings
Initially internally all coatings were removed by method of abrasive blasting. Internally the existing was extremely thick and had been extremely poorly applied, with the tank lining in excess of 10mm thick in the tank base.
The blast profile was checked using a surface profile needle gauge and the steel checked for soluble salts as part of our standard quality assurance. Both are imperative to ensure the performance of the new tank lining and protective coatings as expected.
Applying Acothane DW
Internally Acothane DW was applied to a thickness of 1000 micrometers in two coats by method of brush and roller. As per good tank lining practice, separate stripe coats were applied at each stage of the tank lining process to areas such as welds and seams where paint pulls thin through gravity and surface tension. This is essential to ensure the correct thickness of the tank lining which dictates its anti-corrosion performance.
As part of our standard quality assurance the new tank lining was checked for porosity using a DC holiday spark tester and the dry film thickness tested and recorded for handover in the project completion file. Where found defects where marked with chalk prior to touching in using the same material applied by brush.
Externally the tank was first primed using Corroless EPF rust stabilising epoxy primer. The benefit this material brought to this project was that it mean that costly encapsulation and climatic control could be avoided. Corroless EPF contains a mined pigment that converts corrosion present to stable iron oxides such as magnetite thus preventing further corrosion. Corroless EPF also contains self-leafing glass flake that laminate within the coating to create a more tortuous route for oxygen and moisture to reach the steel substrate, offering improved corrosion performance.
This was followed by the application of a high build epoxy intermediate coat and UV stable polyurethane finish. As per the internal lining, separate stripe coats were applied at each stage of the coating cycle. The total coating thickness was in excess of 350 micrometers.
