The Glass Fused to Steel (GFtS) sludge storage tanks were suffering from perforations as a result of the breakdown of the glass enamel finish. This can be a common problem and more information about this can be found here.
This meant that the tanks were having to be operated at reduced levels which was proving disruptive to the site functionality.
We proposed the application of a proven epoxy tank lining system, combining our primer specifically developed to adhere to this challenging substrate with our flexible epoxy tank lining Corrolast Tank Guard.
Following clean down and access to the tanks it was discovered that the launder was corroded beyond repair or relining.
The client therefore made the decision to remove the launder as it was not critical for the tanks operations. We arranged for an engineering contractor to attend site and remove this to create a surface suitable to apply the new tank lining to.
All existing sealant/pointing was then removed using scrapers and the tanks cleaned by steam cleaning. Removal of the sealant is essential as for many tank manufacturers the edges of the panels are not coated with the same glass enamel, meaning that these areas are prone to corrosion.
Failure to remove this sealant and treat corrosion that will likely be present will undermine any tank lining applied.
Cleaning is essential as it is highly probable that soluble salts will be present on the surfaces to be coated. If these are left in place this will likely lead to osmotic blistering as a result of moisture being drawn through the tank lining film by hygroscopic action, leading to premature tank lining failure and corrosion of the steel.
As part of our standard tank lining quality assurance the effectiveness of these washing operations was confirmed by the conduction of Chlor tests.
All surfaces to be coated were then prepared by method of abrasive blasting to provide a clean and profiled surface for the new tank lining to adhere to. Any exposed steel was prepared to SA2.5 as per ISO8501-1.
Because of our specifically developed primer for application to GFtS tanks we do not need to remove all of the existing glass enamel. Glass enamel does not profile in the same way as steel and it should not be assumed that steel primers will adhere to GFtS.
All surfaces were vacuumed clean and the effectiveness of the cleaning operations confirmed by the conducting of dust tape assessments.
Prior to and during coating application works the climatic conditions were tested and recorded to ensure compliance with manufacturer recommendations.
Galvanized steel plates which were to be used to bridge perforations were degreased and abraded to ensure excellent adhesion.
All surfaces were primed using Corrolast DSP applied by brush and roller to a nominal thickness of 100 microns.
Once cured the previously prepared galvanized steel plates were bonded in place over perforations using a Thixotropic epoxy adhesive.
During cure these plates were secured in place using tapes.
All plate overlaps and bolts received a heavy stripe coat of Corrolast Tank Guard applied by brush and roller. Stripe coating of these areas is essential in order to ensure sufficient tank lining film build in areas where coatings pull thin through surface tension.
A full coat of Corrolast Tank Guard was then applied by method of airless spray to a wet film thickness of 500 mcirons.
Once cured dry film thickness readings were taken and recorded and a DC Holiday spark test performed to identify any pin holes present.
Any defects identified were marked with chalk prior to touching in using the same material applied by brush.
The application of these tank linings allowed the tanks to be operated at the intended levels. By relining the tanks rather than replacement presented a significant CO2 saving and supported by our 10 year warranty will remain in service for many years.
